Composite substrate and method for manufacture the same

Abstract

To provide a composite substrate that maintains bonding strength suitable for lamination, reduces warpage, and includes an interposed layer having a sufficient thickness, and a method for manufacturing the same.SOLUTION: A composite substrate is composed of a first substrate, an intervening layer that is a SiOX film, and a second substrate. The SiOX film has an O / Si ratio of 1.6 to 1.98. Alternatively, the composite substrate includes the first substrate, the intervening layer that is the SiOX film, and the second substrate. The O / Si ratio of the SiOX film has a distribution in a film formation depth direction. The O / Si ratio is between 1.9 and 2.0 near an interface with the first substrate. The O / Si ratio is between 1.6 and 1.9 near an interface with the second substrate. In addition, the O / Si ratio monotonously increases from the interface with the second substrate toward the interface with the first substrate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a composite substrate used as a material for electronic devices, etc., and a method for producing the same. [Background technology]

[0002] In recent years, active development has been underway to expand the range of applications of conventional functional materials (semiconductors, oxide single crystals, etc.) by bonding different types of substrates to enhance their performance. In the semiconductor field, SOI (Silicon on Insulator) is well-known, while in the oxide single crystal field, methods such as bonding lithium tantalate (LT) to sapphire are well-known. It has been reported that thinning the LT substrate can improve its temperature characteristics and performance (Q value). In such cases, an intervening layer is typically provided between the functional thin film and the supporting substrate to separate it. Materials often used for the intervening layer include SiO2, which has high insulating properties, low high-frequency loss, and is easy to process (flatten). This intervening layer must have several important properties. One is minimal warping during bonding. Significant warping would prevent bonding and the production of composite substrates. The other is ensuring sufficient adhesion during bonding. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2017 / 0033764 Summary of the Invention [Problem to be solved by the invention]

[0004] The first factor that affects adhesion is the flatness (surface roughness) of the substrate. Substrates with high flatness show strong adhesion. This flatness can be easily ensured by polishing the substrate or film surface. The second factor is the adhesion of the intervening layer film itself. Here, while the composition of Si and O in SiO2 obtained by thermally oxidizing silicon is almost the theoretical ratio of 1:2, CVD silicon oxide films, etc., which are commonly used in intervening layers, strictly speaking, are SiO X The composition is as follows: (X≠2) where SiO X The adhesion and warpage of the film vary greatly depending on the composition (ratio of X), and it was difficult to obtain sufficient bonding strength while suppressing warpage. X The thicker the film, the greater the warpage and the more difficult it becomes to bond. Therefore, it has been very difficult to maintain a bonding strength suitable for bonding, reduce warpage, and ensure a certain thickness of the intervening layer.

[0005] An object of the present invention is to provide a composite substrate that maintains a bonding strength suitable for bonding, reduces warping, and has an intervening layer of sufficient thickness, and a method for manufacturing the same. [Means for solving the problem]

[0006] In order to solve the above problems, the composite substrate according to the embodiment of the present invention comprises a first substrate (functional substrate) and a SiO X It consists of an intermediate layer, which is a film, and a second substrate (support substrate), and is made of SiO X The film is characterized by an O / Si ratio, which is the atomic ratio of oxygen to silicon, of 1.6 to 1.98.

[0007] Furthermore, a composite substrate according to another embodiment of the present invention includes a first substrate (functional substrate) and a SiO X It consists of an intermediate layer, which is a film, and a second substrate (support substrate), and is made of SiO XThe O / Si ratio, which is the atomic ratio of oxygen to silicon in the film, has a distribution in the film formation depth direction, characterized in that the O / Si ratio is between 1.9 and 2.0 near the interface with the first substrate, the O / Si ratio is between 1.6 and 1.9 near the interface with the second substrate, and the O / Si ratio monotonically increases from the interface with the second substrate toward the interface with the first substrate.

[0008] In the present invention, the first substrate may include any one of silicon, alumina, sapphire, SiC, quartz glass, silicon nitride, aluminum nitride, lithium tantalate, and lithium niobate, and the second substrate may include any one of silicon, silicon with an oxide film, alumina, sapphire, SiC, quartz glass, silicon nitride, aluminum nitride, lithium tantalate, and lithium niobate.

[0009] Furthermore, a method for manufacturing a composite substrate according to an embodiment of the present invention is a method for manufacturing a composite substrate in which a first substrate (functional substrate) and a second substrate (support substrate) are bonded together via an SiOx film as an intermediate layer, x The method is characterized in that the SiOx film is formed so that the O / Si ratio of the film falls within the range of 1.6 to 1.98.

[0010] Suitable materials for the first substrate (functional substrate) include silicon, alumina, sapphire, SiC, quartz glass, silicon nitride, aluminum nitride, lithium tantalate, and lithium niobate, while suitable materials for the second substrate (support substrate) include silicon, silicon with an oxide film, alumina, sapphire, SiC, quartz glass, silicon nitride, aluminum nitride, lithium tantalate, and lithium niobate.

[0011] In the present invention, before the first substrate and the second substrate are bonded together via the SiOx film layer, they may be heat-treated in an atmosphere containing oxygen.

[0012] In the present invention, the O / Si ratio of the SiOx film after the heat treatment may have a distribution in the depth direction, in which the O / Si ratio may be between 1.9 and 2.0 near the interface with the first substrate, and between 1.6 and 1.9 near the interface with the second substrate, and the O / Si ratio may increase monotonically from the interface with the second substrate toward the interface with the first substrate.

[0013] In the present invention, after the first substrate and the second substrate are bonded together, the first substrate may be thinned by grinding and polishing, ion implantation delamination, or both.

[0014] In the present invention, the method for forming the intervening layer is preferably a CVD method.

[0015] In the present invention, the method for forming the intervening layer may be a method using silane and oxygen as main raw materials, or a method using silane and NO as main raw materials, or a method using TEOS and oxygen as main raw materials.

[0016] In the present invention, the heat treatment time after the formation of the intervening layer is preferably 3 hours or more.

[0017] In the present invention, before bonding, it is preferable to perform a surface activation treatment on the bonding surfaces of the first substrate, the second substrate, or both of them, which may be any of ozone water treatment, UV ozone treatment, ion beam treatment, and plasma treatment. [Effects of the Invention]

[0018] A composite substrate can be realized that maintains a bonding strength suitable for bonding, reduces warping, and has an intervening layer of sufficient thickness. [Brief explanation of the drawings]

[0019] [Figure 1] 2 is a schematic diagram showing the layer structure of a composite substrate 4. FIG. [Figure 2] 10 is a flowchart showing a method for manufacturing a composite substrate 4. [Figure 3]1 is a graph showing the depth profile of the O / Si ratio before and after heat treatment for an SiOX film formed so that the O / Si ratio is about 1.6. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0021] 1 is a schematic diagram showing the layer structure of a composite substrate 4 according to this embodiment. As shown in Fig. 1, the composite substrate 4 includes a first substrate 1 (functional substrate) including a functional region for device fabrication, a second substrate 2 (support substrate) that transfers and supports the first substrate 1, and an intermediate layer 3 provided between the first substrate 1 and the second substrate 2.

[0022] The intermediate layer 3 is a silicon oxide film (SiO X The SiO X The O / Si ratio, which is the element ratio of silicon to oxygen in the film, is preferably 1.6 to 1.98. X The O / Si ratio of the film may have a distribution in the film formation depth direction. In this case, for example, it is preferable that the O / Si ratio is between 1.9 and 2.0 near the interface with the first substrate 1, the O / Si ratio is between 1.6 and 1.9 near the interface with the second substrate 2, and the O / Si ratio increases monotonically from the interface with the second substrate 2 toward the interface with the first substrate 1.

[0023] The first substrate 1 is preferably made of any of silicon, alumina, sapphire, SiC, quartz glass, silicon nitride, aluminum nitride, lithium tantalate, and lithium niobate. The second substrate 2 is preferably made of any of silicon, silicon with an oxide film, alumina, sapphire, SiC, quartz glass, silicon nitride, aluminum nitride, lithium tantalate, and lithium niobate.

[0024] Next, a method for manufacturing the composite substrate 4 will be described with reference to the flowchart shown in FIG. 2. First, a first substrate 1 including a functional region for device fabrication and a second substrate 2 (support substrate) for transferring and supporting the first substrate 1 are prepared (step S01). Next, a silicon oxide film (SiO X ;X<2) is deposited (step S02).

[0025] Chemical vapor deposition (CVD) can be used as a deposition method for the intervening layer 3, and the deposition gases that can be used in this process include a combination of silane gas and oxygen, a combination of silane gas and N2O, and a combination of TEOS (tetraethoxysilane) and oxygen.

[0026] Here, the amount of oxygen is adjusted during SiO2 film formation so that the film is formed with a slight oxygen deficiency compared to the theoretical ratio. X (However, X<2). By slightly deficient in oxygen, it is possible to increase the adhesion and bonding strength. If the oxygen deficiency is excessive, it is easy to bring the composition closer to SiO2 by subsequently performing heat treatment in an oxygen-containing atmosphere. SiO X Since the state of X=2 (SiO2) is the most stable form, when oxygen is taken in and the composition approaches SiO2, the change in composition automatically stops and the optimal SiO X This method produces SiO 2 with a slight oxygen deficiency compared to the theoretical ratio, which is suitable for bonding. X This is thought to be because oxygen in the heat treatment atmosphere penetrates into oxygen-deficient sites in the film, and the incorporation is automatically completed when sufficient oxygen has penetrated.

[0027] On the other hand, excessive oxygen in the SiO X When a film with (X>2) is formed, the excess oxygen is not discharged, and the composition cannot be brought close to SiO2 in the subsequent heat treatment, and the problem cannot be solved. XIf necessary, a film of SiO2 can be formed by subsequent heat treatment to make it closer to SiO2, and the film will have a slight oxygen deficiency. X After this film formation and before bonding, the heat treatment is preferably carried out at a temperature of 250°C or higher. The heat treatment time is preferably 3 hours or longer. X The O / Si ratio of the film may have a distribution in the depth direction, for example, the O / Si ratio may be between 1.9 and 2.0 near the interface with the first substrate 1, the O / Si ratio may be between 1.6 and 1.9 near the interface with the second substrate 2, and the O / Si ratio may increase monotonically from the interface with the second substrate 2 toward the interface with the first substrate 1.

[0028] Then, the formed intervening layer 3 is flattened (step S03), and the first substrate 1 and the second substrate 2 are bonded together via the intervening layer 3 (step S04). X film (or this SiO X By polishing and flattening the surface of the first substrate 1 (a film that has been heat-treated), and then bonding it to the second substrate 2 that serves as the support substrate, a composite substrate 4 with high bonding strength can be manufactured. In this case, it is preferable to subject both or one of the first substrate 1 and the second substrate 2 to a surface activation treatment before the bonding step. The surface activation treatment can be any of ozone water treatment, UV ozone treatment, ion beam treatment, and plasma treatment.

[0029] Thereafter, the bonded composite substrate 4 is heat-treated (step S05), and the first substrate 1 after bonding is thinned (step S06). The heat treatment after bonding is preferably carried out in an atmosphere containing oxygen. Also, thinning is preferably carried out by grinding and / or polishing. Alternatively, the first substrate 1 may be thinned by previously implanting ions into it and then peeling off at the ion-implanted interface. When ion implantation is carried out, the implanted ions are preferably H + Or H2 +The thickness of first substrate 1 after thinning is preferably 100 to 1000 nm, and more preferably 350 to 700 nm, particularly when first substrate 1 is made of lithium tantalate. Composite substrate 4 is produced in the manner described above.

[0030] Below, an experiment conducted to confirm the effects of the present invention will be described as an example. [Example]

[0031] (Experiment 1) SiO was deposited on a 150 mm diameter silicon substrate (first substrate) using the PECVD (Plasma Enhanced Chemical Vapor Deposition) method. X The substrate temperature was set to 150°C and the pressure was set to 1 Torr. As the source gas, nitrogen gas containing 2% SiH4 was flowed at 200 to 400 sccm, and N2O gas as an oxygen source was flowed at 300 to 900 sccm. X The composition of the film was adjusted. The film thickness was about 5 μm. After film formation, the SiO X The composition of the film was analyzed by XPS (X-ray photoelectron spectroscopy). XPS is a method for analyzing the composition of the outermost layer of the target sample. From the results of this composition analysis, SiO X The O / Si ratio, which is the elemental ratio of oxygen to silicon in the film, was calculated. In this case, a silicon substrate (standard substrate) on which a thermal oxide film (a complete oxide film in which Si is oxidized by thermal oxidation, with an O / Si ratio of 2.0) was grown was prepared, and the O / Si ratio obtained from the XPS measurement of this standard substrate was set to 2. X The O / Si ratio of the film was corrected (this is called normalization).

[0032] The substrate on which the film was formed was polished to a mirror finish, and then bonded to a quartz substrate (second substrate) of the same diameter. Prior to bonding, a plasma surface activation treatment was performed. After that, a heat treatment at 300°C was performed, and the bonded substrate was observed. The results are shown in Table 1. Peeling occurred from the periphery when the O / Si ratio was 2 or more. The greater the O / Si ratio, the greater the degree of peeling. Furthermore, no peeling occurred when the O / Si ratio was less than 2. SiO with an excessive amount of oxygen X In the case of (X>2), it is thought that excess oxygen acts as a factor that hinders bonding. To ensure adhesion between the two, it is necessary to use SiO2 that is slightly deficient in oxygen. X It is believed that a film (x<2) is suitable. Specifically, it is believed that a film with an O / Si ratio of 1.98 or less is desirable.

[0033] [Table 1]

[0034] (Experiment 2) SiO under the same conditions as in Experiment 1 X The substrates on which the film was formed were subjected to heat treatment at 350°C in an air atmosphere for 60 hours. The O / Si ratio at this time is shown in Table 2. Substrates with an original O / Si ratio of greater than 2 showed almost no change, whereas those with an O / Si ratio of 2 or less approached 2 after heat treatment. This is thought to be because the heat treatment was performed in an oxygen-containing atmosphere, allowing oxygen to penetrate into the film, bringing it closer to a composition of SiO2. These substrates were polished, bonded together in the same manner as in Experiment 1, and then subjected to heat treatment. The results are shown in Table 2.

[0035] [Table 2]

[0036] These results showed that films with an O / Si ratio of less than 1.6 before heat treatment showed significant warping after heat treatment, making bonding impossible in the first place. This is thought to be because a large amount of oxygen entered the film, generating significant stress in the film and causing the substrate to warp. Furthermore, films with an O / Si ratio of more than 2 continued to peel after heat treatment. Films with an O / Si ratio of 1.6 to 2.0 before heat treatment did not peel after bonding and heat treatment, and no microcracks occurred.

[0037] Considering the results of Experiments 1 and 2, it is considered desirable that the O / Si ratio immediately after film formation be 1.6 or more and 1.98 or less.

[0038] (Experiment 3) SiO2 was deposited on a 150 mm diameter silicon substrate by PECVD. X The film was formed under the conditions of a substrate temperature of 150°C and a film forming pressure of 1 Torr. Under these conditions, nitrogen gas containing 2% SiH4 and N2O gas were flowed in appropriate amounts as source gases, and SiO X The composition of the SiO film was adjusted so that the O / Si ratio was about 1.6. The film thickness was about 4 to 4.5 μm. X It was confirmed by XPS (X-ray photoelectron spectroscopy) that the O / Si ratio of the film was around 1.6. The O / Si ratio in the depth direction of this substrate was also measured by SIMS (secondary ion mass spectroscopy). At this time, a silicon substrate on which a thermal oxide film was grown to the same thickness was prepared, and by setting the O / Si ratio obtained from this substrate to 2, it was possible to obtain SiO X The O / Si ratio of the film was corrected (normalized). This substrate was subjected to heat treatment at 350°C in an air atmosphere for 60 hours. Figure 1 shows the depth profile of the O / Si ratio before and after heat treatment. Figure 1 shows that the O / Si ratio was about 1.6 immediately after film formation, but after heat treatment, the O / Si ratio near the surface approached 2.0, the theoretical ratio for a thermal oxide film, while the interior remained at around 1.6.

[0039] SiO XThe substrate on which the film was formed and heat-treated was polished to a mirror finish, and then bonded to a quartz substrate of the same diameter. Before bonding, the surface was activated using plasma. After that, heat treatment was performed at 300°C, and the bonded substrate was observed. As a result, good bonding was achieved without warping or peeling. From this, it is important that the O / Si ratio at the bonding interface (film-formed surface) is around 2, and SiO was intentionally added to create an oxygen deficiency. X The oxide film grown by growing the oxide film on the surface and then oxidizing it in an oxygen-containing atmosphere to make it closer to SiO2 (i.e., O / Si=2) was found to be suitable for bonding, which is the purpose of this study.

[0040] In addition, SiO with an O / Si ratio of 1.6 to 2.4 before heat treatment X The same experiment was carried out on SiO2, and the results were the same as above. In this case too, the O / Si ratio of the surface layer after heat treatment was 1.9 to 2.0, and the internal layer maintained the composition ratio immediately after film formation. However, SiO2 with a composition greater than 2.0 X In the case of the 1st experiment, peeling occurred after heat treatment and polishing. [Example]

[0041] The oxygen source was changed from NO to oxygen gas, and other experiments were carried out under the same conditions as in Example 1. The results showed the same tendency as in Example 1. From these results, it was found that there was no particular dependency on the type of gas used as the oxygen source, and the results depended only on the O / Si ratio. [Example]

[0042] SiO X An experiment similar to that in Example 1 was carried out using TEOS (tetraethoxysilane) as the film formation source. Specific film formation conditions were a substrate temperature of 60°C, a pressure of 1 Torr, and a source gas of TEOS bubbled with He at a flow rate of 10 sccm, with the flow rate of oxygen adjusted between 20 and 100 sccm. XThe substrate on which the film was formed was subjected to heat treatment at 350°C in an air atmosphere for 60 hours. The substrate was polished to a mirror finish, then subjected to surface treatment and bonded to a quartz substrate. The results showed the same tendency as in Example 1. [Example]

[0043] An experiment similar to that in Example 1 was carried out, except that the first substrate was made of alumina, sapphire, SiC, quartz glass, silicon nitride, aluminum nitride, lithium tantalate, or lithium niobate. X The thickness of the deposited film was 3 μm, and the heat treatment after bonding was carried out at 150° C. for 96 hours. The results were exactly the same as in Example 1. This result demonstrates that the present invention is not dependent on the substrate material on which the film is deposited. [Example]

[0044] An experiment similar to that of Example 1 was carried out, except that the type of second substrate was changed to silicon, silicon with an oxide film, alumina, sapphire, SiC, silicon nitride, aluminum nitride, lithium tantalate, or lithium niobate. The results were exactly the same as in Example 1. These results demonstrate that the present invention is not dependent on the type of support substrate. [Example]

[0045] An experiment similar to that in Example 1 was carried out by changing the temperature of the heat treatment after film formation from 50 to 500°C. As a result, the O / Si ratio approached 2 when the temperature was 250°C or higher. From this result, it is considered that the heat treatment temperature is preferably 250°C or higher. [Example]

[0046] An experiment similar to that in Example 1 was carried out with the post-film heat treatment temperature set to 250°C and the heat treatment time set to (0.5 h, 1.0 h, 2 h, 3 h, 4 h, 5 h). As a result, the O / Si ratio approached 2 when the heat treatment time was 3 hours or more. From these results, it was found that a heat treatment time of 3 hours is desirable. [Example]

[0047] One side of the first substrate of the composite substrate produced by the method of Experiment 3 in Example 1 was thinned by grinding and polishing. The surface was observed, but no abnormalities were found. [Example]

[0048] In the same experiment as in Example 1, hydrogen ions (H + Or H2 + The composite substrate was then peeled off at the ion-implanted interface to produce a thin film composite substrate. The surface was observed, but no abnormalities were found. [Example]

[0049] An experiment similar to that in Example 1 was carried out, except that the surface activation method after film formation was changed to ozone water treatment, UV ozone treatment, and ion beam treatment. The results were exactly the same.

[0050] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included within the technical scope of the present invention. In other words, appropriate modifications are possible within the scope of the technical idea expressed in the present invention, and forms incorporating such modifications and improvements are also included within the technical scope of the present invention. [Explanation of symbols]

[0051] 1 First board 2 Second board 3 Intervening layer 4 Composite board

Claims

1. a first substrate and a SiO Ｘ A composite substrate comprising an intermediate layer which is a film and a second substrate, Ｘ A composite substrate characterized in that the O / Si ratio of the film is 1.6 to 1.

98.

2. a first substrate and a SiO Ｘ A composite substrate comprising an intermediate layer that is a film and a second substrate, The SiO Ｘ A composite substrate characterized in that the O / Si ratio of the film has a distribution in the film formation depth direction, the O / Si ratio is between 1.9 and 2.0 near the interface with the first substrate, the O / Si ratio is between 1.6 and 1.9 near the interface with the second substrate, and the O / Si ratio monotonically increases from the interface with the second substrate toward the interface with the first substrate.

3. 3. The composite substrate according to claim 1, wherein the first substrate includes any one of silicon, alumina, sapphire, SiC, quartz glass, silicon nitride, aluminum nitride, lithium tantalate, and lithium niobate.

4. 3. The composite substrate according to claim 1, wherein the second substrate includes any one of silicon, silicon with an oxide film, alumina, sapphire, SiC, quartz glass, silicon nitride, aluminum nitride, lithium tantalate, and lithium niobate.

5. The first substrate and the second substrate are separated by an intermediate layer of SiO Ｘ A method for manufacturing a composite substrate in which the SiO Ｘ The O / Si ratio of the film is adjusted to be between 1.6 and 1.

98. Ｘ A method for manufacturing a composite substrate, comprising: forming a film of

6. The first substrate and the second substrate are Ｘ 6. The method for producing a composite substrate according to claim 5, wherein a heat treatment is carried out in an atmosphere containing oxygen before bonding via the film.

7. SiO after the heat treatment Ｘ The method for producing a composite substrate according to claim 6, characterized in that the O / Si ratio of the film has a distribution in the depth direction, is between 1.9 and 2.0 near the interface with the first substrate, is between 1.6 and 1.9 near the interface with the second substrate, and the O / Si ratio monotonically increases from the interface with the second substrate toward the interface with the first substrate.

8. 8. The method for manufacturing a composite substrate according to claim 5, further comprising the step of: thinning the first substrate after bonding the first substrate and the second substrate together.

9. 9. The method for producing a composite substrate according to claim 8, wherein the thinning is performed by a grinding / polishing method and / or an ion implantation peeling method.

10. 8. The method for producing a composite substrate according to claim 5, wherein the intermediate layer is formed by a CVD method.

11. 11. The method for producing a composite substrate according to claim 10, wherein the intermediate layer is formed using silane and oxygen as main raw materials.

12. The deposition method of the intermediate layer is a method using silane and N ２ 11. The method for producing a composite substrate according to claim 10, wherein the film is formed using O as a main raw material.

13. 11. The method for producing a composite substrate according to claim 10, wherein the intermediate layer is formed using TEOS and oxygen as main raw materials.

14. 8. The method for producing a composite substrate according to claim 5, wherein the heat treatment time after the formation of the intermediate layer is 3 hours or more.

15. 8. The method for manufacturing a composite substrate according to claim 5, wherein a surface activation treatment is carried out on the bonding surfaces of the first substrate, the second substrate, or both of them before the bonding.

16. 16. The method for manufacturing a composite substrate according to claim 15, wherein the surface activation treatment is any one of ozone water treatment, UV ozone treatment, ion beam treatment, and plasma treatment.

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