U.S. patent application number 09/824090 was filed with the patent office on 2002-03-14 for reverse conducting thyristor.
This patent application is currently assigned to Mitsubishi Denki Kabushiki Kaisha. Invention is credited to Hirano, Noritoshi, Satoh, Katsumi, Yamaguchi, Yoshihiro.
Application Number | 20020030199 09/824090 |
Document ID | / |
Family ID | 18720507 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020030199 |
Kind Code |
A1 |
Hirano, Noritoshi ; et
al. |
March 14, 2002 |
Reverse conducting thyristor
Abstract
Providing a reverse conducting thyristor, wherein a diode and a
GTO thyristor are reverse parallel-connected, with which it is
possible to reduce a surface area size of a separation portion and
avoid variations in insulation characteristics. A separation
portion between a diode and a GTO thyristor includes a
semiconductor substrate of a first conductivity type, a thin film
region of a second conductivity type formed in a major surface of
the semiconductor substrate, and a guard ring region of the second
conductivity type.
Inventors: |
Hirano, Noritoshi; (Fukuoka,
JP) ; Yamaguchi, Yoshihiro; (Fukuoka, JP) ;
Satoh, Katsumi; (Tokyo, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
Mitsubishi Denki Kabushiki
Kaisha
2-3, Marunouchi 2-chome
Chiyoda-ku
JP
|
Family ID: |
18720507 |
Appl. No.: |
09/824090 |
Filed: |
April 3, 2001 |
Current U.S.
Class: |
257/121 ;
257/107; 257/E29.22 |
Current CPC
Class: |
H01L 29/7416
20130101 |
Class at
Publication: |
257/121 ;
257/107 |
International
Class: |
H01L 029/74; H01L
031/111 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 27, 2000 |
JP |
2000-226985 |
Claims
What is claimed is:
1. A reverse conducting thyristor in which a diode and a thyristor
are reverse parallel-connected and formed on the same substrate,
comprising: a semiconductor substrate of a first conductivity type;
a diode region of a second conductivity type of said diode, formed
in a major surface of said semiconductor substrate; and a base
region of the second conductivity type of said thyristor, formed in
said major surface of said semiconductor substrate so as to be
separated from said diode region of the second conductivity type by
a separation region, wherein said separation region includes a thin
film region of the second conductivity type formed in said major
surface of said semiconductor substrate and a guard ring region of
the second conductivity type.
2. The reverse conducting thyristor according to claim 1, wherein
both a distance between said guard ring region and said diode
region of the second conductivity type and a distance between said
guard ring region and said base region of the second conductivity
type are respectively 30 .mu.m or smaller.
3. The reverse conducting thyristor according to claim 1, wherein
the depth of said guard ring region is smaller than the depth of
said diode region of the second conductivity type and the depth of
said base region of the second conductivity type.
4. The reverse conducting thyristor according to claim 1, wherein
there are two or more such guard ring regions.
5. The reverse conducting thyristor according to claim 4, wherein a
distance between said guard ring regions is 30 .mu.m or
smaller.
6. The reverse conducting thyristor according to claim 1, wherein
the depth of said thin film region is 10 .mu.m or smaller.
7. The reverse conducting thyristor according to claim 1, wherein a
concentration of an impurity of the second conductivity type
contained in said thin film region is lower than concentrations of
impurities of the second conductivity type contained in said diode
region of the second conductivity type and said base region of the
second conductivity type.
8. The reverse conducting thyristor according to claim 1, wherein a
concentration of an impurity of the second conductivity type
contained in said guard ring region is higher than concentrations
of impurities of the second conductivity type contained in said
diode region of the second conductivity type and said base region
of the second conductivity type.
9. The reverse conducting thyristor according to claim 1, wherein
concentrations of impurities of the second conductivity type
contained in said guard ring region, said diode region and said
base region of the second conductivity type, and said thin film
region are progressively lower in this order.
Description
BACK GROUND OF THE INVENTION
[0001] The present invention relates to a reverse conducting
thyristor, and more particularly, to a reverse conducting thyristor
in which a gate turnoff thyristor and a diode are connected in
reverse parallel to each other.
[0002] In general, in a reverse conducting thyristor, a gate
turnoff thyristor (hereinafter referred to as "GTO thyristor") and
a free wheel diode are connected in reverse parallel to each other.
FIG. 8 is a cross sectional view of a conventional reverse
conducting thyristor generally indicated by the reference numeral
500. The reverse conducting thyristor comprises a diode portion
denoted at A in FIG. 8, a GTO thyristor portion denoted at B in
FIG. 8, and a separation portion denoted at C sandwiched between
these two portions.
[0003] In this reverse conducting thyristor, a p layer 502 whose
film thickness is about 90 .mu.m is formed on a first major surface
of an N- silicon substrate 501 with the first major surface and a
second major surface. For electrical separation between the diode
portion A and the GTO thyristor portion B, the p layer 502 of the
separation portion C is etched in the form of a groove, about 60
.mu.m in depth and about 5 mm in width. This makes a resistance
value between the diode portion A and the GTO thyristor portion B
about 300 through 500 106 . An n layer 503 is further formed on the
p layer 502 in the GTO thyristor portion B.
[0004] On the other hand, an n+ layer 504 is formed on a second
major surface of the n- silicon substrate 501, and a p layer 505
and an n++ layer 506 are formed on the n+ layer 504.
[0005] Further, a cathode electrode 510 is disposed on the n layer
503 in the GTO thyristor portion B, and a gate electrode 511 is
disposed on the p layer 502. In addition, a cathode electrode 512
is disposed on the p layer 502 in the diode portion A.
[0006] Meanwhile, an anode electrode 513 is disposed on the second
major surface of the n- silicon semiconductor substrate 501, as a
common electrode for the diode portion A and the GTO thyristor
portion B.
[0007] FIG. 9 is a circuitry diagram of the reverse conducting
thyristor 500. The p layer 502 and the n+ layer 504 shown in FIG. 8
form the diode portion, while the n layer 503, the p layer 502, the
n+ layer 504 and the p layer 505 form the GTO thyristor
portion.
[0008] However, in the reverse conducting thyristor 500, a surface
area size of the separation portion C separating the diode portion
A from the GTO thyristor portion B is large, which is an obstacle
against a size reduction of the reverse conducting thyristor 500.
In addition, when a plurality of reverse conducting thyristors 500
are to be fabricated on a large wafer, the p layers 502 are etched
unevenly in terms of depth within the wafer, and therefore,
insulation characteristics of the separation portions C are not
uniform.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a
reverse conducting thyristor wherein a separation portion is small
in surface area size and insulation characteristics is uniform.
[0010] The present invention is directed to a reverse conducting
thyristor in which a diode and a thyristor are reverse
parallel-connected and formed on the same substrate,
comprising:
[0011] a semiconductor substrate of a first conductivity type;
[0012] a diode region of a second conductivity type of said diode,
formed in a major surface of said semiconductor substrate; and
[0013] a base region of the second conductivity type of said
thyristor, formed in said major surface of said semiconductor
substrate so as to be separated from said diode region of the
second conductivity type by a separation region, wherein said
separation region includes a thin film region of the second
conductivity type formed in said major surface of said
semiconductor substrate and a guard ring region of the second
conductivity type.
[0014] In this reverse conducting thyristor, the separation portion
has a small surface area size and variations in insulation
characteristics at the separation portion are reduced. Further,
with the thin film region formed in the separation portion, it is
possible to prevent destruction of the element due to concentration
of a leak current.
[0015] A distance between said guard ring region and said diode
region of the second conductivity type and a distance between said
guard ring region and said base region of the second conductivity
type are both preferably 30 .mu.m or smaller. This is for
increasing the breakdown voltage of the reverse conducting
thyristor.
[0016] The depth of said guard ring region is preferably smaller
than the depth of said diode region of the second conductivity type
and the depth of said base region of the second conductivity
type.
[0017] It is preferable that two or more such guard ring regions
are formed. This is for obtaining sufficient insulation
characteristics at the separation portion.
[0018] A distance between said guard ring regions is preferably 30
.mu.m or smaller. This is for increasing the breakdown voltage of
the reverse conducting thyristor.
[0019] The depth of said thin film region is preferably 10 .mu.m or
smaller. This is for obtaining sufficient insulation
characteristics at the separation portion.
[0020] A concentration of an impurity of the second conductivity
type contained in said thin film region is preferably lower than
concentrations of impurities of the second conductivity type
contained in said diode region of the second conductivity type and
said base region of the second conductivity type.
[0021] A concentration of an impurity of the second conductivity
type contained in said guard ring region is preferably higher than
concentrations of impurities of the second conductivity type
contained in said diode region of the second conductivity type and
said base region of the second conductivity type.
[0022] It is preferable that concentrations of impurities of the
second conductivity type contained in said guard ring region, said
diode region and said base region of the second conductivity type,
and said thin film region are progressively lower in this
order.
[0023] As clearly described above, with the reverse conducting
thyristor according to the present invention, it is possible to
reduce the surface area size of the separation portion, and hence,
to form the element in a small size.
[0024] Also, during fabrication of a plurality of such reverse
conducting thyristors on a wafer, it is possible to reduce
variations in insulation characteristics of the separation portion,
and hence, to ensure that element characteristics are uniform.
[0025] Further, it is possible to prevent destruction of the
element due to a leak current, and hence, to improve a production
yield of the reverse conducting thyristors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a cross sectional view of the reverse conducting
thyristor according to the preferred embodiment of the present
invention;
[0027] FIG. 2 is a cross sectional view of the reverse conducting
thyristor according to the first example of the present
invention;
[0028] FIG. 3 shows the relationship between the gaps between the
p-type regions and the breakdown voltage;
[0029] FIG. 4 is a cross sectional view of the reverse conducting
thyristor according to the second example of the present
invention;
[0030] FIG. 5 shows the relationship between the depth of the thin
film regions and the resistance value;
[0031] FIG. 6 shows the relationship between the concentration of
the thin film regions and the resistance value;
[0032] FIG. 7 is a cross sectional view of the reverse conducting
thyristor according to the third example of the present
invention;
[0033] FIG. 8 is a cross sectional view of the conventional reverse
conducting thyristor; and
[0034] FIG. 9 is a circuitry diagram of the conventional reverse
conducting thyristor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] FIG. 1 is a cross sectional view of a reverse conducting
thyristor according to a preferred embodiment. In the following, a
structure of the reverse conducting thyristor will be described
while referring to manufacturing steps.
[0036] Describing the reverse conducting thyristor generally
indicated by the reference numeral 100, first, an n- silicon
semiconductor substrate 1 with a first major surface and a second
major surface is prepared. An impurity concentration of an n-type
impurity in the semiconductor substrate 1 is about
7.times.10.sup.12 atom/cm.sup.3.
[0037] In a diode portion A, a p layer 2 is formed by diffusing or
the like on the first major surface of the semiconductor substrate
1. An impurity concentration of a p-type impurity in the p layer 2
is about 1.times.10.sup.16 atom/cm.sup.3 to 7.times.10.sup.16
atom/cm.sup.3, and preferably, about 4.times.10.sup.16
atom/cm.sup.3.
[0038] In a GTO thyristor portion B, a p base layer 2' and an n
cathode layer 3 are successively formed on the first major surface.
An impurity concentration of a p-type impurity in the p base layer
2' is approximately the same as that of the p layer 2. Meanwhile,
an impurity concentration of an n-type impurity in the n cathode
layer 3 is about 5.times.10.sup.19 atom/cm.sup.3.
[0039] Then, a region including the separation region C is etched,
thereby exposing the p base layer 2' below the n cathode layer
3.
[0040] On the other hand, an n+ layer 4 is formed by diffusing or
the like in the second major surface of the semiconductor substrate
1. Following this, an n++ layer 6 and the p layer 5 are formed on
the n+ layer 4. The n+ layer 4 and the n++ layer 6 function as an
n-side region of the diode portion A and also as an n base region
of the GTO thyristor portion B. An impurity concentration of an
n-type impurity in the n+ layer 4 is about 3.times.10.sup.15
atom/cm.sup.3, an impurity concentration of an n-type impurity in
the n++ layer 6 is about 1.times.10.sup.20 atom/cm.sup.3, and an
impurity concentration of a p-type impurity in the p layer 5 is
about 1.times.10.sup.18 atom/cm.sup.3.
[0041] Then, in the separation portion B, p-type guard ring regions
7 are formed by diffusing or the like in the first major surface of
the semiconductor substrate 1. An impurity concentration of a
p-type impurity in the guard ring regions 7 is about
1.times.10.sup.16 atom/cm.sup.3 to 1.times.10.sup.17 atom/cm.sup.3,
and preferably, about 5.times.10.sup.16 atom/cm.sup.3.
[0042] With more p-type guard ring regions 7 formed, it is possible
to enhance insulation between the p layer 2 and the p base layer
2'. On the other hand, increasing the number of the guard ring
regions 7 results in an increase in width of the separation portion
C. Noting this, the number of the guard ring regions 7 is
preferably set to an appropriate number. In this embodiment, there
are two guard ring regions 7 formed.
[0043] Then, p thin film regions 8 are formed by diffusing or the
like on the first major surface of the semiconductor substrate 1
exposed to the surface of the separation portion C. An impurity
concentration of a p-type impurity in the thin film regions 8 is
about 5.times.10.sup.15 atom/cm.sup.3 to 5.times.10.sup.16
atom/cm.sup.3, and preferably, is about 1.times.10.sup.16
atom/cm.sup.3.
[0044] At last, a cathode electrode 12 is disposed on the p layer 2
in the diode portion A, a gate electrode 11 is disposed on the p
base layer 2' in the GTO thyristor portion B, and a cathode
electrode 10 is disposed on the n cathode layer 3. On the other
hand, an anode electrode 13 is disposed on the second major surface
of the semiconductor substrate 1, as a common electrode for the
diode portion A and the GTO thyristor portion B.
[0045] In this manner, in the reverse conducting thyristor
according to the preferred embodiment, discrete insulating by means
of the guard ring regions 7 in the separation portion C makes it
possible to decrease the size of the separation portion C. Further,
it is possible to largely decrease variations in insulation
characteristics (resistance value) of the separation portion C.
[0046] Meanwhile, Japanese Patent Application Laid-Open Publication
No. 7-86567 describes a structure that only the guard ring regions
are formed in the separation portion C.
[0047] However, in the case of the structure with only the guard
ring regions, as a defect within the guard ring regions or the like
deteriorates an insulation capability of the guard ring regions,
there is a problem when a leak current is created. That is, a leak
current flows concentrated in the vicinity of the surfaces of the
semiconductor substrate 1 between the guard ring regions 7 and the
p layer 2, for example, which in turn leads to destruction of the
element. In particular, even when the quantity of the leak current
is extremely small so that the reverse conducting thyristor remains
still usable, due to destruction of the element induced by the
concentration of the leak current, the reverse conducting thyristor
eventually becomes unusable in some cases.
[0048] Therefore, the reverse conducting thyristor according to the
preferred embodiment requires to form the thin film regions 8 of
the p type, so that when a leak current is generated, the leak
current flows inside the thin film regions 8. This makes it
possible to prevent concentration of the leak current which occurs
in the case of the conventional techniques, and hence, to prevent
current concentration from destroying the element.
[0049] EXAMPLE 1.
[0050] FIG. 2 shows a first example of the invention. A structure
of a reverse conducting thyristor 100 is the same as that of the
thyristor shown in FIG. 1. In the reverse conducting thyristor 100
shown in FIG. 2, the separation portion C includes two guard ring
regions 7. Further, a gap between the guard ring region 7 and the p
layer 2, a gap between the guard ring region 7 and the p base layer
2', and a gap between the two guard ring regions 7 are respectively
30 .mu.m.
[0051] FIG. 3 shows a relationship between the gaps between the
guard ring regions 7 and the p layer 2 and the like and a breakdown
voltage between the anode electrode and the cathode electrode. The
breakdown voltage between the anode electrode and the cathode
electrode is expressed as a ratio assuming that a breakdown voltage
is 1 when the gaps between the guard ring regions 7 and the p layer
2 and the like are 30 .mu.m. As is clear from FIG. 3, the breakdown
voltage decreases as the gaps exceed 30 .mu.m. When the gaps are 50
.mu.m or narrower, in particular, the breakdown voltage decreases
as much as 25%.
[0052] Hence, as shown in FIG. 2, the gaps between the guard ring
regions 7 and the p layer 2 and the like are preferably 30 .mu.m or
smaller.
[0053] EXAMPLE 2.
[0054] FIG. 4 shows a second example of the invention. A structure
of a reverse conducting thyristor 100 is the same as that of the
thyristor shown in FIG. 1. In the reverse conducting thyristor 100
shown in FIG. 4, the separation portion C includes two guard ring
regions 7. The gaps between the guard ring regions 7 and the p
layer 2 and the like are respectively 30 .mu.m.
[0055] FIG. 5 shows a relationship between the depth of the thin
film regions 8 and a resistance between the cathode electrode 12 of
the diode and the cathode electrode 10 of the GTO thyristor. The
resistance is expressed as a ratio assuming that a resistance is 1
when the depth of the thin film regions 8 is 10 .mu.m.
[0056] As is clear from FIG. 5, the resistance value gradually
increases as the depth of the thin film regions 8 becomes smaller
than about 10 .mu.m. On the other hand, when the depth is about 10
.mu.m or larger, the resistance value is approximately
constant.
[0057] Hence, in order to obtain excellent insulation
characteristics at the separation portion C, the depth of the thin
film regions 8 is preferably 10 .mu.m or smaller.
[0058] Meanwhile, FIG. 6 shows a relationship between a
concentration of the thin film regions 8 and the resistance between
the cathode electrode 12 of the diode and the cathode electrode 10
of the GTO thyristor. The resistance is expressed in percentage (%)
of an increase from a reference resistance value assuming when the
concentration of the thin film regions 8 is 5.times.10.sup.16
atom/cm.sup.3.
[0059] As is clear from FIG. 6, it is possible to increase the
resistance value of the thin film regions 8 as the concentration of
the p-type impurity in the thin film regions 8 is lower.
[0060] Hence, in order to obtain excellent insulation
characteristics at the separation portion C, the concentration of
the thin film regions 8 is preferably 5.times.10.sup.16
atom/cm.sup.3 or lower.
[0061] EXAMPLE 3.
[0062] FIG. 7 shows a third example of the invention. A structure
of a reverse conducting thyristor 100 is the same as that of the
thyristor shown in FIG. 1. In the reverse conducting thyristor 100
shown in FIG. 7, the separation portion C includes two guard ring
regions 7, and the gaps between the guard ring regions 7 and the p
layer 2 and the like are respectively 30 .mu.m or narrower.
Further, the concentrations of the p-type impurities in the guard
ring regions 7, the p layer 2 and the p base layer 2', and the thin
film regions 8 are progressively lower in this order.
[0063] Further, the depth of the guard ring regions 7 is shallower
than the p layer 2 and the p base layer 2'.
[0064] This is to suppress maximum values of electric fields
between P, N and P due to growth of a depletion layer on the
cathode side to the guard ring regions 7, by means of the shallow
guard ring regions 7.
[0065] That is, there is a tendency that the deeper the guard ring
regions 7 are, the higher the electric fields created between P, N
and P are, whereas the shallower the guard ring regions 7 are, the
more the electric fields are moderated. Further, there is a
tendency that the electric fields created between the deep regions
are high and those between the shallow regions are low.
[0066] Hence, with the shallow guard ring regions 7, it is possible
to decrease the electric fields created between P, N and P.
* * * * *