Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1998-12-04
2001-02-06
Loke, Steven H. (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S329000, C257S341000
Reexamination Certificate
active
06184555
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a field effect-controllable semiconductor component comprising a semiconductor body
a) having an inner zone of the first conduction type, which adjoins one of the surfaces of the semiconductor body,
b) having a drain zone, which adjoins the inner zone,
c) having at least one base zone of the second conduction type, which is embedded in said surface of the semiconductor body,
d) having at least one source zone of the first conduction type, which is embedded in the base zone,
e) having at least one source electrode, which in each case makes contact with a base zone and the source zone embedded therein, and
f) having a gate electrode, which is insulated from the entire semiconductor body.
BACKGROUND OF THE INVENTION
Such vertical field effect-controllable semiconductor components have long been prior art. On the one hand, they are known as VMOS field-effect transistors if the drain zone adjoining the inner zone is of the same conduction type as the inner zone. On the other hand, such field effect-controllable semiconductor components are known as IGBTs if the drain zone is designed as anode zone and is of the opposite conduction type to the inner zone.
Furthermore, the invention also relates to field effect-controllable semiconductor components comprising a semiconductor body of the first conduction type,
a) having a source zone and a drain zone of the second conduction type, which are spatially separate from one another and are respectively provided with a source electrode and a drain electrode,
b) having a drift zone of the second conduction type, which lies between the source zone and the drain zone and adjoins the drain zone, and
c) having a gate electrode, which is insulated from the surface of the semiconductor body and partially covers the source zone and the drift zone.
Such lateral field effect-controllable semiconductor components have been known as lateral MOSFETs for a long time.
The semiconductor components mentioned in the introduction are thoroughly discussed in the book by Jens Peer Stengl; Jenö Tihanti: Leistungs-MOSFET-Praxis [Power MOSFET Practice], 2nd edition, Pflaumverlag, Munich, 1992.
All of the semiconductor components mentioned in the introduction have the inherent disadvantage that the forward resistance R
on
of the drain-source load path increases as the dielectric strength of the semiconductor component increases, since the thickness of the inner zone or of the drift zone has to increase. In the case of VMOS MOSFETs, the forward resistance R
on
per unit area is approximately 0.20 ohm/m
2
at a voltage of 50 V and rises to a value of approximately 10 ohm/m
2
, for example, at a reverse voltage of 1000 V.
In order to eliminate this disadvantage, U.S. Pat. No. 5,216,275 presents a vertical MOSFET in which, instead of a homogeneous, for example epitaxially grown inner zone, layers of the first and of the second conduction type are present alternately. The fundamental structure is shown there in particular in
FIGS. 4 and 5
and the associated parts of the description. In particular, the alternating p-type and n-type layers are in that case respectively connected to the base zones and to the drain zones. However, this leads to a severe limitation in the design of a semiconductor component since the edge regions such as the base and drain regions, can no longer be configured freely.
The object of the present invention, therefore, is to develop the field effect-controllable semiconductor components mentioned in the introduction in such a way that, despite a high reverse voltage, a low forward resistance is present and the disadvantages evinced in the prior art are eliminated.
SUMMARY OF THE INVENTION
According to the invention, this object is achieved by means of a vertical power semiconductor component of the type mentioned in the introduction in which one or more depletion zones of the second conduction type and one or more complementary depletion zones of the first conduction type are provided in the inner zone, the total quantity of the doping of the depletion zones corresponding approximately to the total quantity of the doping of the complementary depletion zones.
Furthermore, the object is achieved by means of a field effect-controllable semiconductor component of lateral design in which a multiplicity of depletion zones. of the second conduction type are provided in the drift zone, the total quantity of the doping of the drift zone corresponding approximately to the total quantity of the doping of the depletion zones. Moreover, the depletion zones are embedded in the inner zone, free of direct contact to either the base or source zones. It will be convenient to describe such depletion zones as floating within the inner zone.
The invention has the advantage that by simple introduction of depletion zones and complementary depletion zones—preferably paired in the case of V-MOSFETs and IGBTs—, in particular along the current path, on the one hand a good conductivity is ensured by the complementary depletion zones and on the other hand these regions mutually deplete one another in the event of an increase in the drain voltage, as a result of which a high reverse voltage remains secure.
If a reverse voltage is applied to the semiconductor components designed in this way, then a space charge zone forms proceeding from the pn junction between the inner zone and the base zone or zones in the case of the vertical semiconductor components, the extent of which space charge zone grows as the reverse voltage increases. If the space charge zone borders on the depletion zones, then the latter are connected in a high impedance manner to the base zones via the depleted region of the inner zone. If the reverse voltage continues to rise, the space charge zone extends further, with the result that some of the charge carriers from the depletion zones and complementary depletion zones are also depleted. In the event of a further increase in the reverse voltage, the charge carriers are then completely depleted from a large part of the inner zone and from the depletion zones and complementary depletion zones. The space charge zone is thereby shifted in the direction of the drain or anode zone. At maximum applied voltage, the depletion zones and the complementary depletion zones lie completely in the space charge zone. The function of the depletion zones and complementary depletion zones in the lateral MOSFETs is analogous to this.
Since the total quantity of doping in the depletion zones corresponds approximately to the total quantity of doping in the complementary depletion zones, it is ensured that in the event of an increase in the drain voltage, the p-n-type regions formed in this way mutually deplete one another completely, i.e. behave like a single insulator zone, as a result of which a high reverse voltage remains secure.
In one embodiment of the present invention, the depletion zones and the complementary depletion zones are in each case arranged in pairs in the inner zone. Typically, the depletion zones and complementary depletion zones introduced in pairs in the inner zone then have a distance from one another which is greater than or equal to zero and less than or equal to the width of the space charge zone.
In an alternative embodiment of the present invention, there is introduced in the inner zone a single complementary depletion zone in which a multiplicity of depletion zones are introduced, the distance between the depletion zones within the complementary depletion zone then typically being less than or equal to the width of the space charge zone between the depletion zone and the complementary depletion zone.
In this embodiment, the depletion zones introduced in the complementary depletion zone may have an approximately spherical, parallelepipedal or irregular shape .
The complementary depletion zone expediently corresponds to the entire inner zone in a development of this alternative embodiment of the present invention.
Finally, the invention also relates to a method for fabricating depletion zones
Geiger Heinrich
Strack Helmut
Tihanyi Jeno
Loke Steven H.
Ostroff Irwin
Siemens Aktiengesellschaft
Torsiglieri Arthur J.
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