JPH0638504B2 - Semiconductor integrated circuit - Google Patents

Description

The present invention relates to a semiconductor integrated circuit, and more particularly to a semiconductor integrated circuit incorporating a Zener diode.

(B) Conventional Technology A conventional Zener diode (21) is disclosed in, for example, Japanese Patent Laid-Open No. 58-8.
Japanese Patent No. 5571 and Japanese Patent Application No. 60-288333 have detailed explanations.

For example, as shown in FIG. 3, a P ⁺ type semiconductor substrate (22),
The N-type epitaxial layer (23) formed on the semiconductor substrate (22), the semiconductor substrate (22) and the epitaxial layer (23)
A buried layer (24) formed between the epitaxial layer and
(23) A P ⁺ type isolation region (25) reaching the semiconductor substrate (22) from the surface, and an island region (26) separated into islands by the P ⁺ type isolation region (25), comprising the island region (26) formed on the surface the P ⁺ -type anode region (27), and a cathode region of the N ⁺ type formed in the anode region (27) in (28), the P ⁺ -type The anode region (27) and the N ⁺ type cathode region (28) form a PN junction to form a Zener diode.

And the cathode region (28) is coupled with other circuit elements,
It is configured as a semiconductor integrated circuit.

(C) Problems to be Solved by the Invention In the Zener diode having the above-described structure, the Zener voltage V _Z is determined by the impurity concentrations of the anode region (27) and the cathode region (28), and the anode region The Zener voltage V _z is constant unless the concentrations of (27) and the cathode region (28) are changed. In addition, when the Zener voltage needs to be changed by the integrated circuit formed in another region, the above-mentioned configuration has a problem that the Zener voltage cannot be changed except for changing the impurity profile.

Further, when the anode region (27) is dropped to the ground, it is necessary to connect the ground wiring and the anode region (27) by a pattern that connects them, which causes a problem of increasing the pattern area.

(D) Means for Solving the Problems The present invention has been made in view of the above problems, and PN is provided in at least the region (5) having a lateral concentration gradient in the anode region (5) or the cathode region (7). It has a junction (10) and this P
By providing the N-junction (10) position at a predetermined position of the region (5) having a concentration gradient, the Zener voltage can be arbitrarily determined, and the anode region or the cathode region serves as a separation region, and the separation region is used. By turning it down to the ground, the turn for connecting to the ground is unnecessary and the pattern area can be reduced.

(E) Action For example, when the anode region (5) is formed by thermal diffusion,
Impurities are diffused through the diffusion holes and the concentration decreases from the front surface of the substrate (3) toward the back surface of the substrate (3), and is also diffused laterally from the diffusion holes, and the concentration is horizontal from the diffusion holes. And a concentration gradient of impurities is formed.

When the cathode region (7) is superposed on the region (5) having this concentration gradient and diffused, the Zener voltage V _z is determined, and further, the position of this cathode region (7) is changed in the lateral direction as shown by the thick arrow in FIG. Since the concentration of the PN junction portion (10) can be changed by shifting it to, the Zener voltage can be changed arbitrarily.

Further, since the separation region (5) directly falls to the ground, the separation region (5) is utilized as an anode region (or cathode region), and the cathode region (or anode region) is overlapped with the separation region (5). If a region is formed, it can be directly dropped to the ground through the isolation region without providing a circuit pattern.

(F) Example An example of the present invention will be described below with reference to FIG. A Zener diode (1) of the present invention is shown in FIG. 1. First, a P-type semiconductor substrate (2), an N-type epitaxial layer (3) formed on the semiconductor substrate (2), and the semiconductor substrate An N ⁺ type buried layer (4) formed between the (2) and the epitaxial layer (3), and a P ⁺ type buried layer (4) reaching from the surface of the epitaxial layer (3) to the semiconductor substrate (2). Separation Area (5)
And an island region (6) separated into islands by the P ⁺ type separation region (5), and an N ⁺ type diffusion region overlapping the island region (6) and at least one of the separation regions (5) (7) with and separation area
Zener diode ( 1 ) is composed of (5) and diffusion region (7).

Here, the P ⁺ type isolation region (5) corresponds to the anode region, and the N ⁺ type diffusion region (7) corresponds to the cathode region.

Furthermore, the cathode region (7) is in ohmic contact with the aluminum electrode (8) via a contact, and the electrode (8) is formed on the other region of the semiconductor substrate (2).
It is connected to the semiconductor circuit element (9) as shown in the figure, and the whole constitutes a semiconductor integrated circuit.

Further, the diffusion region (7) falls to the ground via the isolation region (5).

The first feature of the present invention resides in the N ⁺ type diffusion region (7) overlapping the N type island region (6) and the P ⁺ type separation region (5).

For example, a portion indicated by an arrow E on the surface of the P ⁺ -type isolation region (5) indicates one edge of the diffusion hole when the isolation region (5) is formed, and impurities to the right of the arrow E It has a concentration gradient. On the other hand, the arrow E'indicates one edge of the diffusion hole when the N ⁺ type diffusion region (7) is formed, and has an impurity concentration gradient to the left of the arrow E '.

Therefore, by changing the N ⁺ type diffusion region (7) corresponding to the cathode region in the direction of the thick arrow shown in FIG.
The impurity concentration of (10) can be changed, and the Zener voltage V _z can be arbitrarily determined.

However, the concentration gradient described above is preferably as gentle as possible, and the deeply diffused separation region (5) is comparatively gentle in this respect, and the deviation of the Zener voltage V _z due to the mask alignment accuracy of the diffusion region (7) is considered. Can be made smaller.

Further, it is sufficient that the lateral direction impurity concentration distribution is formed only in the separation region (5), and the lateral direction impurity concentration distribution need not necessarily be formed in the diffusion region (7). Separation area, for example
(5) thermally diffuses, and the Zener voltage V _z can be arbitrarily changed even if a diffusion region is formed by ion implantation in a region having a lateral impurity concentration distribution in this region (5).

As shown in FIG. 2, the second characteristic of the present invention is that it is grounded via the anode region (or cathode region) (5).

Therefore, without using another diffusion region for the anode region (5),
Since the isolation region (5) incorporated in the substrate is used as a substitute and the isolation region (5) falls to the ground, wiring from the other diffusion region or anode region to the ground is unnecessary, and the chip size can be reduced. .

(G) Effect of the Invention As described above, at least the anode region (5)
(Or the cathode region (7)) has a PN junction (10) in a region having a lateral concentration gradient, and the PN junction (10) is provided at a predetermined position in the region (5) having a concentration gradient. Since the Zener voltage can be arbitrarily determined and directly dropped to the ground via the isolation region (5), the pattern area can be reduced and the chip size can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor integrated circuit of the present invention, FIG. 2 is a circuit diagram of a semiconductor integrated circuit of the present invention, and FIG. 3 is a sectional view of a conventional semiconductor integrated circuit. (1) is a Zener diode, (2) is a semiconductor substrate, (3) is an epitaxial layer, (4) is a buried layer, (5) is an isolation region, (6) is an island region, (7) is a diffusion region, (8) is an electrode, (9) is a semiconductor circuit element, and (10) is a PN junction.

Claims (1)

[Claims] 1. A semiconductor substrate of one conductivity type, an opposite conductivity type epitaxial layer formed on the semiconductor substrate, and a surface of the epitaxial layer reaching the semiconductor substrate.
An isolation region of one conductivity type which is one region of the diode,
The opposite conductivity type diffusion region, which is the other region of the diode, is formed so that the PN junction is located in a portion having a concentration gradient due to the lateral diffusion of the isolation region, and the opposite conductivity type diffusion region is provided in the semiconductor. A semiconductor integrated circuit comprising a connecting means for connecting to a circuit element in another region of the substrate.