Compound semiconductor amplifiers and circuit modules

Abstract

To suppress electromagnetic wave propagation while also reducing heat generation.SOLUTION: In a compound semiconductor amplifier having a compound semiconductor and an amplifier on an upper surface of a semi-insulating substrate, the semi-insulating substrate has a substrate thickness within a second range of wavelengths at a first frequency and a metal layer on an underside thereof having a sheet resistance value in a third range, the first frequency is a maximum frequency of frequencies used in the compound semiconductor amplifier, the second range is 1 / 12 to 1 / 2 the wavelength of the first frequency, and the third range is 3 to 1000 ohms.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] The present invention relates to a compound semiconductor amplifier and a circuit module.

Background Art

[0002] In next-generation communication (e.g., Beyond 5G / 6G), utilization of radio waves in the sub-terahertz band is being considered to achieve a communication speed of 100 Gbps or more. Therefore, compound semiconductor amplifiers have attracted attention. Since compound semiconductor amplifiers can operate at higher frequencies and with higher output than silicon-based amplifiers, they are expected to be applied to next-generation communication as sub-terahertz band semiconductor amplifiers.

[0003] On the other hand, in order to stabilize the high-frequency and high-output characteristics of a semiconductor amplifier used in the sub-terahertz band (sub-terahertz band semiconductor amplifier), it is important to suppress unnecessary electromagnetic wave radiation in a very wide frequency band, for example, 250 - 300 GHz. Furthermore, the power-added efficiency of a sub-terahertz band semiconductor amplifier is a few percent, and most of the input power is converted into heat, increasing the amount of heat generated. In addition, in mobile communication, beam control by an array antenna is essential. However, in this frequency band, the size of a sub-terahertz band semiconductor amplifier exceeds half of the wavelength (λ / 2) of air (at a certain frequency wavelength in air). Therefore, a three-dimensional stacked antenna array structure has been proposed, which is more difficult to form a heat dissipation structure (path) of the amplifier than the planar array antenna structure usually used in the millimeter wave band. For this reason, the heat dissipation structure of a sub-terahertz band semiconductor amplifier is important.

[0004] Examples of subterahertz semiconductor amplifiers include high electron mobility transistors (InP-based HEMTs) with an indium aluminum arsenide (InAlAs) electron supply layer / indium gallium arsenide (InGaAs) channel layer formed on an indium phosphide (InP) substrate, HEMTs (metamorphic HEMTs, mHEMTs) with an InAlAs electron supply layer / InGaAs channel layer formed on a gallium arsenide (GaAs) substrate via a metamorphic buffer layer, and heterojunction bipolar transistors (InP-based HBTs) with an InP emitter layer / gallium arsenide antimony (GaAsSb) base layer / In(Al)GaAs collector layer formed on an InP substrate. These compound semiconductor amplifiers are capable of higher frequency and higher output operation than silicon-based amplifiers, and are therefore expected to be applied to Beyond 5G / 6G.

[0005] The following patent documents describe the technology related to amplifiers. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2007-165430 [Patent Document 2] Japanese Patent Publication No. 2011-77557 [Patent Document 3] Japanese Patent Publication No. 2007-165739 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, especially in frequency bands above 250 GHz, two problems exist: transmission loss due to electromagnetic wave propagation within the semi-insulating substrate forming these compound semiconductor amplifiers, and increased heat generation due to a significant decrease in power addition efficiency. The thickness of the semi-insulating substrate forming the sub-terahertz compound semiconductor amplifier is inversely related to these two problems, making a solution difficult.

[0008] Therefore, one disclosure provides a compound semiconductor amplifier and circuit module that suppress electromagnetic wave propagation while also suppressing heat generation. [Means for solving the problem]

[0009] A compound semiconductor amplifier having a compound semiconductor and an amplifier on the upper side of a semi-insulating substrate, wherein the semi-insulating substrate has a substrate thickness that corresponds to a second range of wavelengths internally at a first frequency, and has a metal layer on its lower surface whose sheet resistance is in a third range, the first frequency being the maximum frequency used in the compound semiconductor amplifier, the second range being from 1 / 12 to 1 / 2 of the wavelength of the first frequency, and the third range being from 3 to 1000 ohms. [Effects of the Invention]

[0010] One disclosure allows for suppressing both electromagnetic wave propagation and heat generation. [Brief explanation of the drawing]

[0011] [Figure 1A] Figure 1A shows an example of a cross-sectional view of a semiconductor amplifier 100. [Figure 1B] Figure 1B shows an example of a top view of a semiconductor amplifier 100. [Figure 2A] Figure 2A shows an example of the simulation results in the first embodiment. [Figure 2B] Figure 2B shows an example of the simulation results in the first embodiment. [Figure 2C] Figure 2C shows an example of the simulation results in the first embodiment. [Figure 2D] Figure 2D shows an example of the simulation results in the first embodiment. [Figure 3A] Figure 3A shows an example of the manufacturing process for the semiconductor amplifier 100 in the first embodiment. [Figure 3B] Figure 3B shows an example of the manufacturing process for the semiconductor amplifier 100 in the first embodiment. [Figure 3C] FIG. 3C is a diagram showing an example of a manufacturing process of the semiconductor amplifier 100 in the first embodiment. [Figure 3D] FIG. 3D is a diagram showing an example of a manufacturing process of the semiconductor amplifier 100 in the first embodiment. [Figure 4A] FIG. 4A is a diagram showing an example of a cross-sectional view of the semiconductor amplifier 100 in the second embodiment. [Figure 4B] FIG. 4B is a diagram showing an example of a top view of the semiconductor amplifier 100 in the second embodiment. [Figure 5A] FIG. 5A is a diagram showing an example of a simulation result in the second embodiment. [Figure 5B] FIG. 5B is a diagram showing an example of a simulation result in the second embodiment. [Figure 5C] FIG. 5C is a diagram showing an example of a simulation result in the second embodiment. [Figure 5D] FIG. 5D is a diagram showing an example of a simulation result in the second embodiment. [Figure 5E] FIG. 5E is a diagram showing an example of a simulation result in the second embodiment. [Figure 5F] FIG. 5F is a diagram showing an example of a simulation result in the second embodiment. [Figure 5G] FIG. 5G is a diagram showing an example of a simulation result in the second embodiment. [Figure 5H] FIG. 5H is a diagram showing an example of a simulation result in the second embodiment. [Figure 6A] FIG. 6A is a diagram showing an example of a manufacturing process of the semiconductor amplifier 100 in the second embodiment. [Figure 6B] FIG. 6B is a diagram showing an example of a manufacturing process of the semiconductor amplifier 100 in the second embodiment. [Figure 6C] FIG. 6C is a diagram showing an example of a manufacturing process of the semiconductor amplifier 100 in the second embodiment. [Figure 6D]Figure 6D shows an example of the manufacturing process for the semiconductor amplifier 100 in the second embodiment. [Figure 6E] Figure 6E shows an example of the manufacturing process for the semiconductor amplifier 100 in the second embodiment. [Figure 6F] Figure 6F shows an example of the manufacturing process for the semiconductor amplifier 100 in the second embodiment. [Figure 7] Figure 7 shows an example of a conceptual diagram of a three-dimensional stacked structure of an amplifier-integrated array antenna. [Figure 8] Figure 8 shows an example of a circuit module in which a chip configured according to the second embodiment is flip-chip mounted on a high-frequency circuit board. [Figure 9] Figure 9 shows an example of a circuit module in which the back surface of a chip configured in the second embodiment is mounted on a high-frequency circuit board. [Figure 10] Figure 10 shows an example of Table 1, which illustrates the characteristics of the components used in the substrate. [Modes for carrying out the invention]

[0012] [First Embodiment] A first embodiment will be described.

[0013] <Example of semiconductor amplifier configuration> Figure 1A shows an example of a cross-sectional view of the semiconductor amplifier 100, and Figure 1B shows an example of a top view of the semiconductor amplifier 100.

[0014] The semiconductor amplifier 100 includes, for example, a semi-insulating substrate 10, a compound semiconductor epitaxial layer 11 grown on the semi-insulating substrate 10, an amplifier 12 fabricated on the compound semiconductor epitaxial layer 11, a wiring layer consisting of microstrip wiring 14 and ground wiring 15 formed on the interlayer insulating film 13 on the compound semiconductor epitaxial layer 11, and a metal layer 16. The metal layer 16 is deposited on the back surface of the semi-insulating substrate 10, which has been thinned to a degree of λ / 4 to λ / 2 of a predetermined maximum frequency, with a sheet resistance of 6 to 1000 Ω / □. For example, in the case of an InP substrate or GaAs substrate with a dielectric constant of about 12 at 300 GHz, the substrate thickness of the metal layer 16 is about 75 to 150 μm. The predetermined maximum frequency is, for example, the maximum value of the frequency band of the transmitted radio wave when the semiconductor amplifier 100 is used as an antenna. Alternatively, the predetermined maximum frequency is, for example, the maximum value of the frequency band at the output (or input) of the semiconductor amplifier 100.

[0015] The effects of a configuration in which a metal layer 16 with a sheet resistance of 6 to 1000 Ω / □ is placed on the back surface of a semi-insulating substrate 10 on which a semiconductor amplifier 100 is formed will be explained.

[0016] Figure 2A shows an example of simulation results of the sheet resistance dependence of the transmission characteristics of a microstrip wiring 14 formed on a semi-insulating substrate 10 having a metal layer 16 on the back surface of the substrate.

[0017] The horizontal axis represents frequency, and the vertical axis represents maximum available gain (MAG). The semi-insulating substrate 10 was, for example, an InP substrate. The thickness of the semi-insulating substrate (t1) was, for example, 75 μm. When there is no metal layer 16 on the back surface of the semi-insulating substrate, there is a frequency in the 250-350 GHz range where the MAG drops significantly. This is because propagation occurs within the semi-insulating substrate 10 at certain frequency bands, resulting in transmission loss.

[0018] Figure 2B shows an example of an enlarged view of Figure 2A at 250-300 GHz. As shown in Figure 2B, if the sheet resistance (Rs) of the metal layer 16 placed on the back surface of the semi-insulating substrate is in the range of 5.5 to 1090 Ω / □, the transmission loss due to propagation within the substrate at around 260 GHz is suppressed compared to the case where the metal layer 16 is absent. This is because when electromagnetic waves are applied to the metal layer 16 with a sheet resistance of about 6 to 1000 Ω / □, a conduction current flows, the energy of the electromagnetic waves is converted into heat, and the electromagnetic waves that bend around it are absorbed without being reflected, thereby suppressing electromagnetic wave propagation within the semi-insulating substrate.

[0019] On the other hand, if the sheet resistance of the metal layer 16 becomes less than 1 Ω / □, for example, its metallic behavior may become stronger, causing reflection at the interface between the metal layer 16 and the semi-insulating substrate 10, thereby increasing losses due to electromagnetic wave propagation within the substrate. For this reason, a preferred sheet resistance is, for example, 10.9 to 10⁹ Ω / □.

[0020] Figure 2C shows an example of simulation results for the dependence of the transmission characteristics of a microstrip wiring 14 formed on a semi-insulating substrate 10 having a metal layer 16 on the back surface of the substrate on the semi-insulating substrate thickness. The horizontal axis is Frequency and the vertical axis is MAG. The semi-insulating substrate 10 is, for example, an InP substrate. The sheet resistance of the metal layer 16 is, for example, 55Ω / □. When the semi-insulating substrate thickness (t1) is in the range of 50 to 150 μm, the loss due to electromagnetic wave propagation within the substrate is suppressed and there is almost no difference in transmission loss. However, when the semi-insulating substrate thickness is thinner than 25 μm or thicker than 150 μm, the loss in the 300 GHz band increases. This is because, when it is thinner than 25 μm, electromagnetic waves other than unwanted radiation waves are absorbed by the metal layer 16. Also, this is because when it is thicker than 150 μm, the absorption of unwanted electromagnetic waves by the metal layer 16 becomes weaker.

[0021] Furthermore, Figure 2D shows an example of simulation results for the dependence of the device thermal resistance of a flip-chip mounted compound semiconductor amplifier 100 on the thickness of a semi-insulating substrate. The sub-terahertz compound semiconductor amplifier was assumed to have an output of 10 mW and an efficiency of 4.8%, with a heat source of 0.2 W. The semi-insulating substrate 10 was, for example, an InP substrate. In the conventional millimeter-wave band, such as the 77 GHz band used in automotive collision avoidance radar, the λ / 4 within the semi-insulating substrate is approximately 280 μm. In this frequency band, the device thermal resistance can be assumed to be almost constant. However, in the sub-terahertz band, for example at 300 GHz, without using the metal layer 16, the device thermal resistance increases sharply when the substrate thickness is reduced to approximately 25 μm, which is sufficient to suppress electromagnetic wave propagation within the substrate. This is because, when the thickness of the semi-insulating substrate 10, which has a thermal conductivity of less than 100 W / mK, is less than 75 μm, heat reaches the back surface of the substrate before it can sufficiently diffuse laterally within the substrate, resulting in a smaller heat radiation area and degraded heat dissipation characteristics. However, by placing a metal layer 16 on the back surface of the substrate, the thickness of the semi-insulating substrate can be increased to 150 μm, thereby promoting heat diffusion within the semi-insulating substrate and improving heat dissipation characteristics.

[0022] Based on the above, in a configuration in which a metal layer 16 with a sheet resistance of 6 to 1000 Ω / □ is placed on the back surface of a semi-insulating substrate 10 on which a compound semiconductor amplifier is formed, the semi-insulating substrate thickness that achieves both electromagnetic wave propagation suppression and heat dissipation is 75 to 150 μm, which corresponds to approximately λ / 4 to λ / 2 at a predetermined maximum frequency of 300 GHz.

[0023] <Example of semiconductor amplifier manufacturing process> Figure 3 shows an example of the manufacturing process for semiconductor amplifier 100. First, as shown in Figure 3A, a wafer is fabricated using a BCB interlayer insulating film approximately 6 μm thick, which has a gate electrode, source electrode, drain electrode, MIM capacitor, NiCr resistor, etc., an amplifier 12, and a ground microstrip wiring structure, on top of the compound semiconductor epitaxial layer 11 made of an InP-based HEMT structure with a thickness of approximately 0.5 μm.

[0024] Next, as shown in Figure 3B, adhesive is applied to the wafer surface and attached to the support substrate. Then, the back surface of the InP substrate is ground to reduce the InP substrate thickness to 100 μm. The substrate thickness can be in the range of, for example, 75 to 150 μm. Chemical mechanical polishing (CMP) may or may not be performed. If CMP is performed, the substrate thickness after grinding is, for example, the sum of the final substrate thickness and the film thickness removed by CMP. Specifically, for example, if 10 μm is removed by CMP, and the final substrate thickness is 100 μm, the substrate thickness after grinding will be 110 μm.

[0025] Next, as shown in Figure 3C, titanium (Ti) is deposited on the back surface of the InP substrate at a thickness of 13 nm using methods such as vacuum deposition or sputtering. After removal from the vacuum apparatus, the Ti layer undergoes natural oxidation of approximately 3 nm, resulting in a sheet resistance of approximately 55 Ω / □.

[0026] Next, as shown in Figure 3D, the wafer is peeled from the support substrate and the adhesive is removed with an organic solvent. Then, the back side of the wafer is attached to dicing tape and chipped using conventional blade dicing.

[0027] In the example above, an InP-based HEMT on an InP substrate was used, but an InP-based HBT on an InP substrate, an mHEMT on a GaAs substrate, or a GaN-based HEMT on gallium nitride (GaN), aluminum nitride (AlN), or SiC can also be used. Therefore, the semi-insulating substrate 10 can be made of GaAs, InP, GaN, AlN, or SiC.

[0028] Furthermore, although the above example was described using microstrip wiring 14, coplanar and grounded coplanar wiring structures are also acceptable. In addition, as the interlayer insulating film 13, materials other than BCB, such as methyl silsesquioxane (MSQ) or polyimide, can be used.

[0029] As the metal layer 16, materials other than Ti in the above example may be used, such as W, Mo, Ta, NiCr, Cr, Pt, Al, Au, Cu, Ag, etc. Alternatively, these may be stacked. The preferred thickness of the metal layer 16 is 6 nm or less for W, 20 nm or less for Ta, 3 nm or less for Au, 3 nm or less for Cu, 3 nm or less for Ag, 3 nm or less for Al, 20 nm or less for Cr, 20 nm or less for Pt, 10 nm or less for Mo, and 200 nm or less for NiCr. However, since a native oxide film of several nanometers is formed, the thickness may also be determined by the resulting sheet resistance.

[0030] The compound semiconductor amplifier 100 fabricated as described above can achieve good heat dissipation characteristics while suppressing electromagnetic wave propagation within the semi-insulating substrate.

[0031] [Second Embodiment] A second embodiment will now be described.

[0032] <Example of semiconductor amplifier configuration> Figure 4 shows an example of the configuration of the semiconductor amplifier 100 in the second embodiment. Figure 4A shows an example of a cross-sectional view of the semiconductor amplifier 100, and Figure 4B shows an example of a top view of the semiconductor amplifier 100.

[0033] The semiconductor amplifier 100, for example, has a high heat dissipation substrate 17 in addition to the semiconductor amplifier 100 of the first embodiment. The semiconductor amplifier 100 is formed by joining a semi-insulating substrate 10, which has been thinned to a degree equivalent to λ / 12 to λ / 2 of a predetermined maximum frequency, with a high heat dissipation substrate that has a higher thermal conductivity than the semi-insulating substrate 10 and equivalent or better insulation properties, using a metal layer 16 with a sheet resistance of 3 to 1000 Ω / □.

[0034] For the semi-insulating substrate 10, if it is an InP substrate or a GaAs substrate with a dielectric constant of about 12 at 300 GHz, the substrate thickness should be about 25 to 150 μm. For the high heat dissipation substrate, for example, a silicon carbide (SiC) substrate is used, which has higher thermal conductivity, higher resistivity (insulation), and lower dielectric loss than InP or GaAs substrates. The substrate thickness should be within 1λ of the high heat dissipation substrate. For example, in the case of a SiC substrate with a dielectric constant of 9.74 at 300 GHz (see Table 1 in Figure 10), the substrate thickness should be within about 300 μm. Other high heat dissipation substrates may include, for example, gallium nitride (GaN), aluminum nitride (AlN), diamond, etc. (see Table 1 in Figure 10).

[0035] Next, the effects of a configuration in which a metal layer 16 with a sheet resistance of 3 to 1000 Ω / □ is placed at the junction interface between the formed semi-insulating substrate 10 and a high heat dissipation substrate that has a higher thermal conductivity than the semi-insulating substrate 10 and equivalent or better insulation properties will be explained.

[0036] Figures 5A and 5B show examples of simulation results of the sheet resistance dependence of the metal layer 16 on the transmission characteristics of a microstrip wiring 14 formed on a semi-insulating substrate bonded to a high-heat-dissipation substrate with a metal layer 16. The horizontal axis is Frequency and the vertical axis is MAG. The semi-insulating substrate 10 is, for example, an InP substrate, and the high-heat-dissipation substrate is, for example, a SiC substrate. The thickness (t1) of the semi-insulating substrate 10 was 25 μm (a) and 75 μm (b), respectively, and the thickness (t2) of the high-heat-dissipation substrate was 100 μm.

[0037] As shown in Figure 5A, when the metal layer 16 is absent at the interface between the semi-insulating substrate 10 and the high heat dissipation substrate, there are several frequencies in the 250-350 GHz range where the MAG (magnetism gradient) drops significantly. This is because electromagnetic wave propagation occurs within the semi-insulating substrate 10 and the high heat dissipation substrate at specific frequency bands, resulting in transmission loss.

[0038] Figures 5C and 5D show examples of enlarged views of Figures 5A and 5B at 250-300 GHz, respectively. According to Figures 5A and 5B, if the sheet resistance (Rs) of the metal layer 16 at the interface between the semi-insulating substrate 10 and the high heat dissipation substrate is in the range of 2.75 to 1090 Ω / □, then transmission loss due to electromagnetic wave propagation within the substrate is suppressed more effectively than when the metal layer 16 is absent, even when the semi-insulating substrate thickness (t1) is 25 μm or 75 μm. However, when the sheet resistance of the metal layer 16 becomes approximately 1 Ω / □, the MAG decreases around 280 GHz for a semi-insulating substrate thickness (t1) of 25 μm and around 260 GHz for a semi-insulating substrate thickness (t1) of 75 μm. As a result, the preferred sheet resistance is, for example, 5.5 to 550 Ω / □ when t1 = 25 μm, and 11 to 55 Ω / □ when t1 = 75 μm.

[0039] Figures 5E and 5F show examples of simulation results of the dependence of the transmission characteristics of a microstrip wiring 14 formed on a semi-insulating substrate bonded to a high-heat-dissipation substrate with a metal layer 16 on the high-heat-dissipation substrate on the high-heat-dissipation substrate thickness. The horizontal axis is Frequency and the vertical axis is MAG. The semi-insulating substrate 10 is, for example, an InP substrate, and the high-heat-dissipation substrate is, for example, a SiC substrate. The semi-insulating substrate thickness (t1) was, for example, 25 μm (e) and 75 μm (f). The sheet resistance of the metal layer 16 was, for example, 55 Ω / □. According to Figures 5E and 5F, it can be seen that when the high-heat-dissipation substrate thickness (t2) is in the range of 50 to 350 μm, the transmission loss due to electromagnetic wave propagation within the substrate can be suppressed for both semi-insulating substrate thicknesses (t1) of 25 μm and 75 μm.

[0040] Figure 5G shows an example of simulation results of the dependence of the transmission characteristics of a microstrip wiring 14 formed on a semi-insulating substrate bonded to a high-heat-dissipation substrate with a metal layer 16 on the semi-insulating substrate. The horizontal axis is Frequency and the vertical axis is MAG. The semi-insulating substrate 10 is, for example, an InP substrate, and the high-heat-dissipation substrate is, for example, a SiC substrate. The high-heat-dissipation substrate thickness (t2) was, for example, 100 μm. The sheet resistance of the metal layer 16 was, for example, 55 Ω / □. According to Figure 5G, it can be seen that when the semi-insulating substrate thickness (t1) is in the range of 50 to 150 μm, the loss due to electromagnetic wave propagation within the substrate is suppressed and there is almost no difference in transmission loss. However, it can be seen that when the semi-insulating substrate thickness is thinner than 25 μm or thicker than 150 μm, the transmission loss increases.

[0041] Furthermore, Figure 5H shows an example of simulation results for the dependence of the device thermal resistance of a compound semiconductor amplifier 100, formed on a semi-insulating substrate bonded to a high-heat-dissipation substrate with a metal layer 16, on the thickness of the high-heat-dissipation substrate. Similar to the first embodiment, a flip-chip mounting was used. Also, assuming an output of 10 mW and an efficiency of 4.8% for the subterahertz compound semiconductor amplifier, the heat source was set to 0.2 W. The semi-insulating substrate 10 was, for example, an InP substrate, and the high-heat-dissipation substrate was, for example, a SiC substrate. The thickness of the semi-insulating substrate (t1) was, for example, 25 μm and 75 μm. Also, assuming the use of surface-activated bonding (SAB) or atomic diffusion bonding (ADB) for bonding, the thermal resistance of the bonding interface was set to 5 × 10⁻⁶. -8 m 2The coefficient of heat dissipation is expressed as K / W. These bonding processes are carried out in a vacuum, and the bonding metal layer does not come into direct contact with air, thus preventing oxidation and stabilizing the sheet resistance. Figure 5H shows that the device thermal resistance decreases rapidly when the high heat dissipation substrate thickness (t2) is 30 μm or more. On the other hand, the device thermal resistance is lower when the semi-insulating substrate thickness (t1) is 25 μm than when it is 75 μm, which is different from the trend in the first embodiment. This is because heat dissipation is more efficient when heat is quickly transferred to the high heat dissipation substrate with high thermal conductivity (490 W / mK) via the bonding metal layer and then diffused laterally within the high heat dissipation substrate, rather than diffusing heat laterally within the semi-insulating substrate with low thermal conductivity (68 W / mK).

[0042] Based on the above, a semi-insulating substrate thickness that achieves both electromagnetic wave propagation suppression and heat dissipation is preferably, for example, 25 to 150 μm, which corresponds to approximately λ / 12 to λ / 2 at a predetermined maximum frequency of 300 GHz. Furthermore, a high heat dissipation substrate thickness is preferably, for example, 50 to 350 μm, which corresponds to approximately λ / 6 to 1λ at a predetermined maximum frequency of 300 GHz.

[0043] <Example of semiconductor amplifier manufacturing process> Figure 6 shows an example of the manufacturing process for the semiconductor amplifier 100. Note that the surface device formation in Figure 6A is the same as in Figure 3A in the first embodiment.

[0044] Next, as shown in Figure 6B, adhesive is applied to the wafer surface and attached to the support substrate. Then, the back surface of the InP substrate is ground to reduce the InP substrate thickness to 85 μm. Furthermore, 10 μm is removed by CMP to reduce the surface roughness (Ra) of the InP substrate to less than 1 nm. This results in a final InP substrate thickness of 75 μm. Alternatively, the final InP substrate thickness may be in the range of 25 to 150 μm.

[0045] On the other hand, as shown in Figure 6C, for the SiC substrate, which is a high heat dissipation substrate, adhesive is applied to the wafer surface and attached to the support substrate. Then, the SiC substrate is ground down to a thickness of 100 μm. Furthermore, the surface roughness (Ra) of the SiC substrate is reduced to less than 1 nm by CMP. Since the SiC substrate is an extremely hard material, it is hardly removed by CMP. As a result, the final SiC substrate thickness is also 100 μm.

[0046] Note that while the silicon (Si) side of the SiC substrate is considered the front and the carbon (C) side is considered the back, either side can be used. Also, if the final SiC substrate thickness is around 300 μm, the step of attaching it to a support substrate is not necessary. Furthermore, the SiC substrate thickness can be in the range of 50 to 350 μm.

[0047] Next, as shown in Figure 6D, atomic diffusion bonding is performed on the two wafers described above in a vacuum chamber. First, 5 nm of Ti is deposited simultaneously on the back surfaces of both wafers. Then, both wafers are pressed down with a predetermined pressure to bond the Ti layers deposited on the back surfaces of both wafers. Figure 6E shows an example after bonding.

[0048] In this case, a 10nm thick Ti layer is formed at the junction interface between the InP substrate and the SiC substrate, resulting in a sheet resistance of 55Ω / □. Furthermore, the Ti layer present at the junction interface only needs to be 100nm or less in thickness.

[0049] Next, as shown in Figure 6F, the bonded wafer is peeled off the support substrate, and the adhesive is removed with an organic solvent. Then, the back surface of the SiC substrate is attached to a dicing tape (not shown), and chipped using ultrasonic blade dicing.

[0050] In the above example, an InP-based HEMT on an InP substrate was used, but an InP-based HBT on an InP substrate, an mHEMT on a GaAs substrate, or a GaN-based HEMT on a GaN, AlN, or SiC substrate may also be used. When a GaAs or InP substrate is used as the semi-insulating substrate 10, GaN, AlN, SiC, or diamond can be used as the high-heat-dissipation substrate. When a GaN substrate is used as the semi-insulating substrate 10, AlN, SiC, or diamond can be used as the high-heat-dissipation substrate. When an AlN substrate is used as the semi-insulating substrate 10, SiC or diamond can be used as the high-heat-dissipation substrate. When a SiC substrate is used as the semi-insulating substrate 10, diamond can be used as the high-heat-dissipation substrate.

[0051] Furthermore, although the above example uses microstrip wiring 14 for explanation, coplanar and grounded coplanar wiring structures may also be used. In addition, as the interlayer insulating film 13, materials other than BCB, such as methyl silsesquioxane (MSQ) or polyimide, can be used.

[0052] Furthermore, as the metal layer 16, any material other than Ti may be used, such as W, Mo, Ta, NiCr, Cr, Pt, Al, Au, Cu, or Ag. Alternatively, these can be stacked. In this case, the thickness of the metal layer 16 after bonding should be 6 nm or less for W, 20 nm or less for Ta, 3 nm or less for Au, 3 nm or less for Cu, 3 nm or less for Ag, 3 nm or less for Al, 20 nm or less for Cr, 20 nm or less for Pt, 10 nm or less for Mo, and 200 nm or less for NiCr.

[0053] Furthermore, although atomic diffusion bonding technology was used for joining in the above example, it is also possible to deposit metal on the back surface of the wafer and then join using surface activation bonding technology.

[0054] The semiconductor amplifier 100 fabricated as described above makes it possible to suppress electromagnetic wave propagation within the semi-insulating substrate 10 and the high heat dissipation substrate while stabilizing the heat dissipation characteristics and the sheet resistance of the metal layer 16.

[0055] [Third Embodiment] A third embodiment will be described. In the third embodiment, an example of a circuit module applicable to a three-dimensional stacked structure of an amplifier-integrated array antenna will be described.

[0056] Figure 7 shows an example of a conceptual diagram of a three-dimensional stacked structure of an amplifier-integrated array antenna. It consists of four 1x4 amplifier-integrated array antennas, each with an antenna, compound semiconductor amplifier 100, and phase shifter or mixer, stacked vertically on a single high-frequency circuit board. In this structure, to suppress unwanted grating lobes, the antenna spacing should be less than one wavelength (λ) of air in both the horizontal and vertical directions. Preferably, it should be λ / 2. In other words, controlling the thickness in the vertical direction is crucial.

[0057] Figure 8 shows an example of a circuit module in which a chip configured according to the second embodiment is flip-chip mounted on a high-frequency circuit board. The high-frequency circuit board used is, for example, a Si substrate from the prior application (application number: 2022-056168), a back metal formed on the back surface of the Si substrate, a primary ground metal connected to the back metal by vias through the Si substrate, a resin layer such as polyimide formed on the primary ground metal, and a surface metal connected to the primary ground metal by vias penetrating the resin layer.

[0058] Furthermore, this high-frequency circuit board is supported from above and below by columns (not shown) made of silicon interposers or metal. In this case, the thickness of the high-frequency circuit board (s1) is 245 μm. The bump height (b1) is 15 μm. The device layer thickness (d1) is 10 μm in the case of an InP-based HEMT. The antenna spacing (a1) is 1 mm (1000 μm) when set to 1 λ at a predetermined maximum frequency of 300 GHz, and the difference is 730 μm. The thickness of the metal layer 16 is less than 0.2 μm at most, so it can be ignored. In the second embodiment, the sum of the SiC substrate thickness (t2) and the InP substrate thickness (t1) is at most 500 μm. On the other hand, when the antenna spacing (a1) is λ / 2 (500 μm), the difference is 230 μm. In the second embodiment, mounting is possible if the sum of the SiC substrate thickness (t2) and the InP substrate thickness (t1) is less than 230 μm. For example, even if the InP substrate thickness is 75 μm, the SiC substrate thickness can be up to 150 μm. In addition, a TIM (Thermal Interface Material) material may be sandwiched between the back surface of the flip-chip mounted amplifier 12 chip on the high-frequency circuit board and the high-frequency circuit board above it. Furthermore, since the substrate thickness of the chip in the configuration of the first embodiment is a maximum of 150 μm, it can be easily mounted.

[0059] Figure 9 shows an example of a circuit module in which the back surface of a chip configured according to the second embodiment is mounted on a high-frequency circuit board. The high-frequency circuit board uses a general LTCC (Low Temperature Co-fired Ceramics) substrate. This high-frequency circuit board is supported at the top and bottom by metal pillars (not shown). The high-frequency circuit board has a configuration in which multilayer wiring is embedded in the ceramic layer, a surface metal (ground only) connected to the back metal by vias, and a heat dissipation metal plate is embedded at a position where the surface metal and the surface of the compound semiconductor amplifier chip are flush (after subtracting the mounting material). The metal plate is made of copper (Cu). When the surface metal of the high-frequency circuit board and the microstrip and ground wiring of the compound semiconductor amplifier 100 are connected by wire bonding, the wiring height (w1) will be approximately 90 μm in loop height. If the antenna spacing (a1) is set to 1λ (1 mm) at a predetermined maximum frequency of 300 GHz, the difference will be 910 μm. To prevent contact with the metal backing of the upper high-frequency circuit board, a 10 μm margin is allowed, resulting in a high-frequency circuit board thickness (c1) of 900 μm. The device layer thickness (d1) is 10 μm in the case of an InP-based HEMT. When the amplifier chip is mounted on a metal plate with Ag paste, the mounting thickness (p1) is 25 μm. In the second embodiment, the sum of the SiC substrate thickness (t2) and the InP substrate thickness (t1) is at most 500 μm, so the metal plate thickness (m1) is 415 μm, which functions appropriately as a heat sink. On the other hand, when the antenna spacing (a1) is λ / 2 (500 μm), the high-frequency circuit board thickness (c1) becomes 400 μm. In this case, if the metal plate thickness (m1) is halved to 200 μm, the difference is 200 μm. In the second embodiment, mounting is possible if the sum of the SiC substrate thickness (t2) and the InP substrate thickness (t1) is less than 165 μm, which is obtained by subtracting the mounting thickness (p1) of 25 μm and the device layer thickness (d1) of 10 μm. For example, even if the SiC substrate thickness is 100 μm, the InP substrate thickness can be as low as 65 μm.

[0060] As described above, the circuit module in the third embodiment allows for the vertical stacking of high-frequency circuit boards on which semiconductor amplifiers configured in the first and second embodiments are mounted, with spacing of λ / 2 to λ of air between them. Therefore, beam control with suppressed grating lobes becomes possible with an array antenna to which the circuit module is applied.

[0061] In the third embodiment, by equipping a transceiver with an array antenna to which a circuit module is applied, it becomes possible to provide, for example, communication system equipment for Beyond 5G / 6G.

[0062] [Other embodiments] Each embodiment may be combined with others. For example, the circuit module in the third embodiment may contain both the semiconductor amplifier 100 in the first embodiment and the semiconductor amplifier 100 in the second embodiment, depending on the cost and intended use.

[0063] Furthermore, the components in each embodiment are not limited to the substances described in the examples. For example, components may be replaced with other substances having similar actions, effects, or properties. [Explanation of symbols]

[0064] 10: Semi-insulating substrate 11: Compound semiconductor epitaxial layer 12: Amplifier 13: Interlayer insulating film 14: Microstrip wiring 15: Ground wiring 16: Metal layer 17: High heat dissipation substrate 100: Compound semiconductor amplifier

Claims

1. A compound semiconductor amplifier having a compound semiconductor and an amplifier on the upper side of a semi-insulating substrate, The semi-insulating substrate has a substrate thickness that, at a first frequency, has a wavelength within a second range internally. The lower surface has a metal layer whose sheet resistance value is in the third range, The first frequency is the maximum frequency used in the compound semiconductor amplifier, The second range is 1 / 12 to 1 / 2 of the wavelength of the first frequency, The third range mentioned above is 3 to 1000 ohms. Compound semiconductor amplifier.

2. The second range is 1 / 4 to 1 / 2 of the wavelength of the first frequency, The third range is 6 to 1000 ohms. The compound semiconductor amplifier according to claim 1.

3. The metal layer has a high heat dissipation substrate on the opposite side of the semi-insulating substrate. The high heat dissipation substrate has a thermal conductivity higher than that of the semi-insulating substrate and a resistivity greater than or equal to that of the semi-insulating substrate. The compound semiconductor amplifier according to claim 1.

4. The components of the semi-insulating substrate include gallium arsenide, indium phosphide, gallium nitride, aluminum nitride, or silicon carbide. The compound semiconductor amplifier according to claim 1.

5. The components of the high heat dissipation substrate include gallium nitride, aluminum nitride, silicon carbide, or diamond. The compound semiconductor amplifier according to claim 3.

6. The high heat dissipation substrate has a substrate thickness that is 1 / 6 to 1 of the wavelength of the first frequency internally. The compound semiconductor amplifier according to claim 3.

7. The constituents of the metal layer include titanium, tungsten, molybdenum, tantalum, nichrome, chromium, platinum, aluminum, gold, copper, silver, or a laminate thereof. The compound semiconductor amplifier according to claim 1.

8. A circuit module comprising high-frequency circuit boards for mounting compound semiconductor amplifiers, stacked at a first frequency with intervals of 1 / 2 to 1 wavelength relative to the wavelength in air, The compound semiconductor amplifier has a compound semiconductor and an amplifier on the upper side of a semi-insulating substrate, and the semi-insulating substrate has a substrate thickness that corresponds to a second range of wavelengths internally at the first frequency, and has a metal layer on its lower surface whose sheet resistance value is in the third range. The first frequency is the maximum frequency used in the compound semiconductor amplifier, The second range is 1 / 12 to 1 / 2 of the wavelength of the first frequency, The third range mentioned above is 3 to 1000 ohms. Circuit module.

9. The metal layer has a high heat dissipation substrate on the opposite side of the semi-insulating substrate. The high heat dissipation substrate has a thermal conductivity higher than that of the semi-insulating substrate and a resistivity greater than or equal to that of the semi-insulating substrate. The sum of the thickness of the semi-insulating substrate and the thickness of the high heat dissipation substrate is within the fourth range. The circuit module according to claim 8.

10. The fourth range is 75 to 500 micrometers. The circuit module according to claim 9.

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