Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2001-05-30
2002-07-09
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S336000, C257S341000, C257S342000
Reexamination Certificate
active
06417542
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a field effect-controlled, vertical semiconductor component. The field effect-controlled, vertical semiconductor component is disposed in a semiconductor element and has at least one internal zone of a first conductivity type, at least one basic zone of a second conductivity type which adjoins the internal zone and a first surface of the semiconductor element, and at least one source zone of the first conductivity type which is disposed in each basic zone.
Such field effect-controlled, vertical semiconductor components, which may be embodied as V-MOSFETs, D-MOSFETs, U-MOSFETs, are widely known and have been described in detail, for example, in a reference by B. Jayant Baliga, titled “Power Semiconductor Devices”, PWS Publishing Company, pages 336 to 339.
In the off mode of such vertical semiconductor components, voltages may occur which are higher than the breakdown voltage of the semiconductor component. The drain/source off-state current which is caused by this causes, owing to the ohmic resistance in the basic zone, a voltage drop corresponding to the resistance in the basic zone. If the voltage drop exceeds the switch-off voltage of a parasitic diode at the pn junction between the basic zone and the drain zone, a parasitic bipolar transistor, whose emitter, base and collector are formed by the source zone, the basic zone and the drain zone, is undesirably switched on. The undesired switching on of the parasitic bipolar transistor is also referred to as a latch-up effect. In such a case, the off-state voltage of the semiconductor component drops significantly, i.e. by approximately 30% to 50%, which typically leads to the direct destruction of the semiconductor component itself. The latch-up effect is amplified by the fact that the voltage breakdown generally occurs at the edge of the basic zone, which is promoted by the curvature of the pn junction.
In order to improve the immunity to latching up, the resistance of the layer in the basic zone of the semiconductor component should therefore be as small as possible so that the voltage drop occurring here is as small as possible. However, the threshold voltage of the semiconductor component depends to a very high degree on the doping concentration in the basic zone, as a result of which tight limits are set on the reduction of the layer resistance in the basic zone.
If the doping concentration in the basic zone is nevertheless increased in order to reduce the layer resistance and thus improve the immunity to latching up, this additionally entails the risk of crystal fault formation which can be remedied only to a limited degree when a very high dose is used. In addition, when a very high implantation dose is used there is always also the risk of undesired defusing out of dopants into the semiconductor element. However, a semiconductor component in which the basic zones have, in view of all these measures, a very high doping concentration, with correspondingly off-state current densities in the basic zones will nevertheless latch in all cases.
Alternatively, it is possible that when the drain voltage is changed very rapidly a capacitive current flows which leads to a corresponding voltage drop in the basic zone, with the result that the parasitic bipolar transistor is switched on.
It is therefore necessary to ensure that in the off mode the parasitic bipolar transistor of the semiconductor component does not become active, i.e. is not latched, even when the off-state voltage rises above the breakdown voltage or when there is a rapid change in the drain voltage.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a field effect-controlled, vertical semiconductor component that overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which the possibility of undesired switching on or off of a parasitic transistor is very largely excluded in the off mode.
With the foregoing and other objects in view there is provided, in accordance with the invention, a field effect-controlled, vertical semiconductor component disposed in a semiconductor element. The vertical semiconductor component contains at least one internal zone of a first conductivity type disposed in the semiconductor element, and the semiconductor element has a first surface and a second surface. At least one basic zone of a second conductivity type adjoins the internal zone and the first surface. At least one source zone of the first conductivity type is disposed in the basic zone. An intermediate zone of the first conductivity type is provided. At least one further basic zone of the second conductivity type is disposed in the semiconductor element, the intermediate zone is disposed between the further basic zone and the basic zone for spacing apart the further basic zone from the basic zone. At least one source contact zone connects the source zone, the basic zone and the further basic zone to one another with a low impedance.
Accordingly, a semiconductor component of the type mentioned at the beginning is provided which is characterized by at least one further basic zone of the second conductivity type which is spaced apart from the basic zone by an intermediate zone of the first conductivity type, and at least one source contact zone which connects the source zones, the basic zones and the further basic zones to one another with a low impedance.
The basic principle of the present invention consists in making available different basic zones that are spatially separated from one another. Here, the first basic zone is the actual current-conducting basic zone that is provided for forming the channel in the switched-on state. The further basic zone, which is typically disposed underneath the actual basic zone, is provided in the off mode for receiving an off-state voltage caused by an off-state current. In the off mode, a voltage drop caused by the off-state current occurs exclusively in the further basic zone. The voltage drop in the further basic zone does not, however, lead to charge carrier injection, and thus to switching on the parasitic bipolar transistor; a semiconductor component is thus advantageously made available without a latch-up effect.
A particular advantage of the invention lies, moreover, in the fact that the voltage drop in the further basic zone can be of any desired magnitude without the parasitic bipolar transistor switching on. The doping concentration in the basic zone can thus be adjusted in an optimum way to the setting of the threshold voltage of the semiconductor component; taking into account the immunity to latching up by a suitable selection of the doping concentration plays a small role here. A semiconductor component that advantageously provides greater degrees of freedom to manufacturing technology is thus provided.
The further basic zone is, as already mentioned, usually disposed under the actual basic zone and connected to the basic zone by a highly conductive source contact zone. It is particularly advantageous if the further basic zone is embodied as a layer buried in the internal zone. The highly doped, buried basic zone can typically be introduced into the internal zone by high-dose ion implantation.
In a particularly advantageous embodiment, the further basic zone is composed of two different regions that are disposed one underneath the other and are connected to one another. The two regions each have different penetration depths and different doping concentrations.
It is particularly advantageous if the first region has a high doping concentration and is disposed, with respect to the first surface, above the second region which has a much lower doping concentration. The first highly doped region thus takes up virtually the entire off-state current occurring in the further basic zone, and thus the voltage dropping there. The second region of the further basic zone that has a low doping level advantageously has a compensating effect for the doping in the drain region.
The second region of th
Infineon - Technologies AG
Mayback Gregory L.
Ngo Ngan V.
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