JPH0471273A - Semiconductor rectifier element - Google Patents

Abstract

PURPOSE:To restrain the increase in the voltage effect in the normal direction by a method wherein semiconductor region in higher impurity concentration than that in the substrate region in the same conductivity type as that of the substrate region is formed in the substrate region beneath a semiconductor region in the inverse conductivity type CONSTITUTION:A semiconductor substrate 1 is provided with a pair of main surfaces 11, 12, an n type semiconductor region 13, another n type semiconductor region 14 in higher impurity concentration than that in the semiconductor region 13, a p type semiconductor region 15 in a hollow circular shape located in the semiconductor region 13 from one main surface 11 in higher impurity concentration than that in the semiconductor region 13 and an n type semiconductor region 20 in higher concentration than that in the semiconductor region 13. Next, a main electrode 2 effects a Schottky junction at the interface with the semiconductor region 13 while coming into ohmic contact with the part excluding the parts covered with the semiconductor region 15 and an insulating film 14. Besides, another main electrode 3 comes into ohmic contact with the semiconductor region 14. Through these procedures, the current passing through the semiconductor 14 can be divided into the two currents i.e., one passing through the shortest distance to the Schottky junction part and the other passing through the low resistant semiconductor region 20 thereby enabling the increase in the voltage effect in the normal direction to be restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor device, and particularly to a semiconductor rectifying element with a low forward voltage drop and low loss.

[Prior Art] Pr'1 matching diodes, Schottky junction diodes, and the like are generally known as typical semiconductor rectifying elements. And the Schottky junction diode is pn
Compared to matched diodes, they have the advantage of lower forward voltage drop, but the problem is that the leakage current during reverse bias is more than two orders of magnitude higher than that of pn junction diodes, and losses due to reverse current are large. be.

Therefore, a structure of a semiconductor rectifying element that has a low forward voltage drop and a reduced loss due to reverse current by reducing the reverse leakage current of a Schottky junction diode is disclosed in Japanese Patent Publication No. 59-35183, for example. Japanese Patent Application Publication No. 5
This method has been proposed in JP-A No. 6-2672, JP-A-59-115566, and JP-A-60-74582.

The conventional technology disclosed in the above-mentioned publication is that semiconductor regions of the opposite conductivity type to the substrate region are arranged in parallel at a predetermined interval adjacent to the Schottky junction, and when a reverse voltage is applied, the semiconductor regions of the opposite conductivity type and the substrate By reverse biasing the pn junction between the semiconductor regions, a depletion layer that spreads in the substrate region pinches off the semiconductor regions.

FIG. 8 is a diagram showing the configuration of the semiconductor rectifying element according to the prior art described above. In FIG. 8, 1 is a semiconductor substrate, 2
．． 3 is the main electrode, 4 is the insulating film, 11°12 is the main surface, 13
is a first semiconductor region, 14 is a second semiconductor region, and 15 is a third semiconductor region.

In the prior art shown in FIG. 8, an n-type first semiconductor adjacent to one main surface 11 is placed between a pair of main surfaces of a semiconductor substrate l having a pair of main surfaces 11 and 12 located on opposite sides. region 13 , an n-type second semiconductor region 14 adjacent to the other main surface 12 and the first semiconductor region 13 and having a higher impurity concentration than the first semiconductor region, and one main surface 11
The stripe-like portions extend into the first semiconductor region 13 and have a stripe shape when viewed from one main surface side 11 side, and are arranged in parallel with each other at a predetermined interval with their longitudinal directions aligned. and connecting portions that connect the striped portions at both longitudinal ends of the first semiconductor region 1.
p-type third semiconductor region 1 having an impurity concentration higher than 3;
5.

On one main surface 11 of the semiconductor substrate l, a Schottky junction is formed at the interface with the first semiconductor region 13, and an SiO layer is provided along the outermost periphery of the third semiconductor region 15.
The part excluding the part covered with the insulating film 4 such as PSG,
A first main electrode 2 is provided in ohmic contact with the main surface 11, and a second earth electrode 1'1 is provided in ohmic contact with the second semiconductor region on the other main surface 12 of the semiconductor substrate 1.
lii3 is provided.

The first main electrode 2 is made of an electrode material that forms a barrier against electrons, which are majority carriers in the first semiconductor region 13, such as metals such as Mo and Ti, silicides of these metals,
Alternatively, it is formed using polycrystalline silicon, amorphous silicon, or the like containing metal or other impurities.

In the conventional semiconductor rectifying element configured as described above, when a reverse voltage is applied, the pn junction formed by the first semiconductor region 13 and the third semiconductor region 15 is reverse biased. The depletion layer extending along the interface of the pn junction pinches off the flow path of the leakage current, thereby reducing the leakage current.

[Problems to be Solved by the Invention] The semiconductor rectifier according to the prior art has a first main electrode 2
Since the portion of the third semiconductor region 15 of the conductivity type opposite to that of the substrate, which is formed adjacent to the Schottky junction formed by the first semiconductor region and the first semiconductor region, exists in a form that blocks the current path of the forward current, the current flows in a concentrated manner at the Schottky junction, resulting in an increase in forward voltage drop.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor rectifier element that solves the problems of the prior art and can keep leakage current low and at the same time suppress an increase in forward voltage drop.

[Means for Solving the Problems] According to the present invention, the object is to provide a semiconductor region of a conductivity type opposite to the substrate region adjacent to the Schottky junction, and when a reverse voltage is applied, the semiconductor region of the opposite conductivity type. The pn junction between the semiconductor region and the substrate region is reverse biased, and a depletion layer extending in the substrate region pinches off the path of leakage current, and This is achieved by forming a semiconductor region having a higher impurity concentration than the substrate region having the same conductivity type as the substrate region.

That is, the present invention has a pair of main surfaces, and between the pair of main surfaces, a first semiconductor region of a first conductivity type adjacent to one main surface, and a first semiconductor region adjacent to the other main surface and the first semiconductor region. a second semiconductor region of the first conductivity type that is adjacent to the first semiconductor region and has a higher impurity concentration than the first semiconductor region; When the second part has one or a plurality of missing parts of approximately the same size,
A Schottky junction is formed at an interface between a semiconductor substrate having a third semiconductor region of a conductive type and a first semiconductor region provided on one main surface of the semiconductor substrate and exposed in the missing portion of the third semiconductor region. a first main electrode formed on the other main surface of the semiconductor substrate and in ohmic contact with the third semiconductor region; and a second main electrode provided on the other main surface of the semiconductor substrate and in ohmic contact with the second semiconductor region.
The same conductivity as the first semiconductor formed in at least a portion of the first semiconductor region sandwiched between the main electrode of the main electrode, the bottom of the third semiconductor region, and a portion of the second semiconductor region opposite thereto. and a fourth semiconductor region having a higher impurity concentration than the fourth semiconductor region.

Note that the third semiconductor region described above may have a stripe shape, a polygonal shape, an interconnected stripe shape, a polygonal shape, or a modified shape thereof.

[Function] The semiconductor rectifier according to the present invention has the following effects when a forward voltage is applied:
In the substrate, the current flows not only through the first semiconductor region where the current path is shortest under the Schottky junction, but also through the lower resistance of the first semiconductor region formed under the bottom of the third semiconductor region. Since the current spreads to the fourth semiconductor region having a high current density, current concentration is alleviated, and the isomorphic pressure drop within the substrate can be reduced.

On the other hand, during reverse bias, the first
Since the depletion layer spreads in the semiconductor region, the surface electric field of the Schottky junction is relaxed, thereby making it possible to reduce leakage current to the same extent as in the prior art.

[Example] Hereinafter, an example of a semiconductor rectifier according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing a first embodiment of the present invention. In FIG. 1, 20 is a fourth semiconductor region, and other symbols are the same as in FIG. 8.

The first embodiment of the present invention is an example in which the present invention is applied to a single semiconductor rectifying element.

In FIG. 1, a semiconductor substrate 1 has a pair of main surfaces 11 and 12 located on opposite sides, and an n-type first semiconductor adjacent to one main surface 11 is disposed between the pair of main surfaces 11 and 12. region 13, the other main surface 12 and the first semiconductor region 1
3, an n-type second semiconductor region 14 having a higher impurity concentration than the first semiconductor region, and one main surface side 11
It has a hollow circular shape when viewed from the side, is located within the first semiconductor region 13 from one main surface 11, and is located within the first semiconductor region 1
p-type third semiconductor region 1 having an impurity concentration higher than 3;
5 and an n-type having a higher concentration than the first semiconductor region, which connects the bottom of the third semiconductor region 15 and the surface on the main surface 11 side of the second semiconductor region 14 facing oppositely thereto. A fourth semiconductor region 20 is formed.

The first main electrode 2 is provided on one main surface 11 of the semiconductor substrate 1, forms a Schottky junction at the interface with the first semiconductor region 13, and forms a Schottky junction with the third semiconductor region 15.
Ohmic contact is made at a portion other than a portion covered with an insulating film 4 such as Sin or PSG provided along the outermost periphery. Further, the second main electrode 3 is connected to the semiconductor substrate 1
is in ohmic contact with the second semiconductor region 14 on the other main surface 12 of.

The first main electrode 2 is made of an electrode material that forms a barrier against electrons, which are majority carriers in the first semiconductor region 13, such as metals such as MOTi, silicides of these metals, metals, and other impurities. It is formed using polycrystalline silicon or amorphous silicon containing.

FIG. 2 is a perspective view of essential parts showing a second embodiment of the present invention, and the reference numerals in the figure are the same as those in FIG. 1.

This second embodiment of the present invention is an example in which the present invention is applied to a rectifying element using a semiconductor substrate having a large area in order to increase the forward current.

This embodiment differs from the prior art described with reference to FIG. 8 in that the bottom of the third semiconductor region 15 and the surface on the main surface 11 side of the second semiconductor region 14 facing the third semiconductor region 15 are connected. A fourth n-type semiconductor region having a higher concentration than the first semiconductor region.
The semiconductor region 20 is provided with a semiconductor region 20, and the other structure is the same as that of the prior art.

The important points of the first and second embodiments of the present invention described above are:
The fourth semiconductor region 20 is newly provided, and the function of this fourth semiconductor region 200 will be explained below.

3(a), (b) and FIG. 4(a), (b) are partially enlarged sectional views illustrating the operation of the semiconductor rectifying element.

FIG. 3(a) shows the flow of current during forward bias in a rectifying element according to the prior art using arrows. Since the n-type first semiconductor region 13 has a substantially uniform resistivity,
The current that has passed through the second semiconductor region 14, which has a low resistance, tries to flow in the shortest distance to the Schottky junction on the side of the first main electrode 2, which is the anode electrode, and flows through the n-type first Schottky junction below the Schottky junction. Current concentration occurs in the semiconductor region 13, and the voltage drop in this portion increases.

On the other hand, FIG. 3(b) shows the state at the time of forward bias in the first and second embodiments of the present invention. Since it has the fourth semiconductor region 20, the second semiconductor region 1
The current flowing through Schottky junction 4 is divided into one that attempts to travel the shortest distance to the Schottky junction and one that flows through the fourth semiconductor region 20 of low resistance and then flows into the Schottky junction.

As a result, in the embodiment of the present invention, current concentration as in the case of the prior art shown in FIG. 3(a) is alleviated, and an increase in forward voltage drop can be suppressed.

In FIGS. 3A and 3B, the barrier metal that is the material of the first main electrode 2 forming the Schottky junction is common, the resistivity of the first semiconductor region 13 is ρ1, and the fourth semiconductor The resistivity of the region 20 is ρ4, the widths of the alternating fourth semiconductor region and first semiconductor region are W4 and Wl, respectively, in the cross-sectional view of FIG. 3(b), and the third semiconductor region 15 If the distance from the bottom of the semiconductor region 14 to the second semiconductor region 14 is D, and the current density at the time of forward bias on the side of the second main electrode 3, which is the cathode electrode, is J, then the forward direction in FIG. The difference between the voltage drop Va and the forward voltage drop vb in FIG. 3(b), ΔV, is expressed by the following formula: For example, ρ = 1Ω mark, ρ = 0.5Ω mark, D = 5
μm%W4=10pm%W+=2μm, J.

= 100A/cd, ΔV=0,047V, and in the structure of the embodiment of the present invention shown in FIG.
The forward voltage drop can be reduced by about 0.047V compared to the conventional structure shown in FIG.

FIGS. 4(a) and 4(b) show the spread of the depletion layer when a reverse bias voltage is applied in the prior art and the embodiment of the present invention. The depletion layer extending below the Schottky junction in the first semiconductor region 13 is of the same extent, and the ends 50 of the depletion layer are located at approximately the same position. Therefore, the interfacial electric field at the Schottky junction is also about the same level, the effect of reducing the Schottky barrier due to the electric field is also about the same level, and if the barrier metal is common, the leakage current is also about the same level.

As can be seen from the above description, the semiconductor rectifying elements according to the first and second embodiments of the present invention shown in FIGS. The voltage drop can be reduced, and the forward loss of the semiconductor rectifier can be reduced.

FIG. 5(a) is a sectional view showing a third embodiment of the present invention.

This third embodiment differs from the second embodiment shown in FIG. The fourth semiconductor region 20 is formed deeper than the third semiconductor region 15 before forming the third semiconductor region 15.

This third embodiment of the present invention has the advantage that it can be formed relatively easily by diffusing impurities from the surface of the semiconductor substrate.

FIG. 5(b) is a sectional view showing a fourth embodiment of the present invention.

In this fourth embodiment, a fourth semiconductor region 20 is formed adjacent to the second semiconductor region and separated from the third semiconductor region 15.

In this fourth embodiment of the present invention, the first semiconductor region 13 is largely expanded in a location close to the Schottky junction and is away from the Schottky junction. Since the fourth semiconductor region 20 with lower resistance is spread near the second semiconductor region 14, it is possible to efficiently reduce leakage current during reverse bias and voltage drop during forward bias. It can be realized. Further, in this embodiment, the third semiconductor region 15 forms a pn junction with the first semiconductor region 13 having a lower impurity concentration without contacting the fourth semiconductor region 20, so that the reverse bias This has the effect of improving the withstand pressure at times.

FIG. 5(c) is a sectional view showing a fifth embodiment of the present invention.

This fifth embodiment has a structure that combines the structures of the embodiments shown in FIGS. 5(a) and 5(b),
The forward voltage drop can be made smaller.

FIG. 6 is a perspective view of essential parts showing a sixth embodiment of the present invention.

This sixth embodiment of the present invention is a modification of the second embodiment explained with reference to FIG. This is different from the second embodiment.

In this embodiment, since the surface of the formed recess is away from the pn junction formed between the first semiconductor region and the third semiconductor region, when reverse bias is applied, the third semiconductor on the side wall of the recess The depletion layers extending from the region 15 are likely to pinch each other, which has a large effect of weakening the electric field at the Schottky junction, and has the effect of further reducing leakage current. Furthermore, if the first main electrode 2 on the anode side is formed after burying a conductive material in the recess shown in FIG. 6 to make the main surface flat, disconnection of the first main electrode 2 will not occur. It becomes difficult.

FIG. 7 is a diagram showing a pattern of still another embodiment of the present invention viewed from one main surface 11 side.

In FIG. 7, a one-dot line is a pattern on a horizontal cross section of the fourth semiconductor region 20. In FIG.

FIGS. 7(a) and 7(b) show an embodiment in which the third and fourth semiconductor regions 15, 20 are formed into a large number of rectangular and circular shapes.

These embodiments have the advantage that the area through which the forward current flows can be made wider, compared to the case where the third semiconductor region 15 is formed in a stripe shape.

FIG. 7(c) shows the third and fourth semiconductor regions 15.20.
It has a structure in which it is formed separately into a striped part and a peripheral part, and these parts are not connected. Moreover, FIG. 7(d) is an example in which the missing portions of the third and fourth semiconductor regions 15, 20 are formed as a large number of rectangular portions to reduce the area of the Schottky junction portion.

In the case of these embodiments as well, the same effects as described above can be achieved.

Although the semiconductor rectifying device according to the present invention has been described above using typical examples, the present invention is not limited to these examples, and various modifications can be made within the technical idea of the present invention.

[Effects of the Invention] As explained above, according to the present invention, it is possible to reduce the forward voltage drop while maintaining the same level of reverse leakage current as in the prior art, thereby reducing the trade-off in diode characteristics. It is possible to provide a semiconductor rectifying element with excellent characteristics and low power loss, which can improve the relationship.

[Brief explanation of the drawing]

1 and 2 are perspective views showing the first and second embodiments of the present invention, FIGS. 3 and 4 are partially enlarged sectional views for explaining the present invention in detail, and FIG. 5 , FIG. 6, and FIG. 7 are schematic diagrams showing other embodiments of the present invention, and FIG. 8 is a diagram showing the configuration of the prior art. l...Semiconductor base, 2.3...Main electrode, 4...Insulating film, 11.12...Main surface, 13... -First semiconductor region, 14...
... second semiconductor region, 15 ... third semiconductor region,
20...Fourth semiconductor region. 1st ward 1: 2.3: Standing deaf 1 斑 fig fig (a) (b) (C) (a) (a) fig 4 fig fig fig (b) (b) Figure Figure

Claims (1)

[Claims] 1. A semiconductor region of the opposite conductivity type to the substrate region is provided adjacent to the Schottky junction, and when a reverse voltage is applied, the pn junction between the semiconductor region of the opposite conductivity type and the substrate region is formed. In a semiconductor rectifying element configured to be reverse-biased and pinched off by a depletion layer spreading in a substrate region, a substrate region under the semiconductor region of the opposite conductivity type has a higher impurity concentration than a substrate region of the same conductivity type as the substrate region. A semiconductor rectifying element characterized by forming a semiconductor region with high concentration. 2. Between the pair of main surfaces, a first semiconductor region of the first conductivity type adjacent to one main surface, a semiconductor region adjacent to the other main surface and the first semiconductor region and having a higher impurity content than the first semiconductor region; a second semiconductor region of the first conductivity type having a concentration, and a second semiconductor region extending from one main surface into the first semiconductor region and having one or substantially the same size when viewed from the one main surface side. a semiconductor substrate having a third semiconductor region of a second conductivity type having a plurality of missing portions, the semiconductor substrate being provided on one main surface of the semiconductor substrate and exposed to the missing portions of the third semiconductor region; a first main electrode that forms a Schottky junction at the interface with the first semiconductor region and makes ohmic contact with the third semiconductor region; A second main electrode in ohmic contact, a second main electrode formed in at least a portion of the first semiconductor region sandwiched between the bottom of the third semiconductor region and a portion of the second semiconductor region opposite thereto. 1. A semiconductor rectifying element comprising a fourth semiconductor region having the same conductivity type as the first semiconductor region and having a higher impurity concentration than the first semiconductor region. 3. The fourth semiconductor region is connected to the third semiconductor region and the second semiconductor region.
3. The semiconductor rectifier element according to claim 2, wherein the semiconductor rectifying element is formed in such a manner that these semiconductor regions are connected over substantially the entire area where these semiconductor regions face each other. 4. Striped portions in which the third semiconductor regions are aligned in the longitudinal direction and arranged at approximately equal intervals; and a connecting portion that connects the striped portions at both ends of the striped portion in the longitudinal direction. A semiconductor rectifying element according to claim 2 or 3, characterized in that it consists of: 5. The semiconductor rectifying device according to claim 2 or 3, wherein the missing portion of the third semiconductor region has a polygonal shape when viewed from one main surface side. 6. The third semiconductor region is provided with a recess having an opening on one main surface, and the surface of the recess is separated from the pn junction formed between the first semiconductor region and the third semiconductor region. Claims 2 to 5 characterized in that
The semiconductor rectifying element according to item 1 of the items. 7. The semiconductor rectifying element according to claim 6, wherein the recess is filled with a conductive material.