Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2001-06-05
2003-11-25
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S173000, C257S355000, C257S356000
Reexamination Certificate
active
06653689
ABSTRACT:
Japanese Patent Application No. 2000-172298, filed on Jun. 8, 2000, is hereby incorporated by reference in its entirety.
TECHNICAL FIELD
The present invention relates to a semiconductor device that incorporates an electrostatic protection circuit, and a method of fabrication thereof.
BACKGROUND
The application of a surge voltage due to static electricity to a signal output terminal, signal input terminal, or signal input-output terminal of a semiconductor device could lead to destruction of internal circuitry. For that reason, it is usual to connect a protective circuit to such signal terminals.
In this case, the gate isolation films of the MOS transistors being protected are becoming thinner as micro-processing techniques become ever finer, and the gate withstand voltage (gate dielectrics breakdown voltage) is decreasing.
With processing at the 0.35 &mgr;m or 0.25 &mgr;m level, the gate withstand voltage is still comparatively high, so that breakdown of a Zener diode occurs when a static charge is applied, which acts as a trigger to cause snapback in an NPN bipolar transistor due to the bipolar operation thereof, making it possible to protect again static charges by imposing a voltage clamp state.
With processing below 0.18 &mgr;m, however, the gate withstand voltage decreases even further, so that the response characteristic is improved even further and thus it is not possible to protect a MOS transistor in this way without discharging static rapidly.
In such a case, an electrostatic protection circuit has been proposed that uses a thyristor instead of an NPN bipolar transistor, to employ the self-amplification operation of the thyristor (such as in Japanese Patent Application Laid-Open No. 9-293881, by way of example).
However, a thyristor is formed of a connection between an NPN bipolar transistor and a PNP bipolar transistor, it has a large number of terminals and the surface area thereof is larger, and thus it cannot be applied to micro-processing. Taking the above-mentioned Patent Application as an example, five electrically isolated impurity diffusion regions are required, which increases the surface area.
In addition, a prior-art electrostatic protection circuit has a resistor in the wiring path that is necessary for applying a static charge to a Zener diode, but, since the Zener diode cannot be made to break down rapidly, there is room for further improvement from the viewpoint of the response characteristic.
A further problem lies in the fact that the amplification capability of a bipolar transistor is dependent on the base length thereof, so that a bipolar transistor having a base length that is long in the lateral direction of the substrate, as in the prior art, would have a low amplification capability, and there is room for further improvement in that the capability of a PNP bipolar transistor is even lower.
SUMMARY
An objective of the present invention is to provide a semiconductor device having an electrostatic protection circuit that can be applied to micro-processing at 0.18 &mgr;m or less and which has a small surface area.
Another objective of the present invention is to provide a semiconductor device having an electrostatic protection circuit that has a good response, by causing a Zener diode to break down immediately after a static charge is applied, to act as a trigger for a thyristor.
A further objective of the present invention is to provide a semiconductor device having an electrostatic protection circuit that has a good response, by improving the amplification capabilities of bipolar transistors that form a thyristor.
A semiconductor device in accordance with a first aspect of the present invention relates to a semiconductor device having an electrostatic protection circuit such that static charge of a positive polarity that is applied to a signal terminal is discharged to a VSS power line side.
This semiconductor device comprises:
a semiconductor substrate;
a p-type and an n-type well regions formed on the semiconductor substrate;
a first p-type impurity diffusion region formed in a surface layer of the p-type well region;
a first n-type impurity diffusion region which is formed in a surface layer of the p-type well region and which is electrically isolated from the first p-type impurity diffusion region;
a second p-type impurity diffusion region which is formed in a surface layer of the p-type well region and which is electrically isolated from the first n-type impurity diffusion region;
a second n-type impurity diffusion region which is formed in a surface layer of the p-type and n-type well regions adjacent to the second p-type impurity diffusion region;
a third n-type impurity diffusion region connected to under surfaces of the second p-type and second n-type impurity diffusion regions in the p-type well region;
a third p-type impurity diffusion region connected to an under surface of the third n-type impurity diffusion region; and
a low-resistance layer formed on a surface of the second p-type and n-type impurity diffusion regions.
A Zener diode is formed by a p-n junction between the third n-type and p-type impurity diffusion regions; an NPN bipolar transistor is formed by the first n-type impurity diffusion region, the p-well region, and the n-well region; and a PNP bipolar transistor is formed by the second p-type impurity diffusion region, the third n-type impurity diffusion region, and the third p-type impurity diffusion region.
In addition, the signal terminal is connected to the second p-type and n-type impurity diffusion regions through the low-resistance layer, and the VSS power line is connected to the first p-type and n-type impurity diffusion regions.
A semiconductor device in accordance with a second aspect of the present invention relates to a semiconductor device having an electrostatic protection circuit such that static charge of a negative polarity that is applied to a signal terminal is discharged to a VDD power line side.
The semiconductor device in accordance with the second aspect of the present invention can be fabricated by substituting n-type components for the p-type components of the semiconductor device in accordance with the first aspect of the invention, and substituting p-type components for the n-type components thereof.
REFERENCES:
patent: 5311042 (1994-05-01), Anceau
patent: 5519242 (1996-05-01), Avery
patent: 5607867 (1997-03-01), Amerasekera et al.
patent: 5856214 (1999-01-01), Yu
patent: 62-002660 (1987-01-01), None
patent: 09-008147 (1997-01-01), None
patent: 09-293881 (1997-11-01), None
patent: A-9-293881 (1997-11-01), None
U.S. patent application Ser. No. 09/866,782, Okawa et al., filed May 30, 2001.
U.S. patent application Ser. No. 09/866,800, Okawa et al., filed May 30, 2001.
Flynn Nathan J.
Mondt Johannes P
Oliff & Berridg,e PLC
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