JPH07153975A - Zener diode - Google Patents

Abstract

PURPOSE:To provide a Zener diode stabile in quality wherein current surge resistance is large and it is manufactured in fewer processes. CONSTITUTION:Relating to a Zener diode 9 wherein p-n junction 6 formed between the first area of first conduction type on a semiconductor substrate 1 and the second area of second conduction type 5 is utilized, an electrode 8 is so provided that at least one contact point between the electrode and the first area or second area 5 or a semiconductor layer connected to them has contact resistance.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to Zener diodes. More specifically, it relates to a Zener diode having a large current surge breakdown strength.

[0002]

2. Description of the Related Art A Zener diode is a diode which utilizes the reverse voltage-current characteristics of a pn junction. It has a pn junction formed directly on a semiconductor substrate and an epitaxial growth layer is grown on a low resistance semiconductor substrate. , A pn junction is formed in the epitaxial growth layer.
FIG. 4 is a sectional explanatory view of a Zener diode in which a pn junction is directly formed on a semiconductor substrate, and FIG. 5 is a sectional explanatory diagram of a Zener diode in which a pn junction is formed in an epitaxial growth layer on a semiconductor substrate.

The Zener diode shown in FIG. 4 is manufactured as follows. First, the thickness is about 130 μm,
Moreover, the p ⁺ type diffusion region 32 is provided by diffusing impurities such as boron and indium in the n type semiconductor substrate 31 having a specific resistance of about 100 to 300 mΩ · cm, and the pn junction surface 33 is formed. Next, an insulating film 34 made of silicon oxide or the like is provided on the surface of the semiconductor substrate 31, and a contact hole 35 is opened in a part thereof. On the other hand, an n ⁺ type diffusion layer 36 for obtaining ohmic contact is formed on the back surface of the semiconductor substrate 31. After that, a metal such as aluminum is attached to the upper p ⁺ diffusion region 32 and the lower n ⁺ type diffusion layer 36 of the semiconductor substrate 31 by a sputtering method or the like to provide the upper electrode 37 and the lower electrode 38. Finally, the semiconductor substrate 31 is diced for each diode element to obtain the Zener diode 39. The Zener characteristic of this Zener diode is determined by the specific resistance of the semiconductor substrate, that is, the impurity concentration. Therefore, when the impurity concentration of the semiconductor substrate 31 is low, ohmic contact cannot be obtained between the semiconductor substrate 31 and the electrode, and the n ⁺ -type diffusion layer 3 is formed on the back surface of the semiconductor substrate 31.
6 is provided to form an ohmic contact so that the series resistance does not increase.

The diode shown in FIG. 5 is manufactured as follows. A high impurity concentration n-type semiconductor substrate 40 having a thickness of about 110 μm and a specific resistance of about 5 to 15 mΩ · cm is used, and a specific resistance corresponding to a target Zener characteristic is 100 to 300 mΩ · cm on its surface. Degree n
A type epitaxial growth layer is grown. Then, as in the case of FIG. 4, the p ⁺ type diffusion region 32, the insulating film 34 and the upper electrode 37 are provided. Further, a Zener diode 42 is obtained by directly attaching a metal to the back surface of the semiconductor substrate 40 and providing the lower electrode 38 so as to form an ohmic contact.

[0005]

A reverse voltage is applied to a Zener diode as shown in FIG. 4 or FIG.
Voltage V _R and a current I _R when went increased reverse current
Is as shown in FIG. That is, a reverse voltage is applied to the Zener diode, and when the Zener breakdown voltage is exceeded, a current starts to flow. When a large current flows due to this reverse voltage, the Zener diode is destroyed by the input of I ₂ × V ₂ which is the breakdown withstand capacity (allowable loss point C) of the diode. Therefore, there is a problem that the diode is easily destroyed when noise such as a large surge current enters.

An object of the present invention is to solve the above problems, to provide a Zener diode which can obtain stable quality and has a large current surge breakdown strength with a small number of manufacturing steps.

[0007]

A Zener diode according to the present invention includes a first region of a first conductivity type provided on a semiconductor substrate and a second region of a second conductivity type which is a conductivity type different from the first conductivity type. A Zener diode comprising a pn junction formed by a region and an electrode provided on each of the first region and the second region or a semiconductor layer connected to the first region, at least one of the electrodes being the first region. Alternatively, it is provided so as to have a contact resistance with the second region or the semiconductor layer connected thereto.

The contact resistance of the electrodes is preferably 0.3 to 1.0 Ω.

[0009]

According to the present invention, since the contact between the semiconductor layer and the electrode has a high resistance due to the contact resistance, when a surge current is input, the resistance loss of the contact portion between the semiconductor substrate and the electrode is caused. Heat is generated, and the heat is transmitted to raise the temperature of the pn junction.

[0010] Zener diodes causes a secondary breakdown when the temperature of the pn junction is about 300 ° C., as shown the reverse characteristic of the voltage V _R and a current I _R in Figure 3, the Zener breakdown voltage is V ₁ It goes down to that point. Therefore, if a large surge current noise is input, the Zener breakdown voltage V
_The current begins to flow beyond _Z and the power of A shown in FIG.
The temperature of the n-junction surface rises and secondary breakdown occurs, and the breakdown voltage drops to A ₁ . As a result, the current flowing through the diode flows up to I ₁ , and the power dissipation point B (I ₁ × V ₁ ) is equal to the above-described power dissipation point C (I ₂ × V ₂ ) (see FIG. 6) and the breakdown withstand power is equal. Become. Therefore, if the Zener breakdown voltage becomes 1/10 due to the secondary breakdown, the allowable current is 10
Doubled, it will not be destroyed even with a large surge current.

As a result, according to the present invention, the pn junction is 2
The secondary breakdown occurs, and the diode can withstand a larger surge current without breaking.

On the other hand, with respect to the forward voltage, it is normally used at a low voltage and a small current (several mA to several tens mA).
The resistance component at the contact portion between the semiconductor layer and the electrode is 0.3 to 1.0.
If it is about Ω, the characteristics are not adversely affected.

[0013]

The Zener diode of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional explanatory view showing an embodiment of the Zener diode of the present invention, and FIG. 2 is a sectional explanatory view showing another embodiment of the Zener diode of the present invention.

In FIG. 1, 1 has a thickness of 80 to 200 μm.
a first conductivity type (for example, n type) semiconductor substrate of about m,
The semiconductor substrate directly forms the first region forming the pn junction. A diffusion region 5 of a second conductivity type (for example, p type) different from the first conductivity type is provided on the surface of the semiconductor substrate 1 to form a second region. A pn junction 6 is formed on the boundary surface between the first region and the second region. An insulating film 3 made of silicon oxide or silicon nitride is provided on the surface of the semiconductor substrate, and the upper electrode 7 is provided on the front surface side of the diffusion region (second region) 5 and the rear surface side of the semiconductor substrate (first region) 1, respectively. And the lower electrode 8 are provided, and the Zener diode 9
Are formed. The first conductivity type and the second conductivity type are either n-type or p-type, respectively. If the first conductivity type is n-type, the second conductivity type is p-type, and the first conductivity type is Is p-type, it means that the second conductivity type is n-type.

When the semiconductor substrate 1 is a semiconductor material such as silicon, when it is n-type, impurities such as phosphorus and arsenic,
In the case of p-type, it is a wafer that is doped with impurities such as boron and gallium, and is manufactured by doping the amount of impurities according to the Zener characteristics so that the specific resistance is about 100 to 300 mΩ · cm. Resistivity is 100-300
To obtain mΩ · cm, the doping amount of impurities such as phosphorus can be reduced. On the back surface of the semiconductor substrate 1, a lower electrode 8 is formed by providing a metal film made of chromium, for example. The specific resistance of the semiconductor substrate 1 is 100 to
The contact between the impurity concentration of 300 mΩ · cm and the chromium electrode does not form a perfect ohmic contact,
The connection has a contact resistance of about 1.0Ω. The present invention is thus characterized in that the electrodes are provided so that the semiconductor substrate and the electrodes have a contact resistance.

That is, since the semiconductor substrate 1 and the lower electrode 8 have a contact resistance, the resistance component is 0.3 to
When the surge current flows, resistance loss occurs in the contact resistance portion and the temperature of the semiconductor substrate 1 rises. The temperature is transmitted to the pn junction 6, and the temperature of the pn junction surface is 300 ° C.
When it rises to a certain degree, secondary breakdown occurs, and the breakdown voltage shifts from A to A ₁ and decreases as shown in FIG. The breakdown of the Zener diode due to the surge occurs when the input of the surge exceeds the breakdown withstand capacity of the Zener diode, but the voltage drops in response to the large current surge, and the amount of current that can flow until the breakdown increases, causing a large surge. It can withstand an electric current.

The contact resistance between the semiconductor layer and the electrode is
Although it varies depending on the impurity concentration of the semiconductor material and the combination of the conductivity type and the metal material used as the electrode, a contact state in which the resistance portion has a resistance of 0.3 to 1.0 Ω is preferable. For example, 100 to 30 for n-type semiconductor material
The contact resistance described above can be obtained by using chromium as the electrode material for the impurity concentration which gives the specific resistance of 0 mΩ · cm, and Table 1 shows other combinations. By using the semiconductor material and the electrode material having the specific resistance as shown in Table 1, the above-mentioned contact resistance of 0.3 to 1.0Ω can be obtained.

[0018]

[Table 1]

FIG. 2 is a sectional view showing another embodiment of the Zener diode of the present invention. This embodiment is shown in FIG.
First conductivity type (for example, n-type) similar to the structure shown in
The semiconductor substrate 11 having a low specific resistance (high impurity concentration) is provided with an epitaxial growth layer (first region) 2 of the same conductivity type having a specific resistance capable of obtaining desired zener characteristics, and diffusion of the second conductivity type (for example, p type) is performed. A region (second region) 5 is formed and a pn junction 6 is formed.
Is formed. The insulating film 3, the upper electrode 7, and the lower electrode 8 are the same as those in the above-described embodiment, but in the present embodiment, before the lower electrode 8 is provided, for example, boron or indium, which is an impurity of the second conductivity type (p-type), is added. Of the low impurity concentration layer 1 of about several μm from the back surface by doping the back surface of the semiconductor substrate 1
0 is set. In this way, after the impurity concentration on the back surface of the semiconductor substrate 11 is reduced to about 10 ¹⁷ / cm ³ ,
The back surface electrode 8 is provided by, for example, chrome. That is, in this embodiment, the electrode 8 is provided on the semiconductor layer, which is the low impurity concentration layer 10 electrically connected to the epitaxial growth layer (first region) 2 through the semiconductor substrate 11, so as to have a contact resistance. . Thus, by making the back surface of the semiconductor substrate 11 having a low specific resistance to have a high specific resistance by a thickness of about several μm, the contact with the metal as the electrode has a contact resistance, and the surge current flows as described above. In this case, resistance loss occurs, the temperature of the pn junction 6 rises, and secondary breakdown occurs, which makes it possible to withstand a large surge current.

The specific resistance of the semiconductor substrate 11 is 10 mΩ.
・ The secondary breakdown voltage of the Zener diode manufactured to a voltage of 40 V (Fig. 3)
V ₁ ) is about 4V, and the current surge breakdown withstand capability is 55-
At 60 W, a surge current of 1.5 A or more caused damage. With the conventional structure, a Zener diode having the same Zener voltage of 40 V and a breakdown withstand capacity of 60 W does not cause secondary breakdown, so that it is destroyed by a surge current of 0.15 A, and can withstand up to 10 times the surge current according to the present invention. I was able to prove that.

In each of the above embodiments, the contact between the back surface of the semiconductor substrate and the electrode has a contact resistance. However, a region having a large specific resistance is provided on the surface on the diffusion region (second region) 5 side. Alternatively, the electrode metal may be selected to have a contact resistance. However, generally, the depth of the diffusion region 5 is 8
The thickness is as thin as about 9 μm, and the impurity concentration at the pn junction surface affects the zener characteristics, so control in manufacturing is important.

[0022]

According to the present invention, the pn junction of 2 due to the heat generated due to the contact resistance between the semiconductor layer and the electrode metal is produced.
Since the secondary breakdown is positively used, it can sufficiently withstand a surge input with a large current.

Further, according to the present invention, the secondary breakdown of the pn junction is caused by increasing the specific resistance of the semiconductor layer in contact with the electrode metal or by selecting the electrode material, so that the concentration of the semiconductor substrate and the epitaxial growth layer is free. Because you can choose
It is possible to obtain a Zener diode with high characteristics at a low production cost.

[Brief description of drawings]

FIG. 1 is a sectional explanatory view of an embodiment of a Zener diode of the present invention.

FIG. 2 is a sectional explanatory view of another embodiment of the Zener diode of the present invention.

FIG. 3 is a diagram showing voltage-current characteristics for explaining secondary breakdown of the Zener diode of the present invention.

FIG. 4 is a cross-sectional explanatory view showing an example of a conventional Zener diode.

FIG. 5 is a cross-sectional explanatory view showing another example of a conventional Zener diode.

FIG. 6 is a diagram showing current-voltage characteristics of a conventional Zener diode.

[Explanation of symbols]

 1 semiconductor substrate (first region) 2 epitaxial growth layer (first region) 5 diffusion region (second region) 6 pn junction 7 upper electrode 8 lower electrode 9 Zener diode

Claims (2)

[Claims] 1. A pn junction formed by a first region of a first conductivity type provided on a semiconductor substrate and a second region of a second conductivity type that is a conductivity type different from the first conductivity type; A Zener diode comprising an electrode provided in each of a first region and a second region or a semiconductor layer connected thereto, wherein at least one of the electrodes is the first region.
A Zener diode provided so as to have a contact resistance with the region, the second region, or a semiconductor layer connected thereto. 2. The contact resistance of the electrode is 0.3 to 1.0 Ω.
The Zener diode according to claim 1, which has an electric resistance of 1.