Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-03-18
2001-10-02
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S366000
Reexamination Certificate
active
06297536
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to electrostatic discharge protection for semiconductor integrated circuitry. More particularly , the present invention relates to an improved diode structure compatible with silicide processes for electrostatic discharge protection.
2. Description of the Related Art
In sub-micron MOS-based technology, electrostatic discharge, ESD hereinafter, becomes a reliability concern. As shown in
FIG. 1
, a part of diodes D
1
and D
2
are provided at the pad
1
of a conventional integrated circuit. When ESD occurs at the pad
1
, the diode D
1
or D
2
enters breakdown to bypass the ESD stress so as to protect the internal circuit
2
from ESD damage.
Referring to
FIG. 2
, the diode D
1
or D
2
of
FIG. 1
disposed on semiconductor substrate
20
is illustrated in a cross-sectional view. In
FIG. 2
, an insulator
21
, such as field oxide grown by means of local oxidation, are provided on the P-type semiconductor substrate
20
. An N-type diffusion region
22
is formed in the semiconductor substrate
20
and encircled by the insulator
21
. Therefore, diodes D
1
or D
2
are constituted by the P/N junction between the N-type diffusion region
22
and the P-type substrate
20
. In addition, a silicide layer
23
can be formed over the N-type diffusion region
22
by a so-called self-aligned silicidation (salicide) process to reduce the contact sheet resistance.
However, under high current stressing conditions the ballastic resistance is dramatically reduced. Hence, once the hot spot is initiated at the diffusion edge
24
, there is very little resistance to prevent current localization through the hot spot. Therefore, when the temperature at the silicide reaches up to 1000° C., the silicide can begin to decompose or interact with the silicon, or both, and cause damage to the diode D
1
or D
2
.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a diode structure compatible with the silicide process without additional process steps.
The above object can be realized by providing a diode structure comprising: a semiconductor layer of a first conductivity type, a diffusion region of a second conductivity type formed in the semiconductor layer, and a doped region of the second conductivity type formed in the semiconductor layer around the diffusion region. The doped region has a doping concentration less than the diffusion region to provide a ballastic resistance under a high current stressing condition.
Accordingly, during an ESD event a discharge current can flow through the silicide layer as well as the diffusion junction, and then pass through the P/N junction between the diffusion region and the substrate uniformly. Therefore, the discharge current is prevented from localization through the diffusion edge so as to protect the diode from ESD damage.
REFERENCES:
patent: 3246177 (1966-04-01), Schroeder
patent: 3339086 (1967-08-01), Shockley
patent: 3803461 (1974-04-01), Beneking
patent: 5663587 (1997-09-01), Miyazaki
patent: 5693550 (1997-12-01), Torii
Meier Stephen D.
Nath & Associates PLLC
Novick Harold L.
Winbond Electronics Corp.
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