Silicon carbide epitaxial substrate and silicon carbide semiconductor device
A silicon carbide epitaxial layer includes a first silicon carbide layer, a second silicon carbide layer, a third silicon carbide layer, and a fourth silicon carbide layer. A nitrogen concentration of the second silicon carbide layer is increased from the first silicon carbide layer toward the third silicon carbide layer. A value obtained by dividing, by a thickness of the second silicon carbide layer, a value obtained by subtracting a nitrogen concentration of the first silicon carbide layer from a nitrogen concentration of the third silicon carbide layer is less than or equal to 6×10 23 cm −4 . Assuming that the nitrogen concentration of the third silicon carbide layer is N cm −3 and a thickness of the third silicon carbide layer is X μm, X and N satisfy a Formula 1.
1. A silicon carbide epitaxial substrate comprising:
a silicon carbide substrate including a basal plane dislocation and having a polytype of 4H; and
a silicon carbide epitaxial layer provided on the silicon carbide substrate and having a polytype of 4H, wherein
the silicon carbide epitaxial layer includes
a first silicon carbide layer provided on the silicon carbide substrate,
a second silicon carbide layer provided on the first silicon carbide layer,
a third silicon carbide layer provided on the second silicon carbide layer,
a fourth silicon carbide layer provided on the third silicon carbide layer and constituting a front main surface, and
a fifth silicon carbide layer provided on the third silicon carbide layer,
wherein the fourth silicon carbide layer is provided on the third silicon carbide layer with the fifth silicon carbide layer being interposed between the fourth silicon carbide layer and the third silicon carbide layer,
the front main surface is inclined at an angle of more than 0° and less than or equal to 6° with respect to a (0001) plane,
each of the first silicon carbide layer, the second silicon carbide layer, the third silicon carbide layer, the fifth silicon carbide layer, and the fourth silicon carbide layer includes nitrogen,
a nitrogen concentration of the second silicon carbide layer is increased from the first silicon carbide layer toward the third silicon carbide layer,
a nitrogen concentration of the fifth silicon carbide layer is decreased from the third silicon carbide layer toward the fourth silicon carbide layer,
an absolute value of a nitrogen concentration gradient of the fifth silicon carbide layer is more than an absolute value of a nitrogen concentration gradient of the second silicon carbide layer,
a value obtained by dividing, by a thickness of the second silicon carbide layer, a value obtained by subtracting a nitrogen concentration of the first silicon carbide layer from a nitrogen concentration of the third silicon carbide layer is less than or equal to 6×10 23 cm −4 , and
wherein the nitrogen concentration of the third silicon carbide layer is N cm −3 and a thickness of the third silicon carbide layer is X μm, and X and N satisfy a Formula 1:
X
>
2.348
×
10
4
×
1
3.3
×
10
6
+
1.3
×
10
-
12
×
N
+
1.6
×
10
-
30
×
N
2
.
(
Formula
1
)
2. The silicon carbide epitaxial substrate according to claim 1 , wherein X and N satisfy a Formula 2:
X
>
3.522
×
10
4
×
1
3.3
×
10
6
+
1.3
×
10
-
12
×
N
+
1.6
×
10
-
30
×
N
2
.
(
Formula
2
)
3. The silicon carbide epitaxial substrate according to claim 1 , wherein a nitrogen concentration of the fourth silicon carbide layer is less than the nitrogen concentration of the third silicon carbide layer.
4. The silicon carbide epitaxial substrate according to claim 1 , wherein a nitrogen concentration of the fourth silicon carbide layer is less than the nitrogen concentration of the first silicon carbide layer.
5. The silicon carbide epitaxial substrate according to claim 1 , wherein a nitrogen concentration of the silicon carbide substrate is more than the nitrogen concentration of the first silicon carbide layer and less than the nitrogen concentration of the third silicon carbide layer.
6. The silicon carbide epitaxial substrate according to claim 1 , wherein the thickness of the second silicon carbide layer is less than or equal to 5 μm.
7. The silicon carbide epitaxial substrate according to claim 1 , wherein the thickness of the third silicon carbide layer is less than or equal to 20 μm.
8. A silicon carbide semiconductor device comprising:
a silicon carbide substrate including a basal plane dislocation and having a polytype of 4H;
a silicon carbide epitaxial layer provided on the silicon carbide substrate and having a polytype of 4H;
a first electrode provided on the silicon carbide epitaxial layer; and
a second electrode in contact with the silicon carbide substrate, wherein
each of the silicon carbide substrate and the silicon carbide epitaxial layer has a polytype of 4H—SiC,
the silicon carbide epitaxial layer includes
a first silicon carbide layer provided on the silicon carbide substrate,
a second silicon carbide layer provided on the first silicon carbide layer,
a third silicon carbide layer provided on the second silicon carbide layer,
a fourth silicon carbide layer provided on the third silicon carbide layer and constituting a front main surface, and
a fifth silicon carbide layer provided on the third silicon carbide layer,
wherein the fourth silicon carbide layer is provided on the third silicon carbide layer with the fifth silicon carbide layer being interposed between the fourth silicon carbide layer and the third silicon carbide layer,
the front main surface is inclined at an angle of more than 0° and less than or equal to 6° with respect to a (0001) plane,
each of the first silicon carbide layer, the second silicon carbide layer, the third silicon carbide layer, the fifth silicon carbide layer, and the fourth silicon carbide layer includes nitrogen,
a nitrogen concentration of the second silicon carbide layer is increased from the first silicon carbide layer toward the third silicon carbide layer,
a nitrogen concentration of the fifth silicon carbide layer is decreased from the third silicon carbide layer toward the fourth silicon carbide layer,
an absolute value of a nitrogen concentration gradient of the fifth silicon carbide layer is more than an absolute value of a nitrogen concentration gradient of the second silicon carbide layer,
a value obtained by dividing, by a thickness of the second silicon carbide layer, a value obtained by subtracting a nitrogen concentration of the first silicon carbide layer from a nitrogen concentration of the third silicon carbide layer is less than or equal to 6×10 23 cm −4 , and
wherein the nitrogen concentration of the third silicon carbide layer is N cm −3 and a thickness of the third silicon carbide layer is X μm, and X and N satisfy a Formula 1:
X
>
2.348
×
10
4
×
1
3.3
×
10
6
+
1.3
×
10
-
12
×
N
+
1.6
×
10
-
30
×
N
2
.
(
Formula
1
)
9. The silicon carbide semiconductor device according to claim 8 , wherein X and N satisfy a Formula 2:
X
>
3.522
×
10
4
×
1
3.3
×
10
6
+
1.3
×
10
-
12
×
N
+
1.6
×
10
-
30
×
N
2
.
(
Formula
2
)
10. The silicon carbide semiconductor device according to claim 8 , wherein a nitrogen concentration of the fourth silicon carbide layer is less than the nitrogen concentration of the third silicon carbide layer.
11. The silicon carbide semiconductor device according to claim 8 , wherein a nitrogen concentration of the fourth silicon carbide layer is less than the nitrogen concentration of the first silicon carbide layer.
12. The silicon carbide semiconductor device according to claim 8 , wherein a nitrogen concentration of the silicon carbide substrate is more than the nitrogen concentration of the first silicon carbide layer and less than the nitrogen concentration of the third silicon carbide layer.
13. The silicon carbide semiconductor device according to claim 8 , wherein the thickness of the second silicon carbide layer is less than or equal to 5 μm.
14. The silicon carbide semiconductor device according to claim 8 , wherein the thickness of the third silicon carbide layer is less than or equal to 20 μm.