Active solid-state devices (e.g. – transistors – solid-state diode – With means to increase breakdown voltage threshold – With electric field controlling semiconductor layer having a...
Reexamination Certificate
1996-08-23
2002-09-24
Weiss, Howard (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
With means to increase breakdown voltage threshold
With electric field controlling semiconductor layer having a...
C257S127000, C257S170000, C257S409000, C257S484000, C257S490000
Reexamination Certificate
active
06455911
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a semiconductor component, particularly to a semiconductor component with a high-efficiency barrier junction termination.
BACKGROUND INFORMATION
In general, a semiconductor component contains at least one active semiconductor area and a semiconductor region acting as either an n or p type drift region. Such a semiconductor component also includes two electrodes for applying an operating voltage to the drift region, as well as usually other semiconductor regions for forming component-specific semiconductor structures. In an on state of the component, the drift region carries the electric current of the charge carriers between the two electrodes. In the off state of the component, however, the drift region takes on a depletion region of a p-n junction formed with the drift region or of a metal-semiconductor barrier contact (Schottky contact) which is formed as a result of the operating voltages applied that are relatively high compared to those in the on state. The depletion region is often also called the space charge region or barrier layer. Distinction is made between unipolar and bipolar semiconductor areas. In unipolar active semiconductor areas, only one kind of charge carriers (electrons or holes) determines the operation, while in bipolar active semiconductor areas, both charge carrier types, electrons and holes, contribute to the operation.
In the off state, relatively strong electric fields are created on the surface of the component. Therefore it is important to ensure the stable transition of these electric surface fields into the medium surrounding the component with a maximum field intensity that is clearly below the average field intensity of the surrounding medium. The surrounding medium can be dielectric insulating and/or passivating layers, or a surrounding gas, usually air. The problem of excessively high field intensities on the surface of a component appears especially in the case of high off-state voltages, which occur in power electronics applications in which small dimensions with high field line curvatures or high doping of the semiconductor regions is present. To reduce the field intensity on the surface of the component, a device known as a junction termination is used. The junction termination is produced on the component surface and surrounding the active semiconductor area. In addition to electrically shielding the active semiconductor area outward, the junction termination also reduces the field line curvatures around the active semiconductor area in order to diminish excessively intense fields in the area close to the surface within the semiconductor component.
Different embodiments of junction terminations for p-n junctions of silicon-based power electronics semiconductor components are described in “Modern Power Devices” by B. J. Baliga, 1987, John Wiley & Sons (USA), pp. 79-129. Such p-n junctions are usually produced by diffusion of a dopant into the surface of a silicon layer acting as a drift region, with the diffused region being of the opposite conduction type compared to the silicon layer. Due to field line curvature, an extra-high intensity field is produced at the edge of the diffused region compared to the planar p-n junction, depending on the depth of this region.
In a first known embodiment, floating field rings can be provided as junction terminations, which are also produced through diffusion around the diffused region of the p-n junction of the silicon layer. These field rings are of the same conduction type as the diffused layer of the p-n junction and are insulated from the diffused region and from one another by the silicon layer doped for the opposite conduction type. One or more field rings can be provided. A second method for obtaining a junction termination consists of removing material, and thus charges, from around the edge of the p-n junction by mechanical abrasion or etching (“beveled-edge termination” or “etch contour termination”). Mesa structures are obtained as junction terminations.
A third known junction termination for a p-n junction is a device called a field plate, which is produced by applying an oxide layer to the edge area around the p-n junction and a metallic layer on the oxide layer. A field is applied to the metallic layer to change the surface potential at the edge of the p-n junction. Thus, the depletion region of the p-n junction and, therefore, the field as well can be expanded. The field plate can also be formed using an electrode layer that overlaps the oxide layer in the edge area of the p-n junction, which is provided for the p-n junction for the application of an operating voltage. A junction termination can also be formed by combining field plates and field rings (“Modern Power Devices,” p. 119).
In a fourth known embodiment of a junction termination, ion implantation is used to introduce opposite charges in a controlled manner in the surface of the silicon layer provided as a drift region. Such a junction termination is called a “junction termination extension”. The implanted region is of the same conduction type as the diffused semiconductor region of the p-n junction, and, thus, it not only is doped with the opposite charge compared to the drift region, but it also has a lower doping amount than the diffused region. In this fourth embodiment, in addition to a region diffused into the drift region, the p-n junction can also be formed using a silicon layer arranged on the surface of the drift region with opposite doping in relation to the drift region. Ion implantation into the junction termination then takes place at the edge of the two silicon layers forming the p-n junction. The p-n junction is virtually extended by this “junction termination extension,” the electric field is broadened, and the field curvature is reduced. The breakdown strength of the component is therefore increased.
Another junction termination comparable with the junction termination extension is described in Swiss Patent No. A-659,542 and referred to there as a barrier layer extension area. This junction termination is provided for a p-n junction as a bipolar active semiconductor area of a semiconductor component and can be produced by ion implantation or epitaxial growth. The lateral dimension (W
JER
) of the barrier layer extension area is set greater than approximately one-half of the depletion width (W
id
) of the low-dope side of the p-n junction. For lateral dimensions of more than one-half of the depletion width (W
id
) , no further improvement is obtained in this prior art junction termination.
In “Modern Power Devices,” p. 128, the “junction termination extension” is proposed for bipolar transistors (BJT), field-effect transistors (MOSFETs), and thyristors (silicon-controlled rectifiers or SCRs). Due to the additional parasitic diode created with this junction termination, however, bipolar leak currents are generated in the off state of the component and high stored charges during the operation of the component, which can result in serious problems, especially in the case of a unipolar silicon MOSFET. These leak currents and stored charges increase considerably if the junction termination is enlarged, since the charge carrier injection of the parasitic diode increases with the surface area of the junction termination.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a silicon-based semiconductor component with a junction termination that does not considerably increase the stored charge in the on state of the component.
This object is achieved in accordance with a semiconductor component comprising at least one semiconductor region made of silicon of a first conduction type which acquires a depletion region in the active area of the component when an off-state voltage is applied to the active area. A junction termination for the active area is formed by silicon of the opposite conduction type compared to the semiconductor region taking on a depletion region. The junction termination is arranged around the active area in or on t
Mitlehner Heinz
Stephani Dietrich
Kenyon & Kenyon
Weiss Howard
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