Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device – With switching speed enhancement means
Reexamination Certificate
2001-05-30
2004-02-03
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
With switching speed enhancement means
C257S329000
Reexamination Certificate
active
06686614
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a semiconductor switching element with an integrated Schottky diode.
It is known to use semiconductor switching elements, such as for example MOSFETs (Metal-Oxide Field-Effect Transistors), as switches for driving loads.
FIG. 1
shows an application example in which a MOSFET T
1
is used as a freewheeling element in a switching converter (buck converter) which serves for applying a DC voltage V
1
to a load RL. If in the exemplary embodiment a series connection including a coil L and a parallel connection made up of a capacitance C and a load RL is connected to a supply voltage V
1
via a second MOSFET T
2
with MOSFET T
1
turned off, a current flows through the coil L. After the second MOSFET T
2
is turned off, a voltage is induced in the coil L and could lead to the switching converter being destroyed or damaged if the first MOSFET T
1
were not conducting in order to complete the circuit of the coil L and the capacitance C with the load connected in parallel. Before the MOSFET Ti, driven by a drive circuit IC, conducts fully in this case, a Schottky diode D
1
, connected in parallel with the drain-source path of the MOSFET T
1
, takes over the freewheeling current and consequently prevents destruction of the switching converter.
Use of the MOSFET T
1
has the advantage of lower power loss in comparison with simple use of a diode, since a lower voltage drops across the conducting MOSFET T
1
than across a conducting diode. Unlike in the case of diodes with a pn junction, a charge which could lead to delayed blocking of the diode is not stored in the Schottky diode in the conducting state. With the Schottky diode, the high switching frequencies required in switching converters can consequently be achieved.
Until now, a separate MOSFET and a separate Schottky diode have been used as freewheeling elements, connected in the way represented in FIG.
1
.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a semiconductor switching element and a method of producing the switching element which overcomes the above-mentioned disadvantageous of the prior art apparatus of this general type. In particular, it is an object of the invention to provide a semiconductor switching element in which a transistor which can be controlled by a field effect and a Schottky diode are integrated in a semiconductor body.
With the foregoing and other objects in view there is provided, in accordance with the invention an integrated semiconductor switching element, that includes a semiconductor body having a first connection zone of a first conduction type and a second connection zone of the first conduction type. A body zone of a second conduction type is located in the semiconductor body. The body zone is located between the first connection zone and the second connection zone. A control electrode is located alongside the body zone and is insulated from the semiconductor body. A Schottky barrier is located on the second connection zone. A first connection electrode is electrically conductively connected to the first connection zone and to the Schottky barrier.
In accordance with an added feature of the invention, the body zone is formed in a well-like manner in the second connection zone; the first connection zone is formed in a well-like manner in the body zone; a contact hole is formed in the semiconductor body and passes through the first connection zone and the body zone; and the Schottky barrier is located in the contact hole.
In accordance with an additional feature of the invention, the contact hole has a bottom and side walls; the Schottky barrier is formed on the bottom of the contact hole; and a second insulation layer is located on the side walls of the contact hole.
In accordance with another feature of the invention, the semiconductor body has a front side; the first connection electrode at least partially covers the side walls and the bottom of the contact hole; and the first connection electrode at least partially covers the front side of the semiconductor body for electrically bonding the first connection zone.
In accordance with a further feature of the invention, the Schottky barrier has platinum silicide.
With the foregoing and other objects in view there is provided, in accordance with the invention a process for producing the semiconductor switching element, which includes steps of: providing a semiconductor body having a front side and having a first connection zone of a first conduction type and a second connection zone of the first conduction type, and configuring the first connection zone and the second connection zone one on top of the other; providing the semiconductor body with a body zone of a second conduction type that is located between the first connection zone and the second connection zone; producing at least one control electrode that is insulated from the semiconductor body and that is located alongside the body zone on the front side of the semiconductor body; producing the control electrode such that the first connection zone is at least partially exposed and defines exposed regions of the first connection zone on the front side of the semiconductor body; producing a first contact hole in the semiconductor body that passes from the front side of the semiconductor body through the first connection zone and through the body zone and that reaches into the second connection zone; producing a Schottky barrier in the second connection zone in the contact hole; and producing a first connection electrode that electrically bonds the Schottky barrier and the exposed regions of the first connection zone.
In accordance with an added mode of the invention, before producing the first connection electrode, an insulation layer is applied, at least to regions of the body zone that are exposed in the contact hole.
In accordance with an additional mode of the invention, before producing the first connection electrode, the side faces of the contact hole are completely covered with a first insulation layer.
In accordance with another mode of the invention, the step of producing the control electrode includes: applying an insulation layer to the front side of the semiconductor body; applying an electrode layer to the insulation layer; producing a second contact hole in the electrode layer and in the insulation layer such that the first connection zone is at least partially exposed on the front side of the semiconductor body; and applying a further insulation layer to exposed regions of the control electrode.
In accordance with a further mode of the invention, the first contact hole has a smaller diameter than the second contact hole.
In accordance with a concomitant mode of the invention, the Schottky barrier is produced by doping platinum silicide into the second connection zone.
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 semiconductor switching element with integrated Schottky diode and process for its production, 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: 3956527 (1976-05-01), Magdo et al.
patent: 4823172 (1989-04-01), Mihara
patent: 5886383 (1999-03-01), Kinzer
patent: 6049108 (2000-04-01), Williams et al.
patent: 6191447 (2001-02-01), Baliga
patent: WO 00/51167 (2000-08-01), None
Flynn Nathan J.
Locher Ralph E.
Mondt Johannes P
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