JPH10190010A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve withstand voltage of a diode without lowering integration degree of a semiconductor device. SOLUTION: A diode has a pn junction part comprising an n-type epitaxial layer 102 and a p-type impurities diffusion region 104 formed on an n-type silicon substrate 101, an insulating film 103 formed on the surface of the n-type epitaxial layer 102, and an electrode wiring layer 105 formed on the insulating film 103 within an opening part 103 and in the periphery of the opening part 103a in such away as to be in contact with the p-type impurities diffusion region 104. The thickness of the insulating film 103 is determined so that the degree of concentration of the electric field in field concentration regions A, B formed in the n-type epitaxial layer 102 when a reverse voltage is applied to the pn junction part become substantially equal to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device having a pn junction formed of a semiconductor layer formed on a substrate and an impurity introduction region formed near the surface of the semiconductor layer.

[0002]

2. Description of the Related Art Conventionally, a structure having a pn junction comprising a semiconductor layer of a first conductivity type formed on a substrate and an impurity diffusion layer of a second conductivity type formed near the surface of the semiconductor layer. Is known. As a semiconductor device having such a structure, for example, a diode, a vertical double diffusion MOS transistor, and the like are known.

[0003]

Hereinafter, an example of the structure of a conventional semiconductor device of this type will be described with reference to FIG. 8, taking a case of a diode having a field plate structure as an example.

As shown in FIG. 8, an n-type silicon substrate 8
01, an epitaxial layer 802 of n-type silicon is formed. An insulating film 803 made of silicon oxide or the like is formed on the surface of the epitaxial layer 802, and the insulating film 803 has an opening 803a. In the vicinity of the surface of the epitaxial layer 802, for example, boron is doped using the opening 803a as a mask so that the p-type impurity diffusion region 8 is formed.
04 is formed. Further, an electrode wiring layer 805 as an anode is formed of a conductive material such as aluminum so as to be in contact with the p-type impurity diffusion region 804 through the opening 803a. On the other hand, the n-type silicon substrate 80
An electrode layer 806 as a cathode is formed of a conductive material on the back surface of 1.

With such a structure, a pn layer composed of an n-type epitaxial layer 802 and a p-type impurity diffusion region 804 is formed.
A diode having a junction can be obtained.

In a diode having such a structure,
In the n-type epitaxial layer 802, an electric field concentration region A near the curvature of the p-type impurity diffusion region 804, and an electric field concentration region B near the end 805a of the electrode wiring layer 805,
Each is formed. When the reverse voltage of the diode exceeds the breakdown voltage, breakdown occurs near these electric field concentration regions A and B.

In general, when the specific resistance [Ω · cm] of the n-type epitaxial layer 802 is small, the degree of electric field concentration in the electric field concentration region A increases, and breakdown near the region A is liable to occur. On the other hand, the n-type epitaxial layer 80
When the specific resistance 2 is large, the degree of electric field concentration in the electric field concentration region B increases, and breakdown near the region B tends to occur.

On the other hand, a diode having a guard ring structure as shown in FIG. 9 is conventionally known as a diode in which the degree of electric field concentration in the electric field concentration region A is reduced. In the figure, the components denoted by the same reference numerals as in FIG.
Each shows the same thing as the case of FIG.

As can be seen from FIG. 9, in this diode, a p-type impurity diffusion layer 901 is formed in the n-type epitaxial layer 802 so as to surround the periphery of the p-type impurity diffusion region 804.
And this is used as a guard ring. That is, by providing this p-type impurity diffusion layer 901,
Since the electric field concentration at the curved portion of the p-type impurity diffusion region 804 can be suppressed and the breakdown at this curved portion can be made difficult to occur, the breakdown voltage of the diode can be improved.

[0010] However, when the guard ring structure as shown in FIG. 9 is employed, a problem arises in that the element area becomes large and the degree of integration of the semiconductor device is reduced.

[0011] Such a problem is not limited to a diode, but includes a pn junction formed by a semiconductor layer formed on a substrate and an impurity introduction region formed near the surface of the semiconductor layer. This is common to semiconductor devices.

For the above reasons, conventionally, there has been a demand for a semiconductor device in which the breakdown voltage of the pn junction is improved without lowering the degree of integration.

[0013]

According to the present invention, there is provided a pn junction comprising a semiconductor layer of a first conductivity type and an impurity introduction region of a second conductivity type formed near the surface of the semiconductor layer; And a conductive layer formed on the insulating film in and around the opening so as to be in contact with the impurity introduction region at the opening provided in the insulating film. Is.

The thickness of the insulating film is such that the electric field generated in the vicinity of the curvature portion of the impurity introduction region in the electric field concentration region generated in the semiconductor layer when a reverse voltage is applied to the pn junction. The electric field concentration in the concentration region and the electric field concentration in the electric field concentration region formed near the end of the conductive layer are determined to be substantially the same.

With such a structure, the breakdown voltage of the pn junction can be improved only by changing the thickness of the insulating film on the semiconductor layer without adopting the guard ring structure. There is no reduction in the degree of integration of the device.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the size, shape, and arrangement of each component are only schematically shown to an extent that the present invention can be understood, and numerical conditions described below are merely examples. Please understand that.

First Embodiment An example in which the present invention is applied to a diode having a field plate structure will be described as a first embodiment.

FIG. 1 is a sectional view schematically showing the structure of the diode according to this embodiment.

As shown in the figure, the structure of this diode is almost the same as that of the conventional diode (see FIG. 9).
An epitaxial layer 102 of n-type silicon formed on the surface of an n-type silicon substrate 101, an insulating film 103 of silicon oxide or the like formed on the surface of the epitaxial layer 102, and an opening 10 formed in the insulating film 103.
3a, the p-type impurity diffusion region 104 formed near the surface of the epitaxial layer 102 by doping, for example, boron with the opening 103a as a mask, and the p-type impurity diffusion region 104 through the opening 103a. An electrode wiring layer 105 as an anode formed of a conductive material such as aluminum, and an electrode layer 106 as a cathode formed of a conductive material over the entire rear surface of the n-type silicon substrate 101.

With this structure, the p-type epitaxial layer 102 and the p-type impurity diffusion region 104
A diode having an n-junction can be obtained.

In the diode having such a structure,
In the n-type epitaxial layer 102, an electric field concentration region A is formed in the vicinity of the curved portion of the p-type impurity diffusion region 104, and an electric field concentration region B is formed in the vicinity of the end 105a of the electrode wiring layer 105.
Each is formed.

In the diode according to this embodiment, in the structure as shown in FIG. 1, the thickness of the insulating film 103 is the same as that of the electric field concentration region A and the electric field concentration region B. Is determined so that

The reason for this will be described below with reference to FIGS.

FIGS. 2A and 2B show simulation results of the distribution of the electric field concentration [V / cm] when a reverse voltage of 1000 [V] is applied to the diode having the structure shown in FIG. FIG. Here, FIG.
FIG. 2B shows the case where the thickness of the insulating film 103 is 4.2 μm, and FIG. 2B shows the case where the thickness of the insulating film 103 is 5.8.
[Μm]. Note that the specific resistance of the n-type epitaxial layer 102 is 65 in both FIGS. 2A and 2B.
[Ω · cm].

As can be seen from FIG. 2, the electric field concentration [V / cm] in the n-type epitaxial layer 102 is highest in the electric field concentration regions A and B. In FIG. 2A, the maximum value of the electric field concentration is 267500 [V / cm] in the charge concentration region B.
In (B), the maximum value of the electric field concentration degree is the charge concentration region A
230600 [V / cm].

That is, in order to improve the breakdown voltage of the diode, it is necessary to reduce the degree of electric field concentration in these regions A and B.

FIG. 3 shows that the reverse voltage is 1000 [V] and the specific resistance of the n-type epitaxial layer 102 is 65 [Ω ·
cm], the relationship between the film thickness of the insulating film 103 and the maximum value of the electric field concentration in the n-type epitaxial layer 102 (the higher of the electric field concentration in the electric field concentration regions A and B in FIG. 1). 5 is a graph showing the simulation result of FIG. In the figure, the horizontal axis represents the film thickness [μm] of the insulating film 103, and the vertical axis represents the maximum value [V / cm] of the electric field concentration.

According to the study of the present inventors, the electric field concentration region A
Of the electric field concentration increases as the thickness of the insulating film 103 increases, while the electric field concentration in the electric field concentration region B increases.
3 is smaller as the film thickness is larger. This is because the insulating film 10
This is probably because the larger the film thickness of No. 3 is, the smaller the charge inversion in the electric field concentration region B is.

For this reason, as shown in FIG.
03 is smaller than about 5.5 μm, the electric field concentration in the electric field concentration region B has the maximum value, and when the film thickness of the insulating film 103 is larger than about 5.5 μm, the electric field concentration in the electric field concentration region A is larger. The degree becomes the maximum value. When the thickness of the insulating film 103 is about 5.5 μm, the electric field concentration areas A and B have the same electric field concentration, and the maximum value of the electric field concentration is the smallest.

FIG. 4 is a graph showing the relationship between the thickness of the insulating film 103 and the withstand voltage of the diode when the specific resistance of the n-type epitaxial layer 102 is 65 [Ω · cm].
In the figure, the horizontal axis indicates the thickness [μm] of the insulating film 103, and the vertical axis indicates the breakdown voltage [V].

In FIG. 4, when the film thickness of the insulating film 103 is smaller than about 5.5 μm, the withstand voltage of the diode changes depending on the degree of electric field concentration in the electric field concentration region B, and the withstand voltage increases as the film thickness increases. growing. On the other hand, when the thickness of the insulating film 103 is larger than about 5.5 μm, the breakdown voltage of the diode changes depending on the electric field concentration in the electric field concentration region A,
As the film thickness increases, the breakdown voltage decreases. Therefore,
The specific resistance of the n-type epitaxial layer 102 is 65 [Ω · c
m], the thickness of the insulating film 103 is about 5.5 μm.
When m, the breakdown voltage of the diode is the maximum value (about 1300
[V]).

As can be seen from FIGS. 3 and 4, when the maximum value of the electric field concentration is the smallest, that is, when the electric field concentration of the electric field concentration regions A and B is the same, the breakdown voltage of the diode becomes maximum.

FIG. 5 shows the thickness of the insulating film 103 and the n-type epitaxial layer 10 when the withstand voltage of the diode becomes the maximum value.
It is a graph which shows the relationship with the specific resistance of 2. In the figure, the horizontal axis represents the specific resistance [Ω · cm] and the vertical axis represents the film thickness [μ
m].

As can be seen from FIG. 5, the film thickness when the withstand voltage of the diode becomes the maximum value (that is, the film thickness when the electric field concentration regions A and B have the same electric field concentration) is equal to the n-type epitaxial layer. It changes according to the specific resistance of 102, and the film thickness of the insulating film 103 must be increased as the specific resistance increases.

FIG. 6 is a graph showing the relationship between the specific resistance of the n-type epitaxial layer 102 and the withstand voltage of the diode when the thickness of the insulating film 103 is determined based on FIG. In the figure, the horizontal axis indicates the specific resistance [Ω · cm], and the vertical axis indicates the withstand voltage [V] of the diode.

As described above, the breakdown voltage of the diode depends on the specific resistance of the n-type epitaxial layer 102, and the higher the specific resistance, the higher the breakdown voltage.

As can be seen from FIGS. 5 and 6, the breakdown voltage of the diode is reduced by increasing the specific resistance of the n-type epitaxial layer 102 as much as possible and determining the thickness of the insulating film 103 in accordance with the specific resistance. Can be improved.

As described above, according to the diode of this embodiment, the withstand voltage can be improved without employing the guard ring structure, so that a diode with improved withstand voltage without lowering the degree of integration is provided. can do.

Second Embodiment Next, as a second embodiment, the present invention is applied to a vertical double diffused MOS transistor having a field plate structure (Vert).
ical Diffusion MOS Transistor; hereinafter referred to as “VDMOS transistor”).

FIG. 7 shows a VDMOS according to this embodiment.
It is sectional drawing which shows the structure of a transistor typically.

As shown in the figure, an epitaxial layer 702 of n ⁻ type silicon is formed on the surface of an n ⁺ type silicon substrate 701. In the vicinity of the surface of the epitaxial layer 702, a p ⁻ type impurity diffusion region 703 is formed by introducing boron or the like using a mask not shown. Further, near the surface of the impurity diffusion region 703, an n ⁺ -type impurity diffusion region 704 is formed by introducing arsenic or the like using a mask (not shown). An insulating film 705 made of silicon oxide or the like is formed on the surface of the n ⁻ type epitaxial layer 702. In an opening 705a provided in the insulating film 705, an n ⁺ -type impurity diffusion region 70 is provided.
Source electrode 706 is formed of a conductive material such as aluminum so as to be in contact with No. 4. In addition, the gate electrode 7 is formed on the step portion 705b provided on the insulating film 705.
07 is formed of a conductive material such as aluminum. On the other hand, on the back surface of the n ⁺ type silicon substrate 701,
An electrode layer 708 serving as a drain electrode is formed of a conductive material such as aluminum.

With this structure, it is possible to obtain a VDMOS transistor having a pn junction formed of an n ⁻ type epitaxial layer 702 and a p ⁻ type impurity diffusion region 703.

In the VDMOS transistor having such a structure, at the end of the element forming region in the n ⁻ type epitaxial layer 702, the electric field concentration region A is located near the curvature of the p ⁻ type impurity diffusion region 704, and the source Electrode 70
6, an electric field concentration region B is formed near the end of each.

In this embodiment, the thickness D (see FIG. 7) of the end portion of the element forming region of the insulating film 705 is set to the electric field concentration degree of the electric field concentration area A and the electric field concentration degree of the electric field concentration area B. Are determined to be the same. By determining the thickness D in this manner, it is possible to provide a VDMOS transistor having an improved breakdown voltage without lowering the integration degree for the same reason as in the first embodiment.

In each of the above-described embodiments, the case where the p-type impurity diffusion region is formed in the n-type epitaxial layer on the n-type semiconductor substrate has been described as an example. The present invention can be applied even when the impurity diffusion region is formed in the semiconductor layer or when the impurity diffusion region is directly formed in the semiconductor substrate.

In the above description, the case where the p-type impurity introduction region is formed in the n-type semiconductor layer (including the semiconductor substrate) has been described as an example. However, the n-type impurity introduction region is formed in the p-type semiconductor layer. Of course, the present invention can be applied to the case of forming.

In each of the above embodiments, the case where the present invention is applied to a diode having a pn junction and a VDMOS transistor has been described as an example. However, a semiconductor layer and a semiconductor layer formed near the surface of the semiconductor layer are described. It is needless to say that the present invention can be applied to other semiconductor devices as long as the semiconductor device has a pn junction including the doped region. For example,
The effect of the present invention can also be obtained when applied to a pn junction of a bipolar transistor. In this case,
Collector-base voltage V of bipolar transistor
_The thickness of a semiconductor layer (a layer formed on a semiconductor substrate or a semiconductor substrate) can be reduced while ensuring a withstand voltage against _CBO .

[0048]

As described in detail above, according to the present invention, it is possible to provide a semiconductor device with improved withstand voltage without lowering the degree of integration.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a structure of a semiconductor device according to a first embodiment.

FIGS. 2A and 2B are distribution diagrams showing the results of simulating the distribution of the electric field concentration of the semiconductor device shown in FIG. 1;

3 is a graph showing the relationship between the film thickness of an insulating film and the maximum value of the electric field concentration in the semiconductor layer in the semiconductor device shown in FIG.

4 is a graph showing the relationship between the thickness of an insulating film and the breakdown voltage of the semiconductor device in the semiconductor device shown in FIG.

5 is a graph showing the relationship between the thickness of an insulating film and the specific resistance of a semiconductor layer when the breakdown voltage of the semiconductor device shown in FIG. 1 reaches a maximum value.

6 is a graph showing the relationship between the specific resistance of the semiconductor layer and the breakdown voltage when the thickness of the insulating film is determined based on FIG. 5 in the semiconductor device shown in FIG.

FIG. 7 is a cross-sectional view schematically illustrating a structure of a semiconductor device according to a second embodiment.

FIG. 8 is a cross-sectional view schematically showing one structural example of a conventional semiconductor device.

FIG. 9 is a cross-sectional view schematically showing another example of the structure of a conventional semiconductor device.

[Explanation of symbols]

101 n-type silicon substrate 102 n-type epitaxial layer 103 insulating film 103a opening 104 p-type impurity diffusion region 105 electrode wiring layer 105a end of electrode wiring layer 106 electrode layer 701 n ⁺ type silicon substrate 702 epitaxial layer 703 p ^- type impurity diffusion Region 704 n ⁺ -type impurity diffusion region 705 insulating film 705a opening 705b step 706 source electrode 707 gate electrode 708 drain electrode

Claims (1)

[Claims] 1. A pn junction formed of a semiconductor layer of a first conductivity type and an impurity introduction region of a second conductivity type formed near the surface of the semiconductor layer, and a pn junction formed on the surface of the semiconductor layer, In a semiconductor device having an insulating film having an opening on an impurity introduction region and a conductive layer formed on the insulating film in and around the opening so as to contact the impurity introduction region at the opening, The thickness of the insulating film is such that the electric field concentration region generated in the vicinity of the curvature of the impurity introduction region among the electric field concentration regions generated in the semiconductor layer when a reverse voltage is applied to the pn junction. And the electric field concentration degree of the electric field concentration region of the electric field concentration area near the end of the conductive layer are determined to be substantially the same.