JP4383250B2 - Schottky barrier diode and manufacturing method thereof - Google Patents

Description

  The present invention relates to a Schottky barrier diode, and more particularly to a low-loss Schottky barrier diode in which a forward voltage Vf and an electric capacity are reduced while suppressing reverse leakage current.

In recent years, Schottky barrier diodes are frequently used as rectifying elements in order to save power and increase the speed of electronic products. A Schottky barrier diode has characteristics such as (a) a forward voltage Vf smaller than that of a general PN junction diode and (b) a smaller electric capacity.
The forward voltage Vf of the Schottky barrier diode can be reduced as the Schottky junction barrier is lowered. However, when the Schottky junction barrier is lowered, a current that flows in the reverse direction when a reverse bias is applied, that is, a so-called leakage current increases. Problem arises.

As one of the inventions for solving such a problem, there is a Schottky barrier diode (hereinafter referred to as a preceding Schottky barrier diode) disclosed in the following patent document.
In the preceding Schottky barrier diode, a metal anode electrode that forms a Schottky junction is disposed on the surface of the first conductivity type semiconductor layer, and an ohmic cathode electrode is provided on the back surface side of the first conductivity type semiconductor layer. A second conductivity type semiconductor layer is formed and embedded in the first conductivity type semiconductor layer at intervals such that a depletion layer continues when a reverse bias is applied, and the second conductivity type semiconductor layer (hereinafter referred to as an embedded layer). ) At the same potential as that of the Schottky bonded anode electrode.

According to the above configuration, since the buried layer embedded in the first conductivity type semiconductor layer has the same potential as the anode electrode, when a reverse bias is applied, the buried layer and the first conductivity type semiconductor layer are A depletion layer formed at the boundary portion spreads, and the spread of the depletion layer serves to suppress leakage current.
Japanese Patent Laid-Open No. 11-330498

However, by embedding the buried layer in the first conductivity type semiconductor layer, the passing area of carriers that move beyond the Schottky junction barrier when a forward voltage is applied is reduced, so this becomes a resistance component, and the preceding Schottky barrier This increases the forward voltage Vf of the diode.
In addition, the capacitance of the depletion layer formed at the boundary between the buried layer having the same potential as the anode electrode and the first conductivity type semiconductor layer having the same potential as the cathode electrode causes a reduction in the speed of the switching operation. .

  An object of the present invention is to provide a Schottky barrier diode in which the forward voltage Vf and the electric capacity are made smaller than those of the above-described preceding Schottky barrier diode while suppressing a reverse leakage current, and a method for manufacturing the Schottky barrier diode.

In order to achieve the above object, a Schottky barrier diode according to the present invention includes a first electrode which is a metal layer on the surface of a first conductivity type semiconductor layer and a second electrode on the back surface of the first conductivity type semiconductor layer. In a Schottky barrier diode having an ohmic junction, a second conductivity type first buried layer having a carrier different from that of the first conductivity type semiconductor layer is embedded in the first conductivity type semiconductor layer without contacting the first electrode. A second conductivity type second buried layer is embedded in the first conductivity type semiconductor layer so as to surround the first buried layer without contacting the first electrode and the first buried layer, The second conductivity type guard ring layer is formed in the first conductivity type semiconductor layer so as to be in contact with the first electrode and the second buried layer and to surround the second buried layer.

In addition, the method for manufacturing a Schottky barrier diode according to the present invention includes Schottky junction of a first electrode, which is a metal layer, on the surface of the first conductivity type semiconductor layer, and ohmic contact of the second electrode on the back surface of the first conductivity type semiconductor layer. In the method for manufacturing a bonded Schottky barrier diode, a first conductivity type guard ring layer having a carrier different from that of the first conductivity type semiconductor layer is partially exposed on the surface of the first conductivity type semiconductor layer. A guard ring layer forming step for forming an annular shape in the semiconductor layer and a second conductive type buried layer embedded in the first conductive type semiconductor layer inside the guard ring layer without contacting the guard ring layer and the buried layer forming step for, viewing contains a first electrode forming step of forming the first electrode in contact with the exposed portion of the guard ring layer, in the buried layer forming step, the buried layer co The second buried layer of the second conductivity type, wherein in contact with an annular guard ring layer is characterized by comprising the step of forming so as to surround the buried layer.

In the Schottky barrier diode having the above configuration, since the buried layer is formed inside the guard ring layer without being in contact with the guard ring layer, the area of the buried layer can be reduced more than the preceding Schottky barrier diode. Can do. That is, since the resistance component is suppressed, the forward voltage Vf is smaller than that of the preceding Schottky barrier diode.
Further, since the buried layer is not in contact with the guard ring layer, the area of the second conductivity type semiconductor layer having the same potential as the first electrode is reduced, so that the electric capacity between the electrodes can be reduced. .

  Furthermore, a depletion layer extends from the boundary portion between the guard ring layer, which has the same potential as the first electrode when a reverse bias is applied, and the first conductive semiconductor layer, and at the boundary portion between the buried layer and the first conductive semiconductor layer. Since the inner side of the guard ring layer is filled with the depletion layer by being in contact with the formed depletion layer, carrier movement due to reverse bias application can be prevented by the depletion layer. That is, the leakage current can be suppressed.

Here, the embedded layer may be composed of a plurality of island-shaped members, and each island-shaped member is long and is arranged at substantially equal intervals in a direction perpendicular to the longitudinal direction. You may be out.
With this configuration, the area of the buried layer can be further reduced.
Further, the first conductive semiconductor layer includes a substrate having a high impurity concentration and an epitaxial layer having a low impurity concentration, and the guard ring layer and the buried layer are second conductive semiconductors having a high impurity concentration. It may be formed inside the epitaxial layer.

With this configuration, the spread width of the depletion layer due to + ions in the epitaxial layer having a low impurity concentration can be increased.
In order to achieve the above object, a Schottky barrier diode according to the present invention includes a first electrode that is a metal layer on the surface of the first conductivity type semiconductor layer and a Schottky junction, and a second electrode on the back surface of the first conductivity type semiconductor layer. In a Schottky barrier diode in which two electrodes are ohmically joined, a first conductivity type buried layer having a carrier different from that of the first conductivity type semiconductor layer is buried in the first conductivity type semiconductor layer without contacting the first electrode. And a second conductivity type second buried layer is buried in the first conductivity type semiconductor layer so as to surround the first buried layer without contacting the first electrode and the first buried layer. The second conductivity type guard ring layer is formed inside the first conductivity type semiconductor layer so as to be in contact with the first electrode and the second buried layer and to surround the second buried layer. Yes.

  In the Schottky barrier diode having such a configuration, the first buried layer is formed inside the guard ring layer and the second buried layer without being in contact with the guard ring layer and the second buried layer. The area of the buried layer can be reduced as compared with the preceding Schottky barrier diode. That is, since the resistance component is suppressed, the forward voltage Vf is smaller than that of the preceding Schottky barrier diode.

In addition, since the first buried layer is not in contact with the guard ring layer, the area of the second conductivity type semiconductor layer having the same potential as the first electrode is reduced, so that the capacitance between the electrodes is reduced. Can do.
Furthermore, a depletion layer extends from the boundary portion between the guard ring layer and the second buried layer, which have the same potential as the first electrode when a reverse bias is applied, and the first conductive semiconductor layer, and the first buried layer and the first conductive layer Since the inner side of the guard ring layer is filled with the depletion layer by making contact with the depletion layer formed at the boundary portion with the type semiconductor layer, the carrier movement due to reverse bias application can be prevented by the depletion layer. That is, the leakage current can be suppressed.

Here, the first embedded layer may be formed of a plurality of island-shaped members, and the second embedded layer may be formed in an annular shape, and each island-shaped member has a long shape. These may be arranged at substantially equal intervals in a direction orthogonal to the longitudinal direction.
With this configuration, the area of the buried layer can be further reduced.
The first conductivity type semiconductor layer includes a substrate having a high impurity concentration and an epitaxial layer having a low impurity concentration. The guard ring layer, the first buried layer, and the second buried layer have impurities. It may be a high-concentration second conductivity type semiconductor, and may be formed inside the epitaxial layer.

  With this configuration, the spread width of the depletion layer due to the + ions of the epitaxial layer having a low impurity concentration can be increased.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In addition, when showing the same part in each drawing, the common number is attached | subjected.
<Structure>
FIG. 1 is a plan view of a Schottky barrier diode according to the present invention as viewed from the anode electrode side, and FIG. 2 is a cross-section when the Schottky barrier diode is cut vertically along the line XX ′ shown in FIG. It is a perspective view.

The Schottky barrier diode 1 shown in FIGS. 1 and 2 includes a cathode electrode 15, an n + substrate 10, an n epitaxial layer 11, a guard ring layer 12, a buried layer 13 a, a buried layer 13 b, and an anode electrode 14.
The n + substrate 10 is n-type Si (silicon) with a high concentration of donor, and the n epitaxial layer 11 is n-type Si (silicon) with a low concentration of donor grown and deposited on the n + substrate 10.

In the n epitaxial layer 11, an annular guard ring layer 12, a buried layer 13a, and a buried layer 13b are formed. An anode electrode 14 made of Ti (titanium) and Ag (silver) is Schottky bonded to the upper surface of the n epitaxial layer 11, and a cathode electrode 15 made of Ag is ohmic bonded to the lower surface of the n + substrate 10. .
The guard ring layer 12 is made of p-type Si with a high acceptor concentration, protects a corner portion where current density tends to be high in the Schottky junction surface between the anode electrode 14 and the n epitaxial layer 11, and suppresses deterioration of reverse characteristics. It is formed in an annular shape for the purpose. Further, since the guard ring layer 12 is in contact with the anode electrode 14, it has the same potential as the anode electrode 14.

The buried layer 13a and the buried layer 13b are made of p-type Si having a high acceptor, and the planar shape thereof is indicated by a dotted line in FIG.
FIG. 3 is a diagram clearly showing the planar shapes of the buried layer 13a and the buried layer 13b drawn by dotted lines in FIG.
As shown in FIG. 3, the buried layer 13a is formed in an annular shape. The carrier moves inside the ring in a direction perpendicular to the layer. As shown in FIG. 2, the buried layer 13 a is not in contact with the anode electrode 14, but is in contact with the guard ring layer 12, and therefore has the same potential as the anode electrode 14.

As shown in FIG. 3, the buried layer 13b is made of a plurality of island-like members and is formed inside the ring of the buried layer 13a. The island-shaped members of the buried layer 13b have a long shape and are arranged at approximately equal intervals in a direction orthogonal to the longitudinal direction.
Further, since the buried layer 13 b is not in contact with the guard ring layer 12 and the anode electrode 14, it is not at the same potential as the anode electrode 14.

The interval between the buried layer 13a and the buried layer 13b is determined according to the spread width of the depletion layer that spreads from the PN junction portion, the breakdown voltage structure of the Schottky barrier diode 1, and the conductance when a reverse bias is applied.
<Operation when reverse bias is applied>
Here, the spread of the depletion layer formed in the PN junction portion of the Schottky barrier diode 1 when the reverse bias is applied will be described in detail.

FIG. 4 is a diagram for explaining a depletion layer 111 of + ions spreading to the n epitaxial layer 11 of the Schottky barrier diode 1 when a reverse bias is applied.
Although not shown in the drawing, a depletion layer of − ions also spreads similarly in the guard ring layer 12 and the buried layer 13a.
As for the depletion layer, the guard ring layer 12 having a high impurity concentration and the n epitaxial layer 11 having a low impurity concentration are more likely to expand than the buried layer 13a due to electrically neutral conditions, and the depletion layer is depleted as the reverse bias increases. Layer 111 will be further expanded.

Eventually, the spread depletion layer 111 continues to the depletion layer formed at the boundary between the buried layer 13b and the n epitaxial layer 11, and as shown in FIG. 5, the n epitaxial layer 11 inside the buried layer 13a It is filled with the depletion layer 111. Thereby, the movement of the carrier at the time of reverse bias application can be prevented. That is, reverse leakage current can be suppressed.
<Contrast with prior art>
Here, as a comparison object of the planar shapes of the buried layer 13a and the buried layer 13b, which is a feature of the Schottky barrier diode 1 according to the present invention, it is disclosed in a patent publication (Japanese Patent Laid-Open No. 11-330498) cited as a conventional technique. The planar shape of the buried layer of the preceding Schottky barrier diode will be described.

FIG. 17 is a diagram showing the planar shape of the buried layer of the preceding Schottky barrier diode.
As shown in the figure, the buried layer 100 of the preceding Schottky barrier diode is not separated and integrated as the buried layer 13a and buried layer 13b of the Schottky barrier diode 1 of the present invention. The entire buried layer 100 has a structure having the same potential as the anode electrode.
On the other hand, in the Schottky barrier diode 1 of the present invention, since the buried layer 13b is formed completely separated from the buried layer 13a and the guard ring layer 12, the layer is more than the buried layer 100 of the preceding Schottky barrier diode. The area can be reduced. That is, since the resistance component is suppressed, the forward voltage Vf can be made smaller than that of the preceding Schottky barrier diode.

Further, since only the guard ring layer 12 and the buried layer 13a in contact with the guard ring layer 12 have the same potential as the anode electrode 14, the PN junction area inside the n epitaxial layer 11 is smaller than that of the preceding Schottky barrier diode. can do. That is, since the depletion layer formed at the PN junction is reduced, the capacitance between the electrodes is reduced.
<Manufacturing method of Schottky barrier diode>
Next, a method for manufacturing the Schottky barrier diode 1 described above will be described.

6 to 12 are partial cross-sectional views of the Schottky barrier diode 1 in each manufacturing process for sequentially explaining the manufacturing processes of the Schottky barrier diode 1.
First, as shown in FIG. 6, a silicon oxide film 20 is formed on the n epitaxial layer 11 by thermal oxidation, a resist 21 is applied thereon, and the resist 21 is patterned by a photolithography technique. Thereafter, the silicon oxide film 20 is etched using hydrofluoric acid to form the opening 22.

After the opening 22 is formed, the resist 21 is removed, and boron ions 23 are implanted as impurities for forming the guard ring layer 12 into the formed opening 22 (FIG. 7).
In order to activate the implanted boron ions 23 and diffuse the boron ions 23 to a depth that functions as the guard ring layer 12, heat treatment is performed at 1150 ° C. for 20 minutes. Thus, the guard ring layer 12 is formed (FIG. 8).

Subsequently, a resist 25 is applied again on the silicon oxide film 20, and the resist 25 is patterned by a photolithography technique (FIG. 9).
Then, boron ions 27 forming the buried layer 13a and the buried layer 13b are implanted (FIG. 10). The boron ion implantation conditions at this time are an acceleration voltage of 1250 keV and a dose of 1 × 10 ^ 17 cm ^ 2.

Thereafter, the resist 25 is removed, and a heat treatment at 900 ° C. is performed for 30 minutes in order to activate the implanted boron ions 27 (FIG. 11).
By forming the buried layer 13a and the buried layer 13b at the same time, the accuracy of the interval between the buried layer 13a and the buried layer 13b can be increased.
Finally, Ti and Ag are vapor-deposited on the n epitaxial layer 11 to form the anode electrode 14, and Ag is vapor-deposited on the back surface of the n + substrate 10 to form the cathode electrode 15 (FIG. 12).
<Supplement>
The Schottky barrier diode and the manufacturing method thereof according to an embodiment of the present invention have been described above, but can be changed as appropriate without departing from the spirit of the present invention. That is,
(1) In the present embodiment, the Schottky barrier diode 1 has been described as having both the buried layer 13a and the buried layer 13b. However, the present invention does not form the buried layer 13a, but embeds the buried layer 13a. It may have only the layer 13b.
(2) In the present embodiment, Si is used as the semiconductor constituting the Schottky barrier diode 1, but a compound semiconductor such as SiC or GaAs may be used. In addition, a p + substrate may be used instead of the n + substrate. In this case, an n-type semiconductor with a high impurity concentration may be used for the guard ring layer and the buried layer.
(3) In this embodiment, Ti and Ag are used as the Schottky bonded anode electrode 14, but one kind of metal may be used. Suitable metals other than Ti and Ag include V (vanadium), Mo (molybdenum), Li (lithium), Pb (lead), Ni (nickel), Al (aluminum), and the like. Further, although Ag is used as the cathode electrode 15 subjected to ohmic bonding, any material may be used as long as it can be ohmic-bonded to the substrate.
(4) The present invention is not limited to the shape of the buried layer 13b shown in FIG. 3 described in the present embodiment. For example, the shape shown in FIGS. Good.

The buried layer 131 shown in FIG. 13 includes five island-like members located at the center and island-like members located at both ends of the island-like members of the buried layer 13b shown in FIG. It is divided, and the remaining two are also divided into two.
The buried layer 132 shown in FIG. 14 includes five island-like members located at the center and island-like members located at both ends of the island-like members of the buried layer 13b shown in FIG. It is divided, and the remaining two remain as they are.

The embedded layer 133 shown in FIG. 15 is composed of two annular members that double surround a single rectangular member located at the center.
The embedded layer 134 shown in FIG. 16 has a spiral shape. As shown in the drawing, the spiral direction may be a right-handed, left-handed, or a combination of a plurality of spirals.
(5) In the Schottky barrier diode manufacturing method according to the present invention, the guard ring layer and the buried layer are formed by the ion implantation method, but may be formed by a solid phase diffusion method.

  The Schottky barrier diode according to the present invention, which realizes a reduction in the forward voltage Vf and the electric capacity while suppressing the reverse leakage current, is a rectifying element component of an electronic product for which power saving and high speed are required. It is very useful.

It is the top view which looked at the Schottky barrier diode 1 which concerns on this invention from the anode electrode side. It is a cross-sectional perspective view at the time of cut | disconnecting the Schottky barrier diode 1 perpendicularly along the X-X 'line | wire shown in FIG. It is a figure showing the planar shape of the embedding layer 13a and the embedding layer 13b. 4 is a plan view for explaining a depletion layer 111 that spreads in an n epitaxial layer 11 when a reverse bias is applied. FIG. It is a top view for demonstrating the depletion layer 111 extended to the whole n epitaxial layer 11 inside the buried layer 13a at the time of reverse bias application. It is a partial cross section figure of Schottky barrier diode 1 in the middle of manufacture. It is a partial cross section figure of Schottky barrier diode 1 in the middle of manufacture. It is a partial cross section figure of Schottky barrier diode 1 in the middle of manufacture. It is a partial cross section figure of Schottky barrier diode 1 in the middle of manufacture. It is a partial cross section figure of Schottky barrier diode 1 in the middle of manufacture. It is a partial cross section figure of Schottky barrier diode 1 in the middle of manufacture. It is a partial cross section figure of Schottky barrier diode 1 in the middle of manufacture. It is a figure showing the planar shape of the embedding layer 131 and the embedding layer 13b of the modification 1. It is a figure showing the planar shape of the embedding layer 132 and the embedding layer 13b of the modification 2. It is a figure showing the planar shape of the embedding layer 133 of the modification 3, and the embedding layer 13b. It is a figure showing the planar shape of the embedding layer 134 and the embedding layer 13b of the modification 4. It is a figure showing the plane shape of the embedding layer 100 of a preceding Schottky barrier diode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Schottky barrier diode 10 n + substrate 11 n epitaxial layer 12 Guard ring layers 13a, 13b, 100, 131-134 Buried layer 14 Anode electrode 15 Cathode electrode

Claims (6)

In the Schottky barrier diode in which the first electrode, which is a metal layer, is Schottky joined to the surface of the first conductivity type semiconductor layer, and the second electrode is ohmic joined to the back surface of the first conductivity type semiconductor layer.
A second conductivity type first buried layer having a carrier different from that of the first conductivity type semiconductor layer is embedded in the first conductivity type semiconductor layer without contacting the first electrode, and the second conductivity type second buried layer is formed. The embedded layer is embedded in the first conductive type semiconductor layer so as to surround the first embedded layer without contacting the first electrode and the first embedded layer, and the second conductive type guard ring layer is formed A Schottky barrier diode formed in the first conductivity type semiconductor layer so as to be in contact with the first electrode and the second buried layer and to surround the second buried layer.   2. The Schottky barrier diode according to claim 1, wherein the first buried layer includes a plurality of island-shaped members, and the second buried layer is formed in an annular shape. Wherein each island-like member is a elongated, Schottky barrier diode according to claim 2, characterized in that aligned at equal intervals in a direction perpendicular to the longitudinal direction.   The first conductivity type semiconductor layer includes a substrate having a high impurity concentration and an epitaxial layer having a low impurity concentration. The guard ring layer, the first buried layer, and the second buried layer have a high impurity concentration. 4. The Schottky barrier diode according to claim 3, wherein the Schottky barrier diode is formed in the epitaxial layer.   5. The Schottky barrier diode according to claim 4, wherein the first conductivity type is n-type and the second conductivity type is p-type. In the manufacturing method of the Schottky barrier diode in which the first electrode which is a metal layer is Schottky joined to the surface of the first conductivity type semiconductor layer, and the second electrode is ohmic joined to the back surface of the first conductivity type semiconductor layer.
A guard ring in which a second conductivity type guard ring layer having a carrier different from that of the first conductivity type semiconductor layer is formed in a ring shape in the first conductivity type semiconductor layer by partially exposing the surface of the first conductivity type semiconductor layer. A layer forming step;
An embedded layer forming step of forming an embedded layer of the second conductivity type in the first conductivity type semiconductor layer inside the guard ring layer without contacting the guard ring layer;
A first electrode forming step of forming the first electrode so as to be in contact with an exposed portion of the guard ring layer, and in the buried layer forming step, the second buried type of the second conductivity type together with the buried layer. And a method of manufacturing a Schottky barrier diode, comprising: forming a layer in contact with the ring of the guard ring layer so as to surround the buried layer.

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