Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2001-10-22
2004-10-12
Thomas, Tom (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S242000, C257S263000, C257S328000, C257S329000, C257S409000
Reexamination Certificate
active
06803629
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a field-effect controllable semiconductor component having a low on resistance, high current-carrying strength and a high breakdown voltage, in which a first and a second load terminal can be contact-connected at one side of the semiconductor body.
Published German Patent Application DE 196 04 043 A1 discloses a vertical MOSFET which has a heavily n-doped substrate with a more weakly n-doped epitaxial layer lying above it. P-doped channel zones are introduced into the epitaxial layer, and heavily n-doped source zones are embedded, in turn, in the channel zones. These source zones can be contact-connected at the surface of the semiconductor body. Gate electrodes make it possible to form a conductive channel in the channel zone between the source zone and a drift zone which is formed in the epitaxial layer between the channel zone and the substrate. Furthermore, p-doped first compensation zones and n-doped second compensation zones are formed in the epitaxial layer, resulting first in low on resistance of the MOSFET when the gate electrode is driven, and in a high reverse voltage, or breakdown voltage, when the gate electrode is not driven. When the gate electrode is driven, the n-doped regions in the epitaxial layer enable charge to be transferred between the source zone and the heavily n-doped substrate which forms the drain zone. When the gate electrode is not driven and a drain-source voltage is applied, a space charge zone forms proceeding from the source zone, or the channel zone, and has the effect that free charge carriers of the first and second compensation zones recombine with one another, whereby the number of free charge carriers in the epitaxial layer is considerably reduced, and this results in a high breakdown voltage.
In the known vertical MOSFET, the substrate forms the drain zone which can be contact-connected from the rear side of the semiconductor body, that is to say the side opposite to the side of the source terminal.
Such an arrangement of the source terminal and drain terminal at opposite sides of the semiconductor body is disadvantageous for those applications in which a further chip is applied to the front side of the semiconductor body, or of a chip, in which the MOSFET is accommodated, especially when the terminals of which further chip have to be connected to the source terminal and the drain terminal of the MOSFET. By way of example, a diode may be realized in the second chip, which diode, in specific applications, is connected between the source terminal and the drain terminal of a MOSFET.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a field-effect controllable semiconductor component which overcomes the above-mentioned disadvantages of the prior art apparatus of this general type. In particular, it is an object of the invention to provide a field-effect controllable semiconductor component having a low on resistance, high current-carrying strength and a high breakdown voltage, in which a first and a second load terminal can be contact-connected at one side of the semiconductor body.
With the foregoing and other objects in view there is provided, in accordance with the invention, a field-effect controllable semiconductor component that has a semiconductor body having a first layer of a first conduction type, and lying above the layer, a second layer of the first conduction type. The first layer preferably is doped more heavily than the second layer. At least one first terminal zone is formed in the second layer, which terminal zone can be contact-connected at a first surface of the semiconductor body. The at least one first terminal zone is surrounded within the second layer by a channel zone of a second conduction type.
Furthermore, compensation zones of the second conduction type are formed in the second layer. According to the invention, a second terminal zone of the first conduction type is formed in the second layer, which terminal zone can be contact-connected at the first surface of the semiconductor body. The second terminal zone is formed such that it is spaced apart from the at least one first terminal zone in the lateral direction of the semiconductor body.
In the case of a MOS transistor, the first terminal zone forms the source zone of the transistor, the second terminal zone forms the drain zone of the transistor and a control electrode which is arranged adjacent to the channel zone and is insulated from the semiconductor body forms the gate electrode of the transistor.
The second terminal zone is preferably connected to the first layer by means of a connecting zone which is a good electrical conductor and extends in the vertical direction in or along the second layer. This first layer is preferably doped more heavily than the second layer, and thus conducts better. When a drive potential is applied to the control electrode and a voltage is applied between the first and second terminal zones, a charge current occurs in the semiconductor component, which charge current, in a drift zone formed between the channel zone and the first layer, having emerged from the channel zone, runs in the vertical direction of the semiconductor body to the heavily doped first layer, from where the charge carriers pass via the connecting zone to the second terminal zone.
When the control electrode is not driven and a voltage is applied between the first and second terminal zones, a space charge zone propagates in the semiconductor body proceeding from the channel zone. If this space charge zone encompasses one of the compensation zones, then free charge carriers of this compensation zone recombine with free charge carriers from the regions of the second layer which surround the respective compensation zone. As the reverse voltage increases, or the space charge zone propagates to an increasing extent, charge carriers are thus depleted in the second layer, resulting in a high breakdown voltage. The number of charge carriers of the first conduction type in the second layer preferably corresponds to the number of charge carriers of the second type in the compensation zones, so that the second layer and the compensation zones can mutually completely deplete one another, i.e. there are no longer any free charge carriers in the second layer at the maximum possible reverse voltage.
In accordance with an added feature of the invention, the connecting zone is formed as a heavily doped zone of the first conduction type which extends, in the vertical direction of the semiconductor body, from the second terminal zone that is arranged in the region of the first surface as far as the first layer. In this case, the second terminal zone is preferably formed in the edge region of the semiconductor body.
In accordance with a concomitant feature of the invention, the first layer and the second terminal zone are connected by means of a layer which is a good electrical conductor and is formed on a, preferably inclined, side area of the semiconductor body.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a vertical field-effect transistor with compensation zones and terminals at one side of a semiconductor body, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 5455442 (1995-10-01), Neilson et al.
patent: 6479876 (2002-11-01), Deboy et al.
patent: 6512268 (2003-01-01), Ueno
patent: 6639272 (2003-10-01), Ahlers et al.
patent: 2002124675 (2002-04-01), No
Greenberg Laurence A.
Infineon - Technologies AG
Mayback Gregory L.
Stemer Werner H.
Warren Matthew E.
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