JPH0555241A - Diode and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a diode wherein a collector and a base of a transistor are connected as one electrode while an emitter as the other electrode, having a high backward breakdown strength and an easy assembling structure. CONSTITUTION:In this diode, an electrode connecting a low concentration base layer 4a encircled by separating layers formed on a high impurity concentration emitter layer 3 with collector layers 6 is specified as one electrode while an emitter as the other electrode. Thus, due to the low concentration of the base layer 4a, the backward breakdown strength of emitter junction is higher while due to the high concentration of the emitter, the current amplification factor is large thereby enabling the forward potential decline to be minimized. Furthermore, one and the other electrodes are composed respectively on one and the other surfaces thereby notably facilitating the assembling step.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diode having a low forward voltage and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventional diodes having a rectifying function are P-
The breakdown voltage in the reverse direction, which is formed by the N-junction, can be sufficiently high, and the reverse leakage current is small.

However, the forward voltage drop is about 0.7 V in the case of a diode made of silicon, for example, which results in power loss, and a diode with a low forward voltage drop is required depending on the application.

Therefore, a diode having a Schottky barrier junction has a small forward voltage drop and is used in some applications.

However, a diode having a Schottky barrier junction cannot have a high reverse breakdown voltage and its application is limited.

On the other hand, as shown in the circuit diagram of FIG.
There is a method of use in which the collector and the base of the PN transistor are connected to each other to form the anode 1 and the emitter to form the cathode 2.
When a PNP transistor is used, the only difference is that the anode and cathode are reversed.

The above-mentioned method is smaller in forward voltage drop than a diode having only a normal PN junction.

However, since the normal transistor has a low reverse breakdown voltage of the emitter junction, a diode having a high reverse breakdown voltage cannot be obtained.

Furthermore, since a collector electrode is formed on the back surface and a base electrode and an emitter electrode are formed on the front surface of a normal transistor, a case corresponding to a chip having electrodes on the front and back sides like a normal diode, for example, a DHD (double heat sink diode) is provided. It is difficult to provide an electrode on the chip so that the chip can be housed in the case.

Therefore, as shown in FIG. 6, for example, a method of connecting the base and the emitter of the NPN transistor to form the anode 1a and the collector to the cathode 2a can be considered.

According to this method, the reverse breakdown voltage of the diode is P
Since it is the collector junction of the NP transistor, it can be made sufficiently high.

Further, since the base electrode and the emitter electrode are on the surface side of the chip, the cathode electrode can be easily formed and the patterns can be formed on the front and back sides like the conventional diode chip by the P-N junction. ..

However, according to this method, since the collector having a lower impurity concentration is used as the emitter, the current amplification factor is low, there is almost no effect of reducing the forward voltage drop, and the original P-N junction of the base collector is used. The characteristics are almost the same.

[0014]

Therefore, the present invention has a small forward voltage drop and a high reverse breakdown voltage, and is easy to assemble by forming an anode electrode on one surface of the chip and a cathode electrode on the other surface. It is intended to provide a diode.

[0015]

DISCLOSURE OF THE INVENTION A diode according to the present invention is an emitter layer of one conductivity type having a high impurity concentration, and an emitter layer formed on the emitter layer and having a surface, and having another conductivity type of a low impurity concentration. And a base layer surrounded by a separation layer of one conductivity type that reaches the emitter layer from the surface,
A collector layer of one conductivity type having a high impurity concentration selectively formed on the surface side of the base layer, wherein the electrode connecting the base layer and the collector layer is one electrode, and the emitter is the other electrode. It is characterized by

The manufacturing method is characterized in that a low impurity concentration base layer of opposite conductivity type is formed by epitaxial growth on a high concentration one conductivity type substrate used as an emitter.

As a manufacturing method, one conductivity type impurity is selectively diffused in a high concentration from one surface to the entire surface of the opposite conductivity type substrate having a low impurity concentration serving as a base layer and from the other surface, and an emitter layer, Another feature is that a separation layer is formed at the same time.

[0018]

According to the above structure, since the base layer has a low impurity concentration, the reverse breakdown voltage of the emitter junction is high, and thus the reverse breakdown voltage of the diode is high.

Further, since the emitter is formed of a high concentration impurity, the current amplification factor is high and the diode forward voltage drop is small.

Since the collector is selectively formed on the surface of the base layer, the electrodes for connecting the collector and the base can be easily formed in the same plane.

Further, since the emitter is on the back surface, it is easy to form the anode electrode and the cathode electrode on the opposite surfaces, and the assembly into the case is facilitated.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The diode of the present invention has the same equivalent circuit as that shown in FIG. However, although the reverse withstand voltage of the emitter junction has been low in the past, it is different in the present invention.

An embodiment of the present invention will be described along with a manufacturing method. FIG. 1 is a sectional view of each manufacturing process of the embodiment. Although many diode chips are simultaneously formed on one substrate, only one diode chip is shown in the figure. a) One conductivity type (eg N type) impurity (eg A)
s) is prepared in a high concentration and a Si substrate 3 is prepared, and P containing a relatively low concentration of another conductivity type impurity (for example, B) on its surface.
The mold layer 4 is formed by epitaxial growth. P-type layer 4
It is necessary to appropriately select the impurity concentration and the thickness of the device according to the requirements of the characteristics of the diode. It is preferable that the thickness is thin as long as the reverse breakdown voltage is satisfied. (See FIG. 1-a) b) Next, a separation layer 5 is formed by diffusing P, for example, so as to surround the region 4a serving as the base of the P-type layer 4. The separation layer 5
Is connected to the high-concentration N-type substrate 3 to form an island-shaped base layer 4a.
To separate. Subsequently, an N-type impurity such as P is selectively diffused on the surface of the base layer 4a to form a collector layer 6.

Although not shown, if necessary for making ohmic contact with the surface of the base layer 4a, B or the like is diffused to form a P-type high concentration layer. The P-type high concentration layer may be formed before or after the collector layer 6 is formed.

Although not shown in the figure, it is usually based on a planar technique, and a diffusion mask and an oxide film for passivation are formed. (See FIG. 1b) C) Next, if an electrode 7 connecting the collector layer 6 and the base layer 4a is formed and an electrode 8 is formed on the substrate 3 side, a diode having the electrode 7 as an anode and the electrode 8 as a cathode is formed. Become.

D) After that, by cutting and dividing at the part of the separation layer 5, a diode chip having electrodes on the front and back sides is completed.

According to this embodiment, since the base layer has a low impurity concentration, the breakdown voltage of the emitter can be increased and the current amplification factor can be increased.

The NPN transistor may be replaced by a PNP having a different conductivity type. However, the electrodes as diodes are opposite.

As a modification of the above embodiment, as shown in FIG. 2, the separation layer 5a is formed by dispersing the impurities in the substrate 3 and diffusing the separation layer from the surface before forming the P-type layer 4 of the low concentration impurity by the epitaxial molding. And the separation layer 5 diffused from the substrate 3 side
It may be formed by connecting with b.

Further, as shown in FIG. 3, the separation layer 5a diffused from the surface and the collector layer 6a can be simultaneously formed.

[0031]

Second Embodiment A second embodiment will be described. FIG. 4 is a sectional view of each manufacturing process.

A) A P-type Si substrate 4b having a low impurity concentration is prepared, and the emitter layer 3a is simultaneously diffused over the entire surface from the opposite surface (back surface) of the separation layer 5c selectively from one surface (front surface), and the substantially center is formed. Connect with. The remaining portion becomes an island-shaped base region 4c surrounded by the separation layer 5c. ((See FIG. 4a) b) Next, N-type impurities are selectively diffused from the surface of the base 4c to form the collector layer 6. (See FIG. 4-b.) C) Next, if an electrode 7 connecting the base 4c and the collector 6 and an electrode 8 on the front surface (back surface of the substrate) of the emitter 3a are provided, a diode chip becomes an anode electrode and a cathode electrode, respectively. Become.

In all of the above explanations, the emitter electrode is provided on the back surface, but if necessary, the separation layers 5 and 5 are provided.
It can also be provided on the surfaces of a and 5c.

[0034]

As described above, according to the present invention, since the base layer is made of a low concentration impurity and the base electrode and the collector electrode are provided on the same surface, the collector and the base of the transistor are connected and a diode is formed between the emitter electrode and the collector electrode. When used, the diode chip structure has a high reverse breakdown voltage, a small forward voltage drop and is easy to assemble.

[Brief description of drawings]

FIG. 1 is a sectional view showing a manufacturing process of a first embodiment of the present invention.

FIG. 2 is a sectional view of a modification of the first embodiment.

FIG. 3 is a cross-sectional view of another modification of the first embodiment.

FIG. 4 is a sectional view of a second embodiment of the present invention.

FIG. 5: Equivalent circuit of a conventional diode

FIG. 6 is an equivalent circuit of another conventional diode.

[Explanation of symbols]

 3 High concentration N type Si substrate (emitter layer) 3a High concentration N type diffusion layer (emitter layer) 4 Low concentration P type layer 4a Base layer 4b Low concentration P type Si substrate 4c Base layer 5 Separation layer 5a Separation layer 5b Separation layer 5c Separation layer 6 Collector layer 6a Collector layer 7 Electrode (anode) 8 Electrode (cathode)

Claims (3)

[Claims] 1. An emitter layer of one conductivity type having a high impurity concentration, and one conductivity type which is formed on the emitter layer and has a surface and which reaches the emitter layer from the surface to the periphery. A base layer of another conductivity type surrounded by a separation layer and having a low impurity concentration; and a collector layer of one conductivity type having a high impurity concentration, which is selectively formed on the surface side of the base layer, A diode, wherein the electrode connecting the collector layer and the collector layer is one electrode, and the emitter is the other electrode. 2. A diode according to claim 1, wherein a base layer containing a low concentration of another conductivity type impurity is epitaxially grown on a substrate containing a high concentration of one conductivity type impurity to be an emitter. Method. 3. A substrate containing a low-concentration impurity of another conductivity type serving as a base layer, one impurity of one conductivity type is selectively diffused in a high concentration from one surface to the entire surface of the other surface, and an emitter layer is formed on one side and an impurity is formed on the other side. The method for manufacturing a diode according to claim 1, wherein the separation layer is formed at the same time.