Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1998-09-30
2001-02-27
Saadat, Mahshid (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S357000, C257S358000, C257S359000, C257S360000, C257S361000, C257S362000, C257S363000
Reexamination Certificate
active
06194764
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a semiconductor device disposed in at least one semiconductor body and having at least one protection element for protecting an integrated semiconductor circuit against electrostatic discharge (ESD).
One such so-called electrostatic discharge (ESD) protection element is known from the article “Design and Layout of a High ESD Performance NPN Structure for Submicron BiCMOS/Bipolar Circuits”, Proceeding of the IEEE International Reliability Physics Symposium (1996), pp. 227-32, J. Chen, X. Zhang, A. Amerasekera, T. Vrotsos.
Integrated semiconductor circuits in a chip include protective circuits to protect the inputs or outputs (I/O ports) against electrostatic overvoltages and the electrostatic discharges (ESD) caused thereby. These so-called ESD protection elements are connected between the input pad of an integrated semiconductor circuit and the input or output terminal to be protected. Thus an ESD protection element assures that, when a parasitic overvoltage occurs, the ESD protection element switches, and the parasitic overvoltage pulse is diverted to one of the supply potential conductor tracks. In an extreme case, such overvoltage pulses may destroy the component.
However, under operating conditions, described for instance in the product specification, the ESD protection elements must not impair the function of the integrated semiconductor circuit to be protected. This means that the switching voltage of the ESD protection element must be outside the signal voltage range of the protected terminal pads. To provide a good protective action, the ESC protection element should break through upstream of the most-critical circuit path. As a rule, this requires an exact adjustment of the switching voltage of the respective ESD protection element, under the essential boundary condition that the process control, which has been optimized with regard to the properties of the components of the integrated semiconductor circuit to be protected, is not changed by the addition of the ESD protection elements.
Another essential condition results from the spatial disposition of the terminal pads in the immediate vicinity of the integrated semiconductor circuit to be protected. In particular, because of the relatively high current to be driven, the terminal pads are located in the vicinity of the output drivers. The ESD protection structure is therefore often connected to the supply line supplying current to the output driver.
In protection elements having a pronounced snap-back behavior, such as thyristors and bipolar transistors, rapid switch-on events or unwanted pulses can cause a switching through, even though the breakdown voltage determined by measuring the characteristic curve in the low-current range is outside the specified signal voltage range. This is also known as transient latch-up effect which generally destroys the ESD protection element. The transient latch-up occurs particularly in smart power applications.
Therefore, despite high ESD strength and good protective action, such thyristors or bipolar transistors cannot be employed as ESD protection elements because of the transient latch-up. One is thus limited to using breakdown diodes or transistors with low gain. Yet these components have a much lower ESD strength.
For further details, characteristics, advantages and the modes of operation of ESD protective circuits, Published European Patent Application EP 0 623 958 Al and the aforementioned paper by J. Chen et al. are hereby incorporated by reference in their entirety.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a semiconductor device for ESD protection which overcomes the above-mentioned disadvantages of the heretofore-known protection devices of this general type and which has an adjustable trigger current.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor device, comprising a semiconductor body; an integrated semiconductor circuit in the semiconductor body; a terminal pad; an electrically conductive connecting line connecting the terminal pad to the integrated semiconductor circuit; a first potential rail carrying a first supply potential during an operation of the integrated semiconductor circuit; a second potential rail carrying a second supply potential during the operation of the integrated semiconductor circuit; a protection element for protecting the integrated semiconductor circuit against an electrostatic discharge connected between the terminal pad and the integrated semiconductor circuit and connected to at least one of the first and the second potential rails; the protection element including an integrated vertical protection transistor having a base and having a load path connected between the electrically conductive connecting line and one of the first and second potential rails, a control device controlling the base, and a current carrying configuration dividing a parasitic current pulse into a horizontal component and a vertical component.
In accordance with another feature of the invention, a buried layer of a first conductivity type is formed in the semiconductor body; an epitaxial layer of a first conductivity type includes a base zone of a second conductivity type, the base zone being formed in a partial region of the epitaxial layer spaced apart from the buried layer, the base zone having a given dopant concentration and serving as the base; an emitter zone of the first conductivity type formed in the base zone; a base contact zone of a second conductivity type formed in the base zone and having a dopant concentration greater than the given dopant concentration of the base zone; a base drift zone of the second conductivity type provided between the base zone and the buried layer; and wherein the protection transistor has an emitter and a collector, the emitter zone serves as the emitter and the buried layer serves as the collector.
In accordance with another feature of the invention, the current carrying configuration is defined by a horizontal disposition of the base drift zone relative to the base contact zone and the emitter zone.
In accordance with a further feature of the invention, the control device includes an integrated diode connected in a reverse direction and disposed between the buried layer and the base drift zone.
In accordance with yet another feature of the invention, the control device includes an integrated resistor.
In accordance with another feature of the invention, the integrated resistor has a conductance value defined by the given dopant concentration in the base zone.
In accordance with a further feature of the invention, the base drift zone has a dopant concentration and a thickness, and the protection element has a switching voltage defined by the dopant concentration of the base drift zone and by the thickness of the base drift zone.
In accordance with yet another feature of the invention, a terminal zone is connected to the buried layer and to one of the first and second potential rails.
In accordance with a further feature of the invention, the terminal zone is disposed annularly around the base zone and/or the base drift zone.
In accordance with another feature of the invention, the terminal zone is spaced apart equidistantly by a given distance from the base zone and/or the base drift zone.
In accordance with a further feature of the invention, the buried layer and the partial region each have a lateral cross-sectional area, the lateral cross sectional area of the buried layer being greater than the lateral cross-sectional area of the partial region.
In accordance with yet another feature of the invention, the emitter zone has a dopant concentration being higher than the dopant concentration of the base zone.
In accordance with another feature of the invention, an anode zone provided between the buried layer and the terminal pad.
A semiconductor device according to the invention has the following characteristics:
a) at least one terminal pad, wh
Gossner Harald
Schwetlick Werner
Stecher Matthias
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
Ortiz Edgardo
Saadat Mahshid
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