Active solid-state devices (e.g. – transistors – solid-state diode – Specified wide band gap semiconductor material other than... – Diamond or silicon carbide
Reexamination Certificate
2000-09-15
2001-11-20
Tran, Minh Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Specified wide band gap semiconductor material other than...
Diamond or silicon carbide
C257S472000, C257S476000, C257S481000, C257S485000, C257S603000, C257S653000
Reexamination Certificate
active
06320205
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an edge termination for a semiconductor component formed of silicon carbide and to a Schottky diode having an edge termination. The present invention also relates to a method for producing a semiconductor component having such an edge termination.
The invention relates predominantly to asymmetrically blocking semiconductor components having planar edge terminations. The invention relates in particular to semiconductor components in the form of Schottky diodes. Such semiconductor components and their method of operation have been known for a long time and require no further description.
In semiconductor components of such a type, in particular in the case of high-voltage-resistant power semiconductor components, voltage breakdowns preferably occur in the edge area, since the electrical field strength there is particularly large owing to the curvature of the doped regions as a result of the edge. In order to avoid such voltage breakdowns, edge terminations are provided, which are disposed in the form of rings and typically completely enclose the semiconductor component. The edge terminations weaken or reduce local field strength peaks in the edge area of the semiconductor component. Undesirable voltage breakdowns in the edge area can thus be avoided, and the semiconductor component remains serviceable. A large number of different edge terminations for semiconductor components are described in a reference by B. J. Baliga, titled “Modern Power Devices”, John Wiley and Sons, 1987.
Furthermore, U.S. Pat. No. 5,486,718 describes edge terminations in which chains of zener diodes containing polysilicon are disposed in a spiral shape in the edge area. These zener diodes are intended to control the potential profile of the electrical field in the edge area.
On page 437 of the reference titled “Modern Power Devices”, mentioned above, edge terminations for Schottky diodes are described. Here, one of the edge terminations is in the form of a guard ring that surrounds the Schottky contact and forms a pn-junction with the remaining semiconductor region. Alternatively, the Schottky contact can also be provided directly with an edge termination formed from field plates, that is to say without a pn-junction.
Schottky diodes are majority-carrier semiconductor components and are thus particularly suitable for high-frequency applications, that is to say for applications which require very fast switching processes and a reverse current which is as low as possible during off-commutation. Silicon Schottky diodes are, however, limited to reverse voltages of about 100 V owing to their very large reverse current.
Thus, for these reasons, it is becoming ever more attractive to use other semiconductor materials, which do not have the disadvantages mentioned above, to produce Schottky diodes.
One such material, for example, is silicon carbide (SiC). U.S. Pat. No. 5,789,311 describes an SiC Schottky diode. SiC semiconductor components and SiC Schottky diodes have excellent electrical and physical characteristics in comparison with those semiconductor components produced from silicon, and a number of these will be described in the following text.
The breakdown field strength of SiC is greater than that of silicon by a factor of 10 to 15. Owing to the very high breakdown field strength, SiC semiconductor components can be made very small, which advantageously also results in a very low ON resistance. SiC semiconductor components thus offer a particularly good compromise between a high blocking capability and a low forward voltage.
Owing to the fact that SiC has a considerably shorter charge carrier life than silicon, SiC is particularly suitable for semiconductor components for radio-frequency applications, since considerably higher switching speeds can be achieved here. Owing to the fact that an SiC Schottky diode has virtually no minority charge carriers, the charge carriers can be depleted very quickly during off-commutation, thus making high switching speeds possible.
In comparison to silicon, SiC is thermally extremely stable-SiC has a sublimation temperature of more than 1600° C.—and its thermal conductivity is greater by a factor of 3. Particularly owing to the fact that SiC has a very wide energy gap and, associated with this, a low intrinsic concentration, SiC is particularly suitable for applications at high temperatures.
A major disadvantage of semiconductor components composed of SiC is, however, that high temperatures (>1500° C.) are typically required to heal and activate implanted doped regions, and these high temperatures generally do not allow such SiC semiconductor components to be processed in conventional workshops set up for silicon technology.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an edge termination for a semiconductor component, a Schottky diode having an edge termination, and a method for producing the Schottky diode which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type,
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor component, containing a semiconductor body formed of silicon carbide; an insulation layer disposed on the semiconductor body; and an edge termination having at least one diode chain disposed on the insulation layer and thereby being insulated from the semiconductor body. The diode chain has a large number of semiconductor layers formed of alternating conductivity types.
With the foregoing and other objects in view there is further provided, in accordance with the invention, a Schottky diode containing a semiconductor body of a first conductivity type, formed of silicon carbide, and having a first surface and a second surface. The semiconductor body has a dopant layer of the first conductivity type and a top surface of the dopant layer defines the first surface of the semiconductor body. The dopant layer has a dopant concentration lower than that of the remainder of the semiconductor body. A metallic first electrode is disposed on the first surface and forms a Schottky contact with the semiconductor body. A second electrode contacting the semiconductor body on the second surface is provided. An insulation layer is disposed on the first surface of the semiconductor body. A reference ground potential terminal is provided. An edge termination having at least one diode chain is disposed on the insulation layer and thereby is insulated from the semiconductor body. The diode chain has a large number of semiconductor layers formed of alternating conductivity types, the diode chain is connected to the first electrode and to the reference-ground potential terminal.
The present invention allows all the process steps for the production of the edge terminations for the SiC semiconductor components to be carried out at a temperature (<1250° C.) which is typical in silicon technology. These process steps can be carried out in a conventional silicon production line. In particular, SiC Schottky diodes can thus be manufactured, with the exception of the production of the basic SiC material and the production of the epitaxial layer, entirely independently of the known difficulties with SiC technology.
In accordance with an added feature of the invention, the diode chain is a single, continuous chain of mutually adjacent ones of the semiconductor layers having alternating conductivity types.
In accordance with an additional feature of the invention, at least one field plate is connected to at least one of the semiconductor layers of the diode chain.
In accordance with another feature of the invention, the semiconductor body has an active area, and the field plate is one of a plurality of field plates disposed as concentric interconnects, circular rings, around the active area of the semiconductor body.
In accordance with another feature of the invention, the semiconductor layers of the diode chain have one of an equidistant grid and a non-equ
Pfirsch Frank
Rupp Roland
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
Stemer Werner H.
Tran Minh Loan
LandOfFree
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