Method for separating copper-copper laminate and copper-copper laminate

Abstract

The present invention is a method for separating a copper-copper laminate having a first structure in which a first copper conductor film is provided on a joining surface, a second structure in which a second copper conductor film is provided on a joining surface, and a cross-linking layer that includes nanocrystals of copper(II) oxide and that is located between the joining surfaces of the first and second structures, the method for separating a copper-copper laminate involving cooling the cross-linking layer to a temperature equal to or lower than the antiferromagnetic magnetic transition temperature of copper(II) oxide and separating the joining surfaces of the first and second structures. The temperature to which the cross-linking layer is cooled may be lower than the temperature at which the thermal expansion coefficient of at least the copper(II) oxide transitions to a negative value. The nanocrystals of copper(II) oxide included in the cross-linking layer may be derived from a cross-linked substance produced through a vapor-assisted procedure for irradiating the nanocrystals with vacuum-ultraviolet light.

Description

[Technical field]

[0001] The present invention relates to a method for separating copper-copper laminates and copper-copper laminates suitable for recycling structures such as electronic devices. [Background technology]

[0002] Electronic substrates, clad materials, or composite structures having Cu thin-film electrodes often have a bonding interface between Cu-Cu or between copper-copper laminates. Flexible organic substrates are often used in laminates including electronic devices for the purpose of reducing thickness and weight and achieving biocompatibility, and there is a demand for improving the recovery efficiency of rare materials contained inside flexible organic substrates, etc. Therefore, providing a method that maintains strong bonding strength from material composite (bonding) through actual operation and enables solid phase separation of different materials from the adhesive or bonded interface after the end of their useful life will directly lead to a reduction in the load on intermediate recycling processes.

[0003] In a laminate including such an electronic device, for example, when a copper foil is attached as an electrode pattern on the surface of a flexible organic substrate, a vapor-assisted vacuum ultraviolet irradiation technique (V-VUV) is used. Details of the vapor-assisted vacuum ultraviolet light irradiation method are disclosed in, for example, Patent Documents 1 and 2. The process outline for inorganic materials containing Cu disclosed in these documents is shown below. (1) Pure water vapor is added to the atmospheric pressure nitrogen atmosphere. (2) The sample is introduced into the atmosphere of (1) and irradiated with vacuum ultraviolet light. Irradiation with vacuum ultraviolet light removes contaminants adsorbed on the material surface, partially reduces the native oxide, and forms a cross-linked layer on the cation sites. (3) The surfaces of (2) are brought into contact at room temperature, and then heated to, for example, about 150° C. to promote a dehydration condensation reaction between the crosslinked layers to obtain a bond.

[0004] The vacuum ultraviolet light here is ultraviolet light with a wavelength of 10 to 200 nm. In the wavelength range of 150 to 200 nm, vacuum ultraviolet light is strongly absorbed by oxygen molecules in the air, but is permeable to nitrogen. Therefore, this wavelength range can be used in an atmosphere that does not contain oxygen (generally pure nitrogen) without using an expensive vacuum chamber. Examples include a 193 nm photolithography device (for semiconductor manufacturing) or a circular dichroism spectrometer.

[0005] The bridged layer formed on the Cu surface by the vapor-assisted VUV irradiation method is usually amorphous Cu(OH)2·[H2O]2, which is due to the action of H and OH radical species generated by the separation of water by VUV irradiation. The growth of the bridged layer thickness is proportional to the product of the water vapor density and the VUV irradiation time (exposure amount (s·kg / m)) until the reaction with the cationic sites becomes saturated. 3 ) is proportional to the thermal conductivity of a typical Cu thin film. 3 It has been confirmed that the thickness grows to about 15 to 20 nm and then saturates.

[0006] Conventionally, low-temperature atmospheric pressure bonding has been achieved by using a vapor-assisted vacuum ultraviolet light irradiation method with various combinations of materials. Due to rapid technological advances, the product life of structures including electronic devices is short, about several years to several decades, compared to the life of normal structural materials, and therefore a large amount of waste is generated as the product life passes. However, this waste contains valuable materials such as gold and rare earth elements, and has a higher content than raw stones from normal mines, so it is also called urban mines. Therefore, the importance of recycling technology to recover valuable metal elements and / or rare earth elements from waste laminates including electronic devices is increasing. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2015-051542 A [Patent Document 2] WO2019 / 221288A1 Summary of the Invention [Problem to be solved by the invention]

[0008] Many of the current resource recycling technologies require high temperatures or high energy. In particular, in the case of electronic substrates, the melting points of materials are increasing with the increase in the power output and heat dissipation of devices, so it is possible to adopt resource recycling technologies that function in high temperature ranges above the melting points. However, such technological innovations that are an extension of conventional methods have the problem that intermediate processing such as separation and detoxification of the molten material is very costly and time-consuming, especially in the case of organic or inorganic composite materials. A laminate including an electronic device is a composite material. As a method for physically peeling the interface between different materials of the composite material, a method of introducing a substance with a different thermal expansion coefficient as a peeling layer, or a method of doping the adherend surface with hydrogen in advance to cause foaming by heating have been proposed. However, both of these methods have a problem in that the process is not simple. [Means for solving the problem]

[0009] In order to solve the above problems, the present inventors have investigated whether a compound that has a normal positive thermal expansion coefficient at room temperature but a negative thermal expansion coefficient at a temperature lower than a certain temperature can be applied to the crosslinked layer. That is, the present inventors came up with the idea that if a laminate of a laminated substrate can be formed by using a compound that expands rapidly only near a specific temperature as a crosslinked layer, a laminate having a simple structure derived from the laminated substrate and a structure that can be separated at the joint using the compound when the laminate is discarded can be obtained, and have completed the present invention. According to the configuration of the laminate of the present invention, a substance with a different thermal expansion coefficient can be introduced as a peeling layer, so that physical peeling at the interface is possible by a simple process.

[0010] Aspects or embodiments of the present invention are summarized below, but the present invention is not limited thereto.

[0011] [1] The method for separating a copper-copper laminate of the present invention is a method for separating a copper-copper laminate, as shown in, for example, FIG. 6B(A) and FIG. 1C, which comprises constructing a first structure 14 having a first copper conductor film 10 on its joining surface, a second structure 24 having a second copper conductor film 20 on its joining surface, and a bridging layer 30 containing copper (II) oxide nanocrystals between the joining surfaces of the first structure 14 and the second structure 24, and cooling the bridging layer 30 to a temperature equal to or lower than the magnetic transition temperature of copper (II) oxide, thereby separating the first copper conductor film 10 and the second copper conductor film 20.

[0012] [2] In the method for separating a copper-copper laminate of the present invention, the crosslinked layer preferably has a thickness such that diffusion of copper ions from the first and / or second copper conductor film into the copper(II) oxide reaches the entire film of the crosslinked layer. [3] In the method for separating a copper-copper laminate of the present invention, the crosslinked layer preferably has a thickness of 1 nm or more and 20 nm or less. [4] In the method for separating a copper-copper laminate of the present invention, the cooling temperature of the crosslinked layer is preferably at least equal to the temperature at which the thermal expansion coefficient of copper(II) oxide becomes negative. The temperature at which the thermal expansion coefficient of copper(II) oxide in the present invention becomes negative varies to some extent compared to a completely single crystal, and is therefore in the range of -100°C to -90°C. [5] In the method for separating a copper-copper laminate of the present invention, the copper(II) oxide nanocrystals contained in the crosslinked layer are preferably derived from a crosslinked material produced by a steam-assisted vacuum ultraviolet light irradiation method. Here, the vapor-assisted vacuum ultraviolet light irradiation method refers to irradiating the bonding surfaces of the first structure and the second structure with vacuum ultraviolet light having a wavelength of 150 nm or more and 200 nm or less, humidified with water vapor, in an oxygen-free nitrogen gas atmosphere under atmospheric pressure. The bonding surfaces of the first structure and the second structure are cleaned by irradiating with vacuum ultraviolet light. Thereafter, the bonding surfaces of the first structure and the second structure are pressure-bonded to obtain a copper-copper laminate.

[0013] [6] In the method for separating a copper-copper laminate of the present invention, preferably, the crosslinked layer is an irradiation step of irradiating the first copper conductor film and the second copper conductor film with vacuum ultraviolet light having a wavelength of 150 nm or more and 200 nm or less in an oxygen-free nitrogen gas atmosphere and in the presence of water vapor while the first copper conductor film and the second copper conductor film are spaced apart from each other; an exposure step of exposing at least one of the first copper conductor film or the second copper conductor film to a cross-linking substance; a contacting step of contacting the first copper conductor film with the second copper conductor film; It is preferable that the generated [7] In the method for separating a copper-copper laminate of the present invention, the cross-linking substance is preferably Cu(OH)2·[H2O]2. In this molecular formula, theoretically, [H2O] is 2, but in reality, water molecules are not always evenly distributed in pairs, and the average value for the entire sample is often less than 2. Therefore, Cu(OH)2·[H2O] 2-x The subscript (2-x) in this formula is a relatively common way of writing compound indices in papers.

[0014] [8] As shown in FIG. 6B(A), for example, the copper-copper laminate of the present invention comprises a first structure 14 having a first copper conductor film 10 on its joining surface, a second structure 24 having a second copper conductor film 20 on its joining surface, and a bridging layer 30 containing copper(II) oxide nanocrystals between the joining surfaces of the first structure 14 and the second structure 24. [9] In the copper-copper laminate of the present invention, the crystal grain size of the nanocrystals is preferably 1 nm or more and 10 nm or less. Further, although overlapping with other descriptions, various aspects of the present invention are described below. [1’] A first structure having a first copper conductor film on a bonding surface; a second structure having a second copper conductor film on a bonding surface; A method for separating a copper-copper laminate having a bridging layer containing copper (II) oxide nanocrystals between the joining surfaces of the first structure and the second structure, comprising: A method for separating a copper-copper laminate, comprising cooling the bridge layer to a temperature below the magnetic transition temperature of copper (II) oxide, thereby separating the bonding surfaces of the first structure and the second structure. [2’] The method for separating a copper-copper laminate according to [1'], characterized in that the film thickness of the crosslinked layer is such that diffusion of copper ions from the first and / or second copper conductor film to the copper(II) oxide reaches the entire film of the crosslinked layer. [3’] The method for separating a copper-copper laminate according to [1'] or [2'], wherein the crosslinked layer has a thickness of 1 nm or more and 20 nm or less. [4’] The method for separating a copper-copper laminate according to any one of [1'] to [3'], characterized in that the cooling temperature of the cross-linked layer is at least lower than the temperature at which the thermal expansion coefficient of copper (II) oxide becomes negative. [5’] The method for separating a copper-copper laminate described in any one of [1'] to [4'], characterized in that the copper (II) oxide nanocrystals contained in the crosslinked layer are derived from a crosslinked material generated by a steam-assisted vacuum ultraviolet light irradiation method. [6’] The crosslinked layer is an irradiation step of irradiating the first copper conductor film and the second copper conductor film with vacuum ultraviolet light having a wavelength of 150 nm or more and 200 nm or less in an oxygen-free nitrogen gas atmosphere and in the presence of water vapor while the first copper conductor film and the second copper conductor film are spaced apart from each other; an exposure step of exposing at least one of the first copper conductor film and the second copper conductor film to a cross-linking substance; a contacting step of contacting the first copper conductor film with the second copper conductor film; The method for separating a copper-copper laminate according to any one of [1'] to [5'], wherein the copper-copper laminate is produced by the following procedure. [7’] The cross-linking material is Cu(OH). 2 ·[H 2 O] 2 The method for separating a copper-copper laminate according to [6'], [8’] A first structure having a first copper conductor film on a bonding surface; a second structure having a second copper conductor film on a bonding surface; A copper-copper laminate having a bridging layer containing copper (II) oxide nanocrystals between the joining surfaces of the first structure and the second structure. [9’] The copper-copper laminate according to [8'], wherein the crystal grain size of the nanocrystals is 1 nm or more and 10 nm or less. Effect of the Invention

[0015] According to the method for separating a copper-copper laminate of the present invention, a phenomenon that inevitably occurs in the mechanism of achieving bonding by the vapor-assisted vacuum ultraviolet light irradiation method, i.e., the generation of metal oxide nanocrystals inside the crosslinked layer after bonding, is utilized, and the solid phase separation can be achieved by applying a slight shear stress without adding any special procedure to the bonding process by using cooling at a temperature that can be reached by an industrial freezer. [Brief description of the drawings]

[0016] [Figure 1A] 1A is a schematic diagram of the solid-phase separation method of the present invention by cooling a copper-copper laminate. Fig. 1A(A) is a cross-sectional view of the configuration of a copper-copper laminate in which a general negative thermal expansion coefficient material is sandwiched as a bridging layer, Fig. 1A(B) is an explanatory diagram of partial rupture of a copper conductor film, and Fig. 1A(C) is an explanatory diagram of defect propagation in the bridging layer. [Figure 1B]1B is a schematic diagram of a method for forming a cross-linked layer using a vapor-assisted vacuum ultraviolet light irradiation method and for solid-phase separation by cooling, which is one embodiment of the present invention. Fig. 1B(A) is a cross-sectional view of the structure of a copper-copper laminate sandwiched between cross-linked layers, Fig. 1B(B) is an electron microscope photograph of CuO nanocrystals, and Fig. 1B(C) is an explanatory diagram of the structure in the cross-linked layer. [Figure 1C] 1C(A) is a cross-sectional view of a copper-copper laminate bonded with a bridging layer 30, and FIG.1C(B) is an explanatory diagram of solid-phase separation at the bridging layer 30 of the copper-copper laminate. [Diagram 2] An explanatory diagram of the steps of the vapor-assisted vacuum ultraviolet light irradiation process. Figure 2(A) shows the step of irradiating the surface of the copper conductor film with vacuum ultraviolet light to purify it, Figure 2(B) shows the state after the copper conductor film surface has been purified, Figure 2(C) shows the step of bringing the copper conductor films on the surface of the structure closer to each other to form a bridged layer, and Figure 2(D) shows the step of bonding the surface of the structure with a bridged layer by contact at room temperature and low-temperature heating. [Diagram 3] 3 is an explanatory diagram of the steps of a surface activation room temperature bonding process as a comparative example, and is an explanatory diagram at the atomic level of the copper conductor film surface. Fig. 3(A) shows the organic contaminants 13 and 23 (organic compound dirt) and the atoms or molecules of the native oxide layers 12 and 22 adsorbed on the surfaces of the first copper conductor film 10 and the second copper conductor film 20 in the initial state. Fig. 3(B) shows the cleaning process on the copper conductor film surface using vacuum ultraviolet light. Fig. 3(C) shows the bonding of the copper conductor film in a state without significant heating such as low-temperature heating in a vacuum. [Figure 4]This is a top view of the atmospheric pressure low-temperature bonding apparatus. Here, bonding by the vapor-assisted vacuum ultraviolet light irradiation method and surface activation room temperature bonding process can be performed. In the figure, 41 is a sample entrance, 50 and 52 are waiting rooms, and 72 is a sample stage (41, 50, 52, and 72 may be simply referred to as stages). 40 is an airtight room (airlock room), 60 is an X-ray photoelectron spectroscopy room (XPS room), and 70 is a bonding room (40, 60, and 70 may be simply referred to as chambers). 46 is a vacuum ultraviolet light source, 48 is a temperature and humidity sensor, 42 is a vacuum pump, 44 is a sprayer, and 62 and 64 are an X-ray source and a photoelectron detector. The vacuum ultraviolet light irradiation method is performed in the airtight room (airlock room) 40. After placing the sample at the sample entrance 41, the solvent vapor turned into a fine mist by the sprayer 44 is mixed with high-purity nitrogen, and the mixed vapor is adjusted to a predetermined humidity by the temperature and humidity sensor 48 and introduced into the chamber, and then irradiated with vacuum ultraviolet light from the vacuum ultraviolet light source 46. The sample is then transported via waiting rooms 50 and 52 to the X-ray photoelectron spectroscopy room (XPS room) 60 or the bonding room 70. A heater is built into the sample stage 72 in the bonding room 70, so that the sample can be heated during bonding by the vacuum ultraviolet light irradiation method. [Figure 5A] Figure 5A(A) shows the as-is spectrum of XPS Cu2p3, which shows the change in the chemical bonding state of the CMP-Cu surface before and after VUV irradiation. Figure 5A(B) shows the spectrum in Figure 5A(A) normalized to the maximum intensity, emphasizing the difference in the chemical bonding state of Cu. In the spectrum with VUV irradiation alone, the peaks of -OH and -O originating from contamination are attenuated, but the Cu(OH)2 peak, which is the source of oxide nanoparticles that function as bonding and separation layers, is not fully observed. On the other hand, the surface treated with the vapor-assisted VUV irradiation method shows the peaks originating from Cu(OH)2, suggesting that the process proceeded as intended. [Figure 5B]Figure 5B(A) shows the as-is spectrum of XPS O1s showing the change in the chemical bonding state of the CMP-Cu surface before and after VUV irradiation. Figure 5B(B) shows the spectrum of Figure 5B(A) normalized to the maximum intensity to emphasize the difference in the chemical bonding state of O. The surface treated with the vapor-assisted VUV irradiation method shows a peak due to coordinated molecular water, suggesting the formation of Cu(OH)2. [Figure 6A] 6A shows the shape of the sample. Figure 6A(A) shows the shape of the sample from the side. Figure 6A(B) shows the shape of the sample from above. [Figure 6B] 6B is a schematic explanatory diagram of a test performed on a laminate sample. Fig. 6B(A) is a diagram explaining a method of a shear strength test in the example. Fig. 6B(B) is a diagram illustrating a method of observing an SEM image of a Cu bonding interface (interface observation by an electron microscope). [Figure 7A] This shows a laminate with cross-links formed by the vapor-assisted vacuum ultraviolet light irradiation method, and an example of a sample before cooling treatment. Figure 7A(A) shows that the Cu-Cu interface remains bonded and does not break or peel off, and the base material breaks from inside the Si chip. Figure 7A(B) shows that the adhesive used to fix the sample to the shear strength test stage peels off, and the Cu-Cu interface remains bonded and does not break or peel off. In other words, this shows that solid-phase separation is not possible without cooling treatment. [Figure 7B] Figure 7B(A) shows the laminate with cross-links formed by the vapor-assisted vacuum ultraviolet light irradiation method, and shows an example of a sample after cooling treatment. Figure 7B(B) shows the sample surface after cooling treatment. Figure 7B(B) is an SEM image of the sample surface after cooling treatment. Figure 7B(A) shows an overall image of the two chips being solid-phase separated without any obvious fracture of the Si chip or Cu thin film when stress is applied by direct manual gripping. The enlarged image of Figure 7B(B) shows that no significant fracture of the Cu thin film has occurred, and that the Cu thin film surface has become rough due to the expansion of oxide nanoparticles. [Figure 7C]This is an SEM image showing the structural change of a laminate with cross-links formed by the vapor-assisted VUV irradiation method. An example of a sample before cooling treatment is shown. When no cooling treatment is performed, it can be seen that the adhesion of the Cu thin film is maintained. [Figure 7D] This SEM image shows the structural change of a laminate with cross-links formed by the vapor-assisted vacuum ultraviolet light irradiation method, and shows an example of a sample after cooling treatment. It can be seen that the Cu thin films have been separated by the cooling treatment. The clear separation between the Cu thin films is due to the process of encapsulating the laminate in cold resin during the preparation of the transmission electron microscope sample, which caused the interface to break partially due to the compressive force caused by the resin hardening, allowing the resin to flow into the break and harden. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention will now be described with reference to the drawings. Fig. 1A is a conceptual diagram of a method for solid-phase separation by cooling a copper-copper laminate according to an embodiment of the present invention. Fig. 1A(A) is a cross-sectional view of a copper-copper laminate sandwiching a general negative thermal expansion coefficient material as a bridging layer 30, Fig. 1A(B) is an explanatory diagram of the origin of a defect that occurs involuntarily near the bridging layer of the negative thermal expansion coefficient material and the interface between the bridging layer and the structure (hereinafter sometimes referred to as the base material), and Fig. 1A(C) is an explanatory diagram of how a fracture propagates in an unpredictable direction from the defect origin in Fig. 1A(B). The copper-copper laminate to be processed is composed of a first copper conductor film 10, a second copper conductor film 20, a base material which is a first structure 14, a base material which is a second structure 24, and a bridging layer 30. In the case of an electronic device, the structure (base material) typically includes a silicon substrate, a printed wiring board, or a Si wafer, and a wiring pattern (copper thin film wiring pattern) using copper foil as a copper conductor film is provided on the base material. Therefore, the first copper conductor film 10 is laminated on the surface of the first structure (base material) 14 to form a bonding surface, and the second copper conductor film 20 is laminated on the surface of the second structure (base material) 24 to form a bonding surface (see FIG. 1A(A)). In addition, since the first copper conductor film 10 and the first structure 14, as well as the second copper conductor film 20 and the second structure 24, are thicker than the bridging layer 30, in this figure, the first copper conductor film 10 and the first structure 14 are illustrated as a single unit as the first copper conductor film 10, and the second copper conductor film 20 and the second structure 24 are illustrated as a single unit as the second copper conductor film 20. When a temperature change is applied to the copper-copper laminate to be processed, a stress determined by the temperature change near the magnetic transition temperature of copper (II) oxide and the thermal expansion coefficient acts on the first copper conductor film 10 and the second copper conductor film 20 sandwiching the bridging layer 30. When the stress acts, a peeling fracture 91 occurs inside the bridging layer 30, and a partial fracture 90 of the copper conductor film occurs only near the interface with the bridging layer 30 (see FIG. 1A(B)). After that, the stress acts further, causing a defect propagation 92 in the bridging layer, in which a defect propagates in the bridging layer 30 (see FIG. 1A(C)). In the present invention, the magnetic transition is also called the trigger temperature because a temperature change near the magnetic transition temperature finally causes a solid phase breakage. The magnetic transition temperature of copper(II) oxide in the present invention is −100° C. or higher and −80° C. or lower because it varies compared to a pure copper(II) oxide single crystal.

[0018] Fig. 1B is a conceptual diagram of a method for solid-phase separation by cooling a copper-copper laminate using a vapor-assisted vacuum ultraviolet light irradiation technique according to one embodiment of the present invention. Fig. 1B(A) is a cross-sectional view of the copper-copper laminate sandwiched between crosslinked layers, Fig. 1B(B) is an electron micrograph of copper (II) oxide nanocrystals (sometimes referred to as "CuO nanocrystals" in this specification) taken with a transmission electron microscope (hereinafter sometimes referred to as TEM), and Fig. 1B(C) is an explanatory diagram of the structure within the crosslinked layers. A bridging layer 30 exists between the first copper conductor film 10 and the second copper conductor film 20 (FIG. 1B(A)), and native oxide layers 12 and 22 exist between the first copper conductor film 10 or the second copper conductor film 20 and the bridging layer 30, respectively (FIG. 1B(C)). In the bridging layer 30 formed using the vapor-assisted vacuum ultraviolet light irradiation method, CuO nanocrystals can be generated near the interface over time by the reaction represented by the following formula (1) (see FIG. 1B(B)). Cu(OH)2 → CuO + H2O (1) The CuO nanocrystals are crystals with a crystal grain size of 1 to 20 nm, and the crystal grain size can be measured by an electron microscope such as a transmission electron microscope, as shown in Fig. 1B(B). The crystal grain size of the CuO nanocrystals is preferably 1 nm or more and 10 nm or less.

[0019] Fig. 1C is a diagram illustrating the solid-phase separation state of a copper-copper laminate. Fig. 1C(A) is a cross-sectional view of the copper-copper laminate bonded via a bridging layer 30, and Fig. 1C(B) is an explanatory diagram of solid-phase separation at the bridging layer 30 of the copper-copper laminate. A bridging layer 30 is located between the first copper conductor film 10 and the second copper conductor film 20. The thickness of the bridging layer 30 is, for example, 15 to 20 nm. The CuO nanocrystal layer near the interface expands rapidly with a constant stress near the magnetic transition temperature, which is the trigger temperature (see FIG. 1C(A)). Due to solid-phase detachment at the bridging layer 30 of the copper-copper laminate, remaining bridging layers 34a and 34b are located on the former bonding surface of the first copper conductor film 10 and the second copper conductor film 20, and crushed particulate CuO nanocrystals 34c remain (see FIG. 1C(B)).

[0020] The crosslinked layer structure is formed using a vacuum ultraviolet light irradiation method in a water vapor-containing atmospheric pressure nitrogen atmosphere (vapor-assisted vacuum ultraviolet light irradiation method). Fig. 2 is an explanatory diagram of the steps of the vapor-assisted vacuum ultraviolet light bonding process. Fig. 2(A) shows the step of irradiating the surface of the copper conductor film with vacuum ultraviolet light to purify it, Fig. 2(B) shows the state after the copper conductor film surface has been purified, Fig. 2(C) shows the step of bringing the copper conductor films on the surface of the structure close to each other to form a bridging layer, and Fig. 2(D) shows the step of bonding the surface of the structure with a bridging layer by contact at room temperature and low-temperature heating.

[0021] In FIG. 2(A), the surface of the copper conductor film is irradiated with vacuum ultraviolet light while controlling the amount of exposure. On the surfaces of the copper conductor films 10 and 20, organic contaminants 23 (adherent dirt of organic compounds) and natural oxide layers 12 and 22 are present. In FIG. 2(B), the organic contaminants 23 and the natural oxide layers 12 and 22 present on the surfaces of the copper conductor films 10 and 20 are partially removed by vacuum ultraviolet light. In FIG. 2(C), the natural oxide layers 12 and 22 present on the surfaces of the copper conductor films 10 and 20 are partially reduced to form a bridging layer 30. In FIG. 2(D), after the bridging layer 30 is formed, the first copper conductor film 10 and the second copper conductor film 20 are bonded via the bridging layer 30 to form a copper-copper laminate in which the first structure and the second structure are bonded. A cross-linked layer 30 of hydroxide hydrate having a thickness of several nm is formed on the metal surface modified by the steam-assisted vacuum ultraviolet light irradiation method, and the surfaces are brought into contact with each other at room temperature and then heated to, for example, about 150°C to promote the dehydration condensation reaction, thereby obtaining a strong bond. In the present invention, a film of a metal native oxide (i.e., a native oxide of copper) is partially reduced during the vapor-assisted vacuum ultraviolet light irradiation method, and metal ions (copper ions) are generated. The excess metal ions that do not contribute to the formation of the cross-linked layer react with water molecules generated by the dehydration condensation reaction, and oxide nanocrystals are generated in the cross-linked layer. As a result, at the bonding interface of the laminate of the present invention, the boundary between the cross-linked layer 30 and the native oxide layers 12 and 22 disappears and becomes unclear over time, so that it is possible to prevent the occurrence of breakage at the bonding interface when stress is applied. In the present specification, the above-mentioned change in the interface over time may be referred to as "ion diffusion" focusing on the movement of the generated metal ions. In the present invention, the strength of the bonded body is improved by the above-mentioned dehydration condensation reaction and ion diffusion.

[0022] Fig. 3 is an explanatory diagram of the steps of the surface activation room temperature bonding process as a comparative example, and explains the process at the atomic level. Therefore, in order to verify the effectiveness of the cross-linking layer, the surface activation room temperature bonding method that can obtain an ideal direct bonding interface is used as a comparison. FIG. 3(A) shows organic contaminants (organic compound contaminants) 13 and 23 and atoms or molecules of native oxide layers 12 and 22 adsorbed on the surfaces of the first copper conductor film 10 and the second copper conductor film 20, respectively, in the initial state. FIG. 3(B) shows the cleaning process on the copper conductor film surface using vacuum ultraviolet light. FIG. 3(C) shows the bonding of copper conductor films without significant heating, such as low-temperature heating in a vacuum. The surface activation room temperature bonding method is an ideal direct bonding method that uses the attractive force generated between atomically clean copper conductor films by removing chemically stable layers such as oxides using an Ar fast atom beam 65 (hereinafter referred to as Ar-FAB) in a high vacuum (see FIG. 3(B)). This bonds the first copper conductor film 10 and the second copper conductor film 20 without the inclusion of a bridging layer (see FIG. 3(C)).

[0023] Fig. 4 is a diagram showing the configuration of an atmospheric pressure low-temperature bonding apparatus. This apparatus can perform bonding using a vapor-assisted vacuum ultraviolet light irradiation method and a surface activation room temperature bonding process. In FIG. 4, the atmospheric pressure low-temperature bonding apparatus includes an airtight chamber (airlock chamber) 40, waiting chambers 50 and 52, an X-ray photoelectron spectroscopy chamber (XPS chamber) 60, and a bonding chamber . The airtight chamber (airlock chamber) 40 is provided with a sample inlet 41, a vacuum pump 42, a sprayer 44, a vacuum ultraviolet light source 46, and a temperature and humidity sensor 48. The sample inlet 41 is an entrance for carrying a sample to be processed into the airtight chamber (airlock chamber) 40. The sprayer 44 supplies a nitrogen gas atmosphere containing atomized pure water vapor into the airtight chamber (airlock chamber) 40. The vacuum pump 42 exhausts the air in the airtight chamber (airlock chamber) 40, enabling the sprayer 44 to replace the air with a nitrogen atmosphere. For example, an excimer lamp can be used as the vacuum ultraviolet light source 46. The excimer lamp utilizes light (excimer light) generated by discharge plasma (dielectric barrier discharge) generated in a lamp containing a rare gas. The main wavelengths of excimer lamps are 126 nm (Ar2), 146 nm (Kr2), 172 nm (Xe2), 222 nm (KrCl), and 308 nm (XeCl). For vacuum ultraviolet light, a lamp unit with a main wavelength of 172 nm that uses Xe2 is suitable for surface modification and hydrophilic treatment (wettability improvement). The temperature and humidity sensor 48 is a device that measures the humidity and pressure inside the airtight chamber (airlock chamber) 40.

[0024] The waiting chambers 50 and 52 are waiting locations for sending the sample that has been surface-modified in the airtight chamber (airlock chamber) 40 to the X-ray photoelectron spectroscopy chamber (XPS chamber) 60 and the bonding chamber 70 . The X-ray photoelectron spectroscopy room (XPS room) 60 is a room for taking X-ray photoelectron spectroscopy pictures of the sample surface, and is equipped with X-ray sources 62 and 64. The X-ray sources 62 and 64 can deflect beams in three directions, the XYZ directions, and can irradiate an ion beam at any location on the sample. XPS (X-ray Photoelectron Spectroscopy) is a method for measuring the kinetic energy distribution of photoelectrons emitted by X-ray irradiation, and obtaining information on the type, abundance, and chemical bond state of elements present on the sample surface (at a depth of about a few nm).

[0025] In the bonding chamber 70, the copper conductor films of the samples are bonded together. In the vapor-assisted vacuum ultraviolet light irradiation method, the copper conductor films are bonded together via a bridging layer. On the other hand, in the surface activated room temperature bonding process, the copper conductor films are directly bonded together by utilizing the attractive force generated between atomically clean copper conductor films, and therefore no bridging layer is involved.

[0026] Next, the mechanism of action of the method for separating a copper-copper laminate of the present invention will be described. For example, as shown in FIG. 1C, the following two points are essential for solid-phase separation of a bonding interface containing Cu by cooling: (1) Forming a cross-linked layer with a simple compound derived from a copper conductor film; and (2) The cross-linked layer undergoes a significant volume expansion only in the temperature region very close to the magnetic transition temperature, which is a clear trigger temperature. If the magnetic transition temperature, which is the trigger temperature, is sufficiently lower than the temperature at which electronic devices are normally used, there will be no hindrance to normal use of the electronic devices.

[0027] The cross-linked layer is formed by utilizing the Cu hydroxide hydrate cross-links formed on the Cu surface modified by the vapor-assisted vacuum ultraviolet light irradiation method. Transmission electron microscope (TEM) observations have revealed that CuO nanocrystals precipitate over time within the cross-linked layer (see Figure 1B(B)). These CuO nanocrystals are believed to be primarily generated by a reaction between water molecules generated by the dehydration condensation reaction of Cu(OH)2·[H2O]2 that forms the cross-linked layer and excess metal ions (copper ions) generated when part of the natural oxide film on the material surface is reduced by H radicals due to irradiation with vacuum ultraviolet light in the steam-assisted vacuum ultraviolet light irradiation method (on the other hand, CuO nanocrystals are also believed to be generated by the reaction Cu(OH)2→CuO + H2O in the above formula (1), starting from Cu(OH)2, which is the product of water elimination from Cu(OH)2·[H2O]2). Although the material is different, TEM observation has revealed that oxide nanocrystals are generated by a similar mechanism when the steam-assisted vacuum ultraviolet light irradiation method is applied to an Al surface.

[0028] In the method for separating a copper-copper laminate of the present invention, the laminate is cooled to a temperature below the magnetic transition temperature of copper (II) oxide (CuO) (in the range of -100°C or higher and -80°C or lower), whereby the CuO nanocrystals contained in the crosslinked layer expand, generating stress at the interface, thereby achieving a solid-phase separation effect. The stress generated at the bonding interface is considered to be proportional to the density of nanocrystals. Therefore, the simplest process control condition is to use the exposure amount, which is a parameter of the vapor-assisted vacuum ultraviolet light irradiation method. In addition, since the crosslinked layer thickness is considered to be proportional to the density of nanocrystals, the crosslinked layer thickness may be used as the process control condition. EXAMPLES

[0029] As an example, we present the results of solid-phase separation of a stack of CMP (chemical mechanical polishing)-Cu thin films formed on a Si chip (see Figure 6A). This combination is one of the representative structures for planarizing wiring in multilayer electronic substrates. By using a stack of samples with the same structure, we can eliminate the effects of differences in the thermal expansion coefficients between the materials and extract only the effects of stress caused by the expansion of the bridge layer. In addition, in order to clarify whether the solid-phase separation effect occurs depending on the presence or absence of a cross-linked layer, in addition to the laminate obtained by the vapor-assisted vacuum ultraviolet light irradiation method, samples were also prepared by a surface activated room temperature bonding method (SAB method) using Ar fast atom beam bombardment in a high vacuum, and the change in bonding strength before and after cooling for samples produced by both bonding methods was evaluated by shear tests.

[0030] The CMP-Cu thin film was deposited to a thickness of approximately 1 μm on a Si wafer with a native oxide film, with an average surface roughness of approximately 2 nm (see Fig. 6A). The sample was ultrasonically cleaned in acetone, ethanol, and water, successively for 180 s each, to remove any initial adsorbed material, and then introduced into the atmospheric pressure low-temperature bonding apparatus (Fig. 4). In the atmospheric pressure low-temperature bonding apparatus shown in Fig. 4, XPS observation of the sample surface after each surface modification process can be performed without exposing it to the outside air.

[0031] After introducing the sample into the device, the manufacturing process of the laminate by the vapor-assisted vacuum ultraviolet light irradiation method using the atmospheric pressure low-temperature bonding device will be described. (1) The air in the airtight chamber (airlock chamber) 40 was replaced with a nitrogen atmosphere containing atomized pure water vapor. (2) In the airtight chamber (airlock chamber) 40, a wavelength of 172 nm is applied to a Si wafer as a sample, and the illuminance on the sample is approximately 5 mW / cm. 2 The vacuum ultraviolet light exposure dose was approximately 3.4 s kg / m 3 This value was adopted because previous studies had shown that the bridge layer thickness reaches saturation at about 15 to 20 nm on a typical CMP-Cu thin film. (3) The CMP-Cu surfaces with the cross-linked layers were brought into contact with each other at room temperature, and a load of up to 500 N was applied, after which heating was initiated. (4) Heating was carried out up to 150°C and held at that temperature for 600 seconds to obtain a laminate. For each condition, the wavelength of the vacuum ultraviolet light source was selected from those that had enough energy to decompose water vapor and various adsorbates on the material surface, and that could be irradiated with commercially available equipment. The load applied during contact in (3) above is to follow the inclination of the sample on one side using a rocking jig, since it is difficult to mechanically bring flat surfaces into complete contact at room temperature. Therefore, the applied load is not always necessary. The heating retention time is also a value that depends on the equipment.

[0032] In fact, using an X-ray photoelectron spectrometer (XPS) attached to the bonding apparatus, it was confirmed that hydroxide hydrate bridges were formed on the CMP-Cu surface under the exposure conditions adopted in (2) above (Figure 5). Figures 5A and 5B are XPS (X-ray Photoelectron Spectroscopy) spectra showing the change in the chemical bond state of the CMP-Cu surface before and after vacuum ultraviolet light irradiation. Figure 5A shows Cu2p3, and Figure 5B shows O1s. Figures 5A(A) and 5B(A) show the as-is measured spectra. Figures 5A(B) and 5B(B) show the spectra normalized by the maximum peak intensity. According to Figures 5A(A) and 5A(B), in the spectrum of VUV irradiation alone, the peaks of -OH and -O originating from contamination are attenuated, but the Cu(OH)2 peak, which is the source of oxide nanoparticles that function as bonding and separation layers, does not appear sufficiently. On the other hand, the surface that was subjected to the vacuum ultraviolet light irradiation method shows a peak originating from Cu(OH)2, suggesting that the process proceeded as intended. According to Figures 5B(A) and 5B(B), a peak due to coordinated molecular water appears on the surface subjected to the vacuum ultraviolet light irradiation method, suggesting the formation of Cu(OH)2. In other words, in Cu2p3, the surface treated with the vapor-assisted vacuum ultraviolet light irradiation method had a clear increase in Cu intensity and an increase in the proportion of hydroxide hydrate compared to the other surfaces. A similar tendency was observed for O1s.

[0033] Next, a sample using the surface activated room temperature bonding method was fabricated in the following procedure. (1) Background vacuum pressure: approx. 1.0×10 -6 The CMP-Cu surface was etched by about 15 nm (oxide removal) using an Ar fast atomic beam excited at 2 kV and 20 mA for 300 s under a high vacuum atmosphere of 10 Pa. (2) An atomically clean surface was immediately contacted at room temperature in a similar high vacuum atmosphere. (3) The specimen was held under pressure at room temperature for 600 seconds. For both samples obtained by the vapor-assisted vacuum ultraviolet light irradiation method and the surface activation room temperature bonding method, the load was removed immediately after bonding, and the samples were transported to an industrial freezer (air atmosphere) set at -90°C and kept there for 24 hours (cooling treatment). A shear test was performed on the laminate after the cooling pre-treatment. In the shear test, as shown in FIG. 6B(A), the sample laminate was fixed on a stage 80 via an adhesive 82, and a force was gradually applied to the Si wafer, which is the first structure 14, using a load cell with a maximum load of 500 N, to observe the changes in the bonding strength and fracture mode of the laminate. In addition, the state of the bonding interface of the sample laminate was observed by a scanning electron microscope (hereinafter, SEM) as follows. (1) The cooled sample laminate was submerged in a two-component liquid epoxy resin at room temperature. (2) The epoxy resin was left to stand until it hardened. As the volume of the resin decreased during the hardening process, the laminate of the sample submerged in the liquid epoxy resin was subjected to stress. Since the interface of the laminate of the cooled sample was weakened during this process, the interface broke and the epoxy resin flowed into the gap. (3) After the epoxy resin had hardened, the sample was cut into a size that could be introduced into an electron microscope. To observe the bonding interface of the cut sample, the material was "deep-drilled" into the material with an electron beam (see Figure 6B(B)). (4) The structure near the interface was observed by SEM. Figures 7C and 7D show SEM images of a laminate having a cross-linked layer formed by the vapor-assisted vacuum ultraviolet light irradiation method before and after cooling.

[0034] The effectiveness of crosslinking by the vapor-assisted vacuum ultraviolet light irradiation method on cooling solid-phase separation is demonstrated using Figures 7A to 7D. Figure 7A shows a laminate having a crosslinked layer formed by the vapor-assisted vacuum ultraviolet light irradiation method, and shows an example of a sample before cooling treatment. Figure 7B shows a laminate having a crosslinked layer formed by the vapor-assisted vacuum ultraviolet light irradiation method, and shows an example of a sample after cooling treatment. Figure 7A(A) shows that the Cu-Cu interface remained bonded and did not break or peel off, but the Si chip broke from inside. Figure 7A(B) shows that the adhesive used to fix the sample to the shear strength test stage peeled off, but the Cu-Cu interface remained bonded and did not break or peel off. That is, Figure 7A shows that the laminate cross-linked by the vapor-assisted vacuum ultraviolet light irradiation method maintained a strong bond before cooling. In contrast, as shown in Figure 7B(A), after cooling, the two chips were solid-phase separated by applying stress by direct manual gripping without any clear destruction of the Si chip or Cu thin film. In addition, the enlarged image in Figure 7B(B) shows that no significant breakage of the Cu thin film occurred. Furthermore, the enlarged image in Figure 7B(B) suggests that the Cu surface was covered with a film that expanded into fine particles, which embrittlement was observed. Figure 7C is an SEM image showing the structural change of a laminate having a cross-linked layer formed by the vapor-assisted vacuum ultraviolet light irradiation method, showing an example of a sample before cooling treatment, and Figure 7D is an SEM image showing the structural change of a laminate having a cross-linked layer formed by the vapor-assisted vacuum ultraviolet light irradiation method, showing an example of a sample after cooling treatment. In Figures 7C and 7D, the bright areas are CMP-Cu. In Figure 7C, an interface consisting of Cu native oxide and a bridge layer was confirmed between the CMP-Cu. In Figure 7D, it can be seen that the interface is widely separated. The clear separation between the Cu thin films is due to the process of encapsulating the bonded body in cold resin during the preparation of the transmission electron microscope sample, which caused the interface to break partially due to the compressive force caused by the resin hardening, allowing the resin to flow into the break and harden.

[0035] In the shear strength test shown in Fig. 6B(A), the Cu-Cu interface of the sample before cooling treatment was firmly bonded in both the surface-activated room-temperature bonding method and the vapor-assisted vacuum ultraviolet irradiation method, and the application of stress by direct gripping by hand did not lead to interface fracture. The laminate broke in the adhesive between the stage and the sample or inside the Si chip, and the adhesion of the Cu-Cu interface was maintained even after three shear tests were repeated (see Fig. 7A and Fig. 7C). Fig. 7A(B) shows that the laminate formed by the vapor-assisted vacuum ultraviolet irradiation method did not break or peel off at the Cu-Cu interface, but peeled off from the joint with the stage by the adhesive.

[0036] In particular, the laminate obtained by the surface activated room temperature bonding technique, i.e., the laminate without the cross-linked layer, showed similar behavior even after cooling. This suggests that the presence or absence of a Cu hydroxide hydrate cross-linked layer determines the occurrence of solid-phase separation. In contrast, the bond strength of the laminate obtained by the vapor-assisted vacuum ultraviolet light irradiation method decreased to about 0.7 MPa or less after cooling, and it became possible to peel it off by directly holding it by hand. Peeling of the sample after cooling occurred at the Cu-Cu interface, and there was no significant damage to the CMP-Cu thin film or the Si chip, indicating solid-phase separation (see the external appearance photograph at the time of separation in Figure 7B(A) and the SEM image in the same figure (B)). In SEM observation of the bonded interface before and after cooling of the sample obtained by the vapor-assisted vacuum ultraviolet light irradiation method, it was observed that the interface before cooling was tightly adhered without significant voids, whereas after cooling, adsorbates and cold resin penetrated the embrittled interface, and the gap between the CMP-Cu was significantly enlarged (see Figures 7C and 7D). A similar solid-phase separation effect by cooling was also confirmed at the bonded interface between Cu and polyimide using the vapor-assisted vacuum ultraviolet light irradiation method.

[0037] Although the embodiments shown in Figures 1 to 7 have been shown as examples of the present invention, the present invention is not limited to these, and various embodiments are conceivable within a range that would be obvious to a person skilled in the art, and such obvious ranges are also included in the scope of the present invention. [Industrial Applicability]

[0038] The method for separating a copper-copper laminate of the present invention is suitable for use in recycling structures including electronic devices. Structures including electronic devices often use flexible organic substrates for the purpose of reducing thickness and weight and achieving biocompatibility, and there is a demand for improving the recovery efficiency of rare materials contained inside flexible organic substrates, etc. Therefore, providing a method that maintains a strong bonding force from material composite (bonding) to actual operation and can separate different materials into solid phases from the adhesive or bonded interface after the end of the service life directly leads to a reduction in the load on intermediate recycling processes. In the method for separating copper-copper laminates of the present invention, the growth behavior of the thickness of the cross-linked layer can be controlled by a simple parameter (exposure amount), which enables comprehensive life cycle design of composite materials during bonding and contributes to the efficiency of product manufacturing process design. For example, cross-sectional applications are expected in the next-generation automobile industry, where the cost of IoT (Internet of Things) devices is predicted to exceed 40% of the total. [Explanation of symbols]

[0039] 10: First copper conductor film 12: Native oxide layer of copper conductor film 13: Organic contamination 14: First structure (base material) 20: Second copper conductor film 22: Native oxide layer of copper conductor film 23: Organic contamination 24: Second structure (base material) 30: Crosslinked layer 34a, 34b: Residual crosslinked layer 34c: Particulate CuO nanocrystals 40: Airlock room 41: Sample entrance 42: Vacuum pump 44: Sprayer 46:Vacuum ultraviolet light source 48: Temperature and humidity sensor 50, 52: Waiting room 60:X-ray photoelectron spectroscopy room (XPS room) 62, 64: X-ray source and photoelectron detector 65:Ar fast atomic beam 70:Joining chamber 80: Stage 82: Glue 90: Partial copper conductor film fracture 91: Peeling fracture 92: Defect propagation in the bridge layer 100:Cu interface

Claims

1. a first structure having a first copper conductor film on a bonding surface; a second structure having a second copper conductor film on a bonding surface; A method for separating a copper-copper laminate having a bridging layer containing copper (II) oxide nanocrystals between a joining surface of the first structure and a joining surface of the second structure, comprising the steps of: A method for separating a copper-copper laminate, comprising cooling the bridge layer to a temperature equal to or lower than the magnetic transition temperature of copper (II) oxide, thereby separating the bonding surfaces of the first structure and the second structure.

2. The method for separating a copper-copper laminate according to claim 1, characterized in that the thickness of the cross-linked layer is such that diffusion of copper ions from the first and / or second copper conductor films to the copper (II) oxide reaches the entire film of the cross-linked layer.

3. 2. The method for separating a copper-copper laminate according to claim 1, wherein the cross-linked layer has a thickness of 1 nm or more and 20 nm or less.

4. 2. The method for separating a copper-copper laminate according to claim 1, wherein the cooling temperature of the cross-linked layer is lower than a temperature at which the thermal expansion coefficient of copper (II) oxide becomes negative.

5. The method for separating a copper-copper laminate according to claim 1, characterized in that the copper (II) oxide nanocrystals contained in the cross-linked layer are derived from a cross-linked material produced by a steam-assisted vacuum ultraviolet light irradiation method.

6. The crosslinked layer is an irradiation step of irradiating the first copper conductor film and the second copper conductor film with vacuum ultraviolet light having a wavelength of 150 nm or more and 200 nm or less in an oxygen-free nitrogen gas atmosphere and in the presence of water vapor while the first copper conductor film and the second copper conductor film are spaced apart from each other; an exposure step of exposing at least one of the first copper conductor film and the second copper conductor film to a cross-linking substance; a contacting step of contacting the first copper conductor film with the second copper conductor film; 2. The method for separating a copper-copper laminate according to claim 1, wherein the copper-copper laminate is produced by the steps of:

7. The cross-linking material is Cu(OH). ２ ・[H ２ O] ２ 7. The method for separating a copper-copper laminate according to claim 6,

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