Substrate for high frequency device and manufacturing method thereof

Abstract

To provide a high-frequency device substrate using diamond with excellent high-frequency characteristics, and a method for manufacturing a high-frequency device substrate using diamond with excellent high-frequency characteristics.SOLUTION: A substrate for a high frequency device includes a support substrate having an uneven surface, a diamond layer on the surface of the support substrate, and a silicon oxide film layer on the diamond layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] With the advent of 5G, terminals will need to support a wide range of frequency bands, requiring many high-frequency components such as filters. In particular, semiconductor devices used in high-frequency ranges, i.e., semiconductor devices for radio frequency (RF) applications, are required to have higher performance.

[0003] Conventionally, high-frequency filters using silicon substrates with an SOI structure have been attracting attention because of their compatibility with CMOS processes and their potential for mass production. From the viewpoint of preventing crosstalk, importance is attached to harmonic characteristics, and various measures have been taken to improve these, such as increasing the resistivity of the substrate and introducing a charge storage layer.

[0004] As a specific solution, first of all, there is a need to increase the resistivity of the support substrate. For example, Patent Document 1 states that the specific resistivity value must be typically higher than 500 Ω·cm, preferably higher than 1000 Ω·cm, and more preferably higher than 3000 Ω·cm.

[0005] Furthermore, Patent Document 2 describes a method for manufacturing a high-frequency SOI substrate (TR-SOI substrate) that includes a support substrate of an SOI structure and a new intermediate semiconductor layer (charge trap layer or trap rich: TR layer) such as Poly-Si between the support substrate and a buried oxide layer (BOX layer).

[0006] As an example of the high-frequency characteristics of such a substrate for high-frequency devices, there is a second harmonic (2HD) characteristic that is measured by removing the SOI layer of the TR-SOI substrate and forming a co-planar waveguide (CPW5) with an Al electrode on the BOX layer as shown in Fig. 3. As shown in Figs. 3 and 4, the CPW5 has a structure in which metal electrodes 60a are arranged in parallel with a gap between them, and a linear central metal electrode 60b is formed in parallel with these metal electrodes 60a in the center of the gap, and an electric field 60c from the central metal electrode 60b toward the metal electrodes 60a on both the left and right sides in Fig. 4 and the inside of the measurement target substrate 30, and a magnetic field 60d in the direction surrounding the central metal electrode 60b inside the measurement target substrate 30 transmits electromagnetic waves.

[0007] Harmonics are higher-order frequency components that are integer multiples of the original frequency, with the original frequency being defined as the fundamental wave and the frequency that is twice as high (half the wavelength) as 2HD. In high-frequency circuits, substrates with small harmonics are required to avoid interference caused by harmonics, and for this purpose, as mentioned above, in TR-SOI, a TR layer is formed on the base substrate, and the supporting substrate is made highly resistive, improving the 2HD characteristics.

[0008] Such a substrate for a high frequency device that uses a material other than silicon is described in Patent Document 3. Patent Document 3 describes a structure in which diamond is grown on a base material (silicon in the example) and a piezoelectric material is further formed as a film. For example, a ZnO film is formed, and the electrical resistivity of the piezoelectric material is increased to 10 14 It is stipulated to be Ω·cm or less. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Special Publication No. 2015-503853 [Patent Document 2] JP 2019-129195 A [Patent Document 3] JP 2004-336600 A Summary of the Invention [Problem to be solved by the invention]

[0010] There is a demand for further improvement in the performance of the above-mentioned substrates for high frequency devices.

[0011] The present invention has been made in order to solve the above-mentioned problems, and has an object to provide a substrate for a high frequency device that uses diamond having excellent high frequency characteristics, and a method for manufacturing a substrate for a high frequency device that uses diamond having excellent high frequency characteristics. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides a substrate for a high frequency device, comprising a support substrate having an uneven surface, a diamond layer on the surface of the support substrate, and a silicon oxide film layer on the diamond layer.

[0013] By using diamond, it is expected that the heat dissipation characteristics will be improved by utilizing the high thermal conductivity of diamond, and that the high sound speed of all substances will improve the high frequency characteristics. In addition, by providing a silicon oxide film layer on the diamond layer, it becomes a substrate for high frequency devices with further insulating properties.

[0014] In the present invention, it is preferable that the surface of the supporting substrate has a surface roughness (Sa) of 1 nm or more as measured by AFM.

[0015] Such a substrate for a high frequency device is preferable because the carrier mobility in the supporting substrate is reduced.

[0016] In the present invention, the support substrate having the irregularities on its surface preferably has a resistivity of 500 Ω·cm or more.

[0017] By using a support substrate having such a high resistivity, it is possible to obtain a substrate for a high frequency device having superior high frequency characteristics.

[0018] The present invention also provides a method for producing a substrate for a high frequency device, comprising the steps of: providing a support substrate; forming projections and recesses on a surface of the support substrate; forming a diamond layer on the surface of the support substrate; forming a silicon oxide layer on the diamond layer; The present invention provides a method for producing a substrate for a high frequency device having the above structure.

[0019] By using diamond, it is expected that the heat dissipation characteristics can be improved by utilizing the high thermal conductivity of diamond, and by using a material with the highest sound velocity among all substances, it is possible to manufacture a substrate for a high frequency device with improved high frequency characteristics. Furthermore, by forming a silicon oxide film layer on the diamond layer, it is expected that insulation characteristics can be obtained.

[0020] In the present invention, the step of forming projections and recesses on the surface of the supporting substrate is preferably a step of forming the roughness such that the roughness (Sa) of the surface of the supporting substrate measured by AFM is 1 nm or more.

[0021] Such a substrate for a high frequency device is preferable because the carrier mobility in the supporting substrate is reduced.

[0022] In the present invention, the resistivity of the supporting substrate is preferably 500 Ω·cm or more.

[0023] By using a support substrate having such a high resistivity, a substrate for a high frequency device having better high frequency characteristics can be manufactured. Effect of the Invention

[0024] As described above, the use of diamond in the substrate for high frequency devices of the present invention makes it possible to improve heat dissipation characteristics by utilizing the high thermal conductivity of diamond, to have the highest sound speed of any substance, and to have a highly insulating silicon oxide film, thereby improving high frequency characteristics.

[0025] Furthermore, the method of manufacturing a high frequency device substrate according to the present invention uses diamond, which improves heat dissipation characteristics by utilizing the high thermal conductivity of diamond, and which has the highest sound speed of any material and a highly insulating silicon oxide film, making it possible to manufacture a high frequency device substrate with improved high frequency characteristics. [Brief description of the drawings]

[0026] [Figure 1] 1 is a schematic diagram showing an example of a substrate for a high-frequency device according to the present invention; FIG. [Diagram 2] FIG. 1 is a schematic flow diagram showing an example of a method for producing a high frequency device substrate according to the present invention. [Diagram 3] FIG. 1 is a schematic plan view of an example of a Co-Planar Waveguide (CPW) for evaluating second harmonic characteristics. [Figure 4] FIG. 4 is a cross-sectional view of the CPW taken along line XX in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] As described above, there is a demand for development of a substrate for a high frequency device having excellent high frequency characteristics, and a manufacturing method for manufacturing such a substrate for a high frequency device.

[0028] Therefore, as a result of extensive investigation into the above problems, the inventors have found that it is possible to improve high frequency characteristics by using, as a high frequency device substrate, a support substrate having an uneven surface, a diamond layer laminated on the surface, and a silicon oxide film further laminated on the diamond layer.

[0029] That is, the present invention is a substrate for a high frequency device, comprising a support substrate having an uneven surface, a diamond layer on the surface of the support substrate, and a silicon oxide film layer on the diamond layer.

[0030] The present invention also provides a method for producing a substrate for a high frequency device, comprising the steps of: providing a support substrate; forming projections and recesses on a surface of the support substrate; forming a diamond layer on the surface of the support substrate; forming a silicon oxide layer on the diamond layer; The present invention relates to a method for producing a high frequency device substrate having the above structure.

[0031] In addition, Patent Document 3 discloses a structure in which a piezoelectric film (ZnO film in the example) is formed on diamond grown on a silicon substrate. However, the resistivity of the silicon substrate is not specified, the surface of the silicon substrate is also smooth, and the electrical resistivity of the piezoelectric layer laminated on the diamond is 10 14 Electrical resistivity of silicon oxide film (10 15 Ω cm or more, e.g. 10 17 The value is smaller than the value of the dielectric constant (Ω·cm). The structure and configuration are different from those of the present invention.

[0032] The present invention will be described in detail below, but the present invention is not limited thereto.

[0033] [Substrates for high frequency devices] The substrate for a high frequency device of the present invention is characterized by comprising a support substrate having an uneven surface, a diamond layer laminated on the surface of the support substrate, and a silicon oxide film layer further laminated on the diamond layer.

[0034] In other words, the present invention is a substrate for high frequency devices that uses diamond to improve heat dissipation characteristics by utilizing the high thermal conductivity of diamond, and that improves high frequency characteristics by laminating a silicon oxide film that has the highest sound speed of any material and has excellent insulating properties.

[0035] The surface of the support substrate is provided with irregularities in order to reduce carrier mobility in the support substrate, and it is preferable that the irregularities have a size Sa of 1 nm or more as measured by AFM.

[0036] The resistivity of the support substrate is desirably 500 Ω·cm or more. By using a support substrate with such high resistivity, it is possible to obtain a substrate for a high frequency device having superior high frequency characteristics.

[0037] Next, an example of the substrate for a high frequency device of the present invention will be specifically described with reference to FIG.

[0038] 1 shows a cross-sectional view of a high frequency device substrate 10 of the present invention. The high frequency device substrate 10 includes a support substrate 1, a diamond layer 3, and a silicon oxide film layer 4.

[0039] The unevenness 2 is formed on the surface of the support substrate 1 and serves to hold the electric charge formed between the support substrate 1 and the diamond layer 3 so that it does not move due to application of high frequency waves.

[0040] By stacking the silicon oxide layer 4, a structure similar to an SOI structure is obtained. The high insulating properties of this silicon oxide layer 4, together with the diamond layer 3 and the unevenness acting as carrier traps at the interface, make it possible to block high-frequency signals that flow through the support substrate 1 and reduce distortion of the high-frequency signals.

[0041] It can also be said that the high frequency device substrate 10 has a structure in which a support substrate 1 having an uneven surface, a diamond layer 3, and a silicon oxide film layer 4 are laminated in this order.

[0042] [Method for manufacturing a substrate for a high frequency device] The method for manufacturing a high frequency device substrate of the present invention includes the steps of preparing a support substrate, forming irregularities on the surface of the support substrate, forming a diamond layer on the surface of the support substrate, and forming a silicon oxide film layer on the diamond layer.

[0043] In other words, the present invention is a method for manufacturing a substrate for a high frequency device, which is characterized by using diamond to improve heat dissipation characteristics by taking advantage of the high thermal conductivity of diamond, the property of having the highest sound speed of any substance, and the use of a silicon oxide film layer with high insulating properties to improve high frequency characteristics.

[0044] There are various known methods for synthesizing diamond layers, and for semiconductor substrate applications, there are CVD (Chemical Vapor Deposition) methods such as microwave plasma and hot filament. Among these, the hot filament method is preferred because it can be applied to large diameter substrates.

[0045] The hot filament method is a method in which a substrate is placed in a reduced pressure reaction vessel, methane and hydrogen are introduced as gases, and an electric current is applied to a tungsten filament placed above the substrate to generate high heat, which decomposes and activates the gases to grow diamond.

[0046] When providing unevenness on the surface of the supporting substrate in order to reduce carrier mobility in the supporting substrate, it is preferable that the unevenness has a value of Sa=1 nm or more as measured by AFM.

[0047] The method for forming the unevenness is not particularly limited, but it can be formed, for example, by grinding the surface of the support substrate.

[0048] The unevenness at this time not only serves to reduce the carrier mobility, but also to act as nuclei during diamond growth.

[0049] Conventional thermal oxidation cannot be used to form the silicon oxide film on the diamond layer (because the diamond would be oxidized), so low-temperature film formation methods such as plasma CVD and ALD are preferred.

[0050] Furthermore, it is desirable for the resistivity of the support substrate to be 500 Ω·cm or more. By using a support substrate having such a high resistivity, it is possible to manufacture a high frequency device substrate having superior high frequency characteristics.

[0051] Next, an example of a method for producing a substrate for a high frequency device according to the present invention will be specifically described with reference to FIG.

[0052] First, a support substrate 1 is prepared. Next, the projections and recesses 2 are formed on the surface of this support substrate 1.

[0053] Next, a diamond layer 3 is formed on the irregularities 2 on the surface of the support substrate 1 .

[0054] Next, a silicon oxide film layer 4 is further laminated on the diamond layer 3, whereby a high frequency device substrate 10 can be obtained.

[0055] In this manner, a high frequency device substrate 10 can be obtained, which is composed of a support substrate 1 having projections and recesses 2 on its surface, a diamond layer 3, and a silicon oxide film layer 4, as shown in FIGS. EXAMPLES

[0056] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0057] [Example] A boron-doped high resistivity silicon single crystal substrate (8000 Ω cm) with a diameter of 300 mm was prepared, and its surface was ground using a #8000 grinding wheel to produce a substrate with a surface roughness of Sa = 1 nm. Next, methane (CH 4 ) and hydrogen (H 2) as the raw material, placed in a hot filament CVD device, filament temperature: 2200°C, H 2 Flow rate: 10SLM, CH 4 A diamond layer was formed by growing for 4 hours under the conditions of concentration: 3%, substrate temperature: 850°C, and 5 Torr (667 Pa). After that, a silicon oxide film of 400 nm was formed by growing for 10 minutes using a plasma CVD device with TEOS (tetraethoxysilane) as the raw material, TEOS at 40 sccm, substrate temperature: 350°C, and 100 Torr (13,332 Pa).

[0058] An element was fabricated in which a CPW (line length: 2200 μm) was formed with an aluminum electrode on the substrate having the silicon oxide film, diamond layer, and silicon single crystal substrate thus fabricated. Then, the second harmonic characteristics (2HD characteristics) (frequency: 1 GHz, input output: 15 dBm) were measured. As a result, the 2HD characteristics were -113 dBm, which was an improvement over the comparative example described below.

[0059] [Comparative Example] A boron-doped high-resistivity silicon single crystal substrate (8000 Ω·cm) with a diameter of 300 mm was prepared as a support substrate, and a polysilicon layer of 1.8 μm was grown on this high-resistivity silicon single crystal substrate at 1050 °C. Next, a silicon single crystal substrate with a 400 nm thermal oxide film was prepared and bonded to the high-resistivity silicon single crystal substrate on which the polysilicon layer had been formed. After that, part of the silicon single crystal substrate was removed and the 400 nm thermal oxide film was transferred to the support substrate, producing a TR-SOI substrate with a polysilicon layer as an intermediate layer (trap rich layer) on the high-resistivity silicon single crystal substrate and a thermal oxide film as an insulating film.

[0060] After etching the SOI layer of this TR-SOI substrate with NaOH, an element was fabricated in which a CPW (line length: 2200 μm) was formed with an aluminum electrode on the exposed insulating film. Then, the second harmonic characteristics (2HD characteristics) (frequency: 1 GHz, input output: 15 dBm) were measured. As a result, the 2HD of the comparative substrate was -93 dBm.

[0061] The results shown above demonstrate that a substrate for high frequency devices, which has an uneven surface on which a diamond and silicon oxide film are formed by CVD, exhibits excellent high frequency characteristics.

[0062] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, 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 in the technical scope of the present invention. [Explanation of symbols]

[0063] 1...support substrate; 2...protrusions; 3...diamond layer; 4...silicon oxide film layer, 5...CPW, 6...element, 10...high frequency device substrate, 30...substrate to be measured, 60a...metal electrode, 60b...central metal electrode, 60c...electric field, 60d...magnetic field.

Claims

1. A substrate for a high frequency device, comprising: a support substrate having an uneven surface formed on a silicon single crystal substrate having a diameter of 300 mm; a diamond layer formed on the uneven surface of the support substrate; and a silicon oxide film layer formed on the surface of the diamond layer; The support substrate having an uneven surface has a resistivity of 500 Ω cm or more, The surface of the support substrate has a surface roughness (Sa) of 1 nm or more (excluding 50 to 5000 Å) measured by AFM.

2. A method for manufacturing a high frequency device substrate, comprising the steps of: preparing a silicon single crystal substrate having a diameter of 300 mm as a support substrate; forming projections and recesses on a surface of the support substrate; forming a diamond layer on the textured surface of the support substrate; forming a silicon oxide layer on a surface of the diamond layer; having The resistivity of the support substrate is set to 500 Ω cm or more, The method for manufacturing a high frequency device substrate, characterized in that the step of forming projections and recesses on the surface of the support substrate is a step of forming the roughness such that the roughness (Sa) of the surface of the support substrate measured by AFM is 1 nm or more (excluding 50 to 5000 Å).

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