Substrate joining method and substrate joint structure

Abstract

[Problem] To provide a substrate joining method and a substrate joint structure that make it possible to prevent the occurrence of a reduction in device performance and degradation of a joining state during joining. [Solution] As substrates to be joined, joining layers 12a, 12b containing polysilazane are formed on the surfaces of two wafers 11a, 11b. The surface of the joining layer 12a of at least one wafer 11a is irradiated with plasma to perform hydrophilic treatment. Then, the joining layers 12a and 12b of the respective wafers 11a, 11b are overlaid and joined.

Description

Method and structure for joining substrates

[0001] This invention relates to a method for joining substrates and a substrate joining structure.

[0002] In recent years, wafer bonding technology has advanced significantly in the applied fields of electronics to enhance processing power. Among wafer bonding technologies, bonding technology for substrates made of Si or Si-based materials is particularly widely used in various applications such as MEMS sensor packaging, optical system encapsulation, microfluidic devices, and three-dimensional stacked structures for memory and logic devices.

[0003] In substrate bonding technology, forming an SiO2 layer at the bonding interface is fundamental and highly effective. One bonding method utilizing this SiO2 layer is hydrophilic bonding (see, for example, Non-Patent Documents 1 or 2), and plasma hydrophilic treatment using O2 gas or N2 gas is performed to improve bonding quality at low processing temperatures. Furthermore, in this method, heat treatment at 200 to 600°C after bonding is performed to promote the oxidation of Si at the bonding interface and increase the bonding strength (see, for example, Non-Patent Documents 3 or 4).

[0004] Furthermore, as another bonding method utilizing SiO2 layers, frit-glass bonding using low-melting-point glass paste is widely employed in the field of MEMS packaging (see, for example, Non-Patent Documents 5 or 6). In this bonding method, glass paste is applied to the bonding surface, and the glass layers are remelted by thermocompression bonding at 350 to 600°C to bond the substrates together.

[0005] Furthermore, as another bonding method utilizing the SiO2 layer, a method has been developed in which polysilazane diluted with an organic solvent is applied to the bonding surface of the objects to be bonded, dried at a temperature lower than the silica conversion temperature of the polysilazane, and only the organic solvent is removed, leaving the polysilazane on the bonding surface. With the other objects to be bonded placed on top of this bonding surface, the object is heated in the presence of water vapor or oxygen to convert the polysilazane to silica, thereby bonding a pair of objects to be bonded (see, for example, Patent Document 1). In addition, a method has been developed in which a load is applied during heating while bonding (see, for example, Non-Patent Documents 7 or 8).

[0006] Ventosa, C. et al., “Hydrophilic low-temperature direct wafer bonding”, J. Appl. Phys.,2008, 104, 123524Fournel, F. et al., “Water stress corrosion in bonded structures”, ECS J. Solid State Sci. Technol., 2015, 4, P124-P130. 〈https: / / doi.org / 10.1149 / 2.0031505jss〉Howlader, M. R., Itoh, H., Suga, T. & Kim, M., “Sequential plasma activated process for silicon direct bonding”, ECS Trans., 2006, 3, p.191-202. 〈https: / / doi.org / 10.1149 / 1.2357070〉Takeuchi, K. & Suga, “T. Quantification of wafer bond strength under controlled atmospheres”, Jpn. J. Appl. Phys., 2022, 61, SF1010. 〈https: / / doi.org / 10.35848 / 1347-4065 / ac5e49〉Knechtel, R., “Glass frit bonding: An universal technology for wafer level encapsulation and packaging”, Microsyst. Technol., 2005, 12, p.63-68. 〈https: / / doi.org / 10.1007 / s00542-005-0022-x〉Knechtel, R. Wiemer, M. & Fromel, J., “Wafer level encapsulation of microsystems using glass frit bonding”, Microsyst. Technol., 2006, 12, p.468-472. 〈https: / / doi.org / 10.1007 / s00542-005-0036-4〉Yohei Wada, et al., "Development of a Low-Temperature Bonding Method for SiO2 Wafers Using Polysilazane: Bonding Mechanism and Influence of Sample Size," Proceedings of the 2009 Spring Meeting of the Japan Society for Precision Engineering, 2009, pp. 379-380. Kohei Wada, et al., "Development of a Small Planar Antenna Using Magnetic Material for Biomedical Wireless Sensor Terminals," Proceedings of the 2009 Spring Meeting of the Japan Society for Precision Engineering, 2009, pp. 389-390.

[0007] Japanese Patent Publication No. 2010-95666

[0008] In the hydrophilic bonding described in Non-Patent Documents 3 and 4, heat treatment is performed at 200 to 600°C to increase bonding strength, and in the frit glass bonding described in Non-Patent Documents 5 and 6, thermocompression bonding is performed at 350 to 600°C to bond the substrates together. Furthermore, in the bonding method using polysilazane described in Patent Document 1, heat treatment is performed at 250 to 450°C to convert the polysilazane to silica, and in the bonding methods described in Non-Patent Documents 7 and 8, heat treatment is performed at 150°C or higher. Thus, in conventional bonding methods using SiO2 layers, heat treatment is performed at 150°C or higher, and if the thermal expansion coefficients of the substrates to be bonded are different, there is a problem that the performance of the device will decrease or the bonding state will deteriorate during bonding by heat treatment.

[0009] This invention was made in view of these problems, and aims to provide a substrate bonding method and substrate bonding structure that can prevent a decrease in device performance and deterioration of the bonding state during bonding.

[0010] To achieve the above objective, the first substrate joining method according to the present invention is a substrate joining method for joining two substrates together, characterized by comprising: a joining layer formation step of forming a joining layer containing polysilazane on the surface of each substrate; a plasma irradiation step of irradiating the surface of the joining layer of at least one of the substrates with plasma to perform hydrophilic treatment; and a joining step of overlapping and joining the joining layers of each substrate after the plasma irradiation step.

[0011] Here, polysilazanes undergo hydrolysis upon interaction with water, changing to SiO2. For example, perhydropolysilazane (PHPS; (SiH2NH)) n In this case, as shown in the following reaction equation (1), when it interacts with water, SiO2 is produced, and NH3 and H2 are also released as byproducts. This change from polysilazane to SiO2 proceeds even at room temperature as long as water is present.

[0012]

[0013] In the first substrate bonding method according to the present invention, by irradiating the surface of the bonding layer of at least one of the bonding layers formed on the surface of each substrate with plasma to perform a hydrophilic treatment, the polysilazane contained in that bonding layer interacts with water adsorbed by the hydrophilic treatment and changes into SiO2. Furthermore, by overlapping the bonding layers of each substrate, the polysilazane contained in the bonding layer that has not undergone hydrophilic treatment also interacts with water and changes into SiO2. As a result, each overlapping bonding layer can be transformed into an SiO2-containing layer, and the substrates can be bonded together.

[0014] Thus, the first substrate bonding method according to the present invention allows for bonding of substrates in an environment such as room temperature below 150°C without heat treatment. Therefore, it is possible to prevent a decrease in device performance or deterioration of the bonding state due to heat during bonding.

[0015] In the first substrate bonding method according to the present invention, the plasma irradiation step may involve irradiating the surfaces of the bonding layers of both substrates with plasma, but in order to obtain a higher bonding strength, it is preferable to irradiate only the surface of the bonding layer of one of the substrates with plasma.

[0016] The first substrate joining method according to the present invention is a substrate joining method for joining two substrates together, and may include a joining layer formation step of forming a joining layer containing polysilazane on the surface of one substrate; a plasma irradiation step of irradiating the surface of the joining layer with plasma to perform a hydrophilic treatment; and a joining step of joining the surface of one substrate and the surface of the other substrate with the joining layer in between, after the plasma irradiation step. In this case as well, the polysilazane contained in the joining layer interacts with water adsorbed by the hydrophilic treatment and changes into SiO2. As a result, the joining layer can be changed into a layer containing SiO2, and the substrates can be joined together.

[0017] A second substrate joining method according to the present invention is a substrate joining method for joining two substrates together, comprising: a plasma irradiation step of irradiating the surface of at least one substrate with plasma to perform a hydrophilic treatment; a bonding layer formation step of forming a bonding layer containing polysilazane on the surface of the one substrate irradiated with plasma in the plasma irradiation step, or on the surface of the other substrate; and a joining step of joining the surface of the one substrate and the surface of the other substrate with the bonding layer formed in the bonding layer formation step sandwiched between them.

[0018] In the second substrate bonding method according to the present invention, after irradiating the surface of at least one substrate with plasma to perform a hydrophilic treatment, the substrates are stacked with a bonding layer in between. The polysilazane contained in the bonding layer interacts with the water adsorbed by the hydrophilic treatment and changes into SiO2. As a result, the bonding layer can be transformed into a layer containing SiO2, and the substrates can be bonded together.

[0019] Thus, the second substrate bonding method according to the present invention allows for bonding of substrates in an environment such as room temperature below 150°C without heat treatment. Therefore, it is possible to prevent a decrease in device performance or deterioration of the bonding state due to heat during bonding.

[0020] In the second substrate bonding method according to the present invention, the plasma irradiation step may involve irradiating the surfaces of both substrates with plasma, or irradiating only the surface of one of the substrates with plasma. Furthermore, the bonding layer formation step may involve forming a bonding layer on the surface of a substrate that has not been irradiated with plasma, but it is preferable to form the bonding layer on the surface of a plasma-irradiated substrate in order to rapidly promote the change from polysilazane to SiO2.

[0021] In the first and second substrate bonding methods according to the present invention, the polysilazane may consist of, for example, the perhydropolysilazane (PHPS) shown in reaction formula (1), or it may consist of other types of polysilazane.

[0022] In the first and second substrate bonding methods according to the present invention, each substrate may be of any type, for example, a Si substrate, a substrate made of a Si-based material, a glass substrate, an ND substrate, a lithium niobate (LN) substrate, etc. For example, in the case of a substrate whose surface is made of silicon, such as a Si substrate or a substrate made of a Si-based material, the SiO2 in the bonding layer modified from polysilazane can bond each substrate with particularly high bonding strength. Also, each substrate may be, for example, a wafer, a chip, a panel, etc.

[0023] In the first and second substrate bonding methods according to the present invention, the plasma irradiation step may use any plasma, such as oxygen plasma or nitrogen plasma, as long as it can perform hydrophilic treatment. The bonding layer formed in the bonding layer formation step may contain polysilazane in part, or it may consist solely of polysilazane. The bonding layer formation step may be carried out by any method that allows for the formation of a bonding layer containing polysilazane. For example, the bonding layer may be formed by coating the substrate surface with a solution containing polysilazane in a solvent, forming a film, and then evaporating the solvent. The method for forming the bonding layer or the material of the bonding layer may be any method, such as spin coating, dip coating, or spray coating.

[0024] In the first and second substrate bonding methods according to the present invention, the bonding step is preferably performed in air or water, but may also be performed in a vacuum. When the bonding step is performed in air or water, if there is water adsorbed on the bonding layer during the hydrophilic treatment by plasma irradiation, that water can be used along with the bonding layer. Even if there is no water adsorbed on the bonding layer during the hydrophilic treatment, water adsorbed on the bonding layer during bonding can be used to convert polysilazane to SiO2, thereby bonding each substrate. Furthermore, when the bonding step is performed in a vacuum, the water adsorbed on the bonding layer during the hydrophilic treatment by plasma irradiation can be used to convert polysilazane to SiO2, thereby bonding each substrate.

[0025] The substrate bonding structure according to the present invention comprises two substrates and a bonding layer disposed between each substrate to bond them together, wherein the bonding layer contains Si, O, N, and H. In particular, the bonding layer preferably contains SiO2 and may also contain NH3.

[0026] The substrate bonding structure according to the present invention can be suitably manufactured by the first and second substrate bonding methods according to the present invention. As a result, the substrate bonding structure according to the present invention does not experience a decrease in device performance or deterioration of the bonding state during bonding, and has superior performance compared to bonding that undergoes heat treatment during bonding.

[0027] Furthermore, the substrate bonding structure according to the present invention can increase the bonding strength of each substrate due to the Si and O (SiO2) contained in the bonding layer. In particular, the bonding strength of each substrate due to the bonding layer is 2 J / m 2 Preferably, it is 5 J / m 2 The above is more preferable. Furthermore, in the substrate bonding structure according to the present invention, the bonding layer may have O uniformly dispersed and N uniformly dispersed.

[0028] According to the present invention, it is possible to provide a substrate bonding method and a substrate bonding structure that can prevent a decrease in device performance and deterioration of the bonding state during bonding.

[0029] Figure 3 shows a side view of the substrate bonding method according to the first embodiment of the present invention, including (a) a side view showing the plasma irradiation process, (b) a side view showing the bonding process, and (c) a side view showing the substrate bonding structure according to the embodiment of the present invention. Figure 3 shows a side view of the substrate bonding method according to the second embodiment of the present invention, including (a) a side view showing the plasma irradiation process, (b) a side view showing the bonding layer formation process, (c) the bonding process, and a side view showing the substrate bonding structure according to the embodiment of the present invention. Figure 3 shows a side view of a wafer bonding experiment according to the substrate bonding method according to the first embodiment of the present invention, including (a) a side view showing the process of forming the bonding layer, (b) a side view showing the cases where hydrophilic treatment by plasma irradiation is performed on the bonding layers of both wafers (Both side treatment), where hydrophilic treatment by plasma irradiation is performed on only the bonding layer of one wafer (One side treatment), and where hydrophilic treatment by plasma irradiation is not performed (w / o plasma), and a side view showing the bonding process. Figure 3 shows the XPS spectrum of the bonding layer formed in the wafer bonding experiment, including (a) the O1s peak, (b) the N1s peak, and (c) the Si2p peak. Figure 3 shows infrared (IR) images of the wafer bonding structure obtained in the wafer bonding experiment shown in Figure 3, for (a) when no hydrophilic treatment by plasma irradiation was performed (w / o plasma), (b) when hydrophilic treatment by plasma irradiation was performed on the bonding layers of both wafers (Both-side treatment), and (c) when hydrophilic treatment by plasma irradiation was performed on the bonding layer of only one wafer (One-side treatment). Figure 3 shows a graph of the measured bond strength of the wafer bonding structure obtained in the wafer bonding experiment shown in Figure 3. Figure 3 shows (a) a side view of the wafer bonding structure, (b) a scanning electron microscope (SEM) image of the wafer bonding structure, and (c) an energy-dispersive X-ray spectroscopy (EDX) spectrum along the line crossing the bonding interface of each bonding layer.Figure 3 shows a graph of the atomic ratio of O to N at the delamination surface of the bonded layer, with and without hydrophilic treatment by plasma irradiation, for the wafer bonded structure obtained in a wafer bonding experiment using the substrate bonding method of the first embodiment of the present invention, and for the wafer bonded structure obtained in a wafer bonding experiment using the substrate bonding method of the second embodiment of the present invention. Figure 4 shows infrared images (IR images) of the wafer bonded structure obtained in a wafer bonding experiment using the substrate bonding method of the second embodiment of the present invention, with (a) hydrophilic treatment by plasma irradiation (with plasma) and with (b) hydrophilic treatment by plasma irradiation (without plasma). Figure 5 shows a graph of the measured bond strength of the wafer bonded structure obtained in a wafer bonding experiment using the substrate bonding method of the second embodiment of the present invention. Figure 12 shows the measurement results of the contact angle for each plasma irradiation time of the Si wafer and LN wafer in a wafer bonding experiment using the substrate bonding method of the second embodiment of the present invention. (a) Scanning electron microscope (SEM) image of the wafer bonding structure when hydrophilic treatment is performed (with plasma), and (c) Energy dispersive X-ray spectroscopy (EDX) spectrum along the line crossing the bonding interface of each bonding layer. Figure 12 shows the measurement of the contact angle for each plasma irradiation time of the Si wafer and LN wafer in a wafer bonding experiment using the substrate bonding method of the second embodiment of the present invention. The following are side views of a bonding experiment between a wafer and a chip in water using the substrate bonding method of a second embodiment of the present invention: (a) a side view showing the plasma irradiation process, (b) a side view showing the application of the PHPS solution in the bonding layer formation process, (c) a side view showing the baking process in the bonding layer formation process, and (d) a side view showing the bonding and pressurizing process in pure water in the bonding process.Figure 15 shows the N1s peak of the XPS spectrum of the Si wafer peeled off after bonding (bonding underwater) and the Si wafer after baking treatment shown in Figure 15(c), which are part of the bonded structure obtained in the underwater wafer-chip bonding experiment shown in Figure 15. Figure 15 shows a plan view of the surface of the Si wafer and Si chip peeled off after bonding, which are part of the bonded structure obtained in the underwater wafer-chip bonding experiment shown in Figure 15. Figure 15 shows a side view of the plasma irradiation process, a side view of the bonded layer formation process, and a side view of the bonding process in vacuum, in a wafer bonding experiment in vacuum using the substrate bonding method of the second embodiment of the present invention. Figure 18 shows an infrared image (IR image) of the wafer bonded structure obtained in the wafer bonding experiment in vacuum shown in Figure 18. Figure 18 shows the results of heat treatment tests on the wafer bonding structure obtained in a wafer bonding experiment in a vacuum, (a) no heat treatment (RT), (b) heat treatment temperature of 100°C, (c) 200°C, (d) 300°C, (e) 400°C, (f) 500°C, and (g) 600°C, as shown in the IR images. Figure 20 is a graph showing the tensile strength of each bonding structure after the heat treatment test. Figure 18 shows a transmission electron microscope (TEM) image of a cross-section of the wafer bonding structure obtained in a wafer bonding experiment in a vacuum. (a) is a magnified TEM image of the area near the bonding layer from the TEM image shown in Figure 22, and (b) is an energy-dispersive X-ray spectroscopy (EDX) spectrum along the line crossing the bonding interface of the bonding layer shown in (a). Figure 18 shows the XPS spectra of the debonded surface of the wafer after bonding (Debonded surface) and the as-coated surface of the bonded layer after coating with PHPS solution (As-coated surface), obtained in a wafer bonding experiment in a vacuum, as shown in Figure 18(b). The peaks shown are (a) O1s, (b) N1s, and (c) Si2p.

[0030] Embodiments of the present invention will be described below with reference to the drawings. Figures 1 to 24 show a substrate bonding method and a substrate bonding structure according to embodiments of the present invention.

[0031] Figure 1 shows a substrate joining method according to a first embodiment of the present invention. In the substrate joining method according to the first embodiment of the present invention, first, a bonding layer formation step is performed to form bonding layers 12a and 12b containing polysilazane on the surfaces of two wafers (Si wafers) 11a and 11b, respectively, which are to be joined. In the specific example shown in Figure 1, each substrate to be joined is made of a wafer, but it is not limited to wafers and may be made of panels or chips. Also, although each wafer 11a and 11b is made of Si wafers, it may be a substrate made of Si-based material, a glass substrate, an ND substrate, an LN substrate, etc. The polysilazane may consist of any type of polysilazane, but in the specific example shown in Figure 1, it consists of perhydropolysilazane (PHPS). Also, each bonding layer 12a and 12b may contain polysilazane in part, or may consist only of polysilazane. Furthermore, any method may be used to deposit each bonding layer 12a, 12b or its material, such as spin coating, dip coating, or spray coating.

[0032] Next, as shown in Figure 1(a), a plasma irradiation process is performed to perform hydrophilic treatment on the surface of at least one of the bonded layers 12a and 12b formed by the plasma irradiation process. The plasma used for irradiation can be any plasma capable of performing hydrophilic treatment, such as oxygen plasma or nitrogen plasma. As a result, the perhydropolysilazane contained in the plasma-irradiated bonded layer interacts with the water adsorbed by the hydrophilic treatment and changes into SiO2. Note that the bonded layer subjected to hydrophilic treatment by plasma irradiation may be the bonded layers 12a and 12b of both wafers 11a and 11b, or it may be only the bonded layer 12a of one wafer 11a.

[0033] After hydrophilic treatment, the bonding layers 12a and 12b of each wafer 11a and 11b are superimposed by a bonding process, as shown in Figure 1(b). Although Figure 1(b) shows the state after hydrophilic treatment by plasma irradiation has been performed on the surfaces of the bonding layers 12a and 12b of both wafers 11a and 11b, the wafers 11a and 11b may be superimposed after hydrophilic treatment has been performed on the surface of only the bonding layer 12a of one wafer 11a.

[0034] As shown in Figure 1(c), when the bonding layers 12a and 12b of each wafer 11a and 11b are stacked together and hydrophilic treatment is applied to the bonding layers 12a and 12b of both wafers 11a and 11b, the perhydropolysilazane contained in both bonding layers 12a and 12b is converted to SiO2. Also, even if only the bonding layer 12a of one wafer 11a is hydrophilic treated, the perhydropolysilazane contained in the bonding layer 12b that has not been hydrophilic treated interacts with water adsorbed on the hydrophilic treated bonding layer 12a and is converted to SiO2. As a result, each stacked bonding layer 12a and 12b can be transformed into a layer 13 containing SiO2, and the wafers 11a and 11b can be bonded together. In this way, the bonding structure of the substrate according to the embodiment of the present invention can be obtained.

[0035] In addition, in the first embodiment of the present invention, the method for joining substrates may involve forming a bonding layer 12a containing polysilazane only on the surface of one wafer 11a, irradiating the surface of the bonding layer 12a with plasma to perform a hydrophilic treatment, and then overlapping the surface of one wafer 11a with the surface of the other wafer 11b with the bonding layer 12a in between. In this case as well, the polysilazane contained in the bonding layer 12a interacts with the water adsorbed by the hydrophilic treatment and changes into SiO2. As a result, the bonding layer 12a can be changed into a layer containing SiO2, the wafers 11a and 11b can be joined, and the substrate bonding structure of the embodiment of the present invention can be obtained.

[0036] Figure 2 shows the method for bonding substrates according to the second embodiment of the present invention. In the following description, the same components as those in the method for bonding substrates according to the first embodiment of the present invention are denoted by the same reference numerals, and redundant descriptions are omitted.

[0037] In the method for bonding substrates according to the second embodiment of the present invention, first, as shown in Fig. 2(a), by a plasma irradiation step, either one of the two wafers 11a and 11b to be bonded or both wafers 11a and 11b are irradiated with plasma on their surfaces for hydrophilic treatment. Fig. 2 shows the case where both wafers 11a and 11b are irradiated with plasma on their surfaces for hydrophilic treatment.

[0038] Next, as shown in Fig. 2(b), by a bonding layer formation step, a bonding layer 12 containing polysilazane is formed on the surface of either one of the wafers 11a. The polysilazane may be composed of any type of polysilazane. In the specific example shown in Fig. 2, it is composed of perhydropolysilazane (PHPS). When only one of the wafers 11a is irradiated with plasma, the bonding layer 12 may be formed on the surface of the wafer 11b that is not irradiated with plasma, or the bonding layer 12 may be formed on the surface of the wafer 11a that is irradiated with plasma. When the bonding layer 12 is formed on the surface of the wafer 11a irradiated with plasma, the perhydropolysilazane contained in the bonding layer 12 interacts with the water adsorbed by the hydrophilic treatment and changes to SiO2.

[0039] After the bonding layer 12 is formed, as shown in Fig. 2(c), by a bonding step, with the bonding layer 12 interposed therebetween, the surface of one wafer 11a and the surface of the other wafer 11b are overlapped. As a result, regardless of whether the bonding layer 12 is formed on which wafer 11a or 11b, the perhydropolysilazane contained in the bonding layer 12 interacts with the water adsorbed by the hydrophilic treatment and changes to SiO2. Thereby, the bonding layer 12 can be changed to a layer 13 containing SiO2, and the wafers 11a and 11b can be bonded. Thus, the bonding structure of the substrates according to the embodiment of the present invention can be obtained.

[0040] Thus, the substrate bonding methods according to the first and second embodiments of the present invention can bond the wafers 11a and 11b in an environment such as room temperature lower than 150°C without performing heat treatment. Therefore, it is possible to prevent a decrease in the performance of the device due to heat and deterioration of the bonding state during bonding.

[0041] In the substrate bonding methods according to the first and second embodiments of the present invention, the bonding process is preferably performed in air or water, but may also be performed in a vacuum. When the bonding process is performed in air or water, together with the water adsorbed on the bonding layer 12 during the hydrophilic treatment by the plasma irradiation process, the water adsorbed on the bonding layer 12 during bonding can be used to change polysilazane to SiO2, and the wafers 11a and 11b can be bonded. Also, when the bonding process is performed in a vacuum, the water adsorbed on the bonding layer 12 during the hydrophilic treatment by the plasma irradiation process can be used to change polysilazane to SiO2, and the wafers 11a and 11b can be bonded.

[0042] A wafer bonding experiment was conducted using the substrate bonding method according to the first embodiment of the present invention shown in FIG. 1. In the experiment, a 4-inch Si wafer with a thickness of 525 μm was used as the substrate. Also, for forming the bonding layer, a PHPS solution (product name "Durazane 2200", manufactured by Merck Performance Materials K.K.) containing 20 wt% of perhydropolysilazane in a dibutyl ether solvent was used. When forming the bonding layer on the surface of the wafer, first, as shown in FIG. 3(a), the PHPS solution was applied to the surface of each wafer by spin coating at 2000 rpm for 20 seconds, and then baking treatment was performed on a hot plate at 100°C for 5 minutes to volatilize the solvent. Also, as shown in FIG. 3(b), in the plasma irradiation, nitrogen plasma was irradiated at 150 W for 60 seconds to perform hydrophilic treatment. As shown in FIG. 3(c), in the bonding of each wafer, the bonding layers of each wafer were manually overlapped in an environment of air at room temperature.

[0043] As shown in Figure 3(b), in the experiment, wafer bonding was performed in three patterns: when hydrophilic treatment was applied by plasma irradiation to the bonding layer of both wafers (Both-side treatment), when hydrophilic treatment was applied by plasma irradiation to the bonding layer of only one wafer (One-side treatment), and, for comparison, when no hydrophilic treatment by plasma irradiation was performed (w / o plasma).

[0044] First, to investigate the surface composition of the bonding layer, X-ray photoelectron spectroscopy (XPS) analysis was performed. XPS analysis was performed on the bonding layer after coating (As coated), after baking at 100°C (Baked at 100°C), and after plasma irradiation (Baked and plasma treated). The XPS spectra for each are shown in Figures 4(a) to (c). As shown in Figure 4, in the bonding layer after coating and baking, no oxygen peaks were observed, but prominent peaks of nitrogen and silicon nitride around 101.3 eV were observed. In contrast, in the bonding layer after plasma irradiation, a prominent oxygen peak was observed, and the nitrogen peak was found to be reduced. Furthermore, it was found that the peak around 101.3 eV shifted to around 103.5 eV, indicating the presence of silicon oxide. This is thought to be because, due to the hydrophilic treatment by plasma irradiation, perhydropolysilazane interacted with water and was converted to SiO2, as shown in reaction equation (1).

[0045] Next, to evaluate the bonding quality, the bonded structure after bonding each wafer was observed using infrared imaging (IR imaging), and bonding strength was measured by blade insertion. The IR images of the three patterns shown in Figure 3 are shown in Figures 5(a) to (c), respectively. In IR images, if voids exist at the interface of each bonded layer, these voids can be confirmed as interference fringe patterns.

[0046] As shown in Figures 5(a) and (c), no interference fringes were observed in wafers without hydrophilic treatment (w / o plasma) or in wafers where hydrophilic treatment was applied only to the bonding layer of one wafer (One-side treatment). In contrast, as shown in Figure 5(b), numerous interference fringes were observed in wafers where hydrophilic treatment was applied to the bonding layers of both wafers (Both-side treatment), confirming the presence of voids at the interface of each bonding layer.

[0047] This is thought to be because the bonding layer containing perhydropolysilazane before conversion to SiO2 is relatively soft and has high viscosity, which fills in the irregularities at the interface of the bonding layer and improves adhesion, whereas the bonding layer after perhydropolysilazane has been converted to SiO2 is hard and cannot completely fill in the irregularities at the interface of the bonding layer.

[0048] Figure 6 shows the results of bond strength measurement tests performed by blade insertion for the three patterns shown in Figure 3. As shown in Figure 6, the bond strength of the material without hydrophilic treatment (w / o plasma) was 0.30 J / m 2 The bonding strength of wafers with hydrophilic treatment applied to both sides (Both-side treatment) is 0.64 J / m 2 In contrast, the bonding strength of a wafer where only the bonding layer of one wafer is hydrophilically treated (One-side treatment) is 5.54 J / m 2 It was confirmed that it possesses extremely high strength.

[0049] This is because, without hydrophilic treatment, water is not supplied to the bonding interface, so perhydropolysilazane is not converted to SiO2, and the adhesive strength does not increase. Conversely, when hydrophilic treatment is applied to the bonding layers of both wafers, as shown in Figure 5(b), voids are generated at the interface of each bonding layer, which is thought to reduce bonding quality and thus reduce bonding strength. On the other hand, when hydrophilic treatment is applied to the bonding layer of only one wafer, as shown in Figure 5(c), the bonding quality is good during bonding, and after bonding, it is thought that the bonding strength is increased after bonding because not only the perhydropolysilazane in the hydrophilic-treated bonding layer, but also the perhydropolysilazane in the untreated bonding layer interacts with the water adsorbed by the hydrophilic treatment and is converted to SiO2.

[0050] For wafers where only the bonding layer of one wafer was treated with hydrophilic treatment (one-side treatment), elemental analysis was performed using energy-dispersive X-ray spectroscopy (EDX) along lines crossing the bonding interface of each bonding layer. The results are shown in Figure 7. As shown in Figure 7(c), compared to the regions of each wafer, it was confirmed that the levels of O and N increased and the levels of Si decreased in the regions of each bonding layer. This is thought to be because O and N are not present in each wafer but are present in each bonding layer, while Si is present in each wafer but its density decreases in each bonding layer.

[0051] Furthermore, as shown in Figure 7(c), it was confirmed that in each bonding layer region, O was slightly more abundant on the side of the plasma-treated bonding layer (Plasma-treated PHPS), while N was more abundant on the wafer side of the untreated bonding layer (Untreated PHPS). This is thought to be because, in the plasma-treated bonding layer, the conversion from perhydropolysilazane to SiO2 progresses, but in the untreated bonding layer, the conversion from perhydropolysilazane to SiO2 does not extend to the entire bonding layer, but rather progresses at the bonding interface side and not on the wafer side. In the region where the conversion from perhydropolysilazane to SiO2 progresses, N is due to NH3, a byproduct of reaction equation (1).

[0052] X-ray photoelectron spectroscopy (XPS) was used to analyze the delaminated surface obtained by a bonding strength measurement test using blade insertion. XPS analysis was performed on wafers with hydrophilic treatment applied to only one of the bonding layers (one-side treatment) and wafers without hydrophilic treatment by plasma irradiation (w / o plasma). The atomic ratio of O to N was calculated from the O1s peak and N1s peak obtained from the XPS analysis for each wafer, and the calculation results are shown in Figure 8(a).

[0053] As shown in Figure 8(a), the N ratio was 0.88 in the sample without hydrophilic treatment, while it was confirmed that the N ratio decreased to 0.50 in the sample with hydrophilic treatment on one of the bonding layers. This is thought to be because the perhydropolysilazane in the bonding layer reacted with water adsorbed on the bonding layer due to the hydrophilic treatment, and the N was replaced with O. It should be noted that the O in the sample without hydrophilic treatment is thought to have been produced by the reaction of perhydropolysilazane with water naturally adsorbed on the wafer.

[0054] A wafer bonding experiment was conducted using the substrate bonding method of the second embodiment of the present invention shown in Figure 2. In the experiment, the same wafers and PHPS solution as in Example 1 were used. Before forming the bonding layer, the surface of each wafer was irradiated with oxygen plasma at 150 W for 60 seconds, followed by irradiation with nitrogen plasma at 150 W for 60 seconds to perform hydrophilic treatment. After the hydrophilic treatment, each wafer was rinsed with ultrapure water (de-ionized water) and spin-dried. The bonding layer was formed in the same manner as in Example 1. In bonding each wafer, the wafers were stacked by hand in an air-filled, room-temperature environment, with the bonding layer in between.

[0055] In the experiment, wafer bonding was performed in two patterns: one where hydrophilic treatment was applied to the surface of both wafers by plasma irradiation (With plasma), and another where hydrophilic treatment was not applied by plasma irradiation (Without plasma) for comparison.

[0056] To evaluate the bonding quality, the bonded structure after bonding each wafer was observed using infrared imaging (IR imaging), and bonding strength was measured by blade insertion. Two patterns of IR images, one with hydrophilic treatment and one without, are shown in Figures 9(a) and 9(b), respectively. As shown in Figures 9(a) and 9(b), no interference fringes were observed and no voids were present in either the hydrophilic treated wafer (with plasma) or the untreated wafer (without plasma), confirming good bonding quality.

[0057] This is thought to be because, in wafers that have not undergone hydrophilic treatment, the bonding layer containing perhydropolysilazane is relatively soft and has high viscosity, which fills in surface irregularities in the bonding layer and improves adhesion. Furthermore, even in wafers that have undergone hydrophilic treatment, during the bonding of each wafer, the conversion from perhydropolysilazane in the bonding layer to SiO2 does not extend to the surface of the wafer where the bonding layer was not formed. Since that surface is relatively soft and has high viscosity, it is thought that the surface irregularities of the bonding layer are filled in, resulting in improved adhesion.

[0058] Figure 10 shows the results of bond strength measurement tests conducted by blade insertion for two patterns: with and without hydrophilic treatment. As shown in Figure 10, the bond strength of the pattern without hydrophilic treatment (Without plasma) was 1.07 J / m 2 In contrast, the bonding strength of the hydrophilic treated material (with plasma) is 6.02 J / m 2 It was confirmed that it possesses extremely high strength.

[0059] This is thought to be because, without hydrophilic treatment, water is not supplied to the bonding interface, so perhydropolysilazane is not converted to SiO2, and the adhesive strength does not increase. On the other hand, when hydrophilic treatment is performed, after bonding, water adsorbed by the hydrophilic treatment is supplied from the wafer side where the bonding layer is not formed, so perhydropolysilazane is converted to SiO2 throughout the entire bonding layer, and the adhesive strength increases.

[0060] Elemental analysis was performed using energy-dispersive X-ray spectroscopy (EDX) along a line crossing the bonding layer on the hydrophilic treated (with plasma) wafers. The results are shown in Figure 11. As shown in Figure 11(b), compared to the regions of each wafer, it was observed that the levels of O and N increased and Si decreased in the bonding layer region. This is thought to be because O and N are not present in each wafer but are present in the bonding layer, while Si is present in each wafer but its density decreases in the bonding layer.

[0061] Furthermore, as shown in Figure 11(b), it was confirmed that Si, O, and N were uniformly distributed in the bonding layer region compared to Figure 7(c). This is thought to be because the surfaces of each wafer in contact with both sides of the bonding layer were treated with hydrophilic treatment, and water adsorbed from both sides of the bonding layer was supplied, resulting in a relatively uniform conversion from perhydropolysilazane to SiO2 in the bonding layer. In addition, the presence of N is thought to be due to NH3, a byproduct of reaction equation (1), which diffused uniformly into the bonding layer.

[0062] X-ray photoelectron spectroscopy (XPS) analysis was performed on the delamination surfaces obtained during bonding strength measurement tests using blade insertion. XPS analysis was performed on samples with hydrophilic treatment (with plasma) and samples without hydrophilic treatment (without plasma). The atomic ratio of O to N was calculated from the O1s peak and N1s peak obtained from the XPS analysis for each sample, and the calculation results are shown in Figure 8(b). As shown in Figure 8(b), the N ratio was 0.75 for the sample without hydrophilic treatment, while it was confirmed that the N ratio decreased to 0.30 for the sample with hydrophilic treatment. This is thought to be because the perhydropolysilazane in the bonding layer reacted with water adsorbed on the surface of each wafer due to the hydrophilic treatment, and N was replaced by O. It should be noted that the O in the sample without hydrophilic treatment is thought to have been produced by the reaction of perhydropolysilazane with water naturally adsorbed on the wafer.

[0063] Furthermore, when comparing the hydrophilic treatment in Figure 8(b) with the hydrophilic treatment in Figure 8(a) (One-side treatment), it was confirmed that the ratio of N was significantly smaller. This is thought to be because, in the wafer bonding method shown in Figure 2, the hydrophilic treatment (With plasma) is applied to the surfaces of both wafers, resulting in a relatively larger amount of water in contact with the bonding layer compared to the wafer bonding method shown in Figure 1, where only one bonding layer is hydrophilic (One-side treatment). Additionally, in the wafer bonding method shown in Figure 2, the bonding layer thickness is half that of the wafer bonding method shown in Figure 1, where only one bonding layer is hydrophilic (One-side treatment), which is thought to facilitate the replacement of N with O throughout the entire bonding layer.

[0064] A wafer bonding experiment was conducted using the substrate bonding method of the second embodiment of the present invention shown in Figure 2. In the experiment, a 4-inch Si wafer with a thickness of 525 μm and a 4-inch LN (LiNbO3) wafer with a thickness of 500 μm were used as substrates. The same PHPS (perhydropolysilazane) solution as in Example 1 was used to form the bonding layer. In the experiment, before forming the bonding layer, the surface of each wafer was treated with hydrophilicity by irradiating it with nitrogen plasma at 100 W for 60 seconds. After hydrophilic treatment, each wafer was rinsed with ultrapure water (de-ionized water) and spin-dried. After applying the PHPS solution to the surface of the LN wafer by spin coating, a baking treatment was performed on a hot plate at 100°C for 5 minutes to evaporate the solvent and form a bonding layer. In an air environment at room temperature, the Si wafer and the LN wafer were bonded by placing the bonding layer between them and stacking the Si wafer on top of the bonding layer.

[0065] To examine the hydrophilic performance by plasma irradiation on each wafer surface, the contact angle of water before and after plasma irradiation was measured. Figures 12(a) and (b) show the states of measuring the contact angle before and after plasma irradiation on the LN wafer. Also, the measurement results of the contact angle for each plasma irradiation time (Plasma irradiation time) of the Si wafer and the LN wafer are shown in Figure 13.

[0066] As shown in Figure 13, it was confirmed that the contact angle decreased significantly by plasma irradiation for both the Si wafer and the LN wafer. Also, in the Si wafer, the contact angle gradually decreased as the plasma irradiation time increased, while in the LN wafer, it was confirmed that even when the plasma irradiation time increased, the contact angle remained small and hardly changed. From the results shown in Figure 13, it can be said that high hydrophilicity can be obtained by plasma irradiation for 60 seconds or more for both the Si wafer and the LN wafer.

[0067] Also, five days after bonding the Si wafer and the LN wafer, a bond strength measurement test was conducted by blade insertion. The bond strength was 1.7 J / m 2 It was. Also, for comparison, without plasma irradiation and with other conditions the same, the Si wafer and the LN wafer were bonded, and the bond strength seven days after bonding was measured. The bond strength was 0.2 J / m 2 It was. From this result, it can be said that the hydrophilic treatment by plasma irradiation greatly contributes to the bonding using PHPS.

[0068] The scanning electron microscope (SEM) image of the cross-section of the bonding structure between the Si wafer and the LN wafer is shown in Figure 14. As shown in Figure 14, it was confirmed that the Si wafer and the LN wafer were uniformly bonded by PHPS. The bonding layer by PHPS has a thickness of about 500 nm.

[0069] A bonding experiment between a wafer and a chip in water was conducted using the substrate bonding method of the second embodiment of the present invention shown in Figure 2. In the experiment, a 4-inch Si wafer with a thickness of 525 μm and a 3 mm square Si chip with a thickness of 525 μm were used as substrates. The same PHPS solution as in Example 1 was used to form the bonding layer.

[0070] Figure 15 shows the bonding method used in this experiment. First, as shown in Figure 15(a), the surfaces of the Si wafer 21a and Si chip 21b were treated with hydrophilic treatment by irradiating them with nitrogen plasma (N2 plasma) at 100 W for 60 seconds. After the hydrophilic treatment, as shown in Figure 15(b), the PHPS solution 22 was applied to the surface of the Si wafer 21a by spin coating at 2000 rpm for 20 seconds. Then, as shown in Figure 15(c), baking was performed on a hot plate at 100°C for 1 minute to evaporate the solvent and form a bonding layer 23. As shown in Figure 15(d), the Si chip 21b was placed on top of the bonding layer 23 in pure water 24, with the bonding layer 23 in between (bonding underwater). Subsequently, the Si wafer 21a and Si chip 21b were bonded together by pressing them at 10 MPa for 10 seconds in an air-filled, room-temperature environment.

[0071] First, a die shear test was performed to measure the bonding strength of the bonded structure between the Si wafer 21a and the Si chip 21b. The die shear test was performed on the bonded structure 0.5 hours and 24 hours after bonding, with a blade scanning height of 2 μm and a scanning speed of 0.6 mm / min. The results of the die shear test showed that the bonding strength 0.5 hours after bonding was 0.53 MPa, and the bonding strength 24 hours after bonding was 6.30 MPa.

[0072] Based on the die-shear test results, it is thought that during bonding, PHPS reacts with water remaining in the bonding layer 23 to be converted to SiO2, resulting in increased adhesive strength. Furthermore, since the bonding strength remains high even after bonding, it is thought that the conversion from PHPS to SiO2 continues even after bonding, reacting with moisture and oxygen in the atmosphere.

[0073] Next, 24 hours after bonding, the Si wafer 21a and Si chip 21b were separated, and the surface of the separated Si wafer 21a was analyzed by X-ray photoelectron spectroscopy (XPS). The N1s peak of the XPS spectrum is shown in Figure 16. For comparison, XPS analysis was also performed on the surface of the Si wafer 21a after the baking treatment shown in Figure 15(c), and the N1s peak of its XPS spectrum is also shown in Figure 16.

[0074] As shown in Figure 16, a sharp peak was observed in the Si wafer 21a after baking (labeled "as baked" in the figure), while a relatively gentle peak was observed in the Si wafer 21a peeled off after bonding (labeled "bonding underwater" in the figure). From these results, it is thought that the N1s peak is suppressed by the conversion of PHPS to SiO2 after bonding, and that the water used during bonding underwater contributes as a reaction source for the conversion of PHPS to SiO2. However, since a slight N1s peak is observed in the Si wafer 21a peeled off after bonding, it is thought that the PHPS was not completely converted to SiO2.

[0075] Figure 17 shows the surface conditions of the peeled Si wafer 21a and Si chip 21b. As shown in Figure 17, the surface of the Si wafer 21a and the surface of the Si chip 21b show similar patterns, suggesting that delamination occurred within the bonding layer 23. Considering this result and the result in Figure 16, it is considered that the conversion from PHPS to SiO2 is proceeding within the bonding layer 23.

[0076] A wafer bonding experiment in a vacuum was conducted using the substrate bonding method of the second embodiment of the present invention shown in Figure 2. In the experiment, a 4-inch Si wafer with a thickness of 525 μm was used as the substrate. The same PHPS solution as in Example 1 was used to form the bonding layer.

[0077] Figure 18 shows the bonding method used in this experiment. First, as shown in Figure 18(a), the surfaces of each wafer 31a and 31b were treated with hydrophilic processing by irradiating them with oxygen RIE (reactive ion etching) plasma, nitrogen RIE plasma, and microwave nitrogen radicals at 200 W for 60 seconds each. After hydrophilic processing, each wafer 31a and 31b was rinsed with ultrapure water (de-ionized water) and spin-dried. As shown in Figure 18(b), a PHPS solution was applied to the surface of one wafer 31a by spin coating, and then a baking treatment was performed at 100°C for 1 minute to evaporate the solvent and form a bonding layer 33. As shown in Figure 18(c), the wafers 31a and 31b were stacked inside a vacuum chamber 34 at 100 Pa at room temperature with the bonding layer 33 in between, and bonded by pressurizing at 1000 N for 5 minutes.

[0078] First, to evaluate the bonding quality, the bonded structure, obtained by bonding wafers 31a and 31b in a vacuum, was observed using infrared imaging (IR imaging) and subjected to bonding strength measurement tests by blade insertion. The IR image of the bonded structure bonded in a vacuum is shown in Figure 19. As shown in Figure 19, there are several interference fringes and voids in the peripheral areas of wafers 31a and 31b, but no voids are present in the central areas of wafers 31a and 31b, confirming that they are well bonded by the bonding layer 33. This is thought to be because the bonding layer 33, which contains perhydropolysilazane before conversion to SiO2, is relatively soft and has high viscosity, thus filling in the irregularities at the interface of the bonding layer 33 and improving adhesion.

[0079] Bond strength was measured using blade insertion, and the bond strength of each wafer 31a and 31b was found to be 3.98 J / m 2Thus, it was confirmed that it possessed sufficiently high strength. Here, as shown in Figure 10, in Example 2, the bonding strength of the bonded structure bonded in the atmosphere was 6.02 J / m 2 The result was as follows: PHPS exhibits adhesive properties by converting water adsorbed by hydrophilic treatment into SiO2, forming a bonding layer. Therefore, the amount of water adsorbed by the hydrophilic treatment affects the adhesive performance. In this experiment, when bonding in a vacuum, some of the water adsorbed by the hydrophilic treatment is released, resulting in lower bonding strength compared to bonding in air. However, it can be said that it has sufficiently high strength compared to, for example, materials without hydrophilic treatment.

[0080] Next, heat treatment tests were performed on the bonding structures of each wafer 31a and 31b at 100°C, 200°C, 300°C, 400°C, 500°C, and 600°C. After heat treatment at each temperature, IR images of chips obtained by cutting the bonding structure of each wafer 31a and 31b into 1 cm × 1 cm sections are shown in Figures 20(b) to (g). An IR image of a chip that was not heat-treated (RT) is also shown in Figure 20(a). As shown in Figures 20(a) to (f), no changes were observed in the bonding layer 33 for the untreated and heat-treated samples at 500°C or below. In contrast, as shown in Figure 20(g), partial delamination of the bonding layer 33 was observed in the sample heat-treated at 600°C.

[0081] Furthermore, while NH3 and H2 are generated as byproducts during the conversion from PHPS to SiO2, no foamy voids formed by these byproducts were observed, as shown in Figures 19 and 20. This suggests that these byproducts are not abundant enough to aggregate and form voids, but rather diffuse into the bonding interface.

[0082] Tensile strength measurements were performed at two locations on the bonded structure after heat treatment at each temperature. The results are shown in Figure 21. As shown in Figure 21, in the cases where heat treatment was performed at 300°C or below, each wafer 31a and 31b cracked during the measurement, suggesting that the tensile strength of the bonded layer 33 is greater than the strength of each wafer 31a and 31b, which is 10 MPa. In contrast, the tensile strengths of the cases where heat treatment was performed at 400°C, 500°C, and 600°C were 3.71 MPa, 2.64 MPa, and 0 MPa, respectively, confirming that the tensile strength decreases as the temperature increases. From the results shown in Figure 20, delamination of the bonded layer 33 was observed at 600°C, but from the results shown in Figure 21, it is thought that at temperatures above 400°C, the tensile strength decreases significantly due to the volume contraction of the PHPS layer and the difference in thermal expansion coefficients between Si and PHPS.

[0083] Next, the cross-sections of the bonding structure of each wafer 31a and 31b were observed using a transmission electron microscope (TEM) and elemental analysis was performed using energy-dispersive X-ray spectroscopy (EDX). The TEM images and the elemental analysis results along the line crossing the bonding interface of the bonding layer 33 are shown in Figures 22 and 23, respectively. As shown in Figure 22, it was confirmed that even when bonding in a vacuum, each wafer 31a and 31b was uniformly bonded by the PHPS bonding layer 33. The PHPS bonding layer 33 has a thickness of approximately 400 nm.

[0084] Furthermore, as shown in Figure 23, elemental analysis by EDX revealed the presence of Si, N, and O in the bonding layer 33, along with background C. It was confirmed that Si accounts for approximately 50% of the bonding layer 33 overall. O was found to be present at approximately 40% of the bonding interface, approximately 50% of the coating interface, and approximately 30% near the center of the bonding layer 33. This is thought to be because the coating was performed in air and the bonding was performed in a vacuum, resulting in a higher O content at the coating interface. Additionally, it was confirmed that N was more abundant in the center of the bonding layer 33 and decreased at each interface. This indicates that O is gradually diffusing from each interface towards the center, and it is thought that the N originally contained in the PHPS solution is gradually replaced by O as PHPS is converted to SiO2 after bonding.

[0085] Furthermore, the N content shown in Figure 23 is higher than the result shown in Figure 11, which was obtained by bonding in air. This suggests that the conversion from N to O, i.e., the conversion from PHPS to SiO2, is not completely finished during bonding in a vacuum. This is thought to be because some of the water adsorbed by the hydrophilic treatment is released during bonding in a vacuum.

[0086] Next, X-ray photoelectron spectroscopy (XPS) analysis was performed on the surface of the bonded layer 33 after coating with the PHPS solution shown in Figure 18(b) (As-coated surface), and on the surfaces of wafers 31a and 31b peeled off after bonding (Debonded surface). The respective XPS spectra are shown in Figures 24(a) to (c). As shown in Figures 24(a) to (c), a prominent peak for N, a small peak for O, and a prominent peak for Si2p around 101.55 eV corresponding to the Si-N bond were observed in the bonded layer 33 after coating with the PHPS solution. In contrast, a decrease in the N peak, a significant increase in the O peak, and a peak shift of Si2p to around 102.37 eV were observed in wafers 31a and 31b peeled off after bonding. This is thought to be because N is converted to O during bonding. It is also thought that the Si-N bond is partially converted to a Si-O bond, forming a bond interface where Si-O and Si-N are mixed.

[0087] 11a, 11b Wafer 12a, 12b, 12 Bonding layer 13 Layer containing SiO2 21a Si wafer 21b Si chip 22 PHPS solution 23 Bonding layer 24 Pure water 31a, 31b Wafer 33 Bonding layer 34 Vacuum chamber

Claims

1. A method for joining two substrates, comprising: a bonding layer formation step of forming a bonding layer containing polysilazane on the surface of each substrate; a plasma irradiation step of irradiating the surface of the bonding layer of at least one of the substrates with plasma to perform hydrophilic treatment; and a bonding step of overlapping and joining the bonding layers of each substrate after the plasma irradiation step.

2. The method for joining substrates according to claim 1, characterized in that the plasma irradiation step irradiates only the surface of the bonding layer of one of the substrates with the plasma.

3. A method for joining two substrates, comprising: a bonding layer formation step of forming a bonding layer containing polysilazane on the surface of one substrate; a plasma irradiation step of irradiating the surface of the bonding layer with plasma to perform a hydrophilic treatment; and a bonding step of joining the surface of one substrate and the surface of the other substrate with the bonding layer in between, after the plasma irradiation step.

4. A method for joining two substrates, comprising: a plasma irradiation step of irradiating the surface of at least one substrate with plasma to perform a hydrophilic treatment; a bonding layer formation step of forming a bonding layer containing polysilazane on the surface of the one substrate irradiated with plasma in the plasma irradiation step, or on the surface of the other substrate; and a bonding step of joining the surface of the one substrate and the surface of the other substrate with the bonding layer formed in the bonding layer formation step sandwiched between them.

5. The method for joining substrates according to claim 4, characterized in that the plasma irradiation step involves irradiating the plasma only on the surface of the one substrate, and the bonding layer formation step involves forming the bonding layer on the surface of the one substrate.

6. The method for joining substrates according to any one of claims 1 to 5, characterized in that the polysilazane is composed of perhydropolysilazane (PHPS).

7. A method for joining substrates according to any one of claims 1 to 5, characterized in that each substrate has at least one surface made of silicon.

8. The method for joining substrates according to any one of claims 1 to 5, characterized in that the joining step is performed in air or water.

9. The method for joining substrates according to any one of claims 1 to 5, characterized in that the joining step is performed in a vacuum.

10. A substrate bonding structure comprising two substrates and a bonding layer disposed between each substrate to bond the substrates, wherein the bonding layer contains Si, O, N, and H.

11. The bonding structure for a substrate according to claim 10, characterized in that the bonding layer has N uniformly dispersed.

12. The bonding structure of the substrate according to claim 10, characterized in that the bonding layer contains SiO2 and NH3.

13. The bonding strength of each substrate by the bonding layer is 5 J / m 2 The substrate bonding structure according to claim 10, characterized in that it is as described above.

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