Oxide single crystal composite substrate and method for manufacturing same

Abstract

Provided is an oxide single crystal composite substrate in which both of recovery of polarization and the like of a piezoelectric oxide single crystal thin film that occurs during manufacturing and non-reduction of resistance of a polysilicon layer can be achieved, and from which a satisfactory Q value can be obtained.　This method for manufacturing an oxide single crystal composite substrate, in which a piezoelectric oxide single crystal thin film is laminated on a polysilicon layer laminated on a silicon substrate, comprises executing: a step for subjecting the oxide single crystal composite substrate to heat treatment, as first heat treatment, at a temperature of 300°C or higher under an atmosphere including hydrogen having a hydrogen concentration of 1% or more; and a step for subjecting the resultant oxide single crystal composite substrate to heat treatment, as second heat treatment, at a temperature exceeding 400°C under a non-reducing atmosphere so that the hydrogen concentration in the vicinity of the interface between the silicon substrate and the polysilicon layer is 1.5x1018 atoms / cm3 or more and the hydrogen concentration in the polysilicon layer gradually decreases and becomes 1.0x1018 atoms / cm3 or less as the distance from the interface increases.

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 manufacturing the same. 【0002】 In recent years, the mobile communications market, exemplified by smartphones, has seen a rapid increase in data traffic. To address this problem, the number of necessary bandwidths must be increased, inevitably leading to a demand for smaller and more powerful components. Common piezoelectric materials such as lithium tantalate (LT) and lithium niobate (LN) are widely used as materials for surface acoustic wave (SAW) devices. These materials have the advantage of possessing a large electromechanical coupling coefficient, enabling broadband operation. 【0003】 It is known that thinning LT and LN (hereinafter referred to as "LT / LN") into films thinner than 1 μm can improve their properties and expand their range of applications. Specifically, applications include high-performance filter devices and optical modulators. Thinning LT / LN films is usually done by grinding and polishing, but it is difficult to obtain nanometer-level uniformity of film thickness across the entire substrate. Generally, when a 200-300 μm substrate is thinned to several hundred nanometers by grinding and polishing, it is extremely difficult to obtain nanometer-level uniformity. 【0004】 For LT / LN thin films, it is common to use a substrate in which polysilicon is deposited on the upper surface of a silicon substrate to form a polysilicon layer. This is to minimize the degradation of dielectric loss by trapping carriers such as electrons and holes induced in silicon during device operation at the grain boundaries of the polysilicon. A substrate with a polysilicon layer formed on the upper surface of a silicon substrate is sometimes called a trap-rich silicon substrate. SAW devices completed using a trap-rich silicon substrate are known to exhibit a high Q value. The Q value is an indicator of the sharpness of the response signal of a filter device and is known to be greatly influenced by the quality of the support substrate. 【0005】One method for uniformly obtaining LT / LN thin films is the ion implantation exfoliation method (see, for example, Patent Document 1). This method involves implanting light elements such as hydrogen and helium into a target substrate and exfoliating at the location with the highest concentration (ion implantation interface). In this method, an LT / LN substrate is bonded to the polysilicon layer side of a trap-rich silicon substrate, and after some heat treatment, exfoliation is performed at the ion implantation interface using a method such as the SiGen method (mechanical exfoliation method). This transfers a thin LT / LN film onto the polysilicon layer of the trap-rich silicon substrate. The transferred and laminated thin film is then polished to remove the areas damaged by ion implantation (approximately 100 nm thick) and to make the surface mirror-like. 【0006】 The problem here is that LT / LN has polarization, and polarization is an essential element for exhibiting the properties of a piezoelectric element. When ion implantation is performed on the LT / LN thin film, it is damaged, and its properties are impaired due to disorder in polarization and crystallinity. Therefore, in order to restore polarization and crystallinity, it is necessary to apply a certain amount of heat treatment to the thin film to return it to properties close to those of bulk LT / LN. 【0007】 When heat treatment is performed under an oxidizing or inert atmosphere (nitrogen or argon), the LT / LN thin film becomes insulated, causing charge localization within the film and preventing the recovery of polarization and crystallinity. To prevent this, the use of a reducing atmosphere, more specifically a hydrogen atmosphere, is effective. By performing heat treatment under a hydrogen atmosphere, the reducing properties of the thin film can be maintained, and polarization and crystallinity can be restored. 【0008】 International Publication No. 2016 / 088466 【0009】When heat treatment is performed under a hydrogen atmosphere, the polysilicon layer of the trap-rich silicon substrate that serves as the base for LT / LN takes in hydrogen and becomes lower in resistance, deteriorating (destabilizing) the Q value of the SAW device completed using the oxide single crystal composite substrate manufactured with the trap-rich silicon substrate as the support substrate. It is presumed that the cause of this deterioration lies in the fact that the expected function of polysilicon, which is to capture carriers induced in silicon by hydrogen diffusing into the polysilicon layer and terminating the dangling bonds at grain boundaries, is inhibited. However, the use of hydrogen is essential for the recovery of polarization and crystallinity in the LT / LN thin film. 【0010】 In order to remove the remaining hydrogen and reverse the low-resistance state to obtain a good Q value, for example, it might seem that further heat treatment should be performed under a non-reducing atmosphere so that hydrogen diffuses outside the polysilicon layer. However, since the dangling bonds at grain boundaries are very unstable, simply removing hydrogen and fully exposing the dangling bonds will ultimately result in unstable characteristics and an inability to obtain a good Q value. 【0011】 In view of the above situation, an object of the present invention is to provide an oxide single crystal composite substrate and a method for manufacturing the same, in which the recovery of polarization and the like in the piezoelectric oxide single crystal thin film generated during manufacturing and the non-low-resistance state of the polysilicon layer are compatible, and a good Q value can be obtained. 【0012】 To solve this problem, the inventor of the present invention devised the following method. 【0013】 First, in order to recover the polarization and crystallinity of the piezoelectric oxide single crystal thin film, it was found that it is necessary to perform a first heat treatment at a temperature of 300°C or higher under a reducing atmosphere, specifically, for example, a hydrogen gas atmosphere or a mixed gas (forming gas) atmosphere of hydrogen and an inert gas (refer to preliminary experiments). Subsequently, by performing a second heat treatment using a gas in a non-reducing atmosphere, the hydrogen taken into the polysilicon layer is diffused outward. Thereby, it is intended to solve two conflicting problems: the recovery of polarization and crystallinity of the piezoelectric oxide single crystal thin film and the non-low-resistance state of the polysilicon layer. 【0014】Also, the interface between the polysilicon layer and the silicon layer has a very small grain boundary size, and if dangling bonds are excessively exposed due to the diffusion of hydrogen, the characteristics are likely to deteriorate. Therefore, by performing a second heat treatment so that hydrogen remains to some extent in the vicinity of this interface, the exposure of excessive dangling bonds is prevented, and the characteristics are improved and stabilized. 【0015】 That is, the oxide single crystal composite substrate according to the present invention is formed by laminating a piezoelectric oxide single crystal thin film on the polysilicon layer of a support substrate formed by laminating a polysilicon layer on the upper surface of a silicon substrate. In the oxide single crystal composite substrate, the hydrogen concentration in the polysilicon layer in the vicinity of the interface between the silicon substrate and the polysilicon layer is 1.0×10 １８ atoms / cm ３ or more, and the hydrogen concentration in the polysilicon layer gradually decreases as it moves away from the interface and becomes 1.0×10 １８ atoms / cm ３ or less. 【0016】 In the present invention, it is preferable that the hydrogen concentration in the polysilicon layer within 0.1 μm from the interface between the silicon substrate and the polysilicon layer is 1.0×10 １８ atoms / cm ３ or more, and it is preferable that the hydrogen concentration in the polysilicon layer more than 0.4 μm away from the interface is 1.0×10 １８ atoms / cm ３ or less. 【0017】 In the present invention, it is preferable that the film thickness of the polysilicon layer is 0.45 μm or more and 5.0 μm or less. 【0018】 In the present invention, it is preferable to have an interlayer between the polysilicon layer and the piezoelectric oxide single crystal thin film. 【0019】 In the present invention, the interlayer is SiO Ｘ (where 1.5 ≤ x ≤ 2.5), SiON, or SiN, or includes any of these. 【0020】 In the present invention, the piezoelectric oxide single crystal thin film is preferably lithium tantalate, iron-doped lithium tantalate, lithium niobate, or iron-doped lithium niobate. 【0021】 Furthermore, the present invention provides a method for manufacturing an oxide single crystal composite substrate, in which a piezoelectric oxide single crystal thin film is laminated on a polysilicon layer of a support substrate formed by laminating a polysilicon layer on the upper surface of a silicon substrate. The method for manufacturing the oxide single crystal composite substrate includes the steps of: firstly, performing a heat treatment on the oxide single crystal composite substrate at a temperature of 300°C or higher in a forming gas atmosphere with a hydrogen concentration of 1% or more or in a 100% hydrogen atmosphere; and secondly, following the first heat treatment, performing a heat treatment at a temperature exceeding 400°C in a non-reducing atmosphere, thereby reducing the hydrogen concentration in the polysilicon layer near the interface between the silicon substrate and the polysilicon layer to 1.0 × 10⁻⁶. １８ atoms / cm ３ Thus, the hydrogen concentration within the polysilicon layer gradually decreases as it moves away from the interface, reaching 1.0 × 10⁻⁶. １８ atoms / cm ３ The following steps are performed to ensure the following result. 【0022】 In this invention, the hydrogen concentration within the polysilicon layer within 0.1 μm of the interface between the silicon substrate and the polysilicon layer is 1.0 × 10⁻¹⁰ １８ atoms / cm ３ It is desirable that the hydrogen concentration in the polysilicon layer, located at least 0.4 μm away from the interface, be 1.0 × 10⁻¹⁰. １８ atoms / cm ３ The following would be preferable. 【0023】 In this invention, piezoelectric oxide single crystal thin films are preferably stacked using an ion implantation exfoliation method. 【0024】 In this invention, it is preferable to provide an intervening layer between the polysilicon layer and the piezoelectric oxide single crystal thin film. 【0025】 In this invention, the intervening layer is SiO Ｘ (However, 1.5 ≤ x ≤ 2.5), it may be SiON or SiN, or contain either of these. 【0026】 In the present invention, the piezoelectric oxide single crystal thin film is preferably lithium tantalate, iron-doped lithium tantalate, lithium niobate, or iron-doped lithium niobate. 【0027】 In the present invention, the non-reducing atmosphere in the second heat treatment may consist of nitrogen, argon, helium, oxygen, or a mixture thereof. 【0028】 In this invention, in the ion implantation exfoliation method, the ions to be implanted are H ＋ or H ２ ＋ It would be good if that were the case. 【0029】 In the present invention, when stacking piezoelectric oxide single crystal thin films, it is preferable to perform an activation treatment on the surface of each substrate to be bonded before bonding the base substrate of the piezoelectric oxide single crystal thin film to the support substrate. 【0030】 In the present invention, the activation treatment may be a plasma activation treatment or a vacuum ion beam activation treatment. 【0031】 This is a schematic diagram showing the structure of the oxide single crystal composite substrate 1. This is a table showing the results of preliminary experiment 1. This is a diagram showing the results of preliminary experiment 2. This is a flow chart showing the manufacturing method of the oxide single crystal composite substrate 1. This is a cross-sectional TEM photograph of the support substrate 2. This is a magnified view of the area around interface B in Figure 5. This is a table showing the measurement results of the specific bandwidth and Q value in Example 1. This is a diagram showing the distribution of hydrogen concentration in the depth direction of the polysilicon layer 2b in Example 1. This is a table showing the measurement results of the specific bandwidth and Q value in Example 2. This is a diagram showing the distribution of hydrogen concentration in the depth direction of the polysilicon layer 2b in Example 2. 【0032】 Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same parts will be denoted by the same reference numerals, and parts that have already been described will be omitted from the description as appropriate. 【0033】 Figure 1 is a schematic diagram showing the structure of the oxide single crystal composite substrate 1 according to this embodiment. The oxide single crystal composite substrate 1 has a structure in which piezoelectric oxide single crystal thin films 3 are laminated on a support substrate 2, either directly or via an intervening layer 4 as needed. 【0034】 The support substrate 2 is a so-called trap-rich silicon substrate formed by laminating a polysilicon layer 2b onto the upper surface of a silicon substrate 2a. 【0035】The piezoelectric oxide single crystal thin film 3 is a thin film of a piezoelectric oxide single crystal. The piezoelectric oxide single crystal is preferably lithium tantalate (LT) or lithium niobate (LN), with black LT or black LN being particularly preferred. Black LT (so-called Black-LT) and black LN (so-called Black-LN) are LT and LN that have undergone a treatment to increase conductivity by slightly reducing the oxygen content compared to the stoichiometric ratio. This treatment changes the color of the LT and LN from their original color to black, hence the term "blackening treatment." The piezoelectric oxide single crystal may also be iron-doped LT or iron-doped LN. 【0036】 The piezoelectric oxide single crystal thin film 3 is transferred and laminated onto the polysilicon layer 2b of the support substrate 2, for example, by an ion implantation exfoliation method. Immediately after transfer, the piezoelectric oxide single crystal thin film 3 is damaged by ion implantation and its polarization and crystallinity are disordered. Therefore, the following processing is required to restore these properties. 【0037】 Interlayer 4 is SiO Ｘ (However, 1.5 ≤ x ≤ 2.5), it is preferable to use either SiON or SiN. 【0038】 Next, we will describe the preliminary experiments conducted to clarify the conditions for heat treatment to restore polarization and crystallinity in the piezoelectric oxide single crystal thin film 3. 【0039】 [Preliminary Experiment 1] A support substrate 2, which is a trap-rich silicon substrate, and a matrix substrate for a piezoelectric oxide single crystal thin film 3, with an conductivity of 4.73 × 10⁻⁶ －１１ A black LT substrate with a density of ( / Ωcm), a diameter of 100 mm, and a thickness of 0.35 mm was prepared. A support substrate 2 was used as an intervening layer 4 with SiO ２ A layer is stacked to a thickness of 500 nm, and then a piezoelectric oxide single crystal thin film 3, which is an LT thin film, is transferred to it to a thickness of 500 nm using the ion implantation exfoliation method, resulting in LT on SiO ２A trap-rich silicon substrate was fabricated. The fabricated substrate was subjected to heat treatment for 6 hours each at temperatures of 250°C, 300°C, 350°C, 400°C, 450°C, and 500°C, for a total of 36 hours. A SAW device was then fabricated on the heat-treated substrate, and the specific bandwidth was measured. The specific bandwidth was measured under two conditions: maintaining the heat treatment atmosphere in an air atmosphere (20% oxygen + 80% nitrogen), and starting in a reducing atmosphere (hydrogen atmosphere) and changing to an air atmosphere (20% oxygen + 80% nitrogen) midway through the treatment. For the case where the atmosphere was changed midway, measurements were taken for each of the six different temperature ranges at which the atmosphere was changed. It has been empirically established that the specific bandwidth measurement is a useful indicator of the characteristics of LT thin films alone. 【0040】 The measurement results are shown in Figure 2. From these results, it can be seen that when heat treatment in a reducing atmosphere is performed up to 300°C or higher (conditions 3 to 7), the specific bandwidth is good (i.e., the polarization of LT is restored). On the other hand, when the sample is maintained in an air atmosphere (condition 1) and when heat treatment in a reducing atmosphere is performed only up to 250°C (condition 2), the specific bandwidth deteriorates. From these results, it can be seen that in order to restore polarization and crystallinity, heat treatment in a reducing atmosphere must be performed at a temperature of 300°C or higher. 【0041】 [Preliminary Experiment 2] Conductivity is 1.97 × 10⁻⁶ －１１ A black LT substrate with a density of ( / Ωcm), a diameter of 100 mm, and a thickness of 0.35 mm was prepared. This substrate was heat-treated at 400°C for 6 hours in a 100% hydrogen atmosphere and in a forming gas atmosphere of hydrogen diluted with nitrogen. The heat treatment in the forming gas atmosphere was performed for five different hydrogen concentrations. 【0042】Figure 3 shows the electrical conductivity before and after heat treatment. If the electrical conductivity after heat treatment is higher than the electrical conductivity before heat treatment, it indicates reducing properties. From Figure 3, it can be seen that when the hydrogen concentration is 1% or higher, the electrical conductivity after heat treatment is higher than the electrical conductivity before heat treatment (reference). From this, it can be seen that heat treatment to restore polarization and crystallinity should be performed in an atmosphere with a hydrogen concentration of 1% or higher. 【0043】 Based on findings from preliminary experiments 1 and 2, it was determined that heat treatment to restore polarization and crystallinity is preferably performed at a temperature of 300°C or higher under a reducing atmosphere with a hydrogen concentration of 1% or more. 【0044】 Next, the manufacturing method of the oxide single crystal composite substrate 1, based on the above reference experiments, will be explained with reference to the flowchart shown in Figure 4. 【0045】 First, a support substrate 2, which is a trap-rich silicon substrate, and a base substrate 3 for a piezoelectric oxide single crystal thin film are prepared (Step S1). 【0046】 Ions are implanted into the matrix substrate of the piezoelectric oxide single crystal thin film 3 from the side that will be bonded to the support substrate 2, so that an ion implantation interface is formed at a desired depth (step S2). The ions to be implanted are hydrogen (for example, H ＋ or H ２ ＋ ), it is best to use light elements such as helium. 【0047】 When forming the intervening layer 4, the intervening layer 4 is formed on one or both of the bonding surfaces of the support substrate 2 and the bonding surface of the base material substrate of the piezoelectric oxide single crystal thin film 3 (step S3). Here, the bonding surface of the support substrate 2 is the surface on which the polysilicon layer 2b is formed. 【0048】 Next, the surfaces of each substrate to be bonded are planarized, and if necessary, surface activation treatments such as ozonated water treatment, UV ozone treatment, vacuum ion beam activation treatment, and plasma activation treatment are applied (Step S4). 【0049】Next, the support substrate 2 and the base substrate of the piezoelectric oxide single crystal thin film 3 are bonded together either directly or via the intervening layer 4 to form a bonded substrate (step S5). 【0050】 Next, the piezoelectric oxide single crystal substrate is separated (exfoliated) at the ion implantation interface formed on the piezoelectric oxide single crystal substrate portion of the bonded substrate (step S6). This transfers the piezoelectric oxide single crystal thin film 3 onto the support substrate 2 (so-called ion implantation exfoliation method). 【0051】 Next, the surface of the transferred piezoelectric oxide single crystal thin film 3 is polished to remove the areas damaged by ion implantation (step S7). This yields the oxide single crystal composite substrate 1 before heat treatment. 【0052】 Next, the oxide single crystal composite substrate 1 obtained in step S7, before heat treatment, is subjected to two types of heat treatment under different conditions. First, a first heat treatment is performed at a temperature of 300°C or higher under a reducing atmosphere with a hydrogen concentration of 1% or more (step S8). The forming gas may be hydrogen diluted with nitrogen or argon. 【0053】 Then, following the first heat treatment, a second heat treatment is performed at a temperature of 400°C or higher under a non-reducing atmosphere (step S9). The non-reducing atmosphere may be an atmosphere composed of nitrogen, argon, helium, oxygen, or a mixture thereof. 【0054】 In the second heat treatment, the heat treatment temperature of 400°C or higher and the duration of the heat treatment are appropriately adjusted so that the hydrogen concentration in the polysilicon layer 2b within 0.1 μm from the interface between the silicon substrate 2a and the polysilicon layer 2b is at least 1.0 × 10⁻¹⁶. １８ atoms / cm ３ More preferably 1.5 × 10 １８ atoms / cm ３ As a result, the hydrogen concentration gradually decreases from the interface, and the hydrogen concentration in the polysilicon layer 2b located 0.4 μm or more away from the interface is 1.0 × 10⁻¹⁶. １８ atoms / cm ３The hydrogen concentration distribution should be as follows. The rationale for this hydrogen concentration distribution is shown in the examples described later. By adjusting the hydrogen concentration distribution in this way during the second heat treatment, excessive exposure of dangling bonds, which causes instability in properties, can be prevented, and the Q value, which was degraded by the first heat treatment, can be sufficiently restored. 【0055】 By the above manufacturing method, it is possible to produce an oxide single-crystal composite substrate 1 that achieves both the recovery of polarization and crystallinity in the piezoelectric oxide single-crystal thin film 3 and the non-low resistance of the polysilicon layer 2b, while also obtaining a good Q value. 【0056】 In the following section, the manufacturing method for oxide single-crystal composite substrates will be explained, with reference to examples, under conditions for obtaining oxide single-crystal composite substrates with good properties. 【0057】 [Example 1] A support substrate 2 was prepared by laminating a polysilicon layer 2b to a thickness of 2.0 μm on a silicon substrate 2a and polishing the surface (the thickness of the polysilicon layer after polishing was approximately 1.7 μm). A cross-sectional TEM (transmission electron microscope) image of this support substrate 2 is shown in Figure 5. Figure 6 is a magnified view of the area around interface B in Figure 5. As can be seen from these images, the polysilicon particles are very fine within the polysilicon layer 2b up to about 0.1 μm from interface B between the silicon substrate 2a and the polysilicon layer 2b, and the polysilicon particles become larger as deposition progresses. This is because as deposition progresses, the grain boundaries of the polysilicon annihilate, causing the particle size to increase. 【0058】 On the polysilicon layer 2b of this support substrate 2, there is an intervening layer 4 with a thickness of 500 nm, which is SiO ２ A 600 nm thick piezoelectric oxide single crystal thin film 3, which is an LT thin film, was transferred and stacked via a film. The LT thin film contains hydrogen ions (H) on the LT matrix substrate. ＋ ) with an energy of 110 keV, 7.0 × 10 １６ atoms / cm ２ After injecting with the specified dose, the material was bonded to the support substrate 2 via the intervening layer 4, and then mechanically peeled off at the ion implantation interface to transfer the material (ion implantation peeling method). 【0059】The oxide single crystal composite substrate 1 obtained in this way, before heat treatment, was then subjected to heat treatment and surface polishing, and the result was evaluated. First, 4% H ２ Under a nitrogen and hydrogen forming gas atmosphere containing [unspecified gas], the first heat treatment was carried out at 400°C for 6 hours. Subsequently, under an air atmosphere (20% oxygen + 80% nitrogen), the second heat treatment was carried out in two ways: at 450°C for 3 hours and at 450°C for 5 hours. The oxide single crystal composite substrate 1 after heat treatment was evaluated by actually fabricating a resonator on the substrate and measuring the specific bandwidth and Q value (Qmax) in the 1.6 GHz band. The specific bandwidth reflects the quality of the LT thin film, and the Q value reflects the quality of the trap-rich silicon. 【0060】 The measurement results are shown in Figure 7. The theoretical values ​​are those calculated using simulation (3D-FEM method using COMSOL software). From Figure 7, it can be seen that a good specific bandwidth was obtained as a result of the first heat treatment, indicating that the first heat treatment was successful. Regarding the Q value, the sample that underwent the second heat treatment for 3 hours was significantly inferior to the theoretical value, indicating that the second heat treatment was not successful. On the other hand, the sample that underwent the second heat treatment for 5 hours, although inferior to the theoretical value, was close to the theoretical value, indicating that the second heat treatment was generally successful. 【0061】 Next, the hydrogen concentration in the polysilicon layer 2b of the oxide single crystal composite substrate 1 after heat treatment was measured in the depth direction. The analysis was performed on the LT thin film and SiO ２ The analysis was performed after removing the film by etching. The method used was secondary ion mass spectrometry (SIMS). Figure 8 shows the distribution of hydrogen concentration in the depth direction as determined by the analysis. The dotted line indicates the depth position of interface B. For the purpose of consideration, the range from 0 μm to 0.2 μm was excluded from the analysis because it is thought that accurate measurements could not be obtained due to the influence of surface moisture. 【0062】 Figure 8 shows that when the second heat treatment was performed at 450°C for 3 hours, the hydrogen concentration was 1.0 × 10⁻⁶ throughout the depth direction. １８ atoms / cm ３ In contrast to the above, the method performed at 450°C for 5 hours yielded a depth of 1.0 × 10 up to a certain depth. １８ atoms / cm３ The following applies, but near interface B, it is 1.0 × 10 １８ atoms / cm ３ It can be seen that it exceeds this value. In other words, in order to obtain a Q value close to the theoretical value, the hydrogen concentration in the polysilicon layer 2b must be 1.0 × 10⁻¹⁶ up to a certain depth. １８ atoms / cm ３ The following is required, but near interface B, at least 1.0 × 10 １８ atoms / cm ３ It is considered that the hydrogen concentration must be at the above level. 【0063】 Similar experiments were conducted with a polysilicon layer 2b thickness of 0.45 μm, and nearly the same Q value was observed. Therefore, the minimum thickness of the polysilicon layer 2b was determined to be 0.45 μm. On the other hand, there is no particular upper limit to the thickness of the polysilicon layer 2b; for example, it could be 5 μm, which is the thickness of the polysilicon layer 2b in a typical trap-rich silicon substrate. 【0064】 [Example 2] An oxide single crystal composite substrate 1 was prepared before heat treatment, similar to that in Example 1. The first heat treatment was carried out under the same conditions as in Example 1, and the second heat treatment was carried out under different conditions than in Example 1. The surface was then polished and evaluated. The second heat treatment was carried out in two ways: 6 hours at 500°C and 12 hours at 500°C under an atmospheric environment (20% oxygen + 80% nitrogen). For the evaluation of the oxide single crystal composite substrate 1 after heat treatment, a resonator was fabricated on the substrate in the same manner as in Example 1, and the specific bandwidth and Q value (Qmax) were measured in the 1.6 GHz band. 【0065】 The measurement results are shown in Figure 9. From Figure 9, it can be seen that the specific bandwidth yielded good results, similar to those in Example 1. Regarding the Q value, the sample that underwent the second heat treatment for 6 hours was inferior to the theoretical value, but still close, indicating that the second heat treatment was generally effective. On the other hand, the sample that underwent the second heat treatment for 12 hours was significantly inferior to the theoretical value, indicating that the second heat treatment was not effective. 【0066】Furthermore, the hydrogen concentration in the depth direction of the oxide single crystal composite substrate 1 after heat treatment was analyzed by SIMS. The distribution of hydrogen concentration in the depth direction determined by the analysis is shown in Figure 10. The dotted line indicates the depth position of interface B. For the purpose of consideration, the range from 0 μm to 0.2 μm was excluded from the consideration because it is thought that accurate measurements could not be obtained due to the influence of surface moisture. 【0067】 From Figure 10, the second heat treatment performed at 500°C for 12 hours resulted in a total depth of 1.0 × 10⁻⁶. １８ atoms / cm ３ In contrast to the following, the one that was heated at 500°C for 6 hours showed a depth of 1.0 × 10 up to a certain depth. １８ atoms / cm ３ The following applies, but near interface B, it is 1.0 × 10 １８ atoms / cm ３ It exceeds this, and especially in the very vicinity from interface B to 0.1 μm, it is 1.5 × 10⁻⁶. １８ atoms / cm ３ It can be seen that it exceeds [a certain value]. 【0068】 The reason the Q-value worsened when the second heat treatment time was long is thought to be because the hydrogen present at the grain boundaries near interface B, which is composed of fine particles, was removed, exposing dangling bonds and causing the properties to become unstable. Therefore, it can be said that lowering the hydrogen concentration near the interface too much is undesirable from a property standpoint. In other words, it is considered important to leave a certain amount of hydrogen near interface B. Specifically, within the polysilicon layer 2b, from interface B to 0.1 μm, there should be at least 1.0 × 10⁻¹⁶ hydrogen. １８ atoms / cm ３ More preferably 1.5 × 10 １８ atoms / cm ３ This embodiment shows that the above hydrogen concentration is necessary. Furthermore, the hydrogen concentration in the polysilicon layer 2b gradually decreases from interface B, and at locations 0.4 μm or more away from interface B, it is 1.0 × 10⁻⁶. １８ atoms / cm ３ This example shows that the following is necessary. 【0069】[Example 3] The experiments in Examples 1 and 2 were carried out using LN, iron-doped LT, and iron-doped LN as piezoelectric oxide single crystals instead of LT, but the results were almost the same. 【0070】 [Example 4] The experiments in Examples 1 and 2 were carried out using nitrogen, argon, helium, and oxygen instead of the air atmosphere used in the second heat treatment, but the results were almost the same. 【0071】 [Example 5] The experiments in Examples 1 and 2 were carried out using the same foaming gas as in the first heat treatment, but with argon instead of nitrogen as the atmosphere for diluting hydrogen. The results were almost the same. It was found that any inert gas can be used as the atmosphere for diluting hydrogen, not just nitrogen. 【0072】 [Example 6] The experiments of Examples 1 and 2 were carried out using a structure without the intervening layer 4, but the results were almost the same. It was found that the present invention is not affected by the presence or absence of the intervening layer 4. 【0073】 [Example 7] The experiments of Examples 1 and 2 were carried out with SiO as the intervening layer 4. ２ Instead of using SiO Ｘ (However, excluding 1.5 ≤ x ≤ 2.5 and x = 2), the experiment was performed using both SiON and SiN, and the results were almost identical. 【0074】 [Example 8] The experiments of Examples 1 and 2 were carried out on an LT base material substrate with H ＋ Instead of injecting ions, H ２ ＋ Ion injection was performed, but the results were almost the same. 【0075】 [Example 9] The experiments of Examples 1 and 2 were carried out by performing surface activation treatment on the respective substrate surfaces (bonding surfaces) of the piezoelectric oxide single crystal thin film 3 and the support substrate 2 before bonding, using plasma activation and vacuum ion beam activation methods, respectively, but the results were almost the same. 【0076】The present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and produces similar effects is included within the technical scope of the present invention. In other words, modifications can be made as appropriate within the scope of the technical idea expressed in the present invention, and such modified or improved forms are also included within the technical scope of the present invention. 【0077】 1. Oxide single crystal composite substrate 2. Support substrate 2a. Silicon substrate 2b. Polysilicon layer 3. Piezoelectric oxide single crystal thin film 4. Intervening layer B. Interface

Claims

1. An oxide single-crystal composite substrate in which a piezoelectric oxide single-crystal thin film is laminated on the polysilicon layer of a support substrate formed by laminating a polysilicon layer on the upper surface of a silicon substrate, wherein the hydrogen concentration in the polysilicon layer near the interface between the silicon substrate and the polysilicon layer is 1.0 × 10⁻¹⁰ １８ atoms / cm ３ As described above, the hydrogen concentration in the polysilicon layer gradually decreases as it moves away from the interface to 1.0 × 10 １８ atoms / cm ３ The following oxide single-crystal composite substrates.

2. The hydrogen concentration within the polysilicon layer within 0.1 μm of the interface between the silicon substrate and the polysilicon layer is 1.0 × 10⁻¹⁰ １８ atoms / cm ３ The above is true, and the hydrogen concentration in the polysilicon layer at a distance of 0.4 μm or more from the interface is 1.0 × 10⁻¹⁴. １８ atoms / cm ３ The oxide single crystal composite substrate according to claim 1, which is as follows:

3. The oxide single crystal composite substrate according to claim 1, wherein the thickness of the polysilicon layer is 0.45 μm or more and 5.0 μm or less.

4. The oxide single crystal composite substrate according to claim 1, having an intervening layer between the polysilicon layer and the piezoelectric oxide single crystal thin film.

5. The intervening layer is SiO Ｘ (where 1.5 ≤ x ≤ 2.5), SiON, or SiN, or an oxide single crystal composite substrate according to claim 4 containing any of these.

6. The oxide single crystal composite substrate according to claim 1, wherein the piezoelectric oxide single crystal thin film is lithium tantalate, iron-doped lithium tantalate, lithium niobate, or iron-doped lithium niobate.

7. A method for manufacturing an oxide single-crystal composite substrate, wherein a piezoelectric oxide single-crystal thin film is laminated on the polysilicon layer of a support substrate formed by laminating a polysilicon layer on the upper surface of a silicon substrate, the method comprising: a first heat treatment of the oxide single-crystal composite substrate, which is performed at a temperature of 300°C or higher in a forming gas atmosphere with a hydrogen concentration of 1% or more or in a 100% hydrogen atmosphere; and a second heat treatment following the first heat treatment, which is performed at a temperature exceeding 400°C in a non-reducing atmosphere, such that the hydrogen concentration in the polysilicon layer near the interface between the silicon substrate and the polysilicon layer is 1.0 × 10⁻⁶. １８ atoms / cm ３ As a result, the hydrogen concentration in the polysilicon layer gradually decreases as it moves away from the interface to 1.0 × 10⁻⁶. １８ atoms / cm ３ A method for manufacturing an oxide single crystal composite substrate, comprising the steps described below.

8. The hydrogen concentration in the polysilicon layer within 0.1 μm of the interface between the silicon substrate and the polysilicon layer is 1.0 × 10⁻¹⁰. １８ atoms / cm ３ The above is true, and the hydrogen concentration in the polysilicon layer at a distance of 0.4 μm or more from the interface is 1.0 × 10⁻¹⁴. １８ atoms / cm ３ The method for manufacturing an oxide single crystal composite substrate according to claim 7, which is as follows:

9. The method for manufacturing an oxide single crystal composite substrate according to claim 7, wherein the piezoelectric oxide single crystal thin films are stacked using an ion implantation exfoliation method.

10. The method for manufacturing an oxide single crystal composite substrate according to claim 7, wherein an intervening layer is provided between the polysilicon layer and the piezoelectric oxide single crystal thin film.

11. The intervening layer is SiO Ｘ (wherein 1.5 ≤ x ≤ 2.5), the method for manufacturing an oxide single crystal composite substrate according to claim 10, wherein the material is SiON or SiN, or includes any of these.

12. The method for manufacturing an oxide single crystal composite substrate according to claim 7, wherein the piezoelectric oxide single crystal thin film is lithium tantalate, iron-doped lithium tantalate, lithium niobate, or iron-doped lithium niobate.

13. The method for manufacturing an oxide single crystal composite substrate according to claim 7, wherein the non-reducing atmosphere in the second heat treatment is composed of nitrogen, argon, helium, oxygen, or a mixture thereof.

14. In the ion implantation exfoliation method described above, if the ions to be implanted are H ＋ or H ２ ＋ The method for manufacturing an oxide single crystal composite substrate according to claim 9.

15. The method for manufacturing an oxide single crystal composite substrate according to claim 7, wherein, when stacking the piezoelectric oxide single crystal thin films, an activation treatment is applied to the surface of each substrate to be bonded before bonding the base substrate of the piezoelectric oxide single crystal thin film to the support substrate.

16. The method for manufacturing an oxide single crystal composite substrate according to claim 15, wherein the activation treatment is a plasma activation treatment or a vacuum ion beam activation treatment.

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