Sic epitaxial wafer

Abstract

To provide an SiC epitaxial wafer with large diameter, thin thickness, and high uniformity of carrier concentration.SOLUTION: An SiC epitaxial wafer according to the present embodiment has an SiC substrate and an SiC epitaxial layer. The SiC substrate has a diameter of 195 mm or more and a thickness of 460 μm or less. The SiC epitaxial layer has a carrier concentration variation of 20% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a SiC epitaxial wafer.

Background Art

[0002] Silicon carbide (SiC) has a breakdown electric field one order of magnitude larger and a bandgap three times larger than that of silicon (Si). In addition, silicon carbide (SiC) has characteristics such as a thermal conductivity about three times higher than that of silicon (Si). Therefore, silicon carbide (SiC) is expected to be applied to power devices, high-frequency devices, high-temperature operation devices, etc. For this reason, in recent years, SiC epitaxial wafers have been used for the semiconductor devices as described above.

[0003] A SiC epitaxial wafer is obtained by laminating a SiC epitaxial layer on the surface of a SiC substrate. Hereinafter, the substrate before laminating the SiC epitaxial layer is referred to as a SiC substrate, and the substrate after laminating the SiC epitaxial layer is referred to as a SiC epitaxial wafer. The SiC substrate is manufactured by cutting out from a SiC ingot. SiC devices such as power devices, high-frequency devices, and high-temperature operation devices are obtained by forming a device in the SiC epitaxial layer of a SiC epitaxial wafer and then dicing the SiC epitaxial wafer.

[0004] One of the indexes for evaluating a SiC epitaxial wafer is the carrier concentration. In order to improve the uniformity of chips obtained from one SiC epitaxial wafer, it is preferable that the carrier concentration in the plane of the SiC epitaxial wafer is uniform. For example, Patent Documents 1 and 2 disclose SiC epitaxial wafers having high in-plane uniformity of carrier concentration. Patent Document 3 also discloses a SiC epitaxial growth apparatus capable of increasing the temperature uniformity during manufacturing that affects the in-plane uniformity of carrier concentration.

Prior Art Documents

Patent Documents

[0005] Patent Document 1 Japanese Patent No. 6969628 Patent Document 2 Japanese Unexamined Patent Application Publication No. 2017-84989 Patent Document 3 Japanese Unexamined Patent Application Publication No. 2019-96764 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] In order to increase the number of SiC devices that can be obtained from a single SiC epitaxial wafer, an increase in the diameter of the SiC epitaxial wafer is required. However, increasing the diameter of the SiC epitaxial wafer is not easy.

[0007] When the SiC epitaxial wafer has a large diameter, the internal stress increases, and the shape may change significantly during the manufacturing process. By increasing the thickness of the SiC substrate, the shape change of the SiC epitaxial wafer can be suppressed, but this causes an increase in cost and an increase in the resistance of the device. On the other hand, simply reducing the thickness causes the SiC substrate to warp during the deposition of the SiC epitaxial layer, resulting in a decrease in the uniformity of the carrier density of the SiC epitaxial layer.

[0008] The present invention has been made in view of the above problems, and an object thereof is to provide a SiC epitaxial wafer having a large diameter, a thin thickness, and high uniformity of carrier concentration. MEANS FOR SOLVING THE PROBLEMS

[0009] (1) The SiC epitaxial wafer according to the first aspect has a SiC substrate and a SiC epitaxial layer. The SiC substrate has a diameter of 195 mm or more and a thickness of 460 μm or less. The variation in carrier concentration of the SiC epitaxial layer is 20% or less.

[0010] (2) When viewed in plan view from the stacking direction, the local thickness variation (LTV) in each of a plurality of unit exposure regions divided into 20 mm squares of the SiC epitaxial wafer according to the above aspect may be 4 μm or less.

[0011] (3) When viewed in plan view from the stacking direction, the site flatness (SFQR) in each of a plurality of unit exposure regions divided into 20 mm squares of the SiC epitaxial wafer according to the above aspect may be 2 μm or less.

[0012] (4) The SiC epitaxial wafer according to the above aspect may have a warp of 90 μm or less.

[0013] (5) When the reference plane is a plane connecting a support point located at a position overlapping with a circumference 7.5 mm inside from the outermost periphery and a portion overlapping when viewed from the thickness direction, the bow of the SiC epitaxial wafer according to the above aspect may be 60 μm or less.

[0014] (6) The SiC epitaxial wafer according to the above aspect may have a SORI of 60 μm or less.

[0015] (7) In the SiC epitaxial wafer according to the above aspect, in a first region 60 mm or more and 95 mm or less away from the center when viewed in plan view from the stacking direction, the variation in carrier concentration of the SiC epitaxial layer may be 20% or less.

[0016] (8) The SiC epitaxial wafer according to the above aspect may have a variation in film thickness of the SiC epitaxial layer of 5% or less.

[0017] (9) In the SiC epitaxial wafer according to the above aspect, in a first region 60 mm or more and 95 mm or less away from the center when viewed in plan view from the stacking direction, the variation in film thickness of the SiC epitaxial layer may be 5% or less.

Advantages of the Invention

[0018] The SiC epitaxial wafer according to the above aspect has a large diameter, a thin plate thickness, and high carrier concentration uniformity.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0020] Hereinafter, the SiC epitaxial wafer and the like according to this embodiment will be described in detail with appropriate reference to the drawings. The drawings used in the following description may show, for the sake of convenience, the characteristic parts enlarged in order to make the characteristics of this embodiment easier to understand, and the dimensional ratios of each component may be different from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and it can be appropriately modified and implemented without changing the gist thereof.

[0021] In this specification, individual orientations are indicated by [], and collective orientations are indicated by <>. Regarding negative exponents, in crystallography, a "-" (bar) is to be attached above the number, but in this specification, a negative sign is attached before the number.

[0022] FIG. 1 is a cross-sectional view of the SiC epitaxial wafer 1 according to the present embodiment. FIG. 2 is a plan view of the SiC epitaxial wafer 1 according to the present embodiment.

[0023] The SiC epitaxial wafer 1 includes a SiC substrate 2 and a SiC epitaxial layer 3. The planar shape of the SiC epitaxial wafer 1 is substantially circular. The SiC epitaxial wafer 1 may have a notch 4 for grasping the direction of the crystal axis. Further, the SiC epitaxial wafer 1 may have an orientation flat instead of the notch 4.

[0024] The SiC epitaxial wafer 1 is a wafer of 8 inches (approximately 200 mm) or more. The diameter of the SiC epitaxial wafer 1 is 195 mm or more, preferably 199 mm or more. Also, the diameter of the SiC epitaxial wafer 1 is preferably 205 mm or less, more preferably 201 mm or less. The diameter of the SiC epitaxial wafer may be measured using a laser displacement meter.

[0025] The SiC substrate 2 is made of, for example, n-type SiC. The polytype of the SiC substrate 2 is not particularly limited and may be any of 2H, 3C, 4H, and 6H. The SiC substrate 2 is, for example, 4H-SiC. The diameter of the SiC substrate 2 is the same as the diameter of the SiC epitaxial wafer 1.

[0026] The thickness of the SiC substrate 2 is 460 μm or less, preferably 420 μm or less, more preferably 380 μm or less, more preferably 375 μm or less, more preferably 350 μm or less, more preferably 300 μm or less, more preferably 250 μm or less, more preferably 200 μm or less, more preferably 150 μm or less, more preferably 100 μm or less, and particularly preferably 50 μm or less. The thickness of the SiC substrate 2 may be 1 μm or more. When the thickness of the SiC substrate 2 is small, the yield of SiC devices that can be obtained from one SiC ingot increases. Also, when the thickness of the SiC substrate 2 is small, the increase in the resistance of the SiC device can be suppressed. The thickness of the SiC substrate may be measured using a laser displacement meter.

[0027] The SiC epitaxial layer 3 is laminated on one surface of the SiC substrate 2. The SiC epitaxial layer 3 is made of SiC.

[0028] In addition, the SiC epitaxial layer according to the present embodiment has a variation in carrier concentration of 20% or less, preferably 15% or less, more preferably 12% or less, still more preferably 10% or less, particularly preferably 5% or less, and even more particularly preferably 2% or less. The variation in carrier concentration is obtained by dividing the difference between the maximum value and the minimum value of the carrier concentration of the SiC epitaxial layer 3 measured along a straight line extending in the <11-20> direction passing through the center C of the SiC epitaxial layer 3 by twice the average value. The measurement of the carrier concentration may be performed at equal intervals from the center C on the straight line, or the interval may vary. The measurement of the carrier concentration may be performed at intervals of 10 mm, 15 mm, 20 mm, 25 mm, or 30 mm. The lower limit value of the variation in carrier concentration may be 0.5% or 1.5%.

[0029] For example, when the diameter of the SiC epitaxial wafer 1 is 200 mm (8 inches), along a straight line L extending in the <11-20> direction with the center C as a reference, the carrier concentration is measured at the center and at positions of ±20 mm, ±40 mm, ±60 mm, ±80 mm, and ±95 mm from the center, and the carrier concentration uniformity is determined from the respective carrier concentrations at these measurement points.

[0030] Also, for example, when the diameter of the SiC epitaxial wafer 1 is 250 mm (10 inches), along a straight line L extending in the <11-20> direction with the center C as a reference, the carrier concentration is measured at the center and at positions of ±25 mm, ±50 mm, ±75 mm, ±100 mm, and ±120 mm from the center, and the carrier concentration uniformity is determined from the respective carrier concentrations at these measurement points.

[0031] Also, for example, when the diameter of the SiC epitaxial wafer 1 is 300 mm (12 inches), along a straight line L extending in the <11-20> direction with the center C as a reference, the carrier concentration is measured at the center and at positions of ±30 mm, ±60 mm, ±90 mm, ±120 mm, and ±145 mm from the center, and the carrier concentration uniformity is determined from the respective carrier concentrations at these measurement points.

[0032] Here, the carrier concentration is the effective carrier concentration. The effective carrier concentration is the absolute value of the difference between the donor concentration and the acceptor concentration. The carrier concentration of the SiC epitaxial layer 3 can be measured, for example, by the mercury probe (Hg-CV) method or the secondary ion mass spectrometry (SIMS) method. The Hg-CV method measures the difference between the donor concentration and the acceptor concentration as the effective carrier concentration. The secondary ion mass spectrometry (SIMS) is a method of performing mass spectrometry on the secondary ions that pop out while shaving the layer in the thickness direction. The doping concentration can be measured from the mass spectrometry. The secondary ion mass spectrometry (SIMS) can measure the actual values of the donor concentration and the acceptor concentration respectively, and by obtaining the difference between these, the effective carrier concentration can be obtained.

[0033] The variation in the carrier concentration of the SiC epitaxial layer 3 is preferably 20% or less, more preferably 15% or less, still more preferably 12% or less, even more preferably 10% or less, particularly preferably 5% or less, and even more particularly preferably 2% or less in a first region that is 60 mm or more and 95 mm or less away from the center when viewed in plan from the stacking direction. The first region is located on the outer peripheral side of the SiC epitaxial wafer 1 and is a portion where the carrier concentration is likely to vary. If the variation in this portion is within the above range, the element variation of the SiC device after device formation can be further reduced. The measurement of the carrier concentration in the first region is performed, for example, at points of ±60 mm, ±80 mm, and ±95 mm from the center along a straight line extending in the <11-20> direction with the center C as a reference, and at points of ±60 mm, ±80 mm, +95 mm, and -90 mm along a straight line extending in the <-1100> direction with the center C as a reference. -90 mm is arranged inside to avoid the notch 4. Note that the [11-20] direction or the [-1100] direction is denoted as "+". The lower limit of the variation in the carrier concentration in the first region may be 0.5% or 1.5%.

[0034] Further, the SiC epitaxial layer 3 according to the present embodiment may have a variation in film thickness of 5% or less. The variation in the film thickness of the SiC epitaxial layer 3 is preferably 4% or less, more preferably 3% or less, still more preferably 2% or less, and particularly preferably 1% or less. The variation in film thickness is obtained by dividing the difference between the maximum value and the minimum value of the film thickness of the SiC epitaxial layer 3 measured using infrared spectroscopy along a straight line passing through the center C of the SiC epitaxial layer 3 and extending in the <11-20> direction by twice the average value. The measurement points of the film thickness are the same as those of the carrier concentration. The lower limit of the variation in the film thickness of the SiC epitaxial layer may be 0.3% or 0.9%.

[0035] The thickness variation of the SiC epitaxial layer 3 is preferably 5% or less, more preferably 4% or less, still more preferably 3% or less, still more preferably 2% or less, and particularly preferably 1% or less in a first region that is 60 mm or more and 95 mm or less away from the center when viewed in a plan view from the stacking direction. The first region is located on the outer peripheral side of the SiC epitaxial wafer 1 and is a portion where the film thickness is likely to vary. If the variation in this portion is within the above range, the element variation of the SiC device after device formation can be further reduced. The measurement points of the film thickness are the same as those of the carrier concentration measurement points. In the first region, the lower limit of the thickness variation of the SiC epitaxial layer may be 0.3% or 0.9%.

[0036] Also, for the SiC epitaxial wafer 1 according to the present embodiment, the Warp is preferably 90 μm or less, more preferably 75 μm or less, still more preferably 50 μm or less, and may be 30 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, or 5 μm or less. The SiC epitaxial wafer 1 with a Warp of 90 μm or less is advantageous in terms of transfer to a process device and alignment accuracy. The lower limit of the Warp may be 0 μm or 1.0 μm.

[0037] FIG. 3 is a diagram schematically showing a method for evaluating the shape (deformation) of the SiC substrate due to Warp. The Warp is the distance in the thickness direction between the highest point hp and the lowest point lp of the first surface 1a. The first surface 1a is the outer surface of the SiC epitaxial layer 3. The larger the Warp, the more the SiC epitaxial wafer 1 is judged to be deformed.

[0038] First, place the SiC epitaxial wafer 1 on three support points installed on the flat surface F. The support points are located, for example, at positions overlapping the circumference 7.5 mm inside from the outer peripheral edge of the SiC epitaxial wafer 1. Determine a virtual plane Slp parallel to the flat surface F passing through the lowest point lp on the first surface 1a, and a virtual plane Shp parallel to the flat surface F passing through the highest point hp on the first surface 1a. Warp is determined as the height-direction distance between the virtual plane Slp and the virtual plane Shp. The height direction is orthogonal to the flat surface F and is the direction away from the flat surface F.

[0039] For the SiC epitaxial wafer 1 according to this embodiment, it is preferable that the absolute value of Bow is 60 μm or less, more preferably 45 μm or less, and may be 30 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, or 5 μm or less. The SiC epitaxial wafer 1 with the absolute value of Bow being 60 μm or less can appropriately align the focus on the processing surface even in a fine lithography process, and the SiC epitaxial wafer 1 can be processed with high accuracy. The lower limit value of Bow may be 0.5 μm as an absolute value.

[0040] FIG. 4 is a diagram schematically showing a method for evaluating the shape (deformation) of the SiC epitaxial wafer 1 due to Bow. Bow is the height-direction position of the center c of the SiC epitaxial wafer 1 with respect to the reference plane Sr. In other words, Bow is the signed distance of the center c of the SiC epitaxial wafer 1 from the reference plane Sr. The reference plane Sr is a plane connecting the points sp that overlap each of the three support points when viewed from the thickness direction of the first surface 1a. The three support points are located, for example, at positions overlapping the circumference 7.5 mm inside from the outer peripheral edge of the SiC epitaxial wafer 1. Each of the three support points is located at a position that is rotationally symmetric three times around the center of the SiC epitaxial wafer 1 supported by the support point as the central axis. The reference plane Sr is, for example, a three-point reference plane. The larger the absolute value of Bow, the more it is determined that the SiC epitaxial wafer 1 is deformed.

[0041] First, place the SiC epitaxial wafer 1 on three support points installed on the flat surface F. Connect three points sp on the first surface 1a located on the support points as viewed from the thickness direction to obtain a reference plane Sr. Then, with the reference plane Sr set to 0, the direction away from the flat surface F with respect to the reference plane Sr is defined as +, and the direction approaching the flat surface F with respect to the reference plane Sr is defined as -. Bow is obtained as the height-direction position of the center c of the first surface 1a with respect to the reference plane Sr. In other words, Bow is obtained as the signed distance of the center c of the first surface 1a from the reference plane Sr.

[0042] For the SiC epitaxial wafer 1 according to this embodiment, it is preferable that SORI is 60 μm or less, more preferably 45 μm or less, and may be 30 μm or less, 25 μm or less, 20 μm or less, 10 μm or less, or 5 μm or less. The lower limit value of SORI may be 0 μm or 0.5 μm.

[0043] SORI is one of the parameters indicating the degree of warping of the substrate. When the back surface of the substrate is supported and measured without changing its original shape, it is represented by the sum of the normal distances from the least-squares plane calculated by the least-squares method using all the data on the substrate surface to the highest point and the lowest point on the substrate surface. As shown in FIG. 5, when the least-squares plane of the substrate surface is used as the reference height (least-squares plane height), it represents the sum value ((a)+(b)) of the distance (a) between the height at the highest point on the substrate surface and the reference height and the distance (b) between the height at the lowest point and the reference height. Here, all the data on the substrate surface refers to all the data related to the relative height of the wafer surface from the reference plane obtained using the interference fringe image of the laser light.

[0044] The SiC epitaxial wafer 1 according to this embodiment preferably has a local thickness variation (LTV) of 4 μm or less, more preferably 3 μm or less, still more preferably 2.5 μm or less, and particularly preferably 2 μm or less in each of a plurality of unit exposure regions divided into 20 mm squares. When this condition is satisfied, even in a fine lithography process, the focus can be appropriately adjusted to the processing surface, and the SiC epitaxial wafer 1 can be processed with high precision. The lower limit value of the local thickness variation (LTV) may be 0.1 μm.

[0045] FIG. 6 is a diagram showing a unit exposure region A. The unit exposure region A is each of a plurality of regions divided into squares with a side length of a when viewed in plan from the stacking direction (<0001> direction). The unit exposure regions A are spread over the surface of the SiC epitaxial wafer 1 without gaps. The center of one of the plurality of unit exposure regions A coincides with the center C of the SiC epitaxial wafer 1. For example, in the measurement of LTV, the side length a of the unit exposure region A is 20 mm. The LTV is a value obtained by measuring the highest point and the lowest point within the site surrounded by the unit exposure region A when the SiC epitaxial wafer 1 is adsorbed to a vacuum chuck and obtaining the difference in distance between the highest point and the lowest point.

[0046] The SiC epitaxial wafer 1 according to this embodiment preferably has a site flatness (SFQR) of 2 μm or less, more preferably 1.5 μm or less, and still more preferably 1 μm or less in each of a plurality of unit exposure regions divided into 20 mm squares. The lower limit value of the site flatness (SFQR) may be 0 μm or 0.05 μm.

[0047] The SFQR is represented by the sum of the normal distances from the highest point to the lowest point on the substrate surface, calculated by the least squares method using all the data of the sites surrounded by the unit exposure area A when the SiC epitaxial wafer 1 is adsorbed on the vacuum chuck. The SFQR is different from the SORI in that it is the measurement result of a predetermined site. For example, in the measurement of the SFQR, the length a of one side of the unit exposure area A is set to 20 mm. Here, all the data of the sites surrounded by the unit exposure area A are all the data related to the relative height of the wafer surface from the reference plane.

[0048] Next, a method for manufacturing the SiC epitaxial wafer 1 according to the present embodiment will be described.

[0049] FIG. 7 is a cross-sectional schematic view of an example of a film forming apparatus for a SiC epitaxial wafer according to the present embodiment. The film forming apparatus 100 includes, for example, a chamber 10, a support 20, a lower heater 30, and an upper heater 40. The SiC substrate 2 is placed on the susceptor 50 and transported into the film forming apparatus.

[0050] The support 20 supports the susceptor 50. The support 20 is rotatable about its axis center, for example. The SiC substrate 2 is disposed on the support 20 in a state of being placed on the susceptor 50, for example. The lower heater 30 is, for example, inside the support 20 and heats the SiC substrate 2. The upper heater 40 heats the upper part of the chamber 10.

[0051] The chamber 10 includes, for example, a main body 11, a gas supply port 12, and a gas discharge port 13. The main body 11 surrounds the film forming space S. The gas supply port 12 is an inlet for supplying the gas G to the film forming space S. There are a plurality of gas supply ports 12 above the placement surface of the SiC substrate 2, for example. A film forming apparatus in which the gas supply port 12 is above the placement surface of the SiC substrate 2 is called a vertical furnace. The gas discharge port 13 is an outlet for discharging the gas G and the like staying in the film forming space S. The gas discharge port 13 is, for example, below the placement surface of the SiC substrate 2.

[0052] The gas G is, for example, a source gas, a carrier gas, a dopant gas, or an etching gas. The source gas includes an Si-based source gas and a C-based source gas.

[0053] The Si-based source gas is a source gas containing Si in the molecule. The Si-based source gas is, for example, silane (SiH 4 ), dichlorosilane (SiH 2 Cl 2 ), trichlorosilane (SiHCl 3 ), tetrachlorosilane (SiCl 4 ), etc. The Si-based source gas preferably contains at least one selected from the group consisting of, for example, SiH 3 Cl, SiH 2 Cl 2 and SiHCl 3 .

[0054] The C-based source gas is a source gas containing C in the molecule. The C-based source gas is, for example, propane (C 3 H 8 ), ethylene (C 2 H 4 ), etc. The C-based source gas preferably contains at least one selected from the group consisting of, for example, CH 4 , C 2 H 6 and C 3 H 8 .

[0055] The dopant gas is a gas containing an element serving as a carrier. The dopant gas preferably contains at least one of, for example, nitrogen (N 2 ) and ammonia (NH 3 ).

[0056] The carrier gas is a gas that transports the source gas to the SiC substrate 2 and is a gas inert to SiC. The carrier gas preferably contains, for example, Ar.

[0057] The etching gas is a gas that reacts with SiC at high temperature to etch SiC. For example, hydrogen chloride (HCl) is preferable as the etching gas.

[0058] The susceptor 50 supports the SiC substrate 2. FIG. 8 is a cross-sectional view of the state where the SiC substrate 2 is placed on the susceptor 50. The susceptor 50 has a main body 51 and a frame 52 protruding from the main body 51. The frame 52 prevents the rotating SiC substrate 2 from protruding outward during film formation.

[0059] The diameter R50 of the susceptor 50 is set to be 102.5% or more and 115% or less of the diameter R2 of the SiC substrate 2. By making the size of the susceptor 50 close to that of the SiC substrate 2, the susceptor 50 bends along the curved SiC substrate 2 during epitaxial growth. When the SiC substrate 2 bends, by not greatly changing the distance between the SiC substrate 2 and the susceptor 50, the uniformity of the carrier concentration of the SiC epitaxial layer 3 formed on the SiC substrate 2 can be enhanced.

[0060] Also, the thickness T51 of the main body 51 of the susceptor 50 is set to be 1 mm or more and 4 mm or less. The main body 51 is the part facing the SiC substrate 2. The thickness T51 of the main body 51 has a great influence on the ease of bending of the susceptor 50. Since the thickness T51 of the main body 51 is thin, when the SiC substrate 2 bends, the susceptor 50 can bend following the SiC substrate 2.

[0061] Also, the radial width W52 of the frame 52 of the susceptor 50 is, for example, set to be 10 mm or less. By narrowing the width W52, the whole susceptor 50 becomes easier to bend.

[0062] In the film formation process, an SiC epitaxial layer 3 is formed on the SiC substrate 2. The SiC epitaxial layer is formed by supplying a mixed gas containing an Si-based source gas, a C-based source gas, an etching gas, a carrier gas, and a dopant gas to one surface of the SiC substrate 2. When supplying these mixed gases, it is preferable to locally unevenly discharge a heavy molecular weight carrier gas from some of the plurality of gas supply ports 12. Hereinafter, the gas supply port 12 from which the heavy molecular weight carrier gas is discharged is referred to as the first gas supply port.

[0063] The heavy molecular weight carrier gas is a gas having a molecular weight of 28 or more, for example, Ar. Locally unevenly discharging the heavy molecular weight gas is realized by gathering the first gas supply ports among the plurality of gas supply ports 12 within a certain range. The first gas supply ports among the plurality of gas supply ports 12 are arranged at the central part.

[0064] The area of the portion to which the first gas supply port belongs is set to be 0.3% or more and 2.5% or less of the area of the top plate of the chamber 10. The area of the portion to which the first gas supply port belongs is the area of the region surrounded by the line connecting the outermost first gas supply ports. Also, the total area of the supply ports of the first gas supply port is set to be 10% or more and 30% or less of the total area of the supply ports of the plurality of gas supply ports 12.

[0065] The flow rate of the heavy molecular weight gas supplied from the first gas supply port is set to be 1000 sccm or more and 4000 sccm or less.

[0066] When the heavy molecular weight carrier gas is unevenly distributed and supplied at a predetermined flow rate, the gas G convects in the film formation space S. Although the gas G generally forms a flow passing through the surface of the SiC substrate 2 from the gas supply port 12 and heading toward the gas discharge port 13, by deliberately causing the gas G to convect, the variation in carrier concentration of the SiC epitaxial layer 3 can be suppressed. Also, by causing the gas G to convect, the variation in film thickness of the SiC epitaxial layer 3 can be suppressed.

[0067] As described above, by using a predetermined susceptor 50 and controlling the flow of the gas G in the film formation space S, it is possible to obtain a SiC epitaxial wafer 1 having a large diameter, a thin plate thickness, and high uniformity of carrier concentration.

[0068] The SiC epitaxial wafer 1 according to the present embodiment has a thin plate thickness and high in-plane carrier density uniformity despite its large diameter. Therefore, the SiC epitaxial wafer 1 according to the present embodiment has a high yield of SiC devices. Further, the SiC device fabricated from the SiC epitaxial wafer 1 according to the present embodiment has low resistance and low loss during operation.

[0069] As described above, the preferred embodiments of the present invention have been described in detail. However, the present invention is not limited to specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Example

[0070] 「Example 1」 First, a 4H-SiC substrate having a diameter of 203 mm and a plate thickness of 363 μm was prepared and housed inside a vertical furnace as shown in FIG. 7. The SiC substrate 2 was placed on the susceptor 50 and housed in the chamber 10 together with the susceptor 50. As the susceptor 50, one having a diameter of 230 mm, a thickness of the main body portion of 3 mm, and a radial width of the frame of 10 mm was used.

[0071] Next, a SiC epitaxial layer 3 having a thickness of 11 μm was formed on the SiC substrate 2. The film formation conditions when forming the SiC epitaxial layer 3 were as follows. The carrier gas was Ar. Area ratio of the portion of the carrier gas supply port (first gas supply port) with respect to the top plate of the chamber: 2% Area ratio of the carrier gas supply port (first gas supply port) with respect to all gas supply ports: 20% The flow rate of the carrier gas was set to 1000 sccm or more and 4000 sccm or less.

[0072] The variations in carrier concentration and film thickness of the SiC epitaxial wafer fabricated under the above conditions were measured.

[0073] The carrier concentration was measured using the Hg-CV method. The measurement points were set at the center and positions of ±20 mm, ±40 mm, ±60 mm, ±80 mm, and ±95 mm from the center along a straight line L extending in the <11-20> direction with the center as the reference. The variation in carrier concentration was determined from the respective carrier concentrations at each measurement point. Also, the variation in carrier concentration in the first region was measured. The carrier concentration in the first region was measured at points of ±60 mm, ±80 mm, and ±95 mm from the center along a straight line extending in the <11-20> direction with the center C as the reference, and at points of ±60 mm, ±80 mm, +95 mm, and -90 mm along a straight line extending in the <-1100> direction with the center C as the reference.

[0074] The film thickness variation was measured by infrared spectroscopy. The film thickness variation was also measured within the first region. The measurement points for the film thickness variation were the same as those for the carrier concentration.

[0075] The variation in carrier concentration of the SiC epitaxial wafer of Example 1 was 5.0%. Also, the variation in carrier concentration in the first region of the SiC epitaxial wafer of Example 1 was 5.1%. Also, the variation in the film thickness of the SiC epitaxial layer of the SiC epitaxial wafer of Example 1 was 2.6%. Also, the variation in the film thickness of the epitaxial layer in the first region of the SiC epitaxial wafer of Example 1 was 1.9%.

[0076] "Example 2" First, a 4H-SiC substrate with a diameter of 200 mm and a plate thickness of 372 μm was prepared and placed inside a vertical furnace as shown in FIG. 7. The SiC substrate 2 was placed on the susceptor 50 and housed in the chamber 10 together with the susceptor 50. The susceptor 50 used had a diameter of 230 mm, a thickness of the main body part of 3 mm, and a radial width of the frame of 10 mm.

[0077] Next, a SiC epitaxial layer 3 with a thickness of 14 μm was formed on the SiC substrate 2. The film formation conditions when forming the SiC epitaxial layer 3 were as follows. The carrier gas was Ar. Area ratio of the portion where the supply port (first gas supply port) of the carrier gas to the top plate of the chamber belongs: 1.5% Area ratio of the supply port (first gas supply port) of the carrier gas to all gas supply ports: 20% The flow rate of the carrier gas was set to be 1000 sccm or more and 4000 sccm or less.

[0078] The variation in carrier concentration and the variation in film thickness of the SiC epitaxial wafer fabricated under the above conditions were measured in the same manner as in Example 1. Also, the variation in carrier concentration in the first region and the variation in film thickness within the first region were measured in the same manner as in Example 1.

[0079] The LTV, SFQR, SORI, Warp, and Bow of the obtained SiC epitaxial wafer were obtained using UltrasortII manufactured by Corning Tropel.

[0080] The variation in carrier concentration of the SiC epitaxial wafer of Example 2 was 13.6%. Also, the variation in carrier concentration in the first region of the SiC epitaxial wafer of Example 2 was 13.1%. Also, the variation in film thickness of the SiC epitaxial layer of the SiC epitaxial wafer of Example 2 was 5.8%. Also, the variation in film thickness of the epitaxial layer in the first region of the SiC epitaxial wafer of Example 2 was 5.8%.

[0081] The LTV of the SiC epitaxial wafer of Example 2 was 3.8 μm. The SFQR of the SiC epitaxial wafer of Example 2 was 1.7 μm. The SORI of the SiC epitaxial wafer of Example 2 was 23.4 μm. The Warp of the SiC epitaxial wafer of Example 2 was 31.7 μm. The Bow of the SiC epitaxial wafer of Example 2 was -10 μm.

[0082] "Example 3" First, a 4H-SiC substrate with a diameter of 200 mm and a thickness of 371 μm was prepared and placed inside a vertical furnace as shown in FIG. 7. The SiC substrate 2 was placed on the susceptor 50 and accommodated in the chamber 10 together with the susceptor 50. The susceptor 50 used had a diameter of 230 mm, a thickness of the main body part of 3 mm, and a radial width of the frame of 10 mm.

[0083] Next, a SiC epitaxial layer 3 with a thickness of 11 μm was formed on the SiC substrate 2. The film formation conditions when forming the SiC epitaxial layer 3 were as follows. The carrier gas was Ar. Area ratio of the portion where the supply port (first gas supply port) of the carrier gas to the top plate of the chamber: 1.5% Area ratio of the supply port (first gas supply port) of the carrier gas to all gas supply ports: 30% The flow rate of the carrier gas was set to be 1000 sccm or more and 4000 sccm or less.

[0084] The variation in carrier concentration and the variation in film thickness of the SiC epitaxial wafer fabricated under the above conditions were measured in the same manner as in Example 1. Also, the variation in carrier concentration in the first region and the variation in film thickness within the first region were measured in the same manner as in Example 1.

[0085] The LTV, SFQR, SORI, Warp, and Bow of the obtained SiC epitaxial wafer were obtained in the same manner as in Example 2.

[0086] The variation in carrier concentration of the SiC epitaxial wafer of Example 3 was 18.2%. Also, the variation in carrier concentration in the first region of the SiC epitaxial wafer of Example 3 was 18.4%. Also, the variation in film thickness of the SiC epitaxial layer of the SiC epitaxial wafer of Example 3 was 5.7%. Also, the variation in film thickness of the epitaxial layer in the first region of the SiC epitaxial wafer of Example 3 was 2.6%.

[0087] The LTV of the SiC epitaxial wafer of Example 3 was 1.9 μm. The SFQR of the SiC epitaxial wafer of Example 3 was 0.9 μm. The SORI of the SiC epitaxial wafer of Example 3 was 11.1 μm. The Warp of the SiC epitaxial wafer of Example 3 was 13.8 μm. The Bow of the SiC epitaxial wafer of Example 3 was -0.7 μm.

[0088] "Example 4" First, a 4H-SiC substrate with a diameter of 200 mm and a plate thickness of 368 μm was prepared and placed inside a vertical furnace as shown in FIG. 7. The SiC substrate 2 was placed on the susceptor 50 and housed in the chamber 10 together with the susceptor 50. As the susceptor 50, one with a diameter of 230 mm, a thickness of the main body part of 3 mm, and a radial width of the frame of 10 mm was used.

[0089] Next, a SiC epitaxial layer 3 with a thickness of 11 μm was formed on the SiC substrate 2. The film formation conditions when forming the SiC epitaxial layer 3 were as follows. The carrier gas was Ar. Area ratio of the portion of the carrier gas supply port (first gas supply port) on the top plate of the chamber: 2.5% Area ratio of the carrier gas supply port (first gas supply port) to all gas supply ports: 20% The flow rate of the carrier gas was set to be 1000 sccm or more and 4000 sccm or less.

[0090] The variation in carrier concentration and the variation in film thickness of the SiC epitaxial wafer fabricated under the above conditions were measured in the same manner as in Example 1. Also, the variation in carrier concentration in the first region and the variation in film thickness within the first region were measured in the same manner as in Example 1.

[0091] The LTV, SFQR, SORI, Warp, and Bow of the obtained SiC epitaxial wafer were measured in the same manner as in Example 2.

[0092] The variation in carrier concentration of the SiC epitaxial wafer of Example 4 was 8.8%. Also, the variation in carrier concentration in the first region of the SiC epitaxial wafer of Example 4 was 8.6%. Further, the variation in film thickness of the SiC epitaxial layer of the SiC epitaxial wafer of Example 4 was 4.2%. Also, the variation in film thickness of the epitaxial layer in the first region of the SiC epitaxial wafer of Example 4 was 2.0%.

[0093] The LTV of the SiC epitaxial wafer of Example 4 was 1.9 μm. The SFQR of the SiC epitaxial wafer of Example 4 was 0.8 μm. The SORI of the SiC epitaxial wafer of Example 4 was 15.5 μm. The Warp of the SiC epitaxial wafer of Example 4 was 19.3 μm. The Bow of the SiC epitaxial wafer of Example 4 was -4.0 μm.

[0094] "Example 5" First, a 4H-SiC substrate with a diameter of 203 mm and a plate thickness of 380 μm was prepared and housed inside a vertical furnace as shown in FIG. 7. The SiC substrate 2 was placed on the susceptor 50 and housed in the chamber 10 together with the susceptor 50. As the susceptor 50, one with a diameter of 230 mm, a thickness of the main body part of 3 mm, and a radial width of the frame of 10 mm was used.

[0095] Next, a SiC epitaxial layer 3 with a thickness of 11 μm was formed on the SiC substrate 2. The film formation conditions when forming the SiC epitaxial layer 3 were as follows. The carrier gas was Ar. Area ratio of the portion where the supply port (first gas supply port) of the carrier gas to the top plate of the chamber belongs: 2.5% Area ratio of the supply port (first gas supply port) of the carrier gas to all gas supply ports: 30% The flow rate of the carrier gas was set to be 1000 sccm or more and 4000 sccm or less.

[0096] The variations in carrier concentration and film thickness of the SiC epitaxial wafer fabricated under the above conditions were measured in the same manner as in Example 1. Also, the variation in carrier concentration in the first region and the variation in film thickness within the first region were measured in the same manner as in Example 1.

[0097] The LTV and SFQR of the obtained SiC epitaxial wafer, and SORI, Warp, and Bow were measured in the same manner as in Example 1.

[0098] The variation in carrier concentration of the SiC epitaxial wafer of Example 5 was 6.5%. Also, the variation in carrier concentration in the first region of the SiC epitaxial wafer of Example 5 was 4.8%. Also, the variation in film thickness of the SiC epitaxial layer of the SiC epitaxial wafer of Example 5 was 5.0%. Also, the variation in film thickness of the epitaxial layer in the first region of the SiC epitaxial wafer of Example 5 was 3.7%.

[0099] The LTV of the SiC epitaxial wafer of Example 5 was 2.0 μm. The SFQR of the SiC epitaxial wafer of Example 5 was 1.1 μm. The SORI of the SiC epitaxial wafer of Example 5 was 6.6 μm. The Warp of the SiC epitaxial wafer of Example 5 was 6.2 μm. The Bow of the SiC epitaxial wafer of Example 5 was -1.7 μm.

[0100] "Comparative Example 1" In Comparative Example 1, a susceptor with a diameter of 250 mm, a thickness of the main body of 8 mm, and a radial width of the frame of 20 mm was used. The area ratio of the portion to which the supply port (first gas supply port) of the carrier gas belongs with respect to the top plate of the chamber was 42%, and the area ratio of the supply port of the carrier gas with respect to all the gas supply ports was 71%. Also, the flow rate of the carrier gas in Comparative Example 1 was made smaller than the flow rate in Example 1 and was less than 1000 sccm.

[0101] With other conditions being the same as in Example 1, the variations in carrier concentration and film thickness of the SiC epitaxial wafer of Comparative Example 1 were measured.

[0102] The variation in carrier concentration of the SiC epitaxial wafer of Comparative Example 1 was 26.1%. The variation in carrier concentration in the first region of the SiC epitaxial wafer of Comparative Example 1 was 25.9%. The variation in film thickness of the SiC epitaxial layer of the SiC epitaxial wafer of Comparative Example 1 was 5.3%. The variation in film thickness of the epitaxial layer in the first region of the SiC epitaxial wafer of Comparative Example 1 was 5.3%.

Explanation of symbols

[0103] 1 SiC epitaxial wafer 2 SiC substrate 3 SiC epitaxial layer 4 Notch 10 Chamber 11 Main body 12 Gas supply port 13 Gas discharge port 20 Support 30 Lower heater 40 Upper heater 50 Susceptor 51 Main body 52 Frame A Unit exposure area

Claims

1. A SiC substrate and a SiC epitaxial layer are provided. The SiC substrate has a diameter of 195 mm or more and a thickness of 460 μm or less, A SiC epitaxial wafer, wherein the SiC epitaxial layer has a carrier concentration variation of 20% or less.

2. 2. The SiC epitaxial wafer according to claim 1, wherein, when viewed in a plan view from the stacking direction, a local thickness variation (LTV) in each of a plurality of unit exposure regions divided into 20 mm squares is 4 μm or less.

3. 2. The SiC epitaxial wafer according to claim 1, wherein, when viewed in a plan view from the stacking direction, a site flatness (SFQR) in each of a plurality of unit exposure regions divided into 20 mm squares is 2 μm or less.

4. The SiC epitaxial wafer according to claim 1 , wherein the warp is 90 μm or less.

5. 2. The SiC epitaxial wafer according to claim 1, wherein the bow is 60 μm or less when a surface connecting a support point located at a position overlapping with a circumference 7.5 mm inside from the outermost circumference and an overlapping portion as viewed from the thickness direction is used as a reference surface.

6. 2. The SiC epitaxial wafer of claim 1, wherein the SORI is 60 μm or less.

7. 2. The SiC epitaxial wafer according to claim 1, wherein the SiC epitaxial layer has a carrier concentration variation of 20% or less in a first region that is 60 mm or more and 95 mm or less away from a center when viewed in a planar view from the stacking direction.

8. The SiC epitaxial wafer according to claim 1 , wherein the SiC epitaxial layer has a thickness variation of 5% or less.

9. 9. The SiC epitaxial wafer according to claim 8, wherein the SiC epitaxial layer has a film thickness variation of 5% or less in a first region that is 60 mm or more and 95 mm or less away from a center when viewed in a plan view from the stacking direction.

Images