Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device – Having only two terminals and no control electrode – e.g.,...
Reexamination Certificate
1998-09-14
2001-02-06
Tran, Minh Loan (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
Having only two terminals and no control electrode , e.g.,...
C257S471000, C257S475000, C257S484000
Reexamination Certificate
active
06184545
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a semiconductor component having a metal semiconductor junction, and in particular to a Schottky diode with a low leakage current. The semiconductor component has a metal semiconductor junction between a metal that acts as a first electrode and a semiconductor of a first conductivity type with a drift path.
In IGBT power modules, pn diodes are currently used as freerunning diodes. These diodes have low impedance and a low reverse current. The switching losses, caused by the high concentration of minority carriers in the drift path, are a disadvantage. With regard to the switching losses, Schottky diodes would be ideal, because only majority carriers participate in the current transport. In addition, the lesser forward voltage of only 0.3 to 0.4 V in Schottky diodes, compared with about 0.7 V in pn diodes, is also advantageous for the static losses. A disadvantage of Schottky diodes, however, is the extremely high on-state resistance, because the Schottky diode is a majority carrier component. The reverse current of a Schottky diode is also very high. The reverse current is caused by the so-called Schottky barrier lowering: The high field intensity applied to the metal semiconductor junction in the off-state lowers the Schottky barrier, the consequence of which is a corresponding rise in the reverse current. This is described, for instance, by S. M. Sze in
Physics of Semiconductor Devices,
New York, p. 252.
This typical situation for unipolar components, which is that the on-state voltage, adjusted via the doping, determines the off-state capability of a component also exists in MOSFETs. Commonly owned U.S. Pat. No. 5,438,215 (German 43 09 764) proposed that higher-doped zones of the opposite conductivity type from the drift zone be disposed in the region of the space charge zone, in order to reduce the on-state resistance of a MOSFET. Between these higher-doped zones are zones that have the conductivity type of the inner zone but higher doping.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a Schottky diode with a metal semiconductor junction, which overcomes the above-mentioned disadvantages of the heretoforeknown devices and methods of this general type and in which both the reverse current and the on-state resistance are markedly lower than in Schottky diodes of the prior art.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor component, comprising:
a semiconductor of a first conductivity type with a surface and a drift path;
a first metal electrode disposed on the surface of the semiconductor and forming a metal-semiconductor junction with the semiconductor;
a plurality of supplementary zones of a second conductivity type disposed to extend from the surface into the drift path of the semiconductor; and
a plurality of intermediate zone surrounding the supplementary zones;
wherein a number of foreign atoms in the supplementary zones is substantially equal to a number of foreign atoms in the intermediate zones and does not exceed a number corresponding to a breakdown charge of the semiconductor. (For a silicon semiconductor, the breakdown charge is in the range below 2·10
12
cm
−3
.)
The semiconductor component according to the invention combines the advantages of the pn diode and the Schottky diode.
In accordance with an added feature of the invention, the supplementary zones extend through the entire drift path in the semiconductor.
In accordance with an additional feature of the invention, the intermediate zones between the supplementary zones have a lateral extent substantially similar to a lateral extent of the supplementary zones.
In accordance with another feature of the invention, a lateral extent of the supplementary zones and of the intermediate zones is substantially from 1 to 10 &mgr;m.
In accordance with a further feature of the invention, the semiconductor has a first semiconductor layer bounded by the surface and wherein a concentration of foreign atoms in the intermediate zones is greater than in the first semiconductor layer. The laterally adjoining semiconductor substrate then forms the peripheral region of the semiconductor component.
In accordance with again an added feature of the invention, the supplementary zones are disk-shaped zones or rod-shaped embedded in the intermediate zones.
In accordance with again an additional feature of the invention, each of the supplementary zones includes a junction zone (boundary zone) forming a guard ring adjacent the metal electrode and adjoining the surface of the semiconductor, the junction zone of each supplementary zone having a higher doping than a remainder of the supplementary zone. These junction zones increase the breakdown voltage of the component still further.
In accordance with a concomitant feature of the invention, the doping of the junction zones is selected so that, upon a polarization of the semiconductor component in a blocking direction thereof, charge carriers remain in the junction zones, i.e., not all the moveable charge carriers are removed from the junction zone.
Because of the pnpn column structure, in a semiconductor component according to the invention with a metal semiconductor junction, the drift path can be adjusted to have as low impedance as in a pn diode. The reverse current, because of the junction zone, such as p
+
regions that are locally congruent with the supplementary zones, such as “p-columns”, can be adjusted to be about as low as in a pn diode. If the periphery of the metal semiconductor contact is disposed at a junction zone, for instance a p
+
region, then the p
+
region acts like a guard ring; that is, the portion of the reverse current that occurs because of excessive field intensity at the periphery of a normal Schottky diode is suppressed in the proposed structure.
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 semiconductor component with metal semiconductor junction with low reverse current, 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: H40 (1986-04-01), Buchanan et al.
patent: 4110775 (1978-08-01), Festa
patent: 4134123 (1979-01-01), Shannon
patent: 4862229 (1989-08-01), Mundy et al.
patent: 5017976 (1991-05-01), Sugita
patent: 5081509 (1992-01-01), Kozaka et al.
patent: 5101244 (1992-03-01), Mori et al.
patent: 5371400 (1994-12-01), Sakurai
patent: 5438215 (1995-08-01), Tihanyi
patent: 5917228 (1999-06-01), Matsuda et al.
patent: 43 09 764 A1 (1994-09-01), None
“Physics of Semiconductor Devices” (Sze), Wiley Interscience Publication, 2ndedition, New Jersey, pp. 250-254.
“The Merged P-I-N Schottky (MPS) Rectifier: A High Voltage, High Speed Power Diode” (Baliga et al.), IEDM 1987, pp. 658-661.
Tihanyi Jenoe
Werner Wolfgang
Greenberg Laurence A.
Hu Shouxiang
Infineon - Technologies AG
Lerner Herbert L.
Stemer Werner H.
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