Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-09-02
2001-08-14
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S256000, C257S279000, C257S363000, C257S328000
Reexamination Certificate
active
06274904
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the semiconductor technology field. More specifically, the present invention relates to an edge structure and a drift region (“internal structure”) for a semiconductor component, having a semiconductor body of the one conductivity type, in which at least one active zone of the other conductivity type (opposite to the first conductivity type) is provided.
It is a well known fact that relatively high blocking voltages can be obtained in transistors with a relatively highly doped drift path. Examples of this are junction/trench MOS field effect transistors and transistors with a semiconductor body of the one conductivity type which is provided with floating regions of the other conductivity type.
Junction/trench MOS field effect transistors, such as “CoolMOS” transistors can be fabricated with a plurality of epitaxial depositions of n-type conductive semiconductor layers and implantations of p-type conductive dopant with subsequent diffusion so that p-type conductive “columns” are produced in the n-type conductive semiconductor layers. Here, the entire quantity of dopant of the p-type conductive columns should correspond approximately to the entire quantity of dopant of the n-type conductive semiconductor layers.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a an edge structure and a drift region for a semiconductor component, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which does not require that the entire quantity of the doping of the two conductivity types in the component be precisely the same and the component is distinguished by a high degree of immunity to avalanching. In addition, it is an object to provide a method for fabricating such an edge structure and such a drift region for a semiconductor component.
With the foregoing and other objects in view there is provided, in accordance with the invention, an edge structure and drift region of a semiconductor component, comprising:
a semiconductor body of a first conductivity type formed of a plurality of planes;
an active zone of a second conductivity type opposite the first conductivity type disposed in the semiconductor body;
a plurality of regions of the second conductivity type embedded in at least two mutually different planes in the semiconductor body; and
connection zones formed in an area substantially underneath the active zone, connecting the regions to one another across different the planes, whereby the regions are otherwise floating regions.
In other words, the objects of the invention are satisfied in that at least two mutually different planes in the semiconductor body have embedded in them a plurality of regions of the other conductivity type. In the area essentially underneath the active zone the regions are connected to one another by means of connection zones over different planes, but otherwise they float.
If the one conductivity type is n-type doping with, for example, phosphorus, and the other conductivity type is p-type doping with, for example, boron, in the edge structure according to the invention, or the drift region according to the invention, the quantity of p-type dopant in the edge region may be greater than the quantity of n-type dopant since it is not disadvantageous if some or all of the floating p-type regions are not completely emptied under off-state conditions. The floating regions also permit uniform reduction of the field strength in the edge region, which can be easily proven with two-dimensional simulation.
In accordance with an added feature of the invention, an insulation layer is formed on the semiconductor body and field plates are disposed in the insulation layer. Each of the field plates is electrically connected to the regions of an uppermost plane of the semiconductor body.
In accordance with an additional feature of the invention, protective rings of the second conductivity type are formed in a surface region of the semiconductor body and connected to the field plates.
In accordance with another feature of the invention, in an edge region, a quantity of dopant of the second conductivity type is higher than a quantity of dopant of the first conductivity type.
The connection zones are preferably more weakly doped than the regions themselves which are connected to one another underneath the active zone of the semiconductor component by means of these connection zones.
In accordance with a further feature of the invention, the semiconductor body is formed of silicon or of silicon carbide. Composite semiconductors are also possible.
With the above and other objects in view there is also provided, in accordance with the invention, a method of fabricating the above-summarized configuration, i.e., an edge structure and a drift region of a semiconductor component with a semiconductor body of a first conductivity type and an active zone of a second conductivity type opposite the first conductivity type disposed in the semiconductor body. The method comprises the following steps:
epitaxially forming successive individual semiconductor layers on a semiconductor substrate of the first conductivity type;
following the formation of each individual layer, introducing dopant of the second conductivity type into each respective epitaxial layer in a region underneath the active zone and introducing dopant of the second conductivity type in the rest of the edge region into at least every other epitaxial layer (or each third or fourth epitaxial layer). The dopant is preferably introduced by ion implantation and/or by diffusion.
In accordance with an alternative mode of the invention, the invention comprises the following steps:
successively forming individual semiconductor layers of the first conductivity type by epitaxy on a semiconductor substrate; and
following the formation of each semiconductor layer, forming a V-shaped trench in a region underneath the active zone with a highly doped base, highly doped collar regions, and weakly doped side walls.
In accordance with a concomitant feature of the invention, doping is effected by ion implantation at an oblique angle.
After the implantation has been carried out, a further epitaxial layer is deposited, the trench thus being filled. This procedure is repeated several times until the desired electrical connection zones in the individual epitaxial layers between the regions of the other conductivity type are produced. After a possible diffusion, the regions of the other conductivity type and the weakly doped conduction zones between these regions underneath the active zone of the semiconductor component finally flow apart so that a structure is produced in which highly doped regions of the other conductivity type in different planes are connected to one another by means of weakly doped connection zones of the other conductivity type underneath the active zone of the semiconductor component, while in the edge region outside the region underneath the active zone the areas of the other conductivity type float and are not connected to one another by means of conduction zones in different planes.
In accordance with yet another feature of the invention, service life killer atoms are introduced in the regions, for instance in the trenches, making it possible, for example, to obtain small storage charges for diodes.
The semiconductor component may be a junction/trench MOS field effect transistor, a diode, an IGBT (bipolar transistor with insulated gate), a SiC junction field effect transistor etc.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an edge structure and drift region for a semiconductor component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalent
Chaudhuri Olik
Greenberg Laurence A.
Lerner Herbert L.
Louie Wai-Sing
Siemens Aktiengesellschaft
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