SiC EPITAXIAL WAFER AND SiC DEVICE

Abstract

An SiC epitaxial wafer according to the present invention comprises: a substrate; and an SiC epitaxial layer formed on a first surface of the substrate, wherein the SiC epitaxial layer has a thickness of 50 μm or greater, and the depth direction uniformity of the carrier concentration of the SiC epitaxial layer is less than 8.8 (%).

Description

SiC epitaxial wafers and SiC devices

[0001] The present invention relates to a SiC epitaxial wafer, a method for manufacturing a SiC epitaxial wafer, and a SiC device.

[0002] Silicon carbide (SiC) has a dielectric breakdown field that is an order of magnitude larger and a band gap that is three times larger than that of silicon (Si). Furthermore, SiC has properties such as a thermal conductivity that is approximately three times higher than that of silicon (Si). Therefore, SiC is expected to have applications in power devices, high-frequency devices, and high-temperature operating devices. For this reason, SiC epitaxial wafers have recently come into use in semiconductor devices such as those mentioned above.

[0003] SiC epitaxial wafers are obtained by depositing a SiC epitaxial layer on a SiC substrate using chemical vapor deposition (CVD). The SiC epitaxial layer becomes the active region of the SiC device.

[0004] Patent Document 1 describes a carrier concentration of 1 × 10 １３ cm －３ The above 1 x 10 １６ cm －３ A SiC epitaxial wafer comprising a SiC epitaxial layer within the following range is disclosed.

[0005] Japanese Patent Publication No. 2016-132604

[0006] Impurities such as donors and acceptors within the SiC epitaxial layer affect the properties of the SiC device; therefore, it is preferable to be able to control the carrier concentration within the SiC epitaxial layer. The carrier concentration within the SiC epitaxial layer affects the breakdown voltage characteristics, resistance, carrier lifetime, and other related properties.

[0007] However, controlling the carrier concentration during the deposition process of the epitaxial layer is difficult, and it has been found that conventional SiC epitaxial wafers tend to have large variations in carrier concentration in the depth direction. This tendency was more pronounced as the thickness of the SiC epitaxial layer increased. One reason for this is that environmental changes within the equipment progress more rapidly as the thickness increases. Therefore, conventional SiC epitaxial wafers have had problems with carrier concentration uniformity in the depth direction and its reproducibility.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a SiC epitaxial wafer and a SiC device in which variation in carrier concentration in the depth direction is suppressed in a SiC epitaxial wafer having a large SiC epitaxial layer of 50 μm or more thickness.

[0009] To solve the above problems, the present invention provides the following means.

[0010] [1] A SiC epitaxial wafer according to one embodiment of the present invention comprises a SiC substrate and a SiC epitaxial layer formed on the first surface of the SiC substrate, wherein the thickness of the SiC epitaxial layer is 50 μm or more, and the depth-direction uniformity of the carrier concentration of the SiC epitaxial layer is 8.8% or less.

[0011] [2] The diameter of the SiC epitaxial wafer in [1] above may be 149 mm or more.

[0012] [3] The diameter of the SiC epitaxial wafer in [1] above may be 199 mm or more.

[0013] [4] When the SiC epitaxial wafer described in [1] to [3] above has a central coordinate in plan view of (0,0) and radius R, the carrier concentration at all measurement points at coordinates (0,0), (±R / 2,0) and (0,±R / 2) is 1.0 × 10 １3 cm －３ The above 1.0 x 10 １7 The following is also acceptable.

[0014] [5] The SiC epitaxial wafers described in [1] to [4] above may satisfy equation (1) when the central coordinate in a plan view is (0,0) and the radius is R, and the maximum value Max, minimum value Min, and average value mean of the carrier concentration at all measurement points at coordinates (0,0), (±R / 2,0), and (0,±R / 2) satisfy equation (1). [{(Max - Min) / mean} × 100] < 16.8 (%) ... (1)

[0015] [6] A SiC device according to one aspect of the invention comprises a SiC substrate and a SiC epitaxial layer formed on a first surface of the SiC substrate, wherein the thickness of the SiC epitaxial layer is 50 μm or more, and the depth-direction uniformity of the carrier concentration of the SiC epitaxial layer is 8.8 (%) or less.

[0016] According to the present invention, it is possible to provide a SiC epitaxial wafer and a SiC device that have a thick SiC epitaxial layer and suppress depth-direction variation in carrier concentration in the depth direction of the SiC epitaxial layer.

[0017] This is a cross-sectional view showing an example of the configuration of a SiC epitaxial wafer according to one embodiment of the present invention. This is a plan view showing an example of the configuration of the SiC epitaxial wafer in Figure 1. This is a plan view showing an example of the configuration of the cross section along the cutting line III-III of the SiC epitaxial wafer in Figure 1. Figure 4(a) is an enlarged view of the region enclosed by the dashed line in Figure 1, and Figures 4(a) and 4(b) are schematic diagrams for explaining the depth-direction uniformity of carrier concentration in a SiC epitaxial wafer according to one embodiment of the present invention. This is a schematic diagram showing an example of a method for manufacturing a SiC epitaxial wafer according to one embodiment of the present invention. This is an image of setting the target value of the exhaust gas C / Si ratio. This is an image of setting the target value of the exhaust gas C / Si ratio in accordance with the change in carrier concentration over time. This is an image diagram for correcting the target value of the exhaust gas C / Si ratio based on the deposit area. This is a plan view for explaining the configuration of a SiC device according to one embodiment of the present invention. This is a graph showing the carrier concentration fluctuation when a method for manufacturing a SiC epitaxial wafer including C / Si ratio control (in-situ) according to Example 1 is performed. This graph shows the calculated carrier concentration fluctuations when a SiC epitaxial wafer manufacturing method without C / Si ratio control (in-situ) is performed according to Comparative Example 1.

[0018] The present embodiment will be described in detail below with reference to the drawings as appropriate. In the drawings used in the following description, characteristic parts may be enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of each component may differ from those in reality. The materials, dimensions, etc. exemplified in the following description are examples only, and the present invention is not limited to them, and can be implemented with appropriate modifications without changing the essence of the invention.

[0019] [SiC Epitaxial Wafer] Figure 1 is a cross-sectional view showing an example of the configuration of a SiC epitaxial wafer according to one embodiment of the present invention. The SiC epitaxial wafer 10 shown in Figure 1 comprises a SiC substrate 1 and a SiC epitaxial layer 2 formed on the first surface 1A of the SiC substrate 1, wherein the thickness of the SiC epitaxial layer 2 is 50 μm or more, and the depth-direction uniformity of the carrier concentration of the SiC epitaxial layer 2 is less than 8.8 (%).

[0020] The SiC substrate 1 is, for example, cut out from a SiC ingot. The SiC ingot grows, for example, on a SiC seed crystal using the sublimation method.

[0021] The SiC epitaxial layer 2 is formed on the first surface 1A of the SiC substrate 1. The film thickness of the SiC epitaxial layer is 50 μm or more, for example, 500 μm or less, and may be 60 μm or more and 300 μm or less, or 75 μm or more and 200 μm or less. The greater the film thickness of the SiC epitaxial layer 2, the longer the film formation time, and while the growth conditions in the same plane are considered to be uniform, there is also a concern that the growth conditions will change due to external factors such as deposition in the growth of surfaces with different depth positions, and the control of the depth direction uniformity of the carrier concentration tends to become difficult.

[0022] The SiC epitaxial layer 2 is formed on the SiC substrate 1 using, for example, the CVD method. The SiC epitaxial layer 2 has dopants composed of donors and acceptors inside. The SiC epitaxial layer 2 has dopants 3 inside. The carrier concentration can be calculated from the donor concentration and acceptor concentration in the SiC epitaxial layer 2. Specifically, the difference in the magnitude of the donor concentration [N ｄ and acceptor concentration [N ａ in the SiC epitaxial layer 2 (| [N ｄ - [N ａ |). In the case of the n-type, the donor concentration is higher than the acceptor concentration, and in the case of the p-type, the acceptor concentration is higher than the donor concentration.

[0023] The depth direction uniformity of the carrier concentration in the SiC epitaxial layer 2 is 8.8 (%) or less as described above, preferably 6.6 (%) or less, and more preferably 4.4 (%) or less. The depth direction uniformity of the carrier concentration in the SiC epitaxial layer 2 is analyzed by the analysis method described later. Hereinafter, the analysis method for the depth direction uniformity of the density of the carrier concentration in the SiC epitaxial layer 2 will be described with reference to the plan view of the SiC epitaxial wafer 10.

[0024] Figure 2 is a plan view showing an example of the configuration of the SiC epitaxial wafer shown in Figure 1. Figure 2 shows Z １／２ Measurement point SP for measuring center density ａ１ ~SP ｅ１ This is shown. When the central coordinates of the SiC epitaxial wafer 10 in plan view are (0,0) and the radius is R, the measurement point SP ａ１ SP ｂ１ SP ｃ１ SP ｄ１ SP ｅ１ The (X,Y) coordinates are represented as (0,0), (-R / 2,0), (0,-R / 2), (R / 2,0), and (0,R / 2), respectively.

[0025] The above measurement point SP ａ１ ~SP ｅ１ For this, the donor concentration [N] was determined by the mercury probe (Hg-CV) method. ｄ ] and acceptor concentration [N ａ The carrier concentration at each measurement point is calculated by measuring the [value]. To do this, the tip of the probe (capillary) is placed at each measurement point and the measurement is performed.

[0026] The carrier concentration is measured using the Hg-CV method, for example, by applying a voltage that extends to a depth of approximately 3 to 7 μm from the measurement surface of the SiC epitaxial wafer 10. For example, when measuring from the surface S, an applied voltage is applied to the SiC epitaxial wafer 10 to a depth of approximately 3 to 7 μm from the surface S of the SiC epitaxial wafer 10.

[0027] To obtain depth-direction uniformity of carrier concentration, it is then necessary to measure the carrier concentration near the first surface 1A of the SiC substrate 1. Figure 3 is a plan view showing an example of the cross-sectional configuration along the cutting line III-III of the SiC epitaxial wafer in Figure 1. Figure 3 shows the surface S' near the first surface 1A of the SiC epitaxial wafer 10. Measurement point SP shown in Figure 3 ａ２ ~SP ｅ２ Each of these is the measurement point SP ａ１ ~SP ｅ１ Each of them overlaps in the depth direction. That is, measurement point SP ａ２ SP ｂ２ SP ｃ２SP ｄ２ SP ｅ２ The (X,Y) coordinates are represented as (0,0), (-R / 2,0), (0,-R / 2), (R / 2,0), and (0,R / 2), respectively.

[0028] Figure 4(a) is an enlarged view of the region enclosed by the dashed line in Figure 1, and Figures 4(a) and 4(b) are schematic diagrams illustrating the depth-direction uniformity of carrier concentration in a SiC epitaxial wafer 10 according to one embodiment of the present invention. The outermost surface S and the surface S' where the carrier concentration is measured after the outermost surface S of the SiC epitaxial wafer 10 shown in Figure 2 are separated by a distance D in the depth direction. Therefore, the measurement areas when the carrier concentration is measured by the Hg-CV method under the same conditions on the outermost surface S and surface S' are also separated by a distance D. In this embodiment, the distance D used to measure the depth-direction uniformity of carrier concentration is 30 μm. When performing a similar evaluation, the distance D can be changed as appropriate, for example, a distance in the range of 15 μm to 100 μm, a distance in the range of 20 μm to 60 μm, or a distance in the range of 25 μm to 40 μm can be set as appropriate. Figures 4(a) and 4(b) show the measurement point SP shown in Figure 2. ａ１ ~SP ｅ１ When carrier concentration is measured using either of the following methods, the measurement region R1 and SP shown in Figure 3 are... ａ２ ~SP ｅ２ The measurement region R2 is shown when the carrier concentration is measured using either of the methods. As shown in Figures 4(a) and 4(b), the distance D is set so that the measurement regions R1 and R2 do not overlap. The thickness of the measurement regions R1 and R2 is the same. The thickness of the measurement regions R1 and R2 can be, for example, 3 to 7 μm.

[0029] Taking a configuration in which the carrier concentration is measured at two locations in the depth direction from the thickness of the SiC epitaxial layer 2 as an example, the depth-direction uniformity of the carrier concentration of the SiC epitaxial wafer 10 is measured at measurement point SP ａ１ and SP ａ２ SP ｂ１ and SP ｂ２ SP ｃ１ and SP ｃ２ SP ｄ１ and SPｄ２ , and SP ｅ１ and SP ｅ２ The difference can be multiplied by 100 and divided by the average value of the carrier concentration at the measurement point to calculate the unit (%). For example, the depth-direction uniformity of the carrier concentration at the center of the plan view of the SiC epitaxial wafer 10 is the measurement point SP ａ１ Carrier concentration and measurement point SP ａ２ Z １／２ Difference in center density (cm －３ The value obtained by multiplying the result by 100 and dividing by the average value of the carrier concentration at the measurement location is calculated in units (%). In order to measure the carrier concentration on the surface S after measuring the carrier concentration on the outermost surface S, the SiC epitaxial layer 2 of a predetermined thickness is removed before measuring the carrier concentration. When the thickness of the SiC epitaxial layer 2 exceeds 60 μm and the carrier concentration is measured at three or more locations in the depth direction, and the depth-direction average of the carrier concentration is calculated, after measuring the carrier concentration on the outermost surface S, the removal of the SiC epitaxial layer 2 of a predetermined thickness and the measurement of the carrier concentration are repeated two or more times, and the difference between the maximum and minimum values ​​of the carrier concentration at each of the five locations in a plan view is divided by the average value of the carrier concentrations at the five locations and multiplied by 100 to calculate the average.

[0030] In this embodiment, the SiC epitaxial wafer 10 has a depth-direction uniformity of 8.8% or less, preferably 6.6% or less, more preferably 4.4% or less, and even more preferably 2.2% or less for all five measurement areas in the plan view.

[0031] The average value of the carrier concentration at all measurement points is, for example, 1.0 × 10⁻⁶. １3 cm －３ The above 1.0 x 10 １7 cm －３ The following is true: 2.0 × 10 １3 cm －３ The above 1.0 x 10 １6 cm －３ Preferably, it is 5.0 × 10 １3 cm －３ The above 3.0 x 10 １5 cm －３The following is more preferable:

[0032] Carrier concentrations may vary depending on the position in the in-plane direction. That is, at the five measurement points SP on the outermost surface S ａ１ ~SP ｅ１ and five measurement points SP on the surface S' near the first surface 1A ａ２ ~SP ｅ２ Each of these values ​​may differ. The variation in carrier concentration within the same plane at the above measurement points is preferably 8.0% or less. The variation in carrier concentration within the same plane is, in the case of the outermost surface S, at the measurement point SP ａ１ ~SP ｅ１ It is calculated by dividing the difference between the maximum and minimum carrier concentrations by the average value and multiplying the result by 100, expressing it in units of percentage (%).

[0033] When the maximum carrier concentration at all measurement points is denoted as Max and the minimum carrier concentration as Min, it is preferable that the maximum value Max and the minimum value Min satisfy the following equation (1). Typically, the maximum value Max and the minimum value Min represent the carrier concentrations at measurement points on different surfaces. If carrier concentrations are measured at n locations in the depth direction, the number of measurement points will be 5 × n.

[0034] [{(Max - Min) / mean} × 100] < 16.8 (%) ... (1) (mean: average value of carrier concentration at all measurement points (cm³) －３ )) The right-hand side of equation (1) above is the sum of the carrier concentration depth-direction uniformity of 8.8% (or less) and the carrier concentration in-plane average uniformity of 8.0% (or less). The in-plane uniformity of carrier concentration is preferably less than 8.0% and more preferably less than 6.0% at any measurement surface. The in-plane uniformity of carrier concentration can be calculated by multiplying the difference between the maximum and minimum values ​​of carrier concentration at the five measurement points by 100 and dividing by the average value. Furthermore, the right-hand side of equation (1) above is preferably 12.6% and more preferably 8.4%.

[0035] Regarding doping concentrations, for n-type drugs, a lower acceptor concentration is preferable, and for p-type drugs, a lower donor concentration is preferable. For n-type drugs, the acceptor concentration is, for example, 1 × 10⁻⁶. １３ cm －３ The following, preferably 1 × 10 １２ cm －３ The following applies: For type p, the donor concentration is, for example, 1 × 10⁻⁶. １３ cm －３ The following, preferably 1 × 10 １２ cm －３ The following applies:

[0036] The diameter of the SiC epitaxial wafer 10 is, for example, 100 mm or more, preferably 150 mm or more, and more preferably 200 mm or more. Here, the diameters described in this paragraph are not strict, and an error of about ±1 mm is permitted. That is, a wafer with a diameter of 100 mm means a wafer with a diameter of 99 mm or more and 101 mm or less, a wafer with a diameter of 150 mm means a wafer with a diameter of 149 mm or more and 151 mm or less, and a wafer with a diameter of 200 mm means a wafer with a diameter of 199 mm or more and 201 mm or less. The diameter of the SiC epitaxial wafer 10 may also be, for example, 305 mm or less (306 mm or less with an error of 1 mm permitted).

[0037] The drift layer is the layer through which drift current flows, and where elements such as transistors are formed when fabricating SiC devices, as described later. Drift current is the current generated by the flow of carriers when a voltage is applied to a semiconductor.

[0038] Next, in order to describe the method for manufacturing SiC epitaxial wafers according to this embodiment, we will first describe a growth apparatus that can be used for manufacturing SiC epitaxial wafers.

[0039] [Growth Apparatus] Figure 5 is a schematic diagram showing an example of a method for manufacturing a SiC epitaxial wafer according to one embodiment of the present invention. The growth apparatus 100 shown in Figure 5 includes, for example, a chamber 20, a support 30, a susceptor 40, a lower heater 50, and an upper heater 60. Figure 5 shows the state in which the SiC substrate 1 is placed on the susceptor 40. The growth apparatus 100 shown in Figure 5 is an example of an apparatus that can be used in the method for manufacturing a SiC epitaxial wafer according to this embodiment, and other configurations are also possible. For example, the growth apparatus 100 is a vertical furnace that supplies raw material gas from above the first surface 1A of the SiC substrate 1, but it may also be a horizontal furnace that supplies raw material gas parallel to the first surface 1A of the SiC substrate 1. Alternatively, a single-wafer furnace capable of simultaneously depositing films on multiple SiC substrates 1 may be used.

[0040] The chamber 20 includes, for example, a main body 21, a gas supply port 22, and a gas outlet 23. The gas outlet 23 is connected to an exhaust pump 80. An analyzer 70 is also provided at the gas outlet 23. The analyzer 70 is, for example, a quadrupole mass analyzer. The analyzer 70 can analyze the components of the gas exhausted from the gas outlet 23.

[0041] The support 30 supports the SiC substrate 1. The support 30 is rotatable around its axis. The SiC substrate 1 is placed on the support 30, for example, with the SiC substrate 1 placed on the susceptor 40. The susceptor 40 is transported into the chamber 20 with the SiC substrate 1 placed on it. The lower heater 50 is located, for example, inside the support 30 and heats the SiC substrate 1. The upper heater 60 heats the upper part of the chamber 20. The member exposed in the film deposition space S is, for example, a carbon member, and its surface may be coated with SiC or TaC.

[0042] [Method for Manufacturing SiC Epitaxial Wafers] A method for manufacturing SiC epitaxial wafers according to one embodiment of the present invention includes a formation step of forming a SiC epitaxial layer on the first surface of a SiC substrate by chemical vapor deposition using a growth apparatus having a gas supply port and a gas outlet for supplying Si-based gas and C-based gas.

[0043] <Formation Process> The formation process includes an adjustment process in which the gas discharged from the gas outlet 23 is analyzed by quadrupole mass spectrometry, and if the analyzed C / Si ratio is lower than the target value, the amount of C-based gas supplied to the Si-based gas is increased, and if the analyzed C / Si ratio is higher than the target value, the amount of C-based gas supplied to the Si-based gas is decreased.

[0044] The formation process includes, for example, a heating step, a growth step, and a cooling step.

[0045] The heating process raises the temperature inside the growth apparatus 100 to the growth temperature T. ２ Raise it up to this point. Growth temperature T ２ This refers to a temperature in the range of 1500°C to 1750°C, for example.

[0046] The growth process is the process after the heating process, and the growth temperature T ２ Si-based gas and C-based gas are supplied, and a SiC epitaxial layer 2 is epitaxially grown on the SiC substrate 1. The above preparation step is a step within the growth process.

[0047] The cooling process is a process that follows the growth process and lowers the temperature inside the growth apparatus 100.

[0048] Here, the temperature inside the growth apparatus 100 is the temperature of the SiC substrate 1 or SiC epitaxial wafer 10 as measured by a radiation thermometer (pyrometer).

[0049] Si-based gases are source gases that contain silicon in their molecules. Examples of Si-based gases include silanes (SiH). ４ ), dichlorosilane (SiH ２ Cl ２ ), trichlorosilane (SiHCl ３ ), tetrachlorosilane (SiCl ４ ) etc. C-type gases are source gases that contain C in their molecules. C-type gases include, for example, propane (C ３ H ８ ), ethylene (C ２ H ４), etc. The dopant gas is a gas containing an element serving as a carrier. The dopant gas is, for example, nitrogen, ammonia, etc. The purge gas is a gas for transporting these gases to the SiC substrate 1 and is hydrogen or the like that is inert to SiC.

[0050] In the formation process, as described above, the gas discharged from the gas outlet is analyzed by quadrupole mass spectrometry (QMS analysis). When the C / Si ratio of the analyzed gas is lower than the target value, the supply amount of the C-based gas with respect to the Si-based gas is increased. When the analyzed C / Si ratio is higher than the target value, the supply amount of the C-based gas with respect to the Si-based gas is decreased. The adjustment process is a process during the growth process and is performed in parallel with the formation of the SiC epitaxial layer 2 on the SiC substrate 1. That is, the adjustment process is a process performed (in-situ).

[0051] During the formation process, the raw material gas supplied into the chamber 20 may not be supplied to the SiC substrate 1 at the intended C / Si ratio due to, for example, deposition occurring on the upstream side close to the gas supply port 22 with respect to the SiC substrate 1 within the chamber 20.

[0052] In such a case, in the adjustment process, when the C / Si ratio of the raw material gas discharged from the gas outlet 23 is lower than the target value, the supply amount of the C-based gas is increased. When the C / Si ratio of the raw material gas discharged from the gas outlet 23 is higher than the target value, the supply amount of the C-based gas is decreased. The adjustment process is preferably performed so that the C / Si ratio is always within the range of the target value ±0.005, and more preferably within the range of the target value ±0.003.

[0053] By controlling the flow rate of the raw material gas in the growth process as described above, the C / Si ratio supplied to the SiC substrate 1 can be made closer to an ideal value. In this embodiment, the formation of the Z １／２ center associated with carbon vacancies is suppressed, and the depth direction uniformity of the Z １／２ center density within the SiC epitaxial layer 2 can be improved.

[0054] Furthermore, the method for manufacturing a SiC epitaxial wafer according to this embodiment may further include one or more test steps and feedback steps before the formation step, and a target value for the raw material gas supply in the formation step may be set based on the results of the test steps.

[0055] In the process of forming the SiC epitaxial layer 2, if the C / Si ratio changes by 0.005, Z １／２ Center density (cm²) －３ Since the C / Si ratio is expected to fluctuate by 5%, controlling the C / Si ratio during growth is important. Furthermore, the external environment may be changing in the early stages of growth and just before completion, so it is desirable that the C / Si ratio in the supplied raw material gas takes the external environment into consideration.

[0056] <Testing Process> The testing process includes a first forming step, an analysis step, and a measurement step, and more preferably further includes a preliminary measurement step. The testing process is performed at least once, but may be performed multiple times.

[0057] (Preliminary Measurement Process) In the preliminary measurement process, the weight and specific surface area of ​​the by-products (depots) in the growth apparatus 100 are measured. In the growth apparatus 100, by-products may be generated in the chamber 20 in the region between the gas supply port 22 and the gas outlet 23 (i.e., the region between the growth area and the exhaust gas). The weight of the by-products in the growth apparatus 100 is measured, for example, by an electronic weighing scale. The above region is a specific region at any position between the gas supply port 22 and the gas outlet 23. In the series of steps of this test process, the above specific region is fixed and not changed.

[0058] The surface area of ​​the by-products within the growth apparatus 100 can be confirmed by sampling the by-products in the above-mentioned area (growth area to exhaust gas) and measuring them with a laser microscope. The deposit area (weight of deposit × specific surface area) measured in the preliminary measurement step may be used to correct the predetermined target value of the C / Si ratio by using the same method as described later.

[0059] (First Forming Process) In the first forming process, a SiC epitaxial layer is formed on the first surface of a test SiC substrate using the growth apparatus 100 that performed the preliminary measurement process, while analyzing the gas discharged from the gas outlet 23 by quadrupole mass spectrometry. The growth is carried out while analyzing the gas discharged from the gas outlet by quadrupole mass spectrometry (QMS analysis). The process is carried out so that the C / Si ratio of the gas analyzed by QMS analysis is constant at a target value. For example, the first forming process includes an adjustment process in which the amount of C-based gas supplied to the Si-based gas is increased when it is lower than the target value, and the amount of C-based gas supplied to the Si-based gas is decreased when the analyzed C / Si ratio is higher than the target value. The adjustment process is a process within the first forming process and is carried out in parallel with the formation of the SiC epitaxial layer 2 on the SiC substrate 1. That is, the adjustment process is an in-situ process. It is preferable to control the C / Si ratio by PID control (Proportional-Integral-Differential Controller). During growth, the C / Si ratio of the analyzed gas is controlled to remain constant at a predetermined target value. Preferably, the C / Si ratio of the analyzed gas is controlled to always be within the range of ±0.005 of the predetermined value, more preferably to ±0.004, and even more preferably to ±0.003. In other words, the C / Si ratio in the exhaust gas is preferably controlled so that the difference from the target value is ±0.005 or less, more preferably to ±0.004 or less, and even more preferably to ±0.003 or less. Note that the C / Si ratio represents 1 when the flow rates of the C-based gas and the Si-based gas are the same. That is, when the C / Si ratio is 1, it means that the ratio of the flow rate of the C-based gas to the flow rate of the Si-based gas is 100%. Therefore, a C / Si ratio of 0.001 corresponds to 0.1%, 0.003 to 0.3%, 0.004 to 0.4%, and 0.005 to 0.5%.

[0060] In the adjustment process, QMS analysis primarily measures the gas species contributing to the reaction to perform a qualitative evaluation of the C / Si ratio. For systems containing only Si-based and C-based gases, for example, [C2H2 + ] / [Si+ , if the system contains a Cl-based gas in addition to the Si-based gas and the C-based gas, for example, [C2H2 + / [SiCl2 + , determine the ion species to be measured according to each reaction process, and adjust the increase or decrease of the ratio so that it becomes constant at a target value as the qualitative increase or decrease of the C / Si ratio.

[0061] (Analysis step) In the analysis step, the depth direction uniformity of the carrier concentration of the SiC epitaxial layer of the SiC epitaxial wafer formed in the first formation step is analyzed.

[0062] Measure the variation in the carrier concentration in the depth direction of the SiC epitaxial layer. In the analysis step, when measuring the variation in the carrier concentration in the depth direction of the SiC epitaxial layer, it is possible to measure by the same method as in the above embodiment. That is, the analysis step is performed by a destructive inspection and includes a film thickness measurement step, a plurality of evaluation steps, and a removal step.

[0063] In the film thickness measurement step, the film thickness of the SiC epitaxial layer 2 is measured by Fourier transform infrared spectroscopy (FT-IR method).

[0064] In the evaluation step, measurement is performed by the Hg-CV method at five locations of (0, 0), (±R / 2, 0), and (0, ±R / 2) from the outermost surface S of the SiC epitaxial wafer with a planar view center (0, 0) and a radius R, and the carrier concentration on the surface near the outermost surface is measured. For the measurement of the carrier concentration on the surface near the outermost surface, for example, in the Hg-CV method, a voltage is applied to the SiC epitaxial wafer 10 such that the depth from the surface S of the SiC epitaxial wafer 10 is about 3 to 7 μm. Thus, the voltage is applied so that the thickness of the measurement region R1 is about 2 to 5 μm, such as (7 - 3 =) 4 μm.

[0065] In the removal process, the SiC epitaxial layer 2 is thinned by removing it in the thickness direction so that the carrier concentration measurement points are equally spaced, according to the thickness of the SiC epitaxial layer 2, in order to evaluate the results of the film thickness measurement process and the uniformity of carrier concentration in the depth direction. For example, if the film thickness of the SiC epitaxial layer 2 is 110 μm, the Hg-CV method is performed at the outermost surface, a depth of 30 μm from the outermost surface, a depth of 60 μm from the outermost surface, and a depth of 90 μm from the outermost surface, and the layer is removed so that the carrier concentration can be measured. Under these conditions, the uniformity of carrier concentration in the depth direction can be measured with high accuracy. The removal process can be carried out by grinding, polishing, etc.

[0066] After the removal process, the evaluation process is repeated under the same conditions as the previous evaluation process. Specifically, in the evaluation process after the removal process, the carrier concentration is measured on the surface near the surface exposed after the removal process using the Hg-CV method. The conditions for the evaluation process can be the same as those for the first evaluation process. That is, the carrier concentration is measured using the Hg-CV method at five locations in a plan view: (0,0), (±R / 2,0), and (0,±R / 2), such that the depth of the measurement area from the surface S exposed after removal is 3 to 7 μm.

[0067] If there are three or more measurement points for carrier concentration in the depth direction, the removal process is then repeated. In this way, the evaluation process and removal process are repeated according to the number of measurement points necessary for evaluating the uniformity of carrier concentration in the depth direction.

[0068] The depth-direction uniformity of carrier concentration is analyzed from the maximum, minimum, and average values ​​of carrier concentration at the measurement locations obtained from the above measurements. Alternatively, the variation in carrier concentration within the SiC epitaxial layer 2 may be analyzed based on equation (1) using the maximum and minimum values ​​(Max and Min) of carrier concentration at all measurement locations.

[0069] [{(Max - Min) / mean} × 100] < 16.8 (%) ... (1) (mean: average value of carrier concentrations at 10 locations (cm) －３ ))

[0070] (Measurement Process) In the measurement process, the weight and surface area of ​​the by-products in the growth apparatus 100 after the first forming process are measured. The weight and surface area of ​​the by-products in the growth apparatus 100 can be measured in the same manner as in the preliminary measurement process described above. The area in which the measurement is performed in the measurement process is the area between the gas supply port 22 and the gas outlet 23, and is the same specific area as the area in which the measurement process was performed.

[0071] <Feedback Process> The feedback process sets target values ​​for the supply amounts of Si-based gas and C-based gas in the formation process of the main process, which actually manufactures the SiC epitaxial wafer 10, based on the results of the test process. That is, a standard (target value) for the amount of raw material gas to be flowed in the formation process is set based on the results of the (preliminary measurement process,) analysis process and measurement process. The standard (target value) for raw material gas may be constant over time, or it may change over time. First, a constant value is set as the target value of the exhaust gas C / Si ratio based on the C / Si ratio in the exhaust gas QMS analysis. Figure 6 shows an image of setting the target value of the exhaust gas C / Si ratio.

[0072] Next, if the carrier concentration undergoes a specific change over time, a target value for the C / Si ratio that changes over time is set to correspond to that change. For example, the target value can be made proportional to the growth time. Specifically, if the carrier concentration decreases over time, the standard (target) C / Si ratio is set to decrease over time, and if the carrier concentration increases over time, the standard (target) C / Si ratio is set to increase over time (first adjustment step). Figure 7 shows an image of setting the target value for the exhaust gas C / Si ratio in accordance with the change over time of the formed carrier concentration. The adjustment can be made according to the dashed line in Figure 7(b) in accordance with the result of the dashed line in Figure 7(a), or according to the dashed line in Figure 7(b) in accordance with the result of the dashed line in Figure 7(a).

[0073] Next, considering that a discrepancy occurs between the exhaust gas C / Si ratio measurement value and the C / Si ratio of the growth area in relation to the deposit area within the apparatus (weight of the deposit × specific surface area of ​​the deposit), the target value of the exhaust gas C / Si ratio set in the first adjustment step is corrected in relation to the deposit area within the apparatus (second adjustment step). Figure 8 is an illustrative diagram of how the target value of the exhaust gas C / Si ratio is corrected based on the deposit area. The correction amount is set based on a map like Figure 8(a) obtained in advance through multiple tests. Here, it is preferable to use a map relating to the deposit area measurement locations. Figure 8(b) shows the case where the required correction amount (p) calculated from the map in Figure 8(a) is corrected from the measured deposit area, as shown by the solid line graph in Figure 8(b). The larger the deposit area, the greater the discrepancy between the exhaust gas C / Si measurement value and the growth area C / Si, the C / Si ratio of the by-product deposit is < 1, and the amount of by-product generated increases with the deposit area. Therefore, the deposit area needs to be larger than the growth area C / Si measured in the exhaust gas.

[0074] In this way, target values ​​can be set for the supply amounts of Si-based gas and C-based gas in the formation process of this process.

[0075] According to the SiC epitaxial wafer manufacturing method of the above embodiment, the carrier lifetime can be estimated because the carrier concentration can be measured, and a SiC epitaxial wafer can be provided in which the variation in carrier concentration in the depth direction of the SiC epitaxial layer is suppressed. Furthermore, according to the SiC epitaxial wafer manufacturing method of the above embodiment, a SiC epitaxial wafer with a uniform carrier concentration can be provided without performing a process to reduce the carrier concentration after the formation of the SiC epitaxial layer 2.

[0076] [SiC Device] A SiC device according to one embodiment of the present invention comprises a SiC substrate and a SiC epitaxial layer formed on the first surface of the SiC substrate, wherein the depth-direction uniformity of the carrier concentration in the SiC epitaxial layer is 8.8% or less. As the SiC substrate and SiC epitaxial layer provided in the SiC device, the SiC substrate and SiC epitaxial layer of the SiC epitaxial wafer according to the above embodiment can be used.

[0077] The SiC device is obtained from the SiC epitaxial wafer 10 according to the above embodiment. Figure 9 is a plan view illustrating the configuration of a SiC device according to one embodiment of the present invention. The SiC device 200 can be manufactured by forming devices such as transistors on the SiC epitaxial wafer 10 and then chipping it. In Figure 9, each rectangular section of the SiC epitaxial wafer 10 is a SiC device. The SiC device 200 may also be manufactured by forming devices such as transistors and diodes on the SiC epitaxial wafer 10 after chipping it.

[0078] The SiC device 200 according to this embodiment comprises a chipped SiC substrate and a SiC epitaxial layer provided on one surface of the chipped SiC substrate. Devices such as transistors are formed in the drift layer of the SiC epitaxial layer. The configurations of the SiC substrate, buffer layer, and drift layer in the SiC device 200 are the same as those of the SiC epitaxial wafer 10 before chipping.

[0079] If the SiC device 200 further comprises components other than the SiC substrate and the SiC epitaxial layer, the carrier concentration in the SiC epitaxial layer of the SiC device 200 can be measured after removing the regions other than the SiC substrate and the SiC epitaxial layer from the SiC device 200. These regions can be removed, for example, by grinding or polishing. There is no change in the carrier concentration distribution in the SiC epitaxial layer during the process of removing these regions. The carrier concentration in the SiC epitaxial layer of the SiC device 200 can be measured by measuring the depth-direction uniformity at a single point 201, the center of the SiC device 200 in a plan view, in the same manner as in the above embodiment. That is, taking a configuration in which the epitaxial layer thickness is less than 60 μm as an example, first, the carrier concentration at the center 201 of the chip in a plan view can be measured on the surface of the SiC epitaxial layer of the SiC device, and then the carrier concentration at the center 201 in a plan view can be measured on the surface exposed by the removal process.

[0080] The depth-direction uniformity of the carrier concentration in the SiC epitaxial layer of the SiC device 200 is 8.8% or less, preferably 6.6% or less, more preferably 4.4% or less, and even more preferably 2.2% or less.

[0081] Furthermore, the carrier concentration in the SiC epitaxial layer of the SiC device 200 is, for example, 1.0 × 10⁻⁶. １3 cm －３ The above 1.0 x 10 １7 cm －３ The following is true: 2.0 × 10 １3 cm －３ The above 1.0 x 10 １6 cm －３ Preferably, it is 5.0 × 10 １3 cm －３ The above 3.0 x 10 １5 cm －３ The following is more preferable: The carrier concentration of this SiC epitaxial layer should be achieved as a result of the carrier concentration measurement at the measurement site of the center 201 in each chip.

[0082] As described above, the SiC epitaxial wafer 10 according to the above embodiment exhibits excellent depth-direction uniformity of carrier concentration in the buffer layer, and similarly, the depth-direction uniformity of carrier concentration in the SiC epitaxial layer of the SiC device 200 is also excellent. Therefore, carrier lifetime can be evaluated more accurately.

[0083] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims. Furthermore, the upper and / or lower limits of the numerical ranges described herein can be arbitrarily combined to define a preferred range. For example, a preferred range can be defined by arbitrarily combining the upper and lower limits of the numerical ranges, by arbitrarily combining the upper limits of the numerical ranges, and by arbitrarily combining the lower limits of the numerical ranges.

[0084] [Example 1] The C / Si ratio was adjusted in situ by the SiC epitaxial wafer manufacturing method of the present invention, and the carrier concentration ([N) of the SiC epitaxial wafer was adjusted. d ]-[N a The film thickness dependence of the fluctuations in the SiC epitaxial layer was estimated. Specifically, the carrier concentration in the SiC epitaxial layer was calculated from the fluctuations in the C / Si ratio and the flow rate ratio of the C-based gas and Si-based gas when the C / Si ratio was adjusted by adjusting the flow rate ratio of the C-based gas and Si-based gas in situ. In Example 1, it is assumed that the configuration was adjusted so that the difference between the C / Si ratio in the exhaust gas and the target value of the C / Si ratio in the exhaust gas was within ±0.005. By adjusting the C / Si ratio in situ, it is assumed that the difference from the target value of the C / Si ratio will change in a sinusoidal curve with respect to the film thickness of the SiC epitaxial layer, as shown in Figure 10.

[0085] Figure 10 is a graph showing the calculated carrier concentration fluctuations when a SiC epitaxial wafer manufacturing method including C / Si ratio control (in-situ) according to Example 1 is performed. The carrier concentration is considered to depend largely on the ratio of C-based gas and Si-based gas. In this example, the SiC epitaxial layer was not actually removed and the carrier concentration was not measured. Instead, the carrier concentration fluctuations were calculated based on a configuration in which information on the C / Si fluctuations up to the outermost surface and the corresponding carrier concentration information is retained across the entire depth direction. The carrier concentration fluctuations were calculated using the following formula. The average value of the carrier concentration is the average value of the carrier concentration from the SiC epitaxial layer thickness of 0 μm to the outermost surface. The carrier concentration fluctuations differ from the method described as formula (1) in the above embodiment in that they are calculated based on measurement data across the entire depth direction, but it is considered that they show values ​​that are approximately the same as the results based on actual measurements.

[0086] Carrier concentration fluctuation = [{(Maximum carrier concentration) - (Minimum carrier concentration)} / (Average carrier concentration)}] × 100 (%) ... (2) Figure 11 shows the dependence of the difference between the target C / Si ratio and the SiC epitaxial layer thickness on the thickness of the SiC epitaxial layer, and the corresponding values ​​of carrier concentration fluctuation for each SiC epitaxial layer thickness.

[0087] Table 1 summarizes the difference between the target C / Si ratio and the actual value, as well as the carrier concentration fluctuations, for SiC epitaxial layer thicknesses of 10 μm, 40 μm, 70 μm, 100 μm, 130 μm, and 160 μm. In Table 1, the difference between the target C / Si ratio and the actual value is positive when the C-based gas flow rate ratio in the exhaust gas is higher than the C-based gas flow rate ratio at the target value.

[0088]

[0089] [Comparative Example 1] The only difference from Example 1 was that the C / Si ratio was not controlled in situ, and the carrier concentration was calculated. The dependence of the carrier concentration fluctuation on the film thickness of the SiC epitaxial layer is shown in the graph. In Comparative Example 1, since the C / Si ratio is not controlled in situ, it is possible that the C / Si ratio will either increase or decrease over time. In Comparative Example 1, an increasing trend was assumed, so it was assumed that the C / Si ratio would increase as the film thickness of the SiC epitaxial layer increased, that is, as time progressed. In other words, in Comparative Example 1 as well, the dependence of the carrier concentration fluctuation on the film thickness of the SiC epitaxial layer was calculated using equation (2).

[0090] Figure 11 is a graph showing the calculated carrier concentration density fluctuations when a SiC epitaxial wafer manufacturing method without C / Si ratio control (in-situ) according to Comparative Example 1 is used.

[0091] Table 2 summarizes the difference between the target C / Si ratio and the carrier concentration variation for SiC epitaxial layer thicknesses of 10 μm, 40 μm, 70 μm, 100 μm, 130 μm, and 160 μm.

[0092]

[0093] As can be seen by comparing Figures 11 and 12, or Tables 1 and 2, in the formation process of forming a SiC epitaxial layer by supplying Si-based gas and C-based gas, it was confirmed that carrier concentration fluctuations can be reduced at any film thickness by controlling the C / Si ratio in-situ and minimizing the difference from the target value of the C / Si ratio.

[0094] 1: SiC substrate, 1A: First surface, 2: SiC epitaxial layer, 3: Dopant, 10: SiC epitaxial wafer, 20: Chamber, 21: Main body, 22: Gas supply port, 23: Gas exhaust port, 30: Support, 40: Susceptor, 50: Lower heater, 60: Upper heater, 100: Growth apparatus, S: Outer surface

Claims

1. A SiC epitaxial wafer comprising a SiC substrate and a SiC epitaxial layer formed on the first surface of the SiC substrate, wherein the thickness of the SiC epitaxial layer is 50 μm or more, and the depth-direction uniformity of the carrier concentration of the SiC epitaxial layer is 8.8% or less.

2. The SiC epitaxial wafer according to claim 1, wherein the diameter is 149 mm or more.

3. The SiC epitaxial wafer according to claim 1, wherein the diameter is 199 mm or more.

4. When the center coordinates in a plan view are (0,0) and the radius is R, the carrier concentration at all measurement points at coordinates (0,0), (±R / 2,0) and (0,±R / 2) is 1.0 × 10⁻¹⁰. １３ cm －３ The above 1.0 x 10 １７ The SiC epitaxial wafer according to claim 1, which is as follows:

5. When the central coordinates in a plan view are (0,0) and the radius is R, the maximum value Max, minimum value Min, and average value mean of the carrier concentration at all measurement points at coordinates (0,0), (±R / 2,0), and (0,±R / 2) satisfy equation (1), the SiC epitaxial wafer according to claim 1. [{(Max - Min) / mean} × 100] < 16.8 (%) ... (1) 6. A SiC device comprising a SiC substrate and a SiC epitaxial layer formed on the first surface of the SiC substrate, wherein the thickness of the SiC epitaxial layer is 50 μm or more, and the depth-direction uniformity of the carrier concentration of the SiC epitaxial layer is 8.8 (%) or less.

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