Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device – Bidirectional rectifier with control electrode
Reexamination Certificate
2003-02-19
2004-07-27
Pham, Long (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
Bidirectional rectifier with control electrode
C257S104000, C257S106000, C257S199000, C257S471000, C257S481000, C257S603000
Reexamination Certificate
active
06768138
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to diodes, and more particularly to diodes having a structure, in which a semiconductor crystal has been epitaxially grown in narrow grooves.
BACKGROUND OF THE INVENTION
FIG. 21
is a plan view of a conventional diode
101
, and
FIG. 22
is a cross-sectional view taken along the line P—P in FIG.
21
.
This diode
101
includes an N-type silicon substrate
111
. An N-type epitaxial layer
112
is formed on the surface of the silicon substrate
111
.
The grooves whose planar shape is that of a rectangular ring surface are provided on the surface of the epitaxial layer
112
. In the case shown, three rectangular ring-shaped grooves are provided, and these ring-shaped grooves are arranged concentrically. The ring-shaped grooves are each filled with a semiconductor layer containing P-type impurities and formed by epitaxial growth.
The innermost of these rectangular ring-shaped semiconductor layers is an intermediate withstand voltage portion
128
. Two outer withstand voltage portions
127
1
and
127
2
are arranged concentrically on the outside this intermediate withstand voltage portion
128
. A plurality of narrow grooves with a rectangular planar shape are arranged on the inner side of the intermediate withstand voltage portion
128
. These narrow grooves are arranged parallel to one another. The narrow grooves are filled with narrow groove withstand voltage portions
125
1
to
125
3
made of semiconductor layers containing P-type impurities and formed by epitaxial growth.
A thermal oxide film
114
and a PSG (Phospho-Silicate glass) film
115
are formed in that order on the surface of the epitaxial layer
112
. An anode electrode
118
made of a metal thin film is disposed on the PSG film
115
. An opening is formed in the thermal oxide film
114
and the PSG film
115
at the same position. The epitaxial layer
112
, the narrow groove withstand voltage portions
125
1
to
125
3
and the intermediate withstand voltage portion
128
are exposed at the bottom of this opening and are in contact with the anode electrode
118
.
The anode electrode
118
is a metal thin film forming a Schottky junction with the epitaxial layer
112
and forming an ohmic junction with the narrow groove withstand voltage portions
125
1
to
125
3
and the intermediate withstand voltage portion
128
.
When a positive voltage is applied to the anode electrode
118
and a negative voltage is applied to the cathode electrode
119
of the diode
101
with this structure, then the Schottky junction between the anode electrode
118
and the epitaxial layer
112
is forward biased, and a current flows from the anode electrode
118
to the cathode electrode
119
.
When, conversely, a negative voltage is applied to the anode electrode
118
and a positive voltage is applied to the cathode electrode
119
, then the Schottky junction between the anode electrode
118
and the epitaxial layer
112
and the PN junctions between the narrow groove withstand voltage portions
125
1
to
125
3
and the intermediate withstand voltage portion
128
and the epitaxial layer
112
are reverse biased, and no current flows. In this situation, a depletion layer spreads from the PN junctions in the lateral direction in the epitaxial layer
112
.
Conventionally, the widths and spacings between the narrow groove withstand voltage portions
125
1
to
125
3
, the intermediate withstand voltage portion
128
and the outer withstand voltage portions
127
1
and
127
2
were not set with withstand voltage in mind, so that even when the epitaxial layer
112
is depleted between the long side of the narrow groove withstand voltage portions
125
1
to
125
3
and the inner ring circumference of the intermediate withstand voltage portion
128
, the epitaxial layer
112
was not necessarily depleted between the short side of the narrow groove withstand voltage portions
125
1
to
125
3
and the inner ring circumference of the intermediate withstand voltage portion
128
. Thus, electric fields concentrated at the locations where no depletion layer is formed, and the withstand voltage was decreased.
It is thus an object of the present invention to overcome these problems of the related art and to provide a diode element with high withstand voltage.
SUMMARY OF THE INVENTION
In order to attain the above-described object, in a first aspect of the present invention, a diode element includes a substrate of a first conductivity type, a plurality of grooves formed in a main surface of the substrate, a semiconductor filler that is made of a semiconductor of a second conductivity type, which is opposite to the first conductivity type, filled into the grooves, and an electrode film arranged on the main surface, wherein a Schottky junction is formed at a portion where the electrode film contacts the surface of the substrate, and an ohmic junction is formed at a portion where the electrode film contacts the surface of the semiconductor filler, wherein the grooves comprise a first narrow groove ring, whose planar shape is a ring and whose inner circumference is quadrilateral, and a plurality of rectangular narrow grooves, whose planar shape is a narrow rectangle, which are arranged at positions on the inner side of the inner ring circumference of the first narrow groove ring, and four sides of the rectangular narrow groove are arranged parallel to the inner ring circumference of the first narrow groove ring, wherein one intermediate withstand voltage portion and a plurality of narrow groove withstand voltage portion are constituted by the semiconductor filler filled into the first narrow groove ring and the rectangular narrow grooves, wherein the surface of the narrow groove withstand voltage portions and the substrate surface between the narrow groove withstand voltage portions is in contact with the electrode film, and wherein, the distance a between the long sides of the narrow groove withstand voltage portions opposing to the inner ring circumference of the intermediate withstand voltage portion and the inner ring circumference of the intermediate withstand voltage portion is set to substantially twice the distance b between the short sides of the narrow groove withstand voltage portions and the inner ring circumference of the intermediate withstand voltage portion.
According to a second aspect of the present invention, in a diode element according to the first aspect of the present invention, the intermediate withstand voltage portion does not contact the electrode film and is at floating potential.
According to a third aspect of the present invention, in a diode element according to the first aspect of the present invention, the grooves further include a ring-shaped second narrow groove ring enclosing the first narrow groove ring, wherein an outer withstand voltage portion is constituted by the semiconductor filler filled into the second narrow groove ring, wherein the intermediate withstand voltage portion contacts the electrode film, and wherein the outer withstand voltage portion does not contact the electrode film and is at floating potential.
According to a fourth aspect of the present invention, a diode element according the first aspect of the present invention, includes a plurality of narrow groove withstand voltage portions, wherein the narrow groove withstand voltage portions are arranged in parallel to one another at a distance d between the long sides of the narrow groove withstand voltage portions; and wherein this distance d is substantially the same as the distance a between the long sides of the narrow groove withstand voltage portions opposing to the inner ring circumference of the intermediate withstand voltage portion and the inner ring circumference of the intermediate withstand voltage portion.
According to a fifth aspect of the present invention, in a diode element according to third or fourth aspect of the present invention, a ring width w of the outer withstand voltage portion and the intermediate withstand voltage portion is substantially the same as a width y of
Kitada Mizue
Kunori Shinji
Ohsima Kosuke
Armstrong, Kratz, Quintos Hanson & Brooks, LLP.
Louie Wai-Sing
Pham Long
Shindengen Electric Manufacturing Co. Ltd.
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