Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device – Device protection
Reexamination Certificate
2002-10-22
2004-11-30
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
Device protection
C257S107000, C257S110000, C257S111000, C257S121000, C257S355000, C257S367000
Reexamination Certificate
active
06825504
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a semiconductor integrated circuit device and a manufacturing technique therefore; and more particularly, the invention relates to a technique effective for use in a semiconductor integrated circuit device, provided with a protection circuit having a thyristor structure, and a manufacturing technique therefore.
With advances in miniature processing technology in a semiconductor manufacturing process, miniaturization of elements, interconnections, etc. constituting a semiconductor integrated circuit device, is now receiving considerable attention. With such miniaturization, the performance of the semiconductor integrated circuit device is increasingly improving.
On the one hand, however, a problem arises in that the miniaturized elements, interconnections, etc. are extremely susceptible to an excessive voltage or overvoltage, such as static electricity or the like, and are easily broken. There has been a strong demand for elucidation of the mechanism which causes the deterioration and the destructive phenomena due to static electricity and the establishment of a protective structure with a view toward ensuring the reliability of the semiconductor integrated circuit device.
Meanwhile, the present inventors have discussed a protection circuit having a thyristor structure. This protection circuit is electrically connected to a wiring path for connecting an external terminal and an internal circuit to one another. Described more specifically, the protection circuit is constructed by electrically connecting, for example, a thyristor having p
+
, n, p and n
+
between an external terminal and a ground potential.
In the present protection circuit, a discharge path varies according to the polarity of the voltage applied from the outside. The protection circuit has a structure wherein, when an excessive voltage or overvoltage applied from the outside is positive, the protection circuit is discharged in accordance with the operation of the thyristor; and, when the overvoltage is negative, it is discharged in accordance with the operation of each lateral bipolar transistor.
A known protection circuit has been described in, for example, the IEEE, 1991, CUSTOM INTEGRATED CIRCUIT CONFERENCE 27.2.1. According to this reference, since parasitic bipolar transistors, each having a large drive capability, are used as protection elements, a surge current is allowed to escape satisfactorily so that the electro static discharge (hereinafter called “ESD”) resistance can be enhanced.
Further, a protection circuit having a thyristor structure has been described in, for example, the 1988 EOS/ESD SYMPOSIUM PROCEEDINGS [A PROCESS-TOLERANT INPUT PROTECTION CIRCUIT FOR ADVANCED CMOS PROCESSES], P201-P205. The basic device structure and operation of a thyristor constituting the protection circuit have been explained in this publication.
Another known protection circuit having a thyristor structure has been disclosed in, for example, Japanese Patent Application Laid-Open No. 4-196352 (reference 1) or Japanese Patent Application Laid-Open No. 6-62529 (reference 2). According to these references 1 and 2, a diode (corresponding to reference numeral
300
in
FIG. 3
or the like in the reference 1 or symbol D
1
in
FIG. 1
or the like in the reference 2) for the protection circuit is provided in a stage posterior to a thyristor for the protection circuit. In these references, however, the diode is provided in a stage posterior to a resistor for the protection circuit, which has been intentionally added to the stage posterior to the thyristor, and is provided in a region different from a well in which the thyristor is provided in a semiconductor substrate.
SUMMARY OF THE INVENTION
However, the present inventors have discovered a problem in the protection circuit having a thyristor structure in that a difference in the ESD resistance tends to occur according to the polarity of an overvoltage applied from the outside.
That is, the protection circuit having a thyristor structure has a problem in that, when the holding voltage is low and the amount of energy used up or consumed through the discharge path is dispersed in a low state when the discharge is carried out through the thyristor (when a positive overvoltage is applied), the ESD resistance is high; whereas when the holding voltage is high, the amount of energy consumed through the discharge path is large and the discharge current is easily concentrated on a reverse junction when the discharge is carried out through each lateral bipolar transistor (when a negative overvoltage is applied), the ESD resistance is low.
Therefore, an object of the present invention is to provide a technique which is capable of eliminating the difference in ESD resistance caused by different polarities of overvoltages applied to an external terminal, and which is capable of enhancing the ESD resistance of a semiconductor integrated circuit device to both positive and negative overvoltages.
The above and other objects and novel features of the present invention will become apparent from the description provided in the present specification and the accompanying drawings.
A summary of typical features of the invention as disclosed in the present application will be described in brief in the following manner.
According to one aspect of the present invention, there is provided a semiconductor integrated circuit device comprising:
a protection element having a thyristor structure, which is electrically connected between an external terminal and a ground potential, the protection element being provided on a semiconductor substrate, and
a diode serving as a protection element electrically connected between the external terminal and the ground potential so that the diode is connected in the forward direction when a negative overvoltage is applied to the external terminal.
Thus, since a diode for allowing a negative overvoltage to escape is provided as a protection element as well as a thyristor for allowing a positive overvoltage to escape, an excessive current or overcurrent is allowed to promptly escape from a ground potential to an external terminal through the diode when the negative overvoltage is applied to the external terminal. It is therefore possible to enhance the ESD resistance to a negative overvoltage. That is, according to the present invention, since a high ESD resistance to both positive and negative overvoltages applied to the external terminal can be obtained, the yield and reliability of the semiconductor integrated circuit device can be enhanced.
Further, since a protection circuit element is made up of a diode of relatively small area, the entire occupied area of a protection circuit will not significantly increase. Therefore, a high ESD resistance to both positive and negative overvoltages applied to the external terminal can be obtained.
According to another aspect of the present invention, there is provided a semiconductor integrated circuit device, wherein a protection element having the thyristor structure includes;
a first semiconductor region of a conductivity type opposite to that of the semiconductor substrate, which is formed in an upper layer of the semiconductor substrate;
a second semiconductor region of a conductivity type opposite to that of the semiconductor substrate, the second semiconductor region being formed in an upper layer of the semiconductor substrate so as to be spaced away from the first semiconductor region;
a third semiconductor region corresponding to a region of a conductivity type opposite to that of the first semiconductor region, the third semiconductor region being formed between at least the first semiconductor region and the second semiconductor region in the semiconductor substrate;
a fourth semiconductor region formed within the first semiconductor region, constructed by a semiconductor region of the same conductivity type as that of the first semiconductor region and electrically connected to the external terminal;
a fifth semiconductor region formed within
Ishizuka Hiroyasu
Kubota Katsuhiko
Okuyama Kousuke
Flynn Nathan J.
Sefer Ahmed N.
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