Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-02-08
2002-09-03
Jackson, Jr., Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S355000, C257S361000, C257S362000, C257S578000, C257S591000
Reexamination Certificate
active
06445040
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and, particularly, to a lateral bipolar type input/output protection device to be used for a semiconductor integrated circuit.
2. Description of the Related Art
A conventional lateral bipolar type input/output protection device is formed by the structure which includes a field oxide formed in a well region formed on a semiconductor substrate of the same conductivity type with the well region such as field isolation structure disclosed in Japanese Patent Application Laid-open Nos. H8-51188 and H7-122715.
FIG. 3
is a cross section of a conventional lateral bipolar type input/output protection device. As shown in
FIG. 3
, an N type collector diffusion layer
12
, an N type emitter diffusion layer
13
and a P type diffusion layer
14
for grounding a substrate are formed on a P type well
17
of the P type substrate
19
and the respective layers
12
,
13
, and
14
are isolated from each other by a field oxide film
16
formed by the Local Oxidation of Silicon (LOCOS). In this structure, when a negative high voltage pulse is applied to an input/output terminal
11
due to electrostatic discharge (ESD), etc., a PN junction between the N type collector diffusion layer
12
and the P type well
17
is forward-biased, so that over-current flows from the input/output terminal
11
through the P type diffusion layer
14
to a ground terminal
15
, by the forward diode formed by the PN junction. When a positive high voltage pulse is applied to an input/output terminal
11
due to ESD, etc., the PN junction between the N type collector diffusion layer
12
and the P type well
17
is reverse-biased, and, when the applied voltage exceeds a breakdown voltage of the junction, avalanche breakdown current as well as a substrate current due to impact ionization in an end portion of the junction flow to the P type well
17
. With the avalanche breakdown current and the substrate current flowing to the P type well
17
, a potential of the P type well
17
rises with respect to the ground terminal
15
, due to an influence of a parasitic resistance component of the P type well
17
. When the potential of the P type well
17
rises and the PN junction between the P type well
17
and the N type emitter diffusion layer
13
becomes forward-biased, a lateral NPN bipolar transistor turns ON and a voltage between the input/output terminal
11
and the ground terminal
15
is clamped at a low value. As mentioned, when the positive high voltage pulse is applied to the input/output terminal
11
due to ESD, etc., the lateral NPN bipolar transistor turns ON to release the over-current to the ground terminal
15
.
Conventional input/output protection devices themselves are also disclosed in Japanese Patent Application Laid-open Nos. S62-224057, S63-278267 and H3-272180.
In a recent semiconductor integrated circuit, in order to increase the integration density, a shallow trench isolation (STI) structure is becoming popular as the field isolation structure in lieu of the LOCOS structure. In the STI structure, however, it is necessary, in order to keep a fine isolation, to provide an isolation oxide film deeper compared with that of the LOCOS structure. If such STI structure, in which a field oxide film is formed deeper, were applied to the conventional lateral bipolar type input/output protection device, a base width should be increased during a bipolar operation thereof and current amplification is lowered, so that the bipolar operation hardly occurs. Therefore, the STI structure can not be applied to the conventional lateral bipolar type input/output protection device since the ESD protection performance is degraded.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a lateral bipolar type input/output protection device whose protection performance is not degraded even when a deep field isolation structure such as the STI structure is applied.
A lateral bipolar type input/output protection device according to the present invention has a well formed below an emitter impurity diffusion layer and having the same conductivity type as that of the emitter impurity diffusion layer. Therefore, it is possible to easily perform a bipolar operation and to prevent protection performance from being degraded. As a result, it is obtained sufficient ESD robustness even when the size of the semiconductor integrated circuit is smaller by using the field isolation structure such as STI structure.
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patent: 4038680 (1977-07-01), Yagi et al.
patent: 4760433 (1988-07-01), Young et al.
patent: 5945726 (1999-08-01), Prall et al.
patent: 6051458 (2000-04-01), Liang et al.
patent: 62224057 (1987-10-01), None
patent: 63278267 (1988-11-01), None
patent: 403159246 (1989-11-01), None
patent: 3272180 (1991-12-01), None
patent: 405190564 (1993-07-01), None
patent: 7122715 (1995-05-01), None
patent: 851188 (1996-02-01), None
patent: 8-111508 (1996-04-01), None
patent: 9-36357 (1997-02-01), None
patent: 10-261764 (1998-09-01), None
patent: 2000-200694 (2000-07-01), None
Hayes & Soloway P.C.
Jackson, Jr. Jerome
NEC Corporation
Nguyen Joseph
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