Semiconductor device containing a lateral MOS transistor

Details Semiconductor device containing a lateral MOS transistor Semiconductor device containing a lateral MOS transistor

1998-09-25

2001-01-23

Loke, Steven H. (Department: 2811)

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

Field effect device

Having insulated electrode

C257S329000, C257S330000, C257S331000, C257S339000, C257S347000

Reexamination Certificate

active

06177704

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device containing a lateral MOS transistor. More specifically, the present invention relates to technology suitable for use in a high breakdown voltage, low on-resistance, lateral power MOSFET that can be microminiaturized.
2. Description of the Related Art
A high breakdown voltage lateral trench MOSFET disclosed in the Japanese Patent Application Laid-Open No. 8-97411 has, as shown in
FIG. 12
, a p-type well region
2
formed on a p-type substrate
1
, a diffusion layer comprising a source region
9
and a body region
8
formed within the above well region
2
using a double diffusion process with a self alignment technique, and a gate oxide layer
6
and a gate electrode
7
located on top of the structure. Further, a trench
3
is formed by a trench work within a drain drift region
4
to secure the drift length for accomplishing a high breakdown voltage. In the above-described structure, when a gate voltage is applied, electric current flows from a drain region
11
through the drain drift region
4
along the perimeter (A-B-C-D) of the trench
3
to reach a channel region
10
. Note that the symbol
5
in
FIG. 12
represents an insulation layer formed within the trench
3
.
The high breakdown voltage lateral trench MOSFET of the Japanese Patent Application Laid-Open No. 8-97411 has the advantage of achieving a high breakdown voltage by allowing the drift current to flow through the trench region
3
thereby securing a sufficient drift length. However, since the breakdown voltage is determined by the length of the drain drift region
4
, it is necessary to make the drift length longer to obtain a higher breakdown voltage. This has presented a disadvantage of a steep rise in on-resistance of a transistor through the increased resistive component of a drain drift region
4
. Moreover, when the drain drift region
4
is created by ion implantation and thermal diffusion processes through the trench region
3
, this creates an overlapped region between the n-drain drift region
4
and the p-channel region
10
. This leads to an increase in the residual crystal defects or crowding of the current flow paths within the diffusion layer which forms a channel, thereby making the device liable to cause a reduction in electron mobility.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor device containing a lateral MOS transistor with a high breakdown voltage and a low on-resistance, which can be fabricated with a decreased dimension for the drain drift region and, therefore, can be microminiaturized.
The semiconductor device containing a lateral MOS transistor according to the present invention is characterized in comprising:
a semiconductor substrate;
a first semiconductor layer of a first conductive type formed on the semiconductor substrate to constitute a drain drift region;
a second semiconductor layer of a second conductive type formed in the first semiconductor layer to constitute a body region, the body region including a portion in which a channel region is formed;
a third semiconductor layer of the first conductive type formed in the second semiconductor layer to constitute a source region;
a fourth semiconductor layer of the first conductive type formed in the first semiconductor layer to constitute a drain region; and
an insulation layer disposed in a trench which is formed in the first semiconductor layer by filling the trench with insulating material along two sides of the fourth semiconductor layer;
wherein the fourth semiconductor layer extends greater than the insulation layer in depth to contact the first semiconductor layer below the insulation layer.
In the above described semiconductor device, insulation layers are formed at the two sides of a drain region (the fourth semiconductor layer) and the drain region is formed into a deeper region than the insulation layer. By having the drain region come into contact with the drain drift region (the first semiconductor layer) at a portion beneath the insulation layer, the drift length can be shortened while ensuring a sufficient level of breakdown voltage.
In other words, by providing an insulation layer at a portion of the boundary between the drain region and the drain drift region (from the top of the first semiconductor layer extending to a required depth), the electric field applied to the drain-source regions is distributed with a high degree of uniformity within the above-mentioned insulation layer. Since the above structure is less prone to uneven electric field distribution, this allows a greater breakdown voltage for the device.
The structure of the semiconductor device of the present invention, as shown for example in
FIG. 1
, has an insulation layer to ensure the breakdown voltage by allowing the drift current to flow through the path (A-B-C) along the two sides of the insulation layer. The structure at the same time contributes to shortening the drain length, and therefore to reducing the on-resistance.
Since the design permits a drain length on a plane as projected laterally on the semiconductor substrate to be relatively short for a same required breakdown voltage, this enables a reduction in projected area of the drain drift region to accomplish a microminiaturization of the device.
Further, since the insulation layer is arranged to cover both sides of the drain region so as to block the impurity diffusion in the horizontal direction of the drain region, the doping level inside the drain region can be made sufficiently high. Consequently, the drain drift region, the drain region, and the drain electrode can be connected with a good ohmic contact.
While the drain region can be constituted of either a single layer or a multi-layer structure, considering the depth of the drain region, it is desirable to ensure a better ohmic contact be established, for example, by building a first drain region having a higher dopant concentration level near the region contacting the drain electrode, and a second drain region having a lower dopant concentration where it connects to the lightly doped drain drift region. Additionally, the ohmic contact can also be improved by causing a drain electrode to be formed to penetrate into the drain region.
The breakdown voltage in the aforementioned semiconductor device can be controlled by regulating the width and depth of the insulation layer.
Moreover, although there are no specific limitations for the structure of the insulated gate in the semiconductor device of the present invention, further microminiaturization can be achieved by designing the semiconductor device with a trench gate structure.
Specifically, it is desirable that the semiconductor device in the present invention contain a lateral MOS transistor which comprises:
a semiconductor substrate;
a drain drift region of a first conductive type formed on said semiconductor substrate;
an insulation layer disposed in a trench which is formed in said drain drift region by filling a trench with insulating material;
a drain region formed along one side of the insulation layer;
a body region of a second conductive type located on the other side of the insulation layer and formed in the drain drift region, the body region including a portion in which a channel region is formed;
a source region of the first conductive type formed on the surface of the body region; and
a trench gate having a gate insulation layer formed along the surface of a trench boring through the source region, the body region and the drain drift region, and a gate electrode formed in the trench and arranged through the gate insulation layer;
wherein the drain region extends greater than the insulation layer in depth to contact the drain drift region below the insulation layer.
In the above described semiconductor device, the drift current mainly flows from a direction parallel to the main surface of the above-mentioned semiconductor substrate in a direction along the aforementioned gate insulation layer, thereby acc

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