Composite substrate and method for manufacturing for composite substrate

Abstract

This composite substrate has: a functional substrate comprising a functional material; a support substrate that is formed from a semiconductor material or an insulator material, is bonded to the functional substrate, and supports the functional substrate; and a bonding layer disposed between the functional substrate and the support substrate. The bonding layer, or the bonding layer and one of either the support substrate or the functional substrate, contains impurities internally, and a maximum value of the content of the impurities exists at two locations in the depth direction.

Description

Composite substrate, method for manufacturing a composite substrate

[0001] The present invention relates to a composite substrate and a method for manufacturing the same.

[0002] Conventionally, LN(LiNbO ３ : Lithium niobate or LT (LiTaO) ３ A composite substrate is known that is formed by joining a functional substrate made of a piezoelectric material such as lithium tantalate to a support substrate made of a semiconductor material such as Si, and is used in applications such as surface acoustic wave devices. For example, Patent Document 1 discloses a POI (Piezoelectric On Insulator) substrate as an example of a composite substrate for such a surface acoustic wave device, in which a charge trap layer for absorbing charge is provided between the piezoelectric layer and the support substrate. In a POI substrate, for example, polycrystalline silicon, amorphous silicon, porous silicon, etc. are used as the trap-rich layer.

[0003] In composite substrates like the one described in Patent Document 1, it is necessary to ensure insulation between the functional substrate and the support substrate while bonding them with sufficiently high bonding strength in order to suppress noise and loss. The technology described in Patent Document 2 is known to solve this problem. Patent Document 2 discloses a composite substrate in which a bonding layer having the composition Si(1-x)Ox (0.008≦x≦0.408) is provided between the piezoelectric single crystal substrate and the support substrate, and the piezoelectric single crystal substrate and the support substrate are bonded via this bonding layer, thereby increasing the insulation in the bonding layer and increasing the bonding strength between the support substrate and the piezoelectric single crystal substrate.

[0004] Japan Special Table No. 2023-544271 Japanese Patent No. 6375471

[0005] In recent years, composite substrates for surface acoustic wave devices have required further improvements in bonding strength due to the increasing integration and miniaturization of the devices.

[0006] The present invention has been made in view of the above, and its main objective is to further improve the bonding strength in a composite substrate in which a functional substrate and a support substrate are bonded together.

[0007] The composite substrate according to the present invention comprises a functional substrate composed of a functional material, a support substrate made of a semiconductor material or an insulating material, which is bonded to the functional substrate and supports the functional substrate, and a bonding layer disposed between the functional substrate and the support substrate, wherein the bonding layer, or either the support substrate or the functional substrate, and the bonding layer contain impurities internally, and there are two locations in the depth direction where the maximum value of the impurity content is present. A method for manufacturing a composite substrate according to the present invention comprises a functional substrate comprising a functional substrate comprising a functional material, a support substrate supporting the functional substrate, and a bonding layer disposed between the functional substrate and the support substrate, and includes a bonding layer deposition step of forming the bonding layer on at least one of the functional substrate and the support substrate; a planarization step of reducing the surface roughness of the bonding layer formed in the bonding layer deposition step; an activation step of using a rare gas to activate the surface of the bonding layer formed on either the functional substrate or the support substrate and the surface of the other substrate, or the surface of the bonding layer formed on both the functional substrate and the support substrate, respectively, after the planarization step; a bonding step of joining the surfaces of the bonding layer, the functional substrate, or the support substrate, respectively, which were activated in the activation step, to form a bonded body; a thinning step of thinning the functional substrate so that the thickness of the functional substrate in the bonded body formed in the bonding step is reduced; and a heating step of heating the bonded body to a temperature of 300°C or higher.

[0008] According to the present invention, it is possible to further improve the bonding strength in a composite substrate in which a functional substrate and a support substrate are bonded together.

[0009] This is a schematic cross-sectional view showing the general configuration of a composite substrate according to the first embodiment of the present invention. This is a diagram showing an example of the manufacturing process of a composite substrate according to the first embodiment of the present invention. This is a diagram showing an example of the manufacturing process of a composite substrate according to the first embodiment of the present invention. This is a diagram showing an example of the manufacturing process of a composite substrate according to the first embodiment of the present invention. This is a schematic cross-sectional view showing the general configuration of a composite substrate according to the second embodiment of the present invention. This is a diagram showing an example of the manufacturing process of a composite substrate according to the second embodiment of the present invention. This is a diagram showing an example of the manufacturing process of a composite substrate according to the second embodiment of the present invention. This is a table summarizing the bonding strength, the number of peaks in Ar content, and the presence or absence of delamination at the interface between the functional substrate and the dielectric layer in each of the examples and comparative examples. This is a diagram showing observation photographs of the comparative examples and examples.

[0010] The embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. In addition, the drawings may be schematically represented in terms of the width, thickness, shape, etc. of each part compared to the embodiments in order to make the explanation clearer, but these are merely examples and do not limit the interpretation of the present invention.

[0011] (First Embodiment) Figure 1 is a schematic cross-sectional view showing the general configuration of a composite substrate according to the first embodiment of the present invention. The composite substrate 100 in this embodiment is used for various applications, such as optical elements that constitute optical waveguides, piezoelectric elements that constitute surface acoustic wave (SAW) filters, and various semiconductor elements. It has a structure in which a functional substrate 10 made of functional materials such as piezoelectric materials and semiconductor materials is bonded to a support substrate 30 via a bonding layer 20 and a dielectric layer 40.

[0012] The material of the functional substrate 10 is, for example, LN(LiNbO ３ : Lithium niobate or LT (LiTaO) ３ (Lithium tantalate), quartz, silica, AlN (aluminum nitride), PZT (Pb(Zr,Ti)O ３Piezoelectric materials such as lead zirconate titanate are used. The material of the functional substrate 10 can be arbitrarily selected according to the application of the composite substrate 100. For example, in addition to piezoelectric materials, the functional substrate 10 may be constructed using semiconductor materials such as Si, SiC, InP, GaN, GaP, and diamond, or materials having electro-optic effects such as lithium niobate-lithium tantalate, KTP (potassium titanate phosphate), or glass. In addition to these, a functional substrate 10 made of various functional materials can be used depending on the application of the composite substrate 100.

[0013] The bonding layer 20 is placed between the functional substrate 10 (including the dielectric layer 40) and the support substrate 30, and is bonded to these substrates, thereby bonding the functional substrate 10 and the support substrate 30 to each other. Examples of materials used for the bonding layer 20 include Si, Ge, hafnium oxide, niobium oxide, tantalum oxide, aluminum oxide, aluminum nitride, silicon nitride, silicon nitride oxide, and aluminum nitride oxide. Alternatively, the bonding layer 20 may be constructed using Si(1-x)Ox (where 0.008 ≤ x ≤ 0.408). The various materials used for the bonding layer 20 may be single crystals, polycrystalline, or amorphous, regardless of their crystalline properties.

[0014] The support substrate 30 supports the functional substrate 10 (including the dielectric layer 40) via the bonding layer 20. Any suitable substrate can be used as the support substrate 30. The support substrate 30 may be made of a single crystal or a polycrystalline material.

[0015] The material used to construct the support substrate 30 can be a semiconductor material such as Si, Ge, SiC, InP, or GaN. Alternatively, the support substrate 30 may be constructed using an insulating material such as aluminum nitride, silicon nitride, sapphire, or diamond. The thickness of the support substrate 30 is, for example, 0.2 to 1 mm, but any other appropriate thickness can be adopted.

[0016] A dielectric layer 40 made of a dielectric material is placed between the functional substrate 10 and the bonding layer 20. The dielectric material constituting the dielectric layer 40 can be, for example, an oxide or nitride or oxynitride of Si, Ta, or Al, and preferably silicon oxide or silicon oxynitride. The dielectric layer 40 may also have two or more layers made of different materials, such as a silicon oxide layer and a silicon oxynitride layer.

[0017] Although not shown in the figures, the composite substrate 100 may have additional layers of any choice. The type, function, number, combination, and arrangement of such layers can be appropriately determined according to the purpose.

[0018] The composite substrate 100 can be manufactured in any suitable shape. In one embodiment, the composite substrate 100 can be manufactured in the form of a so-called wafer. The size of the composite substrate 100 can also be appropriately set according to the purpose, for example, with a wafer (substrate) diameter of 50 mm to 150 mm.

[0019] Figures 2, 3, and 4 show an example of the manufacturing process for a composite substrate according to the first embodiment of the present invention.

[0020] Figure 2(a) shows the preparation step in the manufacturing process of the composite substrate 100. In this step, a functional substrate 10 made of a functional material having a predetermined thickness, for example, 50 nm to 30,000 nm, is prepared.

[0021] Figure 2(b) shows the dielectric layer 40 deposition process in the manufacturing process of the composite substrate 100. In this process, the dielectric material described above is deposited on the functional substrate 10 prepared in the preparation process shown in Figure 2(a) to a predetermined thickness, for example, 5 nm to 30,000 nm, using any deposition method such as sputtering or various CVD (Chemical Vapor Deposition) to form the dielectric layer 40.

[0022] Figure 2(c) shows the film deposition process for the bonding layer 20, which is part of the manufacturing process of the composite substrate 100. In this process, the bonding layer 20 is formed by depositing the aforementioned bonding layer 20 material onto the surface of the dielectric layer 40 formed on the functional substrate 10 in the film deposition process shown in Figure 2(b) to a predetermined thickness, for example, 5 nm to 3000 nm, using any film deposition method such as sputtering or various CVD (Chemical Vapor Deposition).

[0023] In the film formation process for the bonding layer 20, the bonding layer 20 may be formed such that it includes a region in which the hydrogen and oxygen content in the bonding layer 20 decreases as the thickness of the formed bonding layer 20 increases. That is, the bonding layer 20 formed in the film formation process shown in Figure 2(c) has a region in which the hydrogen and oxygen content gradually increases as it approaches the functional substrate 10. This is thought to be because residual moisture in the chamber used in the film formation process is incorporated into the bonding layer 20, and the residual moisture decreases over time. However, if the amount of oxygen in the bonding layer 20 is too high, it will lead to a decrease in the bonding strength between the bonding layer 20 and the support substrate 30 in the bonding process described later. For this reason, for example, when the bonding layer 20 is formed from amorphous silicon, it is preferable to have an O / Si composition ratio of 0.2 or less in the bonding layer 20.

[0024] Figure 2(d) shows the planarization step of the bonding layer 20 in the manufacturing process of the composite substrate 100. In this step, the surface of the bonding layer 20 formed in the film deposition step shown in Figure 2(c) is polished to reduce the surface roughness of the bonding layer 20 and flatten it. This makes the surface of the bonding layer 20, which will become the bonding surface in the bonding step described later, a flat surface.

[0025] Figure 3(e) shows the activation step in the manufacturing process of the composite substrate 100. In this step, a support substrate 30 made of a semiconductor material of a predetermined thickness is prepared, and the surface of the bonding layer 20 formed on the functional substrate 10 (including the dielectric layer 40) in the film formation step of Figure 2(c), and the surface of the support substrate 30 are irradiated with a high-speed atomic beam (hereinafter referred to as FAB) using a noble gas such as Ar as the atomic species for a predetermined time to perform an activation treatment. The irradiation time of the FAB at this time is preferably about 15 to 120 seconds.

[0026] Figure 3(f) shows the bonding process in the manufacturing process of the composite substrate 100. In this process, the surfaces of the bonding layers 20 and the support substrate 30, which were activated in the activation process shown in Figure 3(e), are bonded to each other. As a result, the functional substrate 10 (including the dielectric layer 40) and the support substrate 30 are bonded to each other via the bonding layers 20, and a bonded body is obtained. Note that in Figures 3(f) and later, the positional relationship between the functional substrate 10 and the support substrate 30 is shown upside down compared to Figures 2(a) to 3(e).

[0027] Figure 3(g) shows the bonded body obtained after the bonding process shown in Figure 3(f). As described above, the functional substrate 10 and the support substrate 30 are bonded to each other via the bonding layer 20 by the bonding process shown in Figure 3(f), and a bonded body like the one shown in Figure 3(g) is obtained, having a bonding interface 50 between the bonding layer 20 and the support substrate 30.

[0028] In the bonded structure shown in Figure 3(g), regions containing noble gases such as Ar, which were irradiated as FAB in the activation process shown in Figure 3(e), are formed near the bonding interface between the bonding layer 20 and the support substrate 30. Furthermore, due to the residual moisture mentioned above in the film formation process shown in Figure 2(c), the bonding layer 20 includes regions where the hydrogen content and O / Si composition ratio gradually increase as it approaches the functional substrate 10.

[0029] Figure 4(h) shows the primary thinning process in the manufacturing process of the composite substrate 100. In this process, the functional substrate 10 is polished to a predetermined thickness so that it is thinner than the original thickness of the bonded body shown in Figure 3(g). For example, the functional substrate 10 can be polished and thinned using grinding, CMP (Chemical Mechanical Polish) processing, or surface planarization processing using a gas cluster ion beam.

[0030] Figure 4(i) shows the heating step in the manufacturing process of the composite substrate 100. In this step, the bonded body, which has been thinned in the primary thinning step of the functional substrate 10 in Figure 3(h), is heated to a predetermined temperature. The heating temperature at this time is preferably around 300 to 600°C. In addition, in order to prevent polarization reversal of the functional substrate 10, it is preferable to set the heating and cooling rate to 10°C per minute or less. This makes it possible to improve the bonding strength between the bonding layer 20 and the support substrate 30.

[0031] Figure 4(j) shows the secondary thinning process in the manufacturing process of the composite substrate 100. In this process, the functional substrate 10 is further polished and thinned to the bonded body that has been cooled to room temperature after the heating process shown in Figure 4(i). This adjusts the thickness of the functional substrate 10 to a thickness suitable for forming a surface acoustic wave device.

[0032] Through the above steps, a composite substrate 100 with the structure shown in Figure 1 is manufactured.

[0033] In the above description, an example was given in which the bonding layer 20 is formed on the surface of the dielectric layer 40 formed on the functional substrate 10 during the film formation process shown in Figure 2(c). However, the bonding layer 20 may be formed on the support substrate 30 side instead of the functional substrate 10 side. Alternatively, the bonding layer 20 may be formed on both the functional substrate 10 side and the support substrate 30 side. In other words, in the film formation process shown in Figure 2(c), the bonding layer 20 can be formed on at least one of the functional substrate 10 (including the dielectric layer 40) and the support substrate 30.

[0034] Here, if the bonding layer 20 is formed on the support substrate 30 side, in the activation step shown in Figure 3(e), the surfaces of the bonding layer 20 formed on the support substrate 30 in the film deposition step shown in Figure 2(c) and the surface of the dielectric layer 40 formed on the functional substrate 10 in the film deposition step shown in Figure 2(b) are irradiated with FAB to activate these surfaces. Also, if the bonding layer 20 is formed on both the functional substrate 10 side and the support substrate 30 side, in the activation step shown in Figure 3(e), the surfaces of the bonding layer 20 formed on the functional substrate 10 (including the dielectric layer 40) and the support substrate 30, respectively in the film deposition step shown in Figure 2(c), are irradiated with FAB to activate these surfaces. Then, in the subsequent bonding step shown in Figure 3(f), the surfaces of the bonding layer 20, the functional substrate 10, or the support substrate 30, which were activated in the activation step shown in Figure 3(e), are joined together to form a bonded body. As a result, a bonding interface 50 is formed at the interface between the bonding layer 20 and the functional substrate 10 (dielectric layer 40), or within the bonding layer 20. With this bonding interface 50 in between, the bonding layer 20 and the dielectric layer 40, or within the bonding layer 20, contains as an impurity a rare gas such as Ar, which was irradiated as FAB in the activation process shown in Figure 3(e).

[0035] (Second Embodiment) Figure 5 is a schematic cross-sectional view showing the general configuration of a composite substrate according to the second embodiment of the present invention. The composite substrate 110 in this embodiment has a structure in which the dielectric layer 40 is not disposed between the functional substrate 10 and the bonding layer 20, compared to the composite substrate 100 of Figure 1 described in the first embodiment.

[0036] In this embodiment, as in the first embodiment described above, the composite substrate 110 may further have arbitrary layers. The type, function, number, combination, and arrangement of such layers can be appropriately set according to the purpose. Furthermore, the composite substrate 110 can be manufactured in any appropriate shape according to the purpose.

[0037] Figures 6, 7, and 8 show an example of the manufacturing process for a composite substrate according to a second embodiment of the present invention.

[0038] Fig. 6(a) shows the preparation process in the manufacturing process of the composite substrate 110. In this process, a functional substrate 10 made of a functional material with a predetermined thickness is prepared in the same manner as the process of Fig. 2(a) described in the first embodiment.

[0039] Fig. 6(c) shows the film formation process of the bonding layer 20 in the manufacturing process of the composite substrate 110. In this process, the material of the bonding layer 20 is formed into a film with a predetermined thickness on the surface of the functional substrate 10 prepared in the preparation process of Fig. 6(a) by using a film formation method such as sputtering, thereby forming the bonding layer 20. Note that, unlike the first embodiment, since the composite substrate 110 does not have a dielectric layer 40 in this embodiment, the film formation process of the dielectric layer 40 as shown in Fig. 2(b) is not performed.

[0040] Fig. 6(d) shows the planarization process of the bonding layer 20 in the manufacturing process of the composite substrate 110. In this process, the surface roughness of the bonding layer 20 is reduced and planarized by polishing the surface of the bonding layer 20 formed in the film formation process of Fig. 6(c). Thereby, the surface of the bonding layer 20 that becomes the bonding surface in the bonding process described later is made into a flat surface.

[0041] Fig. 7(e) shows the activation process in the manufacturing process of the composite substrate 110. In this process, in the same manner as the process of Fig. 3(e) described in the first embodiment, for example, a support substrate 30 made of a semiconductor material with a predetermined thickness is prepared, and the surface of the bonding layer 20 formed on the functional substrate 10 in the film formation process of Fig. 6(c) and the surface of the support substrate 30 are each subjected to an activation treatment by irradiating FAB using a rare gas such as Ar as the atomic species for a predetermined time.

[0042] Fig. 7(f) shows the bonding process in the manufacturing process of the composite substrate 110. In this process, in the same manner as the process of Fig. 3(f) described in the first embodiment, the surface of the bonding layer 20 and the surface of the support substrate 30 that are each activated in the activation process of Fig. 7(e) are bonded to each other. Thereby, the functional substrate 10 and the support substrate 30 are bonded to each other via the bonding layer 20, and these bonded bodies are obtained.

[0043] Figure 7(g) shows the joined body obtained after the joining process of Figure 7(f). By the joining process of Figure 7(f), as described above, the functional substrate 10 and the support substrate 30 are joined to each other via the joining layer 20, and a joined body as shown in Figure 7(g) having a joining interface 50 between the joining layer 20 and the support substrate 30 is obtained.

[0044] In the joined body of Figure 7(g) as well, similar to the joined body of Figure 3(g) described in the first embodiment, in the vicinity of the joining interface 50 between the joining layer 20 and the support substrate 30, portions containing noble gases such as Ar irradiated as FAB in the activation process of Figure 7(e) as impurities are respectively formed. Further, due to the residual moisture in the film formation process of Figure 6(c), in the joining layer 20, regions where the hydrogen content and the O / Si composition ratio gradually increase as approaching the functional substrate 10 are included.

[0045] Figure 8(h) shows the primary thinning process in the manufacturing process of the composite substrate 110. In this process, similar to the process of Figure 4(h) described in the first embodiment, the functional substrate 10 of the joined body shown in Figure 7(g) is polished to a predetermined thickness to be thinned.

[0046] Figure 8(i) shows the heating process in the manufacturing process of the composite substrate 110. In this process, similar to the process of Figure 4(i) described in the first embodiment, the joined body in which the functional substrate 10 is thinned in the primary thinning process of Figure 8(h) is heated to a predetermined temperature.

[0047] Figure 8(j) shows the secondary thinning process in the manufacturing process of the composite substrate 110. In this process, similar to the process of Figure 4(j) described in the first embodiment, the functional substrate 10 of the joined body cooled to room temperature after performing the heating process of Figure 8(i) is further polished to be thinned. Thereby, the thickness of the functional substrate 10 is adjusted to be a thickness suitable for forming an elastic surface wave device.

[0048] Through the above respective processes, the composite substrate 110 having the structure shown in Figure 5 is manufactured.

[0049] In this embodiment, as in the first embodiment, the bonding layer 20 may be formed on the support substrate 30 side instead of the functional substrate 10 side during the film formation process shown in Figure 6(c). Alternatively, the bonding layer 20 may be formed on both the functional substrate 10 side and the support substrate 30 side. In other words, in the film formation process shown in Figure 6(c), the bonding layer 20 can be formed on at least one of the functional substrate 10 and the support substrate 30.

[0050] Here, if the bonding layer 20 is formed on the support substrate 30 side, in the activation step shown in Figure 7(e), the surfaces of the bonding layer 20 formed on the support substrate 30 in the film formation step shown in Figure 6(c) and the surface of the functional substrate 10 are activated by irradiating them with FAB, respectively. Also, if the bonding layer 20 is formed on both the functional substrate 10 side and the support substrate 30 side, in the activation step shown in Figure 7(e), the surfaces of the bonding layer 20 formed on the functional substrate 10 and the support substrate 30, respectively in the film formation step shown in Figure 6(c), are activated by irradiating them with FAB, respectively. Then, in the subsequent bonding step shown in Figure 7(f), the surfaces of the bonding layer 20, the functional substrate 10, or the support substrate 30, which were activated in the activation step shown in Figure 7(e), are joined together to form a bonded body. As a result, a bonding interface 50 is formed at the interface between the bonding layer 20 and the functional substrate 10, or within the bonding layer 20. With this bonding interface 50 in between, the bonding layer 20 and the functional substrate 10, or within the bonding layer 20, contains as an impurity a noble gas such as Ar, which was irradiated as FAB in the activation process shown in Figure 7(e).

[0051] The following describes specific examples for verifying the structure of the composite substrate according to the present invention. Unless otherwise specified, the following procedures were performed at room temperature.

[0052] (Example 1) A bonded body was fabricated according to the manufacturing process described with reference to Figures 2, 3, and 4. Specifically, an LT wafer having an orientation flat portion, a diameter of 4 inches, and a thickness of 250 μm was prepared and used as the functional substrate 10. The surface of the functional substrate 10 was mirror-polished to an arithmetic mean roughness Ra of 0.3 nm, and then a dielectric layer 40 was formed on the surface by a film deposition process using sputtering, using SiO ２A 500 nm thin film was deposited. Furthermore, the deposited SiO ２ A 500 nm layer of amorphous Si was deposited on the dielectric layer 40 as a bonding layer 20 by a sputtering deposition process, and its surface was planarized by grinding, thereby forming a flat bonding surface on the bonding layer 20.

[0053] Furthermore, a Si wafer with an orientation flat portion, a diameter of 4 inches, and a thickness of 230 μm was prepared and used as the support substrate 30. The surface of the support substrate 30 was then mirror-polished to an arithmetic mean roughness Ra of 0.5 nm.

[0054] The functional substrate 10 (including the dielectric layer 40 and the bonding layer 20) and the support substrate 30 obtained above were placed in a vacuum chamber in which FAB guns were installed facing upwards and downwards, respectively, so that the substrates were located within the irradiation range of each FAB gun, and the surfaces of the bonding layer 20 formed on the functional substrate 10 and the support substrate 30 were facing each other. In this state, the inside of the vacuum chamber was 10 －６ The system was vacuumed up to the Pa stage, and both surfaces were activated by irradiating the bonding layer 20 on the functional substrate 10 and the support substrate 30 with Ar gas from each FAB gun for a predetermined time.

[0055] Subsequently, the activated bonding layer 20 and the surface of the support substrate 30 were directly bonded together. Specifically, the beam-irradiated surface of the functional substrate 10 on which the bonding layer 20 was formed (the surface of the bonding layer 20) and the beam-irradiated surface of the support substrate 30 were superimposed, and the two substrates were bonded together by applying pressure of 10,000 N for 2 minutes at room temperature to obtain a bonded body.

[0056] Furthermore, the functional substrate 10 of the resulting bonded body was thinned by polishing the surface on the side where the support substrate 30 was not bonded until the thickness of the functional substrate 10 was 2000 nm, and then the heating process described in Figure 4(i) was carried out. In this heating process, the bonded body was placed in a constant temperature bath and heated from room temperature to 300°C in a nitrogen atmosphere, and this state was maintained for 1 hour. After that, it was cooled back to room temperature. The heating rate at this time was 7°C per minute.

[0057] After the heating process described above, the surface of the functional substrate 10 was further polished to thin it down to a thickness of 1000 nm. This resulted in obtaining a composite substrate 100 with the structure shown in Figure 1.

[0058] (Example 2) A composite substrate 100 was manufactured according to the manufacturing process described with reference to Figures 2, 3, and 4, but with a higher temperature during the heating process than in Example 1. Specifically, the bonded structure of the functional substrate 10 (including the dielectric layer 40 and the bonding layer 20) and the support substrate 30, obtained in the same manner as in Example 1, was thinned to a thickness of 2000 nm, and then placed in a constant temperature bath. It was then heated from room temperature to 400°C in a nitrogen atmosphere and maintained at that state for 1 hour. After that, it was cooled back to room temperature. The heating and cooling rate at this time was 7°C per minute, the same as in Example 1.

[0059] Subsequently, the surface of the functional substrate 10 was further polished to thin it down to a thickness of 1000 nm. This resulted in obtaining a composite substrate 100 with the structure shown in Figure 1.

[0060] (Example 3) A composite substrate 100 was fabricated according to the manufacturing process described with reference to Figures 2, 3, and 4, by increasing the temperature during the heating process compared to Examples 1 and 2, and by performing the heating process in an atmospheric environment. Specifically, the bonded structure of the functional substrate 10 (including the dielectric layer 40 and the bonding layer 20) and the support substrate 30 obtained in the same manner as in Examples 1 and 2 was thinned to a thickness of 2000 nm, and then placed in a constant temperature bath. It was then heated from room temperature to 500°C in an atmospheric environment and maintained at that state for 1 hour. After that, it was cooled back to room temperature. The heating and cooling rate at this time was 7°C per minute, the same as in Examples 1 and 2.

[0061] Subsequently, the surface of the functional substrate 10 was further polished to thin it down to a thickness of 1000 nm. This resulted in obtaining a composite substrate 100 with the structure shown in Figure 1.

[0062] (Example 4) A composite substrate 100 was fabricated by performing a heating process in a nitrogen atmosphere at the same temperature as in Example 3, following the manufacturing process described with reference to Figures 2, 3, and 4. Specifically, the bonded structure of the functional substrate 10 (including the dielectric layer 40 and the bonding layer 20) and the support substrate 30 obtained in the same manner as in Examples 1 to 3 was thinned to a thickness of 2000 nm, and then placed in a constant temperature bath. It was then heated from room temperature to 500°C in a nitrogen atmosphere and maintained at that state for 1 hour. After that, it was cooled back to room temperature. The heating and cooling rate at this time was 7°C per minute, the same as in Examples 1 to 3.

[0063] Subsequently, the surface of the functional substrate 10 was further polished to thin it down to a thickness of 1000 nm. This resulted in obtaining a composite substrate 100 with the structure shown in Figure 1.

[0064] (Example 5) In the manufacturing process described with reference to Figures 2, 3, and 4, the heating step in Figure 4(i) was performed after the secondary thinning step in Figure 4(j) instead of after the primary thinning step in Figure 4(h) to produce the composite substrate 100. The heating temperature and atmosphere at this time were the same as in Example 4. Specifically, the bonded structure of the functional substrate 10 (including the dielectric layer 40 and the bonding layer 20) and the support substrate 30 obtained in the same manner as in Examples 1 to 4 was thinned until the thickness of the functional substrate 10 was 1000 nm, and then placed in a constant temperature bath. It was then heated from room temperature to 500°C in a nitrogen atmosphere and maintained at that state for 1 hour. After that, it was cooled back to room temperature. The heating rate at this time was 7°C per minute, the same as in Examples 1 to 4. As a result, a composite substrate 100 with the structure shown in Figure 1 was obtained.

[0065] (Example 6) A composite substrate 100 was fabricated according to the manufacturing process described with reference to Figures 2, 3, and 4, with the heating temperature being even higher than in Examples 1 to 5. Specifically, the bonded structure of the functional substrate 10 (including the dielectric layer 40 and the bonding layer 20) and the support substrate 30, obtained in the same manner as in Examples 1 to 5, was thinned to a thickness of 2000 nm, and then placed in a constant temperature bath. It was then heated from room temperature to 600°C in an atmospheric environment and maintained at that temperature for 1 hour. After that, it was cooled back to room temperature. The heating and cooling rate at this time was 7°C per minute, the same as in Examples 1 to 5.

[0066] Subsequently, the surface of the functional substrate 10 was further polished to thin it down to a thickness of 1000 nm. This resulted in obtaining a composite substrate 100 with the structure shown in Figure 1.

[0067] (Comparative Example 1) To confirm the effects of the present invention, a composite substrate 100 was prepared as Comparative Example 1 without performing a heating process. Specifically, the functional substrate 10 (including the dielectric layer 40 and the bonding layer 20) obtained in the same manner as in Examples 1 to 6 and the support substrate 30 were thinned by polishing the surface of the functional substrate 10 until its thickness was 1000 nm, without performing the heating process shown in Figure 4(i). As a result, a composite substrate 100 with the structure shown in Figure 1 was obtained.

[0068] (Comparative Example 2) As a comparative example, a composite substrate 100 was fabricated using a lower temperature during the heating process than in Examples 1 to 6. Specifically, the bonded structure of the functional substrate 10 (including the dielectric layer 40 and the bonding layer 20) and the support substrate 30, obtained in the same manner as in Examples 1 to 6, was thinned to a thickness of 2000 nm, and then placed in a constant temperature bath. It was then heated from room temperature to 250°C in a nitrogen atmosphere and maintained at that temperature for 1 hour. After that, it was cooled back to room temperature. The heating and cooling rate at this time was 7°C per minute, the same as in Examples 1 to 6.

[0069] Subsequently, the surface of the functional substrate 10 was further polished to thin it down to a thickness of 1000 nm. This resulted in obtaining a composite substrate 100 with the structure shown in Figure 1.

[0070] (Verification of Bonding Strength and Ar Peak) For each of the composite substrates 100 fabricated in Examples 1 to 6 and Comparative Examples 1 and 2, test pieces were prepared by dicing each composite substrate 100 into chips of 10×10 mm ２ and a tensile test was performed on each test piece to evaluate the bonding strength. Also, line element analysis by STEM-EDX was performed on the bonding interface 50 of each composite substrate 100 and its vicinity to investigate the change in the Ar composition ratio in the depth direction. From the investigation results, in a predetermined range including the bonding interface 50, specifically in the range of ±25 nm in the depth direction from the position of the bonding interface 50, the number of peaks (maxima) of the Ar content in the depth direction (the direction in which the functional substrate 10, the bonding layer 20, and the support substrate 30 are laminated) was confirmed under the following analysis conditions.

[0071] (Analysis Conditions) Using a scanning transmission electron microscope with a spherical aberration correction function (HD-2700 manufactured by Hitachi High-Tech Corporation) equipped with an energy dispersive X-ray analyzer (X-Max 100TLE manufactured by Oxford Instruments) as a detector, line analysis of the composition was performed on the above range in each of the composite substrates 100 fabricated in Examples 1 to 6 and Comparative Examples 1 and 2 at intervals of approximately 0.25 nm in the depth direction under the conditions of an acceleration voltage of 200 keV and a beam diameter of approximately 0.1 nm, and the Ar content was measured. Further, in order to grasp the overall trend of the change in the Ar content according to the depth direction, smoothing treatment was performed on the obtained measurement results of the Ar content by a 5-point moving average. For the smoothed peak waveform, one or more Gaussian functions, Lorentz functions, Voigt functions, G-L functions, or mixed functions thereof with a peak half-width of 1 nm or more were used for fitting so that the square error was minimized. The maximum value of the peak height of the waveform obtained by fitting with a peak height of 1 atomic% or more was defined as the Ar content peak.

[0072] Figure 9 is a table summarizing the bonding strength, the number of Ar content peaks, and the presence or absence of peeling at the interface between the functional substrate 10 and the dielectric layer 40 for each of Examples 1 to 6 and Comparative Examples 1 and 2.

[0073] ​​From the table in Figure 9, it can be seen that in Comparative Examples 1 and 2, there is only one peak in the Ar content, indicating insufficient bonding strength. On the other hand, in Examples 1 to 6, there are two peaks in the Ar content in the depth direction, indicating that sufficiently high bonding strength can be obtained in these cases.

[0074] However, in Example 5, although sufficient bonding strength was obtained, delamination was observed at the interface between the functional substrate 10 and the dielectric layer 40. For these reasons, in the heating process, it is preferable to heat the bonded body while leaving a certain thickness of the functional substrate 10, preferably about 2000 nm, remaining, as in Examples 1 to 4 and 6.

[0075] (Confirmation of Laminated Structure) Of the composite substrates 100 prepared in Examples 1 to 6 and Comparative Examples 1 and 2, the laminated structure of each composite substrate 100 was confirmed by performing transmission electron microscopy (TEM) observation of the cross-section including the bonding interface 50 of Comparative Example 1 and Example 1. Figure 10(a) shows the observation photograph of Comparative Example 1, and Figure 10(b) shows the observation photograph of Example 1.

[0076] In the observation photograph of Comparative Example 1 shown in Figure 10(a), the bonding interface 50 between the bonding layer 20 and the support substrate 30 is clearly visible. Furthermore, it can be seen that in a certain area of ​​the support substrate 30 close to the bonding interface 50, the cross-section is different from that of other areas and is closer to the cross-section of the bonding layer 20. This is thought to be due to the fact that, as mentioned above, Ar atoms irradiated as FAB in the activation process penetrate from the surface into the interior of the support substrate 30, changing the crystal structure of Si and resulting in an amorphous state.

[0077] On the other hand, in the observation photograph of Example 1 shown in Figure 10(b), the bonding interface 50 between the bonding layer 20 and the support substrate 30 is not clearly visible. This is thought to be because the heating process diffused the Ar that had entered the bonding layer 20 and the support substrate 30 due to FAB irradiation, and also promoted the rearrangement of Si atoms near the bonding interface 50, resulting in stronger bonding of Si atoms at the bonding interface 50. As a result, as mentioned above, in Example 1, there are two peaks in the Ar content, with the bonding interface 50 in between, suggesting that the bonding strength is higher than in Comparative Example 1.

[0078] (Other confirmation points) Furthermore, the following confirmation results were obtained from Examples 1 to 6 and Comparative Examples 1 and 2.

[0079] In Comparative Example 2 and Examples 1 to 6, it was confirmed that the warping of the composite substrate 100 was reduced by performing the heating process. Specifically, for example, in Comparative Example 2, the amount of warping of the composite substrate 100 with the functional substrate 10 placed on the upper side was 35 μm in the convex direction before the heating process, whereas the amount of warping of the composite substrate 100 after the heating process was reduced to 25 μm in the convex direction. Therefore, it can be seen that performing the heating process makes it possible to suppress the warping of the composite substrate 100 and improve the yield.

[0080] According to the embodiments of the present invention described above, the following effects and advantages are achieved.

[0081] (1) The composite substrates 100 and 110 each include a functional substrate 10 made of a functional material, a support substrate 30 which is bonded to the functional substrate 10 and supports the functional substrate 10, and a bonding layer 20 which is disposed between the functional substrate 10 and the support substrate 30. At least one of the bonding layer 20, the support substrate 30, and the functional substrate 10 contains impurities (noble gases such as Ar) internally, and there are at least two maximum values ​​of the impurity content in the depth direction. In this way, in the composite substrates 100 and 110, impurities introduced during the activation treatment when bonding the functional substrate 10 and the support substrate 30 can be sufficiently diffused by heating, and as a result, the bonding strength can be further improved.

[0082] (2) The support substrate 30 is made of a semiconductor material or an insulating material. In this way, the support substrate 30 can be constructed using an appropriate material depending on the application of the composite substrates 100 and 110.

[0083] (3) The composite substrate 100 further has a dielectric layer 40 made of a dielectric material between the functional substrate 10 and the bonding layer 20. In this way, noise and loss in the functional substrate 10 can be suppressed and the electrical characteristics can be improved.

[0084] (4) The bonding layer 20 contains hydrogen and has regions in which the hydrogen content gradually increases as it approaches the functional substrate 10. Alternatively, the bonding layer 20 may be made of amorphous silicon containing oxygen. In this case, it is preferable that the O / Si composition ratio in the bonding layer 20 is 0.2 or less and that it has regions in which the O / Si composition ratio gradually increases as it approaches the functional substrate 10. In this way, a bonding layer 20 capable of obtaining sufficient bonding strength can be formed during the film formation process of the bonding layer 20.

[0085] (5) A method for manufacturing composite substrates 100, 110 comprising a functional substrate 10 made of a functional material, a support substrate 30 supporting the functional substrate 10, and a bonding layer 20 disposed between the functional substrate 10 and the support substrate 30, comprising: a bonding layer deposition step (Figure 2(c), Figure 6(c)) in which the bonding layer 20 is formed on at least one of the functional substrate 10 and the support substrate 30; a planarization step (Figure 2(d), Figure 6(d)) in which the surface roughness of the bonding layer 20 formed in the bonding layer deposition step is reduced; and after the planarization step, the surface of the bonding layer 20 formed on either the functional substrate 10 or the support substrate 30 is reduced using a rare gas such as Ar. The method includes an activation step (Figures 3(e) and 7(e)) for activating the surface of the other substrate, or the surface of the bonding layer 20 formed on both the functional substrate 10 and the support substrate 30; a bonding step (Figures 3(f) and 7(f)) for joining the surfaces of the bonding layer 20, the functional substrate 10, or the support substrate 30 that were activated in the activation step to form a bonded body; a thinning step (Figures 4(h) and (j), 8(h) and (j)) for thinning the functional substrate 10 so that the thickness of the functional substrate 10 in the bonded body formed in the bonding step is reduced; and a heating step (Figures 4(i) and 8(i)) for heating the bonded body to a temperature of 300°C or higher. In this way, composite substrates 100 and 110 can be manufactured that have further improved bonding strength compared to conventional methods.

[0086] (6) The thinning process includes a primary thinning process (Figures 4(h) and 8(h)) performed before the heating process and a secondary thinning process (Figures 4(j) and 8(j)) performed after the heating process. In this way, the thickness of the functional substrate 10 can be adjusted to a desired value while suppressing the occurrence of delamination during the heating process.

[0087] (7) The manufacturing method of the composite substrate 100 further includes a dielectric layer deposition step (Figure 2(b)) which is performed before the bonding layer deposition step and in which a dielectric layer 40 made of oxide or nitride is formed on the functional substrate 10. In this way, a composite substrate 100 having a dielectric layer 40 between the functional substrate 10 and the bonding layer 20 can be manufactured.

[0088] (8) The bonding layer 20 contains at least one of oxygen and hydrogen. In the bonding layer deposition process, the bonding layer 20 is formed such that it includes a region in which the content of at least one of oxygen and hydrogen decreases as the thickness of the bonding layer 20 increases. In this way, a bonding layer 20 capable of obtaining sufficient bonding strength can be formed.

[0089] It should be noted that the present invention is not limited to the embodiments described above, and can be implemented using any components without departing from the spirit of the invention. For example, it is expected that similar tendencies can be obtained with composite substrates bonded by atomic diffusion bonding.

[0090] The embodiments and modifications described above are merely examples, and the present invention is not limited to these, as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments conceivable within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention.

[0091] 10: Functional substrate 20: Bonding layer 30: Support substrate 40: Dielectric layer 50: Bonding interface 100, 110: Composite substrate

Claims

1. A composite substrate comprising: a functional substrate composed of a functional material; a support substrate bonded to the functional substrate and supporting the functional substrate; and a bonding layer disposed between the functional substrate and the support substrate, wherein at least one of the bonding layer, the support substrate, and the functional substrate contains impurities internally, and the maximum value of the impurity content exists at least two locations in the depth direction.

2. A composite substrate according to claim 1, wherein the support substrate is made of a semiconductor material or an insulating material.

3. A composite substrate according to claim 1, further comprising a dielectric layer made of a dielectric material between the functional substrate and the bonding layer.

4. A composite substrate according to claim 1, wherein the impurity is a noble gas.

5. A composite substrate according to claim 1, wherein the bonding layer contains hydrogen and has regions in which the hydrogen content gradually increases as it approaches the functional substrate.

6. A composite substrate according to claim 1, wherein the bonding layer is made of amorphous silicon containing oxygen, the O / Si composition ratio in the bonding layer is 0.2 or less, and the composite substrate has a region in which the O / Si composition ratio gradually increases as it approaches the functional substrate.

7. A method for manufacturing a composite substrate comprising a functional substrate composed of a functional material, a support substrate for supporting the functional substrate, and a bonding layer disposed between the functional substrate and the support substrate, comprising: a bonding layer deposition step of forming the bonding layer on at least one of the functional substrate and the support substrate; a planarization step of reducing the surface roughness of the bonding layer formed in the bonding layer deposition step; an activation step of using a rare gas to activate the surface of the bonding layer formed on either the functional substrate or the support substrate and the surface of the other substrate, or the surface of the bonding layer formed on both the functional substrate and the support substrate, respectively, after the planarization step; a bonding step of joining the surfaces of the bonding layer, the functional substrate, or the support substrate, respectively, that have been activated in the activation step, to form a bonded body; a thinning step of thinning the functional substrate so that the thickness of the functional substrate in the bonded body formed in the bonding step is reduced; and a heating step of heating the bonded body to a temperature of 300°C or higher.

8. A method for manufacturing a composite substrate according to claim 7, wherein the thinning step includes a primary thinning step performed before the heating step and a secondary thinning step performed after the heating step.

9. A method for manufacturing a composite substrate according to claim 7, wherein in the bonding layer deposition step, the bonding layer is formed with a thickness of 10 nm or more and 3000 nm or less.

10. A method for manufacturing a composite substrate according to claim 7, further comprising a dielectric layer deposition step performed before the bonding layer deposition step, wherein a dielectric layer made of an oxide or nitride is formed on the functional substrate.

11. A method for manufacturing a composite substrate according to claim 7, wherein the bonding layer contains at least one of oxygen and hydrogen, and in the bonding layer deposition step, the bonding layer is formed such that it includes a region in which the content of at least one of oxygen and hydrogen decreases as the thickness of the bonding layer increases.

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