Silicon carbide substrate and method for manufacturing silicon carbide substrate

Abstract

This silicon carbide substrate has a first main surface and a second main surface opposite the first main surface. The silicon carbide substrate includes screw dislocations and pits each having a maximum diameter of 1 μm to 10 μm in a direction parallel to the first main surface. When the screw dislocations and the pits are observed in the first main surface, the ratio of the number of the pits divided by the number of the screw dislocations is 1% or less. In the first main surface, the concentration of magnesium is less than 1×1011 atoms / cm2.

Description

[Technical field]

[0001] The present disclosure relates to a silicon carbide substrate and a method for manufacturing a silicon carbide substrate. This application claims priority to Japanese Patent Application No. 2019-218126, filed on December 2, 2019. The entire contents of the Japanese patent application are incorporated herein by reference. [Background technology]

[0002] WO 2019 / 111507 (Patent Document 1) describes a process for performing chemical mechanical polishing on a silicon carbide single crystal substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 111507 Summary of the Invention

[0004] A silicon carbide substrate according to the present disclosure includes a first main surface and a second main surface opposite to the first main surface. The silicon carbide substrate includes screw dislocations and pits having a maximum diameter of 1 μm or more and 10 μm or less in a direction parallel to the first main surface. When screw dislocations and pits are observed on the first main surface, the ratio of the number of pits divided by the number of screw dislocations is 1% or less. The magnesium concentration on the first main surface is 1×10 11 atoms / cm 2 is less than.

[0005] A method for manufacturing a silicon carbide substrate according to the present disclosure includes the following steps: A silicon carbide single crystal substrate is prepared, the silicon carbide single crystal substrate having a first main surface and a second main surface opposite to the first main surface. The silicon carbide single crystal substrate is subjected to chemical mechanical polishing using a polishing liquid. After the step of chemical mechanical polishing the silicon carbide single crystal substrate using the polishing liquid, the silicon carbide single crystal substrate is treated using a solution containing an organic acid having two or more carboxy groups in one molecule. The polishing liquid has a Brix value of 10 or more. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic plan view showing the configuration of a silicon carbide substrate in accordance with the present embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 3 is an enlarged schematic view of region III in FIG. [Figure 4] FIG. 4 is a flow diagram illustrating roughly the method for manufacturing a silicon carbide substrate according to the present embodiment. [Diagram 5] FIG. 5 is a schematic cross-sectional view showing a first step of the method for manufacturing a silicon carbide substrate in accordance with the present embodiment. [Figure 6] FIG. 6 is a schematic cross-sectional view showing a second step of the method for manufacturing a silicon carbide substrate in accordance with the present embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view showing a third step of the method for manufacturing a silicon carbide substrate in accordance with the present embodiment. [Figure 8] FIG. 8 is a schematic cross-sectional view showing a fourth step of the method for manufacturing a silicon carbide substrate in accordance with the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] [Problem that this disclosure aims to solve] An object of the present disclosure is to provide a silicon carbide substrate capable of improving cleanliness and a method for manufacturing a silicon carbide substrate. [Effects of this disclosure] According to the present disclosure, it is possible to provide a silicon carbide substrate capable of improving cleanliness, and a method for manufacturing a silicon carbide substrate. [Description of the embodiments of the present disclosure] (1) A silicon carbide substrate 10 according to an embodiment of the present disclosure includes a first main surface 1 and a second main surface 2 opposite to the first main surface 1. The silicon carbide substrate 10 includes screw dislocations 13 and pits 11 having a maximum diameter of 1 μm or more and 10 μm or less in a direction parallel to the first main surface 1. When the screw dislocations 13 and the pits 11 are observed on the first main surface 1, the ratio of the number of pits 11 divided by the number of screw dislocations 13 is 1% or less. The magnesium concentration on the first main surface 1 is 1×10 11 atoms / cm 2 is less than.

[0008] (2) In silicon carbide substrate 10 according to (1) above, the concentrations of calcium, aluminum, sodium, potassium, and manganese in first main surface 1 are each 1×10 11 atoms / cm 2 It may be less than.

[0009] (3) In silicon carbide substrate 10 according to (1) above, the concentrations of magnesium, calcium, aluminum, sodium, potassium, and manganese in first main surface 1 are each 5×10 10 atoms / cm 2 It may be less than.

[0010] (4) In the silicon carbide substrate 10 according to any one of (1) to (3) above, the areal density of screw dislocations 13 on the first main surface 1 is 100 cm -2 More than 5000cm -2 It may be the following.

[0011] (5) According to silicon carbide substrate 10 according to any one of (1) to (4) above, first main surface 1 may have a maximum diameter of 150 mm or more.

[0012] (6) A method for manufacturing a silicon carbide substrate 10 according to an embodiment of the present disclosure includes the following steps. A silicon carbide single crystal substrate 100 having a first main surface 1 and a second main surface 2 opposite to the first main surface 1 is prepared. The silicon carbide single crystal substrate 100 is subjected to chemical mechanical polishing using a polishing liquid 40. After the step of chemical mechanical polishing the silicon carbide single crystal substrate 100 using the polishing liquid 40, the silicon carbide single crystal substrate 100 is treated using a solution 52 containing an organic acid having two or more carboxy groups in one molecule. The polishing liquid 40 has a Brix value of 10 or more.

[0013] (7) The method for manufacturing silicon carbide substrate 10 according to (6) above may further include a step of immersing silicon carbide single crystal substrate 100 in alkaline solution 51 after the step of chemically mechanically polishing silicon carbide single crystal substrate 100 with polishing liquid 40 and before the step of treating silicon carbide single crystal substrate 100 with solution 52 containing an organic acid having two or more carboxy groups in one molecule.

[0014] (8) According to the method for manufacturing silicon carbide substrate 10 according to (6) or (7) above, the organic acid having two or more carboxy groups in one molecule may be oxalic acid or citric acid.

[0015] (9) According to any one of the methods for manufacturing silicon carbide substrate 10 described above in (6) to (8), the Brix value may be 30 or less. [Details of the embodiment of the present disclosure] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are given the same reference numerals, and the description thereof will not be repeated. In the crystallographic description in this specification, an individual orientation is indicated by [], a collective orientation by <>, an individual plane by (), and a collective plane by {}. In addition, for negative indices, a "-" (bar) is placed before the number in crystallography, but in this specification, a negative sign is placed before the number.

[0016] First, the configuration of the silicon carbide substrate according to the present embodiment will be described. Fig. 1 is a plan view schematic diagram showing the configuration of the silicon carbide substrate according to the present embodiment. Fig. 2 is a cross-sectional view schematic diagram taken along line II-II in Fig. 1.

[0017] As shown in Figs. 1 and 2, silicon carbide substrate 10 according to this embodiment mainly has a first main surface 1, a second main surface 2, and an outer peripheral surface 5. As shown in Fig. 2, second main surface 2 is on the opposite side to first main surface 1. Silicon carbide substrate 10 is made of silicon carbide of polytype 4H. Silicon carbide substrate 10 contains n-type impurities such as nitrogen (N). The conductivity type of silicon carbide substrate 10 is, for example, n-type. The concentration of n-type impurities in silicon carbide substrate 10 is, for example, 1 x 10 17 cm -3 More than 1×10 20 cm -3 The following is the result.

[0018] As shown in FIG. 1 , the maximum diameter A of the first main surface 1 is, for example, 150 mm or more (6 inches or more). The maximum diameter A of the first main surface 1 may be, for example, 200 mm or more (8 inches or more). The maximum diameter A of the first main surface 1 is the longest linear distance between two different points on the outer peripheral surface 5 of the silicon carbide substrate 10 when viewed in a direction perpendicular to the first main surface 1. In this specification, 6 inches means 150 mm or 152.4 mm (25.4 mm / inch × 6 inch). 8 inches means 200 mm or 203.2 mm (25.4 mm / inch × 8 inch).

[0019] The first main surface 1 is, for example, a {0001} plane or a plane inclined at an off angle of more than 0° and not more than 8° with respect to the {0001} plane. The off angle may be, for example, 1° or more, or 2° or more. The off angle may be 7° or less, or 6° or less. Specifically, the first main surface 1 may be a (0001) plane or a plane inclined at an off angle of more than 0° and not more than 8° with respect to the (0001) plane. The first main surface 1 may be a (000-1) plane or a plane inclined at an off angle of more than 0° and not more than 8° with respect to the (000-1) plane. The inclination direction of the first main surface 1 is, for example, the <11-20> direction.

[0020] As shown in FIG. 1 , the outer peripheral surface 5 may have, for example, a first flat 3 and an arc-shaped portion 4. The first flat 3 extends, for example, along a first direction 101. The arc-shaped portion 4 is continuous with the first flat 3. The outer peripheral surface 5 may have, for example, a second flat (not shown) extending, for example, along a second direction 102. The second direction 102 is, for example, a <1-100> direction. The first direction 101 is parallel to the first main surface 1 and perpendicular to the second direction 102. The first direction 101 is, for example, a <11-20> direction.

[0021] The first main surface 1 is, for example, a surface on which an epitaxial layer is formed. From another perspective, a silicon carbide epitaxial layer (not shown) is provided on the first main surface 1. The second main surface 2 is, for example, a surface on which a drain electrode is formed. From another perspective, a drain electrode (not shown) of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is formed on the second main surface 2.

[0022] As shown in FIG. 2, silicon carbide substrate 10 includes a plurality of screw dislocations 13, pits 11, and silicon carbide regions 22. The plurality of screw dislocations 13 include a first screw dislocation 6 that is continuous with pit 11, and a second screw dislocation 7 that is not continuous with pit 11. From another perspective, pit 11 is caused by first screw dislocation 6. Pit 11 opens to first main surface 1, but does not open to second main surface 2. First screw dislocation 6 is continuous with second main surface 2. Second screw dislocation 7 is continuous with each of first main surface 1 and second main surface 2. From another perspective, second screw dislocation 7 penetrates silicon carbide region 22 from first main surface 1 to second main surface 2.

[0023] FIG. 3 is an enlarged schematic diagram of region III in FIG. 2. As shown in FIG. 3, the width (diameter) of the pit 11 decreases from the first main surface 1 toward the second main surface 2. The pit 11 may be, for example, substantially conical. When viewed in a direction perpendicular to the first main surface 1, the pit 11 is substantially circular. The maximum diameter (first diameter W) of the pit 11 in a direction parallel to the first main surface 1 is 1 μm or more and 10 μm or less. The first diameter W may be 2 μm or more, or may be 3 μm or more. The maximum diameter of the pit 11 is the longest linear distance between two different points on the outer periphery of the pit 11 exposed to the first main surface 1. The maximum depth (first depth D) of the pit 11 in a direction perpendicular to the first main surface 1 may be, for example, 3 nm or more and 1 μm or less.

[0024] 2, the number of screw dislocations 13 is greater than the number of pits 11. Specifically, when screw dislocations 13 and pits 11 are observed on the first main surface 1, the ratio of the number of pits 11 divided by the number of screw dislocations 13 is 1% or less. The ratio of the number of pits 11 divided by the number of screw dislocations 13 may be, for example, 0.5% or less, 0.4% or less, or 0.3% or less. The lower limit of the ratio of the number of pits 11 divided by the number of screw dislocations 13 is not particularly limited, but may be, for example, 0.01% or more, or 0.1% or more.

[0025] The areal density of the screw dislocations 13 on the first main surface 1 is, for example, 100 cm-2 More than 5000cm -2 The lower limit of the areal density of the screw dislocations 13 on the first main surface 1 is not particularly limited, but may be, for example, 200 cm -2 It may be more than 500cm -2 The upper limit of the areal density of the screw dislocations 13 on the first main surface 1 is not particularly limited, but may be, for example, 4500 cm -2 It may be less than 4000cm -2 The following may also be present.

[0026] (Method of measuring screw dislocations) The number of screw dislocations 13 can be measured, for example, by using an X-ray topography method. The measurement device is, for example, an XRTmicron manufactured by Rigaku. Specifically, the number of screw dislocations 13 can be measured based on an X-ray topographic image of the first main surface 1 of the silicon carbide substrate 10. The X-ray topographic image is obtained by (0008) reflection. A Cu target is used as the X-ray source during measurement. The pixel size of the X-ray camera is 5.4 μm.

[0027] (Pit measurement method) The number of pits 11 can be measured using, for example, a defect inspection device equipped with a confocal differential interference microscope. The defect inspection device is, for example, a WASAVI series "SICA 6X" manufactured by Lasertec Corporation. The magnification of the objective lens is, for example, 10 times. Specifically, light with a wavelength of 546 nm is irradiated onto the first main surface 1 of silicon carbide substrate 10 from a light source such as a mercury xenon lamp, and the reflected light of the light is observed by a light receiving element such as a CCD (Charge-Coupled Device).

[0028] The difference between the brightness of a pixel in the observed image and the brightness of the pixels surrounding the pixel is quantified. The detection sensitivity threshold of the defect inspection device is determined using a standard sample. By using the defect inspection device, the diameter of the pits 11 formed in the sample to be measured can be quantitatively evaluated. The first main surface 1 of the silicon carbide substrate 10 is observed to detect pits 11 having a maximum diameter (first diameter W) of 1 μm or more and 10 μm or less.

[0029] As shown in FIG. 3 , metal impurities 8 are present on the first main surface 1. The metal impurities 8 include, for example, magnesium (Mg). Magnesium is present on the first main surface 1. The metal impurities 8 are, for example, inside pits 11. The metal impurities 8 may be on screw dislocations 13. The magnesium may be in contact with the screw dislocations 13. The metal impurities 8 may be on the first main surface 1 outside the pits 11.

[0030] The concentration of magnesium in the first main surface 1 is 1×10 11 atoms / cm 2 In the first main surface 1, the concentration of magnesium is, for example, 5×10 10 atoms / cm 2 may be less than 1 x 10 10 atoms / cm 2 The lower limit of the magnesium concentration in the first main surface 1 is not particularly limited, but may be, for example, 1×10 6 atoms / cm 2 It may be more than that.

[0031] The metal impurities 8 may include, for example, calcium (Ca), aluminum (Al), sodium (Na), potassium (K) and manganese (Mn). Each of calcium, aluminum, sodium, potassium and manganese may be present on the first main surface 1. Each of calcium, aluminum, sodium, potassium and manganese may be, for example, inside a pit 11. Each of calcium, aluminum, sodium, potassium and manganese may be on a screw dislocation 13. Each of calcium, aluminum, sodium, potassium and manganese may be in contact with the screw dislocation 13. Each of calcium, aluminum, sodium, potassium and manganese may be on the first main surface 1 outside the pit 11.

[0032] The concentration of calcium on the first main surface 1 is 1×10 11 atoms / cm 2 In the first main surface 1, the concentration of calcium may be, for example, 5×10 10 atoms / cm 2 may be less than 1 x 10 10 atoms / cm 2 The lower limit of the calcium concentration in the first main surface 1 is not particularly limited, but may be, for example, 1×10 6 atoms / cm 2 It may be more than that.

[0033] The aluminum concentration in the first main surface 1 is 1×10 11 atoms / cm 2 In the first main surface 1, the aluminum concentration may be, for example, 5×10 10 atoms / cm 2 may be less than 1 x 10 10 atoms / cm 2 The lower limit of the aluminum concentration in first main surface 1 is not particularly limited, but may be, for example, 1×10 6 atoms / cm 2 It may be more than that.

[0034] The concentration of sodium on the first main surface 1 is 1×10 11 atoms / cm 2 In the first main surface 1, the concentration of sodium may be, for example, 5×10 10 atoms / cm 2 may be less than 1 x 10 10 atoms / cm 2 The lower limit of the sodium concentration in the first main surface 1 is not particularly limited, but may be, for example, 1×10 6 atoms / cm 2 It may be more than that.

[0035] The concentration of potassium on the first main surface 1 is 1×10 11 atoms / cm 2 In the first main surface 1, the concentration of potassium may be, for example, 5×10 10 atoms / cm 2 may be less than 1 x 10 10 atoms / cm 2 In the first main surface 1, the lower limit of the potassium concentration is not particularly limited, but may be, for example, 1×10 6 atoms / cm 2 It may be more than that.

[0036] In the first main surface 1, the concentration of manganese is 1×10 11 atoms / cm 2 In the first main surface 1, the concentration of manganese may be, for example, 5×10 10 atoms / cm 2 may be less than 1 x 10 10 atoms / cm 2 The lower limit of the manganese concentration in the first main surface 1 is not particularly limited, but may be, for example, 1×10 6 atoms / cm 2 It may be more than that.

[0037] In the first main surface 1, the concentrations of magnesium, calcium, aluminum, sodium, potassium, and manganese are each 5×10 10 atoms / cm 2 In the first main surface 1, the concentration of each of magnesium, calcium, aluminum, sodium, potassium, and manganese may be less than 1×10 10 atoms / cm 2 It may be less than.

[0038] (Method for measuring the concentration of metal impurities) Next, a method for measuring the concentration of metal impurities 8 on the first main surface 1 will be described.

[0039] First, acid is dropped onto the entire surface of first main surface 1 of silicon carbide substrate 10 using a horizontal substrate inspection device. The acid also gets into pits 11. As a result, metal impurities 8 on first main surface 1 are taken into the acid. Next, the entire amount of acid containing metal impurities 8 is collected from the entire surface of first main surface 1. The sample preparation is performed in a class 10 clean draft installed in a class 100 clean room.

[0040] The concentration of the metal impurities 8 can be measured by ICP-MS (Inductively Coupled Plasma Mass Spectrometry). For example, an ICP-MS8800 manufactured by Agillent can be used as a measuring device. The mass (ng) of the metal impurities 8 elements obtained by the measurement is divided by the atomic weight of each element to convert to the number of moles, and then multiplied by Avogadro's number to convert to the number of atoms. Next, the number of atoms is divided by the area of ​​the first main surface 1 to convert to the number of atoms per unit area. The concentration of the metal impurities 8 refers to the number of atoms per unit area.

[0041] Next, a method for manufacturing a silicon carbide substrate according to this embodiment will be described. Fig. 4 is a flow chart that outlines the method for manufacturing a silicon carbide substrate according to this embodiment.

[0042] As shown in FIG. 4, the method for manufacturing silicon carbide substrate 10 according to this embodiment mainly includes a step of preparing a silicon carbide single crystal substrate (S10), a chemical mechanical polishing step (S20), a step of treating with an alkaline solution (S30), a water-rinsing step (S40), a step of treating with a solution containing an organic acid having two or more carboxy groups in one molecule (S50), a water-rinsing step (S60), and a drying step (S70).

[0043] First, a step (S10) of preparing a silicon carbide single crystal substrate is performed. Specifically, for example, an ingot made of a silicon carbide single crystal of polytype 4H is formed by sublimation. After the ingot is shaped, the ingot is sliced ​​by a wire saw device. Thus, a silicon carbide single crystal substrate 100 is cut out from the ingot.

[0044] Silicon carbide single crystal substrate 100 is made of hexagonal silicon carbide of polytype 4H. Silicon carbide single crystal substrate 100 has a first main surface 1 and a second main surface 2 on the opposite side of first main surface 1. First main surface 1 is a surface that is off-angled, for example, by 4° or less in the <11-20> direction with respect to the {0001} plane. Specifically, first main surface 1 is a surface that is off-angled, for example, by about 4° or less with respect to the (0001) plane. Second main surface 2 is a surface that is off-angled, for example, by about 4° or less with respect to the (000-1) plane.

[0045] 5, silicon carbide substrate 10 has first main surface 1, second main surface 2, a plurality of screw dislocations 13, and silicon carbide region 22. The plurality of screw dislocations 13 are continuous with each of first main surface 1 and second main surface 2. From another perspective, the plurality of screw dislocations 13 penetrate silicon carbide region 22 from first main surface 1 to second main surface 2. In this manner, silicon carbide single crystal substrate 100 having first main surface 1 and second main surface 2 opposite to first main surface 1 is prepared.

[0046] Next, a step of mechanically polishing silicon carbide single crystal substrate 100 is carried out. Specifically, first main surface 1 is arranged to face a surface plate (not shown). Next, a slurry is introduced between first main surface 1 and the surface plate. The slurry contains, for example, diamond abrasive grains. The diamond abrasive grains have a diameter of, for example, 1 μm or more and 3 μm or less. A load is applied to first main surface 1 by the surface plate. As a result, silicon carbide single crystal substrate 100 is mechanically polished at first main surface 1.

[0047] Next, a chemical mechanical polishing step (S20) is performed. Specifically, the silicon carbide single crystal substrate 100 is subjected to chemical mechanical polishing using a polishing liquid 40. The polishing liquid 40 includes abrasive grains 41 and a liquid 42. The abrasive grains 41 are, for example, colloidal silica. The average grain size of the abrasive grains 41 is, for example, 20 nm. The polishing liquid 40 includes, for example, a lubricant, an oxidizing agent, and a dispersing agent. The lubricant is, for example, a sugar such as sucrose or glucose. The lubricant may be, for example, a polyhydric alcohol. The oxidizing agent is, for example, an aluminum nitrate aqueous solution. The dispersing agent includes, for example, magnesium (Mg).

[0048] As shown in FIG. 6, the chemical mechanical polishing apparatus 200 mainly includes a polishing cloth 33, a polishing plate 31, a rotary support member 32, and a polishing liquid supply unit 34. The silicon carbide single crystal substrate 100 is attached to the polishing plate 31. The second main surface 2 of the silicon carbide single crystal substrate 100 faces the polishing plate 31. The first main surface 1 of the silicon carbide single crystal substrate 100 faces the polishing cloth 33. The polishing cloth 33 is, for example, a suede polishing cloth. The polishing liquid supply unit 34 supplies a polishing liquid 40. The polishing liquid 40 supplied from the polishing liquid supply unit 34 is supplied between the first main surface 1 of the silicon carbide single crystal substrate 100 and the polishing cloth 33.

[0049] As shown in FIG. 6, polishing plate 31 is attached to a rotary support member 32. Rotation of rotary support member 32 around rotation axis B in rotation direction C causes silicon carbide single crystal substrate 100 to rotate. The rotation speed of rotary support member 32 is, for example, 60 rpm. The rotation speed of a surface plate on which a polishing cloth is provided is, for example, 60 rpm. The processing surface pressure is, for example, 300 g / cm. 2 The polishing time is, for example, 5 hours.

[0050] According to the method for manufacturing silicon carbide substrate 10 of this embodiment, polishing liquid 40 contains sugars and the like, so that the sugar content of polishing liquid 40 is high. Specifically, the Brix value of polishing liquid 40 is 10 or more. The Brix value of polishing liquid 40 may be, for example, 12 or more, or 15 or more. The upper limit of the Brix value may be, for example, 30 or less, or 20 or less. This increases the viscosity of polishing liquid 40. As a result, polishing liquid 40 is easily supplied between first main surface 1 of silicon carbide single crystal substrate 100 and polishing cloth 33.

[0051] Next, a method for measuring the Brix value will be described. The Brix value can be measured using a handheld refractometer manufactured by AS ONE Corporation. The model number of the handheld refractometer is RAB-10. The polishing liquid is dropped onto the prism of the handheld refractometer, and the Brix value is measured. The Brix value can be adjusted by the concentration of colloidal silica, the type of sugar, the amount of sugar, etc. By adding sugar to the polishing liquid, the viscosity and lubricity of the polishing liquid can be adjusted, and the surface tension of the polishing liquid can be changed.

[0052] Next, the step of treating with an alkaline solution (S30) is performed. In the step of treating with an alkaline solution (S30), silicon carbide single crystal substrate 100 is immersed in alkaline solution 51. As shown in FIG. 7, alkaline solution 51 is placed in container 50. Silicon carbide single crystal substrate 100 is immersed in alkaline solution 51 while being held on polishing plate 31. Alkaline solution 51 is, for example, tetramethylammonium hydroxide. Alkaline solution 51 has a pH of 10 or higher. Immersing silicon carbide single crystal substrate 100 in alkaline solution 51 removes abrasive grains 41 adhering to silicon carbide single crystal substrate 100.

[0053] Next, a water washing step (S40) is performed. In the water washing step (S40), silicon carbide single crystal substrate 100 is washed with water. Silicon carbide single crystal substrate 100 is washed with water while being held on polishing plate 31. As a result, alkaline solution 51 adhering to silicon carbide single crystal substrate 100 is washed away with water.

[0054] Next, a step (S50) of treating with a solution containing an organic acid having two or more carboxy groups in one molecule is performed. In the step (S50) of treating with a solution containing an organic acid having two or more carboxy groups in one molecule, silicon carbide single crystal substrate 100 is immersed in acid. As shown in Fig. 8, solution 52 containing an organic acid having two or more carboxy groups in one molecule is placed in container 50. With silicon carbide single crystal substrate 100 held on polishing plate 31, silicon carbide single crystal substrate 100 is immersed in solution 52 containing an organic acid having two or more carboxy groups in one molecule.

[0055] The organic acid having two or more carboxy groups in one molecule is, for example, oxalic acid or citric acid. The organic acid having two or more carboxy groups in one molecule may be, for example, malic acid. The organic acid having two or more carboxy groups in one molecule has a chelating effect. Specifically, the metal impurities 8 are captured between the two carboxy groups. In particular, divalent cations such as magnesium or calcium are easily captured between the two carboxy groups. The silicon carbide single crystal substrate 100 is immersed in a solution 52 containing an organic acid having two or more carboxy groups in one molecule, whereby the metal impurities 8 attached to the silicon carbide single crystal substrate 100 are removed. The metal impurities 8 are, for example, magnesium, calcium, aluminum, sodium, potassium, manganese, or the like.

[0056] As described above, after the step of chemically mechanically polishing silicon carbide single crystal substrate 100 using polishing liquid 40, silicon carbide single crystal substrate 100 is treated using solution 52 containing an organic acid having two or more carboxy groups in one molecule. Furthermore, the step of immersing silicon carbide single crystal substrate 100 in alkaline solution 51 is carried out after the step of chemically mechanically polishing silicon carbide single crystal substrate 100 using polishing liquid 40 and before the step of treating silicon carbide single crystal substrate 100 with solution 52 containing an organic acid having two or more carboxy groups in one molecule.

[0057] Next, a water washing step (S60) is performed. In the water washing step (S60), silicon carbide single crystal substrate 100 is washed with water. Silicon carbide single crystal substrate 100 is washed with water while being held on polishing plate 31. As a result, oxalic acid or citric acid adhering to silicon carbide single crystal substrate 100 is washed away with water.

[0058] Next, a drying step (S70) is performed. The silicon carbide single crystal substrate 100 is dried, for example, by a spin dryer. The rotation speed of the spin dryer is, for example, 800 rpm. The drying time is, for example, 120 seconds. This dries the silicon carbide single crystal substrate 100. Next, the silicon carbide single crystal substrate 100 is removed from the polishing plate 31. In this manner, the silicon carbide substrate 10 (see FIG. 1 ) according to this embodiment is obtained. Note that if the silicon carbide single crystal substrate 100 is dried in a state in which metal impurities 8 remain on the surface of the silicon carbide single crystal substrate 100, the metal impurities 8 will adhere firmly to the surface of the silicon carbide single crystal substrate 100. For this reason, it is desirable to perform the step (S50) of treating with a solution containing an organic acid having two or more carboxy groups in one molecule before the drying step (70).

[0059] Next, the effects of the silicon carbide substrate and the method for manufacturing the silicon carbide substrate according to the present embodiment will be described.

[0060] When chemical mechanical polishing is performed on silicon carbide single crystal substrate 100 having screw dislocations 13, the portion of silicon carbide near screw dislocations 13 is mechanically weak and is therefore likely to be scraped off by collision between silicon carbide single crystal substrate 100 and abrasive grains 41, etc. As a result, pits 11 are likely to be formed on the surface of silicon carbide single crystal substrate 100.

[0061] In order to reduce the collision between the silicon carbide single crystal substrate 100 and the abrasive grains 41, etc., it is necessary to introduce the polishing liquid 40 having an appropriate thickness between the silicon carbide single crystal substrate 100 and the polishing cloth 33 in the chemical mechanical polishing process. However, since silicon carbide has a higher hardness than other semiconductor materials, chemical mechanical polishing is performed under high rotation speed and high pressure conditions. Therefore, it is difficult for the normal polishing liquid 40 to penetrate between the silicon carbide single crystal substrate 100 and the polishing cloth 33. In addition, since silicon carbide has a lower chemical reactivity than other semiconductor materials, it is difficult to increase the retention of the polishing liquid 40 by increasing the hydrophilicity of the surface of the silicon carbide single crystal substrate 100 through a chemical reaction.

[0062] The inventors have conducted extensive research into measures to suppress the formation of pits 11 on the surface of silicon carbide single crystal substrate 100, and have obtained the following findings. Specifically, the lubricating effect of polishing liquid 40 is enhanced to facilitate the incorporation of polishing liquid 40 between silicon carbide single crystal substrate 100 and polishing cloth 33. Specifically, the Brix value of polishing liquid 40 is set to 10 or more. This makes it possible to increase the viscosity of polishing liquid 40, so that polishing liquid 40 is more likely to be incorporated between silicon carbide single crystal substrate 100 and polishing cloth 33. As a result, it is possible to reduce the strength of the impact when abrasive grains 41 collide with silicon carbide single crystal substrate 100 due to mechanical factors such as vibration of abrasive grains 41 or polishing equipment. As a result, it is possible to suppress the formation of pits 11 on the surface (first main surface 1) of silicon carbide single crystal substrate 100.

[0063] Furthermore, the polishing solution 40 for chemical mechanical polishing may contain a dispersant having a divalent cation such as magnesium or calcium. If pits 11 are present on the surface of the silicon carbide single crystal substrate 100, metal impurities 8 such as magnesium will get into the pits 11. If the metal impurities 8 get into the pits 11, it will be difficult to completely remove the metal impurities 8 in the cleaning step. As a result, the cleanliness of the silicon carbide single crystal substrate 100 will deteriorate.

[0064] The inventors have conducted extensive research into measures for suppressing deterioration in the cleanliness of the surface of silicon carbide single crystal substrate 100, and have obtained the following findings. Specifically, they have found that metal impurities 8 adhering to silicon carbide single crystal substrate 100 in the step of chemical mechanical polishing can be removed by treating silicon carbide single crystal substrate 100 with an acid having a chelating effect. Specifically, after the step of chemical mechanical polishing silicon carbide single crystal substrate 100 with polishing liquid 40, silicon carbide single crystal substrate 100 is treated with solution 52 containing an organic acid having two or more carboxy groups in one molecule. This can improve the cleanliness of silicon carbide single crystal substrate 100. EXAMPLES

[0065] (Sample preparation) First, silicon carbide substrates 10 according to Samples 1 to 6 were prepared. Silicon carbide substrates 10 according to Samples 1 to 3 were used as comparative examples. Silicon carbide substrates 10 according to Samples 4 to 6 were used as examples. In the method for manufacturing a silicon carbide substrate according to Samples 3 to 6, a polishing liquid 40 having a Brix value of 10 or more was used in the chemical mechanical polishing step (S20). In the method for manufacturing a silicon carbide substrate 10 according to Samples 2 and 4 to 6, a step (S50) of treating with a solution containing an organic acid having two or more carboxy groups in one molecule was performed. That is, in the method for manufacturing a silicon carbide substrate 10 according to Samples 4 to 6, a polishing liquid having a Brix value of 10 or more was used in the chemical mechanical polishing step (S20), and a step (S50) of treating with a solution containing an organic acid having two or more carboxy groups in one molecule was performed.

[0066] In the manufacturing method of silicon carbide substrate 10 according to Samples 1 and 2, the Brix value of polishing liquid 40 was set to 5. In the manufacturing method of silicon carbide substrate 10 according to Samples 3, 5 and 6, the Brix value of polishing liquid 40 was set to 20. In the manufacturing method of silicon carbide substrate 10 according to Sample 4, the Brix value of polishing liquid 40 was set to 30. In the manufacturing method of silicon carbide substrate 10 according to Samples 2 and 4, 5% citric acid was used. In the manufacturing method of silicon carbide substrate 10 according to Sample 5, 3% citric acid was used. In the manufacturing method of silicon carbide substrate 10 according to Sample 6, 3% oxalic acid was used. In the silicon carbide substrate 10 according to Samples 1 to 6, the density of screw dislocations 13 was 390 / cm. 2 , 430 pieces / cm 2 , 420 pieces / cm 2 , 420 pieces / cm 2 , 300 pieces / cm 2 and 480 pieces / cm 2 It was. (Evaluation method) X-ray topography was used to measure the density of screw dislocations 13 on first main surfaces 1 of silicon carbide substrates 10 in Samples 1 to 6. A defect inspection device was used to measure the density of pits 11 on first main surfaces 1 of silicon carbide substrates 10 in Samples 1 to 6. The maximum size (diameter) of pits 11 was 1 μm or more and 10 μm or less. ICP-MS was used to measure the concentration of metal impurities 8 over the entire surface of first main surface 1 of silicon carbide substrates 10 in Samples 1 to 6. (Evaluation Results)

[0067] [Table 1]

[0068] As shown in Table 1, the density of pits 11 on first main surface 1 of silicon carbide substrate 10 in samples 1 to 6 was 12 pits / cm 2 , 14 pieces / cm 2 , 1.2 pieces / cm 2 , 0.7 pieces / cm 2 , 1.5 pieces / cm 2 and 1.0 pieces / cm 2 The values ​​obtained by dividing the density of pits 11 on first main surface 1 of silicon carbide substrate 10 in samples 1 to 6 by the density of screw dislocations 13 were 3.0%, 3.3%, 0.3%, 0.2%, 0.5% and 0.2%, respectively.

[0069] The Mg concentration in the first main surface 1 of the silicon carbide substrate 10 in Samples 1 to 6 was 93×10 9 atoms / cm 2 , 65×10 9 atoms / cm 2 , 85×10 9 atoms / cm 2 , 2×10 9 atoms / cm 2 Less than 3×10 9 atoms / cm 2 and 5×10 9 atoms / cm 2 The Ca concentration in the first main surface 1 of the silicon carbide substrate 10 in Samples 1 to 6 was 269×10 9atoms / cm 2 , 54×10 9 atoms / cm 2 , 121×10 9 atoms / cm 2 , 4×10 9 atoms / cm 2 Less than 4×10 9 atoms / cm 2 Less than and 48×10 9 atoms / cm 2 It was.

[0070] The Al concentration in the first main surface 1 of the silicon carbide substrate 10 in Samples 1 to 6 was 134×10 9 atoms / cm 2 , 60×10 9 atoms / cm 2 , 66×10 9 atoms / cm 2 , 2×10 9 atoms / cm 2 Less than 2×10 9 atoms / cm 2 and 15×10 9 atoms / cm 2 The Na concentration in the first main surface 1 of the silicon carbide substrate 10 in Samples 1 to 6 was 671×10 9 atoms / cm 2 , 103×10 9 atoms / cm 2 , 138×10 9 atoms / cm 2 , 4×10 9 atoms / cm 2 , 2×10 9 atoms / cm 2 Less than and 12×10 9 atoms / cm 2 It was.

[0071] The K concentration in the first main surface 1 of the silicon carbide substrate 10 in Samples 1 to 6 is 130×10 9 atoms / cm 2 , 46×10 9 atoms / cm 2 , 73×109 atoms / cm 2 , 4×10 9 atoms / cm 2 Less than 4×10 9 atoms / cm 2 Less than and 4×10 9 atoms / cm 2 The Mn concentration in the first main surface 1 of the silicon carbide substrate 10 in Samples 1 to 6 was less than 8×10 9 atoms / cm 2 , 5×10 9 atoms / cm 2 , 12×10 9 atoms / cm 2 , 2×10 9 atoms / cm 2 Less than 2×10 9 atoms / cm 2 Less than and 2×10 9 atoms / cm 2 It was less than.

[0072] From the above results, it was confirmed that by using a polishing solution with a Brix value of 10 or more in the chemical mechanical polishing step (S20) and performing a step (S50) of treating with a solution containing an organic acid having two or more carboxy groups in one molecule, it is possible to suppress the generation of pits 11 caused by screw dislocations 13 and reduce the Mg concentration.

[0073] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered as limiting. The scope of the present invention is defined by the claims, not the above description, and is intended to include the meaning equivalent to the claims and all modifications within the scope. [Explanation of symbols]

[0074] 1 first principal surface, 2 second principal surface, 3 first flat, 4 arc-shaped portion, 5 outer peripheral surface, 6 first screw dislocation, 7 second screw dislocation, 8 metal impurity, 10 silicon carbide substrate, 11 pit, 13 screw dislocation, 22 silicon carbide region, 31 polishing plate, 32 rotating support member, 33 polishing cloth, 34 polishing agent supply unit, 40 polishing agent, 41 abrasive grains, 42 polishing liquid, 50 container, 51 alkaline solution, 52 solution, 100 silicon carbide single crystal substrate, 101 first direction, 102 second direction, 200 chemical mechanical polishing apparatus, A maximum diameter, B rotation axis, C rotation direction, D first depth, W first diameter.

Claims

1. A silicon carbide substrate having a first main surface and a second main surface opposite the first main surface, the silicon carbide substrate includes screw dislocations and pits having a maximum diameter of 1 μm or more and 10 μm or less in a direction parallel to the first main surface, when the screw dislocations and the pits are observed on the first main surface, a ratio of the number of the pits divided by the number of the screw dislocations is 1% or less; The concentration of magnesium in the first main surface is 1×10 6 atoms / cm 2 or more and 1×10 11 atoms / cm 2 A silicon carbide substrate having a thickness of less than 100 nm.

2. In the first principal surface, the concentration of each of calcium, aluminum, sodium, potassium and manganese is 1×10 11 atoms / cm 2 The silicon carbide substrate of claim 1 .

3. In the first principal surface, the concentration of each of magnesium, calcium, aluminum, sodium, potassium and manganese is 5×10 10 atoms / cm 2 The silicon carbide substrate of claim 1 .

4. The areal density of the screw dislocations on the first main surface is 100 cm -2 More than 5000cm -2 The silicon carbide substrate according to claim 1 , wherein:

5. The silicon carbide substrate according to claim 1 , wherein the first main surface has a maximum diameter of 150 mm or greater.

6. providing a silicon carbide single crystal substrate having a first main surface and a second main surface opposite the first main surface; performing chemical mechanical polishing on the silicon carbide single crystal substrate using a polishing liquid; and after a step of chemically and mechanically polishing the silicon carbide single crystal substrate using the polishing liquid, a step of treating the silicon carbide single crystal substrate using a solution containing an organic acid having two or more carboxy groups in one molecule, The polishing liquid contains magnesium, The method for manufacturing a silicon carbide substrate, wherein the polishing liquid has a Brix value of 10 or more.

7. 7. The method for manufacturing a silicon carbide substrate according to claim 6, further comprising the step of immersing said silicon carbide single crystal substrate in an alkaline solution after the step of performing chemical mechanical polishing on said silicon carbide single crystal substrate with said polishing liquid and before the step of treating said silicon carbide single crystal substrate with said solution containing an organic acid having two or more carboxy groups in one molecule.

8. 8. The method for producing a silicon carbide substrate according to claim 6, wherein the organic acid having two or more carboxy groups in one molecule is oxalic acid or citric acid.

9. The method for manufacturing a silicon carbide substrate according to claim 6 , wherein the Brix value is 30 or less.

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