JPH0590566A - Schottky barrier diode - Google Patents

Abstract

PURPOSE:To improve the breakdown strength of a breakdown voltage or the amount of a current by a method wherein a single crystal layer of the same conductivity type as that of a semiconductor substrate is formed on the one conductivity type semiconductor substrate containing a high-concentration impurity and a Schottky electrode of the same depth as that of a guard ring is formed in the guard ring formed in such a way as to encircle a prescribed region shallower than the thickness of the single crystal layer with a layer of a conductivity type inverse to that of the single crystal layer. CONSTITUTION:An epitaxial layer 2 is formed on a substrate 1 and thereafter, a P<+> layer is formed at a part including a region to be formed with a guard ring 3 and a Schottky electrode 5 in a depth shallower than the thickness of the layer 2. Then, the P<+> layer located at the center part of the P layer is etched leaving the outer periphery only, which is used as the ring 3, of the P<+> layer to make the n-type layer expose and the electrode 5 is formed in an etching pit including the upper part of the ring 3 in the same depth as that of the ring 3. Accordingly, the breakdown strength of a breakdown voltage can be improved without reducing the amount of current or the amount of the current can be improved keeping the breakdown voltage intact.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Schottky barrier diode having a high breakdown voltage.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a conventional example of a Schottky barrier diode. In the figure, 1 is a substrate of one conductivity type (here, n ⁺ ) containing a high concentration of impurities, 2 is a substrate 1
Is a single crystal (n) layer having the same conductivity type as the substrate formed on the surface of the substrate by the epitaxial growth. Reference numeral 3 is a guard ring composed of a p ⁺ layer formed so as to surround a predetermined region in a ring shape with a depth shallower than the thickness of the single crystal layer 2, and this guard ring contributes to the improvement of breakdown voltage. .. 4 is S
An insulating film made of iO ₂ , Si ₃ N _4, etc., 5 is a Schottky electrode made of a metal material (Al, Pt, W, Au, etc.) formed on the epitaxial layer (n) in the guard ring, 6 is It is an ohmic electrode formed on the back surface of the substrate 1.

In the Schottky barrier diode having the above structure, the conductive component is the majority carrier, and since the minority carrier is hardly injected, the minority carrier is not accumulated. Therefore, the switching time is short and it is suitable for high-speed operation. Further, unlike the diode of the pn junction, since one side is made of metal, the rising voltage is low and the series resistance is low for the same semiconductor substrate concentration.

[0004]

However, in the above conventional Schottky barrier diode, the position below the guard ring (p ⁺ layer) 3 is deeper than the Schottky electrode on the substrate (n + layer) 1 side. Since the electric field is concentrated at the tip of the guard ring when a reverse voltage is applied, there is a problem that the depletion layer reaches the n ⁺ layer due to the electric field and breakdown easily occurs. In order to prevent the breakdown, the n layer 2 should be thickened and the distance between the bottom of the guard ring and the substrate (n +) 1 should be lengthened, but in that case the forward current flow becomes worse. ， As a result, the loss will increase.

FIG. 3 shows how the depletion layer 8 spreads when a reverse voltage is applied to the Schottky barrier diode. For example, the depth ds from the n layer 2 to the substrate 1 (n ⁺ ) is 4 μm, p When the depth of the + layer is 2.2 μm, the thickness dg of the n layer is 1.8 μm. Therefore, the depletion layer on the guard ring (p + layer) side becomes deeper than the depletion layer on the Schottky electrode 5 side, and the electric field strength further increases, resulting in breakdown.

That is, the thickness of each layer is as described above, the impurity concentration of the n layer is 2 × 10 ¹⁵ , and the impurity concentration of the p + layer is 10 ×.
^The result calculated by using a simplified formula known as ¹⁹ causes a breakdown at about 67V. The breakdown voltage and the forward resistance have a complementary relationship that if one is improved, the other is deteriorated. It is an object of the present invention to improve the breakdown voltage of a breakdown voltage without reducing the amount of current flowing, or to provide a shot key barrier diode in which the amount of current is increased while keeping the breakdown voltage unchanged. And

[0007]

In order to solve the above-mentioned problems, the present invention is to form a single crystal layer of the same conductivity type on a semiconductor substrate of one conductivity type containing a high concentration of impurities. In a Schottky barrier diode, a card ring is formed by surrounding a predetermined region having a depth shallower than a thickness with a layer of an opposite conductivity type, and a Schottky barrier diode is formed in the card ring. And the Schottky electrodes are formed to have the same depth.

[0008]

Since the depth of the guard ring is formed to be the same as the depth of the Schottky electrode, the guard ring and the depletion layer under the Schottky electrode are averaged and the protrusion is eliminated.

[0009]

FIG. 1 is a sectional view showing an embodiment of the present invention (however, the right half of the drawing is omitted with the center line as a boundary). The same elements as those in the conventional example are designated by the same reference numerals. That is, in the present invention, after the epitaxial layer 2 is formed on the substrate 1, a p ⁺ layer is formed by ion implantation or diffusion in the portion including the region where the guard ring 3 and the Schottky electrode 5 are to be formed (this p + The layer depth is, for example, about 2.2 μm if the thickness of the epitaxial layer 2 is 4 μm).

Next, only the outer periphery to be the guard ring 3 is
The central p + layer is etched leaving the n layer exposed.
(In this state, the bottom of the etching hole is the n layer and the surrounding wall
Is p ⁺Has become). Next, including on the guard ring 3
A Schottky electrode 5 is formed in the etching hole. Up
In the above configuration, the same conditions as those shown in the conventional example,
That is, the impurity concentration of the n layer is 2 × 10¹⁵, P + layer impurities
Concentration 10¹⁹From the n layer 2 to the substrate 1 (n⁺) Up to
The depth ds is 4 μm, and the depth of the p + layer is 2.2 μm. So
In the case of, the depth of the p + layer is the same as before, so it is broken down.
The voltage is about 67V as before, but the Schottky electrode
And the distance between the substrate 1 and dg is reduced from 4 μm to 1.8 μm.
Therefore, the resistance decreases and the amount of current increases.

Further, the thickness of the epitaxial layer 2 is 6 μm.
If the p + layer to be the guard ring 3 is formed to a depth of 2 μm from the surface, the distance from the Schottky electrode 5 to the substrate 1 (n ⁺ ) is 4 μm as in the conventional case. Therefore, leave the current amount unchanged and set the breakdown voltage to about 97.
It can be improved to V. In addition, in each of the above steps, a step of forming an insulating film as a mask and patterning are required, but these are manufactured by using a known semiconductor technique. Further, in this embodiment, when forming the guard ring and the Schottky electrode, the p ⁺ layer is formed on the entire surface of a predetermined region, and then the central portion is etched except for the outer peripheral portion to be the guard ring. A Schottky electrode is formed on the etched portion, but the method is not limited to this. For example, after forming the p ⁺ layer in a ring shape, the epitaxial layer in the ring may be etched by vapor phase HCl. In that case, the etching depth should be p ⁺
It is necessary to match the depth of the layer, but the etching depth can be accurately controlled with time.

[0012]

As described above in detail with reference to the embodiments, according to the Schottky barrier diode of the present invention, the guard ring and the Schottky electrode are formed to have the same depth. The breakdown voltage of the breakdown voltage can be improved without lowering the breakdown voltage, or the Schottky barrier diode in which the amount of current is improved can be realized while keeping the breakdown voltage unchanged.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a Schottky barrier diode of the present invention.

FIG. 2 is a sectional view showing an embodiment of a conventional Schottky barrier diode.

FIG. 3 is a diagram showing a state of a depletion layer in a conventional example.

[Explanation of symbols]

 1 substrate 2 epitaxial layer 3 guard ring 4 insulating film 5 Schottky electrode 6 ohmic electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hisako Suga Inventor Yokogawa Denki Co., Ltd. 2-932 Nakamachi 2-chome, Musashino-shi, Tokyo

Claims (1)

[Claims] 1. A single crystal layer of the same conductivity type is formed on a semiconductor substrate of one conductivity type containing a high concentration of impurities, and a predetermined region having a depth shallower than the thickness of the single crystal layer is formed as a layer of the opposite conductivity type. In a Schottky barrier diode in which a card ring is formed surrounded by and a Schottky electrode is formed in the card ring, the guard ring and the Schottky electrode are formed to have the same depth. Shot key barrier diode.