JP3620344B2 - Schottky barrier diode and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a Schottky barrier diode (hereinafter referred to as “SBD”) having a reverse-conducting guard ring layer on the surface of an epitaxial layer.
[0002]
[Prior art]
As is well known, an SBD is a diode that utilizes a potential barrier generated by contact between a metal and a semiconductor, and has an advantage that the forward voltage is lower than that of a PN junction diode, but generally has a low breakdown voltage and a reverse characteristic. Has the disadvantage of being bad.
[0003]
As a means for solving this drawback, an SBD having a structure provided with a guard ring layer has been conventionally used. As shown in FIG. 3, an annular thermal oxide film 5 is formed on the surface of an N ⁻ type epitaxial layer 2 formed on an N ⁺ type silicon substrate 1, and an opening 9 surrounded by the thermal oxide film 6 is formed. A metal layer 7 serving as a Schottky metal is formed in contact with the surface of the epitaxial layer 2 to form a Schottky junction surface 3.
[0004]
Electric field concentration is likely to occur at the periphery of the Schottky junction surface 3, which causes the reverse direction characteristics to deteriorate, such as a decrease in breakdown voltage. For this reason, a P-type guard ring layer 4 is formed in an annular shape in contact with the metal layer 7 around the Schottky junction surface 3, and a depletion layer 8 generated from the PN junction between the guard ring layer 4 and the epitaxial layer 2 at the time of reverse bias. The spread of the pressure prevents a decrease in breakdown voltage.
[0005]
[Problems to be solved by the invention]
In recent years, it has been required to further reduce the forward voltage of the SBD in order to reduce power consumption of portable devices and the like. Although the forward voltage of the SBD can be lowered by reducing the thickness of the epitaxial layer, there is a problem that when the thickness of the epitaxial layer is reduced, the range in which the depletion layer extends becomes narrower and the breakdown voltage decreases. That is, in the conventional SBD, the thickness of the epitaxial layer is, for example, about 4.0 to 6.0 μm, and the thickness of the guard ring layer is, for example, about 1.5 μm. When the thickness is reduced to about 3.0 μm, the forward voltage can be lowered, but the distance from the guard ring layer to the semiconductor substrate is shortened, so that the range in which the depletion layer extends becomes narrow and the withstand voltage decreases.
[0006]
The present invention solves the above problems, and an object of the present invention is to provide an SBD in which the breakdown voltage does not decrease even when the thickness of the epitaxial layer is reduced.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, the SBD according to the present invention has a second conductive type guard ring layer formed in an annular shape from the surface of the epitaxial layer formed on the first conductive type semiconductor substrate. The Schottky barrier diode has a metal layer in contact with the guard ring, and the guard ring layer has a thickness in the range of 0.2 to 0.5 μm. According to the present invention, by forming the guard ring layer as thin as 0.5 μm or less, the range in which the depletion layer can spread is widened, and the breakdown voltage can be increased. The reason why the thickness of the guard ring layer is 0.2 μm or more is to prevent the guard ring layer from being destroyed by silicide formed when the metal layer is formed when the thickness is less than this. Moreover, it is preferable that the thickness of an epitaxial layer is about 2.0-3.0 micrometers. Thus, by forming the epitaxial layer thinner than before, the forward voltage can be lowered and the breakdown voltage can be prevented from lowering.
[0008]
In addition, the SBD manufacturing method according to the present invention includes forming a second conductivity type guard ring layer in an annular shape from the surface of the epitaxial layer formed on the first conductivity type semiconductor substrate, and contacting the epitaxial layer and the guard ring layer. A method of manufacturing a Schottky barrier diode in which a layer is formed, wherein a polysilicon film is formed on a surface of an epitaxial layer, and a second conductivity type impurity is cyclically introduced from the polysilicon film to form a guard ring layer Is. According to the present invention, since the impurity is introduced from the polysilicon film, a thin guard ring layer of about 0.2 to 0.5 μm can be formed.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0010]
FIG. 1 is a cross-sectional view of an SBD according to this embodiment. On the surface of the N ⁻ type epitaxial layer 2 formed on the N ⁺ type silicon substrate 1, a thermal oxide film 5 is formed in a ring shape. A P-type guard ring layer 4 is formed in an annular shape from the surface of the epitaxial layer 2 in the opening 9 surrounded by the thermal oxide film 5. A part of the surface of the guard ring layer 4 is covered with a polysilicon film 6 to protect the outer peripheral edge of the guard ring layer 4. A metal layer 7 serving as a Schottky metal is formed in contact with the epitaxial layer 2 surrounded by the guard ring layer 4 and a part of the guard ring layer 4, thereby forming a Schottky junction surface 3. For the Schottky metal, for example, a metal material selected from Ti, Mo, and Cr is used. In the conventional SBD, the thickness of the epitaxial layer 2 was, for example, about 4.0 to 6.0 μm, but the SBD according to the present invention has a thickness of the epitaxial layer 2 as thin as about 2.0 to 3.0 μm. The forward voltage can be lowered by lowering the series resistance. Further, in the conventional SBD, the thickness of the guard ring layer 4 is about 1.5 μm, for example, but in the SBD according to the present invention, the thickness of the guard ring layer 4 is as thin as about 0.2 to 0.5 μm. Even if the epitaxial layer 2 is formed thin, the range in which the depletion layer 8 can be expanded at the time of reverse bias is not narrowed, and a decrease in breakdown voltage can be prevented. If the thickness of the guard ring layer 4 is 0.2 μm or less, the guard ring layer 4 is destroyed by silicide formed when a metal layer is formed thereon.
[0011]
Hereinafter, the manufacturing method of the SBD according to the present embodiment will be described with reference to FIG. As shown in FIG. 2A, an epitaxial layer having a specific resistance of about 1 to 2 Ωcm and a thickness of about 2.0 to 3.0 μm is formed on a silicon substrate 1 having a specific resistance of about 3 to 5 mΩ and a thickness of about 400 μm. 2 is grown to form a thermal oxide film 5 having an opening 9 on the epitaxial layer 2.
[0012]
Next, as shown in FIG. 2B, a polysilicon film 6 is formed on the thermal oxide film 5 including the opening 9, and a P-type impurity is deposited on the opening 9 from the polysilicon film 6. The guard ring layer 4 is formed by drive diffusion at a temperature of about 1000 ° C. for about 30 minutes. At this time, since impurities are deposited and diffused from the polysilicon film 6, a thin guard ring layer 4 of about 0.2 to 0.5 μm can be formed.
[0013]
Next, as shown in FIG. 2C, the thermal oxide film 5 and the polysilicon film 6 formed inside the center of the surface of the guard ring layer 4 are removed by etching, and the epitaxial layer 2 and the guard ring layer 4 are exposed. Let
[0014]
Thereafter, as shown in FIG. 2 (d), a metal layer 7 that becomes Schottky metal is formed in contact with a part of the epitaxial layer 2 and the guard ring layer 4, and a Schottky junction surface 3 is formed.
[0015]
【The invention's effect】
As described above, according to the present invention, since the guard ring layer is formed by introducing impurities from the polysilicon film, an extremely thin guard ring layer of 0.5 μm or less can be formed. For this reason, the range in which the depletion layer can be expanded during reverse bias can be widened, and the breakdown voltage can be improved.
[Brief description of the drawings]
1 is a cross-sectional view of an SBD according to an embodiment of the present invention. FIG. 2 is a manufacturing process diagram of an SBD according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a conventional SBD.
DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Epitaxial layer 3 Schottky junction surface 4 Guard ring layer 5 Thermal oxide film 6 Polysilicon film 7 Metal layer 8 Depletion layer 9 Opening

Claims (1)

Manufacturing a Schottky barrier diode in which a second conductivity type guard ring layer is formed annularly from the surface of an epitaxial layer formed on a first conductivity type semiconductor substrate, and a metal layer in contact with the epitaxial layer and the guard ring layer is formed. In this method, a polysilicon film is formed on the surface of the epitaxial layer, and impurities of a second conductivity type are introduced from above the polysilicon film so that the thickness of the guard ring layer is 0.2 to 0.5 μm. A method for manufacturing a Schottky barrier diode, comprising: forming a Schottky barrier diode.

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