JPH02237167A - Semiconductor device - Google Patents

Abstract

PURPOSE:To avoid characteristics effect from a layer constitution formed on a p-n junction by forming an n<->-type diffusion layer on an upper part of a side surface of an n<+>-type emitter layer, and by forming a p-type diffusion layer whose impurity concentration is higher than that of a p-type base layer to an outside thereof. CONSTITUTION:In a section where a diode junction by a first semiconductor layer 4 of a first conductivity type and a second high concentration semiconductor layer 6 of a second conductivity type is in contact with an oxide film 10, a third low concentration semiconductor layer 7 of a second conductivity type whose impurity concentration is made fully lower than that of the second high concentration semiconductor layer 6 is formed to an upper area of a side surface of the second high concentration semiconductor layer 6, and a fourth high concentration semiconductor layer 8 of a first conductivity type whose impurity concentration is made higher than that of the first semiconductor layer 4 is formed to an outside thereof. Therefore, an interface where a diode junction is in contact with an oxide film at breakdown, that is, an electric field in an area near an interface of Si-SiO2 is relaxed, thereby producing the breakdown inside a bulk at the side of Si rather than in an interface of Si-SiO2. According to this constitution, a rise of a breakdown voltage as well as the deterioration of characteristics of a device can be reduced remarkably.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a semiconductor device, and more specifically, to an improvement in a Zener diode structure used in a bibolar integrated circuit by breaking down by applying a reverse voltage. be.

(Prior art) As a conventional example of this type of Zener diode, this S
FIG. 2 shows a schematic cross-sectional configuration of a Zener diode (emitter-paste Zener) formed using the emitter and base of a vertical NPN transistor in a bipolar integrated circuit.

In the conventional configuration shown in FIG. 2, an n-type epitaxial layer 2 (hereinafter referred to as an n-type epitaxial layer) is deposited on a p-type silicon substrate l by an epitaxial growth method, and this n-type epitaxial layer 2 is A p-type isolation layer 3 is formed by selectively injecting boron B or the like into the layer 2 and thermally diffusing it. Here, this p-type separation layer 3 separates the semiconductor elements respectively formed within the n-type layer 2.

Further, boron ions B4 and the like are widely and selectively implanted and diffused into the upper layer of the n-type layer 2 between the p-type separation layers 3 in the center thereof to form the p-type base layer 4. In addition, boron B or the like is selectively implanted and diffused into a portion of the p type base layer 4 to form a p+ type diffusion layer 5. This p1 type diffusion layer 5 is provided in order to reduce the contact resistance between the p type base layer 4 and a metal wiring described later.

In the upper layer of the other part of the p-type base layer 4,
Similarly, arsenic ions As'' or the like are selectively implanted and diffused to form an n1 type emitter layer 6.This n+ type emitter layer 6 has a p type base on its bottom and side sides. A pn junction is formed between the layer 4 and the layer 4.

Furthermore, the p" type diffusion layer 5 and the n+ type emitter layer 6
A series of silicon oxide films 10 are coated on the upper surfaces of the p-type base layer 4 containing Separate metal wirings 9 are electrically connected to each of the p+ type diffusion layer 5 and the n-type emitter layer 6, and each of these metal wirings 9 and the silicon oxide film I
For example, the entire surface of O is coated with 250
A protective coating is provided with a highly moisture-resistant plasma nitride film 11 deposited at a temperature of about 400°C.

In addition, in the same figure. Reference numeral 12 is a region where reverse breakdown occurs.

That is, in a device configuration of two or more, the p-type base layer 4
The desired Zener diode structure is obtained by the pn junction between the n+ type emitter layer 6 and the n+ type emitter layer 6.

Also, FIG. 3 shows impurity profiles in the depth direction of the p-type base layer 4 and the n1-type emitter layer 6 in the Zener diode structure, and in the figure,
ND is the donor concentration in the 9-type emitter layer 6, NA is the acceptor concentration in the p-type base layer 4, FIG. 4 shows the current-voltage V characteristics of the Zener diode, and FIG. It shows the change in breakdown voltage v2 with respect to the reverse voltage application time in the same Zener diode as above, and is the Zener diode used in a reverse breakdown state?
If this continues, the reverse breakdown voltage will increase.

Generally, in the Zener diode installed in this type of bipolar integrated circuit, the base of the vertical NPN transistor is the anode (corresponding to the p-type base layer 4), and the emitter is the cathode (n+ type Emitter layer 6
This can be determined by using the breakdown voltage characteristics (Figure 5) when a reverse voltage (the potential of the cathode is set higher than the potential of the anode) is applied between the anode and cathode. It is used in voltage circuits and surge protection circuits.

The conventional Zener diode with the above configuration is
It has an impurity profile as shown in Figure 3,
Since the breakdown voltage (2) is determined approximately by X in the region with a high base concentration, in the case of this conventional configuration, the breakdown voltage (2) is determined between the silicon and the silicon oxide film lO on the substrate side shown in FIG. In this case, a breakdown phenomenon occurs in the thin region l2 near the Si--SjO2 interface.

[The burden that the invention attempts to solve]

However, in the conventional Zener diode having the above-mentioned configuration, as mentioned earlier, a breakdown phenomenon occurs in the region 12 near the Si-SiO2 interface, so that there is a certain As shown in Figure 5, if voltage is continued to be applied in a damaged state, the breakdown voltage v2 will increase due to its influence.
There is a problem that J: gradually increases.

Here, Fig. 5 shows the change over time in the breakdown voltage v2 when a DC voltage of 8 cm is applied to the Zener diode and a current with a current density of 100 μA/μm2 is continuously passed. The hydrogen concentration in the plasma nitride film jl is estimated to be about 5×10” cm −3 .

By the way, the mechanism behind the change in breakdown voltage v2 over time shown in FIG. It has been found that it depends on hydrogen concentration, etc., and considering these points, the following model cannot be considered.

In other words, in the Zener diode with this conventional configuration, electrons and positive The holes move, and the high-energy electrons and holes (hereinafter referred to as hot carriers) are injected into the silicon oxide film IO. In addition, the plasma nitride film 1l is an indispensable insulating film as the final passivation film of an integrated circuit because it has a large protective effect on the element structure, but on the other hand, it contains a large amount of hydrogen. Therefore, after the film is formed, hydrogen contained in the film is diffused into the silicon oxide film IO region only by heat treatment at a relatively low temperature. The following reaction occurs between hydrogen and the hot carriers injected into the silicon oxide film 10 as described above.

e−+ h”+ 82 −+ 28 Then, the binding energy of this injected electron and hole is the bond of H2 molecule (the binding energy of t1 is about 4.5 eV) as shown in the same equation. The H atoms dissociated in this way form an interface level at the Si-Sin interface through the reaction Si}1+++→Si'+}+2. Si) is generated.

In other words, when an acceptor type interface state is generated by injection of hot carriers in this way, the emitter (corresponding to the n+ type emitter layer 6) and base (corresponding to the p type base layer 4) near the Si-Sin2 interface at the junction. The electric field is relaxed, and as seen in FIG. 5, the breakdown voltage (2) becomes higher.

This invention was made to solve these conventional problems, and its purpose is to improve the characteristics by using a layer structure such as a silicon oxide film or a plasma nitride film formed on the pn junction. This type of semiconductor device, which allows a stable constant voltage to be obtained without being affected by any influence, provides a Zener diode.

[Means for solving problem a]

In order to achieve the above object, a semiconductor device according to the present invention has an n+
An n-type diffusion layer is formed on the side surface of the type emitter layer, and a p-type diffusion layer having an impurity concentration higher than that of the p-type base layer is formed outside of the n-type diffusion layer.

That is, the present invention provides a diode formed by a junction between a first semiconductor layer of a first conductivity type and a second high concentration semiconductor layer of a second conductivity type selectively formed within the first semiconductor layer. First of all, I have a hard time. In the structure in which the tops of the second semiconductor layers are insulated with an oxide film and the tops of the oxide layers are protectively coated with a plasma nitride film, the second semiconductor layer is insulated on the upper side of the second high-concentration semiconductor layer of the second conductivity type. A third low concentration semiconductor layer of a second conductivity type having an impurity concentration sufficiently lower than that of the second high concentration semiconductor layer, and a third low concentration semiconductor layer of a second conductivity type having an impurity concentration higher than that of the first semiconductor layer of the first conductivity type on the outside thereof. high? The fourth conductivity type
This is a semiconductor device characterized in that high-concentration semiconductor layers are individually formed.

[For production]

That is, in the present invention, the diode junction formed by the first semiconductor layer of the first conductivity type and the second high-concentration semiconductor layer of the second conductivity type is in contact with the oxide film;
A third low-concentration semiconductor layer of the second conductivity type having a sufficiently lower impurity concentration than the second high-concentration semiconductor layer is provided on the upper side of the high-concentration semiconductor layer, and a first semiconductor layer is provided outside of the third low-concentration semiconductor layer of the second conductivity type. Since a fourth high-concentration semiconductor layer of the first conductivity type with a higher impurity concentration than the Si-S
The electric field near the in,+ interface is relaxed, and breakdown occurs within the bulk on the Si side of this Si-SiO■ interface, significantly reducing the rise in feedback voltage and, by extension, the deterioration of device characteristics. can be done.

〔Example〕

Hereinafter, embodiments of a semiconductor device according to the present invention will be described in detail with reference to FIG.

FIG. 1 is a sectional view schematically showing the general structure of a semiconductor device using a Zener diode according to this embodiment.
In the configuration of the embodiment shown in FIG. 1, the same reference numerals as in the prior art configuration shown in FIG. 2 indicate the same or corresponding parts.

That is, even in the embodiment configuration shown in FIG.
An n-type epitaxial layer 2 is deposited on a p-type silicon substrate 1 by an epitaxial growth method, and boron B or the like is selectively implanted and diffused into this n-type epitaxial layer 2 to create a separation between semiconductor elements. A p-type separation layer 3 is formed to prevent counterfeiting.

In this case, boron ions B+ and the like are widely and selectively implanted and diffused into the upper central part of the n-type base layer 2 between the p-type separation layers 3 to form the p-type base layer 4. At the same time, in a part of this p-type base layer 4, a ρ1-type diffusion layer 5 is formed in which boron B or the like is selectively implanted and diffused to lower the contact resistance. By selectively implanting and diffusing arsenic ions, etc., into the ρ-type base layer 4, an n
A 4-type emitter layer 6 is formed.

Further, there is a low type diffusion layer 7 which is located on the side surface of the n+ type emitter layer 6 and has a donor concentration ND sufficiently lower than that of the n1 type emitter layer 6, and this n'' type diffusion layer 7. A p-type diffusion layer 8 having a higher acceptor concentration than the p-type base layer 4 is formed on the outside of the p-type base layer 4, the low-type diffusion layer 7, and the p-type diffusion layer 8. A Zener diode is constituted by a pn junction with an n''' type emitter layer 6 containing .

In this step, for the n-type diffusion layer 7 and the p-type expansion layer 8, first, the n+-type emitter layer 6 is formed by diffusion from selectively provided polysilicon containing a large amount of n-type impurities. Then, using this polysilicon as a mask, for example, a high concentration ρ type impurity and a low concentration n type impurity are selectively implanted around the n+ type emitter layer 6. These can be easily formed by diffusion.

Furthermore, on each upper surface of the p-type base N 4 , p''-type diffusion layer 5 and n0-type emitter layer 6, an n-type diffusion layer 7 and a p-type diffusion layer of the pn junction in each of these layers 4 and 5 are provided. 8 and covered with a series of silicon oxide films 10, and each opening 1 made in this silicon oxide film 10.
Separate metal wirings 9 are electrically connected to each of the p0 type diffusion layer 5 and the n+ type emitter layer 6 through 0a, and further, the entire surface of each of these metal wirings 9 and the silicon oxide film IO is For example, by plasma CVD method 2
A protective coating is provided by a highly moisture-resistant plasma nitride film 11 deposited at a temperature of about 50 to 400°C.

Therefore, in the Zener diode structure constructed as described above, this rod is placed on the upper side of the n3 type emitter layer 6 which forms a pn junction with the p type base layer 4.
An n-type diffusion layer 7 whose impurity concentration is sufficiently lower than that of the type emitter layer 6 is formed on the outside of this low-type diffusion layer 7.
Since a p-type diffusion layer 8 with a higher impurity concentration than the ρ-type base layer 4 is formed in each of them, the electric field near the Si-Sin 2 interface due to the silicon oxide film of the p-n junction at the time of breakdown is relaxed, and the breakdown is This phenomenon occurs within the bulk on the Si side of the Si-Sin2 interface, and can significantly reduce the injection of carriers into the silicon oxide film.As a result, the generation of interface states is effectively suppressed. This makes it possible to prevent depletion of the surface of the base layer due to the influence of the interface states and the like, and to prevent changes in the Zener breakdown voltage over time, thereby significantly improving the reliability of the device.

In the above example configuration, the case of a base-emitter Zener diode was described, but a combination of a p + type diffusion layer 5 and an emitter may also be used. If p
Of course, a 4-n junction may also be used.

〔Effect of the invention〕

As described in detail above, according to the present invention, a first semiconductor layer of a first conductivity type and a second highly doped semiconductor layer of a second conductivity type selectively formed in the first semiconductor layer are formed. It has a diode by junction with a semiconductor layer, and this? In the structure of a semiconductor device in which the first and second semiconductor layers are insulated with an oxide film and the oxide film is protectively coated with a plasma nitride film, the first semiconductor layer and the second semiconductor layer are At the part where the die junction with the high-concentration semiconductor layer contacts the oxide film, a third low-conductivity layer of the second conductivity type with a sufficiently lower impurity concentration is placed on the upper side of the second high-concentration semiconductor layer. a first semiconductor layer having a higher impurity concentration than the first semiconductor layer, and a first semiconductor layer having a higher impurity concentration than the first semiconductor layer.
Since the conductivity type and fourth high-concentration semiconductor layers are formed respectively, the electric field near the interface in contact with the oxide film of the diode junction at breakdown, that is, near the Si-SiO2 interface, is relaxed, and this Si - Breakdown occurs within the bulk on the Si side of the Si02 interface, thereby effectively reducing the injection of carriers into the oxide film and effectively suppressing the generation of interface states.As a result, Zener It can effectively prevent changes in breakdown voltage over time and improve the reliability of the device, and has excellent features such as being relatively simple in structure and can be provided easily and inexpensively.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view schematically showing the general structure of a semiconductor device using a Zener diode according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of a semiconductor device using a conventional Zener diode. FIG. 3 is a cross-sectional view schematically showing the general structure. FIG. 3 is a graph showing the impurity profile in the depth direction of the p-type base layer and n4- type emitter layer in the Zener diode structure as described above. FIG. The current-voltage characteristic diagram, FIG. 5, is a graph showing the change over time of the breakdown voltage with respect to the reverse voltage application time in the same Zener diode. l...p-type silicon substrate, 2...n-type epitaxial layer, 3...p-type separation layer, 4...p-type base layer (first semiconductor of first conductivity type) layer), 5...p+
type diffusion layer, 6... n+ type emitter layer (second high concentration semiconductor layer of second conductivity type), 7... n1 type diffusion layer (third low concentration semiconductor layer of second conductivity type). layer), 8... p-type diffusion layer (first conductivity type fourth high concentration semiconductor layer), 9...
-Metal wiring, 10...Oxide film, IT...Plasma nitride film, 12...Region where reverse breakdown occurs. Figure 1

Claims (1)

[Claims] It has a diode formed by a junction between a first semiconductor layer of a first conductivity type and a second high concentration semiconductor layer of a second conductivity type selectively formed within the first semiconductor layer. 1. In a configuration in which each of the second semiconductor layers is insulated with an oxide film, and the oxide film is protectively coated with a plasma nitride film, on the upper side surface of the second high concentration semiconductor layer of the second conductivity type. , a third low-concentration semiconductor layer of a second conductivity type having an impurity concentration sufficiently lower than that of the second high-concentration semiconductor layer; A semiconductor device characterized in that a fourth highly doped semiconductor layer of a first conductivity type with a high concentration is formed respectively.