JPH02278760A - Semiconductor integrated circuit device - Google Patents

Abstract

PURPOSE:To make concentration of electric current difficult by a method wherein a buried diffusion layer of a second conductivity type is buried between a semiconductor substrate of a first conductivity and an epitaxial layer, the epitaxial layer is set to be of the first conductivity type and an impurity concentration of this layer is made higher than that of the semiconductor substrate. CONSTITUTION:A buried diffusion layer 2 of a second conductivity type is buried between a semiconductor substrate 1 of a first conductivity type and an epitaxial layer. The epitaxial layer 3 is of the first conductivity type and its impurity concentration is made higher than that of the semiconductor substrate 1. A diffusion layer 5, of the first conductivity type, whose impurity concentration is higher than that of the epitaxial layer 3 is formed on the upper-part surface of the buried diffusion layer 2. An external terminal is connected to the buried diffusion layer of the second conductivity type. A P-N junction is formed of the following: the buried diffusion layer 2 of the second conductivity type; the semiconductor substrate 1; the epitaxial layer 3. An internal distance of the diffusion layer 5, of the first conductivity type, which has been formed on the surface is made small; an electric current acts so as to flow on a whole face which faces the buried diffusion layer 2; accordingly, it is possible to make concentration of electric current difficult.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application 1] The present invention relates to the structure of a semiconductor integrated circuit device, and particularly relates to a structure that increases the amount of static 11ii4 in a semiconductor integrated circuit device.

[Prior Art] In order to protect internal elements from overvoltage such as static electricity applied to the external terminals of a semiconductor integrated circuit device, a series resistance (R) as shown in FIG. 5(a) and a recovery lower than the breakdown voltage of the internal elements are used. A protection circuit consisting of a diode (Di) with a possible breakdown voltage is used. Also the fifth
As shown in Figure (b), the diffusion layer resistance of the diode is the series resistance (R
) may also be used. As shown in FIG. 6, this diode is usually composed of a PN junction composed of a semiconductor substrate 10 and a diffusion layer 11 of the opposite conductivity type. Contact with the substrate is brought out to the surface through a diffusion layer 12 of the same conductivity type as the substrate, which is disposed so as to surround the diffusion layer 11.

[Problems to be Solved by the Invention] However, the conventional diode described above is a diffused ff1l
The breakdown voltage of 1 is determined around the diffusion layer with a small radius of curvature, and the low resistance diffusion layer 12 for contacting the semiconductor substrate exists surrounding it, so the main current circuit is limited to the periphery. Therefore, current concentration tends to occur, and the junction breakdown or leakage current increases due to heat generated by the current concentration, impairing the functionality of the semiconductor integrated circuit device.

Since the current path is limited, the internal resistance of the PN junction tends to increase. In order to reduce the internal resistance, it is necessary to increase the peripheral length, which increases the area occupied on the surface. Further, a high internal resistance has the problem that even if the break-down voltage is low, when a large current flows, the voltage between its terminals becomes high and the function as a protection element is impaired. SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and its purpose is to provide a diode that is less likely to cause current concentration, has a low internal resistance, and occupies a small surface area.

[Means for Solving the Problems] A semiconductor integrated circuit device of the present invention includes a buried diffusion layer of a second conductivity type buried between a semiconductor substrate of a first conductivity type and an epitaxial layer, and the epitaxial layer is a buried diffusion layer of a first conductivity type. The impurity concentration is higher than that of the semiconductor substrate in the epitaxial layer, and a first layer having an impurity concentration higher than that of the epitaxial layer is formed on the upper surface of the buried diffusion layer.
It is characterized by being provided with a conductive type diffusion layer.

The external terminal is connected to the second conductivity type buried diffusion layer, and a PN junction is formed between the second conductivity type buried diffusion layer, the semiconductor substrate, and the epitaxial layer. Since the impurity concentration of the first conductivity type epitaxial layer is higher than the impurity concentration of the semiconductor substrate, breakdown can occur on the upper surface side of the buried diffusion layer.

The first conductivity type diffusion layer formed on the surface reduces the internal resistance (
At the same time, since current flows across the entire surface facing the buried diffusion layer, current concentration can be made less likely to occur.

[Embodiment 1] FIGS. 1 to 3 show main parts of an embodiment of the present invention, and FIG. 1(a) is a plan view of a diode.

(b) is a sectional view taken along line A-A' in plan view (a).

(c) schematically shows the impurity concentration along line B-B" in cross-sectional view (b).1 For example, an N-type diffusion layer is formed on a 100 cm P-type semiconductor substrate l by selective diffusion. On this, an N-type diffusion layer is formed by epitaxial method. A P-type epitaxial layer 3 of 1 Ωcm is formed. This N-type diffusion layer becomes the buried diffusion layer 2. After that, an isolation oxide 1114 is formed by selective oxidation, and the upper high concentration P is formed.
A type diffusion layer 5 and an N-type diffusion layer 6 for a pulling electrode of a buried diffusion layer are formed. This is completed by forming metal electrodes 7 on 5 and 6. The external electrode is connected to a buried diffusion layer 2, which forms a PN junction with a P-type semiconductor substrate l and an epitaxial layer 3. Since the concentration of the epitaxial layer is higher than the concentration of the semiconductor substrate, breakdown occurs between the epitaxial layer and the upper epitaxial layer. Since the heavily doped P-type diffusion layer 5 is formed on this upper surface, the breakdown current flows over the entire surface facing the buried It itt layer 2 . This prevents current concentration and lowers internal resistance.

FIGS. 2(a) to 2(C) show another embodiment, in which a medium concentration P-type diffusion layer 8 is placed between the buried diffusion layer 2 and the high (growth P-type diffusion layer 5) to adjust the breakdown voltage. By forming this, it becomes an effective protection element.

FIGS. 3(a) to 3(c) show another embodiment in which an N-type epitaxial layer is formed on a P-type semiconductor substrate, and a buried diffusion layer 2 is formed so as to be enclosed by a P-type medium concentration diffusion layer 8. This embodiment has a structure similar to that of the embodiment shown in FIG. At this time, the medium concentration diffusion layer 8 must reach the semiconductor substrate l.

FIG. 4 shows an example in which the buried diffusion layer is used as a protection diode and a protection resistor at the same time using the structure shown in FIG. 1. FIG. 4(a) shows a plan view, and FIG. 4(b) shows a cross-sectional view.The structure of the diode part is shown in FIG.
It goes without saying that the image shown in FIG. 3 may also be used.

It goes without saying that the present invention has the same effect even if the conductivity types of P and N are switched.

[Effect of the invention 1] As described above, according to the present invention, the breakdown of the PN junction formed between the buried diffusion layer and the epitaxial layer connected to the external terminal occurs on the upper surface side of the buried diffusion layer, and the breakdown occurs on the surface side. The formed first conductivity type diffusion layer reduces the internal resistance and allows current to flow over the entire surface facing the buried diffusion layer (thereby making it difficult to cause current concentration).

This has made it possible to improve the performance of the protection element and improve the reliability of the semiconductor integrated circuit device.

[Brief explanation of drawings]

1 to 4 are diagrams showing one embodiment of the semiconductor integrated circuit device of the present invention, in which (a) is a plan view, and (b) is an A
-A' cross-sectional view, (c) shows the impurity concentration profile of B-B'. FIG. 5 is a diagram showing an example of a protection circuit. FIG. 6 is a diagram showing the structure of a conventional protection diode,
(a) shows a plan view, and (b) shows a cross-sectional view taken along line AA'. Semiconductor substrate buried diffusion layer Epitaxial layer isolation oxide film Top high concentration diffusion layer Pulling up buried diffusion layer Diffusion layer for electrical bridge Metal electrode Middle concentration diffusion layer Insulating film Semiconductor substrate diffusion layer Semiconductor substrate contact diffusion layer Separation oxide film 1tIll Metal electrode Applicant Seiko Epson Co., Ltd. Agent Patent Attorney Kizobe Suzuki (and 1 other person) Ohgi, At. (&)

Claims (1)

[Claims] A buried diffusion layer of a second conductivity type is buried between the first conductivity type semiconductor substrate and the epitaxial layer, the epitaxial layer is of the first conductivity type and has an impurity concentration higher than that of the semiconductor substrate, and the buried diffusion layer is of the first conductivity type and has an impurity concentration higher than that of the semiconductor substrate. 1. A semiconductor integrated circuit device comprising a first conductivity type diffusion layer having a higher impurity concentration than the epitaxial layer on an upper surface thereof.