Substrate for high-frequency device and method for manufacturing same

Abstract

The present invention is a substrate for a high-frequency device in which a nitride semiconductor film is formed on an SOI substrate, the SOI substrate being a TRSOI substrate in which a trap-rich layer formed on a base substrate and an SOI layer comprising single crystal silicon are bonded with an oxide film interposed therebetween, the SOI layer having a resistivity of 1 k [omega] * cm or more and a crystal plane orientation of (111). And the oxygen concentration is 14.8 ppma or less. As a result, a substrate for a high-frequency device having excellent high-frequency characteristics and a method for manufacturing the same are provided.

Description

Technical Field

[0001] The present invention relates to a substrate for high-frequency devices and a method for manufacturing the same. Background Art

[0002] Nitride semiconductors represented by GaN are expected to be next-generation semiconductor materials that exceed the limits of materials such as silicon (Si). In recent years, the manufacturing of high-frequency devices has been carried out by epitaxially growing nitride semiconductors on single-crystalline silicon substrates. In addition, in high-frequency devices, characteristic degradation caused by the substrate, losses due to the substrate, and degradation of the second and third harmonic characteristics have been observed.

[0003] Generally, for substrates for high-frequency devices, high-resistivity substrates are used to perform epitaxial growth of GaN layers and the like to fabricate high-frequency devices. By using a high-resistivity substrate, signals do not flow from the epitaxial layer to the underlying Si substrate. In addition, when a nitride semiconductor epitaxial layer is stacked on a high-resistivity silicon substrate, the nitride semiconductor epitaxial layer is stacked by designing a buffer layer as a stress relaxation layer.

[0004] In addition, as described in Patent Documents 1 and 2, as substrates for high-frequency devices, TR substrates that usually have a rich trap (TR) layer are becoming popular, and frequency characteristics are improved by using high-resistivity substrates. Patent Document 1 and the like describe a structure composed of a TR layer, a dielectric layer (buried oxide film), and a semiconductor layer on a high-resistivity base substrate.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent No. 7098851

[0008] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2022-70890 Summary of the Invention

[0009] (I) Technical Problem to be Solved

[0010] Generally, in high-frequency devices using TR substrates, there is a limit to the improvement of the second harmonic (2HD). In order to further improve high-frequency characteristics, a GaN-on-TRSOI substrate formed by combining a TRSOI substrate with a GaN layer having excellent high-frequency characteristics is considered to have prospects.

[0011] However, even in a GaN on TRSOI substrate formed by stacking a GaN layer on a TRSOI substrate, the second harmonic characteristics may not be improved due to the influence of the characteristics (resistivity or oxygen concentration) of the Si substrate.

[0012] The present invention is completed to solve the above technical problems, and its object is to provide a substrate for high-frequency devices with excellent high-frequency characteristics and a manufacturing method thereof.

[0013] (2) Technical solution

[0014] To achieve the above object, the present invention provides a substrate for high-frequency devices, which is a substrate for high-frequency devices formed by forming a nitride semiconductor film on an SOI substrate, and is characterized in that

[0015] the SOI substrate is a TRSOI substrate in which a trap-enriched layer formed on a base substrate and an SOI layer composed of single crystal silicon are joined via an oxide film,

[0016] the resistivity of the SOI layer is 1 kΩ·cm or more, the crystal plane orientation is (111), and the oxygen concentration is 14.8 ppma or less.

[0017] If the substrate formed with a nitride semiconductor film in such a manner is a TRSOI substrate, and the SOI layer of the TRSOI substrate has the above high resistivity of 1 kΩ·cm or more, and its oxygen concentration is within the above numerical range, then a substrate for high-frequency devices with excellent high-frequency characteristics can be manufactured. For example, in existing products (TR substrates, etc.), the limit of 2HD is about -91 dBm, but in the present invention, its 2HD can be further reduced, and further excellent harmonic characteristics can be exhibited.

[0018] In addition, by having the above crystal plane orientation of the SOI layer, the nitride semiconductor film on the SOI layer can be formed well.

[0019] At this time, the oxygen concentration of the SOI layer can be made 5.2 ppma or less, and the high-frequency characteristics can be made further excellent.

[0020] Furthermore, the oxygen concentration of the SOI layer can be made 0.5 ppma or less, and the high-frequency characteristics can be made even more excellent.

[0021] In addition, the base substrate can be made a Czochralski (CZ) single crystal silicon substrate with a crystal plane orientation of (100).

[0022] The base substrate with a crystal plane orientation of (100) using the CZ method has a tendency of good production yield, low price and high quality, and can even become a low-price and high-precision substrate for high-frequency devices.

[0023] In addition, the resistivity of the base substrate can be made 1 kΩ·cm or more.

[0024] If the base substrate has such a high resistivity of 1 kΩ·cm or more, the high-frequency characteristics can be made more excellent.

[0025] In addition, the present invention provides a method for manufacturing a substrate for a high-frequency device, which is a method for manufacturing a substrate for a high-frequency device formed with a nitride semiconductor film on an SOI substrate, and is characterized by including:

[0026] A step of preparing a TRSOI substrate as the SOI substrate, where the TRSOI substrate is a TRSOI substrate formed by thinning a bonding substrate in a bonding substrate to form an SOI layer, and the bonding substrate is obtained by bonding a trap enrichment layer formed on a base substrate and the bonding substrate made of single crystal silicon with an oxide film interposed therebetween; and,

[0027] A step of forming the nitride semiconductor film on the SOI layer;

[0028] As the bonding substrate, a bonding substrate having a resistivity of 1 kΩ·cm or more, a crystal plane orientation of (111), and an oxygen concentration of 14.8 ppma or less is used.

[0029] If it is the manufacturing method of the present invention like this, a substrate for a high-frequency device having excellent high-frequency characteristics (such as second harmonic characteristics, etc.) can be manufactured, and a nitride semiconductor film can also be formed well.

[0030] At this time, as the bonding substrate, a bonding substrate having an oxygen concentration of 5.2 ppma or less can be used, and a substrate with further excellent high-frequency characteristics can be obtained.

[0031] Furthermore, as the bonding substrate, a bonding substrate having an oxygen concentration of 0.5 ppma or less can be used, and a substrate with even more excellent high-frequency characteristics can be obtained.

[0032] In addition, as the base substrate, a CZ single crystal silicon substrate having a crystal plane orientation of (100) can be used.

[0033] A high-quality base substrate with a crystal plane orientation of (100) can be prepared at low cost.

[0034] In addition, as the base substrate, a base substrate having a resistivity of 1 kΩ·cm or more can be used.

[0035] If carried out in this way, a substrate with more excellent high-frequency characteristics can be obtained.

[0036] (III) Beneficial effects

[0037] If it is the substrate for a high-frequency device and its manufacturing method of the present invention, a substrate for a high-frequency device with excellent high-frequency characteristics such as 2HD can be obtained. Brief description of the drawings

[0038] Figure 1 It is a schematic explanatory diagram showing an example of the substrate for a high-frequency device of the present invention.

[0039] Figure 2 It is a process diagram showing an example of a method for manufacturing a substrate for a high-frequency device of the present invention.

[0040] Figure 3 It is a schematic structural diagram showing an example of a composite body in which a coplanar waveguide (CPW) electrode is formed on a substrate for a high-frequency device.

[0041] Figure 4 It is a schematic plan view of the CPW electrode.

[0042] Figure 5 It is a graph showing the measurement results of the harmonic characteristics (2HD) of Examples 1 to 3 and Comparative Examples 1 to 3. Detailed Description

[0043] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

[0044] First, as described above, the present invention relates to a substrate for a high-frequency device having an SOI structure, and particularly to a substrate for a high-frequency device having a support substrate (base substrate) that resists the formation of an inversion layer in a region close to the oxide film (i.e., buried oxide film: BOX film) of the SOI structure.

[0045] In a semiconductor substrate with a relatively high resistivity (such as a silicon wafer), it is easy to form a charge inversion layer or a charge storage layer with a relatively high conductivity at the interface between the BOX film and the support substrate. As a result, the effective resistivity of the substrate decreases, parasitic power loss occurs, and when the device operates at a radio frequency (RF) frequency, nonlinearity of the device occurs.

[0046] A method has been developed for capturing charges in any induced inversion layer (or storage layer) so that a high resistivity of the substrate can be maintained even in a region very close to the surface. It is known that the performance of an RF device fabricated using an SOI substrate is improved by providing a charge trapping layer (CTL) between a high-resistivity support substrate and a buried oxide film. A variety of methods for forming such a highly captureable interface layer have been proposed. For example, one method of forming a semiconductor device on an insulator with a charge trapping layer (such as silicon-on-insulator, i.e., SOI) for RF device applications is based on the following steps: depositing an undoped (not doped) polysilicon film on a silicon substrate with a relatively high resistivity; and forming a stack of an oxide film and a silicon layer provided on the oxide film. The polysilicon layer functions as a layer with many defects between the silicon substrate and the buried oxide film.

[0047] In academic research, it has been shown that by setting a polysilicon layer between the oxide film and the substrate, the separation of the device can be improved, the loss of the transmission line can be reduced, and the harmonic distortion can be reduced. For example, refer to the following literature.

[0048] ·H.S.Gamble,et al.“Low-loss CPW lines on surface stabilized highresistivity silicon, ”Microwave Guided Wave Lett., 9(10), pp.395-397, 1999

[0049] ·D.Lederer, R.Lobet and J.-P.Raskin, “Enhanced high resistivity SOIwafers for RF applications, ”IEEE Intl. SOI Conf., pp.46-47, 2004

[0050] ·D.Lederer and J.-P.Raskin, “New substrate passivation methoddedicated to high resistivity SOI wafer fabrication with increased substrateresistivity, ”IEEE Electron Device Letters, vol.26, no.11, pp.805-807, 2005

[0051] ·D.Lederer, B.Aspar,C .Laghae and J.-P.Raskin, “Performance of RFpassive structures and SOI MOSFETs transferred on a passivated HR SOIsubstrate, ”IEEE International SOI Conference, pp.29-30, 2006

[0052] ·Daniel C. Kerret al. “Identification of RF harmonic distortion on Si substrates and its reduction using a trap-rich layer”, Silicon Monolithic Integrated Circuits in RF Systems, 2008. SiRF 2008 (IEEE Topical Meeting), pp.151-154, 2008

[0053] In the past, although the use of a TR substrate such as Patent Document 1 has been attempted to improve high-frequency characteristics as a substrate for high-frequency devices, such improvement has reached its limit (for example, 2HD is -91 dBm).

[0054] Under such circumstances, the inventors of the present application conducted intensive research and found that in a high-frequency device substrate such as GaN on TRSOI (TRSOI substrate + nitride semiconductor film), the improvement of the above high-frequency characteristics is related to the oxygen concentration of the SOI layer. Moreover, the inventors of the present application found that if the oxygen concentration of the SOI layer (high resistivity [1 kΩ·cm or more], crystal plane orientation (111)) is 14.8 ppma or less, more excellent high-frequency characteristics can be obtained, thus completing the present invention.

[0055] The high-frequency device substrate of the present invention will be described. Figure 1 An example of the high-frequency device substrate of the present invention is shown. The high-frequency device substrate 1 of the present invention has an SOI substrate 2 and a nitride semiconductor film 3 on the SOI substrate 2. Moreover, the SOI substrate 2 has the following structure: a trap-rich layer 5 (TR layer), an oxide film 6 (buried oxide film (BOX film)), and an SOI layer 7 (single-crystalline silicon layer) are sequentially stacked on a base substrate 4.

[0056] Each part will be described in detail below.

[0057] The above SOI substrate 2 is a TRSOI substrate formed by bonding the TR layer 5 formed on the base substrate 4 and the SOI layer 7 with the oxide film 6 interposed therebetween. For example, the structure of the above TRSOI substrate can be obtained by bonding a structure composed of the base substrate 4 and the TR layer 5 to a portion of a bonding substrate that serves as the SOI layer 7 and has oxide films 6 formed on either one surface or both surfaces, and thinning the bonding substrate.

[0058] The base substrate 4 can be, for example, a silicon substrate, and in particular, a single-crystalline silicon substrate using the CZ method with a crystal plane orientation of (100). The reason is that it is easy to prepare a low-cost and high-quality base substrate.

[0059] In addition, the resistivity of the base substrate 4 is not particularly limited. In order to easily control warping, it can be a low-resistivity base substrate with a large fracture load. By increasing the dopant concentration, the strength of the base substrate can be increased to suppress warping. On the other hand, it can also be a high-resistivity base substrate, for example, a base substrate of 1 kΩ·cm or more. In this case, a substrate for a high-frequency device with more excellent high-frequency characteristics can be manufactured. It is preferably 3 kΩ·cm or more, and more preferably 5 kΩ·cm or more, which is more advantageous in terms of high-frequency characteristics. The upper limit of this resistivity is not particularly limited. The higher the value, the more the improvement of high-frequency characteristics can be pursued. For example, it can be set to 50 kΩ·cm.

[0060] The TR layer 5 refers to a layer having the effect of capturing charges through defects in the layer. As long as it has this function, it can be, for example, an undoped polysilicon layer or a damaged layer formed on the surface of the base substrate by ion implantation.

[0061] The oxide film 6 can be, for example, a silicon oxide film based on thermal oxidation.

[0062] The resistivity of the SOI layer 7 is 1 kΩ·cm or more, the crystal plane orientation is (111), and the oxygen concentration is 14.8 ppma or less.

[0063] Since it is a high resistivity of 1 kΩ·cm or more, the high-frequency characteristics of the high-frequency device substrate 1 are improved. It is preferably 3 kΩ·cm or more, and more preferably 5 kΩ·cm or more, which is more advantageous in terms of high-frequency characteristics. The upper limit of this resistivity is not particularly limited. The higher the value, the more the improvement of high-frequency characteristics can be pursued. For example, it can be set to 150 kΩ·cm.

[0064] In addition, by having the crystal plane orientation of (111), a good nitride semiconductor film can be appropriately formed on the SOI layer 7.

[0065] In addition, as described above, the inventors of the present application found that the high-frequency characteristics depend on the oxygen concentration of this SOI layer 7. If the oxygen concentration is 14.8 ppma or less, high-frequency characteristics more excellent than those of existing products can be obtained.

[0066] For example, regarding the second harmonic (2HD), there is a limit to improvement at around -91 dBm in existing products, but in the present invention, it can be further improved compared to such existing products. For example, it can be reduced to around -95 dBm for improvement. Moreover, if the oxygen concentration is 5.2 ppma or less, it can be improved to around -105 dBm, and if it is further 0.5 ppma or less, it can also be improved to around -115 dBm or higher. Additionally, the lower the oxygen concentration, the more preferable it is for improving high-frequency characteristics, and there is no lower limit that can be set.

[0067] In addition, in the present application specification, the value of the oxygen concentration in the present invention (and the value of the oxygen concentration in the existing products of the following respective comparative examples) is based on the JEIDA-61-2000 standard.

[0068] As the nitride semiconductor film 3, there is no particular limitation, and a nitride semiconductor can be adopted according to the purpose. Examples thereof include GaN, AlN, AlGaN, and combinations thereof.

[0069] If it is the high-frequency device substrate 1 of the present invention as described above, the high-frequency characteristics can be more excellent than those of existing products.

[0070] Subsequently, an explanation will be given of Figure 1 the manufacturing method of the high-frequency device substrate of the present invention that can manufacture the high-frequency device substrate 1. Figure 2 is an example of the process of the manufacturing method of the present invention. It includes a process of preparing a TRSOI substrate and a process of forming a nitride semiconductor film.

[0071] Hereinafter, each process will be described in detail while showing specific examples.

[0072] <Preparing a TRSOI Substrate>

[0073] First, a base substrate is prepared, and a TR layer is formed thereon.

[0074] For example, a base substrate (Si substrate) with a high resistivity (1 to 50 kΩ·cm) and a diameter of 150 mm is prepared. In particular, a single-crystalline silicon ingot with a crystal axis orientation of <100> can be grown by the Czochralski method and sliced using a wire saw device to prepare a single-crystalline silicon substrate with a crystal plane orientation of (100) (base substrate: (100) just substrate). Regarding the base substrate, although the (100) just substrate is exemplified above for explanation, it can also have an inclination angle.

[0075] On the substrate prepared in such a manner, a polycrystalline silicon (poly-Si) layer with a thickness of only 100 nm to 3 μm as a trap-rich layer (TR layer) is grown by a reduced-pressure chemical vapor deposition (reduced-pressure CVD) method. As an example of the growth conditions, the temperature inside the reaction tube of the vapor deposition apparatus can be set to 590 °C or higher, and for example, silane (SiH 4 ) gas and phosphine (PH 3 ) gas are introduced into the reaction tube, and growth is carried out while maintaining the inside of the reaction tube at a specified vacuum level. Alternatively, there is also the following method: using disilane (Si 2 H 6 ) gas, an amorphous silicon film is formed at a temperature of 580 °C or lower, and this thin film is annealed at a temperature of around 600 to 1000 °C to make it polycrystalline.

[0076] As described above, the TR layer refers to a layer having the effect of capturing charges through defects in the layer, and as long as it has this function, it is not limited to polycrystalline silicon. For example, it can be set as a damaged layer formed on a Si crystal by ion implantation. For example, the above-mentioned damaged layer can be formed on the surface of the substrate.

[0077] Subsequently, a bonding substrate made of single-crystalline silicon is prepared, and the substrate and the bonding substrate are bonded with an oxide film interposed therebetween to obtain a bonded substrate. Then, by thinning the bonding substrate in the bonded substrate, an SOI layer is formed (fabrication of a TRSOI substrate).

[0078] First, a bonding substrate is prepared. For example, it can be set as a CZ single-crystalline substrate, or it can also be set as a floating zone melting method (FZ) single-crystalline substrate. Since it will become the SOI layer later and a nitride semiconductor film is laminated and formed thereon, a bonding substrate with a crystal plane orientation of (111) is prepared. For example, by appropriately adjusting the ingot manufacturing conditions in the CZ method or the FZ method to grow an ingot with a crystal axis orientation of <111> and perform slicing (bonding substrate: (111) just substrate).

[0079] In addition, regarding the bonding substrate, it can also be set to have an inclination angle, and in particular, it is preferably set to within ±1 degree. At this time, the nitride semiconductor film to be formed thereon can be made more uniformly and of higher quality.

[0080] At this time, the dopant concentration is appropriately adjusted to make a high resistivity (1 kΩ·cm or more).

[0081] Further, the oxygen concentration in the crystal is controlled to be 14.8 ppma or less. In the case of the CZ method, the oxygen concentration in the ingot can be adjusted by adjusting the rotation speed of the crucible in the CZ pulling apparatus, etc., and more preferably it can be adjusted to 5.2 ppma or less. In addition, in the case of the FZ method, even a substrate with a low oxygen concentration such as 0.5 ppma or less can be easily prepared. By reducing the oxygen concentration in the bonded substrate (SOI layer), the high-frequency characteristics are further improved, and 2HD can be further reduced.

[0082] Then, an oxide film (to be the BOX film) of, for example, 200 nm is formed on the polysilicon layer formed on the base substrate, and after bonding (joining) with the above-mentioned (111) bonded substrate (1 to 150 kΩ·cm, preferably 3 kΩ·cm or more, more preferably 5 kΩ·cm or more) as the SOI layer, the bonded substrate is thinned to form the SOI layer. The thickness of the SOI layer can be set to 100 nm, for example.

[0083] The oxide film can be formed such that the film thickness of the oxide film interposed between the base single-crystal substrate and the bonded single-crystal substrate is, for example, 2 nm or more and 470 nm or less. Of course, the film thickness of the oxide film after bonding the two substrates can be 2 nm or more and 470 nm or less. In addition, the oxide film can be formed on the polysilicon layer side formed on the base substrate, or on the bonded substrate side. Further, it can also be formed on both of them.

[0084] As long as the base substrate and the bonded substrate can be bonded, the conditions (atmosphere, temperature, time, etc.) of the heat treatment (bonding heat treatment) are not particularly limited. For example, it can be set to a bonding heat treatment at a temperature of 400°C or more and 1200°C or less for 1 to 12 hours in a nitrogen atmosphere.

[0085] As a method for thinning the bonded substrate, for example, the ion implantation lift-off method can be cited. An ion implantation layer can be formed on the bonded substrate in advance, and after bonding, for the bonded substrate, lift-off heat treatment is performed to lift off with the ion implantation layer, or it can be mechanically lifted off with the ion implantation layer.

[0086] <Forming a nitride semiconductor film>

[0087] After preparing the TRSOI substrate in the above manner, a nitride semiconductor film is formed on the SOI layer.

[0088] On the TRSOI substrate, for example, an AlN initial layer is stacked, and then an AlGaN layer, a GaN layer, and an SLs layer (a superlattice layer of AlGaN / GaN or AlN / GaN) are stacked, and a GaN layer is stacked on top of them to make a total thickness of 1.8 μm. These layers can be formed by epitaxial growth according to the metalorganic chemical vapor deposition (MOCVD) method.

[0089] In addition, it is unlikely that thermal donors are generated due to oxygen in the substrate. The reason is that the epitaxial growth temperature is around 1200 to 1050, and a thermal history of at least 4 hours is applied. It is considered that thermal donors will not be formed, and the cooling is also close to rapid cooling.

[0090] The film thickness, resistivity, process temperature, etc. of each part other than the resistivity (1 kΩ·cm or more), crystal plane orientation (111), and oxygen concentration (14.8 ppma or less) in the SOI layer listed in the description of the above process are only one example, and the present invention is not limited to these values.

[0091] By the manufacturing method of the present invention as described above, a substrate 1 for high-frequency devices with improved high-frequency characteristics compared to the prior art can be manufactured, and a substrate 1 for high-frequency devices with a 2HD ratio further reduced than -91 dBm can be obtained.

[0092] Examples

[0093] Hereinafter, examples and comparative examples are shown to more specifically illustrate the present invention, but the present invention is not limited to these examples.

[0094] (Example 1)

[0095] Manufacture according to Figure 2 the process of Figure 1 the substrate 1 for high-frequency devices shown (TRSOI substrate + nitride semiconductor film).

[0096] Base substrate 4: CZSi single crystal substrate, (100) plane as the main plane, 8 kΩ·cm

[0097] TR layer 5: polysilicon layer, thickness of 1.8 μm

[0098] Oxide film 6 (BOX film): thickness of 200 nm

[0099] SOI layer 7 (bonding substrate): CZSi single crystal, (111) plane as the main plane, 5 kΩ·cm, oxygen concentration of 14.8 ppma, thickness of 100 nm

[0100] Nitride semiconductor film 3: A buffer layer composed of an AlN initial layer, an AlGaN layer, and an SLs structure of GaN / AlN is stacked, and a GaN layer is stacked on top of it, with a total thickness of 1.8 μm

[0101] The manufacturing conditions of the TR layer, oxide film, SOI layer, and nitride semiconductor film are as described below.

[0102] TR layer: After forming a polysilicon layer as a trap enrichment layer (charge trapping layer) on the base substrate at 1050 °C, the surface is polished to make the thickness 1.8 μm.

[0103] Oxide film: Formed by thermally oxidizing the bonded substrate.

[0104] SOI layer: Hydrogen is implanted from the top surface (the side bonded to the base substrate) of the bonded substrate to form a micro-bubble layer (ion implantation layer) inside the bonded substrate. The bonded substrate with the micro-bubble layer is attached to the surface of the polysilicon layer of the previously formed base substrate. Next, by performing heat treatment, the bonded substrate is separated using the micro-bubble layer as the peeling interface, thereby forming a thin bonded layer remaining on the oxide film, that is, the SOI layer. Next, the SOI layer is subjected to contact polishing to obtain an SOI layer with a film thickness of 100 nm.

[0105] Nitride semiconductor: The growth temperature of each layer is as described below. The initial layer AlN is 1050 - 1200 °C, the AlGaN layer is 1150 - 1050 °C, the SLs structure is 1100 - 1000 °C, and GaN is 1000 - 900 °C.

[0106] An RF electrode is formed on the above-mentioned substrate for high-frequency devices for characteristic evaluation.

[0107] Specifically, for the substrate 1 for high-frequency components, an Al electrode (thickness: 1 μm, length: 2199 μm) of a coplanar waveguide (CPW) is formed using a photolithography process, and heat treatment is performed. In this way, Figure 3 (Structural diagram) and Figure 4 (Plan view) shown composite body 20.

[0108] The composite body 20 includes the substrate 1 for high-frequency devices and the CPW electrode 10 formed on the surface of its nitride semiconductor film 3.

[0109] The CPW electrode 10 includes a center electrode 11 with a length L ( Figure 4 ) of 2199 μm and a width of 15 μm, and peripheral electrodes 12. The thickness of the center electrode 11 and the peripheral electrodes 12 is 1 μm.

[0110] Then, the harmonic characteristic (2HD) is obtained using the CPW electrode 10 as the RF characteristic of the substrate 1 for high-frequency devices.

[0111] In addition, regarding the measurement conditions, the shape of the above-mentioned CPW electrode 10 in Example 1 and the following various examples and comparative examples, and the output P of the fundamental frequency (H1) f0 = 0.9 GHz out = 15 dBm are made consistent.

[0112] In Example 1, the result is -95 dBm.

[0113] (Example 2)

[0114] Except that the oxygen concentration of the SOI layer is 5.2 ppma, a substrate for high-frequency devices and CPW electrodes were fabricated in the same manner as in Example 1, and the harmonic characteristics (2HD) were obtained.

[0115] The result was -104.8 dBm.

[0116] (Example 3)

[0117] Except that the oxygen concentration of the SOI layer is 0.3 ppma (the bonding substrate is FZSi single crystal), a substrate for high-frequency devices and CPW electrodes were fabricated in the same manner as in Example 1, and the harmonic characteristics (2HD) were obtained.

[0118] The result was -114.2 dBm.

[0119] (Comparative Example 1)

[0120] Except that the resistivity of the base substrate is 5 kΩ·cm and the oxygen concentration of the SOI layer is 17.1 ppma, a substrate for high-frequency devices and CPW electrodes were fabricated in the same manner as in Example 1, and the harmonic characteristics (2HD) were obtained.

[0121] The result was -89.9 dBm.

[0122] (Comparative Example 2)

[0123] A GaN on Si structure was fabricated. Specifically, on a Si substrate (FZSi single crystal substrate, (111) plane as the main plane, 5 kΩ·cm, oxygen concentration of 0.5 ppma), buffer layers such as an SLs structure were laminated in the same manner as in Example 1 as a nitride semiconductor film, and a GaN layer was laminated thereon. The total thickness was 1.8 μm.

[0124] Although this Comparative Example 2 has a nitride semiconductor film, it is different from each of the embodiments of the product of the present invention in that the nitride semiconductor film is formed on a Si substrate instead of a TRSOI substrate.

[0125] CPW electrodes were fabricated in the same manner as in Example 1, and the harmonic characteristics (2HD) were obtained.

[0126] The result was -84 dBm.

[0127] (Comparative Example 3)

[0128] In order to evaluate the high-frequency characteristics of the TR substrate, the SOI layer was removed from the TRSOI substrate to fabricate a TR substrate with an oxide film. Specifically, the manufacturing method of the TRSOI substrate was to form a polysilicon layer with a thickness of 1.8 μm on a Si substrate ((100) plane as the main plane, 5 kΩ·cm, oxygen concentration of 13.1 ppma) of the base substrate, form an oxide film or a microbubble layer with a thickness of 200 nm on the Si substrate of the bonding substrate, attach the oxide film side of the bonding substrate to the surface of the polysilicon layer of the base substrate, and then perform heat treatment to separate the bonding substrate using the microbubble layer as the peeling interface, thereby forming the SOI layer. Then, contact polishing was performed to thin the SOI layer to obtain the TRSOI substrate. Then, the above SOI layer was peeled off to obtain a TR substrate with an oxide film.

[0129] On the oxide film of this TR substrate with an oxide film, CPW electrodes were fabricated in the same manner as in Example 1, and the harmonic characteristics (2HD) were obtained.

[0130] The result was -91 dBm.

[0131] In addition, the difference from each embodiment of the product of the present invention is that this Comparative Example 3 does not have the SOI layer 7 and the nitride semiconductor film in the product of the present invention.

[0132] The measurement results of the harmonic characteristics (2HD) of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Figure 5 . In Comparative Examples 1 to 3, although Comparative Example 3 was able to minimize 2HD to the greatest extent, it remained at -91 dBm. In contrast, in Examples 1 to 3 of the present invention, it was possible to reduce it to more than -91 dBm, which was extremely good.

[0133] (Example 4)

[0134] Except that the oxygen concentration of the SOI layer was 0.5 ppma (the bonding substrate was an FZSi single crystal), a high-frequency device substrate and CPW electrodes were fabricated in the same manner as in Example 1, and the harmonic characteristics (2HD) were obtained.

[0135] The result was -112.4 dBm.

[0136] (Example 5)

[0137] Except that the resistivity of the SOI layer was 1 kΩ·cm, a high-frequency device substrate and CPW electrodes were fabricated in the same manner as in Example 1, and the harmonic characteristics (2HD) were obtained.

[0138] The result was -94 dBm.

[0139] (Comparative Example 4)

[0140] Except that the oxygen concentration in the SOI layer is 17.1 ppma, a high-frequency device substrate and a CPW electrode are fabricated in the same manner as in Example 1, and the harmonic characteristic (2HD) is obtained.

[0141] The result is -89.6 dBm.

[0142] In Examples 4 and 5, with respect to 2HD, it is also possible to reduce it to more than -91 dBm. On the other hand, in Comparative Example 4, it is not possible to reach -91 dBm of Comparative Example 3.

[0143] This specification includes the following aspects.

[0144] [1]: A high-frequency device substrate formed by forming a nitride semiconductor film on an SOI substrate, wherein

[0145] the SOI substrate is a TRSOI substrate in which a trap-enriched layer formed on a base substrate and an SOI layer made of single-crystalline silicon are joined via an oxide film,

[0146] the resistivity of the SOI layer is 1 kΩ·cm or more, the crystal plane orientation is (111), and the oxygen concentration is 14.8 ppma or less.

[0147] [2]: The high-frequency device substrate according to the above [1], wherein the oxygen concentration of the SOI layer is 5.2 ppma or less.

[0148] [3]: The high-frequency device substrate according to the above [1], wherein the oxygen concentration of the SOI layer is 0.5 ppma or less.

[0149] [4]: The high-frequency device substrate according to any one of the above [1] to [3], wherein the base substrate is a CZ single-crystalline silicon substrate with a crystal plane orientation of (100).

[0150] [5]: The high-frequency device substrate according to any one of the above [1] to [4], wherein the resistivity of the base substrate is 1 kΩ·cm or more.

[0151] [6]: A method for manufacturing a high-frequency device substrate, which is a method for manufacturing a high-frequency device substrate formed by forming a nitride semiconductor film on an SOI substrate, and includes:

[0152] a step of preparing a TRSOI substrate as the SOI substrate, the TRSOI substrate being a TRSOI substrate formed by thinning a bonding substrate in a bonding substrate to form an SOI layer, and the bonding substrate being obtained by bonding a trap-enriched layer formed on a base substrate and the bonding substrate made of single-crystalline silicon via an oxide film; and

[0153] A step of forming the nitride semiconductor film on the SOI layer;

[0154] A manufacturing method of a substrate for a high-frequency device, using, as the bonding substrate, a bonding substrate having a resistivity of 1 kΩ·cm or more, a crystal plane orientation of (111), and an oxygen concentration of 14.8 ppma or less.

[0155] [7]: The manufacturing method of the substrate for a high-frequency device according to [6] above, wherein, as the bonding substrate, a bonding substrate having an oxygen concentration of 5.2 ppma or less is used.

[0156] [8]: The manufacturing method of the substrate for a high-frequency device according to [6] above, wherein, as the bonding substrate, a bonding substrate having an oxygen concentration of 0.5 ppma or less is used.

[0157] [9]: The manufacturing method of the substrate for a high-frequency device according to any one of [6] to [8] above, wherein, as the base substrate, a CZ single-crystalline silicon substrate having a crystal plane orientation of (100) is used.

[0158]

[10] : The manufacturing method of the substrate for a high-frequency device according to any one of [6] to [9] above, wherein, as the base substrate, a base substrate having a resistivity of 1 kΩ·cm or more is used.

[0159] In addition, the present invention is not limited to the above embodiments. The above embodiments are illustrative, and technical solutions having the same constitution as the technical idea described in the claims of the present invention and exhibiting the same effects are all included in the technical scope of the present invention.

Claims

1. A substrate for a high-frequency device, which is a substrate for a high-frequency device formed by forming a nitride semiconductor film on an SOI substrate, characterized in that, the SOI substrate is a TRSOI substrate in which a trap-rich layer formed on a base substrate and an SOI layer made of single-crystalline silicon are joined with an oxide film interposed therebetween, the resistivity of the SOI layer is 1 kΩ·cm or more, the crystal plane orientation is (111), and the oxygen concentration is 14.8 ppma or less.

2. The substrate for a high-frequency device according to claim 1, characterized in that, the oxygen concentration of the SOI layer is 5.2 ppma or less.

3. The substrate for a high-frequency device according to claim 1, characterized in that, the oxygen concentration of the SOI layer is 0.5 ppma or less.

4. The substrate for a high-frequency device according to any one of claims 1 to 3, characterized in that, the base substrate is a CZ single-crystalline silicon substrate with a crystal plane orientation of (100).

5. The substrate for a high-frequency device according to any one of claims 1 to 3, characterized in that, the resistivity of the base substrate is 1 kΩ·cm or more.

6. The substrate for a high-frequency device according to claim 4, characterized in that, the resistivity of the base substrate is 1 kΩ·cm or more.

7. A method for manufacturing a substrate for a high-frequency device, which is a method for manufacturing a substrate for a high-frequency device formed by forming a nitride semiconductor film on an SOI substrate, characterized in that, it includes: a step of preparing a TRSOI substrate as the SOI substrate, the TRSOI substrate being a TRSOI substrate formed by thinning a bonding substrate in a bonding substrate to form an SOI layer, the bonding substrate being obtained by bonding a trap-rich layer formed on a base substrate and the bonding substrate made of single-crystalline silicon with an oxide film interposed therebetween; and a step of forming the nitride semiconductor film on the SOI layer, as the bonding substrate, a bonding substrate having a resistivity of 1 kΩ·cm or more, a crystal plane orientation of (111), and an oxygen concentration of 14.8 ppma or less is used.

8. The method for manufacturing a substrate for a high-frequency device according to claim 7, characterized in that, as the bonding substrate, a bonding substrate having an oxygen concentration of 5.2 ppma or less is used.

9. The method for manufacturing a substrate for a high-frequency device according to claim 7, characterized in that, as the bonding substrate, a bonding substrate having an oxygen concentration of 0.5 ppma or less is used.

10. The method for manufacturing a substrate for a high-frequency device according to any one of claims 7 to 9, characterized in that, as the base substrate, a CZ single-crystalline silicon substrate with a crystal plane orientation of (100) is used.

11. The method for manufacturing a substrate for a high-frequency device according to any one of claims 7 to 9, characterized in that, as the base substrate, a base substrate having a resistivity of 1 kΩ·cm or more is used.

12. The method for manufacturing a substrate for a high-frequency device according to claim 10, characterized in that, as the base substrate, a base substrate having a resistivity of 1 kΩ·cm or more is used.

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