Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-10-22
2001-03-13
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S133000, C257S137000
Reexamination Certificate
active
06201279
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the semiconductor technology field. More specifically, the present invention relates to a semiconductor component having a small forward voltage and a high blocking ability, in which at least one drift path suitable for taking up voltage is formed in a semiconductor body between two mutually spaced-apart electrodes.
Power MOS field-effect transistors should inherently have, on the one hand, a predetermined minimum breakdown voltage, but on the other hand the highest possible conductance with regard to the area of a semiconductor body that is used for them (“silicon area”). However, the minimum breakdown voltage and the conductance are coupled with one another in the case of customary semiconductor components: high conductivity is only obtained by a high doping and/or a small thickness or drift path length, which leads, however, to a low breakdown voltage and hence to a low blocking ability. In other words, a relatively high breakdown voltage and at the same time a high conductance cannot be achieved with conventional semiconductor components. This also applies to other unipolar semiconductor components such as, for example, Schottky diodes (in this context, see B. J. Baliga: “Modern Power Devices”, John Wiley & Sons, 1987, in particular Equation 6.60, FIG. 6.23 and also pages 421 ff. and 132 ff.).
In addition to the power MOSFET disclosed above, various possibilities have already been conceived of with the aim of avoiding the problem of the coupling of breakdown voltage and conductivity, so that each of these two properties can be optimized in favor of itself.
In the first instance, there are semiconductor components known as IGBTs (insulated gate bipolar transistors), which are also referred to as IGT (insulated gate transistor) or as COMFET (conductivity modulated FET). In the case of such a semiconductor component, the inherently weakly doped drift path, that is to say the “central region” which has to take up the reverse voltage, is flooded, in the case of forward-biasing, with an electron-hole plasma having a considerably higher conductivity than the weak doping of the central region (cf. B. J. Baliga, pages 350-53).
Moreover, U.S. Pat. No. 4,941,026 discloses a semiconductor component in which the electric charge contained in the drift path doping is compensated for, in the case of reverse-biasing, by charges from a gate arranged in a deep trench. In the case of such a structure, the charge in the drift path contributes to the build-up of the vertical field strength between the two electrodes only is a greatly reduced manner and, therefore, can be chosen to be considerably higher compared with customary semiconductor components. Thus, by way of example, it is possible to introduce up to twice the breakdown charge as doping in a drift path region between two trenches.
Finally, consideration has also already been given for a relatively longtime to so-called compensation components, in the case of which compensation of the drift path charge in the case of reverse-biasing of the semiconductor component is provided by means of regions arranged parallel to the drift path or zones having an opposite doping to the drift path doping (in this respect, see U.S. Pat. No. 4,754,310 and U.S. Pat. No. 5,216,275). However, in the case of those prior art semiconductor components, too, the doping of the individual regions must not exceed twice the breakdown charge (2×10
12
charge carriers cm
−2
in the case of Si).
These so-called compensation components are based on mutual compensation of the charge of n- and p-doped regions in the drift path of a MOS transistor, for example. In this case, these regions are spatially arranged such that the line integral against the doping remains below the material-specific breakdown charge specified above, in other words below approximately 2×10
12
cm
−2
in the case of silicon. By way of example, in a vertical transistor of the kind that is customary in power electronics, p- and n-type “pillars” or “plates”, etc. may be arranged in pairs. In a lateral structure, p- and n-conducting layers may be stacked alternately one above the other laterally between a trench occupied by a p-conducting layer and a trench occupied by an n-conducting layer (cf. U.S. Pat. No. 4,754,310).
The aforementioned compensation components require relatively accurate setting of the dopant concentrations in the individual zones and regions in order to actually achieve the desired compensation. This setting of the dopant concentrations has proved to be relatively difficult if, in particular, doping is intended to be performed over a relatively long period of time on different semiconductor chips.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a semiconductor component having a small forward voltage and a high blocking ability, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which, in terms of its functionality, is independent of the variations in the process parameters which are customary in semiconductor fabrication.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor component having a small forward voltage and a high blocking ability, comprising:
two mutually spaced-apart electrodes;
a semiconductor body disposed between the two electrodes and defining therein at least one drift path suitable for taking up voltage; and
at least one semi-insulating layer extending parallel to the drift path.
In accordance with an added feature of the invention, the semiconductor body is of a first conductivity type and which further comprises regions of a second conductivity type, opposite the first conductivity type, formed in the semiconductor body and extending parallel to the semi-insulating layer.
Examples of material that can be used for the semi-insulating layer are semi-insulating polycrystalline silicon (SIPOS), amorphous silicon optionally doped with H (a-Si:H) or amorphous carbon optionally doped with hydrogen (a-C:H). It goes without saying that other materials having semi-insulating properties can also be used.
In accordance with a further feature of the invention, the semi-insulating layer has a defined resistivity in a range from 10
8
to 10
11
ohms cm, for instance 1×10
10
ohms cm.
Semi-insulating layers are known for other purposes in semiconductor technology: thus, by way of example, there are resistive field plates in the case of edge terminations with a high blocking capability which comprise SIPOS (cf. Baliga, pages 126 ff. and Jaume et al., “High-Voltage Planar Devices Using Field Plate and Semi-Resistive Layers,” IEEE Transactions on Electron Devices, Vol. 38, No. 7, pp. 1681-84 (1991)).
In accordance with again an added feature of the invention, the semiconductor body is formed with a pn junction having two sides, and the semi-insulating layer is disposed adjacent at least one of the two sides.
In accordance with again an additional feature of the invention, a doping in the drift path does not exceed a breakdown charge of the component. In an exemplary embodiment, the drift path is formed of silicon and the doping in the drift path does not exceed 1×10
12
charge carriers cm
−2
.
In the case of the semiconductor component according to the invention, by way of example, a narrow strip of a pn junction is provided with a semi-insulating layer on one or both sides. When a reverse voltage is applied to the pn junction, even a relatively low current flow through the semi-insulating layer then leads to a linear rise in the potential between the two electrodes and thus to an essentially constant electric field. In this case, the space charge zone extends over the entire depth of the drift path. However, the doping in the drift path, that is to say an n-conducting semiconductor region for example, integrated over the width of the drift path, must not exceed the breakdown charge, approximately 1×
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
Meier Stephen D.
Stemer Werner H.
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