Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-02-24
2001-04-24
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S339000, C257S487000
Reexamination Certificate
active
06222231
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a semiconductor element of a high voltage applied to, for example, a MOS transistor, an IGBT (Insulated Gate Bipolar Transistor), etc., and more particularly to a semiconductor device of a junction terminal structure and its manufacturing method.
In semiconductor devices of a high voltage, a high electric field may be locally generated and breakdown may occur depending upon the shape of a junction or by the influence of an external charge. To prevent such breakdown, a semiconductive film such as a polysilicon layer is formed on the surface of a semiconductor area of a low impurity density which will serve as a depletion layer.
As shown in
FIG. 7
, first, ion implantation and diffusion is executed in, for example, an n-type semiconductor substrate
11
. As a result, for example, a p-type anode layer
12
is selectively formed in a surface of the semiconductor substrate
11
, and, for example, an n
+
-type channel stopper layer
13
is selectively formed in the same surface of the substrate
11
with a predetermined distance from the anode layer
12
. Further, an n
+
-type cathode layer
14
is formed on the reverse surface of the semiconductor substrate
11
.
Subsequently, a thermally oxidized film (not shown) is formed on the semiconductor substrate
11
by thermal oxidation. Then, that portion of the thermally oxidized film, which is located between the anode layer
12
and the channel stopper layer
13
, is etched.
After that, a semiconductive film
15
with a thickness of, for example, 1.5 &mgr;m is formed by low pressure CVD on the entire top surface of the resultant structure. Then, those portions of the semiconductive film
15
, which are located on the anode layer
12
and the channel stopper layer
13
, are etched, and the semiconductive film on the reverse surface is selectively etched.
Thereafter, an oxide film
17
is formed on the entire top surface of the resultant structure by atmospheric pressure CVD. Then, those portions of the thermally oxidized film and the oxide film
17
, which are located on the anode layer
12
and the channel stopper layer
13
, are etched.
In the next stage, a metallic film formed of, for example, aluminum is provided on the entire top surface. This metallic film is then selectively etched so as to expose the surface of the oxide film
17
. As a result, an anode electrode
18
connected to the anode layer
12
and a channel stopper electrode
19
connected to the channel stopper layer
13
are formed.
Lastly, a cathode electrode
20
made of, for example, aluminum is formed on the reverse surface of the semiconductor substrate
11
.
The semiconductive film
15
is formed by low pressure CVD and mixed with oxygen, for example, of a predetermined density. However, since the film is formed by a high temperature treatment, it is in a state in which oxygen is liable to diffuse until, for example, it reaches a density higher than a predetermined value and a position out of a predetermined range. Accordingly, while transferring it from the furnace to the outside air, oxygen is absorbed from the atmosphere and diffuses to a deep portion of the semiconductive film
15
heated to a high temperature, whereby the semiconductive film
15
inevitably has an area of high oxygen concentration. As a result, as is shown in
FIG. 8
, the area in which the oxygen concentration varies extends from the surface of the semiconductive film
15
to a depth of about 1 &mgr;m, whereas an area in which the oxygen concentration is constant extends over a length of only 0.5 &mgr;m in the depth direction.
Therefore, when implanting carriers into the semiconductive film
15
, they are trapped in a high oxygen concentration area located at an upper portion of the film
15
. The charge accumulated in this area disturbs an electric field generated in the device under the semiconductive film, thereby degrading the breakdown voltage. Furthermore, since the semiconductive film
15
has a small area of constant oxygen concentration, the device shows a high resistivity.
BRIEF SUMMARY OF THE INVENTION
The present invention has been developed to solve the above-described problems, and aims to provide a semiconductor device capable of suppressing diffusion of oxygen in a semiconductive film to thereby minimize degradation of its breakdown voltage, and also to provide a method of manufacturing the semiconductor device.
To attain the aim, the invention uses the following means.
A first semiconductor device according to the invention comprises an element area formed in a surface of a semiconductor substrate and having a high voltage element; an anode layer formed in a surface of the element area of the semiconductor substrate; a channel stopper layer formed in a junction terminal section with a predetermined distance from the anode layer; a semiconductive film formed on the semiconductor substrate between the anode layer and the channel stopper layer; and a first insulating film covering the semiconductive film, wherein an area of the semiconductive film, in which the concentration of oxygen is constant, has a thickness sufficient to keep an electric field undisturbed.
A second semiconductor device according to the invention comprises an element area formed in a surface of a semiconductor substrate and having a high voltage element; an anode layer formed in a surface of the element area of the semiconductor substrate; a channel stopper layer formed in a junction terminal section with a predetermined distance from the anode layer; a semiconductive film formed on the semiconductor substrate between the anode layer and the channel stopper layer; a first insulating film covering the semiconductive film; and a second insulating film formed between the semiconductive film and the first insulating film, wherein an area of the semiconductive film, in which the concentration of oxygen is constant, has a thickness sufficient to keep an electric field undisturbed.
In the above-described first and second semiconductor devices, the semiconductive film is formed of a material obtained by adding at least one of oxygen, nitrogen and carbon to silicon. Further, the semiconductive film has a specific resistance of 10
7
-10
13
&OHgr;·cm. Moreover, the concentration of oxygen contained in an area of the semiconductive film is constant, which is located at a distance of 1 &mgr;m or more from the surface of the semiconductor substrate.
A first method of manufacturing a semiconductor device according to the invention comprises the steps of: selectively forming a first area of a second conductivity type in one surface of a semiconductor substrate of a first conductivity type; selectively forming a second area of a first conductivity type in the one surface of the semiconductor substrate with a predetermined distance from the first area; selectively forming a third area of the first conductivity type in another surface of the semiconductor substrate; forming a first insulating film on the semiconductor substrate; removing that portion of the first insulating film which is located between the first and second areas; forming a semiconductive film on the entire one surface of the resultant structure in a first furnace; forming a conducting film on the semiconductive film in the first furnace continuously the forming of the semiconductive film; carrying a wafer with the resultant structure out of the first furnace to thereby reduce the temperature of the wafer; carrying the wafer into a second furnace to remove the entire conducting film; removing those portions of the semiconductive film which are located on the first and second areas; forming a second insulating film on the resultant structure; and removing those portions of the first and second insulating films which are located on the first and second areas.
In the first method of the invention, the semiconductive film is formed of a material obtained by adding at least one of oxygen, nitrogen and carbon to silicon. Further, the semiconductive film has a specific resistance of 10
7
-10
13
&
Satou Shingo
Tsuchitani Masanobu
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Ngo Ngan V.
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