Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having schottky gate
Reexamination Certificate
2001-03-26
2003-11-18
Chaudhuri, Olik (Department: 2823)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having schottky gate
C438S243000, C438S268000, C438S270000
Reexamination Certificate
active
06649459
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor component having a semiconductor element with a blocking pn-type junction. The blocking pn-type junction is formed by a first zone of a first conduction type and an adjoining zone of a second conduction type that is opposite to the first conduction type. The first zone of the first conduction type is connected to a first electrode. A second zone of the first conduction type is connected to a second electrode. The side of the zone of the second conduction type which faces the second zone forms a first surface. Areas of the first and second conduction types are integrated together in the region between the first surface and a second surface lying between the first surface and the second zone.
Such semiconductor components are also referred to as compensation components. Such compensation components are, for example, n-type or p-type channel MOS field effect transistors, diodes, thyristors, GTOs or else other elements. However, the following text will be based on an example of a field effect transistor (also referred to as “transistor” for short).
Various theoretical investigations have been made into compensation components over a long period of time (see U.S. Pat. No. 4,754,310 and U.S. Pat. No. 5,216,275), but these investigations have been directed toward improving the switchover resistance RSDon. They have not been directed toward improving the stability under current loading, and in particular, have not been directed toward improving the robustness in relation to avalanche and short-circuiting with high current and a high source-drain voltage. Compensation components are based on mutual compensation of the charge of n-type and p-type doped areas in the drift region of the transistor. The areas are spatially configured here in such a way that the line integral over the doping along a line running vertically with respect to the pn-type junction remains in each case below the breakdown charge specific to the material (silicon approximately 2*10
12
cm
−2
). For example, in a vertical transistor such as is customary in power electronics, it is possible to configure p-type and n-type columns or plates etc., in pairs. In a lateral structure, p-type and n-type conductive layers can be stacked alternately one on top of the other in a lateral configuraion between a trench covered by a p-type conductive layer and a trench covered by an n-type conductive layer (see U.S. Pat. No. 4,754,310).
The large degree of compensation of the p-type and n-type doping enables the doping of the current-conducting region (the n-type region for n-type channel transistors and the p-type region for p-channel transistors) to be significantly increased in compensation components, which results in a significant gain in switch-on resistance RDSon despite the loss of current-conducting area. The switch-off capability of the transistor depends here essentially on the difference between the two dopings. Because doping of the current-conducting area which is at least one order of magnitude higher is desired in order to reduce the switch-on resistance, a controlled setting of the compensation degree, which can be defined for values in the region ≦±10%, is required to control the switch-off voltage. When the gain in terms of switch-on resistance is higher, the aforesaid region becomes even smaller. The degree of compensation can be defined in such a case by:
(p-type doping-n-type doping)
-type doping; or by
charge difference/charge of a doping area.
However, other definitions are also possible.
For this reason, the aim is to obtain a robust semiconductor component which is defined by a high degree of immunity to avalanching and which can withstand high current loads before and in the breakdown state, and which also can be manufactured easily in terms of the technological tolerance ranges of manufacturing processes with properties which can be satisfactorily reproduced.
Such a completely novel semiconductor component is obtained if the areas of the first and second conduction types are doped in such a way that charge carriers of the second conduction type predominate in regions close to first surface, and charge carriers of the first conduction type predominate in regions near the second surface.
The areas of the second conduction type preferably do not extend as far as the second zone, with the result that a weakly doped region of the first conduction type remains between the second surface and the second zone. However, it is possible to allow the width of this region to approach “zero”. However, the weakly doped region provides various advantages such as an increase in the switch-off voltage, a “gentle” profile of the field strength and an improvement in the commutation properties of the inverse diode.
In areas of the second conduction type, a degree of compensation brought about by the doping is varied in such a way that atomic cores of the second charge type dominate close to the first surface, and atomic cores of the first charge type dominate close to the second surface. There are therefore layer sequences p, p
−
, n
−
, n or n, n
−
, p
−
, p between the two surfaces.
The effect of the nested areas of alternately different conduction type on the electrical field is, in contrast to, for example, a classic DMOS transistor, as follows (“lateral” and “vertical” relate below to a vertical transistor):
(a) there is a transverse field which is “lateral” with respect to the connecting direction between the electrodes, the strength of the transverse field depending on the proportion of lateral charge (line integral perpendicular to the lateral pn-type junction) relative to the breakdown charge. This field leads to the separation of electrons and holes and to a reduction in the current-carrying cross section along the current paths. This fact is of basic importance for understanding the processes in the avalanche, the breakdown characteristic curve and the saturation region of the characteristic curve field.
(b) The “vertical” electrical field which is parallel to the connecting direction between the electrodes is determined locally by the difference between the adjacent dopings. This means that when there is an excess of donors (n-type loading: in the charge in the n-type conductive areas exceeds the charge in the p-type areas) on the one hand, a DMOS-like field distribution (field at maximum at the blocking pn-type junction, field reducing in the direction of the opposite rear side of the component) occurs. The gradient of the field is, however, significantly lower than that which would correspond to the doping of the n-type area alone. However, on the other hand, a field distribution which rises in the direction of the rear side (p-type loading, excess of acceptors over donors) is possible as a result of overcompensation of the n-type conductive area with acceptors. In such a configuration, the field is at a maximum at the bottom of the p-type area. If the two dopings compensate one another precisely, a horizontal field distribution is produced.
The breakdown voltage is at a maximum with a precisely horizontal field distribution. If the acceptors or the donors predominate, the breakdown voltage respectively decreases. If the breakdown voltage is consequently plotted as a function of the degree of compensation, a parabolic profile is obtained.
Constant doping in the p-type and n-type conductive areas or even locally varying doping with periodic maximum values of the same magnitude leads here to a comparatively extreme maximum of the “compensation parabola”. In order to arrive at a “fabrication window” (inclusion of the tolerances of all the individual relevant processes), a comparatively high breakdown voltage must be aimed at in order to achieve reliable yields and production reliability. The objective must therefore be to make the compensation parabolas as flat and wide as possible.
If switch-voltage is applied to the component, the drift path,
Deboy Gerald
Friza Wolfgang
Häberlen Oliver
Rüb Michael
Strack Helmut
Brewster William M.
Chaudhuri Olik
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