Reverse conducting thyristor

Details Reverse conducting thyristor Reverse conducting thyristor

2001-04-03

2002-05-14

Nelms, David (Department: 2818)

Active solid-state devices (e.g., transistors, solid-state diode

Regenerative type switching device

Bidirectional rectifier with control electrode

C257S127000

Reexamination Certificate

active

06388276

ABSTRACT:

BACK GROUND OF THE INVENTION
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.
In general, in a reverse conducting thyristor, a gate turnoff thyristor (hereinafter referred to a “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.
In this reverse conducting thyristor, a p layer
502
whose film thickness is about 90 &mgr;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 &mgr;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&OHgr;. An n layer
503
is further formed on the p layer
502
in the GTO thyristor portion B.
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
.
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.
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.
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.
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
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.
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: 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.
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.
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 &mgr;m or smaller. This is for increasing the breakdown voltage of the reverse conducting thyristor.
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.
It is preferable that two or more such guard ring regions are formed. This is for obtaining sufficient insulation characteristics at the separation portion.
A distance between said guard ring regions is preferably 30 &mgr;m or smaller. This is for increasing the breakdown voltage of the reverse conducting thyristor.
The depth of said thin film region is preferably 10 &mgr;m or smaller. This is for obtaining sufficient insulation characteristics at the separation portion.
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.
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.
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.
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.
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.
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.


REFERENCES:
patent: 4791470 (1988-12-01), Shinohe et al.
patent: 5345095 (1994-09-01), Niwayama
patent: 5682044 (1997-10-01), Tamamushi et al.
patent: 6091086 (2000-07-01), Zommer
patent: 62-57250 (1987-03-01), None
patent: 07-86567 (1995-03-01), None

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