JPS62155548A - Electrostatic protection circuit elements for semiconductor integrated circuits - Google Patents

Abstract

PURPOSE:To prevent the short circuits among input/output terminals and substrate potential by simple structure by forming a diffusion layer having a conductivity type different from that of a semiconductor substrate just under junction sections among the terminals and polycrystalline silicon. CONSTITUTION:Input/output terminals 3 are connected to a protective resistor 4, and connected to other elements from other terminals, but a diffusion layer 15 having a conductivity type different from that of a substrate 11 is formed just under polycrystalline silicon in the protective resistor 4, the diffusion layer 15 is particularly isolated from other diffusion layers, and the diffusion layer 15 is not supplied with potential and is brought to a floating state. Consequently, thickness corresponding to the depth of a diffusion layer is added to the thickness of a conventional insulating film 12 among sections up to the substrate 11 from junction regions 14 among conventional input/output terminals and protective resistor, thus acquiring an electrostatic protective circuit element in which field breaking strength to the substrate is further increased. When a region such as a well region in a complementary MOS integrated circuit device is used as the diffusion layer 15, no process is added, and the titled element can be realized at cost the same as conventional devices.

Description

[Detailed description of the invention] ['Industrial application field] The present invention relates to an electrostatic protection circuit element for a semiconductor integrated circuit.

[Conventional technology]

Conventionally, in this type of electrostatic protection circuit element, as shown in FIG.
and further connected to the gate of an element 10 (inverter in this case) to be protected via a protective resistor 9, and the protective resistor 4 was formed on an oxide film on the semiconductor substrate. . Element 10 to be protected by flowing it to the positive or negative power terminals 1 and 2 via the resistor 4 and the diode 7 or 8 when static electricity is applied to the terminal 3.
is protected by applying only a voltage as low as the voltage across the diode. Here, 5.6 is the internal resistance of the diode 7.8.

FIG. 3 is a sectional view of a protective resistor section of a conventional electrostatic protection circuit element. In FIG. 3, 11 is a substrate, an oxide film 12 is formed on the substrate 11, a protective resistor 4 made of polycrystalline silicon is formed on the oxide film 12, and the protective resistor 4 is connected to an insulating layer 13.
The protective resistor 4 is coated with an opening and a terminal 3 is provided at both ends of the protective resistor 4. Note that 16 is a surface protective film.

[Problem that the invention seeks to solve]

As shown in the cross-sectional view of FIG. 3, the conventional protective resistor 4 described above is formed on the oxidized layer 12 on the semiconductor substrate 11, so that static electricity is applied between the terminal 3 and the substrate 11. An electric field breakdown occurs in the substrate 11 from the junction region 4 between the terminal 3 and the protective resistor 4 through the polycrystalline silicon 4 and the oxide film 12.
There is a problem in that the terminal 3 and the substrate 11 are electrically short-circuited.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrostatic protection circuit element for a semiconductor integrated circuit that eliminates the problems of the conventional art and can prevent short circuits between terminals and substrate potential with a simple structure.

[Means for solving problems]

An electrostatic protection circuit element for a semiconductor integrated circuit according to the present invention is an electrostatic protection circuit element for a semiconductor integrated circuit having an input/output terminal directly connected to polycrystalline silicon on a semiconductor substrate. It has a structure in which a diffusion layer having a conductivity type different from that of the semiconductor substrate is formed directly below the junction with silicon.

〔Example〕

FIGS. 1(a) and 1(b) are a plan view and a sectional view of an embodiment of the present invention.

As shown in FIGS. 1(a) and 1(b), in the embodiment, the input/output terminal 3 is connected to the protective resistor 4, and the other end is connected to the pond element, but directly below the polycrystalline silicon of the protective resistor 4. board 1
In particular, the diffusion layer 15 is separated from other diffusion layers, and the diffusion layer 15 has a conductivity type different from that of the diffusion layer 15.
Floating without supplying potential. When scolded,
From the conventional input/output terminal and protective resistor junction area 14 to the board 11
Since the thickness corresponding to the depth of the diffusion layer is added to the thickness of the conventional insulating film 12, an electrostatic protection circuit element with further increased electric field breakdown strength to the substrate can be obtained. . Incidentally, if a well region of a complementary MOS integrated circuit device is used as the diffusion layer 15, no additional process is required and the cost can be the same as that of the conventional method.

In addition, in FIG. 1, there is a diffusion layer 1 immediately below the protective resistor
However, a diffusion layer may be formed only directly under the junction region 14 of the protective resistor 4.

〔Effect of the invention〕

As explained above, in the present invention, by forming a diffusion layer under a polycrystalline silicon protective resistor, the insulating region from the junction area of the terminal and the protective resistor to the substrate has the thickness of the insulating film formed on the substrate. The thickness corresponding to the depth of the diffusion layer is added to the layer, and the electric field breakdown strength to the substrate can be further increased.

[Brief explanation of drawings]

Figures 1 (a) and (b) are a plan view and a sectional view of an embodiment of the present invention, Figure 2 is a conventional general input protection circuit diagram, and Figure 3 is a conventional electrostatic protection circuit diagram. FIG. 3 is a cross-sectional view of a circuit element. 1.2... Power supply, 3... Terminal, 4.9... Protection resistor, 5.6... Resistor, 7.8... Protection diode,
DESCRIPTION OF SYMBOLS 10... Inverter, 11... Substrate, 12... Oxide film, 13... Insulating layer, 14... Joint part, 15...
- Diffusion layer, 16... surface protection film.

Claims (1)

[Claims] In an electrostatic protection circuit element for a semiconductor integrated circuit having an input/output terminal directly connected to polycrystalline silicon on a semiconductor substrate, there is a conductive layer different from that of the semiconductor substrate immediately below the junction between the input/output terminal and the polycrystalline silicon. An electrostatic protection circuit element for a semiconductor integrated circuit, characterized in that a diffusion layer having a shape is formed.