Method of evaluating SiC substrate, method of manufacturing SiC epitaxial wafer, and method of manufacturing SiC device
This method of evaluating a SiC substrate includes a preparation step of preparing two or more SiC substrates obtained from the same SiC ingot grown from the same seed crystal, a defect position specifying step of specifying positions of defects in the substrates by observing a main surface of each of the two or more SiC substrates, and a comparison step of comparing the positions of the defects of the two or more SiC substrates, in which, in the preparation step, a SiC substrate positioned closest to the seed crystal is used as a reference wafer among the two or more SiC substrates, and the comparison step comprises a sub-step wherein a first defect of the reference wafer is compared with a second defect of a SiC substrate other than the reference wafer, it is judged whether a defect distance of the two compared defects in a [11-20] direction is 0.6 mm or more or less than 0.2 mm, and the two compared defects are determined to be defects not associated with the same threading defect when the defect distance is 0.6 mm or more, and the two compared defects are determined to be defects associated with the same threading defect when the defect distance is less than 0.2 mm.
1. A method of evaluating a SiC substrate which is used for forming a SiC epitaxial layer thereon, comprising:
a preparation step of preparing two or more SiC substrates before a SiC epitaxial layer is formed, wherein the SiC substrates are used for forming a SiC epitaxial layer and are obtained from the same SiC ingot grown from the same seed crystal,
a defect position specifying step of specifying positions of defects in the substrates by observing a main surface of each of the two or more SiC substrates before a SiC epitaxial layer is formed, with a confocal differential interference microscope or an optical surface inspection device, and
a comparison step of comparing the positions of the defects of the two or more SiC substrates, wherein,
in the preparation step, a SiC substrate positioned closest to the seed crystal is used as a reference wafer among the two or more SiC substrates, and
the comparison step comprises a sub-step wherein
a first defect of the reference wafer is compared with a second defect of a SiC substrate other than the reference wafer,
it is judged whether a defect distance of the two compared defects in a [11-20] direction is 0.6 mm or more or less than 0.2 mm, and
the two compared defects are determined to be defects not associated with the same threading defect when the defect distance is 0.6 mm or more, and
the two compared defects are determined to be defects associated with the same threading defect when the defect distance is less than 0.2 mm.
2. The method of evaluating a SiC substrate according to claim 1 , wherein a defect distance between the first defect and the second defect in a [1-100] direction, which are compared in the sub step, is 0.2 mm or less.
3. The method of evaluating a SiC substrate according to claim 1 , wherein the comparison step further comprises a sub-step wherein
it is judged whether a defect distance of the first defect and the second defect in a [1-100] direction is 0.2 mm or less, and
the first defect and the second defect are determined to be defects associated with the same threading defect when the defect distance of the first defect and the second defect in a [1-100] direction is 0.2 mm or less.
4. The method of evaluating a SiC substrate according to claim 1 , further comprising a correlation determination step, wherein
three or more SiC substrates are prepared from the same SiC ingot in the preparation step, and
when the defect distance of the two defects in the [11-20] direction obtained by comparison in the comparison step is 0.2 mm or more and less than 0.6 mm, the correlation determination step includes:
a sub-step of obtaining a determination coefficient from a position of the first defect, a position of the second defect, a position of a third defect which is present in a SiC substrate different from any of the SiC substrates in which the first defect and the second defect are present and whose defect distances from itself to the first defect and the second defect in the [11-20] direction are each less than 0.6 mm, and a branch number indicating an order of each SiC substrate of the substrates; and
a sub-step of determining a correlation of the defects in which the first defect, the second defect, and the third defect are judged to be defects associated with the same threading defect when the determination coefficient is 0.7 or more.
5. The method of evaluating a SiC substrate according to claim 4 , wherein the determination coefficient is 0.5 or more.
6. The method of evaluating a SiC substrate according to claim 1 , further comprising an identification step of identifying that the defect that has been judged to be associated with the same threading defect in the comparison step is also present at the same position of all the SiC substrates formed from the same SiC ingot.
7. The method of evaluating a SiC substrate according to claim 1 , wherein the reference wafer is a SiC substrate taken out from a range within ¼ of a thickness of the SiC ingot from a surface of the SiC ingot.
8. The method of evaluating a SiC substrate according to claim 1 , wherein a position of a threading defect present in a SiC substrate other than the SiC substrates in which the first defect and the second defect are present and obtained from the same SiC ingot is estimated on the basis of the position of the defect that has been judged to be a defect associated with the same threading defect in the comparison step.
9. The method of evaluating a SiC substrate according to claim 1 , wherein the reference wafer is a SiC substrate positioned closest to the seed crystal among SiC substrates obtained from the same SiC ingot.
10. A method of manufacturing a SiC epitaxial wafer comprising a recognition step of recognizing a position of a threading defect using the method of evaluating a SiC substrate according to claim 1 .
11. A method of manufacturing a SiC device comprising a recognition step of recognizing a position of a threading defect using the method of evaluating a SiC substrate according to claim 1 .
12. The method of evaluating a SiC substrate according to claim 4 , wherein the determination coefficient is obtained by expression 1 below;
R
2
=
{
∑
i
=
1
N
(
n
i
-
n
a
)
(
x
i
-
x
a
)
}
2
{
∑
i
=
1
N
(
n
i
-
n
a
)
2
}
×
{
∑
i
=
1
N
(
x
i
-
x
a
)
2
}
[
Expression
1
]
(R 2 represents determination coefficient,
N represents number of substrates used in the correlation determination step,
n represents branch number of substrates,
x represents X direction component of a defect,
i represents an order of the substrates from a seed crystal side,
ni represents a branch number of i-th SiC substrate from the seed crystal side,
na represents an arithmetic mean of the branch numbers,
xi represents an X direction component of a defect that determines a correlation,
xa represents an arithmetic mean of the X direction components).
13. The method of evaluating a SiC substrate according to claim 1 , further comprising
a step of manufacturing a SiC epitaxial wafer wherein a SiC epitaxial layer is formed on the SiC substrates, wherein
the step of manufacturing a SiC epitaxial wafer is performed after the comparison step.
14. The method of evaluating a SiC substrate according to claim 1 , wherein
the SiC substrates means wafers before a SiC epitaxial layer has been formed thereon, and
SiC epitaxial wafers means wafers after a SiC epitaxial layer has been formed thereon.
15. The method of manufacturing a SiC epitaxial wafer according to claim 10 , further comprising
a step of manufacturing a SiC epitaxial wafer wheerein a SiC epitaxial layer is formed on the SiC substrates, wherein
the step of manufacturign a SiC epitaxial wafer is performed after the recognition step.
16. The method of evaluating a SiC substrate according to claim 1 , wherein
in a case wherein the SiC substrates do not have an offset angle, the defect distance between the two compared defects in the SiC substrates in a [11-20] direction is obtained by
providing orthogonal coordinates respectively on surfaces of the SiC substrates, wherein the centers of the substrates are provided as centers of the coordinates, the [11-20] direction represents an X-axis direction of the coordinates and a [1-100] direction represents a Y-axis direction of the coordinates, and
obtaining an absolute value of a differents (X−x), as the defect distance, wherein the absolute value is obtained by subtraction using a position coordinate (X, Y) of the first defect in the reference wafer and a position coordinate (x, y) of the second defect of the SiC substrate other than the reference wafer.
17. The method of evaluating a SiC substrate according to claim 1 , wherein
in a case where the SiC substrates have an offset angle with respect to a [11-20] direction, the defect distance between the two compared defects is obtained based on an orthogonal projection from position coordinates of orthogonal coordinates, which are provided respectively on a main surface of the SiC substrates where defects are respectively observed.
18. The method of evaluating a SiC substrate according to claim 1 , wherein the preparation step is performed by slicing the SiC ingot to prepare the two or more SiC substrates.