Oxide single crystal composite substrate and method for manufacturing the same

Abstract

To provide an oxide single crystal composite substrate and a method for manufacturing the substrate, the substrate having one of a SiON film and an SiN film with improved adhesion.SOLUTION: The composite substrate according to an embodiment of the present invention includes an oxide single crystal layer, an interlayer, a SiO2 thin film, and a support substrate. The interlayer is one of a SiON film and a SiN film, and the SiO2 thin film is provided between the interlayer and the support substrate. The O / Si ratio, which is the elemental ratio of oxygen to silicon in the SiO2 thin film, is preferably in the range of 1.8 to 2.2. The thickness of the SiO2 thin film is preferably in the range of 3 to 100 nm.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[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. [Background technology]

[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 (to 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 since 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 reaches 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 delaminated surface must be polished to remove the ion-implanted damaged layer (approximately 150 nm) and achieve a mirror finish. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2016 / 088466 Summary of the Invention [Problem to be solved by the invention]

[0006] When adopting such a thin-film laminated structure, a structure in which an intervening layer is sandwiched between a thin LT or LN film and a supporting substrate is common. Here, a material with a high acoustic velocity is ideal for the intervening layer in order to more efficiently confine energy within the thin LT or NT film. To increase the acoustic velocity, it is possible to select a SiON or SiN film in which some of the oxygen in SiO2 is replaced with nitrogen. The incorporation of nitrogen makes the intervening layer harder, increasing the acoustic velocity and potentially improving device performance.

[0007] However, SiON and SiN films have poor adhesion, and even when deposited on LT or LN, peeling occurs frequently, adversely affecting reliability, device characteristics, product yield, and other factors. Figure 1 shows an optical microscope image of actual peeling on a composite substrate (LT on SiON on Si) fabricated using 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 problems, and an object of the present invention is to provide an oxide single crystal composite substrate having a SiON film or SiN film with improved adhesion, and a method for manufacturing the same. [Means for solving the problem]

[0009] In order to solve the above problems, a composite substrate according to an embodiment of the present invention comprises an oxide single crystal layer, an intervening layer, an SiO2 thin film, and a support substrate, the intervening layer being a SiON film or a SiN film, and the SiO2 thin film being provided between the intervening layer and the oxide single crystal layer.

[0010] In the present invention, the O / Si ratio, which is the element ratio of oxygen to silicon in the SiO2 thin film, is preferably between 1.8 and 2.2, and the thickness of the SiO2 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) 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, a manufacturing method for a composite substrate according to an embodiment of the present invention includes the steps of forming a thin SiO2 film on a first substrate, which is an oxide single crystal substrate; forming a SiON film or SiN film as an intermediate layer on top of the thin SiO2 film; planarizing the surface of the intermediate layer; bonding the first substrate, on which the thin SiO2 film and the intermediate layer have been formed, to a second substrate, which is a support substrate; thinning the first substrate to form an oxide single crystal layer in the bonded substrate; and heat-treating the bonded substrate.

[0015] In the present invention, the PVD method and the CVD method can be used to form the SiON film and the SiN film. Similarly, the PVD method and the CVD method can be used to form the SiO2 film. Here, by thinning the SiO2 film, it is possible to prevent the deterioration of device characteristics due to a decrease in the sound velocity. Furthermore, the O / Si ratio, which is the atomic ratio of oxygen (O) to silicon (Si) in the SiO2 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 H2 + 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. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0019] [Figure 1] An optical microscope photograph of a composite substrate fabricated with SiON as an intervening layer is shown. [Figure 2] FIG. 2 is a schematic diagram showing the layer structure of a composite substrate 5. [Figure 3] 10 is a flowchart showing a method for manufacturing a composite substrate 5. [Figure 4]1A and 1B are diagrams showing an example of a method for preparing a porous optical fiber preform 100 using an OVD method. DETAILED DESCRIPTION OF THE INVENTION

[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 an SiO2 thin film 4.

[0022] The oxide single crystal layer 1 contains lithium tantalate (LT) or lithium niobate (LN). The oxide single crystal layer 1 may have a thickness of 0.3 to 15 μm. The oxide single crystal layer 1 may be doped with iron (Fe) at 80 to 120 ppm. The support substrate 2 may be made of silicon, silicon with an oxide film, sapphire, aluminum nitride, silicon carbide, quartz, or glass. The intermediate layer 3 is a SiON film or SiN film. The SiO2 thin film 4 is provided between the intermediate layer 3 and the oxide single crystal layer 1. The O / Si ratio, which is the atomic ratio of oxygen to silicon in the SiO2 thin film 4, is preferably 1.8 to 2.2. The SiO2 thin film 4 may have a thickness of 3 to 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). Next, an SiO2 thin film 4 is formed on the oxide single crystal substrate 10 (step S02), and a SiON film or SiN film to become the intermediate layer 3 is formed on the SiO2 thin film 4 (step S03). The SiO2 thin film 4 and the SiON film or SiN film to become the intermediate layer 3 may be formed by either physical vapor deposition or chemical vapor deposition.

[0024] Then, the surface of the intervening layer 3 is planarized (step S04), and the oxide single crystal substrate 10 on which the SiO2 thin film and the intervening layer are 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 and then 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 H2 + It is preferable that the method includes any one of the following: 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) A Si substrate with a thermal oxide film (T-SiO2) grown to approximately 200 nm (2) A Si substrate with a 200 nm SiO2 film formed by PVD (hereinafter referred to as PVD-SiO2) (3) A Si substrate on which a 200 nm SiON film (hereinafter referred to as PVD-SiON) is formed by PVD. (4) A Si substrate on which a 200 nm SiN film (hereinafter referred to as PVD-SiN) is formed by PVD. (5) LT substrate with 200 nm PVD-SiO2 (6) LT substrate with 200 nm PVD-SiON film (7) LT substrate with 200 nm PVD-SiN film (8) Si substrate with thermal oxide film on which 200 nm of PVD-SiON is deposited (9) Si substrate with thermal oxide film on which 200 nm of PVD-SiN is deposited

[0028] The refractive indices of the PVD-SiO2, PVD-SiON, and PVD-SiN films on each substrate after deposition were 1.45, 1.54, and 1.97, respectively. The adhesion of these samples 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] [Table 1]

[0030] The measured values ​​indicate the test load at which film peeling occurred; the higher the measured value, the stronger the adhesion. These results quantitatively confirmed that PVD-SiON and PVD-SiN films have lower adhesion to Si and LT substrates than PVD-SiO2 films. No peeling was observed on the Si substrates on which a thermal oxide film had been grown. On the other hand, PVD-SiON and PVD-SiN films deposited on Si substrates with a thermal oxide film were found to have relatively high adhesion. Similar experiments were performed for (2) to (8) using CVD instead of PVD, with similar results. These results demonstrate that high adhesion can be achieved for Si and LT substrates by depositing SiON and SiN films via SiO2.

[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 in an oxide single crystal composite substrate, it is believed that providing a SiO2 film between the film and the support substrate is effective in ensuring adhesion. Below, the effectiveness of an oxide single crystal composite substrate having a structure in which a SiO2 film is provided between a SiON film or a SiN film as an intermediate layer and a support substrate, and the conditions under which favorable characteristics can be obtained, will be explained with reference to examples and comparative examples.

[0032] [Example 1] An LT substrate with a diameter of 100 mm, a thickness of 0.35 mm, and an orientation of 38.5°Y was prepared as the oxide single crystal substrate. A 50 nm thick SiO2 film was deposited on this substrate using the PVD method, followed by a 600 nm SiON film, also using the PVD method, and then mirror polished to a total thickness of 500 nm for the SiO2 / SiON film. This substrate was then bonded to a supporting Si substrate, and the LT substrate was thinned to approximately 500 nm using grinding and polishing methods. It was then heat-treated at 350°C to improve adhesion. The entire surface of the completed substrate was observed using an optical microscope. No defects were observed.

[0033] [Comparative Example 1] An experiment similar to that in Example 1 was carried out without the SiO2 film, but in this case many defects similar to those in FIG. 1 were observed within the field of view of the optical microscope.

[0034] Comparison between Example 1 and Comparative Example 1 revealed 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 with a diameter of 100 mm, a thickness of 0.35 mm, and a 38.5°Y orientation was prepared as the oxide single crystal substrate. A SiO2 film (PVD-SiO2) was deposited on this substrate using the PVD method to thicknesses of 0, 3, 5, 10, 20, 35, 50, 100, 200, 300, 400, and 500 nm. A 600 nm SiON film (PVD-SiON) was then deposited using the PVD method and polished. The polishing amount was adjusted so that the total thickness of the SiO2 / SiON film after polishing was 500 nm. This substrate was bonded to a silicon substrate and heat-treated at 150°C. The LT substrate was then 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. The relative bandwidth is a numerical value that indicates the filter performance of the SAW device; the higher the relative bandwidth, the better the characteristics; a bandwidth of 4% or more is desirable.

[0036] The results are shown in Figure 4. When no SiO2 is present (SiO2 film thickness 0 nm), numerous defects are formed, resulting in a low relative bandwidth. Furthermore, when the SiO2 thickness exceeds 100 nm, the results are the same as when the intervening layer is composed of SiO2 alone, and the effect of using SiON is not observed. When the SiO2 film thickness is greater than 0 but less than 100 nm, the relative bandwidth is around 4.4%, a higher value than when SiO2 alone is used, demonstrating the full effect of the SiON film, which is a high acoustic velocity film. Therefore, the appropriate thickness of the PVD-SiO2 film interposed between the LT film and the SiON film is between 3 nm and 100 nm.

[0037] [Example 3] An experiment similar to that in Example 2 was conducted, but 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 PVD-SiO2 film thickness range of 3 nm to 100 nm. This result revealed that the appropriate SiO2 thickness does not change even when the main intermediate layer is SiN.

[0038] [Example 4] Experiments similar to those in Examples 2 and 3 were carried out, except that the SiON and SiN film deposition method 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 SiON or SiN film deposition method.

[0039] [Example 5] Experiments similar to those in Examples 2 and 3 were carried out, but the SiO2 film formation method 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 SiO2 growth method.

[0040] [Example 6] Experiments similar to those in Examples 2 and 3 were 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 demonstrate 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 in 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 identical to those in Example 1. These results demonstrate that the effects of the present invention can be obtained regardless of the thin film formation method.

[0042] [Example 8] The same experiment as in Example 2 was carried out, but the supporting substrate used was changed to Si with an oxide film, sapphire, aluminum nitride, silicon carbide, quartz crystal, glass, etc., but the tendency was exactly the same. From these results, it was found that the effect of the present invention can be obtained regardless of the type of supporting substrate.

[0043] [Example 9] An experiment similar to that in Example 2 was carried out by changing the composition of the SiO2 used. The composition was analyzed using X-ray photoelectron spectroscopy (XPS). An experiment similar to that in Example 2 was carried out by changing the composition ratio (element ratio of oxygen (O) and silicon (Si); hereinafter referred to as O / Si ratio) from 1.8 to 2.2, and the results were similar to those in Example 2. It was found that the effects of the present invention can be obtained when the O / Si ratio of the SiO2 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. These results demonstrate 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 varied between 0.3 and 20 μm, and the results showed the same tendency as in Example 2. However, if the LT thickness was too thick, the effect of SiON was weakened, and the effect could only be discerned between 0.3 and 15 μm. From these results, it was found that the effect of the present invention can be obtained without being significantly 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. [Explanation of symbols]

[0048] 1. Oxide single crystal layer 2 Support substrate 3 Intervening layer 4. SiO2 thin film 5 Composite board

Claims

1. The oxide single crystal layer, the intervening 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. 3. The composite substrate according to claim 1, wherein the oxide single crystal layer contains lithium tantalate (LT) or lithium niobate (LN).

5. 3. The composite substrate according to claim 1, wherein the oxide single crystal layer has a thickness of 0.3 to 15 μm.

6. 3. The composite substrate according to claim 1, 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. 3. The composite substrate according to claim 1, wherein the oxide single crystal layer is doped with Fe at 80 to 120 ppm.

8. The first substrate is an oxide single crystal substrate. ２ forming a thin film; The SiO ２ forming a SiON film or SiN film as an intervening layer on the thin film; planarizing the surface of the intermediate layer; The SiO ２ a step of bonding the first substrate on which the thin film and the 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 substrates. A method for manufacturing a composite substrate comprising:

9. 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. 9. The method for producing a composite substrate according to claim 8, wherein the thinning step is performed 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.

Images