Semiconductor device manufacturing: process – Avalanche diode manufacture
Reexamination Certificate
1999-03-30
2001-10-23
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Avalanche diode manufacture
C438S383000, C438S395000, C438S413000
Reexamination Certificate
active
06306717
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the manufacturing of avalanche diodes in integrated circuits, for example, power integrated circuits.
BACKGROUND OF THE INVENTION
In such circuits, it is often required to define several triggering thresholds, for example, to create various devices of protection against electrostatic discharges, battery inversions, or others.
Generally, as shown in
FIG. 1
, an avalanche diode is made by forming in a substrate
1
of a first conductivity type a region
2
of the opposite conductivity type. It should be noted that “substrate” is here used to designate a region or upper layer of a semiconductor component, for example, an integrated circuit. Region
2
generally is heavily doped and the breakdown threshold of the avalanche diode is essentially determined by the doping level of substrate
1
(the less the substrate is doped, the higher the breakdown voltage of the device).
FIG. 2
shows another example of an avalanche diode currently used in integrated circuits. In substrate
1
of the first conductivity type, a diffused (or implanted-diffused) region
3
of the same conductivity type is created. A region
2
of the opposite conductivity type is formed to laterally protrude from region
3
to obtain a breakdown independent from edge and surface effects. Assuming that substrate
1
of
FIG. 2
is the same as that of
FIG. 1
, the avalanche voltage of junction
2
-
3
, which depends on the doping level of region P, necessarily is lower than that of junction
2
-
1
since the concentration of region
3
at its junction with region
2
necessarily is higher than that of region
1
.
Thus, generally, in any method of manufacturing of a semiconductor component or of an integrated circuit, the various types of diffusion provided for the manufacturing of other components of the integrated circuit can be used to form avalanche diodes. However, the breakdown thresholds of the various diodes are determined without any possible choice by the doping level of the existing regions and, in many simple lines of manufacturing of integrated circuits such as power integrated circuits, there are only the two possibilities, which are illustrated in
FIGS. 1 and 2
.
Thus, in an existing device, to obtain a diode with a specific avalanche threshold, a specific diffused region
3
should be provided, that is, a region with a specific implantation dose or a specific anneal duration. It is of course impossible in an integrated circuit to provide an area with a specific anneal duration since the anneal performed for this area would react upon the other areas of the integrated circuit. On the other hand, to perform this implantation at a specific dose would increase the number of integrated circuit manufacturing steps, which is always attempted to be avoided in an existing line.
SUMMARY OF THE INVENTION
Thus, an object of the present invention is to provide a method of manufacturing an avalanche diode of selected threshold, distinct from the thresholds naturally existing by using the existing junctions of that process, this threshold being choosable without adding any additional processing step to the existing steps.
To achieve these objects, the present invention provides a method of manufacturing an avalanche diode of determined threshold in a substrate of a first conductivity type with a low doping level, including the steps of diffusing in the substrate at least one first region of the first conductivity type; diffusing in the substrate a second region of the second conductivity type protruding from the first region. The opening of a mask of definition of the first region has a lateral extent smaller than the diffusion depth of the first region in the substrate, this lateral extent being chosen smaller corresponding to as the desired avalanche threshold being higher.
According to an embodiment of the present invention, each diffusion is preceded by an implantation.
According to an embodiment of the present invention, each first region includes a plurality of separate and identical sub-regions.
The present invention also provides a method of simultaneously manufacturing several avalanche diodes of distinct and determined thresholds in a substrate of a first conductivity type of low doping level including the steps of diffusing in the substrate first regions of the first conductivity type; diffusing in the substrate second regions of the second conductivity type, each of which protrudes from a first region. The openings of the masks of definition of each of the first regions have lateral extents smaller than the diffusion depths of the first regions, the lateral extent being smaller corresponding to as the desired avalanche threshold being higher.
The foregoing objects, features and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings.
REFERENCES:
patent: 4064620 (1977-12-01), Lee et al.
patent: 4416708 (1983-11-01), Abdoulin et al.
patent: 5032534 (1991-07-01), Ducreux
patent: 57122579 (1982-07-01), None
patent: 59079578 (1984-05-01), None
patent: 59079578 (1984-08-01), None
Bowers Charles
Galanthay Theodore E.
Huynh Yennhu B.
Seed IP Law Group PLLC
STMicroelectronics S.A.
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