JP7521407B2 - Silicon carbide epitaxial substrate inspection method, silicon carbide epitaxial substrate manufacturing method, and silicon carbide epitaxial substrate inspection device - Google Patents

Description

This disclosure relates to a method for inspecting a silicon carbide epitaxial substrate, a method for manufacturing a silicon carbide epitaxial substrate, and an inspection device for a silicon carbide epitaxial substrate.

JP2018-518063A (Patent Document 1) describes a system and method for measuring semiconductor doping concentration using surface potential corona charging.

Special table 2018-518063 publication

The objective of the present disclosure is to provide a method for inspecting a silicon carbide epitaxial substrate that can stably measure carrier concentration, a method for manufacturing a silicon carbide epitaxial substrate, and an inspection device for a silicon carbide epitaxial substrate.

The method for inspecting a silicon carbide epitaxial substrate according to the present disclosure includes the following steps: A silicon carbide epitaxial substrate having a main surface is prepared. The main surface is irradiated with ultraviolet light having a wavelength of 200 nm or more and 400 nm or less. After the step of irradiating with ultraviolet light, a charge is supplied to the main surface, and then a probe is placed in a non-contact state with the main surface, and a potential of the main surface is measured using the probe. A carrier concentration of the silicon carbide epitaxial substrate is calculated based on the charge and the potential. In the step of irradiating with ultraviolet light, the number of photons per unit area of the ultraviolet light is 30×10 ¹⁶ /cm ² or more.

A method for manufacturing a silicon carbide epitaxial substrate according to the present disclosure includes the following steps: A silicon carbide epitaxial substrate having a main surface is prepared. The main surface is irradiated with ultraviolet light having a wavelength of 200 nm or more and 400 nm or less. In the step of irradiating with ultraviolet light, the number of photons per unit area of the ultraviolet light is 30×10 ¹⁶ /cm ² or more.

The silicon carbide epitaxial substrate inspection device according to the present disclosure includes an irradiation device section and a measurement device section. The irradiation device section irradiates the main surface of the silicon carbide epitaxial substrate with ultraviolet light having a wavelength of 200 nm or more and 400 nm or less. The measurement device section supplies an electric charge to the main surface, then places a probe in a non-contact state with the main surface, and uses the probe to measure the electric potential of the main surface.

The present disclosure provides a method for inspecting a silicon carbide epitaxial substrate that can stably measure carrier concentration, a method for manufacturing a silicon carbide epitaxial substrate, and an inspection device for a silicon carbide epitaxial substrate.

FIG. 1 is a partial cross-sectional schematic diagram showing the configuration of a measurement device section of an inspection device for a silicon carbide epitaxial substrate according to the present embodiment. FIG. 2 is a partial schematic cross-sectional view showing the configuration of an irradiation device section of the silicon carbide epitaxial substrate inspection apparatus according to this embodiment. FIG. 3 is a schematic diagram showing the configuration of an inspection apparatus for a silicon carbide epitaxial substrate according to this embodiment. FIG. 4 is a flow diagram showing the method for inspecting a silicon carbide epitaxial substrate according to the present embodiment. FIG. 5 is a schematic plan view showing the configuration of a silicon carbide epitaxial substrate. FIG. 6 is a schematic cross-sectional view taken along line VI-VI in FIG. FIG. 7 is a schematic plan view showing a step of irradiating the main surface with ultraviolet light. FIG. 8 is a flow diagram that outlines the method for manufacturing a silicon carbide epitaxial substrate according to the present embodiment. FIG. 9 is a graph showing the relationship between the number of photons per unit area of ultraviolet light irradiated onto the first main surface of the silicon carbide epitaxial substrate according to Sample 1 and the carrier concentration of the silicon carbide epitaxial substrate. FIG. 10 is a graph showing the relationship between the number of photons per unit area of ultraviolet light irradiated onto the first main surface of the silicon carbide epitaxial substrate according to Sample 2 and the carrier concentration of the silicon carbide epitaxial substrate. FIG. 11 is a graph showing the relationship between the number of photons per unit area of ultraviolet light irradiated onto the first main surface of the silicon carbide epitaxial substrate according to Sample 3 and the carrier concentration of the silicon carbide epitaxial substrate. FIG. 12 is a graph showing the relationship between the number of photons per unit area of ultraviolet light irradiated onto the first main surface of the silicon carbide epitaxial substrate according to Sample 4 and the carrier concentration of the silicon carbide epitaxial substrate. FIG. 13 is a graph showing the relationship between the number of photons per unit area of ultraviolet light irradiated onto the first main surfaces of the silicon carbide epitaxial substrates according to Samples 5 to 7 and the carrier concentration of the silicon carbide epitaxial substrates.

[Summary of the embodiment of the present disclosure]
First, an overview of the embodiments of the present disclosure will be described. In the crystallographic description in this specification, an individual orientation is represented by [ ], a collective orientation by <>, an individual plane by ( ), and a collective plane by { }. A negative index in crystallography is usually represented by placing a "-" (bar) above the number, but in this specification, a negative index in crystallography is represented by placing a negative sign before the number.

(1) A method for inspecting a silicon carbide epitaxial substrate 10 according to the present disclosure includes the following steps: A silicon carbide epitaxial substrate 10 having a main surface 1 is prepared. The main surface 1 is irradiated with ultraviolet light having a wavelength of 200 nm or more and 400 nm or less. After the step of irradiating the ultraviolet light, a charge is supplied to the main surface 1, and then a probe 113 is placed in a non-contact state with the main surface 1, and the potential of the main surface 1 is measured using the probe 113. A carrier concentration of the silicon carbide epitaxial substrate 10 is calculated based on the charge and the potential. In the step of irradiating the ultraviolet light, the number of photons per unit area of the ultraviolet light is 30×10 ¹⁶ /cm ² or more.

(2) According to the method for inspecting a silicon carbide epitaxial substrate 10 according to (1) above, the main surface 1 may be inclined at an off angle of 8° or less with respect to the (000-1) plane or the (000-1) plane.

(3) According to the method for inspecting silicon carbide epitaxial substrate 10 in accordance with (1) above, main surface 1 may be inclined at an off angle of 8° or less with respect to the (0001) plane or the (0001) plane. The number of photons per unit area may be 550× ¹⁰ /cm or ^more .

(4) The method for manufacturing a silicon carbide epitaxial substrate 10 according to the present disclosure includes the following steps. The method for inspecting a silicon carbide epitaxial substrate 10 described in any one of (1) to (3) above is performed. The silicon carbide epitaxial substrates 10 are selected based on the carrier concentration.

(5) A method for manufacturing silicon carbide epitaxial substrate 10 according to the present disclosure includes the following steps: Silicon carbide epitaxial substrate 10 having main surface 1 is prepared. Main surface 1 is irradiated with ultraviolet light having a wavelength of 200 nm or more and 400 nm or less. In the step of irradiating with ultraviolet light, the number of photons per unit area of the ultraviolet light is 30×10 ¹⁶ /cm ² or more.

(6) The inspection device 300 for the silicon carbide epitaxial substrate 10 according to the present disclosure includes an irradiation device section 200 and a measurement device section 100. The irradiation device section 200 irradiates the main surface 1 of the silicon carbide epitaxial substrate 10 with ultraviolet light having a wavelength of 200 nm or more and 400 nm or less. The measurement device section 100 supplies a charge to the main surface 1, and then places a probe 113 in a non-contact state with the main surface 1, and measures the electric potential of the main surface 1 using the probe 113.

[Details of the embodiment of the present disclosure]
Hereinafter, the details of the embodiments of the present disclosure will be described. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description thereof will not be repeated.

First, the configuration of the measurement device section 100 of the inspection device for the silicon carbide epitaxial substrate 10 according to this embodiment will be described. FIG. 1 is a partial cross-sectional schematic diagram showing the configuration of the measurement device section 100 of the inspection device for the silicon carbide epitaxial substrate 10 according to this embodiment.

The measurement device section 100 of the inspection device for the silicon carbide epitaxial substrate 10 according to this embodiment is a non-contact carrier concentration measuring device. As shown in FIG. 1, the measurement device section 100 mainly includes a chuck 111, a corona electrode 112, and a probe 113. The probe 113 is, for example, a Kelvin probe. The chuck 111 holds the silicon carbide epitaxial substrate 10. The chuck 111 is made of a conductive material. The chuck 111 is, for example, electrically grounded. The chuck 111 has a substrate holding surface 110. The chuck 111 may be movable along a direction parallel to the substrate holding surface 110.

The corona electrode 112 is disposed opposite the substrate holding surface 110 of the chuck 111. The corona electrode 112 generates a corona charge. The tip of the corona electrode 112 is, for example, conical. The corona electrode 112 supplies a charge to the main surface 1 of the silicon carbide epitaxial substrate 10. By applying a voltage to the corona electrode 112, the air is ionized and a charge is generated. This forms a depletion layer in the silicon carbide epitaxial substrate 10.

The probe 113 is disposed facing the substrate holding surface 110 of the chuck 111. The probe 113 is disposed away from the main surface 1 of the silicon carbide epitaxial substrate 10. From another perspective, the probe 113 is a non-contact probe. The probe 113 can measure the electric potential (surface potential) of the main surface 1 of the silicon carbide epitaxial substrate 10. The tip of the probe 113 is, for example, cylindrical. The diameter of the tip of the probe 113 is, for example, 2 mm.

After supplying a charge to the main surface 1 of the silicon carbide epitaxial substrate 10, the measuring device 100 places a probe 113 in a non-contact state with the main surface 1 of the silicon carbide epitaxial substrate 10 and uses the probe 113 to measure the potential of the main surface 1 of the silicon carbide epitaxial substrate 10. The measuring device 100 may have a calculation unit (not shown) that calculates the carrier concentration of the silicon carbide epitaxial substrate 10 based on the charge supplied to the main surface 1 of the silicon carbide epitaxial substrate 10 and the potential of the main surface 1 of the silicon carbide epitaxial substrate 10.

Next, the configuration of the irradiation device section 200 of the inspection device for the silicon carbide epitaxial substrate 10 according to this embodiment will be described. FIG. 2 is a partial cross-sectional schematic diagram showing the configuration of the irradiation device section 200 of the inspection device for the silicon carbide epitaxial substrate 10 according to this embodiment.

As shown in FIG. 2, the irradiation device section 200 mainly includes a substrate holding section 201 and an ultraviolet light irradiation section 204. The substrate holding section 201 has a substrate holding surface 210. The substrate holding section 201 is, for example, a stand that holds a substrate. The substrate holding section 201 may be fixed or movable. The substrate holding section 201 may be movable in a direction parallel to the substrate holding surface 210 while holding the silicon carbide epitaxial substrate 10.

The ultraviolet light irradiation unit 204 has a UV light 203 (ultraviolet light) and a light holding unit 202. The UV light 203 has an elongated shape. The length of the UV light 203 may be greater than the diameter of the silicon carbide epitaxial substrate 10. The shape of the UV light 203 may be ring-shaped. The UV light 203 may be a surface-emitting light. The shape of the UV light 203 may be arbitrary. The light holding unit 202 holds the UV light 203. The UV light 203 is provided facing the surface of the substrate holding surface 210. The UV light 203 may be fixed or movable. The UV light 203 may be movable in a direction parallel to the substrate holding surface 210.

The ultraviolet light irradiation unit 204 irradiates ultraviolet light onto the main surface 1 of the silicon carbide epitaxial substrate 10. The ultraviolet light has a wavelength of 200 nm or more and 400 nm or less. The ultraviolet light irradiation unit 204 may be capable of irradiating ultraviolet light of two different wavelengths. The two different wavelengths are, for example, 254 nm and 365 nm. For example, SLUV-6 manufactured by AS ONE Corporation can be used as the ultraviolet light irradiation unit 204. It is particularly preferable that the wavelength of the ultraviolet light is 240 nm or more and 385 nm or less. This is because UV light is inexpensively available. It is particularly preferable that the wavelength of the ultraviolet light is 254 nm or more and 365 nm or less. This is because the light source has a relatively long life and requires less frequent maintenance.

Next, the configuration of the inspection device 300 for the silicon carbide epitaxial substrate 10 according to this embodiment will be described. FIG. 3 is a schematic diagram showing the configuration of the inspection device 300 for the silicon carbide epitaxial substrate 10 according to this embodiment. As shown in FIG. 3, the inspection device 300 for the silicon carbide epitaxial substrate 10 according to this embodiment mainly includes an irradiation device section 200, a measurement device section 100, and a transport section 310.

The transport section 310 is disposed between the irradiation device section 200 and the measurement device section 100. The transport section 310 connects the irradiation device section 200 and the measurement device section 100. The transport section 310 can transport the silicon carbide epitaxial substrate 10 between the irradiation device section 200 and the measurement device section 100. The transport section 310 can automatically transport the silicon carbide epitaxial substrate 10 to the measurement device section 100, for example, after the irradiation device section 200 completes the irradiation of the silicon carbide epitaxial substrate 10 with ultraviolet light. The transport section 310 is, for example, a belt conveyor.

Figure 4 is a flow diagram showing the method for inspecting silicon carbide epitaxial substrate 10 according to this embodiment. As shown in Figure 4, the method for inspecting silicon carbide epitaxial substrate 10 according to this embodiment includes the steps of preparing a silicon carbide epitaxial substrate having a main surface (S10), irradiating the main surface with ultraviolet light (S20), supplying an electric charge to the main surface and then placing a probe in a non-contact state with the main surface and measuring the electric potential of the main surface using the probe (S30), calculating the carrier concentration of the silicon carbide epitaxial substrate based on the electric charge and the electric potential (S40), and selecting silicon carbide epitaxial substrates (S50).

First, a step (S10) of preparing a silicon carbide epitaxial substrate having a main surface is carried out. FIG. 5 is a plan view schematic diagram showing the configuration of silicon carbide epitaxial substrate 10. FIG. 6 is a cross-sectional schematic diagram taken along line VI-VI in FIG. 5.

As shown in FIG. 5 and FIG. 6, the silicon carbide epitaxial substrate 10 according to this embodiment has a silicon carbide substrate 11 and a silicon carbide epitaxial layer 12. The silicon carbide epitaxial layer 12 is on the silicon carbide substrate 11. The silicon carbide epitaxial layer 12 has a first main surface 1 and a second main surface 2. The second main surface 2 is on the opposite side of the first main surface 1. The second main surface 2 is in contact with the silicon carbide substrate 11. The silicon carbide substrate 11 has a third main surface 3 and a fourth main surface 4. The fourth main surface 4 is on the opposite side of the third main surface 3. The third main surface 3 is in contact with the silicon carbide epitaxial layer 12.

As shown in FIG. 5, when viewed in the thickness direction of the silicon carbide epitaxial substrate 10, the silicon carbide epitaxial substrate 10 has an outer peripheral edge 15. The outer peripheral edge 15 has, for example, an orientation flat 13 and an arc-shaped portion 14. The orientation flat 13 extends along the first direction 101. As shown in FIG. 5, when viewed in the thickness direction of the silicon carbide epitaxial substrate 10, the orientation flat 13 is linear. The arc-shaped portion 14 is continuous with the orientation flat 13. When viewed in the thickness direction of the silicon carbide epitaxial substrate 10, the arc-shaped portion 14 is arc-shaped.

As shown in FIG. 5, when viewed in the thickness direction of the silicon carbide epitaxial substrate 10, the first main surface 1 extends along each of the first direction 101 and the second direction 102. When viewed in the thickness direction of the silicon carbide epitaxial substrate 10, the first direction 101 is perpendicular to the second direction 102.

The first direction 101 is, for example, the <11-20> direction. The first direction 101 may be, for example, the [11-20] direction. The first direction 101 may be a direction obtained by projecting the <11-20> direction onto the first principal surface 1. From another perspective, the first direction 101 may be, for example, a direction that includes a <11-20> directional component.

The second direction 102 is, for example, the <1-100> direction. The second direction 102 may be, for example, the [1-100] direction. The second direction 102 may be, for example, a direction obtained by projecting the <1-100> direction onto the first principal surface 1. From another perspective, the second direction 102 may be, for example, a direction that includes a <1-100> directional component.

As shown in FIG. 5, the diameter (first width W1) of the silicon carbide substrate 11 is not particularly limited, but is, for example, 100 mm (4 inches) or more. The first width W1 may be 125 mm (5 inches) or more, or 150 mm (6 inches) or more. The upper limit of the first width W1 is not particularly limited. The first width W1 may be, for example, 200 mm (8 inches) or less.

In this specification, 4 inches means 100 mm or 101.6 mm (4 inches x 25.4 mm/inch). 5 inches means 125 mm or 127.0 mm (5 inches x 25.4 mm/inch). 6 inches means 150 mm or 152.4 mm (6 inches x 25.4 mm/inch). 8 inches means 200 mm or 203.2 mm (8 inches x 25.4 mm/inch).

As shown in FIG. 6, the first main surface 1 constitutes the front surface of the silicon carbide epitaxial substrate 10. The fourth main surface 4 constitutes the back surface of the silicon carbide epitaxial substrate 10. The polytype of the silicon carbide constituting the silicon carbide substrate 11 is, for example, 4H. The polytype of the silicon carbide constituting the silicon carbide epitaxial layer 12 is, for example, 4H.

The first main surface 1 of the silicon carbide epitaxial substrate 10 may be inclined at an off angle of 8° or less with respect to the {0001} plane or the {0001} plane. Specifically, the first main surface 1 may be inclined at an off angle of 8° or less with respect to the (0001) plane or the (0001) plane. The first main surface 1 may be inclined at an off angle of 8° or less with respect to the (000-1) plane or the (000-1) plane.

The upper limit of the off angle is not particularly limited, but may be, for example, 6° or less, or 4° or less. The lower limit of the off angle is not particularly limited, but may be, for example, 2° or more, or 1° or more. The off direction is not particularly limited, but may be, for example, the <11-20> direction or the <0001> direction.

The silicon carbide substrate 11 contains an n-type impurity such as nitrogen (N). The conductivity type of the silicon carbide substrate 11 is, for example, n-type (first conductivity type). The thickness of the silicon carbide substrate 11 is not particularly limited, but is, for example, 200 μm or more and 500 μm or less. The silicon carbide epitaxial layer 12 contains an n-type impurity such as nitrogen. The conductivity type of the silicon carbide epitaxial layer 12 is, for example, n-type. The thickness of the silicon carbide epitaxial layer 12 is not particularly limited, but is, for example, 5 μm or more and 100 μm or less. The concentration of the n-type impurity contained in the silicon carbide epitaxial layer 12 may be lower than the concentration of the n-type impurity contained in the silicon carbide substrate 11.

The carrier concentration of silicon carbide epitaxial layer 12 can be 1×10 ¹⁵ /cm ³ or more and 1×10 ¹⁷ /cm ³ or less. The carrier concentration of silicon carbide epitaxial layer 12 can be particularly 3×10 ¹⁵ /cm ³ or more and 5×10 ¹⁶ /cm ³ or less. The conductivity type of silicon carbide epitaxial layer 12 is, for example, n-type. The dopant of silicon carbide epitaxial layer 12 is preferably nitrogen. The dopant of silicon carbide epitaxial layer 12 may be phosphorus.

Next, a step (S20) of irradiating the main surface with ultraviolet light is performed. As shown in FIG. 2, the silicon carbide epitaxial substrate 10 is placed on the substrate holding part 201. The fourth main surface 4 of the silicon carbide epitaxial substrate 10 is in contact with the substrate holding surface 210. The ultraviolet light irradiation part 204 is placed above the silicon carbide epitaxial substrate 10. The UV light 203 of the ultraviolet light irradiation part 204 faces the first main surface 1 of the silicon carbide epitaxial substrate 10. In a direction perpendicular to the first main surface 1, the distance (separation distance D) between the UV light 203 and the first main surface 1 is, for example, 50 mm.

Figure 7 is a schematic plan view showing the process of irradiating ultraviolet light to the main surface 1. As shown in Figure 7, the UV light 203 of the ultraviolet light irradiation unit 204 has a rectangular shape when viewed in a direction perpendicular to the first main surface 1. The lengthwise width (second width W2) of the UV light 203 is larger than the width in the short direction (third width W3). The second width W2 is, for example, larger than the diameter (first width W1) of the first main surface 1 of the silicon carbide epitaxial substrate 10. The second width W2 is, for example, 154 mm. The third width W3 is smaller than the first width W1. The third width W3 is, for example, 47 mm. The ultraviolet light irradiation unit 204 is arranged so that the lengthwise direction of the UV light 203 is parallel to the orientation flat 13 when viewed in a direction perpendicular to the first main surface 1.

Ultraviolet light irradiation unit 204 irradiates first main surface 1 of silicon carbide epitaxial substrate 10 with ultraviolet light. The ultraviolet light has a wavelength of 200 nm or more and 400 nm or less. The wavelength of the ultraviolet light is, for example, 365 nm. The intensity of the ultraviolet light at a location 50 mm away from UV light 203 is, for example, 1274 μW/cm ^2. In the step of irradiating first main surface 1 with ultraviolet light, the number of photons per unit area of the ultraviolet light is 30×10 ¹⁶ /cm ² or more. First main surface 1 is irradiated with the ultraviolet light for, for example, 5 minutes or more.

When first main surface 1 is inclined at an off angle of 8° or less with respect to the (000-1) plane or the (000-1) plane, the number of photons per unit area of the ultraviolet light may be 50×10 ¹⁶ /cm ² or more, or 60×10 ¹⁶ /cm ² or more. There is no particular limitation on the upper limit of the number of photons per unit area of the ultraviolet light, but it may be 120×10 ¹⁶ /cm ² or less, or 80×10 ¹⁶ /cm ² or less.

When the first main surface 1 is inclined at an off angle of 8° or less with respect to the (0001) plane or the (0001) plane, the number of photons per unit area of the ultraviolet light may be 550×10 ¹⁶ /cm ² or more. The upper limit of the number of photons per unit area of the ultraviolet light is not particularly limited, but may be 700×10 ¹⁶ /cm ² or less, or may be 800×10 ¹⁶ /cm ² or less. The upper limit of the number of photons per unit area of the ultraviolet light is not particularly limited, but may be 1800×10 ¹⁶ /cm ² or less, or may be 1200×10 ¹⁶ /cm ² or less.

Next, we will explain how to calculate the number of photons per unit area.

First, the number of photons per second can be calculated using the following formula 1.

_Ns = (W × λ) ÷ (h × c) (Formula 1)
N _s : Number of photons per second (photons/second)
W: UV light irradiation intensity (W/cm ² )
h: Planck's constant = 6.626 x 10 ^-34 (J·sec)
c: Speed of light in a vacuum = 2.998 x 10 ⁸ (m/sec)
λ: wavelength of light (m)
The number of photons is calculated using the following formula 2.

_Nt = _Ns ×t...(Formula 2)
_Nt : number of photons (pieces)
t: light irradiation time (seconds)
The number of photons per unit area irradiated onto main surface 1 of silicon carbide epitaxial substrate 10 can be calculated by the following equation 3.

N=( _Nt ×W)÷(L×S)...(Formula 3)
N: number of photons per unit area irradiated onto the main surface (pcs/ ^cm2 )
W: diameter of main surface (cm)
L: UV light length (cm)
S: area of main surface (cm ² )
The irradiation intensity of the UV light on the main surface 1 of the silicon carbide epitaxial substrate 10 is measured using, for example, an illuminometer (intensity meter). The illumination intensity is obtained.

The number of photons can be calculated from the irradiation intensity using the following formula 4.

N _t = (W1×λ) ÷ (h×c)×t (Formula 4)
_Nt : number of photons (pieces)
W1: UV light irradiation intensity on the main surface (W/cm ² )
λ: wavelength of light (m)
h: Planck's constant = 6.626 x 10 ^-34 (J·sec)
c: Speed of light in a vacuum = 2.998 x 10 ⁸ (m/sec)
t: light irradiation time (seconds)
Next, a step (S30) is performed in which a probe is placed in a non-contact state with the main surface after supplying an electric charge to the main surface, and the electric potential of the main surface is measured using the probe. Silicon carbide epitaxial substrate 10 is attached to chuck 111. Fourth main surface 4 of silicon carbide epitaxial substrate 10 contacts substrate holding surface 110 of chuck 111. Chuck 111 is made of a conductive material. The chuck 111 is electrically grounded. A corona electrode 112 and a probe 113 are disposed above the first main surface 1 of the silicon carbide epitaxial substrate 10. The corona electrode 112 is The corona electrode 112 is spaced apart from the first main surface 1 .

By applying a voltage to the corona electrode 112, the air is ionized and an electric charge is generated. Due to the mirror effect of the electric charge, carriers in the silicon carbide epitaxial layer move, forming a depletion layer in the silicon carbide epitaxial layer 12. The probe 113 is arranged in a non-contact state with the first main surface 1. The probe 113 is spaced apart from the first main surface 1. The probe 113 is arranged, for example, above the center of the first main surface 1. The electric potential of the first main surface 1 is measured using the probe 113. As described above, after supplying an electric charge to the first main surface 1, the probe 113 is arranged in a non-contact state with the first main surface 1, and the electric potential of the first main surface 1 is measured using the probe 113.

Next, a step (S40) of calculating the carrier concentration of the silicon carbide epitaxial substrate based on the charge and potential is performed. The carrier concentration of the silicon carbide epitaxial substrate 10 is determined based on the charge supplied to the first main surface 1 of the silicon carbide epitaxial substrate 10 and the potential of the first main surface 1 measured by the probe 113.

The carrier concentration of the silicon carbide epitaxial substrate 10 is calculated using the following formula 5:

Q ² =(2×e×ε _S ×ε ₀ )×(V−V _d )×N _d (Formula 5)
Q: Corona charge amount (C)
e: Elementary charge = 1.602×10 ^-19 (C)
ε _S : relative dielectric constant of silicon carbide epitaxial substrate ε ₀ : dielectric constant of vacuum = 8.854 × 10 ^-14 (F/cm)
V: potential measured by the probe (V)
V _d : Reference potential (V)
N _d : Carrier concentration of silicon carbide epitaxial substrate (cm ⁻³ )
Next, a step (S50) of selecting silicon carbide epitaxial substrates is performed. Specifically, the carrier concentration calculated in the step (S40) of calculating the carrier concentration of the silicon carbide epitaxial substrate is compared with a reference carrier concentration. If the carrier concentration calculated in the step (S40) of calculating the carrier concentration of the silicon carbide epitaxial substrate is within the range of the reference carrier concentration, the silicon carbide epitaxial substrate 10 is determined to be a good product. On the other hand, if the carrier concentration calculated in the step (S40) of calculating the carrier concentration of the silicon carbide epitaxial substrate is outside the range of the reference carrier concentration, the silicon carbide epitaxial substrate 10 is determined to be a defective product. As described above, the silicon carbide epitaxial substrate 10 is selected based on the carrier concentration of the silicon carbide epitaxial substrate 10.

(Method of manufacturing silicon carbide epitaxial substrate)
Next, a method for manufacturing the silicon carbide epitaxial substrate 10 according to this embodiment will be described. Fig. 8 is a flow diagram that illustrates a schematic diagram of the method for manufacturing the silicon carbide epitaxial substrate according to this embodiment. As shown in Fig. 8, the method for manufacturing the silicon carbide epitaxial substrate 10 according to this embodiment mainly includes a step (S10) of preparing a silicon carbide epitaxial substrate having a main surface, and a step (S20) of irradiating the main surface with ultraviolet light.

First, a step (S10) of preparing a silicon carbide epitaxial substrate having a main surface is performed. The step (S10) of preparing a silicon carbide epitaxial substrate having a main surface in the manufacturing method of silicon carbide epitaxial substrate 10 according to this embodiment is similar to the step (S10) of preparing a silicon carbide epitaxial substrate having a main surface in the inspection method of silicon carbide epitaxial substrate 10 according to this embodiment.

Next, a step (S20) of irradiating the main surface with ultraviolet light is carried out. The step (S20) of irradiating the main surface with ultraviolet light in the method for manufacturing silicon carbide epitaxial substrate 10 according to this embodiment is similar to the step (S20) of irradiating the main surface with ultraviolet light in the method for inspecting silicon carbide epitaxial substrate 10 according to this embodiment. In this manner, silicon carbide epitaxial substrate 10 is prepared.

Next, the effects of the method for inspecting the silicon carbide epitaxial substrate 10, the method for manufacturing the silicon carbide epitaxial substrate 10, and the inspection device 300 for the silicon carbide epitaxial substrate 10 according to this embodiment will be described.

There are two methods for measuring the carrier concentration of silicon carbide epitaxial substrate 10: a contact type measurement method using a mercury probe and a non-contact type measurement method using a non-contact probe. The non-contact type measurement method has the advantage that it is possible to suppress the occurrence of contamination in silicon carbide epitaxial substrate 10 because it is not necessary to contact probe 113 with silicon carbide epitaxial substrate 10. However, the non-contact type measurement method has the problem that the reproducibility of the carrier concentration is low and the carrier concentration cannot be calculated stably.

The inventors have intensively studied measures to solve the above problems, and have obtained the following findings, and have found a method for inspecting a silicon carbide epitaxial substrate 10, a method for manufacturing a silicon carbide epitaxial substrate 10, and an inspection device 300 for a silicon carbide epitaxial substrate 10 according to the present disclosure. Specifically, it has been found that the carrier concentration can be stably measured by irradiating the silicon carbide epitaxial substrate 10 with ultraviolet light of a certain wavelength for a certain period of time. Further investigation has revealed that the stability of the carrier concentration depends on the amount of photons of ultraviolet light per unit area. As a result of detailed experiments, it has been found that the carrier concentration can be stably measured by setting the number of photons per unit area of ultraviolet light irradiated to the silicon carbide epitaxial substrate 10 to 30×10 ¹⁶ /cm ² or more.

According to the method for inspecting a silicon carbide epitaxial substrate 10 according to the present embodiment, a silicon carbide epitaxial substrate 10 having a main surface 1 is prepared. The main surface 1 is irradiated with ultraviolet light having a wavelength of 200 nm or more and 400 nm or less. After the step of irradiating the ultraviolet light, a charge is supplied to the main surface 1, and then a probe 113 is placed in a non-contact state with the main surface 1, and the potential of the main surface 1 is measured using the probe 113. The carrier concentration of the silicon carbide epitaxial substrate 10 is calculated based on the charge and the potential. In the step of irradiating the ultraviolet light, the number of photons per unit area of the ultraviolet light is 30×10 ¹⁶ /cm ² or more. This allows the carrier concentration of the silicon carbide epitaxial substrate 10 to be stably measured.

Furthermore, according to the method for inspecting silicon carbide epitaxial substrate 10 according to this embodiment, main surface 1 may be inclined at an off angle of 8° or less with respect to the (000-1) plane or the (000-1) plane. This allows the carrier concentration of silicon carbide epitaxial substrate 10 to be stably measured when main surface 1 is a carbon plane or is inclined at an off angle of 8° or less with respect to the carbon plane.

Furthermore, according to the method for inspecting silicon carbide epitaxial substrate 10 according to the present embodiment, main surface 1 may be inclined at an off angle of 8° or less with respect to the (0001) plane or the (0001) plane. The number of photons per unit area may be 550× ¹⁰¹⁶ / ^cm2 or more. This allows the carrier concentration of silicon carbide epitaxial substrate 10 to be stably measured when main surface 1 is the silicon plane or is inclined at an off angle of 8° or less with respect to the silicon plane.

According to the method for manufacturing the silicon carbide epitaxial substrate 10 of this embodiment, the above-described method for inspecting the silicon carbide epitaxial substrate 10 is performed. The silicon carbide epitaxial substrates 10 are selected based on the carrier concentration. This allows the silicon carbide epitaxial substrates 10 to be selected with high accuracy. As a result, the yield of the silicon carbide epitaxial substrates 10 is increased.

According to the method for manufacturing silicon carbide epitaxial substrate 10 according to this embodiment, silicon carbide epitaxial substrate 10 having a main surface 1 is prepared. Main surface 1 is irradiated with ultraviolet light having a wavelength of 200 nm or more and 400 nm or less. In the step of irradiating with ultraviolet light, the number of photons per unit area of the ultraviolet light is 30×10 ¹⁶ /cm ² or more. This makes it possible to obtain silicon carbide epitaxial substrate 10 in which the carry concentration can be stably measured.

The inspection device 300 for the silicon carbide epitaxial substrate 10 according to this embodiment includes an irradiation device section 200 and a measurement device section 100. The irradiation device section 200 irradiates the main surface 1 of the silicon carbide epitaxial substrate 10 with ultraviolet light having a wavelength of 200 nm or more and 400 nm or less. The measurement device section 100 supplies a charge to the main surface 1, and then places a probe 113 in a non-contact state with the main surface 1, and measures the potential of the main surface 1 using the probe 113. This makes it possible to obtain a silicon carbide epitaxial substrate 10 in which the carry concentration can be stably measured.

(Sample preparation)
Silicon carbide epitaxial substrates 10 according to Samples 1 to 7 were prepared. First main surfaces 1 of silicon carbide epitaxial substrates 10 according to Samples 1 to 3 and 5 to 7 were the (000-1) plane. First main surface 1 of silicon carbide epitaxial substrate 10 according to Sample 4 was the (0001) plane.

(experimental method)
As shown in FIG. 2, the silicon carbide epitaxial substrate 10 was placed on the substrate holding unit 201. The ultraviolet light irradiation unit 204 was placed above the silicon carbide epitaxial substrate 10. The UV light 203 of the ultraviolet light irradiation unit 204 was placed facing the first main surface 1 of the silicon carbide epitaxial substrate 10. In a direction perpendicular to the first main surface 1, the distance between the UV light 203 and the first main surface 1 was set to 50 mm. As shown in FIG. 7, the UV light 203 of the ultraviolet light irradiation unit 204 has a rectangular shape when viewed in a direction perpendicular to the first main surface 1. The second width W2 was set to 154 mm. The third width W3 was set to 47 mm. The ultraviolet light irradiation unit 204 was placed so that the longitudinal direction of the UV light 203 was parallel to the orientation flat when viewed in a direction perpendicular to the first main surface 1. As the ultraviolet light irradiation unit 204, SLUV-6 manufactured by AS ONE Corporation was used.

The first main surface 1 of the silicon carbide epitaxial substrate 10 of sample 1 was irradiated with ultraviolet light having a wavelength of 365 nm. The UV light 203 was fixed without being moved. The number of photons per unit area was changed by changing the irradiation time of the ultraviolet light.

The first main surface 1 of the silicon carbide epitaxial substrate 10 of sample 2 was irradiated with ultraviolet light having a wavelength of 254 nm. The UV light 203 was fixed without being moved. The number of photons per unit area was changed by changing the irradiation time of the ultraviolet light.

The first main surface 1 of the silicon carbide epitaxial substrate 10 of sample 3 was irradiated with ultraviolet light having a wavelength of 365 nm. The UV light 203 was moved from the orientation flat along the second direction 102. The number of photons per unit area was changed by changing the irradiation time of the ultraviolet light.

The first main surface 1 of the silicon carbide epitaxial substrate 10 of sample 4 was irradiated with ultraviolet light having a wavelength of 365 nm. The UV light 203 was fixed without being moved. The number of photons per unit area was changed by changing the irradiation time of the ultraviolet light.

First main surface 1 of silicon carbide epitaxial substrate 10 of sample 5 was irradiated with ultraviolet light having a wavelength of 365 nm. The ultraviolet light intensity at first main surface 1 was set to 498 μW/cm ^2. The distance (separation distance D) between UV light 203 and first main surface 1 was set to 8 mm. The number of photons per unit area was changed by changing the irradiation time of the ultraviolet light.

The first main surface 1 of the silicon carbide epitaxial substrate 10 of Sample 6 was irradiated with ultraviolet light having a wavelength of 365 nm. The ultraviolet light intensity on the first main surface 1 was set to 1274 μW/cm ^2. The distance (separation distance D) between the UV light 203 and the first main surface 1 was set to 5 mm. The number of photons per unit area was changed by changing the irradiation time of the ultraviolet light.

The first main surface 1 of the silicon carbide epitaxial substrate 10 of Sample 7 was irradiated with ultraviolet light having a wavelength of 365 nm. The ultraviolet light intensity at the first main surface 1 was set to 7963 μW/cm ^2. The distance (separation distance D) between the UV light 203 and the first main surface 1 was set to 2 mm. The number of photons per unit area was changed by changing the irradiation time of the ultraviolet light.

(Experimental result)
9 is a diagram showing the relationship between the number of photons per unit area of ultraviolet light irradiated onto the first main surface 1 of silicon carbide epitaxial substrate 10 according to sample 1 and the carrier concentration of silicon carbide epitaxial substrate 10. As shown in Fig. 9, the carrier concentration of silicon carbide epitaxial substrate 10 when the number of photons per unit area of ultraviolet light is small is higher than the carrier concentration of silicon carbide epitaxial substrate 10 when the number of photons per unit area of ultraviolet light is large. When the number of photons per unit area of ultraviolet light is 30 x ¹⁰¹⁶ / ^cm2 or more, the carrier concentration was an approximately constant value regardless of the number of photons per unit area of ultraviolet light.

Fig. 10 is a diagram showing the relationship between the number of photons per unit area of ultraviolet light irradiated onto first main surface 1 of silicon carbide epitaxial substrate 10 relating to sample 2 and the carrier concentration of silicon carbide epitaxial substrate 10. As shown in Fig. 10, the carrier concentration of silicon carbide epitaxial substrate 10 when the number of photons per unit area of ultraviolet light is small is higher than the carrier concentration of silicon carbide epitaxial substrate 10 when the number of photons per unit area of ultraviolet light is large. When the number of photons per unit area of ultraviolet light is 30 x ¹⁰¹⁶ / ^cm2 or more, the carrier concentration was an approximately constant value regardless of the number of photons per unit area of ultraviolet light.

Fig. 11 is a diagram showing the relationship between the number of photons per unit area of ultraviolet light irradiated onto first main surface 1 of silicon carbide epitaxial substrate 10 relating to sample 3 and the carrier concentration of silicon carbide epitaxial substrate 10. As shown in Fig. 11, the carrier concentration of silicon carbide epitaxial substrate 10 when the number of photons per unit area of ultraviolet light is small is higher than the carrier concentration of silicon carbide epitaxial substrate 10 when the number of photons per unit area of ultraviolet light is large. When the number of photons per unit area of ultraviolet light is 30 x ¹⁰¹⁶ / ^cm2 or more, the carrier concentration was an approximately constant value regardless of the number of photons per unit area of ultraviolet light.

Fig. 12 is a diagram showing the relationship between the number of photons per unit area of ultraviolet light irradiated onto first main surface 1 of silicon carbide epitaxial substrate 10 relating to sample 4 and the carrier concentration of silicon carbide epitaxial substrate 10. As shown in Fig. 12, the carrier concentration of silicon carbide epitaxial substrate 10 when the number of photons per unit area of ultraviolet light is small is higher than the carrier concentration of silicon carbide epitaxial substrate 10 when the number of photons per unit area of ultraviolet light is large. When the number of photons per unit area of ultraviolet light is 550 x ¹⁰¹⁶ / ^cm2 or more, the carrier concentration was an approximately constant value regardless of the number of photons per unit area of ultraviolet light.

13 is a diagram showing the relationship between the number of photons per unit area of ultraviolet light irradiated on the first main surface 1 of the silicon carbide epitaxial substrate 10 according to Samples 5 to 7 and the carrier concentration of the silicon carbide epitaxial substrate 10. The silicon carbide epitaxial substrates 10 according to Samples 5 to 7 are indicated by "○", "△" and "□", respectively. As shown in FIG. 13, in the case of all ultraviolet light intensities, the carrier concentration of the silicon carbide epitaxial substrate 10 when the number of photons per unit area of the ultraviolet light is small is higher than the carrier concentration of the silicon carbide epitaxial substrate 10 when the number of photons per unit area is large. In the case of all ultraviolet light intensities, when the number of photons per unit area of the ultraviolet light is 30×10 ¹⁶ /cm ² or more, the carrier concentration was almost constant regardless of the intensity of the ultraviolet light. From the above results, it was confirmed that the carrier concentration can be stably measured by setting the number of photons per unit area of ultraviolet light to 30×10 ¹⁶ /cm ² or more.

The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is indicated by the claims rather than the above-described embodiments and examples, and is intended to include all modifications within the scope of the claims and meanings equivalent thereto.

1 First main surface (main surface)
2 Second main surface 3 Third main surface 4 Fourth main surface 10 Silicon carbide epitaxial substrate 11 Silicon carbide substrate 12 Silicon carbide epitaxial layer 13 Orientation flat 14 Arc-shaped portion 15 Outer periphery 100 Measurement device portion 101 First direction 102 Second direction 110, 210 Substrate holding surface 111 Chuck 112 Corona electrode 113 Probe 200 Irradiation device portion 201 Substrate holding portion 202 Light holding portion 203 UV light 204 Ultraviolet light irradiation portion 300 Inspection device 310 Transport portion D Separation distance W1 First width W2 Second width W3 Third width

Claims (6)

providing a silicon carbide epitaxial substrate having a main surface;
irradiating the main surface with ultraviolet light having a wavelength of 200 nm or more and 400 nm or less;
a step of, after the step of irradiating the ultraviolet light, supplying an electric charge to the main surface, disposing a probe in a non-contact state with the main surface, and measuring an electric potential of the main surface using the probe;
and calculating a carrier concentration of the silicon carbide epitaxial substrate based on the charge and the potential;
A method for inspecting a silicon carbide epitaxial substrate, wherein in the step of irradiating with ultraviolet light, the number of photons per unit area of the ultraviolet light is 30×10 ¹⁶ /cm ² or more. The method for inspecting a silicon carbide epitaxial substrate according to claim 1, wherein the main surface is inclined at an off angle of 8° or less with respect to the (000-1) plane or the (000-1) plane. the main surface is a (0001) plane or is inclined at an off angle of 8° or less with respect to the (0001) plane,
2. The method for inspecting a silicon carbide epitaxial substrate according to claim 1, wherein the number of photons per unit area is 550×10 ¹⁶ /cm ² or more. A step of performing the method for inspecting a silicon carbide epitaxial substrate according to any one of claims 1 to 3;
and selecting the silicon carbide epitaxial substrate based on the carrier concentration. providing a silicon carbide epitaxial substrate having a main surface;
irradiating the main surface with ultraviolet light having a wavelength of 200 nm or more and 400 nm or less ;
a step of, after the step of irradiating the ultraviolet light, supplying an electric charge to the main surface, disposing a probe in a non-contact state with the main surface, and measuring an electric potential of the main surface using the probe;
A method for producing a silicon carbide epitaxial substrate, wherein in the step of irradiating with ultraviolet light, the number of photons per unit area of the ultraviolet light is 30×10 ¹⁶ /cm ² or more. an irradiation device unit that irradiates a main surface of the silicon carbide epitaxial substrate with ultraviolet light having a wavelength of 200 nm or more and 400 nm or less;
a measurement device unit that, after supplying an electric charge to the main surface, places a probe in a non-contact state with the main surface and measures a potential of the main surface using the probe;
The silicon carbide epitaxial substrate inspection apparatus, wherein in the step of irradiating with ultraviolet light, the number of photons per unit area of the ultraviolet light is 30×10 ¹⁶ /cm ² or more .

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