Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-06-28
2001-02-20
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S355000, C257S409000
Reexamination Certificate
active
06191456
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a lateral insulated gate bipolar transistor (LIGBT) in a silicon on insulator (SOI) configuration having a top side and an underside, and a drain zone of a first conductivity type extending to the top side. An anode zone of a second conductivity type is incorporated in the drain zone and the anode zone extends to the top side. Furthermore, a base zone of the second conductivity type is incorporated in the drain zone, the base zone extending to the top side and there being incorporated in the base zone a source zone of the first conductivity type, which source zone extends to the top side. The underside of the lateral IGBT forms a substrate of the second conductivity type. A lateral insulation layer is provided between the drain zone and the substrate.
Circuit configurations having power semiconductor switches are used in the automotive sector, in the telecommunications sector, in the consumer sector and also for the purpose of load control and many other applications. The LIGBT is one of the components used most in circuit configurations of this type. A high blocking voltage can be obtained with LIGBTs, on account of the long drift zone, but the current-carrying capacity is unsatisfactory in comparison with a vertical IGBT.
In order to be able to ensure a required reverse voltage for a predetermined thickness of the drain zone, suitable doping of the drain zone is performed. In this case, the blocking voltage is taken up not only by the drain zone but also, to a significant proportion, by the insulation layer situated underneath.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a lateral IGBT in an SOI configuration and a method for its fabrication which overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, which has lower turn-off losses in comparison with the prior art without simultaneously decreasing the reverse voltage in the process.
With the foregoing and other objects in view there is provided, in accordance with the invention, a lateral IGBT in an SOI configuration having a top side and an underside. The lateral IGBT has a drain zone of a first conductivity type, which drain zone extends to the top side. An anode zone of a second conductivity type is incorporated in the drain zone and the anode zone runs to the top side. Furthermore, a base zone of the second conductivity type is incorporated in the drain zone and the base zone extends to the top side. There being incorporated in the base zone a source zone of the first conductivity type, which source zone extends to the top side. The underside of the LIGBT forms a substrate of the second conductivity type. The LIGBT has a source electrode that is in contact with the source zone and the base zone. Furthermore, it contains a drain electrode that is in contact with the anode zone. A gate insulating layer disposed on the top side is situated between the source zone and the anode zone. A gate electrode is disposed on the gate insulating layer. A lateral insulation layer is provided between the drain zone and the substrate.
The invention is based on the concept that at least one laterally formed region of the second conductivity type is provided in the drain zone, in the vicinity of the insulation layer. In this case, the laterally formed region has a smaller area than the lateral insulation layer that is provided.
This configuration has the advantage that the terrace-shaped profile of the voltage rise during the turn-off of the LIGBT is shifted toward a lower voltage value and, at the same time, the terrace phase is shortened in the process. This results in a smaller power loss. At the same time, however, the maximum reverse voltage is maintained.
The reason why the turn-off losses can be reduced without the maximum reverse voltage being simultaneously decreased in the process is that the laterally formed regions of the second conductivity type provided in the vicinity of the lateral insulation layer are formed in the source-drain direction and, at the same time, have interruptions and, consequently, do not areally cover the entire lateral insulation layer. At least partial regions of the drain zone are thus in contact with the lateral insulation layer. These interruptions enable the electric field to penetrate the insulation oxide in the event of the IGBT being subjected to reverse voltage loading. The penetration of the electric field into the insulation oxide is of relevance, primarily in respect to the reverse voltage endurance. On the other hand, the laterally formed regions of the second conductivity type enable the stored charge to be depleted more rapidly during the switching-off operation of the LIGBT and, consequently, the switch-off losses to be reduced.
In one development, the LIGBT has a vertical and insulating boundary in the form of a trench, which boundary extends from the top side to as far as the lateral insulating layer. The vertical insulation region (in the form of a trench) enables the LIGBT to be integrated with any other semiconductor components (e.g. logic elements) on a semiconductor substrate.
In a further refinement of the LIGBT, the anode zone lies in a drain extension of the first conductivity type and the drain extension adjoins the top side. The drain extension has a higher doping than the drain zone and serves to keep the space charge zone away from the anode zone during the switching-off operation of the LIGBT.
In one development, the LIGBT has a field plate covering the drain extension on the gate insulating layer. Favorable influencing of the electric field within the LIGBT is obtained as a result of this.
In a further refinement, the LIGBT has a vertically running region of the second conductivity type, which region abuts the insulation region in the form of a trench. In this case, the vertically running region of the second conductivity type is connected to the base zone. The latter serves to control the inversion layer on the underside of the LIGBT. If the LIGBT is in the blocking state, the transition between the vertically running region of the second conductivity type and the drain zone of the first conductivity type is controlled in the reverse direction and, in this way, prevents the formation of an inversion layer between the drain zone and the lateral insulation layer.
Furthermore, in an advantageous refinement, the LIGBT is characterized in that the substrate is at a fixed potential. The latter may be a fixed voltage or, in an advantageous manner, ground. However, it is also conceivable for the potential to float. In this case, the substrate can take up a higher reverse voltage. The insulation. region in the form of a trench should be at the lowest potential of the component. It is preferable for the insulation region in the form of a trench to be connected to the ground potential.
In a further refinement, the LIGBT is constructed mirror-symmetrically in a lateral orientation. In this case, the anode zone and the drain electrode situated thereon lie in the center of the semiconductor component. The insulation regions in trench form in this case form the lateral outer boundary of the LIGBT. It is advantageous if the LIGBT has a finger-shaped form, since a utilization that is particularly efficient in respect of area can thereby be obtained in the event of a plurality of LIGBTs being connected in parallel on a semiconductor substrate.
In a further refinement, the lateral regions provided in the drain zone have a polygonal form and are spaced apart from one another regularly lying in one plane. In this case, the lateral regions of the second conductivity type may have any desired form, provided that it is ensured that two lateral regions lying next to one another are respectively spaced apart from one another by a certain distance. It is advantageous if the configuration is effected in a regular sequence. The lateral regions may in this case have a square, rectangular, octagonal or else round form.
In another refinement, the
Stoisiek Michael
Vietzke Dirk
Greenberg Laurence A.
Lerner Herbert L.
Meier Stephen D.
Siemens Aktiengesellschaft
Stemer Werner H.
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