Semiconductor component which can be controlled by a field...

Details Semiconductor component which can be controlled by a field... Semiconductor component which can be controlled by a field...

1999-03-01

2001-08-07

Thomas, Tom (Department: 2811)

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

Field effect device

Having insulated electrode

C257S328000

Reexamination Certificate

active

06271562

ABSTRACT:

BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a power semiconductor component that can be controlled by a field effect and has a multiplicity of parallel-connected individual components disposed in each case in cells. The cells are disposed tightly packed on a relatively small space in a cell array. The cell arrary includes a semiconductor body, having:
a) at least one inner zone of a first conductivity type, which borders at least partially on a first surface of the semiconductor body;
b) at least one drain zone which borders on the inner zone,
c) at least one base zone embedded in the semiconductor body on the first surface and having a second conductivity type;
d) at least one source zone embedded in the base zones and having the first conductivity type;
e) at least one source electrode which in each case makes contact with the base zones and the source zones embedded therein; and
f) at least one gate electrode insulated against the entire semiconductor body.
Such semiconductor components that can be controlled by a field effect have long been part of the prior art. On the one hand, they are known as MOS field effect transistors to the extent that the drain zone bordering on the inner zone is of the same conductivity type as the inner zone. On the other hand, such semiconductor components which can be controlled by a field effect are known as insulated gate bi-polar transistors (IGBTs) to the extent that the drain zone is constructed as an anode zone and is of the opposite conductivity type to the inner zone.
Such vertical MOSFETs or IGBTs are described in detail in Jens Peer Stengl, Jenoe Tihanyi, Leistungs-MOSFET-Praxis [Power MOSFET Praxis], 2nd Edition, Pflaum-Verlag, Munich, 1992.
U.S. Pat. No. 5,008,725 discloses a generic semiconductor component in which a multiplicity of parallel-connected individual components which are disposed in each case in cells and are disposed tightly packed in a cell array.
Inherent in all the semiconductor components mentioned at the beginning is the disadvantage that the forward resistance per unit area RDS
on
, that is to say the resistance between a drain terminal and source terminal in the turned-on state, increases with the increasing voltage endurance of the semiconductor component. The reason for this is the thickness of the inner zone, which is also designated as the drift zone in power semiconductor components and which essentially determines the voltage endurance. When a reverse voltage is applied, the drift zone takes up the reverse voltage and thus prevents undesired switching-through in the reverse direction. The thickness of the drift zone is thus approximately proportional to the reverse voltage which can be taken up by the drift zone, and thus to the voltage endurance of the power semiconductor component. In the case of vertically constructed power MOSFETs, the forward resistance per unit area RDS
on
is usually approximately 12 &OHgr;mm
2
for a voltage of 600 V.
It is therefore necessary for doping-structured bulk regions to be introduced into the drift zone of such semiconductor components in order to reduce the forward resistance per unit area. Semiconductor components with doping-structured bulk regions in the drift zone are described in detail in International Patent Application WO 97/29518 and in U.S. Pat. No. 4,754,310. Technology described there permits a substantial reduction in the forward resistance per unit area. By reducing the chip area, it is possible to produce very cost-effective components in conjunction with a forward resistance RDS
on
per unit area that is the same or better.
However, as a consequence of introducing additional charge carriers of the opposite conductivity type into the drift zone, a substantially smaller portion of the active chip area (typically 60%) is available for transporting the load current. In addition, as a consequence of the high voltage take-up of the semiconductor component and of the doping-structured bulk regions prescribed by the technology, a very high electric transverse field, which leads to an additional constriction of the active chip area participating in the current flow, is built up in the saturation region of the characteristic diagram which is traversed, for example, upon switching inductive loads in short-circuit operation. The current density in this current filament reaches values in the range of a few kA cm
−2
as a result of this. If the electron concentration necessary for the forward current reaches the region of the basic doping of the drift zone, the electric vertical field likewise rises steeply, the characteristic of its field distribution rising as a function of the depth. However, the reverse voltage of the semiconductor component drops as a result, and charge carriers are generated by impact ionization.
As a result of this, a critical current density J
crit
is defined which specifies the maximum permissible current density in the drift zone, and for which the electric vertical field is still negligibly small. The critical current density J
crit
is defined as follows in this case:
J
crit
≦xqN
D
&ngr;
Sat
.
Here, q denotes the elementary charge, N
D
the doping concentration in the drift zone, and &ngr;
Sat
the saturation drift velocity (typically 107 cm sec
−1
). X specifies a so-called reduction factor whose value is between 0 and 1. Typically, the user selects a reduction factor x between 0.1 and 0.2 depending on application.
In order to avoid the critical current density from being reached, relatively large cell grid spacings are used in the technology currently employed for power semiconductor components, in particular power MOSFETS, because of the absolutely dominant epitaxial component in the total forward resistance of the semiconductor component. In the case of a MOSFET configured for a reverse voltage of 600 V, the epitaxial component is, for example, approximately 99% of the forward resistance. For such a MOSFET, the individual cells can have a relatively large cell grid spacing of L
R
≧40 &mgr;m. However, with individual cells which are so large it is the case, on the one hand, that the channel width per cell area used is relatively slight. On the other hand, as a consequence of the limitation of the maximum permissible power loss, the high total forward resistance of the MOSFET permits only a relatively low forward current of typically 6 to 8 A.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a semiconductor component which can be controlled by a field effect that overcomes the above-mentioned disadvantages of the prior art devices of this general type, which can be controlled by a field effect in such a way that despite a high reverse voltage, a low forward resistance is achieved and the disadvantages indicated in the prior art are eliminated.
With the foregoing and other objects in view there is provided, in accordance with the invention, an improved power semiconductor component which can be controlled by a field effect and has a multiplicity of parallel-connected individual components disposed in each case in cells, the cells are disposed tightly packed on a relatively small space in a cell array, the improvement includes:
a semiconductor body having a surface, including:
a) at least one inner zone of a first conductivity type bordering at least partially on the surface;
b) at least one drain zone bordering the at least one inner zone;
c) at least one base zone disposed in each of the cells and having a second conductivity type, the at least one base zone is embedded in the surface;
d) at least one source zone disposed in each of the cells and having the first conductivity type, the at least one source zone is embedded in the at least one base zone; and
e) shadow regions are disposed in at least one of the at least one source zone of the cells, the shadow regions reduce an effective ratio of a channel width to the channel length;
at least one source electrode makes contact with the at least one base zone and the at least one source zone; an

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