JP2015115585A - Schottky diode and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Schottky diode using silicon carbide and silicon and excellent in performance, by minimizing performance degradation of a semiconductor device due to crystal defect occurring at the interface of silicon carbide and silicon, and to provide a manufacturing method therefor.SOLUTION: The surface of an n-type silicon carbide epitaxial film of a silicon epitaxial substrate and the first principal surface of a p-type silicon substrate are irradiated with argon plasma. Following to argon plasma irradiation, the surface of an n-type silicon carbide epitaxial film and the first principal surface of a silicon substrate are press-bonded at room temperature and annealed, thus manufacturing a Schottky diode having a small value of built-in potential and excellent voltage current characteristics.

Description

  The present invention relates to a Schottky diode and a manufacturing method thereof, and more particularly, to a silicon carbide Schottky diode and a manufacturing method thereof.

  Silicon carbide (silicon carbide, SiC) is expected to be a material for various semiconductor devices because its forbidden body width is about 3 times that of silicon, dielectric breakdown electric field is about 10 times, and thermal conductivity is about 3 times larger. ing. Furthermore, since silicon carbide can form a silicon oxide film by thermal oxidation and can control n-type and p-type conductivity by impurity doping, various structures realized in conventional silicon devices can be obtained. It has a feature that is significantly different from other compound semiconductor materials, such that a device having the above can be manufactured.

  For this reason, a semiconductor device having a heterojunction between silicon carbide and silicon using a combination of both silicon carbide and silicon has been proposed, and researched and developed, a heterojunction between silicon carbide and silicon. Various field effect transistors including, for example, high breakdown voltage fast switching pn diodes, Schottky diodes, bipolar transistors, and high breakdown voltage low on-resistance metal-oxide-semiconductor junction field effect transistors (MOSFETs) (FET).

In order to improve the performance of a semiconductor device using silicon carbide, it is important to control the heterojunction interface between silicon carbide and silicon. For this reason, research and development have been conducted on a heterojunction interface between silicon carbide and silicon and a semiconductor device including such a heterojunction.
For example, in Non-Patent Document 1 and Non-Patent Document 2, a semiconductor device having a heterojunction between silicon carbide and silicon is studied.
As recent research, Non-Patent Document 3 studies the characteristics of a Schottky diode having a silicon carbide / silicon interface.

S. Yamagami et al., Material Science Forum Vols. 717-720 (2012) pp1005-1008 A. Perez-Tomas et al., Journal of Applied Physics 014505 (2007) J. Liang et al., 10th Topical Workshop on HeterostructureMicroelectronics TWHM Final Program and Abstracts, 133-134 (2013)

  However, there is a large lattice mismatch between silicon carbide and silicon. For this reason, crystal defects generated at the silicon carbide / silicon interface have caused problems that the breakdown voltage is lowered, and the performance of the semiconductor device is lowered such that the recombination current and the reverse leakage current are increased.

  An object of the present invention is to provide a Schottky diode excellent in performance using silicon carbide and silicon, and a method for manufacturing the same, by suppressing a decrease in performance of a semiconductor device caused by crystal defects generated at a silicon carbide / silicon interface. To do.

  In order to solve the above problems, a method for manufacturing a Schottky diode according to the present invention includes an epitaxial substrate having a first conductivity type silicon carbide epitaxial film formed on a first main surface of a first conductivity type silicon carbide substrate. The surface of the silicon carbide epitaxial film and the surface of the silicon substrate of the second conductivity type opposite in polarity to the first conductivity type are arranged to face each other by a vacuum apparatus, and the silicon carbide epitaxial film of the silicon carbide epitaxial film arranged to face is arranged. The surface and the surface of the silicon substrate are activated by irradiating with plasma, the surface of the silicon carbide epitaxial film disposed opposite to the surface of the silicon substrate is brought into contact, and the epitaxial substrate and the silicon substrate are added. The epitaxial substrate and the silicon substrate are bonded by pressing, and bonded Wherein the annealing serial epitaxial substrate and the silicon substrate.

  The method for manufacturing a Schottky diode according to the present invention includes the step of bonding the epitaxial substrate and the silicon substrate, and forming the first electrode on the second main surface of the silicon carbide substrate, The silicon substrate may be annealed.

  The Schottky diode manufacturing method of the present invention may be characterized in that after the first electrode is formed on the second main surface of the silicon carbide substrate and annealed, the epitaxial substrate and the silicon substrate are joined. .

  A Schottky diode of the present invention includes a first conductivity type silicon carbide substrate, a first conductivity type silicon carbide epitaxial film formed on a first main surface of the silicon carbide substrate, a first main surface, A second conductivity type silicon substrate having a second main surface and having a polarity different from that of the first conductivity type, wherein the first main surface joins the silicon carbide epitaxial film together with the surface of the silicon carbide epitaxial film. After the plasma is irradiated and activated, the first main surface is formed from the silicon substrate pressure-bonded to the surface of the silicon carbide epitaxial film, and is annealed together with the silicon carbide epitaxial film. And a second conductivity type silicon layer.

  The Schottky diode of the present invention is a second conductivity type guard ring ring region provided on the surface of the first conductivity type silicon carbide epitaxial film and at a position corresponding to the second conductivity type silicon layer. It is good also as providing.

  The Schottky diode of the present invention may be characterized in that the measured built-in potential is a value of 1.3 V or less.

  The Schottky diode of the present invention may be characterized in that the measured turn-on voltage value is 0.9 V or less.

  After the surface of the n-type silicon carbide epitaxial film of the silicon epitaxial substrate and the first main surface of the p-type silicon substrate are irradiated and activated by the manufacturing method of the present invention, the n-type silicon carbide epitaxial film is activated. The surface of the silicon substrate and the first main surface of the silicon substrate are pressure-bonded at room temperature and annealed to produce a Schottky diode having a small diffusion potential value and excellent voltage-current characteristics according to the present invention.

It is a figure which shows the Schottky diode which concerns on embodiment of this invention. It is a figure which shows the 1st Example of the manufacturing method of the Schottky diode which concerns on embodiment of this invention. It is a figure which shows the 2nd Example of the manufacturing method of the Schottky diode which concerns on embodiment of this invention. It is a figure which shows the 3rd Example of the manufacturing method of the Schottky diode which concerns on embodiment of this invention. It is a figure which shows the measurement result of the CV characteristic of the Schottky diode which concerns on embodiment of this invention. It is a figure which shows the measurement result of the voltage-current characteristic of the Schottky diode which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a Schottky diode according to an embodiment of the present invention.
A Schottky diode 1 according to an embodiment of the present invention includes a first conductivity type silicon carbide substrate 3 and a first conductivity type silicon carbide formed on a first main surface of the first conductivity type silicon carbide substrate 3. An epitaxial film 5 and a silicon carbide epitaxial film doped with a first conductivity type are formed on the surface of the epitaxial film 5 and have a second conductivity type silicon layer 9 having a polarity different from that of the first conductivity type.
The first electrode 10 is provided on the second main surface of the first-conductivity-type silicon carbide substrate 3 according to the needs of the application in which the Schottky diode 1 according to the embodiment of the present invention is used. A second electrode 11 is provided on the uppermost surface of the mold silicon layer 9.

The second conductivity type silicon layer 9 is formed from the second conductivity type silicon substrate 8. The second conductivity type silicon substrate has a first main surface and a second main surface. In the manufacturing process of the Schottky diode according to the embodiment of the present invention, both the surface of the first conductivity type silicon carbide epitaxial film 5 and the first main surface of the second conductivity type silicon substrate 8 are irradiated with argon plasma. After being activated, pressure bonding is performed. The second conductivity type silicon layer 9 is formed from this pressure bonded silicon substrate 8. In the Schottky diode 1 according to the embodiment of the present invention, desired characteristics of the Schottky diode are realized by annealing the interface between the first conductivity type silicon carbide epitaxial film and the second conductivity type silicon layer. The
Details of the manufacturing method and desired characteristics of the Schottky diode according to the embodiment of the present invention will be described below.

  Hereinafter, embodiments of the present invention will be described by taking as an example a case where the first conductivity type is n-type and the second conductivity type is p-type. When the first conductivity type is n-type and the second conductivity type is p-type, the first electrode is a cathode and the second electrode is an anode.

FIG. 2 is a diagram showing a first example of a method for manufacturing a Schottky diode according to an embodiment of the present invention.
Silicon carbide obtained by growing an n − type silicon carbide epitaxial film 5 having an impurity concentration of 1 × 10 ¹⁴ to 1 × 10 ¹⁷ cm ^{−3 on} the first main surface having the crystal axis <0001> of the n + type silicon carbide substrate 3 Epitaxial substrate 6 is prepared. (Fig. 2 (a))

  The surface of the n-type silicon carbide epitaxial film 5 of the silicon carbide epitaxial substrate 6 and the first main surface of the p + -type silicon substrate 8 are arranged facing each other in a vacuum apparatus. Then, the first main surface of the opposing p + type silicon substrate and the surface of the n − type silicon carbide epitaxial film 5 are irradiated with argon plasma to be activated. Here, the silicon carbide epitaxial substrate 6 and the p + type silicon substrate are both single crystal substrates. (Fig. 2 (b))

  The first main surface of the p + -type silicon substrate 8 and the surface of the n − -type silicon carbide epitaxial film 5 are brought into contact with each other at room temperature, and a force is applied to the p + -type silicon substrate 8 and the silicon carbide epitaxial substrate 6 to form the p + -type silicon substrate 8. The first main surface of the silicon substrate 8 and the surface of the n − type silicon carbide epitaxial film 5 are pressure bonded. (Fig. 2 (c))

  Thereafter, the interface between the p + type silicon substrate 8 and the n − type silicon carbide epitaxial film 4 is annealed. The annealing temperature is 600 to 1000 ° C. In addition, in FIG.2 (e) mentioned later, it can also serve as the annealing at the time of forming the cathode electrode 12 in the 2nd main surface (back surface) of the n + type silicon carbide substrate 3. FIG. (Fig. 2 (d))

A part of the second main surface of the p + type silicon substrate 8 is covered with a resist film by photolithography. Then, the region of the p + type silicon substrate 8 that is not covered with the resist film is removed by etching, so that the surface of the n − type silicon carbide epitaxial film 5 is partially exposed. Thereby, the p-type silicon layer 9 is formed from the p-type silicon substrate 8, and this p-type silicon layer 9 becomes the anode pad 9a.
Next, nickel (Ni) is deposited on the second main surface (back surface) of the n + type silicon carbide substrate 3 to form the cathode electrode 12 and annealed at about 1000 ° C. At this time, the interface between the p-type silicon layer 9 and the n-type silicon carbide epitaxial film 5 may be annealed. (Fig. 2 (e))

  Aluminum (Al) is deposited on the partially exposed surface of the n-type silicon carbide epitaxial film 5 and the surface of the anode pad 9a. Next, a resist mask that covers the surface of the anode pad 9a is formed. Then, the aluminum in the region not covered with the resist mask is removed, and the anode electrode 14 is formed on the surface of the anode pad 9a. (Fig. 2 (f)

FIG. 3 is a diagram showing a second example of the manufacturing method of the Schottky diode according to the embodiment of the present invention.
Silicon carbide in which an n − type silicon carbide epitaxial film 5 having an impurity concentration of 1 × 10 ^{14 to} 3 × 10 ¹⁷ cm ⁻³ is grown on the first main surface having the crystal axis <0001> of the n + type silicon carbide substrate 3. Epitaxial substrate 6 is prepared. (Fig. 3 (a))

  Nickel (Ni) is deposited on the back surface of the silicon carbide epitaxial substrate 6 (second main surface of the silicon carbide substrate) to form the cathode electrode 22 and annealed at about 1000 ° C. (Fig. 3 (b))

  The surface of the n − type silicon carbide epitaxial film 5 of the silicon carbide epitaxial substrate 6 and the first main surface of the p + type silicon substrate 8 are arranged facing each other in a vacuum apparatus. Then, the first main surface of the opposing p + type silicon substrate 8 and the surface of the n− type silicon carbide epitaxial film 5 are irradiated with argon plasma to be activated. Here, the silicon carbide epitaxial substrate 6 and the p + type silicon substrate are both single crystal substrates. (Fig. 3 (c))

  The first main surface of the p + type silicon substrate 8 and the surface of the n− type silicon carbide epitaxial film 5 are brought into contact with each other, and a force is applied to the p + type silicon substrate 8 and the silicon carbide epitaxial substrate 6 to thereby form the p + type silicon substrate. The first main surface 8 and the surface of the n − type silicon carbide epitaxial film 5 are pressure bonded. (Fig. 3 (d))

  A part of the second main surface of the p + type silicon substrate 8 is covered with a resist film by photolithography. Then, the region of the p + type silicon substrate 8 that is not covered with the resist film is removed by etching, so that the surface of the silicon carbide epitaxial film 5 is partially exposed. Thereby, a p + type silicon layer 9 is formed from the p + type silicon substrate 8, and this p + type silicon layer 9 becomes an anode pad 9a. (Fig. 3 (e))

  Next, the silicon carbide epitaxial substrate 6 including the anode pad 9a bonded by bonding is annealed at 600 to 1000 ° C. Thereby, the interface between the anode pad 9a formed from the p + type silicon substrate 8 and the n− type silicon carbide epitaxial film 5 is annealed, and the characteristics of the Schottky diode according to the embodiment of the present invention can be realized. Become. (Fig. 3 (e))

  Aluminum (Al) is deposited on the partially exposed surface of the silicon carbide epitaxial film 5 and the surface of the anode pad 9a. Next, a resist mask that covers the surface of the anode pad is formed. Then, the aluminum in the region not covered with the resist mask is removed, and the anode electrode 24 is formed on the surface of the anode pad 9a. (Fig. 3 (f))

FIG. 4 is a diagram showing a third example of the Schottky diode manufacturing method according to the embodiment of the present invention.
Silicon carbide in which an n − type silicon carbide epitaxial film 5 having an impurity concentration of 1 × 10 ¹⁴ to 1 × 10 ¹⁷ cm ⁻³ is formed on the first main surface having the crystal axis <0001> of the n + type silicon carbide substrate 3. Epitaxial substrate 6 is prepared. (Fig. 4 (a))

  A p-type impurity is selectively ion-implanted into the surface of the n − -type silicon carbide epitaxial film 5 constituting the silicon carbide epitaxial substrate 6 so as to align with the periphery of a region where an anode electrode is to be formed later. A p-type region 18 to be a guard ring layer is formed. (Fig. 4 (b))

  Nickel (Ni) is deposited on the back surface of the silicon carbide epitaxial substrate 6 (second main surface of the silicon carbide substrate 3) to form a cathode electrode 32, which is then annealed at about 1000 ° C. (Fig. 4 (c))

  The surface of the n − type silicon carbide epitaxial film 5 of the silicon carbide epitaxial substrate 6 and the first main surface of the p + type silicon substrate 8 are arranged facing each other in a vacuum apparatus. Then, the first main surface of the opposing p + type silicon substrate 8 and the surface of the n− type silicon carbide epitaxial film 5 are irradiated with argon plasma to be activated. Here, the silicon carbide epitaxial substrate 6 and the p + type silicon substrate are both single crystal substrates. (Fig. 4 (d))

  The first main surface of the p + -type silicon substrate 8 and the surface of the n − -type silicon carbide epitaxial film 5 are brought into contact with each other, and a force is applied to the silicon substrate 8 and the silicon carbide epitaxial substrate 6 to The main surface of 1 and the surface of the n-type silicon carbide epitaxial film 5 are pressure bonded. (Fig. 4 (e))

  A part of the second main surface of the p + type silicon substrate 8 is covered with a resist film by photolithography. Then, the region of the p + type silicon substrate 8 that is not covered with the resist film is removed by etching, so that the surface of the silicon carbide epitaxial film 5 is partially exposed. Thus, the p + type silicon layer 9 is formed from the p + type silicon substrate 8 at a position corresponding to the p type guard ring region 18. This p + type silicon layer 9 becomes the anode pad 9a. (Fig. 4 (f))

  Next, the silicon carbide epitaxial substrate 6 including the anode pad 9a bonded by bonding is annealed at 600 to 1000 ° C. Thereby, the interface between the anode pad 9a formed from the p + type silicon substrate 8 and the n− type silicon carbide epitaxial film 5 is annealed, and the characteristics of the Schottky diode according to the embodiment of the present invention can be realized. Become. (Fig. 4 (f))

  Aluminum (Al) is deposited on the partially exposed surface of the silicon carbide epitaxial film 5 and the surface of the anode pad 9a. Next, a resist mask that covers the surface of the anode pad 9a is formed. Then, the aluminum in the region not covered with the resist mask is removed, and the anode electrode 34 is formed on the surface of the anode pad 9a. (Fig. 4 (g))

  According to the third example of the manufacturing method of the Schottky diode of the embodiment of the present invention, the p-type guard ring region 18 is formed at a position corresponding to the anode pad 9 a formed from the p-type silicon substrate 8. As a result, a Schottky diode excellent in voltage resistance is produced.

  In the embodiment and each example of the present invention, the case where the surface of the n-type silicon carbide epitaxial film of the silicon carbide epitaxial substrate and the first main surface of the p-type silicon substrate are irradiated with argon plasma has been described. Xenon plasma may be irradiated instead of argon plasma.

The measurement results of the Schottky diode according to the embodiment of the present invention will be described below.
The measurement was performed on a Schottky diode according to an embodiment of the present invention and a prototype Schottky diode created in the process of reaching the embodiment of the present invention.

The measured Schottky diode and prototype Schottky diode according to the embodiment of the present invention were both fabricated by bonding and bonding a silicon carbide epitaxial substrate and a silicon substrate. In the silicon carbide epitaxial substrate, an n-type silicon carbide buffer layer having an impurity concentration of 2 × 10 ¹⁸ cm ⁻³ is interposed on the first main surface of an n-type silicon carbide single crystal substrate having an impurity concentration of 1 × 10 ¹⁹ cm ^−3. Thus, an n-type silicon carbide epitaxial film having an impurity concentration of 1 × 10 ¹⁷ cm ⁻³ was formed. A p-type silicon single crystal substrate having an impurity concentration of 2 × 10 ¹⁹ cm ⁻³ was used as the silicon substrate.

In the process of creating the Schottky diode and the prototype Schottky diode according to the embodiment of the present invention, both the surface of the n-type silicon carbide epitaxial film of the silicon epitaxial substrate and the first main surface of the p-type silicon substrate are subjected to argon. After the plasma is irradiated and activated, the first main surface is pressure-bonded at room temperature to the surface of the silicon carbide epitaxial film and the first main surface of the silicon substrate. Schottky diodes and prototype Schottky diodes were prepared. Furthermore, the Schottky diode according to the embodiment of the present invention was annealed after being pressure bonded. On the other hand, the prototype Schottky diode was not annealed after being pressure bonded.
The above-described annealing treatment of the Schottky diode according to the embodiment of the present invention was performed at 1000 ° C. for 1 minute, for example.

FIG. 5 shows measurement results of CV characteristics of the Schottky diode and the prototype Schottky diode according to the embodiment of the present invention. The measurement was performed at room temperature with a CV measurement frequency of 100 kHz.
In the Schottky diode according to the embodiment of the present invention annealed at 1000 ° C. for 1 minute, the value of the diffusion potential Vd obtained by extrapolating the measured value of the CV characteristic is 1.0V.
On the other hand, in a prototype Schottky diode that has not been annealed, the value of the diffusion potential Vd obtained by extrapolating the measured value of the CV characteristic is 1.6V. It can be understood that the value of the diffusion potential is low in the Schottky diode according to the embodiment of the present invention.

FIG. 6 shows voltage-current characteristics of the Schottky diode and the prototype Schottky diode according to the embodiment of the present invention. Compared to a prototype Schottky diode that has not been annealed, in an annealed Schottky diode according to an embodiment of the present invention, the n value is reduced from 1.5 to 1.1 and the turn-on voltage is from 1.6V. Reduced to 0.7V. Here, the turn-on voltage refers to Vf at 100 mA / cm ² . The Schottky diode according to the embodiment of the present invention has improved diode characteristics. Since the reverse leakage current is also reduced, it can be seen that defects at the heterojunction interface are also reduced. Thus, a favorable hetero interface can be formed by the method proposed in the present application.

1: Schottky diode 3: Silicon carbide substrate 5: Silicon carbide epitaxial film 6: Silicon carbide epitaxial substrate 8: Silicon substrate 9: Silicon layer 9a: Anode pad 10: First electrode 11: Second electrode 12, 22, 32: Cathode electrodes 14, 24, 34: Anode electrode 18: Guard ring region

Claims (7)

The surface of the silicon carbide epitaxial film of the epitaxial substrate in which the first conductive type silicon carbide epitaxial film is formed on the first main surface of the first conductive type silicon carbide substrate and the second polarity opposite to the first conductive type. Place the surface of the conductive type silicon substrate opposite to the surface of the vacuum device,
The surface of the silicon carbide epitaxial film disposed opposite to the surface of the silicon substrate and the surface of the silicon substrate are activated by irradiation with plasma,
Contacting the surface of the silicon carbide epitaxial film and the surface of the silicon substrate that are arranged to face each other, and bonding the epitaxial substrate and the silicon substrate by pressurizing the epitaxial substrate and the silicon substrate,
A method for manufacturing a Schottky diode, comprising annealing the bonded epitaxial substrate and silicon substrate.   The bonded epitaxial substrate and the silicon substrate are annealed when the first electrode is formed on the second main surface of the silicon carbide substrate after the epitaxial substrate and the silicon substrate are bonded. A method for manufacturing a Schottky diode according to claim 1.   2. The method for manufacturing a Schottky diode according to claim 1, wherein the first electrode is formed on the second main surface of the silicon carbide substrate, and the epitaxial substrate and the silicon substrate are joined after annealing. A silicon carbide substrate of a first conductivity type;
A silicon carbide epitaxial film of a first conductivity type formed on a first main surface of the silicon carbide substrate;
A silicon substrate of a second conductivity type having a first main surface and a second main surface and having a polarity different from that of the first conductivity type, and bonded to the silicon carbide epitaxial film together with the surface of the silicon carbide epitaxial film After the first main surface is activated by irradiation with plasma, the first main surface is formed from the silicon substrate pressure bonded to the surface of the silicon carbide epitaxial film, and the silicon carbide epitaxial is formed. A Schottky diode comprising a silicon layer of a second conductivity type annealed with a film.   2. A second conductivity type guard ring ring region provided on a surface of the first conductivity type silicon carbide epitaxial film at a position corresponding to the second conductivity type silicon layer. Item 5. A Schottky diode according to Item 4.   6. The Schottky diode according to claim 4, wherein the built-in potential to be measured is a value of 1.3 V or less.   The Schottky diode according to any one of claims 4 to 6, wherein a measured turn-on voltage value is 0.9 V or less.

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