Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1998-09-15
2001-04-03
Loke, Steven (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S501000, C257S502000, C257S330000, C257S331000, C257S337000
Reexamination Certificate
active
06211549
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a high breakdown voltage semiconductor device in which a first semiconductor element with high breakdown voltage and a second semiconductor element acting as the control circuit thereof are integrally formed and more particularly to a high breakdown voltage semiconductor device in which the first semiconductor element with high breakdown voltage is formed of insulated gate bipolar transistors (IGBTs) having trench structures or the like and the control circuit is formed of a field effect transistor, bipolar transistor or the like formed of polycrystalline semiconductor.
2. Discussion of the Background
In the field of power electronics, an IGBT having a high speed switching characteristic and high power characteristic is widely used as an excellent power switching element. At the time of operation of this type of switching element, a control circuit such as a gate driver circuit or overcurrent protection circuit is simultaneously used.
Therefore, it is expected that the cost can be greatly reduced and the area of the device can be reduced by integrally and simultaneously forming the control circuit and the IGBTs.
Specifically, it is possible to form a thin film transistor (TFT) of polysilicon as the control circuit on the pads of the IGBTs with an insulating film disposed therebetween.
FIG. 1
is a cross sectional view showing the structure of a high breakdown voltage semiconductor device in which vertical IGBTs and a control circuit are integrated. In the high breakdown voltage semiconductor device, p-type impurity is selectively ion-implanted from the surface to form p-type base regions (wells)
5
by use of a resist mask. Then, a field oxide film
2
is formed by oxidation to a thickness of approximately 500 nm to 1 &mgr;m on the surface of an n
−
-type substrate
1
formed of single crystal silicon. On the rear surface of the n
−
-type substrate
1
, an n-type buffer layer
3
and p
+
-type drain layer
4
are formed by diffusion. Then, a drain electrode
4
a
is formed on the rear surface of p
+
-type drain layer
4
.
After this, amorphous silicon is deposited on the field oxide film
2
and then the amorphous silicon is annealed to grow as a polysilicon layer
6
in a solid phase. Then, a p-type active layer
7
is formed in the polysilicon layer by ion-implantation for a channel layer. After this, gate oxide films
8
,
9
and gate electrodes
10
,
11
of the vertical IGBT and TFT are simultaneously formed.
Then, n
+
-type source layers
12
of the vertical IGBT and an n
+
-type source region
13
and n
+
-type drain region
14
of the TFT are simultaneously formed in a self-alignment manner by ion-implantation using the gate electrodes
10
and
11
each as a mask. Electrodes are connected to the respective areas to complete an integrated structure of the vertical IGBTs and the control circuit.
Recently, as the IGBT, a trench structure is used instead of the planer structure described above in order to enhance the current density.
However, in order to form an IGBT of trench structure, it is required to form an n
+
-type source layer on the surface of the p-type base layer, then form a trench and bury a gate electrode in the trench. On the other hand, in the TFT, a gate electrode is formed and source and drain regions are formed in a self-alignment manner with the gate electrode used as a mask. Thus, in the TFT and IGBT of the trench structure, the order in which the gate electrode and the source region are formed is reversed, it is difficult to simultaneously form them, and it is not preferable to integrally form them.
BRIEF SUMMARY OF THE INVENTION
An object of this invention is to provide a high breakdown voltage semiconductor device in which a first semiconductor element including, for example, IGBTs of trench structure and a second semiconductor element including a TFT or bipolar transistor acting as a control circuit thereof are easily integrated.
The main feature of this invention lies in that the IGBT of trench structure and the control circuit including a TFT or bipolar transistor can be integrated by forming the device structure such that the source layer of the first conductivity type or the buried gate electrode of the first semiconductor element of trench structure and part of the second semiconductor element can be simultaneously formed.
In order to attain the above object, a semiconductor device of a first aspect of this invention comprises a first semiconductor element and a second semiconductor element, wherein the first semiconductor element includes a base layer of a first conductivity type with high resistance having a first and a second main surface; a base layer of a second conductivity type formed on the first main surface of the base layer of the first conductivity type; a source layer of the first conductivity type formed in a surface area of the base layer of the second conductivity type; a drain layer of anyone of the first and the second conductivity type formed on anyone of the first and the second main surface of the base layer of the first conductivity type; a gate electrode buried and formed in a trench which penetrates the source layer of the first conductivity type and the base layer of the second conductivity type with a first insulating film disposed therebetween; a source electrode formed in contact with the source layer of the first conductivity type and the base layer of the second conductivity type; and a drain electrode formed in contact with the drain layer, and the lateral semiconductor element includes a gate layer of the first conductivity type formed in another surface area of the base layer of the second conductivity type; a base region of the second conductivity type formed on the gate layer of the first conductivity type with a second insulating film disposed therebetween; and a source and a drain region of the first conductivity type insulatively formed on the first main surface to hold the base region of the second conductivity type therebetween.
The source layer of the first conductivity type can be formed to have the same depth as the gate layer of the first conductivity type.
The gate electrode includes a first gate electrode formed in and along the trench with the gate insulating film disposed therebetween and a second gate electrode formed on the first gate electrode with a third insulating film disposed therebetween to fill the trench, and the first gate electrode may have the same impurity concentration as the source region of the first conductivity type.
The second gate electrode may have substantially the same impurity concentration as the drain region of the first conductivity type.
A high breakdown voltage semiconductor device according to a second aspect of this invention comprises a first semiconductor element and a second semiconductor element, wherein the first semiconductor element includes a base layer of a first conductivity type with high resistance having a first and a second main surface; a base layer of a second conductivity type formed on the first main surface of the base layer of the first conductivity type; a source layer of the first conductivity type formed in a surface area of the base layer of the second conductivity type; a drain layer of anyone of the first and the second conductivity type formed on anyone of the first and the second main surface of the base layer of the first conductivity type; a gate electrode buried and formed in a trench which penetrates the source layer of the first conductivity type and the base layer of the second conductivity type with a first insulating film disposed therebetween; a source electrode formed in contact with the source layer of the first conductivity type and the base layer of the second conductivity type; and a drain electrode formed in contact with the drain layer; and the second semiconductor element includes a base region of the second conductivity type insulatively formed on a surface of the base layer of the second conduct
Funaki Hideyuki
Nakagawa Akio
Kabushiki Kaisha Toshiba
Loke Steven
Oblon, Spivak, McClelland, Maier & Neustadt, P.C
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