Manufacturing and joining processes for composite bodies

Abstract

A method for manufacturing a composite body includes: an activation step of activating respective surfaces of a first substrate and a second substrate, each of which contains SiO2 as a main component, with a plasma; a bonding step of bonding the activated surfaces of the first substrate and the second substrate at a vacuum degree of 1 mbar or more and 400 mbar or less; and a heating step of heating the bonded first substrate and the second substrate. As a result, the manufacturing method and the bonding method of a composite body capable of combining the reduction of void generation and the bonding strength are provided.

Description

Technical area

[0001] The present invention relates to a manufacturing method and a joining method for a composite body. Technical background

[0002] For example, an SOI substrate containing a high-resistance Si / SiO2 thin film / Si thin film is often used to implement a high-performance semiconductor device. Plasma activation has been used to implement an SOI substrate. This method allows the substrate to be bonded at relatively low temperatures (400°C). To improve the properties of a piezoelectric device, a composite substrate containing a Si / SiO2 thin film / piezoelectric thin film, similar to an SOI substrate, has been proposed.

[0003] PTL 1 discloses a method for manufacturing a composite wafer.The method for producing a composite wafer includes at least a step of injecting a hydrogen atom ion or a hydrogen molecule ion from the surface and forming an ion implantation layer inside an oxide single crystal wafer; a step of subjecting at least one of the ion-implanted surface of the oxide single crystal wafer and the surface of the support wafer to a surface activation treatment; a step of bonding the ion-implanted surface of the oxide single crystal wafer and the surface of the support wafer and obtaining a composite body; a step of heat-treating the composite body at a temperature equal to or higher than 90°C and causing no cracks; and a step of irradiating the heat-treated composite body with visible light and obtaining an oxide single crystal thin film, which is peeled off along the ion implantation layer and transferred to the support wafer. Citation listPatent literature

[0004] PTL 1: Japanese Patent Application Publication No. 2016-225537 Brief description of the inventionTechnical problem

[0005] For example, to manufacture a substrate having a Si substrate / SiO2 thin film / piezoelectric thin film structure, SiO2 formed on a Si substrate and SiO2 formed on a piezoelectric material are subjected to plasma activation and bonded thereto.

[0006] Subsequently, an annealing treatment is performed, forming a covalent bond via the OH group generated by plasma activation to improve the strength of the joint. However, if too much moisture is present at the joint interface during this step, the moisture may be generated in the form of a void after annealing, so there is room for improvement. On the other hand, if the moisture at the joint interface is too low, the strength of the joint will be poor.

[0007] It is an object of the present invention to provide a manufacturing method and a method for joining a composite body, which method is capable of combining the reduction of the formation of voids and the strength of the joint. Solution to the problem

[0008] To solve the above problem, the present invention provides a method for producing a composite body, the method including: an activation step of activating respective surfaces of a first substrate and a second substrate, the surfaces each containing SiO2 as a main component, by a plasma; a bonding step of bonding the surfaces of the first substrate and the second substrate at a vacuum degree of 1 mbar or more and 400 mbar or less; and a heating step of heating the first substrate and the second substrate bonded to each other in this order.

[0009] Furthermore, the present invention provides a joining method comprising an activation step of activating the respective surfaces of a first SiO2 layer and a second SiO2 layer by a plasma, a joining step of joining the first SiO2 layer and the second SiO2 layer at a vacuum degree of 1 mbar or more and 400 mbar or less, and a heating step of heating the joined first SiO2 layer and the second SiO2 layer joined to each other and removing water generated at a joining surface thereof, in this order. Advantageous effects of the invention

[0010] The present invention can provide a manufacturing method and a joining method of a composite body, the methods being capable of combining the reduction of void generation with the strength of the joint. Short description of the drawings [ Fig. 1] Fig. 1 is a view showing a composite body of the present embodiment. [ Fig. 2] Fig. 2 is a flow chart illustrating a method for producing a composite body 1. [ Fig. 3] Fig. 3(A) to 3(E) are each a view showing the state corresponding to each Fig. 2 shows the step shown. [ Fig. 4] Fig. Figure 4 is a view showing the results of Example 1. [ Fig. 5] Fig. 5(A) to 5(C) are each a view showing the results of Comparative Examples 1 to 3. [ Fig. 6] Fig. Figure 6 shows the relationship between the degree of vacuum and the number of cavities. Description of the embodiments

[0011] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. <Beschreibung der Konfiguration des Verbundkörpers>

[0012] Fig. Figure 1 shows a view of a composite body 1 of the present embodiment. The composite body 1 shown has a structure in which a piezoelectric layer 11a, a dielectric layer 12, and a support substrate 13 are stacked one above the other in this order from the top of the drawing.

[0013] The piezoelectric layer 11a is a layer containing a piezoelectric material. The piezoelectric material is selected according to the application in which the composite body 1 is used. The piezoelectric materials may include, but are not limited to, LiNbO3 (LN) and LiTaO3 (LT). Silicon (Si), gallium arsenide (GaAs), silicon carbide (SiC), gallium nitride (GaN), zinc oxide (ZnO), solid solution ceramic (PZT), or the like are appropriately selected.

[0014] The dielectric layer 12 is the layer disposed beneath the piezoelectric layer 11a. In the present embodiment, the dielectric layer 12 contains SiO2 as its main component. Therefore, the dielectric layer 12 may also be referred to as an SiO2 film or SiO2 layer.

[0015] The carrier substrate 13 serves as a support for the entire composite body 1. Furthermore, the carrier substrate 13 is connected to the piezoelectric layer 11a via the dielectric layer 12. Any suitable substrate can be used as the carrier substrate 13. The carrier substrate 13 can contain a single-crystal body or a polycrystalline body. Alternatively, the carrier substrate 13 can contain a metal.

[0016] The material constituting the support substrate 13 is preferably selected from the group consisting of silicon, SiAlON, sapphire, cordierite, mullite, glass, quartz, rock crystal, alumina, SUS, iron-nickel alloy (Alloy 42), and brass. Although the thickness of the support substrate 13 is, for example, 0.2 to 1 mm, other suitable thicknesses may also be selected.

[0017] The silicon can be single-crystal silicon, polycrystalline silicon, or high-resistance silicon. Alternatively, the carrier substrate 13 can be SOI (silicon on insulator).

[0018] Typically, SiAlON is a ceramic obtained by sintering a mixture of silicon nitride and aluminum oxide and has, for example, a composition characterized by Si 6-w Al w O w N 8- , is represented. Specifically, SiAlON has a composition obtained by mixing aluminum oxide in silicon nitride, and w in the formula represents the mixing ratio of aluminum oxide. w is preferably 0.5 or more and 4.0 or less.

[0019] Typically, the sapphire is a single-crystalline body with the composition Al2O3, and the aluminum oxide is a polycrystalline body with the composition Al2O3. Aluminum oxide is preferably translucent aluminum oxide.

[0020] Typically, cordierite is a ceramic with a composition of 2MgO· 2Al2O3· 5SiO2 and mullite is a ceramic with a composition ranging from 3Al2O3 · 2SiO2 to 2Al2O3 · SiO2. <vorrichtung>

[0021] The structure of the illustrated composite body 1 can be used as the respective structure of various devices. Examples of the device may include a high-frequency device, a power semiconductor, a semiconductor laser, a surface acoustic wave filter (SAW filter), and a piezoelectric thin-film MEMS (Micro Electro Mechanical Systems). <Beschreibung des Verfahrens zur Herstellung des Verbundkörpers 1>

[0022] Next, a method for manufacturing the composite body 1 will be described. Fig. Figure 2 is a flow chart illustrating the process for producing the composite body 1. The Fig. 3(A) to 3(E) are also views showing the state corresponding to the individual steps in Fig. 2 show.

[0023] First, a substrate made of piezoelectric material 11 is prepared, and a dielectric layer 12a is formed on the surface of the substrate made of piezoelectric material 11 (step 101). Furthermore, the support substrate 13 is prepared, and a dielectric layer 12b is formed on the surface of the support substrate 13 (step 102). Steps 101 and 102 form dielectric layers 12a and 12b on the surfaces of the substrate made of piezoelectric material 11 and the support substrate 13 (dielectric layer formation step: Fig. 3(A)). Incidentally, steps 101 and 102 can be reversed in order. Furthermore, the "surface" here refers to the main surface of the piezoelectric material substrate 11 or the support substrate 13, not the side surface thereof.

[0024] In the present embodiment, the piezoelectric material substrate 11 including the dielectric layer 12a formed therein is an example of a first substrate having a surface (surface layer) containing SiO2 as a main component. Furthermore, the support substrate 13 including the dielectric layer 12b formed therein is an example of a second substrate having a surface (surface layer) containing SiO2 as a main component. Moreover, in this case, it can also be said that the first substrate is obtained by depositing SiO2 on the piezoelectric material substrate 11, and the second substrate is obtained by depositing SiO2 on the support substrate 13.

[0025] The dielectric layers 12a and 12b each contain SiO2 as the main component. The dielectric layers 12a and 12b are bonded to be integrated in a later step, resulting in a dielectric layer 12 containing SiO2 as the main component. The dielectric layers 12a and 12b can be formed by reactive sputtering using a reactive sputtering device. The piezoelectric material substrate 11 and the support substrate 13 are arranged in the reactive sputtering device. A target containing silicon (Si) is also arranged in the reactive sputtering device. Argon gas (Ar) and oxygen radicals are also introduced into the reactive sputtering device.Then, silicon, which forms the target, is sputtered by a sputtering power supply, thereby depositing a silicon film on the piezoelectric material substrate 11 and the support substrate 13. This film is oxidized by oxygen radicals, resulting in a silicon oxide (SiO2) film. This makes it possible to form dielectric layers 12a and 12b, each containing SiO2 as a main component, on the surfaces of the piezoelectric material substrate 11 and the support substrate 13.

[0026] Furthermore, the dielectric layers 12a and 12b can also be polished to flatten them. This improves the strength of the connection for subsequent bonding.

[0027] Subsequently, the respective surfaces of the dielectric layers 12a and 12b are activated by a plasma (step 103: activation step) ( Fig. 3(B)). An N2 plasma can be used as the plasma. This results in, as in Fig. As shown in Figure 3(C), SiO2, which configures the dielectric layers 12a and 12b, is activated to generate a hydroxyl group (OH group) as a hydrophilic functional group. Accordingly, this step can also be understood as a hydrophilization step of hydrophilizing the respective surfaces of the dielectric layers 12a and 12b using a plasma.

[0028] Furthermore, in the activation step, the discharge power of the plasma with respect to the respective surfaces of the piezoelectric material substrate 11 and the support substrate 13 is preferably 30 to 100 W. When the discharge power of the plasma is equal to or greater than 30 W, the plasma is more stabilized, so that sufficient hydroxy groups are generated, which leads to a further improvement in the bonding strength in a later step. On the other hand, even if the discharge power of the plasma exceeds 100 W, the reflected wave of the plasma becomes larger, and the degree of activation is not changed, so that a further improvement in the bonding strength is not expected. Accordingly, from the viewpoint of efficiency, the discharge power of the plasma is preferably equal to or less than 100 W.

[0029] Furthermore, the surfaces of the dielectric layers 12a and 12b are connected to each other after the activation step (step 104: connecting step) ( Fig. 3(D)). The bonding is performed, for example, by bringing the surfaces of the dielectric layers 12a and 12b into contact with each other and pressing the dielectric layers 12a and 12b under a predetermined pressure. This bonds the piezoelectric material substrate 11 and the support substrate 13 together via the dielectric layers 12a and 12b.

[0030] Furthermore, in this step, joining is performed at a vacuum level of 1 mbar or more and 400 mbar or less. Incidentally, joining can also be performed in the atmosphere at 1 mbar or more and 400 mbar or less. This makes it possible to produce the composite body 1 that combines the reduction of void formation with the strength of the joint. If the vacuum level is less than 1 mbar, the strength of the joint is likely to be poor. Conversely, if the vacuum level exceeds 400 mbar, the probability of excessive void formation increases.

[0031] In addition, the vacuum time of the bonding step is preferably 30 to 120 seconds. When the vacuum time of the bonding step is equal to or greater than 30 seconds, it becomes easier to control the amount of OH groups by adjusting the degree of vacuum. Therefore, sufficient bond strength is preferably ensured. When the vacuum time is equal to or less than 120 seconds, the particles that are likely to be deposited on the wafer surface are also suppressed, which is preferable.

[0032] Then, the bonded piezoelectric material substrate 11 and the support substrate 13 are heated (step 105: heating step) ( Fig. 3(E)). Heating is performed, for example, at a predetermined temperature and for a predetermined time by placing the bonded piezoelectric material substrate 11 and the support substrate 13 in a heating device such as a furnace. Heating covalently bonds the hydroxyl groups generated on the surfaces of the dielectric layers 12a and 12b. Subsequently, the dielectric layers 12a and 12b are bonded together, forming the dielectric film 12. This firmly bonds the piezoelectric material substrate 11 and the support substrate 13 via the dielectric film 12. Furthermore, in this step, the reaction [Si-OH] + [OH+Si] → [Si-O-Si] + H2O occurs, generating water (H2O). The water is discharged to the outside of the dielectric layer 12. If too much water is generated, the water remains as a void in the dielectric layer 12.

[0033] Incidentally, the heating step can also be understood as a step (annealing step) in which the bonded substrate of piezoelectric material 11 and the carrier substrate 13 are subjected to an annealing treatment.

[0034] Furthermore, a step of grinding the piezoelectric material substrate 11 and the support substrate 13 after heating may be provided (grinding step). In the present embodiment, the piezoelectric material substrate 11 is ground into a thin film, thereby Fig. 1 is formed. Incidentally, the edges of the piezoelectric material substrate 11 and the support substrate 13 can be ground. Through the steps performed up to this point, the composite body 1 can be manufactured. Examples (Example 1)

[0035] A black LiTaO3 (LT) substrate with a 42Y finish and a thickness of 0.25 mm was prepared as the substrate for the piezoelectric material 11, with both surfaces mirror-polished. A high-resistance (≥ 2 kΩ cm) Si substrate with a thickness of 0.23 mm was prepared as the carrier substrate 13.

[0036] Next, 0.5 µm SiO2 films were deposited on the LT substrate and the Si substrate as dielectric layers 12a and 12b, respectively (dielectric layer formation step), and the surface was polished by CMP (chemical mechanical polishing) to flatten it by about 0.1 µm.

[0037] After activating the SiO2 film surfaces of the LT substrate and the Si substrate using an N2 plasma with a discharge power of 100 W (on the LT substrate side) and 65 W (on the Si substrate side) (activation step), bonding was performed at a prescribed vacuum level (bonding step). The vacuum level in the bonding chamber during this step was 30.2 mbar. Furthermore, the vacuum time during the bonding step was 120 seconds.

[0038] To increase the strength of the bond, the bonded substrates were placed in a 130°C oven and heated for 4 hours (heating step). The LT surface of the bonded substrate removed from the oven was thinned to 1 µm by grinding and polishing.

[0039] Subsequently, the composite body 1 was manufactured and the entire surface of the wafer was examined using a high-resolution inspection device for external appearance.

[0040] The results are in Fig. 4 shown.

[0041] As in Fig. As can be seen in Figure 4, no voids were created and the strength of the connection was sufficient. (Comparison example 1)

[0042] Composite body 1 was prepared in the same manner as in Example 1, except that the vacuum degree for bonding the SiO2 film surfaces of the LT substrate and the Si substrate was set to 1013 mbar (1 atm). Then, observation was performed in the same manner as in Example 1.

[0043] The results are in Fig. 5(A).

[0044] As in Fig. As shown in Figure 5(A), excessive moisture forms near the periphery after heating in the form of a void V. The joint strength was otherwise sufficient. This can be attributed to the fact that too high a vacuum level resulted in excessive moisture remaining at the joint interface. (Comparison example 2)

[0045] Composite body 1 was manufactured in the same manner as in Example 1, except that the vacuum level for bonding the SiO2 film surfaces of the LT substrate and the Si substrate was set to 0.16 mbar. Then, observation was performed in the same manner as in Example 1.

[0046] The results are in Fig. 5(B).

[0047] As in Fig. As can be seen in Figure 5(B), the moisture content at the bonding interface became insufficient, resulting in H exfoliation due to insufficient bond strength. This can be attributed to the fact that too low a vacuum level led to a lack of moisture at the bonding interface, which in turn led to a lack of OH groups for covalent bonding. Furthermore, in Comparative Example 2, voids were also generated throughout the wafer. (Comparison example 3)

[0048] Composite body 1 was manufactured in the same manner as in Example 1, except that the vacuum level for bonding the SiO2 film surfaces of the LT substrate and the Si substrate was set to 0.0001 mbar. Then, observation was performed in the same manner as in Example 1.

[0049] The results are in Fig. 5(C).

[0050] As in Fig. As shown in Figure 5(C), a large number of exfoliated Hs were generated due to the very small amount of moisture at the bonding interface and the remarkably low bonding strength. This can be attributed to the following fact: The vacuum degree was further reduced compared to Comparative Example 2, so the moisture remaining at the bonding interface further decreased, resulting in a further shortage of OH groups that could covalently bond. In addition, voids were also generated throughout the wafer in Comparative Example 3.

[0051] It can be seen that the number of cavities and the strength of the joint depend on the degree of vacuum during joining.

[0052] In addition, the composite body 1 was fabricated by further changing the conditions for activating the SiO2 film surfaces of the LT substrate and the Si substrate by an N2 plasma, as well as the vacuum time and vacuum degree during bonding.

[0053] The modified conditions are shown in Table 1 below. It shows that the plasma discharge power on the LT substrate side (plasma power (top)) and the plasma discharge power on the Si substrate side (plasma power (bottom)) at the time of activation, as well as the vacuum time and vacuum degree at the time of bonding, were changed. Then, the number of cavities was calculated under the respective conditions. Incidentally, the number of cavities is the number on the entire wafer with a diameter of 150 mm.

[0054] An excessive presence of voids results in a defective device. The case where the number of voids is equal to or less than 500 is considered a success, and the case where the number of voids exceeds 500 is considered a failure. The number of voids is indicated as the void count in Table 1 below. [Table 1] Plasma power (above) Plasma power (below) Vacuum time during bonding Vacuum level during bonding Number of defects Nr. [W] [W] [s] [mbar] 1 100 65 120 30,2 144 2 30 100 30 1,41 404 3 100 100 70,5 1000 972 4 68,5 100 30 269 10 5 100 44 79,5 12,6 9 6 65 72 70,5 1,41 40 7 58 100 120 12,6 35 8 100 79 30 1,41 96 9 68,5 30 30 1,41 142 10 30 58 30 1000 599 11 30 30 120 30,2 14 12 61,5 68,5 75 12,6 19 13 75,5 65 120 1000 913 14 61,5 68,5 75 8,13 69 15 30 30 48 1,41 241 16 30 68,5 120 0,16 2177 17 100 100 120 0,16 1463 18 93 30 120 0,16 1737 19 30 100 97,5 1000 1046

[0055] In Table 1, numbers 1 to 2, 4 to 9, 11 to 12, and 14 to 15 are designated as successes, and the others as failures. The results so far show that the number of cavities depends primarily on the degree of vacuum.

[0056] Fig. 6 is a view showing the relationship between the degree of vacuum and the number of cavities.

[0057] In Fig. 6, the horizontal axis represents the degree of vacuum and the vertical axis represents the number of cavities. It is shown that the number of cavities at a predetermined degree of vacuum falls within the range bounded by the dashed lines.

[0058] When the vacuum degree at the time of bonding is 1 mbar or more and 400 mbar or less, the number of voids is in a range of 500 or less. However, when the vacuum degree is less than 1 mbar and more than 400 mbar, the number of voids tends to exceed 500. In other words, by bonding under an atmosphere with a vacuum degree, it is possible to regulate the amount of moisture at the bonding interface. At the time of bonding, an atmosphere with a certain vacuum degree is achieved, which reduces the moisture adsorbed at the bonding interface and suppresses voids after heating. On the other hand, a vacuum degree is achieved at which the moisture necessary to ensure the strength of the bond is retained.

[0059] According to the results obtained so far, the degree of vacuum in the joining step is preferably determined by the joining strength between the LT substrate and the Si substrate and by the degree of voids formed on the joining surface after the heating step.

[0060] Furthermore, for the activation step, the discharge power of the plasma with respect to the respective surfaces of the first substrate and the second substrate is preferably determined by the bonding strength and the degree of voids after the heating step.

[0061] Incidentally, although the above steps have been described as a method for manufacturing the composite body 1, they can also be understood as a method for bonding two SiO2 layers. In other words, the above steps can also be understood as the bonding method, which includes an activation step of activating the respective surfaces of the first SiO2 layer (in the above example, the dielectric film 12a) and the second SiO2 layer (in the above example, the dielectric film 12b) with a plasma; a bonding step of bonding the surfaces of the first SiO2 layer and the second SiO2 layer at a vacuum degree of 1 mbar or more and 400 mbar or less; and a heating step of heating the bonded first SiO2 layer and the second SiO2 layer and removing water generated at the bonding surface, in this order.

[0062] Up to this point, the present embodiment has been described. However, the technical scope of the present invention is not limited to the scope described in the embodiments. It will be understood from the description of the appended claims that the variously modified or improved embodiments described above also fall within the technical scope of the present invention. List of reference symbols 1 composite body 11 Substrate made of piezoelectric material 11a piezoelectric layer 12, 12a, 12b dielectric layer 13 Carrier substrate V cavity H Peeling QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2016-225537

[0004] < / vorrichtung>

Claims

[1] A method for producing a composite body, the method comprising: an activation step of activating respective surfaces of a first substrate and a second substrate, the surfaces each containing SiO2 as a main component, by a plasma; a bonding step of bonding the surfaces of the first substrate and the second substrate at a vacuum degree of 1 mbar or more and 400 mbar or less; and a heating step of heating the first substrate and the second substrate bonded to each other in this order. [2] A method for producing a composite body according to claim 1, wherein the vacuum time of the bonding step is 30 to 120 seconds. [3] A method for producing a composite body according to claim 2, wherein for the activation step, a discharge power of the plasma with respect to the respective surfaces of the first substrate and the second substrate is 30 to 100 W. [4] A method for producing a composite body according to any one of claims 1 to 3, further comprising a grinding step of grinding the first substrate after heating. [5] A method for producing a composite body according to any one of claims 1 to 3, wherein the first substrate is obtained by applying SiO2 to a substrate made of piezoelectric material and the second substrate is obtained by applying SiO2 to a support substrate. [6] Joining process comprising: an activation step for activating the respective surfaces of a first SiO2 layer and a second SiO2 layer by a plasma; a bonding step of bonding the surfaces of the first SiO2 layer and the second SiO2 layer at a vacuum degree of 1 mbar or more and 400 mbar or less; and a heating step of heating the first SiO2 layer and the second SiO2 layer bonded to each other and removing water generated at a bonding surface thereof, in this order.

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