JPH08330605A - Semiconductor device - Google Patents

Abstract

PURPOSE: To reduce defects a semiconductor device due to the leakage current of its protective diode by forming it such that a potential pick up electrode formed on a base region and electrode formed on an emitter region are shorted and a collector electrode formed at the pick up region from a second conductivity type buried region forms other terminal. CONSTITUTION: A GND electrode 12 for electrically connecting a P-type base region 6 to an N<+> -type emitter region 11 is formed and connected to a ground potential Vss. A terminal 13 for electrically connecting to an N<+> -type collector contact region 10 is formed. Wiring from PAD is connected to the terminal electrode 13. When a semiconductor substrate 1 is set at the ground potential, P-N junction diode composed of the substrate 1 and N-type buried layer is also forward biased to allow substantially same quantity of current as conventional to flow. P-base contact region contg. high-concn. impurities disappears to result in reduction of defects due to the leakage current from a protective diode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a structure of an input protection diode of the semiconductor device.

[0002]

2. Description of the Related Art A semiconductor integrated circuit of a semiconductor device formed on a semiconductor substrate is composed of various semiconductor elements. Then, in order to prevent the destruction of the semiconductor element due to a high voltage instantaneously applied from the outside, for example, a high voltage due to static electricity,
A protective element is provided between a semiconductor element and a wiring from a pad (PAD) on the semiconductor substrate that serves as an external terminal. A typical example of this protective element is a protective diode using a P-N junction provided on a semiconductor substrate.

Such a conventional protection diode will be described with reference to FIGS. 7 and 8. As shown in FIG. 7, an N-type embedded layer 22 is selectively formed on the surface of a semiconductor substrate 21 having a P-type conductivity, and the semiconductor substrate 2 including the N-type embedded layer 22.
An N ⁻ type epitaxial layer 23 is formed on the first layer 1. Then, LOCOS is formed on the surface of the N ⁻ type epitaxial layer 23.
(Local Oxidation of Silic
on) method, the field oxide film 24 is formed. Next, an N ⁺ type collector diffusion region 25 is formed in a predetermined region, that is, a region surrounded by the field oxide film 24. The depth of the surface portion of the N ⁻ type epitaxial layer 23 is 0.
A shallow junction P-type base region 26 of 5 μm or less is formed,
A P ⁺ type base contact region 27 is formed in a part of the P type base region 26.

Further, an insulating thin film 28 is formed on the N ⁻ type epitaxial layer 23 and the field oxide film 24. The insulating thin film 28 is selectively removed on the N ⁺ type collector diffusion region 25 and the P type base region 26, and the N ⁺ type polycrystalline silicon film 29 is formed on the removed region. Then, N ⁺ -type collector contact region 30 and the N ⁺ -type emitter region 31 on the surface of the N ⁺ type collector diffusion region 25 and the P-type base region 26 are formed.

Then, the P ⁺ type base contact region 27 is formed.
And the N ⁺ emitter region 31 are connected to the GND electrode 32, which is connected to the ground potential Vss. Further, a terminal electrode 33 connected to the N ⁺ type polycrystalline silicon film 29 on the N ⁺ collector contact region 30 is formed.

In such a protection diode, the PA
The wiring from D is connected to the above-mentioned terminal electrode 33. The wiring from this pad includes a power wiring, a wiring electrically connected to the base (B) or the emitter (E) of the semiconductor element, and the like.

The protection diode shown in this prior art has the same structure as a semiconductor element used inside a semiconductor integrated circuit. The size is designed to be about 10 times that of the internal semiconductor element. This is essential for ensuring the protection capability of the protection diode.

[0008]

However, in the above-mentioned conventional protection diode, the thick field oxide film 24 by the LOCOS method exists near the PN junction such as the base-emitter or the base-collector. Further, there is a P ⁺ type base contact region 27 containing a high concentration of boron impurities of 1 × 10 ¹⁸ atoms / cm ³ or more. Then, as described above, the size of these semiconductor elements is large and the area thereof is wide.

Due to such a structure, the crystal strain of the surface portion of the N ⁻ type epitaxial layer 23, especially the emitter or base region becomes very large. Then, the frequency of occurrence of crystal defects increases in this region. An example of such a defect occurrence will be described with reference to FIG. Here, FIG. 8 is an enlarged sectional view of the base and emitter regions of FIG.

As shown in FIG. 8, the junction depth is 0.4 μm.
When dislocations are generated in the shallow junction P-type base region 26 of about m and then the N ⁺ -type emitter region 31 is formed, abnormal diffusion of impurities occurs along the dislocations and the pipe-shaped diffusion region 3 is formed.
1a is formed. Then, the leak current between the emitter and the collector increases, and the yield of the semiconductor integrated circuit decreases. Here, FIG. 7 shown in FIG.
The same reference numerals as those used in FIG. 7 indicate the same things as those described with reference to FIG.

An object of the present invention is to provide a method for solving such a problem, to reduce the frequency of occurrence of the above-mentioned leakage current of the protection diode and improve the yield of the semiconductor integrated circuit.

[0012]

To this end, in the semiconductor device of the present invention, a semiconductor epitaxial layer is formed on a semiconductor substrate of the first conductivity type via a buried layer of the second conductivity type. A semiconductor device in which island regions electrically separated from each other are formed by a semiconductor oxide film selectively formed on a surface and a semiconductor element is formed in these island regions, and does not have a layer containing a high concentration impurity. A collector electrode provided in the extraction region from the second conductivity type buried layer, wherein the potential extraction electrode formed in the base region and the electrode formed in the emitter region are short-circuited to form one terminal and fixed to the ground potential. Has a protection diode serving as the other terminal.

Here, the diffusion layer forming the base region and the diffusion layer forming the emitter region together form a shallow junction.

Alternatively, a diffusion layer forming the emitter region is formed in a region separated from the selectively formed semiconductor oxide film.

According to the present invention, in the protection diode of the bipolar transistor, when the above-mentioned P ⁺ base contact region containing a high concentration of impurities is eliminated, defects due to the leak current of the protection diode are significantly reduced. It is based on.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a protection diode of the present invention. FIG.
, The impurity concentration is 10 ¹⁴ to 10 ¹⁵ atoms / cm 3.
^The N type buried layer 2 is formed on the surface of the semiconductor substrate 1 whose conductivity type is P type ³
There are selectively formed, the N type buried layer impurity concentration on the semiconductor substrate 1 including two of about 10 ¹⁵ atoms / cm ³ N ^- -type epitaxial layer 3 is formed. Here, the film thickness of the N ⁻ epitaxial layer 3 is about 4 μm. And
A field oxide film 4 is formed on the surface of the N ⁻ type epitaxial layer 3 by the LOCOS method. Here, the film thickness of the field oxide film 4 is 1.5 to 2 μm.

Next, the concentration is 10 ¹⁸ to 10 ¹⁹ atoms / cm 3.
N ⁺ -type collector diffusion region 5 containing the phosphorus impurity is formed. Then, a shallow junction P-type base region 6 having a depth of 0.4 μm or less is formed on the surface portion of the N ⁻ -type epitaxial layer 3. Here, the concentration of boron contained in the P-type base region 6 is set to 10 ¹⁷ to 10 ¹⁸ atoms / cm ³ . In this case, P as described in the related art is used.
^{+ No} base contact area is provided.

Next, an insulating thin film 8 is formed on the N ⁻ type epitaxial layer 3 and the field oxide film 4 and selectively removed on the N ⁺ type collector diffusion region 5 and the P type base region 6, and this removal is performed. An N ⁺ type polycrystalline silicon film 9 is formed in the formed region. The N ⁺ type collector contact region 10 and the N ⁺ type emitter region 11 are formed on the surfaces of the N ⁺ type collector diffusion region 5 and the P type base region 6, respectively.
Is formed. Here, in the N ⁺ type polycrystalline silicon film,
Contains arsenic impurities. The depth of the N ⁺ type emitter region 11 is set to about 0.2 μm.

Next, a GND electrode 12 that electrically connects the P type base region 6 and the N ⁺ type emitter region 11 is formed. The GND electrode 12 is connected to the ground potential Vss. Further, the terminal electrode 13 electrically connected to the N ⁺ type collector contact region 10 is formed. And PA
The wiring from D is the above-mentioned terminal electrode 13 as shown in FIG.
Connected to.

Generally, the formation of the P ⁺ type base contact region in the base region is essential in the structure of the semiconductor element inside the semiconductor integrated circuit for the purpose of reducing the base resistance. This is because it is indispensable for improving the high frequency characteristics or noise characteristics of the semiconductor integrated circuit.
On the other hand, the protection diode is mainly required to have an electrostatic breakdown preventing function. In fact, even if the base resistance of the protection diode increases, it does not cause a big problem.

FIG. 2 shows the forward characteristic of such a protection diode in comparison with the conventional case. Here, in the conventional case, the P ⁺ base contact region is formed in the protection diode. In the case of the present invention, the amount of current is lower in the large current region than in the conventional case. However, the protection diode operates in the forward direction when a negative voltage is applied to the terminal electrode 13. Therefore, if the semiconductor substrate 1 is set to the ground potential, P- composed of the semiconductor substrate and the N-type buried layer is formed.
The N-junction diode also moves in the forward direction, and a current also flows in this direction, so that the amount of current does not change much from the conventional case. That is, the driving ability in the forward direction does not decrease as compared with the conventional one.

Next, the leakage defect rate of the protective diode structure of the present invention when a reverse voltage is applied will be described with reference to FIG. 3 in comparison with the conventional case. The leak defect rate shown in FIG. 3 is a measurement result of 100 protection diodes. As can be seen from FIG. 3, in the case of the conventional protection diode structure, the leak defect rate is about 10%, but in the protection diode structure of the present invention, it is significantly reduced to about 1.5%.

The leak defect rate is further reduced by increasing the distance between the field oxide film and the N ⁺ type emitter region. Next, this will be described with reference to FIG.
FIG. 4 is a sectional view of a protection diode according to the second embodiment of the present invention. Here, the same components as those in FIG. 1 described in the first embodiment are designated by the same reference numerals. The protective diode structure in this case is almost the same as that of the first embodiment and is as follows.

An N type buried layer 2 is selectively formed on the surface of a semiconductor substrate 1 having a P type conductivity, and an N ⁻ type epitaxial layer 3 is formed on the semiconductor substrate 1 including the N type buried layer 2. To be done. Here, the film thickness of the N ⁻ epitaxial layer 3 is 4 μm.
m. Then, field oxide films 4 and 4a are formed on the surface of the N ⁻ type epitaxial layer 3.

Next, an N ⁺ type collector diffusion region 5 containing phosphorus impurities is formed. Then, a shallow junction P-type base region 6 is formed on the surface of the N ⁻ -type epitaxial layer 3. Also in this case, the P ⁺ base contact region is not provided.

Next, an insulating thin film 8 is formed on the N ^-- type epitaxial layer 3 and the field oxide films 4 and 4a.
^{The +} type collector diffusion region 5 and the P type base region 6 are selectively removed, and the N ⁺ type polycrystalline silicon film 9 is formed in the removed region. The N ⁺ type collector contact region 10 and the N ⁺ type emitter region 11a are formed on the surfaces of the N ⁺ type collector diffusion region 5 and the P type base region 6.
Is formed. Here, in the N ⁺ type polycrystalline silicon film,
Contains arsenic impurities. The N ⁺ type miter region 11a is formed in a region apart from the field oxide film 4a.

Next, a GND electrode 12 for electrically connecting the P-type base region 6 and the N ⁺ -type emitter region 11a is formed and connected to the ground potential Vss. Further, the terminal electrode 13 electrically connected to the N ⁺ type collector contact region 10 is formed. The wiring from the PAD is connected to the above-mentioned terminal electrode 13 as shown in FIG.

The effect of this embodiment will be described with reference to FIG. FIG. 5 shows the relationship between the leak defect rate and the separation distance between the field oxide film and the emitter described above. Here, this separation distance is represented by L shown in FIG. As can be seen from FIG. 5, if the separation distance is 10 μm or more, the leak defect rate described above is reduced to 0.5% or less. Although the area of the protection diode increases when the separation distance L is increased in this way, the area of the protection diode is originally large and the area increased by the structure of this embodiment is 10 to 20%, which is not a big problem.

Next, a third embodiment of the present invention will be described with reference to FIG. In this case, the field oxide film is not formed between the collector diffusion region and the base region described above. Also in this case, the protection diode structure is similar to that described in FIG. That is, the N-type buried layer 2 is selectively formed on the surface of the semiconductor substrate 1 having a P-type conductivity, and the N ⁻ -type epitaxial layer 3 is formed on the semiconductor substrate 1 including the N-type buried layer 2. It Then, a field oxide film 4 is formed on the surface of the N ⁻ type epitaxial layer 3.

Next, an N ⁺ type collector diffusion region 5 containing phosphorus impurities is formed. Then, a shallow junction P-type base region 6 is formed on the surface of the N ⁻ -type epitaxial layer 3. Also in this case, the P ⁺ base contact region is not provided.

Next, an insulating thin film 8 is formed on the N ⁻ type epitaxial layer 3 and the field oxide film 4 and selectively removed on the N ⁺ type collector diffusion region 5 and the P type base region 6, and this removal is performed. An N ⁺ type polycrystalline silicon film 9 is formed in the formed region. Then, N ⁺ -type collector contact region 10 and N ⁺ -type emitter region 11 on the surface of the N ⁺ type collector diffusion region 5 and the P-type base region 6 is formed. Here, the N ⁺ type polycrystalline silicon film contains arsenic impurities.

Next, a GND electrode 12 that electrically connects the P-type base region 6 and the N ⁺ -type emitter region 11 is formed. The GND electrode 12 is connected to the ground potential Vss. Further, the terminal electrode 13 electrically connected to the N ⁺ type collector contact region 10 is formed. And PA
The wiring from D is the above-mentioned terminal electrode 13 as shown in FIG.
Connected to.

In the case of this embodiment, no field oxide film is formed between the N ⁺ type collector diffusion region 5 and the P type base region 6. Therefore, the N ⁻ type epitaxial layer 3
The crystal strain on the surface of is greatly reduced. Then, the occurrence of crystal defects is also reduced. In this case, there is an effect that the area of the protection diode is reduced as compared with the case of the first or second embodiment. However, the usable voltage is reduced.

In the above embodiments, the case of the protection diode composed of the NPN type bipolar transistor has been described. It should be noted that the same effect can be obtained when the protection diode is a PNP type bipolar transistor.

[0035]

As described above, in the present invention, the P ⁺ type base contact region is eliminated in the protection diode having the bipolar transistor structure. Further, the emitter region is formed in a region separated from the formation region of the field oxide film which is an element isolation insulating film. Then, both the emitter and the base region forming the protection diode are fixed to the ground potential, and the wiring from the PAD for applying an external voltage is connected to the collector electrode of this protection diode.

By adopting such a structure, the crystal defects in the region where the protection diode is formed are significantly reduced, and the leak defect rate of the protection diode is 1/1 as compared with the conventional technique.
Significantly reduced to 0 to 1/20. Then, the yield of the semiconductor integrated circuit is significantly improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a protection diode illustrating a first embodiment of the present invention.

FIG. 2 is a graph of forward characteristics of a protection diode for explaining the present invention.

FIG. 3 is a graph showing the effect of the first embodiment of the present invention.

FIG. 4 is a sectional view of a protection diode for explaining a second embodiment of the present invention.

FIG. 5 is a graph showing the effect of the second embodiment of the present invention.

FIG. 6 is a sectional view of a protection diode for explaining a third embodiment of the present invention.

FIG. 7 is a sectional view of a protection diode for explaining a conventional technique.

FIG. 8 is a sectional view of a protection diode for explaining the problems of the conventional technique.

[Explanation of symbols]

1, 21 semiconductor substrate 2, 22 N type buried layer 3, 23 N ⁻ type epitaxial layer 4, 4 a, 24 field oxide film 5, 25 N ⁺ type collector diffusion region 6, 26 P type base region 8, 28 insulating thin film 9, 29 N ⁺ type polycrystalline silicon film 10, 30 N ⁺ type collector contact region 11, 11a, 31 N ⁺ type emitter region 12, 32 GND electrode 13, 33 terminal electrode 27 P ⁺ type base contact region 31a Pipe-shaped Diffusion area

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 29/73 H01L 29/90 D // H01L 29/866

Claims (3)

[Claims] 1. A semiconductor epitaxial layer is formed on a semiconductor substrate of the first conductivity type via a buried layer of the second conductivity type, and a semiconductor oxide film selectively formed on a surface of the semiconductor epitaxial layer electrically connects to each other. A semiconductor device in which island regions that are spaced apart from each other are formed, and a semiconductor element is formed in these island regions, wherein a potential extraction electrode and an emitter region are formed in a base region that does not have a layer containing high-concentration impurities. A protective diode short-circuited with the electrode to be fixed and fixed to the ground potential to form one terminal, and the collector electrode provided in the extraction region from the second conductivity type buried layer constitutes the other terminal. A semiconductor device having. 2. The semiconductor device according to claim 1, wherein the diffusion layer forming the base region and the diffusion layer forming the emitter region both form a shallow junction. 3. The semiconductor device according to claim 1, wherein the diffusion layer forming the emitter region is formed in a region separated from the selectively formed semiconductor oxide film.