SiC polycrystalline substrate, SiC bonded substrate, and method for manufacturing SiC polycrystalline substrate

Abstract

The present invention provides a SiC polycrystalline substrate, a SiC bonded substrate, and a method for manufacturing a SiC polycrystalline substrate, which are capable of realizing a reduction in volume resistivity. Nitrogen concentration C contained in SiC crystal N Carrier concentration C C The carrier activation rate (C C / C N ) is 0.82 or more and the (110) plane ratio is 30% or less, and a SiC polycrystalline substrate, a SiC bonded substrate, and a method for manufacturing the SiC polycrystalline substrate.

Description

[Technical Field]

[0001] The present invention relates to a SiC polycrystalline substrate, a SiC bonded substrate, and a method for manufacturing a SiC polycrystalline substrate. [Background technology]

[0002] Silicon carbide (hereinafter referred to as SiC) is a wide bandgap semiconductor with a wide bandgap of 2.2 to 3.3 eV, and due to its excellent physical and chemical properties, research and development is being conducted on it as an environmentally resistant semiconductor material. In particular, in recent years, SiC has attracted attention as a material for high-voltage and high-power electronic devices, high-frequency electronic devices, and short-wavelength optical devices in the blue to ultraviolet wavelength range, and research and development has been active. However, it has been difficult to produce high-quality large-diameter single crystals of SiC.

[0003] To solve this problem, an improved Lely method has been developed, which uses a SiC single crystal substrate as a seed crystal and performs sublimation recrystallization. This improved Lely method allows SiC single crystals to be grown while controlling the crystal polytype (4H-SiC, 6H-SiC, 15R-SiC, etc.), shape, carrier type, and concentration. Optimization of this improved Lely method has significantly reduced the crystal defect density, making it possible to fabricate electronic devices such as Schottky diodes and field-effect transistors using SiC single crystal substrates.

[0004] However, in the improved Lely process, which uses a SiC single crystal substrate as a seed crystal to produce an ingot, the manufacturing cost of SiC single crystal substrates is high due to the slow crystal growth rate of the SiC single crystal and the high processing costs involved in processing the high-rigidity, high-mechanical-strength SiC single crystal ingot into wafers. This high manufacturing cost is also a factor hindering the practical application of SiC devices, and there has been a strong demand for the development of technology that can provide inexpensive SiC substrates for semiconductor device applications, particularly for high-voltage, high-power electronic elements.

[0005] One solution to reducing the cost of SiC substrates is the development of bonded SiC substrates, which utilize substrate bonding technology. Bonded SiC substrates are based on the concept of reducing the overall cost of SiC substrates by minimizing the thickness of high-quality SiC single crystal substrates. These substrates have a multilayer structure in which a thin layer of high-quality SiC single crystal substrate with the thickness required for device formation and a substrate material (hereinafter referred to as the support substrate) that supports the thin layer are integrated using substrate bonding technology. By selecting a low-cost material for the support substrate that has the mechanical strength and heat resistance required for the device manufacturing process, it is possible to manufacture bonded SiC substrates that combine high quality (thin SiC single crystal layer) and low cost (support substrate) (Patent Document 1).

[0006] One of the materials for the support substrate is a SiC polycrystalline substrate. Like SiC single crystal substrates, SiC polycrystalline substrates are made of silicon carbide, and because they offer greater flexibility in manufacturing methods than SiC single crystal substrates, they are expected to be a low-cost support substrate material.

[0007] When using a SiC polycrystalline substrate as a support substrate for a SiC bonded substrate, volume resistivity is particularly important among its various properties. Volume resistivity is defined as the volume resistance per unit volume and is a measure of a material's electrical conductivity. The application fields of SiC devices are primarily high-voltage, high-power electronic elements, and minimizing heat loss caused by the application of large currents is crucial. To suppress Joule heat generation due to substrate resistance, SiC substrates must have low resistivity. For example, currently available SiC single-crystal substrates are specified with a volume resistivity of 0.015 to 0.028 Ω cm. However, further reductions in resistivity are extremely difficult due to the adverse effects on crystal quality associated with lower resistivity.

[0008] On the other hand, in the case of SiC bonded substrates, the parts that affect the crystal quality (parts of the SiC single crystal substrate) and the parts that affect the substrate resistance (parts of the SiC polycrystalline substrate) are independent, so by lowering the resistance of the SiC polycrystalline substrate, it is possible to reduce the substrate resistance without adversely affecting the crystal quality. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2015-15401 A Summary of the Invention [Problem to be solved by the invention]

[0010] To improve the performance of SiC substrates for high-voltage, high-power electronic devices, it is hoped that the resistance of SiC polycrystalline substrates, which are used as support substrates for SiC bonded substrates, can be reduced. However, there are challenges in reducing the resistance of SiC polycrystalline substrates.

[0011] The volume resistivity ρ is expressed as in equation (1) using the elementary charge e, the density of carriers that transport the charge (hereinafter referred to as carrier density) n, and the mobility μ, which indicates the ease of movement of the carriers when an electric field is applied.

[0012]

number

[0013]

number

[0014] According to formula (1), in order to reduce the volume resistivity ρ, it is necessary to increase the carrier density n and mobility μ. In general semiconductors, the carrier density n is controlled by adding impurities that function as a carrier source. In SiC, nitrogen or phosphorus is added in the case of N-type semiconductors.

[0015] However, unlike single-crystal SiC substrates, polycrystalline SiC substrates have boundaries between crystals (hereafter referred to as grain boundaries), which can make it difficult for impurities to function as carrier sources. Therefore, adding more nitrogen is required to lower resistivity, but it is generally known that adding high concentrations of nitrogen to SiC crystals causes lattice distortion. Furthermore, adding high concentrations of nitrogen requires increasing the nitrogen ratio in the raw materials required for SiC crystal growth—in other words, decreasing the ratio of Si to C raw materials—which can affect productivity by slowing down the crystal growth rate. Thus, in terms of both substrate quality and productivity, it is important to limit the amount of nitrogen added to control carrier density.

[0016] Furthermore, according to formula (2), it can be seen that of the various factors that contribute to mobility, the lowest mobility has the greatest effect. Generally, when comparing SiC single crystal substrates with SiC polycrystalline substrates, mobility tends to be lower in polycrystalline substrates. However, unlike SiC single crystal substrates, which are made up of a single crystal, SiC polycrystalline substrates are made up of multiple crystals, and therefore there are many factors that significantly affect various properties, such as the size and orientation of the constituent crystals, and it has not been clarified which factors affect mobility.

[0017] Therefore, an object of the present invention is to provide a SiC polycrystalline substrate, a SiC bonded substrate, and a method for manufacturing a SiC polycrystalline substrate that can achieve a reduction in volume resistivity. [Means for solving the problem]

[0018] The present inventors discovered that by reducing the ratio of a specific plane orientation among the crystals constituting a SiC polycrystalline substrate, the mobility of the added impurities can be increased while maintaining their ability to function as carriers, and have thus completed the present invention. That is, the aspects of the present invention are as follows.

[0019] <1> Nitrogen concentration C contained in SiC crystal N Carrier concentration CC The carrier activation rate (C C / C N ) is 0.82 or more and the (110) plane ratio is 30% or less.

[0020] <2> Nitrogen concentration C contained in SiC crystal N is 4.9 x 10 19 cm -3 More than 5.5cm -3 x10 20 cm -3 Within the following range: <1> The SiC polycrystalline substrate according to claim 1.

[0021] <3> The volume resistivity is 0.015 Ωcm or less. <1> The SiC polycrystalline substrate according to claim 1.

[0022] <4> The (110) plane ratio is the ratio of the area of ​​crystals oriented in the (110) plane. <1> The SiC polycrystalline substrate according to claim 1.

[0023] <5> The (110) plane ratio is determined from an X-ray diffraction spectrum obtained by an X-ray diffractometer. <1> The SiC polycrystalline substrate according to claim 1.

[0024] <6> The (110) plane ratio is calculated based on a first peak intensity value obtained by dividing a first peak integrated intensity value in a first diffraction angle range for the (111) plane in the X-ray diffraction spectrum by a first intensity correction term, a second peak intensity value obtained by dividing a second peak integrated intensity value in a second diffraction angle range for the (200) plane and the (100) plane in the X-ray diffraction spectrum by a second intensity correction term, a third peak intensity value obtained by dividing a third peak integrated intensity value in a third diffraction angle range for the (220) plane and the (110) plane in the X-ray diffraction spectrum by a third intensity correction term, and a fourth peak intensity value obtained by dividing a fourth peak integrated intensity value in a fourth diffraction angle range for the (311) plane in the X-ray diffraction spectrum by a fourth intensity correction term. <5> The SiC polycrystalline substrate according to claim 1.

[0025] <7> <1> 1. A method for producing the SiC polycrystalline substrate according to claim 1, wherein polycrystalline SiC is grown by chemical vapor deposition.

[0026] <8> <1> 10. A SiC bonded substrate comprising the SiC polycrystalline substrate according to claim 1 bonded to a SiC single crystal substrate, the SiC bonded substrate having a volume resistivity of 0.015 Ωcm or less. [Effects of the Invention]

[0027] According to the present invention, it is possible to provide a SiC polycrystalline substrate capable of realizing a reduction in volume resistivity, a method for manufacturing the same, and a SiC bonded substrate using the SiC polycrystalline substrate. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a schematic perspective view of a SiC polycrystalline substrate according to an embodiment of the present invention. FIG. [Figure 2] 1A and 1B are schematic diagrams of a SiC bonded substrate using a SiC polycrystalline substrate according to an embodiment, in which (a) is a perspective view and (b) is a side view. [Figure 3] 1 is a flowchart showing steps of a method for manufacturing a SiC polycrystalline substrate according to an embodiment. [Figure 4] 1 is a flowchart showing steps of a method for manufacturing a SiC bonded substrate using a SiC polycrystalline substrate according to an embodiment. [Figure 5] This is a schematic diagram of the Hall effect measurement element used for Hall effect measurement by the van der Pauw method. [Figure 6] 1 is a graph showing the relationship between the nitrogen concentration and the carrier activation ratio (CC / CN) in the SiC polycrystalline substrates produced in the examples and comparative examples. [Figure 7] 1 is a graph showing the relationship between the mobility and the (110) plane ratio in the SiC polycrystalline substrates produced in the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiment.

[0030] [SiC polycrystalline substrate] First, the SiC polycrystalline substrate according to this embodiment will be described. Fig. 1 is a schematic perspective view showing a SiC polycrystalline substrate 10 according to an embodiment that is an exemplary aspect of the present invention. Fig. 2 is a schematic view showing a SiC bonded substrate 30 using the SiC polycrystalline substrate 10 according to this embodiment, where (a) is a perspective view and (b) is a side view.

[0031] 2, the SiC polycrystalline substrate 10 according to this embodiment is bonded to a SiC single crystal substrate 20 to be used as a support substrate for forming a bonded substrate, i.e., a SiC bonded substrate 30. That is, the SiC bonded substrate 30 is a SiC bonded substrate in which a bonding surface 11 of the SiC polycrystalline substrate 10 and a bonding surface 21 of the SiC single crystal substrate 20 are bonded together with a bonding interface 31 as the boundary.

[0032] The SiC polycrystalline substrate 10 is formed in the shape of a disk, for example, with a thickness of about 0.35 mm and a diameter of 6 inches. The SiC polycrystalline substrate 10 is made of any one of 4H—SiC, 6H—SiC, and 3C—SiC single crystals, or a mixture of two or three of these. The shape is not limited to a disk, and may be, for example, polygonal.

[0033] [SiC single crystal substrate] The SiC single crystal substrate 20 is made of single crystal SiC and is formed in a disk shape with a thickness of, for example, about 1 μm and the same diameter as the SiC polycrystalline substrate. The SiC single crystal of the SiC single crystal substrate 20 is composed of any one of 4H-SiC, 6H-SiC, and 3C-SiC crystals, or a mixture thereof. The SiC single crystal substrate is approximately disk-shaped and may be circular or may have an indicator portion that indicates the orientation of the substrate, such as an orientation flat or notch. It is preferable to use a substrate with a diameter of 100 mm to 305 mm (4 inches to 12 inches). The shape is not limited to an approximately disk shape such as a circle, and may be, for example, polygonal.

[0034] [SiC bonded substrate] Next, a SiC bonded substrate 30 according to this embodiment will be described. As shown in Fig. 2, the SiC bonded substrate 30 is a semiconductor substrate obtained by bonding the SiC polycrystalline substrate 10 according to this embodiment described above and a SiC single crystal substrate 20. The SiC bonded substrate may include a portion of the bonded SiC single crystal substrates peeled or cut parallel to the bonding surface (perpendicular to the thickness direction) and provided on the SiC polycrystalline substrate as a SiC single crystal layer.

[0035] [Career activation rate] The carrier activation rate is determined by the nitrogen concentration C N Carrier concentration C C The ratio (C C / C N The SiC polycrystalline substrate 10 is an N-type semiconductor, and nitrogen is added as an impurity that serves as a carrier supply source. The nitrogen concentration C N can be obtained by chemical analysis, and the nitrogen concentration C N can be obtained by electrical analysis. Whether nitrogen functions as a carrier source can be determined by determining the carrier activation rate.

[0036] Carrier activation rate (C C / C NThe closer the value of ) is to 1, the more nitrogen incorporated into the SiC polycrystalline substrate contributes to reducing the volume resistivity as a carrier supply source. C / C N ), taking into account a measurement error of about 10%, if (1 - 0.1) / (1 + 0.1) = 0.82 or more, it can be considered that all of the added nitrogen is functioning as a carrier source. Therefore, the carrier activation rate (C C / C N ) is preferably 0.82 or more, and more preferably 0.9 or more.

[0037] As a result of intensive research by the inventors, the carrier activation rate (C C / C N ) was found to be correlated mainly with the concentration of nitrogen incorporated into polycrystalline SiC. Specifically, when the nitrogen concentration was 2.3 × 10 19 ~5.5×10 20 (cm -3 ), the carrier activation rate (C C / C N ) was generally found to be 0.82 or higher.

[0038] [(110) surface ratio] The SiC polycrystalline substrate 10 is composed of crystals oriented primarily in four plane orientations ((111), (100), (110), and (311)). The inventors discovered a correlation between the (110) plane ratio, which reflects the proportion of crystals oriented in the (110) plane, and the mobility, which determines the volume resistivity of the substrate. Specifically, they found that mobility can be increased as the (110) plane ratio decreases. As a result of extensive research aimed at achieving a desired volume resistivity, they discovered that high mobility can be achieved without adding excess nitrogen by controlling the (110) plane ratio and nitrogen concentration in the SiC polycrystalline substrate. The composition ratio of crystals oriented in the (110) plane, i.e., the (110) plane ratio, can be defined as the ratio of the area of ​​crystals oriented in the (110) plane to the total area (for example, the sum of the areas of crystals oriented in the (111) plane, (100) plane, (110) plane, and (311) plane).

[0039] In the embodiment, the (110) plane ratio is set to 30% or less, and the carrier activation rate (C C / C N ) is 0.82 or more, the volume resistivity of the SiC polycrystalline substrate can be kept low. In particular, the nitrogen concentration is 4.9 × 10 19 cm -3 Over 5.5 x 10 20 cm -3 By keeping the resistivity within the following range, the volume resistivity of the SiC polycrystalline substrate can be kept even lower, achieving a highly accurate value of 0.015 Ω cm or less. Note that the lower limit for the (110) plane ratio may be 0%, but since this depends on the accuracy of the measurement means, the actual lower limit is around 0.3%.

[0040] The (110) plane ratio can be measured and calculated using an X-ray diffractometer (XRD). The parameters used in the calculation are listed in Table 1 below. First, the X-ray diffraction pattern of the SiC polycrystalline substrate 10 is measured using XRD (2θ / θ scan), and peak intensity values ​​of the four major plane orientations are obtained from the obtained spectrum. For each of the (111) plane, the integrated intensity values ​​of the peaks are obtained in the diffraction angle 2θ range of 34.9 to 36.8°; for the (200) plane (=(100) plane), the diffraction angle 2θ range of 40.7 to 41.45°; for the (220) plane (=(110) plane), the diffraction angle 2θ range of 59.8 to 60.3°; and for the (311) plane, the integrated intensity values ​​of the peaks are obtained in the diffraction angle 2θ range of 71.6 to 72.1°.

[0041] Next, the peak intensity value of each plane orientation is obtained by dividing the integrated intensity value of the peak by the intensity correction term corresponding to the plane orientation listed in Table 1 below ((integrated intensity value of peak) / (intensity correction term)). Finally, the peak intensity value of the (110) plane obtained (110 peak ) is calculated by dividing the sum of the peak intensity values ​​of the four plane orientations (Total peak ) divided by ((110 peak ) / (Total peak )) the (110) plane ratio can be calculated.

[0042] [Table 1]

[0043] That is, the (110) plane ratio can be determined from an X-ray diffraction spectrum obtained from an X-ray diffraction pattern measured using an X-ray diffractometer. More specifically, the (110) plane ratio can be calculated by The first peak integrated intensity value (111) obtained by dividing the first peak integrated intensity value in the first diffraction angle range (for example, the diffraction angle 2θ range of 34.9 to 36.8°) for the (111) plane in the X-ray diffraction spectrum by the first intensity correction term (for example, 100) is peak ), The second peak integrated intensity value (100) obtained by dividing the second peak integrated intensity value in the second diffraction angle range (for example, the diffraction angle 2θ is 40.7 to 41.45°) for the (200) and (100) planes in the X-ray diffraction spectrum by the second intensity correction term (for example, 20) is peak ), The third peak integrated intensity value (110) obtained by dividing the third peak integrated intensity value in the third diffraction angle range (for example, the diffraction angle 2θ range of 59.8 to 60.3°) for the (220) and (110) planes in the X-ray diffraction spectrum by the third intensity correction term (for example, 35) is peak ),and, The fourth peak integrated intensity value (311) obtained by dividing the fourth peak integrated intensity value in the fourth diffraction angle range (for example, the diffraction angle 2θ range of 71.6 to 72.1°) for the (311) plane in the X-ray diffraction spectrum by the fourth intensity correction term (for example, 20) is peak ) Based on (110 peak ) / {(111 peak )+(100 peak )+(110 peak )+(311 peak )}.

[0044] To appropriately reduce the (110) plane ratio in a SiC polycrystalline substrate, various conditions can be controlled during the SiC crystal growth process by chemical vapor deposition (CVD). Specifically, this can be achieved by controlling the crystal growth temperature and the concentration of the C source gas, acetylene (C2H2), or the Si source gas, dichlorosilane (SiH2Cl2).

[0045] That is, to reduce the (110) face ratio in a SiC polycrystalline substrate, SiC crystal growth can be performed by controlling one of the following: lowering the crystal growth temperature, lowering the acetylene concentration, lowering the dichlorosilane concentration, or an appropriate combination of these. According to the inventors' investigations, among these, the crystal growth temperature was found to have a relatively strong correlation with the (110) face ratio in a SiC polycrystalline substrate.

[0046] [Volume resistivity] It is desirable that the volume resistivity of the SiC bonded substrate 30 be low. The application fields of SiC devices are mainly high-voltage, high-power electronic elements, and it is important to suppress the heat loss that occurs when a large current is applied. In order to suppress the generation of Joule heat caused by the substrate resistance, low resistance is required for the SiC substrate. For example, the specification value for currently commercially available SiC single crystal substrates is a volume resistivity of 0.015 to 0.028 Ωcm, and it is desirable that the volume resistivity of the SiC bonded substrate 30 be 0.015 Ωcm or less.

[0047] The volume resistivity of the SiC bonded substrate 30 can be measured using a volume resistivity measuring device that uses an eddy current method. An example of such a device is the EC-80P manufactured by Napson Corporation.

[0048] [Method of manufacturing SiC polycrystalline substrate 10] The following describes an example of a method for manufacturing the SiC polycrystalline substrate 10. FIG.

[0049] As shown in FIG. 3, the method for manufacturing a SiC polycrystalline substrate 10 includes a SiC growth process as step S10. In the SiC growth process, polycrystalline SiC is first grown on a disk-shaped graphite substrate by chemical vapor deposition. Examples of Si source gases include tetrachlorosilane, trichlorosilane, and dichlorosilane. Examples of C source gases include ethane, propane, and acetylene. Alternatively, a single gas such as tetramethylsilane may be used as the source gas. The growth temperature in this chemical vapor deposition process is, for example, 1400°C.

[0050] Next, in step S20, a substrate removal process is performed. In this process, after the polycrystalline SiC is grown, the outer periphery of the disk-shaped member is edge-ground to form it into the desired diameter. The disk-shaped member is then heated in an air atmosphere at 1000°C to remove the graphite disk substrate, yielding a free-standing SiC polycrystalline substrate.

[0051] Next, in step S30, a surface polishing process is performed. In the surface polishing process, the surface of the SiC polycrystalline substrate is first smoothed by high-precision grinding, and then further smoothed by CMP polishing. The polycrystalline SiC obtained after the surface polishing process is used as the SiC polycrystalline substrate 10. In this manner, the SiC polycrystalline substrate 10 is manufactured.

[0052] [Manufacturing method for SiC bonded substrate] Next, a description will be given of an example of a method for manufacturing the SiC bonded substrate 30. Fig. 4 is a flowchart showing a method for manufacturing the SiC bonded substrate 30. Steps S10 to S30 of the example of the method for manufacturing the SiC bonded substrate 30 shown in Fig. 4 are the same as the example of the method for manufacturing the SiC polycrystalline substrate 10 shown in Fig. 3 described above.

[0053] Following the surface polishing step of step S30, a bonding step is carried out as step S40. In the bonding step, first, hydrogen ions are implanted from the front surface side of a previously prepared SiC single crystal substrate 20 toward the front surface of the SiC single crystal substrate, with an implantation energy preset according to the thickness of the SiC single crystal substrate 20.

[0054] As a result, an ion-implanted layer is formed in the SiC single crystal substrate from its surface to a predetermined depth corresponding to the implantation energy. Thereafter, the surface of the SiC single crystal substrate is bonded to the surface of the SiC polycrystalline substrate 10 manufactured in step S30 using a conventionally known surface activation method. The bonded SiC polycrystalline substrate and the SiC single crystal substrate are then heated to recrystallize the amorphous layer at the bonding interface 31 and delaminate at the ion-implanted layer. This results in a SiC bonded substrate 30 in which a SiC single crystal thin film layer approximately 0.6 μm thick is formed (transferred) on the SiC polycrystalline substrate 10. In this manner, the SiC bonded substrate 30 is manufactured. [Example]

[0055] The SiC polycrystalline substrate and SiC bonded substrate of the embodiment will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples in any way.

[0056] [Manufacturing of SiC polycrystalline substrates] It has a diameter of approximately 6 inches (150.1 mm) and a thickness of 3 mm, and its average thermal expansion coefficient from room temperature to 1400°C is 5×10 -6 An isotropic graphite substrate of 1000 K was prepared. Dichlorosilane (DCS) was used as the Si source, and acetylene (C2H2) was used as the C source. Polycrystalline SiC with a thickness of 0.8 mm was grown on the isotropic graphite substrate by chemical vapor deposition. Growth was carried out under nine growth conditions, Condition 1 to Condition 9, as listed in Table 2 below.

[0057] [Table 2]

[0058] The "standard" in the temperature section of Table 2 above refers to 1350°C. The polytypes of the SiC polycrystalline substrates obtained under nine growth conditions, Conditions 1 to 9, were identified by electron backscatter diffraction (EBSD) and found to be 80 to 98% 3C-SiC and 1.6 to 13% 4C-SiC.

[0059] After growing the polycrystalline SiC, the outer periphery of the disk-shaped substrate was ground by 0.05 mm to a diameter of 150 mm. It was then heated in an air atmosphere at 1000°C for 24 hours to remove the isotropic graphite. The front and back sides of the SiC polycrystalline substrate were then ground by 0.2 mm, and 0.05 mm was mechanically polished and CMP polished to produce the SiC polycrystalline substrate.

[0060] [Measurement of properties of SiC polycrystalline substrates] The (110) plane ratio, volume resistivity, carrier concentration, mobility, and nitrogen concentration of the obtained SiC polycrystalline substrate were measured. The measurement methods for each of these properties are described below.

[0061] [(110) surface ratio] To calculate the (110) plane ratio, the X-ray diffraction pattern at the center of each SiC polycrystalline substrate was measured by the XRD method (2θ / θ scan). The measurement equipment and conditions were as follows:

[0062] <Measuring device> Rigaku SmartLab <Analysis conditions> X-ray generator: anticathode: Cu, output: 45 kV, 200 mA Soller slit: incident side: 5.0°, receiving side: 5.0° Slit...Input side: IS=1 / 2°, length limit: 10 (mm), receiving side: RS1=5 (mm), RS2=20.1 (mm) Scanning conditions: Scanning axis: 2θ / θ, Scanning range: 20-80°, Step width: 0.0080°, Scanning speed: 3° / min

[0063] From the obtained X-ray diffraction pattern, the peak intensity values ​​for the (111) plane, (200) plane (=(100) plane), (220) plane (=(110) plane), and (311) plane were obtained using the method described above, and the (110) plane ratio was calculated using these values.

[0064] [Volume resistivity, carrier concentration and mobility] To obtain the volume resistivity, carrier concentration, and mobility, Hall effect measurements were performed using the van der Pauw method. Figure 5 shows a schematic diagram of the Hall effect measurement device used for the van der Pauw Hall effect measurements.

[0065] The SiC polycrystalline substrate specimen 42 shown in Figure 5 as the measurement target was obtained by cutting out a 10 mm x 10 mm square from the center of the SiC polycrystalline substrate. As shown in Figure 5, ohmic electrodes 41 were formed by depositing 1 mm diameter Ni electrodes on the four corners of the cut-out specimen, which was then annealed at 950°C for 5 minutes in an inert gas (argon) atmosphere to obtain a Hall effect measurement element 40. The measurement equipment and conditions used for the Hall effect measurement are described below.

[0066] <Measuring equipment> Toyo Corporation Hall effect measuring device (model number: ResiTest8308) <Measurement conditions> ·Measurement temperature: 300K ·Applied magnetic field: 0.43T ·Applied current: 0.1A

[0067] The accuracy of the Hall effect measurement values ​​is greatly influenced by the quality of the Hall effect measurement element 40. The quality of the Hall effect measurement element 40 can be understood to some extent by obtaining, for example, the F value, which indicates the electrical symmetry of the element, and the directional dependence, which indicates the anisotropy of the Hall electromotive force. The closer the F value is to 1 and the closer the directional dependence is to 0%, the better the quality of the element. The element fabricated this time had an F value of 0.99 to 1.0 and a directional dependence of less than 10%.

[0068] [Nitrogen concentration] To obtain the nitrogen concentration, the impurity concentration was measured using secondary ion mass spectrometry (SIMS). The measurement equipment and conditions are as follows:

[0069] <Measuring equipment> CAMECA IMS-7F <Measurement conditions> Analyzed element: Nitrogen Primary ion species: Cs + Primary acceleration voltage: 15.0 kV Detection area: 30 (μmφ)

[0070] The nitrogen concentration, carrier concentration, and calculated carrier activation rate (C C / C N ), and (110) plane ratio are listed in Table 3 below. C / C NThe SiC polycrystalline substrates satisfying conditions 1 to 4, in which the ratio of the carrier activation rate (C) is 0.82 or more and the (110) plane ratio is 30% or less, are designated as Examples A1 to A4, and the SiC polycrystalline substrates satisfying conditions 5 to 9, in which the ratio of the carrier activation rate (C) is 0.82 or more and the (110) plane ratio is 30% or less, are designated as Comparative Examples A1 to A5. C / C N ) is shown in a graph in Figure 6.

[0071] [Table 3]

[0072] 6, it can be seen that there is a range of nitrogen concentration where the activation rate is 0.82 or more. In Examples 1 to 4 and Comparative Examples 1 and 2, the nitrogen concentration is 2.3×10 19 ~5.5×10 20 (cm ―3 ), an activation rate of ≧0.82 was obtained. On the other hand, for the conditions (Comparative Examples 3 to 5) where the activation rate was not ≧0.82, the (110) plane ratio showed a high value of 37% or more, suggesting a correlation with the (110) plane ratio.

[0073] Table 4 lists the nitrogen concentration, mobility, (110) plane ratio, and volume resistivity of the SiC polycrystalline substrates fabricated under each condition. Figure 7 shows a graph showing the relationship between the mobility and the (110) plane ratio.

[0074] [Table 4]

[0075] The graph in Figure 7 shows a tendency for mobility to increase as the (110) plane ratio decreases, indicating that reducing the (110) plane ratio can improve mobility, which is a key parameter for reducing volume resistivity.

[0076] From the above results, by controlling the nitrogen concentration and (110) plane ratio in the SiC polycrystalline substrate, it is possible to reduce the volume resistivity of the SiC polycrystalline substrate while maintaining both a high activation rate and high mobility. Therefore, by keeping the (110) plane ratio below 30% and the nitrogen concentration below 4.9 × 10 19 ~5.5×10 20 (cm ―3 ) it was confirmed that the volume resistivity of the SiC polycrystalline substrate could be reduced to 0.015 Ωcm or less.

[0077] [Manufacturing SiC bonded substrates] The SiC polycrystalline substrates of Example A2 and Example A4 for producing SiC bonded substrates were produced under the growth conditions of Condition 2 and Condition 4 in Table 2 described above in the section [Production of SiC polycrystalline substrate]. The volume resistivity of the obtained SiC polycrystalline substrates at the substrate center was measured using an EC-80P manufactured by Napson Corporation.

[0078] Two commercially available 150 mm diameter 4H-SiC single crystal substrates were prepared (hereinafter referred to as SiC single crystal substrate B1 and SiC single crystal substrate B2). The substrate surfaces were polished by CMP to a surface roughness Ra of approximately 0.1 nm to form the bonding surface of the SiC single crystal substrates (bonding surface 21 in Figure 2(b)) (surface polishing process). The volume resistivity of the substrate center was measured for both SiC single crystal substrates using an EC-80P manufactured by Napson Corporation, and then hydrogen ions were implanted using an ion implanter in preparation for the bonding process. The conditions for this were an acceleration voltage of 90 kV and a dose of 1 x 10 17 (cm -2 ) was decided.

[0079] In this example, the samples were prepared solely for the purpose of confirming the physical properties of the SiC polycrystalline substrate or SiC bonded substrate, and therefore the substrate removal step, which is one step in the method of manufacturing the SiC polycrystalline substrate or SiC bonded substrate, was omitted. To actually use the substrate as a SiC bonded substrate, the substrate removal step can be carried out prior to the surface polishing step.

[0080] Next, we will explain the bonding process. The bonding process is mainly divided into an irradiation process and a contact process. First, in the irradiation process, particle beams are irradiated onto the bonded bonding surfaces of the SiC polycrystalline substrate and the SiC single crystal substrate. An example of the particle beam is a fast atom beam (FAB). The particle beams are irradiated onto the entire bonded bonding surfaces of the SiC polycrystalline substrate and the SiC single crystal substrate. This removes the oxide film and adsorption layer from the bonded bonding surfaces, exposing the bonds. This state is called the activated state. Furthermore, because the irradiation process is performed in a vacuum, the bonded bonding surfaces are not oxidized, and can maintain their activated state.

[0081] Next, in the contacting step, the bonding surfaces of the SiC polycrystalline substrate and the SiC single crystal substrate are brought into contact in a vacuum. This causes the bonds present on the activated surfaces to bond together, allowing the SiC polycrystalline substrate and the SiC single crystal substrate to be bonded together. The irradiation and contacting steps were carried out using a room-temperature bonding machine MWV-06 / 08-AX-FAB manufactured by Mitsubishi Heavy Industries Machine Tool Co., Ltd.

[0082] The SiC polycrystalline substrate and SiC single crystal substrate bonded together were heated to 1000°C in an inert gas (nitrogen) atmosphere. As a result, the SiC single crystal substrate was fractured at the ion-implanted layer, and a SiC bonded substrate was obtained in which a layer of SiC single crystal substrate approximately 0.001 mm thick was bonded to the surface of the SiC polycrystalline substrate. Finally, CMP polishing was performed on the surface of the SiC single crystal substrate to remove damage from the fracture, and a SiC bonded substrate was produced.

[0083] Hereinafter, the SiC bonded substrate obtained from the SiC polycrystalline substrate of Example A2 will be referred to as Example B2, and the SiC bonded substrate obtained from the SiC polycrystalline substrate of Example A4 will be referred to as Example B4. The prepared SiC single crystal substrate B1 and SiC single crystal substrate B2 will be referred to as the SiC bonded substrates of Comparative Examples B1 and B2, respectively. Table 5 below lists the volume resistivities of each SiC bonded substrate and the SiC polycrystalline substrates used.

[0084] [Table 5]

[0085] While the volume resistivity of the SiC single crystal substrate of the comparative example was approximately 0.02 Ωcm, the SiC polycrystalline substrates of Examples A2 and A4 had low values ​​of 0.015 Ωcm or less. Furthermore, it was confirmed that the low volume resistivity reflecting the volume resistivity of the SiC polycrystalline substrate serving as the support substrate was maintained in Examples B2 and B4, which were SiC bonded substrates fabricated using the SiC polycrystalline substrates of Examples A2 and A4.

[0086] As described above, in the embodiment, it was confirmed that by controlling the nitrogen concentration and the (110) plane ratio of the SiC polycrystalline substrate constituting the support substrate in the SiC bonded substrate, it is possible to reduce the volume resistivity of the SiC polycrystalline substrate while maintaining both a high activation rate and high mobility. Furthermore, it was confirmed that the SiC bonded substrate, which is a SiC bonded substrate fabricated using the SiC polycrystalline substrate of the embodiment, is capable of reducing the volume resistivity, which was difficult to achieve with conventional SiC single crystal substrates, while suppressing deterioration in crystal quality and productivity. [Explanation of symbols]

[0087] 10:SiC polycrystalline substrate, 11: Bonding surface, 20: SiC single crystal substrate, 21: Bonding joint surface, 30: SiC bonded substrate, 31: Bonding interface

Claims

1. Nitrogen concentration C contained in the SiC crystal Ｎ Carrier concentration C Ｃ The carrier activation rate (C Ｃ / C Ｎ ) is 0.82 or more, and the (110) plane ratio is 30% or less.

2. Nitrogen concentration C contained in the SiC crystal Ｎ is 4.9 x 10 １９ cm －３ 5.5cm or more －３ x10 ２０ cm －３ 2. The SiC polycrystalline substrate of claim 1, wherein the SiC polycrystalline substrate has a surface roughness within the following range:

3. 2. The SiC polycrystalline substrate according to claim 1, having a volume resistivity of 0.015 Ωcm or less.

4. The SiC polycrystalline substrate according to claim 1 , wherein the (110) plane ratio is the ratio of the area of ​​crystals oriented in the (110) plane.

5. 2. The SiC polycrystalline substrate according to claim 1, wherein the (110) plane ratio is determined from an X-ray diffraction spectrum obtained by an X-ray diffractometer.

6. The (110) plane ratio is calculated based on a first peak intensity value obtained by dividing a first peak integrated intensity value in a first diffraction angle range for the (111) plane in the X-ray diffraction spectrum by a first intensity correction term, a second peak intensity value obtained by dividing a second peak integrated intensity value in a second diffraction angle range for the (200) plane and the (100) plane in the X-ray diffraction spectrum by a second intensity correction term, a third peak intensity value obtained by dividing a third peak integrated intensity value in a third diffraction angle range for the (220) plane and the (110) plane in the X-ray diffraction spectrum by a third intensity correction term, and a fourth peak intensity value obtained by dividing a fourth peak integrated intensity value in a fourth diffraction angle range for the (311) plane in the X-ray diffraction spectrum by a fourth intensity correction term. The SiC polycrystalline substrate according to claim 5 .

7. 2. A method for producing the SiC polycrystalline substrate according to claim 1, wherein polycrystalline SiC is grown by chemical vapor deposition.

8. The SiC polycrystalline substrate according to claim 1 and a SiC single crystal substrate are bonded together, A SiC bonded substrate having a volume resistivity of 0.015 Ωcm or less.

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