Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2004-01-15
2004-10-12
Loke, Steven (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S129000, C257S132000, C257S139000, C257S138000, C257S140000, C257S141000, C257S342000, C257S343000
Reexamination Certificate
active
06803627
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to power semiconductor components, compensation components, power transistors, and methods for producing power semiconductor components. The power semiconductor component has a drift path of a first conduction type disposed between two electrodes and to a method of producing these power semiconductor components.
Power transistors, such as DMOS transistors, UMOS or trench transistors, and similar semiconductor elements necessarily contain in their structure a “reverse diode” composed of a body region (also called a channel region) and a drain region. In numerous applications, this reverse diode is regularly operated in the flow direction, for example, as a freewheeling diode.
In the case of a reverse diode operated in the flow direction, a current flows through the MOS transistor in the reverse direction. This current in the reverse direction is not a channel current but a diode current associated with a high flood of charge carriers.
If the power transistor previously operated in the reverse or blocking direction is then switched over to the forward direction, then it absorbs voltage in the forward direction. For this purpose, the charge carriers specifically stored in the drift path of the power transistor have to be extracted from the semiconductor body of the power transistor. This process entails a high reverse diode current. Here, the reverse diode current adds to the load current of the power transistor and, in this application, leads to increased switching losses, for example in a second transistor which has to carry the entire current when it is turned on.
In compensation components like those described in U.S. Pat. No. 4,754,310 issued to Coe, the peak value of the reverse current (i.e., “the reverse current peak”) is very high. A high reverse current peak is already accompanied by problems. In addition, the reverse current in compensation components returns to zero very suddenly and “breaks down”. Break down necessarily includes stray inductances that can lead to dangerous overvoltage peaks.
Previously, in order to avoid the above difficulties, a Schottky diode has been connected in antiparallel with the power transistor. The Schottky diode has a lower threshold voltage than the pn-reverse diode of the power transistor. Accordingly, the Schottky diode can accept the reverse current if the Schottky diode has a sufficiently-small, overall forward voltage drop. However, this is barely possible, especially in the case of higher-value blocking semiconductor components, because the Schottky diode would require the same blocking ability as, for example, a power transistor.
A further, previously considered possibility for overcoming the above difficulties with power transistors is not to connect its body or channel region to the source contact. This allows the pn-junction between source region and body region to absorb the necessary reverse-blocking voltage.
In such a power transistor having a body region that is floating and not connected to the source contact is that, in the forward direction between collector and emitter with an open base, one disadvantage is preventing the breakdown of a parasitic npn-(or pnp-) transistor composed of the source region, the body region, and the drain region must be prevented. This is extremely difficult and complicated in technological terms. One possibility is to minimize the gain of this parasitic transistor with an inlaid recombination zone, for example, a floating metal or silicide contact. However, in such a case, the gain remains high in an interspace between such a recombination zone and the gate of the power transistor. For this reason, the interspace should be configured to be as small as possible, in order to prevent breakdown of the parasitic transistor (called the U
CEO
breakdown).
If the body region is not connected to the source contact, then it is not at a fixed potential. The turn-on voltage of the power transistor via the substrate control effect therefore depends on the drain-source voltage applied. In addition, a breakdown must be prevented between collector and emitter with open base of a parasitic npn-(or pnp-) transistor composed of the source region, the body region, and the drain region, which is difficult in technological terms.
U.S. Pat. No. 5,202,750 issued to Gough discloses an emitter switched thyristor, specifically an EST, as it is called, in which, an n-doped emitter region can be connected to the cathode or isolated from the latter via an MOS channel. This thyristor has on its rear, a p-doped region that acts as a p-doped emitter. This structure can switch off the thyristor, which has a very high conductivity as a result of charge carrier flooding with minority charge carriers and majority charge carriers, by driving the MOS channel via the associated gate.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a power semiconductor component, a compensation component, a power transistor, and a method for producing power semiconductor components that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that specifically provide a reverse-blocking power semiconductor component that, in the reverse direction, has a blocking capacity of at least a few volts, so that in the presence of a voltage in the reverse direction, no reverse diode current flows through the semiconductor component. In addition, the method of producing such a reverse-blocking power semiconductor component is to be specified.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a reverse-blocking power semiconductor component. The reverse-blocking power component includes two electrodes, a drift path, a region, and a gate. The drift path of a first conduction type is disposed in an area between the two electrodes. The region is disposed in the drift path and subdividing the drift path into two areas. The region is of the other conduction type, opposed to the one conduction type. The gate is being provided with the region.
With the objects of the invention in view, there is also provided a method of producing the power semiconductor component. According to the method, the region that subdivides the drift path is produced by epitaxy.
The power semiconductor component according to the invention achieves its blocking capacity, which may be restricted to a few volts, in the reverse direction as a result of the fact that in the area of the drift path, an additional region doped opposite to the drift path is provided, so that the drift path is subdivided into two areas. If appropriate, more than just one such region may also be introduced into the drift path. The drift path is then accordingly subdivided into a plurality of areas. If, for example, two regions of the other conduction type, opposed to the conduction type of the drift path, are incorporated into the drift path, then there is a total of three areas, into which the drift path is subdivided.
In the following text, it will be assumed that the drift path is n-doped. In this case, the region inserted into the drift path is p-doped in order to subdivide it of course, however, the opposite conduction type may also be present in each case. This means that in this case a p-doped drift path is then subdivided into at least two areas by an n-doped region.
The p-doped (or n-doped) region inserted into the n-doped (or p-doped) drift path is not connected to the source contact or the body region. However, it divides the drift path into two completely mutually isolated areas, into n+1 areas in the case of n regions, so that at least one pn junction blocking in the reverse direction is produced between the p-doped region and the n-doped area on the source side of the drift path. In this case, in the case of a power transistor as a power semiconductor component, it is assumed that this drain is biased negatively with respect to its source.
Because this additional p-doped region also blocks t
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Loke Steven
LandOfFree
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