Method for manufacturing a bonded substrate and bonded substrate

Abstract

The objective is to provide a method for manufacturing a bonding substrate capable of reliably bonding a diamond film and a semiconductor material, and a bonding substrate for bonding a semiconductor material having a diamond film on the surface of the semiconductor substrate, which can be reliably bonded to the semiconductor material. [Solution] A method for manufacturing a bonded substrate by bonding a bonding substrate having a diamond film on the surface of a semiconductor substrate to a semiconductor material, comprising the steps of: preparing a bonding substrate by forming a diamond film on a semiconductor substrate using the semiconductor substrate as a seed substrate; determining the amount of warpage of the bonding substrate; selecting bonding substrates in which the thickness of the diamond film is greater than the amount of warpage of the bonding substrate; flattening the surface of the diamond film on the selected bonding substrates; and bonding the diamond film on the flattened bonding substrate to the semiconductor material.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing a bonded substrate and a bonded substrate. [Background technology]

[0002] Diamonds possess numerous excellent physical properties, leading to their diverse applications. For example, their high hardness—the hardest of all naturally occurring materials—makes them suitable for use as cutting tools, while their high refractive index and dispersion rate make them highly valued as gemstones. Furthermore, compared to silicon, silicon carbide, and gallium nitride, diamonds have a larger band gap, carrier mobility, and dielectric breakdown voltage, making them promising for power device applications. More recently, their high thermal conductivity has attracted attention as a heat dissipation material. While traditionally, heat dissipation materials included greases mixed with diamond powder, such as diamond grease, are used, recent research is exploring ways to improve device performance by bonding or depositing diamond films onto devices to lower their operating temperature.

[0003] Prior art will be mentioned. Patent document 1 describes a method for planarizing the surface roughness Ra of a diamond layer deposited on a silicon single crystal substrate to 3 nm or less, and then bonding it with a silicon single crystal.

[0004] Patent documents 1 and 2 describe that the warping increases as the thickness of the diamond layer deposited on the single-crystal silicon substrate increases, and therefore it is preferable to make the single-crystal silicon substrate thicker to prevent warping.

[0005] Patent document 3 describes growing single-crystal diamond on a single-crystal silicon substrate with a thickness of 0.03 mm to 20.00 mm. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-62020 [Patent Document 2] Japanese Patent Publication No. 2023-85098 [Patent Document 3] Japanese Patent Publication No. 2011-79683 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] As described above, methods have been proposed in which the surface of a diamond film is planarized before bonding it to a silicon single crystal. Furthermore, methods using a thick single-crystal silicon substrate have been proposed to reduce warping caused by diamond deposition. However, conventional techniques have suffered from a lack of detailed documentation regarding the bonding conditions.

[0008] For example, Patent Document 1 describes planarizing the surface roughness Ra of the diamond layer to 3 nm or less before bonding, but it does not adequately describe how to achieve a surface roughness Ra of 3 nm or less across the entire surface to be bonded.

[0009] Furthermore, while Patent Documents 1 to 3 describe reducing warpage by using a thick single-crystal silicon substrate, the details of the relationship between the diamond film thickness used for bonding and warpage are unclear and have not been sufficiently investigated.

[0010] The present invention has been made in view of the problems of the prior art described above, and aims to provide a method for manufacturing a bonding substrate that can reliably bond a diamond film and a semiconductor material, and a bonding substrate for bonding a semiconductor material having a diamond film on the surface of a semiconductor substrate, which can be reliably bonded to a semiconductor material. [Means for solving the problem]

[0011] The present invention has been made to achieve the above objective, and provides a method for manufacturing a bonded substrate by bonding a bonding substrate having a diamond film on the surface of a semiconductor substrate to a semiconductor material, comprising the steps of: preparing a bonding substrate by forming a diamond film on a semiconductor substrate using the semiconductor substrate as a seed substrate; determining the amount of warpage of the bonding substrate; selecting bonding substrates in which the thickness of the diamond film is greater than the amount of warpage of the bonding substrate; planarizing the surface of the diamond film on the selected bonding substrates; and bonding the diamond film on the planarized bonding substrate to the semiconductor material.

[0012] This method for manufacturing bonded substrates makes it possible to reliably bond a diamond film and a semiconductor material to produce a high-quality bonded substrate.

[0013] In this case, the method for manufacturing a bonding substrate can be such that the amount of warpage of the bonding substrate to be determined is one of the following: the measured amount of warpage of the bonded substrate that was manufactured, the measured amount of warpage of a monitor substrate manufactured in advance under the same conditions as the bonding substrate, or a value estimated using Stoney's equation based on elastic deformation theory.

[0014] This allows for more accurate and / or easier determination of the warp of the bonding substrate.

[0015] In this case, the semiconductor substrate can be one of silicon, aluminum oxide, silicon carbide, or magnesium oxide used as the manufacturing method for the bonded substrate.

[0016] This enables the stable and reliable deposition of diamond films on semiconductor substrates.

[0017] In this case, a method for manufacturing a bonded substrate can be used in which the thickness of the diamond film to be formed is 0.1 μm or more and 100 μm or less.

[0018] If the film thickness of the diamond film is 0.1 μm or more, it can be made more suitable for use as a heat dissipation material. Also, by setting the film thickness of the diamond film to 100 μm or less, it is possible to prevent the diamond film formation from taking too much time.

[0019] At this time, it can be a manufacturing method of a bonding substrate in which the diamond film is a polycrystalline diamond film.

[0020] As a result, since the growth conditions of the diamond film are relaxed, the growth of the diamond film becomes easier.

[0021] At this time, it can be a manufacturing method of a bonding substrate using a disk-shaped semiconductor substrate that does not have a notch and an orientation flat.

[0022] As a result, it is possible to prevent the diamond film from peeling off when flattening the diamond film.

[0023] At this time, it can be a manufacturing method of a bonding substrate in which the semiconductor material is any one of silicon, silicon germanium, indium phosphide, silicon carbide, gallium nitride, aluminum nitride, aluminum gallium nitride, gallium oxide, and germanium dioxide.

[0024] When a semiconductor device using these semiconductor materials is operated, the heat generated in the semiconductor device can be effectively dissipated by the bonded diamond, so that it is possible to manufacture a higher-performance semiconductor device in which the operating temperature of the semiconductor device is lowered.

[0025] At this time, it can be a manufacturing method of a bonding substrate using a semiconductor material having a semiconductor element.

[0026] By forming a semiconductor device in advance and then bonding it to the diamond film, it is possible to more stably prevent peeling at the interface between the semiconductor material and the diamond film.

[0027] In this case, the bonding process can be carried out by irradiating the surfaces of the diamond film and the semiconductor material to be bonded on the planarized bonding substrate with an ion beam or a neutral atomic beam, and then bringing the surfaces of the diamond film and the semiconductor material into contact to bond them.

[0028] This allows for a more reliable bonding between the diamond film and the semiconductor material.

[0029] In this case, the method for manufacturing a bonded substrate can be such that, after the bonding step, a step is performed to thin the semiconductor substrate of the bonding substrate.

[0030] By thinning the semiconductor substrate, the semiconductor substrate, which has higher thermal resistance compared to diamond, is eliminated or made thinner, thus improving the heat dissipation efficiency of the heat sink when a metal heat sink is attached to the back surface of the semiconductor substrate or diamond film. Furthermore, thinning the semiconductor substrate makes it easier to form vias in the diamond film, allowing power and signals to be supplied to the device formed on the semiconductor material from the side bonded to the diamond film.

[0031] The present invention has been made to achieve the above objective, and provides a bonding substrate for bonding with a semiconductor material, comprising a semiconductor substrate and a diamond film on the surface of the semiconductor substrate, wherein the thickness of the diamond film is greater than the amount of warpage of the bonding substrate.

[0032] This type of bonding substrate prevents the semiconductor substrate from being exposed when the surface of the diamond film is planarized, thus ensuring reliable bonding with the semiconductor material.

[0033] In this case, the semiconductor substrate can be a bonding substrate that is one of silicon, aluminum oxide, silicon carbide, or magnesium oxide.

[0034] If the semiconductor substrate is made of these materials, a diamond film can be deposited on the semiconductor substrate stably and reliably.

[0035] In this case, the bonding substrate can be one in which the thickness of the diamond film is 0.1 μm or more and 100 μm or less.

[0036] If the diamond film thickness is 0.1 μm or more, it can be used as a more stable and reliable heat dissipation material. Furthermore, if the diamond film thickness is 100 μm or less, the time required for diamond deposition can be prevented, resulting in higher productivity and lower costs.

[0037] In this case, the bonding substrate can be a polycrystalline diamond film.

[0038] This makes it easy to manufacture and low-cost.

[0039] In this case, the semiconductor substrate can be a bonding substrate that is disc-shaped and does not have notches or orientation flats.

[0040] This prevents the diamond film from peeling off when it is planarized. [Effects of the Invention]

[0041] As described above, the method for manufacturing a bonded substrate according to the present invention makes it possible to reliably bond a diamond film and a semiconductor material to manufacture a bonded substrate. The bonded substrate according to the present invention can reliably bond with a semiconductor material. [Brief explanation of the drawing]

[0042] [Figure 1] This figure shows a flow chart of the method for manufacturing a bonded substrate according to the present invention. [Figure 2] This figure shows a bonding substrate according to the present invention. [Figure 3]This figure shows a bonding substrate after planarization according to the present invention. [Figure 4] This figure shows a bonded substrate according to the present invention. [Figure 5] This figure shows a bonded substrate after the semiconductor substrate A has been thinned after bonding, according to the method for manufacturing a bonded substrate according to the present invention. [Figure 6] This figure shows the bonded substrate after the semiconductor substrate A has been removed following bonding, in the method for manufacturing a bonded substrate according to the present invention. [Figure 7] This figure shows an ultrasonic microscope image of the diamond film after polishing the surface and then bonding it with single-crystal gallium nitride at room temperature in Example 3. [Modes for carrying out the invention]

[0043] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0044] As described above, there was a need for a method for manufacturing a bonding substrate that can reliably bond a diamond film and a semiconductor material, and for a bonding substrate for bonding a semiconductor material having a diamond film on the surface of the semiconductor substrate, which can reliably bond to the semiconductor material.

[0045] As a result of diligent study on the above problems, the inventors have found that a method for manufacturing a bonded substrate by bonding a bonding substrate having a diamond film on the surface of a semiconductor substrate to a semiconductor material, the method comprising the steps of: preparing a bonding substrate by forming a diamond film on a semiconductor substrate using the semiconductor substrate as a seed substrate; determining the amount of warpage of the bonding substrate; selecting bonding substrates in which the thickness of the diamond film is greater than the amount of warpage of the bonding substrate; planarizing the surface of the diamond film on the selected bonding substrates; and bonding the diamond film on the planarized bonding substrate to the semiconductor material, thereby enabling reliable bonding of a diamond film and a semiconductor material to manufacture a bonded substrate, and thus completing the present invention.

[0046] The inventors have also discovered that a bonding substrate for bonding to a semiconductor material, comprising a semiconductor substrate and a diamond film on the surface of the semiconductor substrate, wherein the thickness of the diamond film is greater than the amount of warpage of the bonding substrate, can reliably bond to a semiconductor material, and thus completed the present invention.

[0047] The following explanation will be given with reference to the drawings.

[0048] [Bonded substrate] An example of a bonded substrate 100 according to the present invention is shown in Figure 4-6. The bonded substrate 100 according to the present invention comprises a diamond film 1 bonded to a semiconductor material B. As shown in Figure 4, the bonded substrate 100 according to the present invention may also comprise a semiconductor substrate A as the base for the diamond film 1, which is part of the bonding substrate 10. Furthermore, as shown in Figure 6, the bonded substrate 100 according to the present invention may have the semiconductor substrate A removed. For details of the diamond film 1, semiconductor substrate A, and semiconductor material B, please refer to the description of the method for manufacturing the bonded substrate. Also, matters described in the method for manufacturing the bonded substrate described later may be omitted here.

[0049] [Bonding board] An example of a bonding substrate 10 according to the present invention is shown in Figure 2. As shown in Figure 2, the bonding substrate 10 according to the present invention is a bonding substrate for bonding with a semiconductor material B, comprising a semiconductor substrate A and a diamond film 1 on the surface of the semiconductor substrate A. Furthermore, the thickness d of the diamond film 1 is greater than the warpage h of the bonding substrate 10 (d>h). Such a bonding substrate 10 according to the present invention can prevent the semiconductor substrate A from being exposed when the surface of the diamond film 1 is flattened, thus enabling reliable bonding with the semiconductor material B.

[0050] The semiconductor substrate A is preferably one of silicon, aluminum oxide, silicon carbide, or magnesium oxide. Such materials allow for stable and reliable deposition of a diamond film on the semiconductor substrate.

[0051] The semiconductor substrate A is preferably a disc-shaped substrate without notches or orientation flats. Such a substrate prevents the diamond film from peeling off near notches or orientation flats during the planarization process.

[0052] The thickness of the diamond film 1 is preferably 0.1 μm or more and 100 μm or less. If the thickness of the diamond film is 0.1 μm or more, it can be used as a more stable and reliable heat dissipation material. Also, if the thickness of the diamond film is 100 μm or less, it is possible to prevent the diamond film deposition process from taking too long, resulting in higher productivity and lower costs.

[0053] Furthermore, it is preferable that the diamond film 1 is a polycrystalline diamond film. Compared to single-crystal diamond, polycrystalline diamond allows for the easy production of large-diameter films, resulting in lower costs.

[0054] (Semiconductor materials) The semiconductor material B is not particularly limited in terms of material, shape, etc., as long as it contains a semiconductor. Preferably, the materials constituting semiconductor material B are silicon, silicon germanium, indium phosphide, silicon carbide, gallium nitride, aluminum nitride, aluminum gallium nitride, gallium oxide, or germanium dioxide. Diamond has a higher thermal conductivity than these materials, allowing it to effectively dissipate heat from the semiconductor device.

[0055] [Method for manufacturing bonded substrates] Figure 1 shows a flowchart of the manufacturing method for a bonded substrate according to the present invention.

[0056] (Fabrication of bonding substrate: S11) Step S11 in Figure 1 is a process for fabricating a bonding substrate 10 as shown in Figure 2 by depositing a diamond film 1 on a semiconductor substrate A, which is a seed substrate for the diamond film. The semiconductor substrate A is not particularly limited, but it is preferable to use silicon, aluminum oxide, silicon carbide, or magnesium oxide. With silicon, aluminum oxide, and silicon carbide substrates, a diamond film can be deposited on a large-diameter substrate of 200 mm or more. In addition, magnesium oxide is useful for reducing warping caused by thermal stress because the difference in coefficient of thermal expansion between it and diamond is small.

[0057] In diamond film deposition, it is preferable to use a single-crystal semiconductor substrate A when depositing single-crystal diamond, but a polycrystalline substrate can also be used as semiconductor substrate A when depositing polycrystalline diamond.

[0058] The method for manufacturing semiconductor substrate A is not particularly limited. If semiconductor substrate A is single-crystal silicon, a substrate manufactured by the CZ (Czochralski) method or a substrate manufactured by the FZ (Floating Zone) method may be used. As a single-crystal silicon substrate, a substrate that has undergone ion implantation and heat treatment may be used, or an epitaxial substrate in which a silicon single crystal has been epitaxially grown on a single-crystal substrate may be used. If it is polycrystalline silicon, a substrate manufactured by the casting method may be used.

[0059] If semiconductor substrate A is aluminum oxide, a substrate manufactured by the Bernoulli process, a substrate manufactured by the CZ process, a substrate manufactured by the Kilopoulos process, a substrate manufactured by the heat exchange process, or a substrate manufactured by the EFG (Edge-defined Film-fed Growth) process may be used.

[0060] If semiconductor substrate A is silicon carbide, a substrate manufactured by sublimation or a substrate manufactured by solution growth may be used. If it is magnesium oxide, a substrate manufactured by electrofusion may be used.

[0061] The semiconductor substrate A can be disc-shaped without notches or orientation flats. By not forming notches and orientation flats, it is possible to prevent the diamond film from peeling off from around them when the diamond film is deposited. In addition, a pattern for identifying the crystal orientation can be formed on the back side of the semiconductor substrate A (the side opposite to the side on which the diamond film is formed). For example, dots can be formed at positions indicating the crystal orientation using a laser marker.

[0062] An intermediate layer can be formed on the semiconductor substrate A. By introducing an intermediate layer whose lattice mismatch with the diamond is smaller than the lattice mismatch with the semiconductor substrate A, a diamond film with good crystallinity can be obtained in the diamond deposition process of S11.

[0063] As the intermediate layer, silicon carbide, magnesium oxide, iridium, platinum, strontium titanate, yttria-stabilized zirconia, and boron nitride can be used. Single-crystal diamond can be grown using such materials. In addition, multiple materials can be used as the intermediate layer. For example, iridium can be laminated on strontium titanate or yttria-stabilized zirconia. There are no particular restrictions on the method of forming the intermediate layer. The intermediate layer can be formed by CVD (Chemical Vapor Deposition), sputtering, or vapor deposition. The thickness of the intermediate layer can be 5 nm or more. If the thickness is 5 nm or more, a high-quality single-crystal diamond film can be formed. There is no particular upper limit on the thickness of the intermediate layer.

[0064] It is also preferable to form diamond nuclei before growing the diamond film 1. There are several methods for diamond nucleation, but for example, a method using diamond powder or a method using BEN (Bias Enhanced Nucleation) treatment can be used.

[0065] In the method using diamond powder, diamond nuclei are formed on a semiconductor substrate A (hereinafter sometimes simply referred to as "substrate A") by rubbing or adhering diamond powder to the substrate A. Methods for adhering diamond powder include applying ultrasound while the semiconductor substrate A is immersed in a diamond powder suspension using diamond powder with a sign different from the zeta potential of the semiconductor substrate A in an aqueous solution, or spin-coating by adding a thickening agent to the diamond powder suspension. These methods are suitable for growing polycrystalline diamond films.

[0066] BEN treatment is a method used in microwave plasma CVD (Chemical Vapor Deposition) systems where the methane / hydrogen ratio of the source gas is high and the treatment is performed under high bias conditions. By treating under such conditions, high-energy ions are irradiated onto substrate A, forming diamond nuclei. This method is suitable for growing single-crystal diamond films.

[0067] There are several methods for vapor-phase synthesis of diamond, but two examples can be used: microwave plasma CVD and hot filament CVD. In both methods, hydrogen and methane are used as raw material gases. Gases containing nitrogen, oxygen, argon, boron, and phosphorus can also be added to the raw material gases. In microwave plasma CVD, these raw material gases are decomposed by plasma generated by microwaves to form a film. In hot filament CVD, a high-melting-point metal is heated, and the raw material gas is decomposed by the heat to form a film. At pressures below atmospheric pressure used in CVD, graphite is more stable than diamond. Therefore, while diamond grows, graphite is also formed simultaneously with the growth of carbon sources such as CH3 generated by the decomposition of the raw material gas. On the other hand, hydrogen atoms dissociated from hydrogen molecules etch graphite more easily than diamond, so by introducing hydrogen atoms, it is possible to selectively grow only diamond. In the CVD method, to suppress the formation of graphite, growth is carried out in a high-hydrogen atmosphere where hydrogen accounts for 90% or more of the raw material gas.

[0068] For microwave plasma CVD systems, microwave frequencies of 915 MHz and 2.45 GHz can be used. These frequencies allow for the preparation of a microwave source with sufficient power for diamond synthesis. When generating plasma using a single resonant mode, the area where a uniform plasma can be generated is approximately half the wavelength of the microwave. Therefore, synthesis can be performed in an area of ​​approximately 2 inches (50 mm) in diameter using 2.45 GHz, and approximately 6 inches (150 mm) in diameter using 915 MHz. When generating plasma by superimposing multiple resonant modes, diamond synthesis can be performed over a larger area. Lower microwave frequencies and larger diamond sizes require higher microwave power during synthesis. For example, when using 2.45 GHz, the power can be between 1 kW and 30 kW, and when using 900 MHz, it can be between 5 kW and 100 kW. Since 900 MHz has lower plasma generation efficiency than 2.45 GHz, it requires more power to generate the plasma. Since the microwave output is limited by the maximum output of the microwave source, if a microwave source capable of higher output can be prepared, the microwave output can be increased further to synthesize diamond. Diamond synthesis can be performed, for example, by setting the temperature to 600°C or higher and 1300°C or lower, the pressure to 1 kPa or higher and 50 kPa or lower, the methane concentration to 0.1% or higher and 10% or lower, and the bias voltage to 0 or higher and 300 V or lower. The growth rate can also be increased by adding nitrogen, oxygen, or argon during diamond synthesis. In addition, gases containing dopants such as boron or phosphorus can also be added.

[0069] Diamond growth using a hot filament CVD apparatus can be performed by, for example, using tungsten, tantalum, molybdenum, or rhenium as the filament material, setting the filament temperature to 1700°C or higher and 2400°C or lower, the substrate A temperature to 600°C or higher and 1300°C or lower, the distance between substrate A and the filament to 5 mm or higher and 30 mm or lower, the pressure to 1 kPa or higher and 50 kPa or lower, and the methane concentration to 0.1% or higher and 20% or lower. With a hot filament CVD apparatus, large-area deposition can be easily achieved by lengthening the filament and increasing the number of filaments, allowing for the deposition of polycrystalline diamond films on large-diameter substrates of 300 mm or more in diameter.

[0070] The diamond film 1 is preferably a polycrystalline diamond film. Polycrystalline diamond allows for the easy formation of large-diameter films compared to single-crystal diamond. Even though diamond is polycrystalline, it has a higher thermal conductivity than other semiconductor materials, so there is no problem using it as a heat dissipation material.

[0071] The thickness of the diamond film 1 after deposition is preferably 0.1 μm or more and 100 μm or less. The thermal conductivity of a thin film is limited by phonon scattering at the surface, even if the thin film is a single crystal. For this reason, the thermal conductivity of a diamond film decreases as the diamond film becomes thinner. By making the thickness of the diamond film 0.1 μm or more, it can function more stably as a heat dissipation material. Furthermore, by making the thickness 100 μm or less, it is possible to prevent the diamond film deposition from taking too long, thereby improving productivity and reducing costs.

[0072] There are no particular restrictions on the method for measuring the thickness d of a diamond film. The thickness can be observed in situ during growth, or the thickness of the substrate before and after film formation can be measured using a capacitive film thickness gauge, and the difference can be taken as the thickness. The thickness can also be measured using optical methods such as a laser microscope. If the surface roughness after film formation is small, the thickness can be measured by ellipsometry. Alternatively, the diamond film can be formed in advance, and the thickness of the diamond film can be measured by observing the cross-section with an SEM (Scanning Electron Microscopy) or TEM (Transmission Electron Microscopy), and the diamond film thickness can be estimated using the film formation rate calculated from the film formation time.

[0073] If the surface or back surface of a diamond film is uneven, the film thickness d can be determined by first averaging out the unevenness, and then measuring the distance between the surface and the back surface.

[0074] (Determination of the amount of warping) Step S12 in Figure 1 is a step in determining the amount of warpage h of the bonding substrate 10 after the diamond film 1 shown in Figure 2 has been deposited. The warpage may be convex upwards or convex downwards. The measurement method for determining the warpage is not particularly limited. The amount of warpage may be measured using a contact type, laser type, or capacitive type displacement meter, or the shape of the substrate may be measured using an optical three-dimensional measuring machine and the amount of warpage may be determined from the difference between the maximum height and minimum height on the top surface of the substrate. Determining the amount of warpage by actual measurement in this way is preferable because it allows for highly accurate determination of the amount of warpage.

[0075] Furthermore, the amount of warpage h can also be the value obtained by measuring the amount of warpage of a monitor substrate that has been manufactured under the same conditions as the bonding substrate. Using the amount of warpage measured on the monitor substrate is preferable because it eliminates the need for actual measurement and makes it easy to determine the amount of warpage.

[0076] The amount of warpage h of substrate A due to diamond deposition can also be estimated using Stoney's equation (1) based on the following elastic deformation theory.

[0077]

Number

[0078] Here, γ s is the Poisson's ratio of the semiconductor substrate A, l is the radius of the semiconductor substrate A, σ is the residual stress, d is the thickness of the diamond film, E s is the Young's modulus of the semiconductor substrate A, and b is the thickness of the semiconductor substrate A. The residual stress σ is the sum of the intrinsic stress σ i and the thermal stress σ t , and the thermal stress can be calculated by the following formula (2).

[0079]

Number

[0080] Here, E f is the Young's modulus of the diamond, γ f is the Poisson's ratio of the diamond, T d is the film formation temperature, T r is the room temperature, α f is the linear expansion coefficient of the diamond with temperature as a variable, and α s is the linear expansion coefficient of the semiconductor substrate A with temperature as a variable. As the linear expansion coefficient with temperature as a variable, the value calculated by the first principle calculation can be used. By measuring the intrinsic stress, the warpage can be predicted more accurately. If the value estimated by the Stoney's formula (1) based on the elastic deformation theory is determined as the warpage amount in this way, the actual measurement process can be omitted and the warpage amount can be easily determined, which is preferable.

[0081] Furthermore, the relative magnitudes of the linear expansion coefficients of diamond and semiconductor substrate A can change with temperature, so there may be a deposition temperature at which warping is minimized. For this reason, adjusting the deposition temperature is effective in reducing warping. Also, from equation (1), it can be seen that increasing the thickness of semiconductor substrate A is effective in reducing warping. Warping also depends on the thickness of the diamond film and the radius of semiconductor substrate A, but it is preferable that the thickness of semiconductor substrate A be greater than or equal to the standard thickness and 10 mm or less. If the substrate is of the standard thickness, it is easy to obtain the substrate and thus easy to manufacture substrates with diamond deposition. In addition, by making the substrate thickness 10 mm or less, the substrate can be introduced into commercially available bonding equipment.

[0082] The method for determining the amount of warpage described above allows for more accurate and / or easier determination of the amount of warpage of the bonding substrate.

[0083] (Selection of substrates for bonding) Step S13 in Figure 1 is a process for selecting bonding substrates in which the thickness d of the deposited diamond film is greater than the amount of warpage h. By selecting bonding substrates in this way, it is possible to prevent the diamond film from being removed during polishing and the semiconductor substrate A from being exposed on the surface. At this time, the diamond film thickness d and the amount of warpage h may be measured values ​​as described above, or they may be measured values ​​in advance.

[0084] By using a substrate with a diamond film thicker than the warp of semiconductor substrate A (bonding substrate 10) having a diamond film, it is possible to prevent the semiconductor substrate A from being exposed when the surface of the diamond is flattened, thus ensuring reliable bonding with a dissimilar material (semiconductor material B). Here, bonding with a dissimilar material means bonding with a semiconductor material that is different from the diamond film; the semiconductor substrate A and semiconductor material B of the bonding substrate may be made of the same material.

[0085] One reason why bonding with semiconductor material B becomes difficult when semiconductor substrate A is exposed is that the diamond planarization process is not optimized for planarizing semiconductor substrate A, resulting in a rough surface. Furthermore, when semiconductor substrate A is exposed, the diamond film becomes more prone to peeling from the exposed area, leading to bonding failures.

[0086] Even if the diamond film is thick and has a large amount of warping, if the thickness d of the diamond film is greater than the amount h of warping of the bonding substrate 10, the surface of the diamond film can be flattened, so this does not pose a problem.

[0087] (flattening) Step S14 in Figure 1 is a process for planarizing the surface of the diamond film 1 of the selected bonding substrate (Figure 3). Chemical mechanical polishing can be used as a method for planarizing the diamond film. Alternatively, mechanical polishing or plasma-assisted polishing, in which the diamond film is brought into contact with a surface plate, may be used. Chemical mechanical polishing and mechanical polishing use fine diamond particles for polishing. Plasma-assisted polishing is a method in which a plasma containing oxygen is irradiated onto a part of a surface plate made of oxide, and the diamond film is pressed against the surface plate at a position different from the plasma irradiation area for polishing. These polishing methods may be used in combination.

[0088] Since polishing begins from the convex parts of the surface, if the semiconductor substrate A is convex upwards, polishing starts from the center of the substrate; if it is convex downwards, polishing starts from the outer edge. The amount of warpage does not change during the polishing process, so if the amount of warpage h is greater than the thickness d of the diamond film, the surface of the semiconductor substrate A will be exposed. Since the polishing process is specifically adjusted for polishing diamonds, if the semiconductor substrate A and the diamond are polished simultaneously, the surface roughness of the diamond will be better. For this reason, the surface roughness of the semiconductor substrate A exposed during the polishing process is inferior to that of the diamond.

[0089] (Joining) Step S15 in Figure 1 is a process of bonding diamond and semiconductor material B, as shown in Figure 4. When a semiconductor device is operated, the heat generated limits the performance of the semiconductor device. Therefore, by reducing the temperature rise of the semiconductor device, the performance of the device can be improved. Since diamond has high thermal conductivity, by placing a diamond film near such a semiconductor device, the heat generated by the device can be efficiently dissipated to the diamond film.

[0090] There are no particular restrictions on the size of semiconductor material B. The semiconductor substrate A and semiconductor material B may be the same size, or semiconductor material B may be larger or smaller than semiconductor substrate A. The size of semiconductor material B should be adjusted according to the application.

[0091] There are no particular restrictions on the shape of semiconductor material B. The surface of semiconductor material B may be convex upwards or convex downwards. Regardless of whether it is convex upwards or downwards, the surface of the diamond and the surface of semiconductor material B can be joined without being affected by warping by applying pressure after joining.

[0092] It is preferable to use one of the following as semiconductor material B: silicon, silicon germanium, indium phosphide, silicon carbide, gallium nitride, aluminum nitride, aluminum gallium nitride, gallium oxide, or germanium dioxide. Diamond has a higher thermal conductivity than these materials, so it can effectively dissipate heat from the semiconductor device.

[0093] Semiconductor material B may use a substrate composed of a single material, or it may be composed of multiple different materials. For example, one or more of silicon germanium, indium phosphide, silicon carbide, gallium nitride, aluminum nitride, aluminum gallium nitride, or germanium dioxide may be formed on a silicon substrate; one or more of gallium nitride, aluminum nitride, aluminum gallium nitride, gallium oxide, or germanium dioxide may be formed on an aluminum oxide substrate; or one or more of gallium nitride or germanium dioxide may be formed on a silicon carbide substrate. Furthermore, semiconductor material B may have an intermediate layer formed between any of the above different semiconductor materials.

[0094] At this time, a semiconductor device can be formed on the semiconductor material B. By forming the semiconductor device on the semiconductor material B and then bonding the semiconductor material B to the diamond film 1 of the bonding substrate 10, it is possible to prevent delamination due to thermal stress at the interface between the semiconductor material B and the diamond. For example, a planar FET (Field-Effect Transistor), FinFET (Fin Field-Effect Transistor), GAAFET (Gate All Around Field-Effect Transistor), ForksheetFET (Forksheet Field-Effect Transistor), or CFET (Complementary Field-Effect Transistor) may be fabricated, and then the back side of the substrate may be thinned before bonding with the diamond film. By bonding with a diamond film, the heat generated in these FETs can be effectively dissipated, thereby improving the performance of the FETs.

[0095] In a CFET, the FET layer is divided into two layers, a top layer and a bottom layer, depending on the difference in the conductivity type of the channel. In such a CFET, a diamond film may be bonded to the bottom layer after it has been formed, and then the top layer may be formed. By introducing a diamond film with high thermal conductivity between the top and bottom layers in this way, the formation of hot spots with locally high temperatures can be prevented, thereby improving the performance of the FET.

[0096] Alternatively, a High Electron Mobility Transistor (HEMT) may be formed on semiconductor material B, and the back surface of semiconductor material B may be thinned before bonding it with a diamond film. By bonding the diamond film in this way, the formation of hot spots can be prevented, thereby improving the performance of the HEMT.

[0097] As a method for joining a diamond film 1 and a semiconductor material B, one option is to perform H-termining or OH-termining on each surface before joining. However, it is more preferable to irradiate each surface to be joined with an ion beam or a neutral atomic beam under vacuum before bringing the surfaces of the diamond film 1 and semiconductor material B into contact and joining them. A neutral atomic beam is sometimes called a fast atomic beam. When an ion beam or neutral atomic beam is irradiated onto the diamond film 1 or semiconductor material B, dangling bonds are formed on the surface. By bringing the surfaces with dangling bonds into contact, the diamond film 1 and semiconductor material B can be joined. This method can form a strong bond at room temperature, but heating may be performed after joining to further increase the bonding strength.

[0098] An inert gas can be used as the ion beam or neutral atom beam source. For example, helium, neon, argon, krypton, xenon, and nitrogen can be used. These gases can stably form dangling bonds.

[0099] The energy of the ion beam or neutral atom beam used for irradiation can be between 0.1 kV and 10 kV. A dangling bond can be stably formed at 0.1 kV or higher. Furthermore, by setting the energy to 10 kV or lower, damage to the irradiated material can be prevented.

[0100] The irradiation time of the ion beam or neutral atom beam can be set to 5 seconds or more and 30 minutes or less. Irradiation for 5 seconds or more allows for the formation of dangling bonds. Furthermore, limiting the irradiation time to 30 minutes or less prevents a decrease in productivity due to excessive irradiation time.

[0101] Ion beam or neutral atomic beam irradiation can also be used to remove films of 10 nm or less formed on the surfaces of the diamond film 1 and semiconductor material B. For example, in silicon substrates, a native oxide film several nm thick forms on the surface when stored in the air. Such films can be removed before being introduced into the bonding apparatus, or they can be removed by irradiation with an ion beam or neutral atomic beam after being introduced into the bonding apparatus.

[0102] An intermediate layer may be formed between the diamond film 1 and the semiconductor material B. For example, silicon can be used as the intermediate layer. This is particularly effective when bonding diamond with semiconductor material B containing gallium. The thickness of the intermediate layer can be, for example, 1 nm or more and 100 nm or less. A thickness of 1 nm or more ensures stable function as an intermediate layer. By keeping the thickness below 100 nm, the thermal resistance of the intermediate layer can be kept low. There are no particular restrictions on the method of forming the intermediate layer, but it can be formed by sputtering or vapor deposition, for example.

[0103] The diamond film 1 and the surface of the semiconductor material B can be brought into contact and then pressurized. The pressure at this time can be, for example, 400 MPa or less. By keeping the pressure below 400 MPa, damage to the substrate can be prevented. Since bonding can be performed without pressure, there is no particular lower limit to the pressurized pressure.

[0104] (Thinning of semiconductor substrates) As shown in Figure 5, the semiconductor substrate A can be thinned after the bonding process. By thinning the substrate, the semiconductor substrate A, which has a higher thermal resistance than diamond, is eliminated or made thinner, improving the heat dissipation efficiency of the heat sink when a metal heat sink is attached to the back surface of the semiconductor substrate A or the diamond film 1. Furthermore, thinning the substrate makes it easier to form vias in the diamond film 1, allowing power and signals to be supplied from the side bonded to the diamond film 1 to the device formed on the semiconductor material B. This method of forming vias in a diamond film is suitable for forming BSPDN (Backside Power Delivery Network) in FinFETs, GAAFETs, ForksheetFETs, and CFETs, and for forming wiring between the top and bottom layers in CFETs.

[0105] The method of thinning is not particularly limited. For example, the semiconductor substrate A may be polished, removed by wet etching, or removed by dry etching. Alternatively, a combination of these methods may be used.

[0106] In the thin-film formation process, the semiconductor substrate A may be completely removed as shown in Figure 6. Alternatively, after removing the semiconductor substrate A, planarization may be performed to improve the roughness and warping of the back side of the diamond. The same method used for polishing the surface of the diamond described above can be used for planarization. [Examples]

[0107] The present invention will be described in detail below with reference to examples, but this is not intended to limit the present invention.

[0108] [Examples, Comparative Examples] As the semiconductor substrate A for the bonding substrate 10, a 20 mm diameter single-crystal silicon substrate without notches or orientation flats formed at five different substrate thicknesses was prepared. Conductivity type of substrate: p-type Thickness: 400, 500, 600, 700, 1000 μm Crystal plane orientation: (100) Oxygen concentration: 14 ppm

[0109] The surface of this substrate was polished with diamond powder to form diamond nuclei, and then polycrystalline diamond films of two different thicknesses (5 μm and 10 μm) were deposited using a hot filament CVD apparatus. The filament temperature was 2200°C, the substrate temperature was 650°C or 700°C, the distance between the substrate and filament was 10 mm, and the chamber pressure was 20 kPa.

[0110] The warpage after film deposition was measured using a 3D measuring machine. Table 1 shows the relationship between the thickness of the single-crystal silicon substrate, the thickness of the polycrystalline diamond film, the deposition temperature, the amount of warpage, and the feasibility of bonding with single-crystal gallium nitride for Examples 1-3 and Comparative Examples 1-4.

[0111] [Table 1]

[0112] As shown in Table 1, when the single-crystal silicon substrate thickness was 400, 500, and 600 μm, the amount of warpage was greater than that of the diamond film thickness (Comparative Examples 2-4). Furthermore, when the single-crystal silicon substrate thickness was 700 μm and the deposition temperature was 650°C, the amount of warpage was the same as that of the diamond film thickness (Comparative Example 1). At other levels, the amount of warpage was smaller than that of the diamond film thickness (Examples 1-3). Also, the shape of the warpage after deposition was convex upwards in all cases.

[0113] Subsequently, the surface of the polycrystalline diamond film was polished using plasma-assisted polishing, followed by finish polishing using chemical mechanical polishing. The amount of polishing in the plasma-assisted polishing method was equal to the amount of warpage. The amount of polishing in the chemical mechanical polishing method was 20 nm. In the four levels where the amount of warpage h and the thickness d of the diamond film were equal (Comparative Example 1) or where the thickness d of the diamond film was less than the amount of warpage h (Comparative Examples 2-4), the surface of the single-crystal silicon substrate was exposed during polishing using the plasma-assisted polishing method. In addition, when the thickness of the single-crystal silicon substrate was 400 μm and 500 μm, a portion of the diamond film remaining on the outer edge peeled off during the subsequent chemical mechanical polishing.

[0114] In Examples 1-3 and Comparative Examples 1-4, the surface roughness after polishing was measured using an AFM (Atomic Force Microscope). The results showed that the Ra value in Examples 1-3 was 1 nm or less in all cases. On the other hand, the Ra value in Comparative Examples 1-4 was 5 nm or more.

[0115] As semiconductor material B, a 6-inch (150 mm) diameter single-crystal gallium nitride / single-crystal silicon substrate with an orientation flat was prepared. The thickness of the single-crystal silicon substrate was 630 μm, and the thickness of the single-crystal gallium nitride film on top of it was 2 μm. This single-crystal gallium nitride / single-crystal silicon substrate (semiconductor material B) was bonded to a polycrystalline diamond / single-crystal silicon substrate (bonding substrate 10). For bonding, these substrates were transported into a room-temperature bonding machine, evacuated, and then irradiated with an argon neutral atomic beam onto the surfaces of the single-crystal gallium nitride and polycrystalline diamond. After that, silicon was sputtered in the room-temperature bonding machine to form a 10 nm thick amorphous silicon layer on the surfaces of the polycrystalline diamond film and the single-crystal gallium nitride. Subsequently, the polycrystalline diamond film and single-crystal gallium nitride of the bonding substrate having the amorphous silicon layer were brought into contact and pressurized at 25 MPa. The bonded substrate (bonding substrate 100) was removed from the room-temperature bonding machine. As a result, bonding was not achieved when the single-crystal silicon substrate thickness was 400 μm and 500 μm (Comparative Examples 3 and 4).

[0116] Subsequently, excluding the two levels where bonding was clearly not possible (Comparative Examples 3 and 4), the bonding interface was observed using an ultrasonic microscope. As a result, when the single-crystal silicon substrate thickness was 600 μm and when the single-crystal silicon substrate thickness was 700 μm and the film deposition temperature was 650°C, bonded and unbonded regions were mixed (Comparative Examples 1 and 2).

[0117] On the other hand, in the remaining three levels (Examples 1-3) where the diamond film thickness d was greater than the warpage h, bonding was achieved over almost the entire surface. In Example 3, where the difference between the diamond film thickness and the warpage was small but bonding was achieved, the silicon substrate thickness was 700 μm, the diamond film thickness was 5 μm, and the deposition temperature was 700°C, and the results of observing the bonding interface with an ultrasonic microscope are shown in Figure 7. The black area in Figure 7 is the bonding region, and it was found that bonding was achieved over almost the entire surface with a diameter of 20 mm.

[0118] As described above, it has been found that by selecting a bonding substrate in which the thickness of the diamond film is greater than the amount of warpage of the bonding substrate, as in the embodiment of the present invention, and bonding it to a semiconductor material, the diamond film can be reliably and stably bonded to the semiconductor material.

[0119] This specification includes the following embodiments: [1]: A method for manufacturing a bonded substrate by bonding a bonding substrate having a diamond film on the surface of a semiconductor substrate to a semiconductor material, A step of preparing a bonding substrate by forming a diamond film on the aforementioned semiconductor substrate, using the aforementioned semiconductor substrate as a seed substrate, A step of determining the amount of warping of the bonding substrate, A step of selecting bonding substrates in which the thickness of the diamond film is greater than the amount of warpage of the bonding substrate, A step of flattening the surface of the diamond film on the selected bonding substrate, A method for manufacturing a bonded substrate, comprising the step of bonding the diamond film of the planarized bonding substrate to the semiconductor material. [2]: The method for manufacturing a bonding substrate according to [1], wherein the amount of warpage of the bonding substrate to be determined is one of the values ​​obtained by measuring the amount of warpage of the bonding substrate that has been manufactured, the value obtained by measuring the amount of warpage of a monitor substrate that has been manufactured in advance under the same conditions as the manufacturing conditions of the bonding substrate, or a value estimated using Stoney's formula based on elastic deformation theory. [3]: A method for manufacturing the bonded substrate according to [1] or [2] above, wherein the semiconductor substrate is made of silicon, aluminum oxide, silicon carbide, or magnesium oxide. [4]: A method for manufacturing a bonded substrate according to [1], [2], or [3], wherein the thickness of the diamond film to be formed is 0.1 μm or more and 100 μm or less. [5]: A method for manufacturing the bonded substrate according to [1], [2], [3], or [4], wherein the diamond film is a polycrystalline diamond film. [6]: A method for manufacturing a bonded substrate according to [1], [2], [3], [4] or [5], using a disc-shaped semiconductor substrate that does not have notches and orientation flats. [7]: A method for manufacturing a bonded substrate according to [1], [2], [3], [4], [5], or [6] above, wherein the semiconductor material is one of silicon, silicon germanium, indium phosphide, silicon carbide, gallium nitride, aluminum nitride, aluminum gallium nitride, gallium oxide, or germanium dioxide. [8]: A method for manufacturing a bonded substrate according to [1], [2], [3], [4], [5], [6] or [7] above, using a semiconductor material having semiconductor elements. [9]: A method for manufacturing a bonding substrate according to [1], [2], [3], [4], [5], [6], [7], or [8], wherein in the bonding step, an ion beam or a neutral atomic beam is irradiated onto the bonding surfaces of the diamond film and the semiconductor material of the planarized bonding substrate, and then the surfaces of the diamond film and the semiconductor material are brought into contact and bonded.

[10] : A method for manufacturing a bonded substrate according to [1], [2], [3], [4], [5], [6], [7], [8] or [9], wherein after the bonding step, a step is taken to thin the semiconductor substrate of the bonding substrate.

[11] : A bonding substrate for bonding with a semiconductor material, comprising a semiconductor substrate and a diamond film on the surface of the semiconductor substrate, A bonding substrate in which the thickness of the diamond film is greater than the amount of warpage of the bonding substrate.

[12] : The bonding substrate of

[11] , wherein the semiconductor substrate is silicon, aluminum oxide, silicon carbide, or magnesium oxide.

[13] : The bonding substrate according to

[11] or

[12] , wherein the thickness of the diamond film is 0.1 μm or more and 100 μm or less.

[14] : The bonding substrate according to

[11] ,

[12] , or

[13] , wherein the diamond film is a polycrystalline diamond film.

[15] : The bonding substrate according to

[11] ,

[12] ,

[13] , or

[14] , wherein the semiconductor substrate is disc-shaped and does not have notches and orientation flats.

[0120] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of Symbols]

[0121] 1...Diamond film, 10...Bonding substrate, 100...Bonding substrate. A... Semiconductor substrate, B... Semiconductor material, d... Diamond film thickness, h... Curvature.

Claims

1. A method for manufacturing a bonded substrate by bonding a bonding substrate having a diamond film on its surface to a semiconductor material, A step of preparing a bonding substrate by forming a diamond film on the aforementioned semiconductor substrate, using the aforementioned semiconductor substrate as a seed substrate, A step of determining the amount of warping of the bonding substrate, A step of selecting bonding substrates in which the thickness of the diamond film is greater than the amount of warpage of the bonding substrate, A step of flattening the surface of the diamond film on the selected bonding substrate, A method for manufacturing a bonded substrate, characterized by including a step of bonding the diamond film of the planarized bonding substrate to the semiconductor material.

2. The method for manufacturing a bonding substrate according to claim 1, characterized in that the amount of warpage of the bonding substrate to be determined is one of the following: the amount of warpage of the bonding substrate that has been manufactured, the amount of warpage of a monitor substrate that has been manufactured in advance under the same conditions as the manufacturing conditions of the bonding substrate, or a value estimated using Stoney's formula based on elastic deformation theory.

3. The method for manufacturing a bonded substrate according to claim 1, characterized in that the semiconductor substrate is one of silicon, aluminum oxide, silicon carbide, or magnesium oxide.

4. The method for manufacturing a bonded substrate according to claim 1, characterized in that the thickness of the diamond film to be formed is 0.1 μm or more and 100 μm or less.

5. The method for manufacturing a bonded substrate according to claim 1, characterized in that the diamond film is a polycrystalline diamond film.

6. The method for manufacturing a bonded substrate according to claim 1, characterized in that a disc-shaped semiconductor substrate without notches and orientation flats is used as the semiconductor substrate.

7. The method for manufacturing a bonded substrate according to claim 1, characterized in that the semiconductor material is any of silicon, silicon germanium, indium phosphide, silicon carbide, gallium nitride, aluminum nitride, aluminum gallium nitride, gallium oxide, or germanium dioxide.

8. The method for manufacturing a bonded substrate according to claim 1, characterized in that the semiconductor material used has semiconductor elements.

9. The method for manufacturing a bonded substrate according to claim 1, characterized in that, in the bonding step, an ion beam or a neutral atomic beam is irradiated onto the bonding surfaces of the planarized bonding substrate and the semiconductor material, and then the surfaces of the diamond film and the semiconductor material are brought into contact and bonded.

10. A method for manufacturing a bonded substrate according to any one of claims 1 to 9, characterized in that, after the bonding step, a step is performed to thin the semiconductor substrate of the bonding substrate.

11. A bonding substrate for bonding with a semiconductor material, comprising a semiconductor substrate and a diamond film on the surface of the semiconductor substrate, A bonding substrate characterized in that the thickness of the diamond film is greater than the amount of warpage of the bonding substrate.

12. The bonding substrate according to claim 11, characterized in that the semiconductor substrate is one of silicon, aluminum oxide, silicon carbide, or magnesium oxide.

13. The bonding substrate according to claim 11, characterized in that the thickness of the diamond film is 0.1 μm or more and 100 μm or less.

14. The bonding substrate according to claim 11, characterized in that the diamond film is a polycrystalline diamond film.

15. The bonding substrate according to any one of claims 11 to 14, characterized in that the semiconductor substrate is disc-shaped and does not have notches and orientation flats.

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