Composite substrate and production method of same

Abstract

Provided are a composite substrate that maintains bonding strength suitable for bonding, reduces warpage, and has an intervening layer of sufficient thickness, and a production method for the same.　The composite substrate is characterized by comprising a first substrate, an intervening layer which is an SiOX film, and a second substrate, wherein the O / Si ratio of the SiOX film is 1.6-1.98. Alternatively, the composite substrate is characterized by comprising a first substrate, an intervening layer which is an SiOX film, and a second substrate, wherein: the O / Si ratio of the SiOX film has a distribution in the film formation depth direction, the O / Si ratio in the vicinity of the interface with the first substrate being between 1.9 and 2.0 and the O / Si ratio in the vicinity of the interface with the second substrate being between 1.6 and 1.9; and the O / Si ratio monotonously increases from the interface with the second substrate toward the interface with the first substrate.

Description

Composite substrate and method of manufacturing the same

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

[0002] In recent years, in order to expand the range of applications of conventional functional materials (semiconductors, oxide single crystals, etc.), active development has been conducted to improve performance by bonding different types of substrates. In the field of semiconductors, SOI (Silicon on Insulator) is known, and in the field of oxide single crystals, a method of bonding lithium tantalate (LT) to sapphire or the like is known. Here, it has been reported that thinning the LT substrate improves the temperature characteristics and improves the performance value (Q value). In such cases, it is common to provide an intervening layer between the functional thin film and the supporting substrate for the purpose of separation. Specifically, the intervening layer is made of SiO ２ Materials with high insulation properties, low high-frequency loss, and easy processing (flattening), such as those mentioned above, are often used. This intervening layer must have several important properties. One is that it must have minimal warping when bonded. If there is significant warping, bonding will not be possible, making it impossible to produce a composite substrate. The other is that it must be possible to ensure good adhesion when bonding.

[0003] US Patent Application Publication No. 2017 / 0033764

[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 itself. Here, SiO obtained by thermally oxidizing silicon ２ The composition of Si and O in the silicon dioxide film is approximately the theoretical ratio of 1:2. However, the CVD silicon oxide film, which is usually used as an intermediate layer, is strictly SiO Ｘ (X≠2). Here, SiO Ｘ The adhesion and warpage of the film vary greatly depending on the composition (ratio of X), and it has been difficult to obtain sufficient bonding strength while suppressing warpage. ＸThe 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.

[0006] In order to solve the above problems, a composite substrate according to an embodiment of the present invention includes a first substrate (functional substrate) and a SiO Ｘ The intervening layer is a film, and the second substrate (support substrate) is made of SiO Ｘ The film is characterized in that the O / Si ratio, which is the atomic ratio of oxygen to silicon, is 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 The intervening layer is a film, and the second substrate (support substrate) is made of SiO Ｘ The 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] In addition, the method for manufacturing a composite substrate according to an embodiment of the present invention is a method for manufacturing a composite substrate by bonding a first substrate (functional substrate) and a second substrate (support substrate) to an intermediate layer of SiO Ｘ A method for manufacturing a composite substrate in which layers are bonded together via a film, comprising the steps of: Ｘ The O / Si ratio of the film is adjusted to be between 1.6 and 1.98.Ｘ The present invention is characterized in that a film is formed by:

[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, the first substrate and the second substrate are made of SiO Ｘ Before lamination via the film layer, heat treatment may be performed in an atmosphere containing oxygen.

[0012] In the present invention, SiO after heat treatment Ｘ The O / Si ratio of the film may have a distribution in the depth direction, in which case it 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 is preferably a method using silane and oxygen as main raw materials. ２ The film formation method may be a method using O as the main raw material, or a method using TEOS and oxygen as the 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.

[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.

[0019] 1 is a schematic diagram showing the layer structure of the composite substrate 4. FIG. 2 is a flowchart showing a method for manufacturing the composite substrate 4. FIG. 3 is a diagram showing a SiO film formed so that the O / Si ratio is about 1.6. Ｘ 1 is a graph showing the depth profile of the O / Si ratio before and after heat treatment.

[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 intervening 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 atomic 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 one 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 one 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] The intermediate layer 3 can be formed by chemical vapor deposition (CVD), and the film formation gas used in this process can be a combination of silane gas and oxygen, or a combination of silane gas and N ２ A combination of TEOS (tetraethoxysilane) and oxygen, or a combination of TEOS and oxygen, etc., can be used.

[0026] Here, SiO ２ The amount of oxygen is adjusted during film formation so that the amount of oxygen is slightly less than the theoretical ratio. This results in a silicon oxide film with a composition of SiO Ｘ (However, X<2). By slightly deficient in oxygen, it is possible to increase the adhesion and bond strength. If the oxygen deficiency is excessive, the composition can be changed to SiO by subsequently performing heat treatment in an oxygen-containing atmosphere. ２ It is also possible to easily approach SiO Ｘ is in the state of X=2 (SiO ２ ) is the most stable form, so it takes in oxygen and the composition becomes SiO ２ When the composition approaches the optimum SiO Ｘ By this method, SiO2 having a slight oxygen deficiency compared to the theoretical ratio, which is suitable for bonding, can be obtained. ＸThis 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 film formation Ｘ When (X>2) is formed, excess oxygen is not discharged, and the composition is changed to SiO ２ The problem cannot be solved by using a slightly oxygen-deficient SiO Ｘ If necessary, the SiO ２ By bringing it closer to Ｘ After the 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] The formed intervening layer 3 is then 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 The surface of the first substrate 1 (a film obtained by heat-treating the first substrate 1) is polished and flattened, and then the first substrate 1 is bonded to the second substrate 2, which serves as a support substrate, to produce a composite substrate 4 with high bonding strength. 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 may 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 performed in an atmosphere containing oxygen. The thinning is preferably performed by grinding and / or polishing. Alternatively, the first substrate 1 may be thinned by previously implanting ions into the first substrate 1 and then peeling off at the ion-implanted interface. When performing ion implantation, the implanted ions are preferably H ＋ Or H ２ ＋ The thickness of the first substrate 1 after thinning is preferably 100 to 1000 nm, and more preferably 350 to 700 nm, particularly when the first substrate 1 is made of lithium tantalate. Composite substrate 4 is manufactured in the manner described above.

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

[0031] (Experiment 1) SiO was deposited on a silicon substrate (first substrate) with a diameter of 150 mm by PECVD (Plasma Enhanced Chemical Vapor Deposition). Ｘ The substrate temperature was 150° C. and the pressure was 1 Torr. The source gas was 2% SiH ４ and nitrogen gas containing 200 to 400 sccm and N as an oxygen source. ２ O gas was flowed at 300 to 900 sccm, and SiO 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 atomic 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 surface, 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 larger 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 excessive oxygen Ｘ In the case of (X>2), it is thought that excess oxygen acts as a factor that hinders bonding. In order to ensure adhesion of the bonded layers, it is necessary to use SiO2 that is slightly deficient in oxygen. Ｘ Specifically, it is considered that a film having an O / Si ratio of 1.98 or less is desirable.

[0033]

[0034] (Experiment 2) SiO under the same conditions as Experiment 1 Ｘ The substrate on which the film was formed was 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. Those with an O / Si ratio of more than 2 to begin with showed almost no change, whereas those with an O / Si ratio of 2 or less approached 2 after the heat treatment. This is because the heat treatment was performed in an oxygen-containing atmosphere, and oxygen entered the film, causing the SiO ２ These substrates were polished, bonded together in the same manner as in Experiment 1, and then heat treated. The results are shown in Table 2.

[0035]

[0036] From these results, it was found that films with an O / Si ratio of less than 1.6 before heat treatment had a large warp 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 large stress in the film and causing the substrate to warp. Furthermore, films with an O / Si ratio of more than 2 still peeled off after heat treatment. Films with an O / Si ratio of 1.6 to 2.0 before heat treatment did not peel off 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 is 1.6 or more and 1.98 or less.

[0038] (Experiment 3) SiO was deposited on a silicon substrate with a diameter of 150 mm by the PECVD method. 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, the source gas contained 2% SiH ４ Nitrogen gas containing N ２ An appropriate amount of O gas was flowed, and SiO Ｘ The composition of the substrate 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 the O / Si ratio obtained from this substrate was set to 2, thereby obtaining 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. From Figure 1, it can be seen 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, which is the theoretical ratio for a thermal oxide film, while the interior remained at around 1.6.

[0039] SiO Ｘ The 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. 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. 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 is grown, and the surface is subsequently etched in an oxygen-containing atmosphere to form SiO ２ It was found that an oxide film with an O / Si ratio close to 2 was suitable for bonding, which was the objective of the present invention.

[0040] In addition, SiO having an O / Si ratio of 1.6 to 2.4 before heat treatment ＸThe same experiment was carried out on SiO2 with a composition greater than 2.0, 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 composition ratio of the interior remained almost the same as immediately after film formation. However, SiO2 with a composition greater than 2.0 Ｘ In the case of the test piece, peeling occurred after heat treatment and polishing, as in Experiment 1.

[0041] The oxygen source is N ２ Each experiment was carried out under the same conditions as in Example 1, except that oxygen gas was used instead of O. 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.

[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. Ｘ The 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 then bonded to a quartz substrate. The results showed the same tendency as in Example 1.

[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 film formed 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 formed.

[0044] An experiment similar to that of Example 1 was carried out, except that the type of the 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. This result demonstrated that the present invention does not depend on the type of support substrate.

[0045] An experiment similar to that in Example 1 was carried out by varying 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 should be 250°C or higher.

[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 this result, it was found that a heat treatment time of 3 hours is desirable.

[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.

[0048] In the same experiment as in Example 1, hydrogen ions (H ＋ Or H ２ ＋ 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.

[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, or 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.

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

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 which is a film and a second substrate, 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. The composite substrate according to claim 1 or 2, wherein the first substrate contains any of silicon, alumina, sapphire, SiC, quartz glass, silicon nitride, aluminum nitride, lithium tantalate, and lithium niobate.

4. The composite substrate according to claim 1 or 2, characterized in that the second substrate contains any of silicon, silicon with an oxide film, alumina, sapphire, SiC, quartz glass, silicon nitride, aluminum nitride, lithium tantalate, and lithium niobate.

5. The first and second substrates are bonded to each other 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 bonded to the SiO 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. The method for manufacturing a composite substrate according to any one of claims 5 to 7, characterized in that after the first substrate and the second substrate are bonded together, the first substrate is thinned.

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. The method for producing a composite substrate according to any one of claims 5 to 7, wherein the intervening layer is formed by a CVD method.

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 method for forming 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. 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. The method for producing a composite substrate according to any one of claims 5 to 7, wherein the heat treatment time after the formation of the intermediate layer is 3 hours or more.

15. A method for manufacturing a composite substrate according to any one of claims 5 to 7, characterized in that, before the bonding, a surface activation treatment is carried out on the bonding surfaces of the first substrate, the second substrate, or both.

16. The method for producing 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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