JPS6092674A - Constant voltage diode - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a constant voltage diode made by silicon epitaxial planar technology, and to improving breakdown voltage characteristics.

Generally, when attempting to create a constant voltage diode in a semiconductor integrated circuit, the reverse breakdown voltage (breakdown voltage) of the base and emitter junction of a transistor is used. By the way, the basic structure of transistors in semiconductor integrated circuits is a planar structure, but when a transistor is made with a planar structure, the end of the PN junction exists on the substrate surface directly under the surface protective film, and diffusion occurs from the surface. It is known that the closer to the substrate surface the higher the impurity concentration gradient, and that the breakdown occurs at the surface of the PN junction. However, due to crystal irregularities and dirt on the surface, breakdown of the PN junction becomes difficult to occur uniformly. A conventional technique for solving this problem is described in Japanese Patent Publication No. 54-9473.

This prior art has the configuration shown in FIG. In FIG. 1, reference numeral 1 denotes a P-type silicon substrate, 2 an N+ type buried diffusion region, 3 an N-type epitaxial island region, and 5.
6 is a heavily doped P-type diffusion region, 7 is a P-type base diffusion region, 8 is an N-type emitter diffusion region, 9 is an N+-type diffusion region for ohmic contact, and 10° 11.12 is an electrode. In this prior art, the bottom portion 15 of the base-emitter junction
The maximum impurity concentration is set to suppress breakdown on the surface. However, in this conventional technology, a base and an emitter are included, and breakdown occurs between the emitter and the highly concentrated base, which not only makes the structure complicated, but also makes it difficult to set and control the breakdown voltage. How many points were there?

The present invention is designed to cause uniform breakdown without changing the breakdown voltage over time, has a simple structure, and allows easy control of the breakdown voltage setting. The purpose is to

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. FIG. 2 is a structural sectional view of this embodiment. In FIG. 2, reference numeral 20 denotes a P-type silicon substrate, and 21 is embedded in the silicon substrate 20.
A buried diffusion region 22 of an N+1 type of conductivity opposite to that of the silicon substrate 20 is epitaxially grown on the silicon substrate 20 and separated into islands by isolation diffusion regions 23 and 24, and an N type epitaxial region of an opposite conductivity type to the silicon substrate 20. The island regions 25 and 26 are of the same conductivity type as the epitaxial island region 22, that is, of the opposite conductivity type to the silicon substrate 20, and penetrate through the epitaxial island region 22 to form the buried diffusion region 2.
two N+ type through diffusion regions with a high impurity concentration reaching 1;
27 is a P-type high impurity concentration diffusion region which is shallowly diffused from one through diffusion region 26 and has the same conductivity type as the silicon substrate 20; 28 is a silicon oxide film; 29 is a cathode electrode;
is a 7-node electrode. In a constant voltage diode having such a structure, the through diffusion region 26 and the high impurity concentration diffusion region 31
Breakdown occurs at the open PN junction interface, and breakdown at the surface is suppressed. Further, unlike the prior art shown in FIG. 1, there are no emitter and base diffusion regions, and the breakdown voltage setting can be easily controlled by controlling the concentration of both regions 26 and 31.

As described above, according to the present invention, the buried diffusion region is embedded in a silicon substrate and has a conductivity type opposite to that of the silicon substrate, and the buried diffusion region is epitaxially grown on the silicon substrate and separated into islands by isolation diffusion regions. and an epitaxial island region having a conductivity type opposite to that of the silicon substrate,
Two through diffusion regions with a high impurity concentration that penetrate the epitaxial island region and reach the buried diffusion region are of a conductivity type opposite to that of the silicon substrate, and a high impurity impurity of the same conductivity type as the silicon substrate is diffused shallowly from one through diffusion region. Since the diode includes a concentration diffusion region, breakdown does not occur on the surface, and therefore the degree of change in breakdown voltage over time is reduced, making it possible to obtain a constant voltage diode with excellent breakdown voltage characteristics. Furthermore, since the structure is simplified, it is easier to control the breakdown voltage setting, and the number of steps in the manufacturing process is reduced compared to the conventional example, making manufacturing easier.

[Brief explanation of drawings]

FIG. 1 is a structural sectional view of a conventional example, and FIG. 2 is a structural sectional view of an embodiment of the present invention. 20 is a P-type silicon substrate, 21 is a buried diffusion region, 2
2 is an epitaxial island region, 25.26 is a through diffusion region, 27 is a high impurity concentration diffusion region, 28 is a silicon oxide film, and 29.30 is an electrode applicant. Hide

Claims (1)

[Claims] (1) A buried diffusion region that is embedded in a silicon substrate and has a conductivity type opposite to that of the silicon substrate, and a buried diffusion region that is epitaxially grown on the silicon substrate and is separated into islands by an isolation diffusion region that is opposite to that of the silicon substrate. An epitaxial island region of conductivity type, two through diffusion regions of high impurity concentration that penetrate through the epitaxial island region and reach the buried diffusion region of the conductivity type opposite to that of the silicon substrate, and a silicon diffusion region that is shallowly diffused from one of the through diffusion regions. A constant voltage diode comprising a highly doped diffusion region of the same conductivity type as the substrate.