U.S. patent application number 14/746018 was filed with the patent office on 2015-10-08 for semiconductor device.
The applicant listed for this patent is SEIKO INSTRUMENTS INC.. Invention is credited to Tomomitsu RISAKI.
Application Number | 20150287714 14/746018 |
Document ID | / |
Family ID | 49379329 |
Filed Date | 2015-10-08 |
United States Patent
Application |
20150287714 |
Kind Code |
A1 |
RISAKI; Tomomitsu |
October 8, 2015 |
SEMICONDUCTOR DEVICE
Abstract
A semiconductor device having a clamp diode has a breakdown
voltage adjusting first conductivity type low concentration region
provided on a semiconductor substrate. A second conductivity type
high concentration region of circular shape is provided within the
breakdown voltage adjusting first conductivity type low
concentration region so as to be surrounded by the first
conductivity type low concentration region but not surrounded by
any other low concentration region. A first conductivity type high
concentration region is provided within the first conductivity type
low concentration region, without being held in contact with the
second conductivity type high concentration region.
Inventors: |
RISAKI; Tomomitsu;
(Chiba-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEIKO INSTRUMENTS INC. |
Chiba-shi |
|
JP |
|
|
Family ID: |
49379329 |
Appl. No.: |
14/746018 |
Filed: |
June 22, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13855781 |
Apr 3, 2013 |
|
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14746018 |
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Current U.S.
Class: |
257/487 |
Current CPC
Class: |
H01L 27/0255 20130101;
H01L 29/0692 20130101; H01L 29/8611 20130101; H01L 27/0676
20130101 |
International
Class: |
H01L 27/02 20060101
H01L027/02; H01L 29/861 20060101 H01L029/861; H01L 29/06 20060101
H01L029/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 17, 2012 |
JP |
2012-094089 |
Claims
1. A semiconductor device, comprising: a semiconductor substrate; a
breakdown voltage adjusting first conductivity type low
concentration region provided on the semiconductor substrate; a
second conductivity type high concentration region provided near a
surface within the breakdown voltage adjusting first conductivity
type low concentration region so as to be surrounded by the first
conductivity type low concentration region but not surrounded by
any low concentration region other than the first conductivity type
low concentration region, the second conductivity type high
concentration region being circular; and a first conductivity type
high concentration region provided on the surface within the
breakdown voltage adjusting first conductivity type low
concentration region without being held in contact with the second
conductivity type high concentration region.
2. A semiconductor device according to claim 1, wherein the first
conductivity type high concentration region has a ring shape and is
provided so as to surround the second conductivity type high
concentration region.
3. A semiconductor device according to claim 2, wherein at least an
inner part of the ring shape of the first conductivity type high
concentration region is circular.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a semiconductor device. In
particular, the present invention relates to a clamp diode used in
a semiconductor device.
[0003] 2. Description of the Related Art
[0004] A clamp diode is a device which uses a junction breakdown
voltage between the p-type semiconductor and the n-type
semiconductor to maintain (clamp) a voltage supplied to a circuit
constant in a semiconductor device. Since a clamp diode is a device
capable of limiting a voltage easily, there is a high demand and a
wide usage in electronic devices.
[0005] When manufacturing a clamp diode, which limits a voltage to
be constant, it is extremely important for the clamp diode to have
small fluctuations in breakdown voltage within a wafer, among
wafers, and among lots, and to have little change over time. In
addition, it is also important for the clamp diode to have a small
leakage current until breakdown occurs. Even though the structure
of the clamp diode is simple, it is not easy to produce a clamp
diode which satisfies all of the above-mentioned
characteristics.
[0006] Japanese Published Patent Application No.11-307787 discloses
the invention for improving the above-mentioned change over time.
FIG. 7 is a cross-sectional view of the structure illustrated in
FIG. 1 of the Japanese Published Patent Application. There is
described that, as illustrated in FIG. 7, a second conductivity
type high concentration region 1 is placed away from an element
isolation insulating film 2 by a predetermined distance, and
further, an electrode 8 is provided through the intermediation of
an insulating film 9, thereby adjusting a voltage of the electrode
8 to improve the change in the clamp diode over time. FIG. 8 is a
cross-sectional view of the structure illustrated in FIG. 6 of the
Japanese Published Patent Application. As shown in this structure,
there is described that the same effect can be obtained even
without the electrode 8 of FIG. 7.
[0007] Though the change over time can be improved by the invention
disclosed in the Japanese Published Patent Application, there is no
description, however, on the degree of fluctuations within a wafer,
between wafers, and among lots, and the presence or absence of
leakage before breakdown occurs. Indeed, in the invention disclosed
in the Japanese Published Patent Application the fluctuations
within a wafer, between wafers, and among lots are not reduced
because of the following reasons.
[0008] Since an electric field corresponding to a voltage applied
to the electrode 8 is applied to a p-n junction through the oxide
film 9 in the structure illustrated in FIG. 7, the electric field
is thought to be constant and the p-n junction breakdown voltage
does not seem to fluctuate due to the electric field. Ideally, when
the same voltage is applied to the electrodes 8, the breakdown
voltages are the same. However, actually, the thicknesses of the
oxide films 9 are not the same within a wafer, between wafers, and
among lots, and hence the electric fields applied to the p-n
junctions by the voltages of the electrodes 8 fluctuate. As a
result, the p-n junction breakdown voltages fluctuate.
[0009] Further, due to the presence of a first conductivity type
region 7 below the element isolation insulating film 2 of FIGS. and
8, impurities in the first conductivity type region 7 affect
impurity distribution near the p-n junction, and the breakdown
voltage of the p-n junction changes. Also in this regard, ideally,
when the first conductivity type regions 7 are produced in the same
condition, the breakdown voltages of the p-n junctions are the
same. Actually the concentrations of impurities in the first
conductivity type regions 7, however, are not the same within a
wafer, between wafers, and among lots, and the p-n junction
breakdown voltages are affected to various degrees. As a result,
the p-n junction breakdown voltages fluctuate.
[0010] According to the Japanese Published Patent Application No.
11-307787, a planar shape of the second conductivity type high
concentration region 1 of FIG. 7 is octagon (not shown in this
specification). In such a structure having corners, electric field
strength is high at a corner portion, and therefore the breakdown
voltage is determined by the corner portion. FIG. 9 shows the
breakdown voltages in the case where the planar shape of the second
conductivity type high concentration region 1 is rectangular and in
the case where the planar shape thereof is circular. It is apparent
that the breakdown voltage is lower in the case of the clamp diode
having the rectangular second conductivity type high concentration
region 1 than in the case of the clamp diode having the circular
second conductivity type high concentration region 1. That is, it
is apparent that the electric field is concentrated at the corner
portions of the rectangle, and the corner portions determine the
breakdown voltage. Ideally, the breakdown voltages of the p-n
junctions will be the same since the shapes of the corner portions
are always the same when lithography is performed in the same
condition. Actually the electric field strength at the corner
portions, however, fluctuates within a wafer, between wafers, and
among lots. As a result, the p-n junction breakdown voltages
fluctuate.
[0011] As described above, there are many factors that cause the
breakdown voltages of the p-n junctions to fluctuate, and, in order
to suppress such fluctuations, the clamp diode needs to have a
structure as simple as possible, and the factors that cause
fluctuations need to be eliminated as much as possible.
SUMMARY OF THE INVENTION
[0012] The present invention has been made in view of the
above-mentioned problems, and the present invention provides a
clamp diode which suppresses deterioration with time, fluctuations
within a wafer surface, among wafers, and among lots, and leakage
before breakdown.
[0013] In order to solve the above-mentioned problems, according to
an exemplary embodiment of the present invention, a semiconductor
device including a clamp diode includes: a breakdown voltage
adjusting first conductivity type low concentration region provided
on a semiconductor substrate; a second conductivity type high
concentration region provided within the breakdown voltage
adjusting first conductivity type low concentration region, the
second conductivity type high concentration region being circular;
an element isolation insulating film provided within the breakdown
voltage adjusting first conductivity type low concentration region,
the element isolation insulating film being provided in a ring
shape and surrounding the second conductivity type high
concentration region without being held in contact therewith; and a
first conductivity type high concentration region provided outside
the ring of the element isolation insulating film within the
breakdown voltage adjusting first conductivity type low
concentration region.
[0014] By the foregoing arrangement, the present invention provides
a clamp diode having little deterioration with time, small
fluctuations within a wafer surface, among wafers, and among lots,
and little leakage before breakdown.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] In the accompanying drawings:
[0016] FIGS. 1A and 1B are diagrams illustrating a representative
example of the present invention;
[0017] FIG. 2 is a graph showing leakage characteristics of a clamp
diode;
[0018] FIG. 3 is a diagram illustrating Modified Example 1 of the
present invention;
[0019] FIGS. 4A and 4B are diagrams illustrating Modified Example 2
of the present invention;
[0020] FIGS. 5A and 5B are diagrams illustrating Modified Example 4
of the present invention;
[0021] FIGS. 6A and 6B are diagrams illustrating Modified Example 5
of the present invention;
[0022] FIG. 7 is a diagram illustrating an embodiment of the
conventional technology;
[0023] FIG. 8 is a diagram illustrating another embodiment of the
conventional technology; and
[0024] FIG. 9 is a graph showing shape dependence of a second
conductivity type high concentration region on a current-voltage
characteristic of the clamp diode.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] A mode for carrying out the present invention is described
below with reference to the attached drawings.
[0026] FIGS. 1A and 1B are diagrams illustrating a clamp diode in a
semiconductor device according to a first embodiment of the present
invention. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional
view along the line A-A' of FIG. 1A.
[0027] A breakdown voltage adjusting first conductivity type low
concentration region 5 is provided on a surface of a semiconductor
substrate 6, and a second conductivity type high concentration
region 1, which has a conductivity type opposite to that of the
breakdown voltage adjusting first conductivity type low
concentration region 5, is provided on a part of a surface of the
breakdown voltage adjusting first conductivity type low
concentration region 5 so as to be circular in a plan view. On the
surface of the breakdown voltage adjusting first conductivity type
low concentration region 5, an element isolation insulating film 2
having a ring shape is provided in such a way that the element
isolation insulating film 2 surrounds the second conductivity type
high concentration region 1 without being held in contact therewith
The ring shape as used herein does not necessarily mean an annular
shape or a doughnut shape, and an inner part of the ring shape of
the element isolation insulating film 2 is circular, but an outer
shape thereof is rectangular in this embodiment. Further, on the
breakdown voltage adjusting first conductivity type low
concentration region 5, a rectangular first conductivity type high
concentration region 3 is provided so as to surround the element
isolation insulating film 2. The second conductivity type high
concentration region 1 and the first conductivity type high
concentration region 3 have surfaces covered with insulating films,
and are respectively connected to different wirings via contacts
4.
[0028] When a voltage is applied between the first conductivity
type high concentration region 3 and the second conductivity type
high concentration region 1, due to breakdown of a p-n junction of
the second conductivity type high concentration region 1 and the
breakdown voltage adjusting first conductivity type low
concentration region 5, the voltage is clamped to be a constant
voltage. Depending on the purposes, the semiconductor device may
include only a clamp diode, or may include a circuit having
components other than the clamp diode, such as a transistor.
Effect 1
[0029] As illustrated in FIGS. 1A and 1B of the present invention,
the second conductivity type high concentration region 1 is
provided without being held in contact with the element isolation
insulating film 2, and hence the inventor(s) of the present
invention have found that there can be obtained not only an effect
of suppressing deterioration with time as described in Japanese
Patent Application Laid-open No. Hei 11-307787 but also an effect
of suppressing a leakage current at a voltage equal to or lower
than a breakdown voltage of the p-n junction. FIG. 2 is a graph
showing voltage-current characteristics of the clamp diode. "Not in
contact" in the graph of FIG. 2 refers to a structure in which the
second conductivity type high concentration region 1 and the
element isolation insulating film 2 are not held in contact with
each other as illustrated in FIGS. 1A and 1B, and "in contact"
refers to a structure in which the second conductivity type high
concentration region 1 and the element isolation insulating film 2
are in contact with each other. As shown in FIG. 2, the structure
in which the second conductivity type high concentration region 1
and the element isolation insulating film 2 are "not in contact"
with each other has a smaller leakage current than the structure in
which the second conductivity type high concentration region 1 and
the element isolation insulating film 2 are "in contact" with each
other. The inventor(s) of the present invention have assumed the
reason for this to be as follows. When forming the element
isolation insulating film 2 held in contact with the second
conductivity type high concentration region 1, a distortion is
generated between the element isolation insulating film 2 and the
breakdown voltage adjusting first conductivity type low
concentration region 5, and a level is formed in a forbidden band
of the breakdown voltage adjusting first conductivity type low
concentration region 5. As a result, a current flows through the
level, and hence a leakage current is large in the structure in
which the second conductivity type high concentration region 1 and
the element isolation insulating film 2 are held in contact with
each other.
[0030] Accordingly, in FIGS. 1A and 1B of the present invention,
together with the effect of suppressing deterioration with time
described in the Japanese Published Patent Application No.
11-307787, the effect of suppressing a leakage current can be
obtained, which is one of the objects of the present invention.
Effect 2
[0031] In FIGS. 1A and 1B of the present invention, there is no
electrode 8 or insulating film 9 of the conventional structure
illustrated in FIG. 7, and hence there is no fluctuation in an
electric field propagating from the electrode 8 to a p-n junction
breakdown voltage, which is one of the objects of the present
invention. As a result, a fluctuation in the p-n junction breakdown
voltage is reduced.
Effect 3
[0032] In FIGS. 1A and 1B of the present invention, there is no
first conductivity type region 7 of the conventional structure
illustrated in FIGS. 7 and 8, and hence the p-n junction breakdown
voltage is not affected by the first conductivity type region 7 to
various degrees, which is one of the objects of the present
invention. As a result, a fluctuation in the p-n junction breakdown
voltage is further reduced along with Effect 2.
Effect 4
[0033] In FIGS. 1A and 1B of the present invention, a planar shape
of the second conductivity type high concentration region 1 is
circular and has no corner, and hence there is no fluctuation in
electric field strength due to fluctuations in corner portions of
the second conductivity type high concentration region 1, which is
one of the objects of the present invention. As a result, a
fluctuation in the p-n junction breakdown voltage is further
reduced along with Effects 2 and 3.
Modified Example 1
[0034] FIG. 3 is a plan view illustrating Modified Example 1 of the
present invention. FIG. 3 illustrates a case where a planar shape
of a part of the element isolation insulating film 2 on the second
conductivity type high concentration region 1 side is rectangular.
When the element isolation insulating film 2 is not held in contact
with the second conductivity type high concentration region 1 as in
this case, even if the planar shape of the element isolation
insulating film 2 is not a circle as illustrated in FIGS. 1A and
1B, but a rectangle, a hexagon, or the like, the above-mentioned
Effects 1 to 4 can be obtained.
Modified Example 2
[0035] FIG. 4A is a plan view illustrating Modified Example 2 of
the present invention, and FIG. 4B is a cross-sectional view. along
the line B-B' of FIG. 4A. In an example illustrated in FIGS. 4A and
4B, there is no element isolation insulating film 2 illustrated in
FIG. 3. In this way, even when there is no element isolation
insulating film 2, the above-mentioned Effects 1 to 4 can be
obtained.
Modified Example 3
[0036] In FIGS. 1A and 1B, FIG. 3, and FIGS. 4A and 4B, the first
conductivity type high concentration region 3 is disposed in a
rectangular ring shape. Even when the first conductivity type high
concentration region 3 has a shape other than a rectangle, or even
when the first conductivity type high concentration region 3 does
not have a ring shape, the above-mentioned Effects 1 to 4 can be
obtained.
Modified Example 4
[0037] In order to clamp a voltage in any current band at the same
voltage, the clamp diode is required to have steep breakdown
characteristics. In order to obtain the steep breakdown
characteristics, a parasitic resistance may be reduced. In the
present invention, the distance between the second conductivity
type high concentration region 1 and the first conductivity type
high concentration region 3 is short, and a parasitic resistance of
the breakdown voltage adjusting first conductivity type low
concentration region 5 is reduced, thereby obtaining the steep
breakdown characteristics.
[0038] FIG. 5A is a plan view illustrating another clamp diode of
FIGS. 1A and 1B, in which the parasitic resistance of the breakdown
voltage adjusting first conductivity type low concentration region
is reduced as much as possible. FIG. 5B is a plan view illustrating
another clamp diode of FIGS. 4A and 4B, in which the parasitic
resistance of the breakdown voltage adjusting first conductivity
type low concentration region 5 is reduced as much as possible.
[0039] As illustrated in FIGS. 5A and 5B, the ring shapes of the
element isolation insulating film 2 and the first conductivity type
high concentration region 3 are all set to be annular shapes of
circles, and each size thereof is set to be a minimum value of the
design rule. In this way, the parasitic resistance of the breakdown
voltage adjusting first conductivity type low concentration region
5 can be reduced as much as possible and it is possible to obtain
the steepest breakdown characteristics.
Modified Example 5
[0040] FIGS. 6A and 6B are plan views respectively illustrating
modified clamp diodes of FIGS. 5A and 5B. Even when outer parts of
the ring shapes of the first conductivity type high concentration
regions 3 have shapes other than a circle as in this case, the
parasitic resistances of the breakdown voltage adjusting first
conductivity type low concentration regions 5 are the same as those
in the case of FIGS. 5A and 5B, and therefore the same effect as
that in Modified Example 4 can be obtained.
Modified Example 6
[0041] In all of the above-mentioned exemplary embodiments of the
present invention, the element isolation insulating film 2 is
assumed to be formed by LOCOS. However, even when the element
isolation insulating film 2 is formed by shallow trench isolation
(STI), the same effect can be obtained. In this manner, the present
invention is not limited to the above-mentioned embodiments, and
can be modified within the scope of the present invention without
departing from the gist thereof.
* * * * *