Oxide single crystal composite substrate and method for manufacturing same

Abstract

The present invention provides: an oxide single crystal composite substrate that has a SiON film and a SiN film both of which have improved adhesion; and a method for manufacturing the same.　A composite substrate according to an embodiment of the present invention comprises an oxide single crystal layer, an interposed layer, a SiO2 thin film, and a support substrate. The interposed layer is a SiON film or a SiN film, and the SiO2 thin film is provided between the interposed layer and the support substrate. The O / Si ratio, which is the elemental ratio of oxygen to silicon in the SiO2 thin film, is preferably 1.8-2.2. The thickness of the SiO2 thin film is preferably 3-100 nm.

Description

Oxide single crystal composite substrate and method for manufacturing the same

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

[0002] In recent years, the mobile communications market, typified by smartphones, has seen a rapid increase in communication traffic. To address this issue, the number of bands required is increasing, inevitably necessitating the miniaturization and performance improvement of various components. Common piezoelectric materials, such as lithium tantalate (also abbreviated as LT) and lithium niobate (also abbreviated as LN), are widely used as materials for surface acoustic wave (SAW) devices. These materials have the advantage of having a large electromechanical coupling coefficient and enabling broadband operation.

[0003] It is known that thinning LT and LN (10 μm or less) improves their properties and expands their range of applications. Specific examples include high-performance filter devices and optical modulators. Thinning typically involves grinding and polishing the LT or LN, but because it is difficult to achieve nanometer-level film thickness uniformity across the entire substrate, ion implantation and delamination are generally considered preferable for film thicknesses of 1 μm or less.

[0004] As disclosed in Patent Document 1 and elsewhere, the ion implantation delamination method involves implanting light elements such as hydrogen and helium into a target substrate and then delaminating at the point where the concentration is at its maximum (the ion-implanted interface), making it a suitable method for obtaining thin films with good uniformity. This method requires bonding LT or LN to a support substrate, performing a certain amount of heat treatment, and then performing delamination using a method such as the SiGen method (mechanical delamination). After delamination, the delamination surface must be polished to remove the ion-implanted damage layer (approximately 150 nm) and achieve a mirror finish.

[0005] International Publication No. 2016 / 088466

[0006] When such a thin film laminated structure is adopted, a structure in which an intervening layer is sandwiched between the LT or LN thin film and the support substrate is generally used. Here, it is preferable to use a material with a high acoustic velocity as the material for the intervening layer in order to more efficiently confine energy within the LT or NT thin film. To increase the acoustic velocity, SiO ２ It is possible to select a film such as a SiON film or a SiN film in which some of the oxygen in the film is replaced with nitrogen. This is because the incorporation of nitrogen makes the intervening layer harder, which increases the speed of sound and is expected to lead to improved device characteristics.

[0007] However, SiON and SiN films have poor adhesion, and even when formed on LT or LN, peeling frequently occurs, adversely affecting reliability, device characteristics, product yield, and other factors. Figure 1 shows an optical microscope photograph of actual peeling on a composite substrate (LT on SiON on Si) fabricated with a SiON interlayer. It can be seen that the film is peeling along some crystal orientation. Other analyses have revealed that the linear peeling occurs along the interface between LT and SiON. This problem has made it difficult to practically use SiON or SiN as an interlayer.

[0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an oxide single crystal composite substrate having an SiON film or SiN film with improved adhesion, and a method for manufacturing the same.

[0009] In order to solve the above problems, a composite substrate according to an embodiment of the present invention includes an oxide single crystal layer, an intermediate layer, and a SiO ２ The intervening layer is a SiON film or a SiN film, and a SiO ２ A thin film is provided.

[0010] In the present invention, SiO ２ The O / Si ratio, which is the atomic ratio of oxygen to silicon in the thin film, is preferably between 1.8 and 2.2. ２ The thickness of the thin film is preferably between 3 and 100 nm.

[0011] In the present invention, the oxide single crystal layer preferably contains lithium tantalate (LT) or lithium niobate (LN), and the thickness of the oxide single crystal layer is preferably between 0.3 and 15 μm.

[0012] In the present invention, the support substrate may be any one of silicon, silicon with an oxide film, sapphire, aluminum nitride, silicon carbide, quartz crystal, and glass.

[0013] In the present invention, the oxide single crystal layer may be doped with Fe at 80 to 120 ppm.

[0014] In addition, the method for manufacturing a composite substrate according to an embodiment of the present invention includes the steps of: forming a first substrate, which is an oxide single crystal substrate, on a first substrate; ２ forming a thin film; and ２ A step of forming a SiON film or SiN film as an intermediate layer on the thin film, a step of planarizing the surface of the intermediate layer, and a step of forming a SiO ２ The method includes a step of bonding a first substrate on which a thin film and an intervening layer are formed to a second substrate serving as a support substrate, a step of thinning the first substrate to form an oxide single crystal layer in the bonded substrate, and a step of heat-treating the bonded substrate.

[0015] In the present invention, the PVD method or the CVD method can be used as a method for forming the SiON film or the SiN film. ２ Similarly, PVD and CVD methods can be applied to the formation of the film. ２ By making the film thinner, it is possible to prevent the deterioration of device characteristics due to a decrease in the sound velocity. ２ The O / Si ratio, which is the atomic ratio of oxygen (O) to silicon (Si) in the film, can be appropriately set between 1.8 and 2.2.

[0016] In the present invention, before the step of bonding the substrates, it is preferable to subject one or both of the substrates to a surface activation treatment, which may be any of ozone water treatment, UV ozone treatment, ion beam treatment, and plasma treatment.

[0017] In the present invention, the oxide single crystal substrate may be thinned by grinding and / or polishing in the step of thinning the oxide single crystal substrate. Alternatively, the oxide single crystal substrate may be thinned by previously implanting ions into the oxide single crystal substrate, and then separating the substrate at the ion-implanted interface after bonding. In this case, the implanted ions may be H ＋ Or H ２ ＋ The thickness of the oxide single crystal substrate after thinning is preferably between 0.3 and 15 μm, particularly when the oxide single crystal substrate is lithium tantalate.

[0018] According to the present invention, when a SiON film or a SiN film is used as an intermediate layer of an oxide single crystal composite substrate, adhesion can be improved and the occurrence of defects can be suppressed.

[0019] 1 shows an optical microscope photograph of a composite substrate fabricated using SiON as an intervening layer. 2 is a schematic diagram showing the layer structure of the composite substrate 5. 3 is a flowchart showing a method for manufacturing the composite substrate 5. 4 is a diagram showing an example of a method for preparing a porous preform 100 for an optical fiber using an OVD method.

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

[0021] 2 is a schematic diagram showing the layer structure of a composite substrate 5 according to this embodiment. As shown in FIG. 2, the composite substrate 4 includes an oxide single crystal layer 1, a support substrate 2, an intermediate layer 3, and a SiO ２ and a thin film 4.

[0022] The oxide single crystal layer 1 contains lithium tantalate (LT) or lithium niobate (LN). The thickness of the oxide single crystal layer 1 is preferably between 0.3 and 15 μm. The oxide single crystal layer 1 may be doped with iron (Fe) at 80 to 120 ppm. The support substrate 2 is preferably silicon, silicon with an oxide film, sapphire, aluminum nitride, silicon carbide, quartz, or glass. The intermediate layer 3 is a SiON film or a SiN film. SiO ２ The thin film 4 is provided between the intermediate layer 3 and the oxide single crystal layer 1. ２ The O / Si ratio, which is the atomic ratio of oxygen to silicon in the thin film 4, is preferably between 1.8 and 2.2.２ The thickness of the thin film 4 is preferably between 3 and 100 nm.

[0023] Next, a method for manufacturing the composite substrate 5 will be described with reference to the flowchart shown in Fig. 3. First, an oxide single crystal substrate (first substrate) 10 and a support substrate (second substrate) 2 are prepared (step S01). Then, a SiO ２ The thin film 4 is formed (step S02), and SiO ２ A SiON film or SiN film that will become the intervening layer 3 is formed on the thin film 4 (step S03). ２ The SiON or SiN film that will become the thin film 4 and the intermediate layer 3 may be formed by either physical vapor deposition or chemical vapor deposition.

[0024] Then, the surface of the intermediate layer 3 is planarized (step S04), and SiO ２ The oxide single crystal substrate 10 on which the thin film and the intervening layer have been formed is bonded to the support substrate 2 via the intervening layer 3 (step S05). By polishing and planarizing the surface of the intervening layer 3 before bonding it to the support substrate 2, a composite substrate 5 with high bonding strength can be produced. In this case, it is preferable to subject both or one of the oxide single crystal substrate 10 and the support substrate 2 to a surface activation treatment before bonding. The surface activation treatment can be any of ozone water treatment, UV ozone treatment, ion beam treatment, and plasma treatment.

[0025] Next, the oxide single crystal substrate 10 in the bonded substrate is thinned to form the oxide single crystal layer 1 (step S06). The thinning can be performed by grinding and polishing. Alternatively, the thinning can be performed by an ion implantation delamination method in which ions are implanted in advance and delamination is performed at the ion implantation interface. When ion implantation is performed, the implanted ions are H ＋ Or H ２ ＋ After that, a heat treatment is performed (step S07), thereby completing composite substrate 5 having the layer structure shown in FIG.

[0026] Below, a description will be given of preliminary experiments, examples, and comparative examples that were conducted to confirm the conditions for obtaining the effects of the present invention.

[0027] (Preliminary Experiment) The following substrates (1) to (9) were prepared: (1) Si substrate with a thermal oxide film (T-SiO2) grown to about 200 nm; (2) SiO by PVD. ２ (3) Si substrate on which a 200 nm PVD SiON film (hereinafter referred to as PVD-SiO2) is formed. (4) Si substrate on which a 200 nm PVD SiN film (hereinafter referred to as PVD-SiN) is formed. (5) LT substrate on which a 200 nm PVD-SiO2 film is formed. (6) LT substrate on which a 200 nm PVD-SiON film is formed. (7) LT substrate on which a 200 nm PVD-SiN film is formed. (8) Si substrate with a thermal oxide film on which a 200 nm PVD-SiON film is formed. (9) Si substrate with a thermal oxide film on which a 200 nm PVD-SiN film is formed.

[0028] On each substrate, the refractive indexes of the PVD-SiO2, PVD-SiON, and PVD-SiN films after deposition were 1.45, 1.54, and 1.97, respectively. The adhesion of these sample films was measured using a scratch test (a thin film adhesion test method conforming to JIS-R3255). The measuring instrument used was a CSR-2000 manufactured by Rhesca Corporation. The results are shown in Table 1.

[0029]

[0030] The measured value indicates the test load at the time when peeling of the film occurs, and the larger the measured value, the higher the adhesion. From these results, it was quantitatively confirmed that PVD-SiON films and PVD-SiN films have lower adhesion to Si substrates and LT substrates compared to PVD-SiO2 films. No peeling was observed on the Si substrate on which a thermal oxide film was grown. On the other hand, it was found that PVD-SiON films and PVD-SiN films formed on Si substrates with a thermal oxide film have relatively high adhesion. Similar experiments were conducted for (2) to (8) by changing the film formation method from PVD to CVD, but the results were almost the same. From these results, it can be seen that SiON and SiN have lower adhesion to Si substrates and LT substrates compared to PVD-SiO2 films. ２ It was found that by forming the film through a substrate, high adhesion to the Si substrate or LT substrate can be ensured.

[0031] According to the findings obtained from the above preliminary experiments, when a SiON film or a SiN film is used as an intermediate layer of an oxide single crystal composite substrate, it is necessary to form an SiO film between the film and the support substrate. ２ It is considered that providing a SiO film between the SiON film or SiN film as an intermediate layer and the support substrate is effective in ensuring adhesion. ２ The effectiveness of the oxide single crystal composite substrate having a structure in which a film is provided, and the conditions under which desirable properties can be obtained will be explained with reference to examples and comparative examples.

[0032] [Example 1] An LT substrate having a diameter of 100 mm, a thickness of 0.35 mm, and an orientation of 38.5°Y was prepared as an oxide single crystal substrate. A 50 nm thick SiO ２ was formed by the PVD method, and then a 600 nm SiON film was formed by the same PVD method, and then the SiO ２ The total thickness of the / SiON film was 500 nm. This substrate was bonded to a Si substrate, which served as a support substrate, and the LT substrate was thinned to about 500 nm using grinding and polishing methods. After this, a heat treatment at 350°C was performed to improve adhesion. The entire surface of the completed substrate was observed with an optical microscope. No defects were observed.

[0033] Comparative Example 1: The same experiment as in Example 1 was carried out using SiO ２ The experiment was carried out without a film, but many defects similar to those shown in Figure 1 were observed within the field of view of the optical microscope.

[0034] Comparison between Example 1 and Comparative Example 1 reveals that the present invention is effective in reducing defects in a composite substrate in which LT and Si are bonded together.

[0035] [Example 2] An LT substrate having a diameter of 100 mm, a thickness of 0.35 mm, and an orientation of 38.5°Y was prepared as an oxide single crystal substrate. SiO ２ A film (PVD-SiO2) was formed to a thickness of (0, 3, 5, 10, 20, 35, 50, 100, 200, 300, 400, 500) nm. Furthermore, a SiON film (PVD-SiON) was formed to a thickness of 600 nm by the PVD method, and then polished. Here, the SiO2 after polishing ２The polishing amount was adjusted so that the total thickness of the / SiON film was 500 nm. This substrate was bonded to a silicon substrate and heat-treated at 150°C, after which the thickness of the LT substrate was thinned to approximately 500 nm using a grinding and polishing method. A resonator device was fabricated on this substrate, and the relative bandwidth was measured. Here, the relative bandwidth is a value that indicates the filter performance of the SAW device; the higher the value, the better the characteristics, and 4% or more is desirable.

[0036] The results are shown in Figure 4. ２ When there is no intervening (SiO ２ In the case of the SiO2 film (thickness 0 nm), many defects are formed, so the relative bandwidth is low. ２ If the thickness exceeds 100 nm, the intermediate layer is SiO ２ The results are the same as when the substrate is made of only SiO, and the effect of using SiON is not observed. ２ When the film thickness is greater than 0 and 100 nm or less, the relative bandwidth is about 4.4%. ２ This shows a higher value than when only the LT film was used, and it is clear that the effect of the SiON film, which is a high acoustic velocity film, is fully exhibited. Therefore, the appropriate thickness of the PVD-SiO2 film interposed between the LT film and the SiON film is 3 nm or more and 100 nm or less.

[0037] [Example 3] An experiment similar to that of Example 2 was conducted, except that the main intermediate layer was changed from PVD-SiON to PVD-SiN. The results showed the same tendency as in Example 2, with the relative bandwidth being 4% or more in the region where the PVD-SiO2 film thickness was 3 nm to 100 nm. From this result, it can be seen that even when the main intermediate layer is SiN, an appropriate SiO ２ It was found that the thickness of

[0038] [Example 4] Experiments similar to those in Examples 2 and 3 were carried out, except that the method for forming SiON and SiN films was changed to chemical vapor deposition (CVD). The results showed the same trends as in Examples 2 and 3. These results demonstrate that the effects of the present invention can be obtained regardless of the method for forming SiON or SiN films.

[0039] [Example 5] Experiments similar to those in Examples 2 and 3 were carried out using SiO ２The film formation method was changed to chemical vapor deposition (CVD). The results showed the same tendency as in Examples 2 and 3. From these results, it can be seen that SiO ２ It has been found that the effects of the present invention can be obtained regardless of the growth method.

[0040] [Example 6] An experiment similar to that of Examples 2 and 3 was conducted, except that the oxide single crystal substrate material was changed from an LT substrate to an LN substrate with a diameter of 100 mm, a thickness of 0.35 mm, and an orientation of 128°Y. The results showed exactly the same trends as in Examples 2 and 3. These results demonstrated that the effects of the present invention can be obtained whether the oxide single crystal substrate material is LT or LN.

[0041] [Example 7] An experiment similar to that of Example 2 was conducted, but with a different method: ions were implanted into the LT substrate beforehand, and the substrate was mechanically peeled off after bonding to form a thin film. After peeling, the surface was polished to a mirror finish at a temperature of approximately 500°C. A resonator was similarly fabricated, and the relative bandwidth was observed; the results were nearly the same as in Example 1. These results demonstrate that the effects of the present invention can be obtained regardless of the method of thinning.

[0042] [Example 8] An experiment similar to that of Example 2 was conducted, but the support substrate used was changed to silicon with an oxide film, sapphire, aluminum nitride, silicon carbide, quartz, glass, etc., but the tendency was exactly the same. From this result, it was found that the effect of the present invention can be obtained regardless of the type of support substrate.

[0043] [Example 9] The same experiment as in Example 2 was carried out using SiO ２ The composition was analyzed using X-ray photoelectron spectroscopy (XPS). The composition ratio (element ratio of oxygen (O) and silicon (Si), hereinafter referred to as O / Si ratio) was changed from 1.8 to 2.2, and the same experiment as in Example 2 was carried out, and the results were the same as in Example 2. ２ It has been found that the effect of the present invention can be obtained when the O / Si ratio of the film is in the range of 1.8 to 2.2.

[0044] [Example 10] The same experiments as in Examples 1 to 3 were carried out, except that the LT substrate was doped with approximately 80 to 120 ppm of Fe. The results were exactly the same as those in the above examples. From these results, it was found that the same effect can be obtained even when the starting material for the LT substrate is doped with iron.

[0045] Example 11 In Example 2, the bonding was performed using a plasma activation method before bonding, but the results were the same as in Example 2. It was found that the present invention does not depend on the bonding method.

[0046] [Example 12] In Example 2, the thickness of LT was changed between 0.3 and 20 μm, and the results showed the same tendency as in Example 2. However, if the LT thickness is too thick, the effect of SiON becomes weak, and the effect can be discerned only between 0.3 and 15 μm. From this result, it was found that the effect of the present invention can be obtained without being largely dependent on the thickness of the oxide single crystal thin film.

[0047] 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.

[0048] 1 Oxide single crystal layer 2 Support substrate 3 Intervening layer 4 SiO ２ Thin film 5 Composite substrate

Claims

1. A single crystal oxide layer, an intermediate layer, and SiO ２ A composite substrate comprising a thin film and a support substrate, wherein the intermediate layer is a SiON film or a SiN film, and the SiO ２ A composite substrate having a thin film formed thereon.

2. The SiO ２ 2. The composite substrate according to claim 1, wherein the O / Si ratio, which is the atomic ratio of oxygen to silicon in the thin film, is between 1.8 and 2.

2.

3. The SiO ２ 3. The composite substrate according to claim 1, wherein the thickness of the thin film is between 3 and 100 nm.

4. The composite substrate according to claim 1 or 2, wherein the oxide single crystal layer contains lithium tantalate (LT) or lithium niobate (LN).

5. The composite substrate according to claim 1 or 2, wherein the thickness of said oxide single crystal layer is between 0.3 and 15 μm.

6. The composite substrate according to claim 1 or 2, wherein the support substrate is made of any one of silicon, silicon with an oxide film, sapphire, aluminum nitride, silicon carbide, quartz, and glass.

7. The composite substrate according to claim 1 or 2, wherein the oxide single crystal layer is doped with Fe at a concentration of 80 to 120 ppm.

8. The first substrate, which is an oxide single crystal substrate, is coated with SiO ２ forming a thin film; ２ forming a SiON film or SiN film as an intermediate layer on the thin film; planarizing the surface of the intermediate layer; ２ A method for manufacturing a composite substrate, comprising: a step of bonding a first substrate, on which a thin film and an intermediate layer are formed, to a second substrate serving as a support substrate; a step of thinning the first substrate to form an oxide single crystal layer in the bonded substrate; and a step of heat-treating the bonded substrate.

9. The method for producing a composite substrate according to claim 8, wherein the thinning step is carried out by using a grinding and polishing method.

10. The method for producing a composite substrate according to claim 8, wherein the thinning step is carried out using an ion implantation delamination method.

11. The SiO ２ 11. The method for manufacturing a composite substrate according to claim 8, wherein the thin film, the SiON film, and the SiN film are formed by physical vapor deposition or chemical vapor deposition.

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