JPH11112005A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device provided with the rectification characteristics of a low ON voltage, high breakdown strength and a small leakage current capable of a high speed operation. SOLUTION: Recessed parts 12 are formed on the surface of a silicon substrate 11 of an N type and low impurity concentration, an anode area 13 is formed between them and the cut-off area 14 of a P type and high impurity concentration is formed at the bottom part of the recessed part 12. An anode electrode 18 composed of a metallic material for forming a Schottky junction with the anode area 13 is provided, and the cut-off area 14 is connected to the anode electrode by a metallic film 15 formed on the inner surface of the recessed part 12. On the surface on the opposite side of the silicon substrate 11, a cathode area 16 of the N type and the high impurity concentration and a cathode electrode 17 on it are formed.

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 semiconductor device having the characteristics of a Schottky diode and a PN diode.

[0002]

2. Description of the Related Art FIG. 1 shows the structure of a Schottky junction type diode which has recently been widely used as a semiconductor rectifier which operates at high speed. An anode region 3 is formed by forming a P-type cutoff region 2 on the surface of an N-type semiconductor substrate 1, and an anode electrode 4 is formed on the surface of the anode region. An N ⁺ -type cathode region 5 is formed on the back surface of the semiconductor substrate 1, and a cathode electrode 6 is formed thereon. The anode electrode 4 is formed of a metal material that forms a Schottky junction with the semiconductor material forming the anode region 3. In such a conventional Schottky junction diode, the Schottky junction area, that is, the area of the anode electrode 4 is equal to or smaller than the cross-sectional area of the channel.
This Schottky junction type diode operates at high speed and has an advantage that an on-voltage (rising voltage) at which a current starts to rise is as low as about 0.2V. Such Schottky junction type diodes are, for example, Nganantha, KGA
"Planar mesa Schottcky barrier diode" by shar,
IBM JK. Res. Devel, 15, 442-445 (1971). On the other hand, a PN junction type diode is widely used as a high voltage semiconductor rectifier. This PN junction type diode has an advantage that a leakage current is small when a high reverse voltage is applied, that is, an advantage that it has a high breakdown voltage.

[0003]

However, the above-mentioned Schottky junction type diode has a drawback that the breakdown voltage is low. Further, the PN junction type diode has a drawback that the rising voltage is as high as about 0.6 V, the reverse recovery time is long due to the minority carrier accumulation effect, and high-speed operation cannot be performed. Conventionally, considering the characteristics of the above-mentioned Schottky junction type diode and PN junction type diode, the ones suitable for each application are used, but they can operate at high speed, have low start-up voltage, and have high breakdown voltage. In many cases, a semiconductor device having a small leakage current at the time of off is desirable. In such a case, one of the characteristics has to be sacrificed.

JP-A-56-2672 and Y. Shimizu,
"IEEEE Trans. On Electron by Y. Terasawa et al
Deivces ", Vol. ED-31 (9), 1314-1319 (1984) states that in order to improve the reverse breakdown voltage of a Schottky junction diode, the conductivity of the surface of the substrate that forms the Schottky barrier in contact with the metal electrode is improved. A region of the opposite conductivity type to the body layer is provided on the same substrate surface, a PN junction is formed between the substrate and the substrate, and the PN junction is reverse-biased with a reverse voltage lower than the reverse breakdown voltage of the Schottky junction. It has been proposed to prevent a large reverse voltage by forming a depletion layer on the entire surface, and in such a device, the area of the Schottky junction when a forward current flows is only the surface integral of the region of the opposite conductivity type. For example, the above-mentioned "IEEEE Trans. On Electron Deiv"
In the case of "ces", the width of the opposite conductive type region forming the PN junction with the substrate is 15 μm, whereas the width of the channel serving as the conductive region is as small as 6 μm. Increases the withstand voltage, but the conduction area is reduced,
There is a problem that the maximum amount of current that can be supplied is limited.

Accordingly, an object of the present invention is to provide a semiconductor device having both good characteristics of the above-described Schottky junction type diode and PN junction type diode, that is, high speed operation and low on-state voltage of the Schottky junction type diode and PN junction diode. An object of the present invention is to provide a semiconductor device having excellent characteristics such as a high breakdown voltage and a small leakage current of a junction diode.

[0006]

A semiconductor device according to the present invention comprises an N-type semiconductor substrate, a plurality of recesses formed on one surface of the semiconductor substrate, and a plurality of recesses on the semiconductor substrate between the recesses. A mesa-type anode region formed by the portion, a P-type cut-off region formed at least at the bottom of the concave portion and expanding a depletion layer at the time of reverse bias to block a current path; and an anode connected to the anode region. An anode electrode forming a Schottky junction with the region, an N-type cathode region formed on the other surface of the semiconductor substrate, and a cathode electrode connected to the cathode region. Is what you do.

In such a semiconductor device according to the present invention, a Schottky junction is formed between the anode region and the anode electrode. When the semiconductor device is turned on, the semiconductor device operates in the same manner as a Schottky junction diode, so that high-speed operation is possible. In addition, a low rising voltage can be realized. When a reverse voltage is applied between the anode electrode and the cathode electrode, a high-resistance depletion region extending from the opposite conductivity type cut-off region formed at the bottom of the recess to the inside of the one conductivity type substrate is connected to each other, and the anode is connected to the anode. Since the current channel between the cathode and the cathode is closed and operates like a PN junction type diode, the breakdown voltage is increased and the leakage current at the time of OFF is reduced.

FIG. 2 shows a semiconductor device according to the present invention in comparison with the conventional semiconductor device shown in FIG. In the present invention, the concave portion 7 is formed on the surface of the N-type semiconductor substrate 1 to form the mesa-type anode region 3, and the P-type cutoff region 2 is formed at the bottom of the concave portion. Other structures are the same as those of the conventional Schottky junction type diode shown in FIG. In the present invention, since the cutoff region 2 of the conductivity type opposite to that of the anode region 3 is not formed on the same plane as the surface of the anode region, there are the following advantages. The pinch-off region when the reverse voltage is applied is separated from the anode region because it is expanded by the opposite conductivity type cut-off region 2 provided on the bottom surface or side surface of the concave portion. Therefore, a cross section perpendicular to the conduction direction of the pinch-off region sandwiched between adjacent cut-off regions, that is, a Schottky junction area larger than the Schottky junction area of the conventional Schottky junction type diode can be obtained. This provides an advantage that a large current can flow with low resistance during conduction.

In a preferred embodiment of the present invention, a metal film is formed on the inner surface of the concave portion, and the cutoff region is connected to the anode electrode via the metal film. In this case, a metal made of a metal material that forms an ohmic contact with the cutoff region when a reverse voltage is applied, forms a non-ohmic contact with a forward voltage when applied with a forward voltage, and forms a Schottky junction with the anode region Preferably, the film is formed uniformly on the surface of the recess and the surface of the anode region. Also,
In the case of a semiconductor device in which a metal plate that forms a Schottky junction between the anode electrode and the anode region is bonded to the surface of the semiconductor substrate, the metal film formed on the concave surface is brought into contact with the anode electrode plate on the surface of the semiconductor substrate. Is preferred. In this case, the metal film formed on the surface of the concave portion may be formed of a metal material that forms ohmic contact with the cutoff region when a reverse voltage is applied.

In the present invention, the conductivity type and the polarity of the electrode can be reversed. That is,
A semiconductor device according to the present invention includes a P-type semiconductor substrate, a plurality of recesses formed on one surface of the semiconductor substrate, and a mesa-type cathode formed by a portion of the semiconductor substrate between the recesses. An N-type cutoff region formed at least at the bottom of the concave portion to expand a depletion layer at the time of reverse bias to cut off a current path; and to form a Schottky junction between the cathode region and the cathode region. A cathode electrode to be formed; a P-type anode region formed on the other surface of the semiconductor substrate; and an anode electrode connected to the anode region.

[0011]

FIG. 3 shows a semiconductor device according to the present invention.
FIG. 3 is a cross-sectional view illustrating the structure of the first embodiment. Explained later
As in the other embodiments, the drawings are shown diagrammatically and
The dimensional relationship of the seed region is different from the actual one. Impure
Substance concentration is 10^13-14Atom / cm^ThreeDegree N^-Type silicon substrate 11
A large number of recesses 12 are formed on one surface of
Formed by the part of the silicon substrate that exists between the parts
One-conductivity-type mesa-shaped protrusion ^-Type anode region 13
To achieve. Such a recess 12 is formed by one isotropic etching.
Can be formed. Further, the bottom of the recess 12 is
Diffusion of impurities of anti-conductivity type, impurity concentration of 10¹⁷Atom / c
m^ThreeDegree P⁺Form a mold region 14. As described below,
This P⁺The mold region 14 applies a reverse bias to the semiconductor device.
In this specification, it has the effect of interrupting the current when
Is referred to as a cut-off region. On the inner surface of the recess 12
Contacts the silicon substrate 11 to form a Schottky junction
An aluminum film 15 is formed as an example of the metal to be formed. This
Aluminum film 15 is P⁺Mold cutoff area 14 and ohmi
Form a contact. Therefore, in the present invention,
Is cut on the surface of the silicon substrate as shown in FIG.
Schottky compared to conventional diodes with
Since the junction area can be increased, the
Can be realized.

On the other surface of the silicon substrate 11, an N ⁺ type cathode region having an impurity concentration of about 10 ¹⁹ to 10 ²⁰ atoms / cm ^{3 is provided.}
Then, a cathode electrode film 17 made of aluminum and having a thickness of about 1 μm is formed thereon. The contact between the cathode region 16 made of N ⁺ -type silicon and the cathode electrode film 17 made of aluminum is an ohmic contact. An anode electrode is provided on one surface of the silicon substrate 11 so as to be in contact with the surface of the anode region 13 described above.
Form 18. In the present invention, this anode electrode 18
Is formed of a material that forms a Schottky junction with the anode region 13. In this example, since the anode region 13 is made of N ^- type silicon, a Schottky junction can be formed by forming the anode electrode 18 with aluminum. As the electrode material for forming the Schottky junction with the N ^- type silicon, aluminum silicon (AlSi), chromium, titanium,
Molybdenum, vanadium, or the like can be used.

In this embodiment, as described above, the anode region 18 made of N ^- type silicon and the anode electrode 18 made of aluminum forming a Schottky junction are constituted by an aluminum plate having a thickness of about 1 mm. Is bonded to one surface of the silicon substrate 11. Therefore, such an anode electrode is also referred to as an anode electrode plate. The bonding between the silicon substrate 11 and the anode electrode plate 18 can be performed by bringing them into contact with each other under pressure and / or without pressure. With such a junction type device, undesired diffusion of the anode electrode film material into the anode region 13 can be suppressed, and the anode electrode plate 18 also functions as a heat sink, so that thermal characteristics are improved. .

Next, the operation of the semiconductor device of this embodiment will be described.
First, when a forward voltage is applied between the anode electrode plate 18 and the cathode electrode film 17, a current flows from the anode region 13 to the cathode region 16. In this case, the P ⁺ type cutoff area
Since the PN junction between 14 and the N ^- type silicon substrate 11 is forward biased, the depletion region does not spread from the cutoff region, and current flows through a channel formed between adjacent cutoff regions. . Therefore, in this state, the semiconductor device operates similarly to the Schottky diode.
In this Schottky junction diode operation, since there is essentially no injection or accumulation of minority carriers, high-speed operation is possible and the ON voltage is as low as about 0.2V. On the other hand, when a voltage in the opposite direction is applied between the anode electrode plate 18 and the cathode electrode film 17, the depletion region expands from the P ⁺ type cutoff region 14, and the adjacent depletion regions communicate with each other to close the channel. The current stops flowing. The behavior in this case is
The operation is the same as that of the PN junction type diode, so that the breakdown voltage is increased and the leakage current is reduced. In this manner, in the semiconductor device according to the present invention, both the characteristics of the Schottky diode such as high-speed operation and low on-voltage and the characteristics of the PN junction diode such as high breakdown voltage and small leakage current can be obtained. become.

FIG. 4 is a schematic sectional view showing the structure of a second embodiment of the semiconductor device according to the present invention. Also in this example, a large number of recesses 22 are formed on one surface of the N ⁻ -type silicon substrate 21 by one isotropic etching, and one conductivity type existing between these recesses is formed on the silicon substrate. A mesa-type anode region 23 is formed by the convex portion. Further, the opposite conductive type, that is, a P ⁺ type cutoff region 24 is provided at the bottom of the concave portion 22.
Is formed by diffusion. An N ⁺ -type cathode region 26 is formed on the other surface of the silicon substrate 21, and a cathode electrode film 27 made of aluminum is formed thereon. The structure up to this point is the same as that of the first embodiment. In the present example, a material that forms an Schottky junction with the anode region 23 on one surface of the silicon substrate 21 and forms an ohmic contact when a reverse voltage is applied between the P ⁺ type cutoff region 24, An anode electrode film 29 made of aluminum is formed. In this example, since the aluminum film covering the anode region 23 and the inner surface of the recess 22 is uniformly formed and the anode electrode film 29 is provided, the configuration is simplified and the manufacturing process is also simplified. . In addition, since the anode electrode film 29 is formed not only on the upper surface but also on the side surface of the mesa-type anode region 23, compared to a conventional Schottky junction diode in which a cut-off region is formed on the surface of the silicon substrate 21, There is also an advantage that the area of the key junction increases and the current capacity increases. The operation of this example is the same as that of the previous example, and has both the advantages of the Schottky junction diode and the advantages of the PN junction diode.

FIG. 5 shows a third embodiment of the semiconductor device according to the present invention.
It is sectional drawing which shows the structure of an Example diagrammatically. In this example, N type
Two-stage isotropic etching on the surface of silicon substrate 41
Silicon present between adjacent recesses, forming recesses 42
A mesa-type anode region 43 is formed by using the substrate.
Diffusion of P-type impurities from the bottom of ⁺Mold cut-off
The buffer region 44 is formed. Further, the surface of the concave portion 42 and the
P to cover the surface of the⁺Die cut-off area
44 forms an ohmic contact with the N-type anode region 43
Is the metal forming the Schottky junction, in this case aluminum
An anode electrode film 45 made of chromium is formed. Also,
N on the surface on the opposite side of the control board 41⁺Mold cathode area 46
Is formed, and a cathode electrode film 47 is formed thereon. This example
The operation of the semiconductor device according to the second embodiment is the same as that of the second embodiment shown in FIG.
Is the same as

FIG. 6 is a sectional view diagrammatically showing the structure of a fourth embodiment of the semiconductor device according to the present invention. Since the configuration of the diode portion of this embodiment is the same as that of the third embodiment shown in FIG. 5, the components used in FIG. 5 are denoted by the same reference numerals and description thereof is omitted. In this example, an electric field limiting ring (field limiting ring) is formed at the same time as the diode is formed. A plurality of recesses 48 are formed so as to surround a region of the N-type silicon substrate 41 where diodes are to be formed, and a P ⁺ type electric field limiting ring 49 is formed at the bottom of these recesses. The inner surface of the concave portion 48 and the surface of the silicon substrate 41 are covered with a silicon oxide film 50. The recess 48 can be formed at the same time as the recess 42, and the electric field limiting ring 49 can be formed at the same time as the cutoff region 44, thus facilitating the process.

FIG. 7 is a schematic sectional view of a fifth embodiment of the semiconductor device according to the present invention. In this example, a concave portion 82 is formed on one surface of an N-type silicon substrate 81 by anisotropic etching, and a mesa-type anode region 83 is defined between adjacent concave portions. P-type impurities are diffused from the bottom of the recess 82 to form a P ⁺ -type cutoff region 84. Further, an anode electrode film 85 made of aluminum is formed so as to uniformly cover the inner surface of the concave portion 82 and the surface of the anode region 83 formed on the silicon substrate 81. As a result, the cutoff region 84 is directly connected to the anode electrode film 85. Further, an N ⁺ type cathode region is provided on the other surface of the silicon substrate 81.
86 is formed thereon, and a cathode electrode film 87 is formed thereon. In this example, the anode electrode 85 contacts not only the upper surface but also the side surface of the anode region 83 as in the second embodiment shown in FIG.
The current capacity increases.

FIG. 8 is a schematic sectional view showing the structure of a sixth embodiment of the semiconductor device according to the present invention. In this example, a concave portion 10 formed by performing anisotropic etching and isotropic etching on one surface of an N-type silicon substrate 101 is used.
2 and an anode region 103 is defined by the silicon substrate between adjacent recesses. That is, first, a concave portion having a trench structure with a high aspect ratio is formed by performing anisotropic etching, and then a concave portion having a curved cross-sectional structure is formed by performing isotropic etching from the bottom surface of the concave portion. Thereby, a concave portion 102 having a shape as shown in FIG. 11 can be formed. As described above, by performing the two-stage etching of the anisotropic etching and the isotropic etching, a concave portion having a high aspect ratio and a large depth can be formed.

Next, a P-type impurity is diffused from the surface of the curved portion of the concave portion 102 to form a P ⁺ -type cutoff region 104. Further, the whole of one surface of the silicon substrate 101 is covered with the aluminum film 105. An N ⁺ type cathode region 106 is formed on the other surface of the silicon substrate 101, and a cathode electrode film 107 is further formed thereon. In this example, the area of the anode region 103 can be made larger than the area of the channel region formed between the adjacent P ⁺ -type cutoff regions 104, so that a large current can be controlled at high speed and the breakdown voltage can be increased. Will be high.

The present invention is not limited only to the above-described embodiment, and many modifications and variations are possible. For example, in the above-described embodiment, the semiconductor substrate is constituted by a silicon substrate, but a substrate made of a semiconductor material other than silicon can be used. In this case, of course, it is necessary to select an anode electrode film material that forms a Schottky junction with the semiconductor material of the substrate. In addition, FIG.
In the first embodiment, an aluminum film 15 is formed on the inner surface of the concave portion 12 to connect the P ⁺ type cutoff region 14 to the anode electrode film 18, but the concave portion 12 is formed in an island shape, The P ⁺ type cutoff region 14 is formed in a portion other than the island-shaped concave portion.
Is extended to the surface of the silicon substrate 11 to form an anode electrode film.
18 may be connected. In this case, the recess 12
May be formed on the inner surface of the substrate. Further, in the above-described embodiment, a large number of concave portions and a large number of anode regions are formed, but the number of concave portions can be at least two. When two recesses are formed, there is one anode region. Further, in all the embodiments described above, the conductivity type of the semiconductor material can be reversed, and the anode and the cathode can be reversed.

[0022]

According to the above-described semiconductor device of the present invention, a high-speed operation and a low on-voltage can be obtained at the time of the on-operation as in the case of the Schottky junction type diode, and the high withstand voltage can be obtained at the time of the off-state like the PN junction type diode. And small leakage current and large current capacity,
It can be applied to a wide range of uses.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a structure of a conventional Schottky junction diode.

FIG. 2 is a diagrammatic sectional view showing a basic structure of a Schottky junction diode which is a semiconductor device according to the present invention.

FIG. 3 is a schematic sectional view showing the structure of a first embodiment of the semiconductor device according to the present invention.

FIG. 4 is a schematic sectional view showing the structure of a second embodiment of the semiconductor device according to the present invention.

FIG. 5 is a schematic sectional view showing the structure of a third embodiment of the semiconductor device according to the present invention.

FIG. 6 is a schematic sectional view showing the structure of a fourth embodiment of the semiconductor device according to the present invention.

FIG. 7 is a schematic sectional view showing the structure of a fifth embodiment of the semiconductor device according to the present invention.

FIG. 8 is a schematic sectional view showing the structure of a fifth embodiment of the semiconductor device according to the present invention.

[Explanation of symbols]

11 N ^- type silicon substrate, 12 recess, 13 N ^- type anode region, 14 P ⁺ type cut-off region, 15 aluminum film, 16 N ⁺ type cathode region, 17 cathode electrode film, 18 anode electrode plate, 21 N ^- type Silicon substrate, 22 recess, 23 N ^- type anode region, 24
P ⁺ type cutoff region, 26 N ⁺ type cathode region,
27 Cathode film, 29 Anode film, 41 N
Type silicon substrate, 42 recess, 43 anode area,
44 P ⁺ cut-off region, 45 anode electrode film, 46
N ⁺ type cathode region, 47 cathode electrode film, 48 concave portion, 49 electric field limiting ring region, 50 silicon oxide film, 81 N type silicon substrate, 82 concave portion, 83 anode region, 84 P ⁺ type cutoff region, 85 anode electrode film , 86 N ⁺ type cathode region, 87 cathode electrode film, 101 N type silicon substrate, 102 recess, 103
Anode region, 104 P ⁺ type cutoff region, 1
05 Aluminum film, 106 N ⁺ type cathode region,
107 Cathode electrode film

Claims (17)

[Claims] 1. An N-type semiconductor substrate, a plurality of recesses formed on one surface of the semiconductor substrate, and a mesa-type anode region formed by a portion of the semiconductor substrate between the recesses. A P-type cut-off region formed at least at the bottom of the concave portion and expanding a depletion layer during reverse bias to block a current path; and a Schottky junction between the P-type cut-off region and the anode region. A semiconductor device comprising: an anode electrode made of a metal material forming the following; an N-type cathode region formed on the other surface of the semiconductor substrate; and a cathode electrode connected to the cathode region. 2. The semiconductor device according to claim 1, wherein said anode electrode comprises a metal plate forming a Schottky junction with an anode region, and said metal plate is bonded to one surface of a semiconductor substrate. 13. The semiconductor device according to claim 1. 3. The semiconductor device according to claim 1, wherein a film of a metal material forming an ohmic junction with the cutoff region is provided on an inner surface of the recess, and the metal film is brought into contact with the anode electrode on one surface of the semiconductor substrate. 2. The semiconductor device according to claim 1, wherein: 4. An anode electrode comprising a metal film formed on the surface of the anode region, wherein the metal film formed on the inner surface of the recess is brought into contact with the anode electrode on the surface of the anode region. 4. The semiconductor device according to 3. 5. The anode electrode comprises a metal plate joined to a surface of the anode region, and a metal film formed on an inner surface of the recess is brought into contact with a back surface of the metal plate. 4. The semiconductor device according to 3. 6. A film of a metal material that forms a Schottky junction with the anode region but forms an ohmic contact when a reverse voltage is applied with the cutoff region is formed on the surface of the anode region and the concave portion. The semiconductor device according to claim 1, wherein the semiconductor device is formed continuously on an inner surface. 7. The semiconductor device according to claim 7, wherein the cutoff region is formed so as to extend to one surface of the semiconductor substrate along an inner surface of the concave portion, and a portion of the cutoff region exposed on the surface of the semiconductor substrate is formed as the anode. The semiconductor device according to claim 1, wherein the semiconductor device is in contact with an electrode. 8. The semiconductor device according to claim 1, wherein a surface of said recess is covered with an insulating film. 9. The semiconductor device according to claim 8, wherein said anode electrode is constituted by a metal film formed on a surface of said anode region. 10. The semiconductor device according to claim 8, wherein said anode electrode is constituted by a metal plate bonded to a surface of said anode region. 11. A concave portion formed simultaneously with the concave portion on one surface of the semiconductor substrate, and an electric field limiting ring region of the opposite conductivity type formed simultaneously with the cutoff region at least at a bottom of the concave portion. The semiconductor device according to claim 1, wherein: 12. The semiconductor device according to claim 1, wherein the concave portion formed on one surface of the semiconductor substrate comprises a concave portion formed by one isotropic etching. 13. The semiconductor device according to claim 1, wherein the concave portion formed on one surface of the semiconductor substrate comprises a concave portion formed by two isotropic etchings. . 14. The semiconductor device according to claim 1, wherein the concave portion formed on one surface of the semiconductor substrate comprises a concave portion formed by one anisotropic etching. . 15. The semiconductor device according to claim 1, wherein the concave portion formed on one surface of the semiconductor substrate comprises a concave portion formed by anisotropic etching and subsequent isotropic etching. 13. The semiconductor device according to claim 1. 16. The semiconductor device according to claim 1, wherein the conductivity type and the polarity of the electrode are reversed. 17. The semiconductor device according to claim 1, wherein an area of said Schottky junction is larger than a channel cross-sectional area.