Semiconductor device and method for producing semiconductor device
Proton irradiation is performed a plurality of times from rear surface of an n-type semiconductor substrate, which is an n − drift layer, forming an n-type FS layer having lower resistance than the n-type semiconductor substrate in the rear surface of the n − drift layer. When the proton irradiation is performed a plurality of times, the next proton irradiation is performed to as to compensate for a reduction in mobility due to disorder which remains after the previous proton irradiation. In this case, the second or subsequent proton irradiation is performed at the position of the disorder which is formed by the previous proton irradiation. In this way, even after proton irradiation and a heat treatment, the disorder is reduced and it is possible to prevent deterioration of characteristics, such as increase in leakage current. It is possible to form an n-type FS layer including a high-concentration hydrogen-related donor layer.
1. A semiconductor device comprising:
a breakdown voltage holding pn junction that is provided in one main surface of an n-type semiconductor substrate; and
an n-type field stop layer that is provided in the other main surface of the n-type semiconductor substrate, has a lower resistance than the n-type semiconductor substrate, and suppresses the spreading of a depletion layer from the breakdown voltage holding pn junction,
wherein the n-type field stop layer has an impurity concentration distribution which includes a plurality of impurity concentration peaks at different positions in a depth direction of the n-type semiconductor substrate,
among the plurality of impurity concentration peaks, a first impurity concentration peak closest to the one main surface of the n-type semiconductor substrate is disposed at a depth of 15 μm or more from the other main surface of the n-type semiconductor substrate, and
a distance between the position of a second impurity concentration peak in the n-type field stop layer and the other main surface of the n-type semiconductor substrate is equal to or more than half of a distance between the position of the first impurity concentration peak and the other main surface of the n-type semiconductor substrate.
2. The semiconductor device according to claim 1 , wherein, among the plurality of impurity concentration peaks, a third impurity concentration peak which is closest to the other main surface of the n-type semiconductor substrate is disposed at a depth of 6 μm to 15 μm from the other main surface of the n-type semiconductor substrate.
3. The semiconductor device according to claim 2 , wherein
the n-type field stop layer includes hydrogen-related donors,
the n-type field stop layer has the impurity concentration distribution that includes a first portion with a local maximum of the impurity concentration and a second portion with a concentration gradient in which impurity concentration is reduced from the local maximum of the first portion to the two main surfaces of the n-type semiconductor substrate,
when a distance index L indicating a distance from an end of a depletion layer, which is spread from the breakdown voltage holding pn junction at the time the semiconductor device is turned off, to the breakdown voltage holding pn junction is represented by the following Expression (1) and a thickness of the n-type semiconductor substrate is W0, a distance X from the position of an impurity concentration peak which the depletion layer reaches first in the n-type field stop layer to the other main surface of the n-type semiconductor substrate satisfies W0−1.4 L≦X≦W0−0.8 L:
L
=
ɛ
S
V
rate
q
(
J
F
qv
sat
+
N
d
)
[
Expression
1
]
(where V rate is a rated voltage, ∈ S is the permittivity of a semiconductor, q is an elementary charge, J F is rated current density, v sat is a saturated velocity of carriers, and N d is the average donor concentration of an n-type semiconductor substrate).
4. The semiconductor device according to claim 1 , wherein
the n-type field stop layer is including hydrogen-related donors,
the n-type field stop layer has the impurity concentration distribution that includes a first portion with a local maximum of the impurity concentration and a second portion with a concentration gradient in which impurity concentration is reduced from the local maximum of the first portion to the two main surfaces of the n-type semiconductor substrate,
when a distance index L indicating a distance from an end of a depletion layer, which is spread from the breakdown voltage holding pn junction at the time the semiconductor device is turned off, to the breakdown voltage holding pn junction is represented by the following Expression (1) and a thickness of the n-type semiconductor substrate is W0, a distance X from the position of an impurity concentration peak which the depletion layer reaches first in the n-type field stop layer to the other main surface of the n-type semiconductor substrate satisfies W0−1.4 L≦X≦W0−0.8 L:
L
=
ɛ
S
V
rate
q
(
J
F
qv
sat
+
N
d
)
[
Expression
1
]
(where V rate is a rated voltage, ∈ S is the permittivity of a semiconductor, q is an elementary charge, J F is rated current density, v sat is a saturated velocity of carriers, and N d is the average donor concentration of an n-type semiconductor substrate).
5. The semiconductor device according to claim 4 , wherein the distance X satisfies W0−1.3 L≦X≦W0−0.8 L.
6. The semiconductor device according to claim 5 , wherein the distance X satisfies W0−1.2 L≦X≦W0−0.9 L.
7. A semiconductor device comprising:
a breakdown voltage holding pn junction that is provided in one main surface of an n-type semiconductor substrate; and
an n-type field stop layer that is provided in the other main surface of the n-type semiconductor substrate, has a lower resistance than the n-type semiconductor substrate, and suppresses the spreading of a depletion layer from the breakdown voltage holding pn junction,
wherein the n-type field stop layer has an impurity concentration distribution which includes a plurality of impurity concentration peaks at different positions in a depth direction of the n-type semiconductor substrate,
among the plurality of impurity concentration peaks, a distance from the other main surface of the n-type semiconductor substrate to a second impurity concentration peak in the n-type field stop layer is greater than a distance between the second impurity concentration peak in the n-type field stop layer and a third concentration peak in the n-type field stop layer.
8. A semiconductor device according to claim 7 , wherein the first impurity concentration peak closest to the one main surface of the n-type semiconductor substrate is disposed at a depth of 15 μm or more from the other main surface of the n-type semiconductor substrate.