Active solid-state devices (e.g. – transistors – solid-state diode – With specified impurity concentration gradient – With high resistivity
Reexamination Certificate
2002-07-16
2004-02-10
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
With specified impurity concentration gradient
With high resistivity
C257S656000, C257S332000
Reexamination Certificate
active
06690085
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-216987, filed Jul. 17, 2001, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to a high-voltage semiconductor device used as a switching element for a power device or the like.
2. Description of the Related Art
The structure and characteristics of a high-voltage diode and high-voltage transistor serving as conventional high-voltage semiconductor devices will be described below.
FIG. 1
is a sectional view showing the structure of a conventional high-voltage diode.
As shown in
FIG. 1
, a high-resistance n
−
-type epitaxial layer
102
is formed on one surface of a low-resistance n
+
-type semiconductor substrate
101
. A low-resistance p
+
-type anode layer
103
is formed on the n
−
-type epitaxial layer
102
. An anode electrode
104
is formed on the p
+
-type anode layer
103
. An anode terminal A is connected to the anode electrode
104
.
A cathode electrode
105
is formed on the other surface of the n
+
-type semiconductor substrate
101
. A cathode terminal K is connected to the cathode electrode
105
.
In the high-voltage diode having the structure shown in
FIG. 1
, a depletion layer spreads from the p
+
-type anode layer
103
to the inside of the n
−
-type epitaxial layer
102
. This relaxes an electric field in this region, thereby implementing a high breakdown voltage.
When a reverse bias is applied, as shown in
FIG. 2
, such a high-voltage diode exhibits an electric field distribution in which an electric field is uniformly reduced from the anode side to the cathode side. To realize a necessary breakdown voltage, the thickness of the n
−
-type epitaxial layer
102
must be increased. However, when the thickness of the n
−
-type epitaxial layer
102
is increased, an ON resistance increases. An increase in ON resistance similarly occurs when this structure is applied to a MOS field effect transistor (to be referred to as a MOSFET hereinafter).
To solve this, a high-voltage diode shown in
FIG. 3
which can obtain a high breakdown voltage without increasing an ON resistance is proposed. This high-voltage diode has the following structure.
As shown in
FIG. 3
, trenches which extend from the upper surface of the p
+
-type anode layer
103
to the n
+
-type semiconductor substrate
101
are formed in the p
+
-type anode layer
103
and n
−
-type epitaxial layer
102
. An oxide film
106
is formed on the inner wall of each trench. A semi-insulating high-resistance element
107
is buried in each trench in which the oxide film
106
is formed.
The high-voltage diode shown in
FIG. 3
has the oxide film
106
between the n
−
-type epitaxial layer
102
and high-resistance element
107
. A large-capacitance capacitor is thus formed between the n
−
-type epitaxial layer
102
and high-resistance element
107
. Letting R be the resistance of the high-resistance element
107
, and C be the capacitance of the capacitor, a CR time constant at the start of operation increases, and depletion layer formation takes a long time, thereby making a leakage current keep flowing until the depletion layer formation ends. This means that a long time is required for obtaining dielectric breakdown. Consequently, when a high voltage is abruptly applied between the anode terminal A and cathode terminal K at the start of operation, sometimes the leakage current increases to damage the high-voltage diode.
In addition, after forming the trenches in the n
−
-type epitaxial layer
102
, the high-voltage diode shown in
FIG. 3
requires the step of oxidizing the inner walls of the trenches and then removing the oxide films on the bottom surfaces of the trenches. This results in the manufacturing disadvantage of the high-voltage diode.
BRIEF SUMMARY OF THE INVENTION
A semiconductor device according to an aspect of the present invention comprises: a first-conductivity-type semiconductor region formed on a first-conductivity-type semiconductor body, the first-conductivity-type semiconductor region having an electric resistance higher than that of the first-conductivity-type semiconductor body; a second-conductivity-type semiconductor region formed on the first-conductivity-type semiconductor region; and a high-resistance region formed in the first-conductivity-type and second-conductivity-type semiconductor regions, the high-resistance region being in contact with the first-conductivity-type and second-conductivity-type semiconductor regions and extending from an upper surface of the second-conductivity-type semiconductor region in a direction of the first-conductivity-type semiconductor body.
REFERENCES:
patent: 5216275 (1993-06-01), Chen
patent: 5241195 (1993-08-01), Tu et al.
patent: 5278443 (1994-01-01), Mori et al.
patent: 6040600 (2000-03-01), Uenishi et al.
patent: 6201279 (2001-03-01), Pfirsch
patent: 6303954 (2001-10-01), Ohoka
patent: 6501146 (2002-12-01), Harada
U.S. patent application Publication by Tihanyl US class 257/328 May 30, 2002.
Kawaguchi Yusuke
Nakagawa Akio
Kabushiki Kaisha Toshiba
Nelms David
Nguyen Thinh T.
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