Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2002-10-23
2004-03-16
Jackson, Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S341000, C257S360000, C257S394000
Reexamination Certificate
active
06707104
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-371568, filed Dec. 27, 1999; and No. 2000-205070, filed Jul. 6, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention relates to a lateral high-breakdown-voltage transistor.
The lateral high-breakdown-voltage MOS transistor is a type of a power MOS transistor, which is switched on when a voltage ranging from several tens to several hundreds volts is applied thereto.
FIG. 13A
is an enlarged plan view illustrating part of the planar pattern of a conventional lateral high-breakdown-voltage MOS transistor.
FIG. 13B
is a sectional view taken along line
13
B—
13
B of FIG.
13
A. In
FIG. 13A
, the gate electrode of the transistor is omitted.
As shown in
FIGS. 13A and 13B
, a low-concentration n
−
drain region
102
is formed in a low-concentration p
−
silicon substrate
101
, and a high-concentration n
+
source region
103
is formed therein, separated from the drain region
102
. A gate electrode
105
is formed on that portion of the substrate
101
, which is located between the drain and source regions
102
and
103
, i.e. on a channel
104
, such that the electrode
105
is electrically isolated from the substrate
101
.
An n
+
drain contact region
106
having a higher impurity concentration than the drain region
102
is formed in the drain region
102
. The drain contact region
106
is sufficiently separated from the channel
104
by means of a field insulating film
108
formed on the substrate
101
. The field insulating film
108
is made of, for example, silicon dioxide, and formed by the LOCOS (Local Oxidation of Silicon) technique, or STI (Shallow Trench Isolation) technique, etc. Further, high-concentration p
+
substrate contact regions
107
are formed in the substrate
101
in contact with the source region
103
.
An interlayer insulating film
109
made of, for example, silicon dioxide is formed on the field insulating film
108
and on those portions of the substrate
101
, in which the aforementioned semiconductor regions are formed. The interlayer insulating film
109
has a contact hole
110
that exposes the drain contact region
106
therethrough, and a contact hole
111
that exposes the source region
103
and the substrate contact regions
107
therethrough. Drain wiring
112
is provided on the interlayer insulating film
109
such that it comes into contact with the drain contact region
106
via the contact hole
110
. Similarly, source wiring
113
is provided on the interlayer insulating film
109
such that it comes into contact with the source region
103
and the substrate contact regions
107
via the contact hole
111
. The drain wiring
112
is electrically connected to the drain region
102
via the drain contact region
106
. In
FIG. 13A
, reference numeral
116
denotes a contact surface between the drain wiring
112
and the drain contact region
106
. The source wiring
113
is electrically connected to the source region
103
, and also to the substrate
101
via the substrate contact regions
107
. Further, in
FIG. 13A
reference numeral
115
denotes a contact surface between the source wiring
113
and the source region
103
, the substrate contact regions
107
.
Since, in the lateral high-breakdown-voltage MOS transistor, the drain and source regions
102
and
103
exist at the same level as shown in
FIG. 13A
, a lateral parasitic bipolar transistor exists which uses the drain region
102
, the substrate
101
and the source region
103
as a collector, a base and an emitter, respectively. When the lateral parasitic bipolar transistor is turned on, it adversely affects the operation of the MOS transistor. The lateral parasitic bipolar transistor is turned on, for example, in the following situation.
When the gate is turned on and the voltage at the drain is increased, avalanche breakdown starts at a curved surface
114
of the drain contact region
106
, whereby a hole current flows toward the substrate
101
. This hole current flows below the source region
103
to the substrate contact regions
107
, and then, usually, to the source wiring
113
via substrate contact regions
107
.
When the voltage at the drain is further increased, the level of the avalanche breakdown increases to thereby increase the hole current. As the hole current increases, a high voltage is generated due to the resistance of a portion of the substrate
101
below the source region
103
. Accordingly, forwardly biasing of the PN junction between the substrate
101
and the source region
103
occurs, thereby turning on the lateral parasitic bipolar transistor. When the lateral parasitic bipolar transistor is turned on, control using the gate cannot be executed, resulting in breakdown of the lateral high-breakdown-voltage MOS transistor.
BRIEF SUMMARY OF THE INVENTION
The present invention has been developed to solve the above-described problem, and aims to provide a lateral high-breakdown-voltage transistor capable of suppressing turn-on of a lateral parasitic bipolar transistor and hence having a higher breakdown voltage.
According to a first aspect of the invention, there is provided a semiconductor device having a lateral high-breakdown-voltage transistor comprising: a first-conductivity-type semiconductor layer; a second-conductivity-type source region formed in the semiconductor layer; a second-conductivity-type drain region formed in or outside the semiconductor layer, separated from the source region; a gate electrode formed above the semiconductor layer between the drain region and the source region, insulated from the semiconductor layer; a second-conductivity-type drain contact region formed in the drain region and having a higher impurity concentration than the drain region; a drain wiring electrically connected to the drain region via the drain contact region; a first-conductivity-type substrate contact region formed adjacent to the source region; and a source wiring electrically connected to the source region, and also connected to the semiconductor layer via the substrate contact region. This transistor is characterized in that the source wiring touches a portion of the source region and the substrate contact region, thereby forming a contact surface therebetween, and the substrate contact region laterally extend from inside the contact surface to outside the contact surface.
Since, in the semiconductor device having the lateral high-breakdown-voltage transistor according to the first aspect, the substrate contact region extend from inside the contact surface of the source wiring to outside the contact surface, the ratio of the contact area of the substrate contact regions and the source wiring to their non-contact area can be increased as compared with the conventional case. As a result, a hole current flowing in the semiconductor layer can easily flow to the source wiring, which makes it difficult to turn on the lateral parasitic bipolar transistor. This enables production of a lateral high-breakdown-voltage transistor of a higher breakdown voltage.
According to a semiconductor device having a second aspect of the invention, there is provided a lateral high-breakdown-voltage transistor comprising: a first-conductivity-type semiconductor layer; a second-conductivity-type source region formed in the semiconductor layer; a second-conductivity-type drain region formed in or outside the semiconductor layer, separated from the source region; a gate electrode formed above the semiconductor layer between the drain region and the source region, insulated from the semiconductor layer; a second-conductivity-type drain contact region formed in the drain region and having a higher impurity concentration than the drain region; a drain wiring electrically connected to the drain region via the drain contact region; a first-conductivity-type substrate contact region formed adjacent to the source region; an
Ito Takao
Matsuoka Keisuke
Watanabe Kiminori
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Jackson Jerome
Kabushiki Kaisha Toshiba
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