METHOD FOR MANUFACTURING SiC SINGLE CRYSTAL AND METHOD FOR MANUFACTURING SiC SINGLE CRYSTAL SUBSTRATE

Abstract

To provide a method for manufacturing a SiC single crystal and a method for manufacturing a SiC substrate, capable of achieving the simplification of a process and cost reduction.SOLUTION: A method for manufacturing a SiC single crystal comprises: a step S100 of preparing a seed crystal formed of a SiC single crystal having a predetermined off angle in a predetermined direction using a (0001) plane or a (000-1) plane as a principal surface; and a step (S130) of forming a growth layer formed of a SiC single crystal on the principal surface of the seed crystal heated in an atmosphere including nitrogen gas using SiC gas obtained by heating and sublimating a raw material including carbon and silicon as a raw material, in which a penetration dislocation appearing on the principal surface of the seed crystal is converted into a dislocation extending in a c in-plane direction in an initial formation layer formed in the initial stage of the growth layer. The predetermined off angle is 14° or more.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a method for producing a SiC single crystal and a method for producing a SiC single crystal substrate. [Background technology]

[0002] Defects in SiC single crystal substrates, such as basal plane dislocations (BPDs), stacking faults, threading screw dislocations (TSDs), and threading edge dislocations (TEDs), are known to adversely affect devices. Basal plane dislocations and stacking faults are defects that occur within the c-plane, and are hereinafter collectively referred to as "basal plane defects." Threading screw dislocations and threading edge dislocations are defects that extend in the c-axis direction, and are hereinafter collectively referred to as "threading dislocations."

[0003] As a single crystal growth method that reduces TSD, a hybrid growth method is known in which a layer (conversion layer) that converts threading dislocations into basal plane defects is formed on a seed crystal by solution growth, and a SiC single crystal layer is then formed on the conversion layer by sublimation growth (see, for example, Non-Patent Document 1).

[0004] As a single crystal growth method that reduces TSD without involving solution growth, a two-stage sublimation growth technique is known in which a conversion layer is formed on a seed crystal under first-stage growth conditions using sublimation, and then a SiC single crystal layer is formed on top of that under second-stage growth conditions, thereby reducing TSD in partial areas (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-88416 A [Patent Document 2] International Publication No. 2016 / 088883 [Non-patent literature]

[0006] [Non-Patent Document 1] T. Mitani et al., Applied Physics Express, 14, (2021) 085506 Summary of the Invention [Problem to be solved by the invention]

[0007] The manufacturing method of converting threading dislocations into basal plane defects by the above-mentioned two-stage growth process using hybrid growth accompanied by solution growth has the problem that the manufacturing process becomes complicated and the manufacturing cost increases. In addition, the two-stage growth process technology of Patent Document 1 and Patent Document 2 has a limited area for reducing TSD, and is problematic as a technology for producing single crystals with reduced threading dislocations. The object of the present invention is to provide a manufacturing method of SiC single crystals and a manufacturing method of SiC substrates that realizes sufficient reduction of TSD while simplifying the process and reducing costs. [Means for solving the problem]

[0008] According to one aspect of the present disclosure, there is provided a method for producing a SiC single crystal, the method including the steps of: preparing a seed crystal of a SiC single crystal having a main surface which is a (0001) plane or a (000-1) plane and which has a predetermined off-angle in a predetermined direction; and forming a growth layer of a SiC single crystal on the main surface of the seed crystal, which is heated in an atmosphere containing nitrogen gas, using SiC gas obtained by heating a raw material containing carbon and silicon and sublimating it, wherein threading dislocations that appear on the main surface of the seed crystal in an initial formation layer formed in the early stage of the growth layer are converted into dislocations extending in a c-plane direction, wherein the predetermined off-angle is 14° or more.

[0009] According to the above aspect, a growth layer of a SiC single crystal is formed directly by sublimated SiC gas on the main surface of a seed crystal in which threading dislocations appear, so that a pre-process for reducing the TSD of the seed crystal is not required, and a method for producing a SiC single crystal can be provided which achieves sufficient reduction in TSD while simplifying the process and reducing costs.

[0010] According to another aspect, there is provided a method for manufacturing a SiC substrate, comprising the steps of: preparing a SiC single crystal formed by the manufacturing method of the above aspect; and cutting out a portion of the growth layer of the SiC single crystal in which threading dislocations are reduced to obtain a SiC substrate.

[0011] According to the other aspect described above, since the SiC single crystal formed on the seed crystal is formed by the manufacturing method of the above aspect, it is possible to provide a manufacturing method of a SiC substrate that reduces costs. [Brief description of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing the configuration of an example of a crystal growth apparatus used in a method for producing a SiC single crystal according to an embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view of a SiC single crystal grown on a seed crystal. [Diagram 3] 1 is a flowchart of a method for producing a SiC single crystal according to one embodiment. [Figure 4] 1 is an example of a transmission X-ray topography photograph of a crystal grown sample of an embodiment under the condition of g=0004. [Diagram 5] Threading dislocation reduction rates for the examples and comparative examples when the heating temperature was 2245° C. are shown. [Figure 6] 1 shows the threading dislocation reduction rates in the examples and comparative examples when the off angle of the seed crystal is 15 degrees. [Figure 7] FIG. 13 is a graph showing the relationship between the nitrogen atom concentration in a crystal growth portion and the nitrogen gas flow rate ratio when the off-angle of the seed crystal is 15 degrees. [Figure 8] 1 is a flowchart of a method for manufacturing a SiC substrate according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that elements common to multiple drawings are denoted by the same reference numerals, and detailed descriptions of those elements will not be repeated.

[0014] [Manufacturing method of SiC single crystal] Fig. 1 is a cross-sectional view showing a schematic configuration of an example of a crystal growth apparatus used in a method for producing a SiC single crystal according to an embodiment. Referring to Fig. 1, the crystal growth apparatus 10 has a crucible container 12 in which a SiC raw material 100 is filled and sublimated, a crucible lid 13, a heat insulating member 14 that covers the crucible container 12 and the crucible lid 13, and a quartz support rod 15 that supports the crucible container 12, inside a cylindrical reaction furnace 11. The crystal growth apparatus 10 has a high-frequency coil 16 that is disposed so as to surround the outer periphery of the heat insulating member 14 and that heats the crucible container 12 and the crucible lid 13 with high frequency. The crystal growth apparatus 10 is connected to an inert gas source (here, Ar gas is used) and a nitrogen gas source (not shown), and has a mass flow controller 17 that controls the flow rate of each gas, a gas flow path 18 that introduces each gas or a mixed gas from the mass flow controller 17 into the reaction furnace 11, and a vacuum exhaust device 19 that exhausts the gas inside the reaction furnace 11. The crucible container 12, the crucible lid 13, and the heat insulating member 14 are made of materials that are permeable to nitrogen gas and inert gas, and the atmosphere inside the crucible container 12 during crystal growth is controlled by the gas supplied into the reaction furnace 11 via the mass flow controller 17.

[0015] The crucible container 12 is, for example, cylindrical and contains the SiC raw material 100 therein. The crucible container 12 is made of, for example, graphite and can withstand the temperature at which the SiC raw material 100 sublimes. The crucible lid 13 covers the upper opening of the crucible container 12 and has a seed crystal 20 placed on its lower surface. The crucible lid 13 is made of the same material as the crucible container 12.

[0016] FIG. 2 is a schematic cross-sectional view of a semiconductor product of a SiC single crystal grown on a seed crystal, as viewed from the [1-100] direction. Referring to FIG. 2, a semiconductor product 21 has a seed crystal 20 and a crystal growth portion 22 grown thereon. The seed crystal 20 is a 4H single crystal SiC substrate, and the main surface (off-plane) 20a is an off-plane tilted at a predetermined angle (i.e., tilt angle (or off-angle)) from the (0001) plane or the (000-1) plane in a predetermined direction. The predetermined direction (i.e., tilt orientation (or off-orientation)) may be either <11-20> or <1-100>, and may be within a range between <11-20> and <1-100>. The predetermined angle (off-angle) is the tilt angle from the (0001) plane or the (000-1) plane. The seed crystal 20 includes threading dislocations 23 (i.e., threading screw dislocations and threading edge dislocations), which extend along the c-axis of the seed crystal 20 and appear on the main surface 20a. The crystal growth portion 22 of the SiC single crystal formed by the manufacturing method according to the present embodiment is formed on the main surface 20a of the seed crystal 20 and includes a basal plane defect region 25 containing many basal plane defects 24 and a threading dislocation reduced region 26 in which the threading dislocations 23 (mainly TSDs) are reduced. The basal plane defect region 25 is a region in which the basal plane defects 24 generated by the conversion of the threading dislocations 23 that appeared on the main surface 20a of the seed crystal 20 are present in an elongated state. The basal plane defect region 25 may also include basal plane defects 24 newly generated on the main surface 20a. The threading dislocation reduced region 26 is formed on the basal plane defect region 25, and is a region of good quality single crystal in which both the threading dislocations 23 and the basal plane defects 24 are suppressed.

[0017] The off angle of seed crystal 20 needs to be 14 degrees or more to increase the rate at which threading dislocations 23 are converted to basal plane defects 24 and the threading dislocations 23 are reduced (threading dislocation reduction rate). As the off angle increases, basal plane defect region 25 containing many basal plane defects 24 becomes more erect with respect to main surface 20a, and the size of the SiC single crystal substrate cut out approximately parallel to the c-plane from threading dislocation reduced region 26 becomes smaller. From this viewpoint, the smaller the off angle, the better, and for example, it is preferably 45° or less, and particularly preferably 20° or less.

[0018] 3 is a flow chart of a method for producing a SiC single crystal according to an embodiment. The method for producing a SiC single crystal according to an embodiment will be described with reference to FIG. 3 together with FIG.

[0019] First, a seed crystal 20 of a 4H SiC single crystal is prepared and placed on the crucible lid 13 with the main surface 20a facing downward (i.e., facing the inside of the crucible container 12) (S100). Specifically, the seed crystal 20 is the 4H SiC single crystal seed crystal 20 described in Fig. 2, and may be obtained by slicing and polishing an ingot with a wire saw so as to have the above-mentioned orientation and angle.

[0020] Next, the SiC raw material 100 is filled into the container of the crucible 12 (S110). The SiC raw material 100 may be a mixed powder of high-purity Si powder and C powder, or SiC powder. In order to suppress the generation of new defects due to high-concentration nitrogen doping, a growth method in which aluminum or boron is co-doped (co-doped) is known. When boron is co-doped into the crystal growth portion 22 for such a purpose, for example, boron carbide powder may be mixed into the SiC raw material 100. When the boron concentration in the crystal after crystal growth is, for example, 1×10 19 cm -3 After the SiC raw material 100 is completely charged into the crucible container 12, the crucible container 12 is covered with the crucible lid 13 to which the seed crystal 20 is attached in S100. The order of S100 and S110 may be reversed.

[0021] Next, after evacuating the inside of the reactor 11, an atmospheric gas is introduced into the reactor 11 from an inert gas source (here, Ar gas is used) and a nitrogen gas source (not shown) (S120). By including nitrogen gas in the atmospheric gas during crystal growth, nitrogen atoms are incorporated into the crystal to form a nitrogen-doped SiC single crystal. Depending on the doping amount, an n-type SiC single crystal can be produced. The combined gas flow rate of Ar gas and nitrogen gas is set to, for example, 100 to 300 sccm. The pressure inside the reactor 11 is set to, for example, 100 to 1000 Pa.

[0022] Next, the SiC raw material 100 in the container of the crucible 12 is heated (S130). The heating temperature is set to, for example, 2100°C to 2350°C at the bottom of the container of the crucible 12. The heating time for crystal growth can be, for example, 10 hours to 200 hours. This heating causes the SiC raw material 100 to sublimate and reach the main surface 20a of the seed crystal, and the SiC single crystal grows. Threading dislocations 23 extending along the c-axis appear on the main surface 20a of the seed crystal, and basal plane defects 24 whose tips extend perpendicularly to the c-plane are formed. The SiC single crystal grows in a direction perpendicular to the main surface 20a of the seed crystal without being affected by the off-angle, so that when the threading dislocations 23 are converted into the basal plane defects 24, a threading dislocation reduced region 22 is formed, which is made of a good quality SiC single crystal in which threading dislocations 22 are suppressed. The crystal growth rate varies depending on the heating conditions and the nitrogen gas flow rate ratio, but is approximately 50 to 300 μm / hour in the direction perpendicular to main surface 20a of the seed crystal. In this manner, a SiC single crystal semiconductor product 21 is formed in which crystal growth portion 22 is formed on seed crystal 20.

[0023] Examples and comparative examples are described below. The seed crystals were prepared by cutting 4H—SiC single crystals (size: 1 inch diameter) from a SiC ingot, with the main surface (off-plane) being at off-angles of 8°, 12°, 14°, 15°, and 45°, respectively, within the <11-20> orientation from the (0001) plane.

[0024] SiC powder (high purity silicon carbide, manufactured by Taiheiyo Cement Corporation) was filled as a SiC raw material in the crucible container 12 of the crystal growth apparatus 10 shown in FIG. 1. Argon and nitrogen gases were supplied into the reaction furnace 11 so that the nitrogen gas flow rate ratio (= nitrogen gas flow rate / (nitrogen gas flow rate+argon gas flow rate)×100) (%) was set to a predetermined ratio between 0 and 100% and the total flow rate was 200 sccm. The crucible container 12 was heated so that the temperature at the bottom where the SiC raw material was filled was 2245° C., and the pressure in the reaction furnace 11 was reduced to 332 Pa after the temperature increase was completed. This pressure and temperature were maintained for 50 hours to perform crystal growth.

[0025] The crystal-grown samples were taken out, and two or more (1-100) cross sections were cut out from each sample. Transmission X-ray topography (X-ray diffraction apparatus (Rigaku Corporation, Model: UltraX18)) was performed under the condition of g=0004. From the obtained topography image, the seed crystal surface and the crystal growth area were identified. <0004> The number of threading dislocations (defects equivalent to TSDs) having a Burgers vector component in the direction was counted, and the threading dislocation reduction rate (= {(number of threading dislocations on the seed crystal surface) - (number of threading dislocations in the crystal growth portion)} / (number of threading dislocations on the seed crystal surface) × 100 (%)) was calculated. The threading dislocations in the crystal growth portion were counted at a position 0.5 mm away from the surface of the seed crystal in the crystal growth direction. The threading dislocation reduction rate was used as the lowest value among two or more cross sections of one sample.

[0026] Fig. 4 is an example of a transmission X-ray topography photograph taken under the condition of g=0004 of a crystal grown sample of an example. This example is a cross section of Example 4 shown in Fig. 6 below. Referring to Fig. 4, it can be seen that the seed crystal has many threading dislocations extending perpendicularly to the main surface of the seed crystal, and many basal plane defects extending diagonally upward to the right are formed in the crystal growth portion on the main surface, but there are almost no threading dislocations formed in the seed crystal.

[0027] Fig. 5 shows the threading dislocation reduction rates of the examples and comparative examples when the heating temperature is 2245°C. Referring to Fig. 5, in Examples 1 to 3, the off-angles of the seed crystal are 14 degrees, 15 degrees, and 45 degrees, and the threading dislocation reduction rates are 71%, 82%, and 94%, respectively, whereas in Comparative Examples 1 to 4, the off-angles of the seed crystal are 8 degrees and 12 degrees, and the threading dislocation reduction rates are 29%, 21%, 7%, and 15%, respectively. From these results, it was found that threading dislocations can be significantly reduced by setting the off-angle of the seed crystal to 14 degrees or more.

[0028] FIG. 6 shows the threading dislocation reduction ratios of the examples and comparative examples when the off-angle of the seed crystal is 15 degrees. Referring to FIG. 6, Examples 4, 2, 5, and 6 are the cases where the nitrogen gas flow ratio is 5, 15, 50, and 100%, and the threading dislocation reduction ratios are 71%, 82%, 81%, and 94%, respectively, whereas Comparative Examples 5 to 8 are the cases where the nitrogen gas flow ratio is 0, 1, 2, and 3.5%, and the threading dislocation reduction ratios are 23%, 6%, 6%, and 34%. From these results, it is preferable that the nitrogen gas flow ratio is 5% or more, and preferably 100% or less. It was also found that the threading dislocations can be significantly reduced as the nitrogen gas flow ratio increases.

[0029] 7 is a diagram showing the relationship between the nitrogen atom concentration in the crystal growth portion and the nitrogen gas flow rate ratio when the off-angle of the seed crystal is 15 degrees. Of the crystal growth portion, the nitrogen atom concentration in threading dislocation reduced region 26 was analyzed. The nitrogen atom concentration was analyzed using a secondary ion mass spectrometry (SIMS) (Model IMS 7f, manufactured by CAMECA Corporation) on a sample cut from a (1-100) cross section. The analyzed area was within a region of good quality SiC single crystal with no basal plane defects and reduced threading dislocations (hereinafter referred to as the "threading dislocation reduced region").

[0030] 7, it can be seen that the nitrogen atom concentration in the crystal growth portion increases as the nitrogen gas flow rate ratio increases. In addition, when the nitrogen gas flow rate ratio is 5% or more, the nitrogen atom concentration in the threading dislocation reduced region is 0.72 to 3.30×10 19 (cm -3 )

[0031] [SiC substrate manufacturing method] 8 is a flow chart of a method for manufacturing a SiC substrate according to an embodiment of the present invention. The method for manufacturing a SiC substrate according to an embodiment of the present invention will be described with reference to FIG. 8 together with FIG.

[0032] First, a SiC single crystal is prepared by growing the crystal on a seed crystal using the method for producing a SiC single crystal according to the embodiment described with reference to FIG. 3 (S200).

[0033] Next, the threading dislocation reduced region of the crystal growth portion shown in FIG. 2 is cut out (S210). Specifically, the threading dislocation reduced region on the seed crystal is sliced ​​at a predetermined angle and a predetermined thickness with a wire saw. The predetermined angle is, for example, an off angle in the range of 4 degrees to 8 degrees with respect to the c-plane of the SiC single crystal. The predetermined thickness is, for example, 300 μm to 2000 μm. The end face shape and flatness of the substrate surface of the cut out substrate are adjusted by a known method. For flatness processing, for example, a surface grinder is used to adjust the flatness, and a CMP (chemical physical polishing) device is used. As a result, a SiC substrate having atomic level flatness is obtained. According to this embodiment, a SiC substrate with reduced threading dislocations is obtained.

[0034] Although preferred embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the invention described in the claims. [Explanation of symbols]

[0035] 10 Crystal growth equipment 12 Crucible container 20 seed crystals 22 Crystal growth part 23 Threading dislocations 24 Basal Plane Defects 25 Basal plane defect region 26 Threading dislocation reduction region

Claims

1. A method for producing a SiC single crystal, comprising the steps of: A step of preparing a seed crystal of a SiC single crystal having a (0001) plane or a (000-1) plane as a main surface and a predetermined off angle in a predetermined direction; a step of forming a growth layer of a SiC single crystal on the main surface of the seed crystal heated in an atmosphere containing nitrogen gas, using SiC gas obtained by heating a raw material containing carbon and silicon and sublimating the SiC gas as a raw material, and converting threading dislocations appearing on the main surface of the seed crystal in an initial formation layer formed at the beginning of the growth layer into dislocations extending in a c-plane direction; The manufacturing method, wherein the predetermined off angle is 14° or more.

2. 2. The method according to claim 1, wherein in the step of forming the growth layer, the concentration of the nitrogen gas is set to 5% to 100%.

3. The method according to claim 1 , wherein the predetermined off angle is 45° or less.

4. A step of preparing a SiC single crystal formed by the manufacturing method according to any one of claims 1 to 3; and cutting out a portion of the growth layer of the SiC single crystal in which threading dislocations are reduced to obtain a SiC substrate.

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