JPH0553307B2 - - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a semiconductor integrated circuit equipped with an input or output protection circuit connected to an external lead-out pin of the integrated circuit and having a surge absorbing MOS transistor. Regarding circuits.

(Prior Art) FIG. 2 shows a circuit diagram of the above-mentioned input protection circuit. This is input pad 1, resistors R1, R2,
It is composed of a field transistor Tr1 and a MOS transistor Tr2. The surge that enters the input pad 1 is slowed down by the resistors R1 and R2, and the surge enters the field transistor Tr1 and the MOS transistor Tr2.
absorbed by.

FIG. 3a is a pattern plan view of the transistor Tr2, and FIG. 3b is a cross-sectional view taken along the line B-B in FIG. 6 is a field insulating film, and 7 is an interlayer insulating film. As shown in this figure, conventionally, the field edge on the drain side (the edge of the field insulating film 6) and the edge of the metal 5 almost coincide as shown by the arrows in the figure.
Alternatively, the metal 5 was on the inside (on the diffusion layer 3 side) due to the field edge.

(Problems to be Solved by the Invention) As described above, conventionally, the metal 5 was almost coincident with the field edge or was located inside the field edge. At this time, when the metal 5 becomes high potential due to a surge, etc., the depletion layer near the field edge narrows, and a particularly strong electric field is applied to that area, damaging the field edge, causing leakage at that area, and damaging the chip itself. It will break. This means that when the field implant layer P ⁺ is deposited under the field insulating film 6, the depletion layer especially near the field edge becomes narrower, so that the pain near the field edge is noticeable.

An object of the present invention is to widen the depletion layer at the field edge portion and protect that portion.

[Structure of the Invention] (Means and Effects for Solving the Problems) The present invention includes an input or output protection circuit connected to an external lead-out pin of an integrated circuit and having a surge absorbing MOS transistor. The drain electrode of the transistor is placed on the field insulating film on the drain side of the MOS transistor for surge absorption of the circuit, and the distance between the field insulating film and the film and the drain electrode thereon is higher than the edge of the field insulating film on the drain side. The device is characterized in that a drain electrode protruding portion is provided that protrudes from the side covering the field insulating film by more than half the thickness of the field insulating film plus the interlayer insulating film. When a surge is input to this drain electrode protrusion from an external lead-out pin via the input pad, the drain electrode is The depletion layer in the field edge section below the protruding section is widened to weaken the electric field and protect that section.

(Example) An example of the present invention will be described below with reference to the drawings. Fig. 1a is a pattern plan view of the main part of the same embodiment, and Fig. 1b is a cross-sectional view of the same, but since this is an example in which it corresponds to Figs. 3a and b, the corresponding parts are The same reference numerals are used to omit the explanation, and the characteristic parts will be explained. The feature of this embodiment is that on the field insulating film 6 on the drain 3 side of the surge absorption transistor of the input protection circuit, the drain electrode 5 of the transistor is placed on the field insulating film 6 on the side of the field insulating film 6 on the drain side. The thickness of the field insulating film 6 is at least half (d/2) of the thickness d, which is the sum of the thickness of the field insulating film 6 and the thickness of the interlayer insulating film 7.
In other words, the drain electrode protruding portion 5a is provided to protrude from the side that covers the drain electrode.

With the above configuration, the drain electrode 5
When a surge is input through the input pad 1, a depletion layer spreads around the drain 3, and this depletion layer, especially at the edge of the field insulating film 6, The surge (high potential) applied to the protruding electrode portion 5a causes it to expand in the direction away from the drain 3, thereby weakening the electric field near the field edge portion and protecting that portion.

According to experiments, the effect is weak when both sides of the drain electrode projecting portion 5a are d/2 or less;
In the case of d/2 or more, an effect that can withstand use was obtained.

Note that the present invention is not limited to the embodiments and can be applied in various ways. For example, in the embodiment, a case where the present invention is applied to an input protection circuit has been explained, but a structure similar to that shown in FIG. It may also be used as an output protection circuit, so
The present invention can also be applied to this case.

[Effects of the Invention] As explained above, according to the present invention, the depletion layer near the field edge expands when the drain electrode receives a surge, weakening the electric field at the field edge, thereby protecting the field edge. The semiconductor integrated circuit that can be obtained can be provided.

[Brief explanation of drawings]

FIG. 1a is a pattern plan view for explaining an embodiment of the present invention, FIG. 1b is a sectional view of the same, FIG. 2 is an input protection circuit diagram, and FIG. Figure b is a sectional view of the same. 2... Source, 3... Drain, 4... Gate electrode, 5... Drain electrode, 5a... Drain electrode protrusion, 6... Field insulating film, 7...
Interlayer insulation film.

Claims (1)

[Claims] 1 Equipped with an input or output protection circuit connected to an external lead-out pin of an integrated circuit and having a surge absorption MOS transistor; The electrode covers the field insulating film by at least half the thickness of the field insulating film plus the interlayer insulating film between the film and the drain electrode above the edge part of the field insulating film on the drain side. A semiconductor integrated circuit characterized by protruding to the side.