JP2012009756A - Schottky barrier diode and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Schottky barrier diode (SBD) and a manufacturing method thereof capable of improving coverage of a barrier metal layer and, in addition, suppressing inverse direction current (IR) without a risk of concentration of stress onto a conductor embedded in a trench.SOLUTION: In an SBD 11 according to the present invention, a trench 3 is formed on a surface 2a of a silicon substrate 2, and an insulation film 12 whose uppermost face 12a is made an inclined plane 22 is formed on the inner surface of the trench 3. In the trench 3, a conductor 13 is embedded so that its uppermost end part 21a locates below a side wall top face 3a of the trench 3. A barrier metal layer 14 and an electrode metal layer 15 are laminated so as to cover the surface 2a of the silicon substrate 2, the insulation film 12, and the conductor 13.

Description

  The present invention relates to a Schottky barrier diode and a method for manufacturing the same.

Conventionally, a Schottky barrier diode (SBD) using a Schottky barrier generated at this interface by bonding a semiconductor and a metal is known (for example, see Patent Document 1).
This SBD preferably has a small voltage drop when a predetermined voltage is applied in the forward direction and a small leakage current when a predetermined voltage is applied in the reverse direction.

FIG. 4 is a cross-sectional view showing a conventional trench structure type Schottky barrier diode (SBD) 1, in which a trench 3 is formed on a surface (one main surface) 2 a of a silicon substrate (semiconductor substrate) 2. An insulating film 4 made of a silicon oxide film is formed on the inner surface, and a conductor made of polycrystalline silicon is buried in the trench 3 to form a conductor 5. The surface 2a of the silicon substrate 2 and the insulating film 4 The uppermost surface 4 a and the upper surface 5 a of the conductor 5 are flush with each other, a barrier metal layer 6 is formed so as to cover them, and an electrode metal layer 7 is laminated on the barrier metal layer 6.
This SBD 1 has a trench 3 formed on the surface 2 a of the silicon substrate 2, an insulating film 4 is formed on the inner surface of the trench 3, and a conductor made of polycrystalline silicon is placed in the trench 3 surrounded by the insulating film 4. By embedding and flattening the upper surface of the conductor by etching, the flat upper surface 5a of the obtained conductor 5 is flush with the surface 2a, and the barrier metal layer 6 and the electrode are covered so as to cover the flat upper surface 5a. It can be produced by laminating the metal layer 7.

JP 2001-68688 A

By the way, in the conventional SBD 1, the controllability of etching of the conductor 5 made of polycrystalline silicon is not sufficient, and the thickness of the conductor 5 may be uneven, and the upper surface 5 a of the conductor 5 is flattened. There was a problem that it was difficult to do. If the upper surface 5a of the conductor 5 is not flattened, a corner portion is easily formed at the contact portion between the barrier metal layer 6 formed on the conductor 5 and the upper surface 5a of the conductor 5, and as a result, the barrier metal There was a problem that the coverage of the layer 6 was lowered.
Further, if the upper surface 5a of the conductor 5 is not flattened, the shape of the conductor 5 becomes an irregular shape deviating from a desired shape, and stress is generated in the barrier metal layer 6 formed on the conductor 5, This stress is locally concentrated on the conductor 5, and as a result, there is a problem that the reverse current (IR) increases.

  The present invention has been made in order to solve the above-described problems, and can improve the coverage of the barrier metal layer. Further, there is no risk of stress concentration on the conductor embedded in the trench, It is an object of the present invention to provide a Schottky barrier diode capable of suppressing reverse current (IR) and a method for manufacturing the same.

  As a result of intensive studies to solve the above problems, the inventor has formed a trench on one main surface of a semiconductor substrate, an insulating film is formed on the inner surface of the trench, and a conductive layer is formed in the trench. In a Schottky barrier diode in which a body is embedded and a barrier metal layer is formed on the conductor, the upper surface of the conductor is positioned below the upper surface of the sidewall of the trench, and the uppermost surface of the insulating film Is a curved surface or inclined surface connecting the upper surface of the sidewall of the trench and the upper surface of the conductor, it becomes difficult to form a corner in the barrier metal layer formed on the conductor, and thus the coverage of the barrier metal layer is reduced. In addition, it has been found that there is no risk of stress concentration on the conductor embedded in the trench, and reverse current (IR) is suppressed, and the present invention has been completed. .

  That is, in the Schottky barrier diode according to claim 1 of the present invention, a trench is formed on one main surface of a semiconductor substrate, an insulating film is formed on the inner surface of the trench, and a conductor is embedded in the trench. In the Schottky barrier diode in which a barrier metal layer is formed on the conductor, the upper surface of the conductor is located below the upper surface of the trench sidewall, and the uppermost surface of the insulating film is the sidewall of the trench. It is a curved surface or an inclined surface connecting the upper surface and the upper surface of the conductor.

  In this Schottky barrier diode, the upper surface of the conductor is positioned below the upper surface of the sidewall of the trench, and the uppermost surface of the insulating film is a curved surface connecting the upper surface of the sidewall of the trench and the upper surface of the conductor. Alternatively, by forming an inclined surface, the portion from the upper surface of the sidewall of the trench to the upper surface of the conductor becomes a smooth surface. Therefore, in the barrier metal layer formed on the insulating film, It is difficult to form a corner portion in the contact portion, and thus the coverage of the barrier metal layer is improved.

  In addition, by positioning the upper surface of the conductor below the upper surface of the sidewall of the trench, the shape of the conductor is defined by the shape of the trench and becomes substantially the same shape as the inner shape of the trench, and the conductor is deformed. To prevent. Furthermore, by forming a barrier metal layer on the conductor in the trench, when the stress generated by the expansion and contraction of the barrier metal layer is applied to the conductor in the trench, the stress applied to the conductor is reduced by the anchor effect. This stress is prevented from being concentrated locally on the conductor. This reduces the reverse current.

A Schottky barrier diode according to a second aspect is the Schottky barrier diode according to the first aspect, wherein an upper surface of the conductor is a concave surface.
In this Schottky barrier diode, by making the upper surface of the conductor concave, the stress applied to the conductor is further relaxed, and this stress is not concentrated locally on the conductor. Therefore, the reverse current is further reduced.

The Schottky barrier diode according to claim 3 is the Schottky barrier diode according to claim 1 or 2, wherein the height of the conductor is 30% or more and 95% or less of the depth of the trench. And
In this Schottky barrier diode, the height of the conductor is not less than 30% and not more than 95% of the depth of the trench, so that the shape of the conductor is the same as the inner shape of the trench, and the conductor has an irregular shape. Further prevent from becoming.

  5. The method of manufacturing a Schottky barrier diode according to claim 4, wherein a trench is formed on one main surface of the semiconductor substrate, an insulating film is formed on the inner surface of the trench, and a conductor is formed in the trench in which the insulating film is formed. By embedding and selectively removing the upper surface of the conductor and the uppermost surface of the insulating film, the upper surface of the conductor is positioned below the upper surface of the sidewall of the trench, and the uppermost surface of the insulating film is disposed on the sidewall of the trench. The barrier metal layer is formed on the conductor by using a curved surface or an inclined surface connecting the upper surface and the upper surface of the conductor.

In this Schottky barrier diode manufacturing method, the upper surface of the conductor buried in the trench and the uppermost surface of the insulating film formed on the inner surface of the trench are selectively removed, thereby removing the upper surface of the conductor from the trench. The uppermost surface of the insulating film is a curved surface or an inclined surface that connects the upper surface of the sidewall of the trench and the upper surface of the conductor.
This makes it difficult to form corners in the contact portion of the barrier metal layer formed on the insulating film with the upper surface of the sidewall of the trench, and stress due to expansion and contraction of the barrier metal layer is applied to the conductor in the trench. Even when it is applied, this stress is not concentrated locally on the conductor. Therefore, the coverage of the barrier metal layer is improved, and a Schottky barrier diode having a very small reverse current can be easily and inexpensively manufactured.

According to the Schottky barrier diode of the present invention, the upper surface of the conductor is positioned below the upper surface of the sidewall of the trench, and the uppermost surface of the insulating film is connected to the upper surface of the sidewall of the trench and the upper surface of the conductor. Since the curved surface or the inclined surface is formed, a portion from the upper surface of the trench sidewall to the upper surface of the conductor can be smoothed. Therefore, the coverage of the barrier metal layer can be improved.
In addition, it is possible to prevent the conductor from being deformed and to prevent the stress caused by the barrier metal layer from being concentrated locally on the conductor. Therefore, the reverse current (leakage current) can be reduced.
As described above, a Schottky barrier diode with improved barrier metal layer coverage and excellent reverse current (IR) characteristics can be provided.

  According to the Schottky barrier diode of the second aspect, since the upper surface of the conductor is concave, the stress applied to the conductor can be dispersed on the concave surface, and the stress applied to the conductor can be further relaxed. This stress can be prevented from concentrating locally on the conductor. Therefore, the reverse current (leakage current) of the Schottky barrier diode can be further reduced.

  According to the Schottky barrier diode according to claim 3, since the height of the conductor is 30% or more and 95% or less of the depth of the trench, the shape of the conductor is the same as the internal shape of the trench. It is possible to prevent the conductor from being deformed.

  According to the method for manufacturing a Schottky barrier diode according to claim 4, the conductor is selectively removed by selectively removing the upper surface of the conductor buried in the trench and the uppermost surface of the insulating film formed on the inner surface of the trench. The upper surface of the insulating film is positioned below the upper surface of the sidewall of the trench, and the uppermost surface of the insulating film is a curved surface or inclined surface connecting the upper surface of the sidewall of the trench and the upper surface of the conductor. A Schottky barrier diode with improved barrier metal layer coverage and excellent reverse current (IR) characteristics can be easily and inexpensively manufactured without the risk of stresses due to stress being concentrated locally on the conductor. be able to.

It is sectional drawing which shows the trench structure type Schottky barrier diode (SBD) of one Embodiment of this invention. It is sectional drawing which shows the shape of the uppermost part of the insulating film of the trench structure type Schottky barrier diode (SBD) of one Embodiment of this invention. It is process drawing which shows the manufacturing method of trench structure type SBD of one Embodiment of this invention. It is sectional drawing which shows the conventional Schottky barrier diode (SBD) of a trench structure type.

A mode for carrying out the Schottky barrier diode and the manufacturing method thereof of the present invention will be described.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[First Embodiment]
FIG. 1 is a cross-sectional view showing a trench structure type Schottky barrier diode (SBD) according to a first embodiment of the present invention. In FIG. 1, the same components as those in FIG. It is.
In FIG. 1, reference numeral 11 denotes a Schottky barrier diode (SBD), and a trench 3 having a rectangular cross section is formed on a surface (one main surface) 2 a of a silicon substrate (semiconductor substrate) 2. An insulating film 12 made of a silicon oxide film is formed, and a conductor 13 made of polycrystalline silicon is embedded in the trench 3 in which the insulating film 12 is formed. The surface 2a of the silicon substrate 2, the insulating film 12 and A barrier metal layer 14 is formed so as to cover the conductor 13, and an electrode metal layer 15 is laminated on the barrier metal layer 14.

The upper surface of the conductor 13 is a concave surface 21 that is curved from the peripheral edge toward the center, and the uppermost end 21 a of the peripheral edge of the concave 21 is positioned below the side wall upper surface 3 a of the trench 3. Embedded in the trench 3.
In the conductor 13, the upper surface is a concave surface 21 that is curved from the peripheral edge toward the center, so that external stress such as tensile stress caused by the electrode metal layer 15 is passed through the barrier metal layer 14. 13, the external stress is dispersed by the concave surface 21 and relaxed, so that the external stress is not locally concentrated on a part of the conductor 13.

  The height h of the conductor 13, that is, the height h from the bottom surface of the conductor 13 in the trench 3 to the lowest portion of the concave surface 21, is preferably 30% or more and 95% or less of the depth d of the trench 3, More preferably, it is 65% or more and 75% or less.

Here, the reason why the height h of the conductor 13 is 30% or more and 95% or less of the depth d of the trench 3 is that this range is desired because the shape of the conductor 13 is defined by the shape of the trench 3. This is because the desired function can be sufficiently exhibited by maintaining the electrical characteristics of the conductor 13.
When the height h of the conductor 13 exceeds 100% of the depth d of the trench 3, the upper portion of the conductor 13 protrudes upward from the trench 3, and the cross-sectional shape of the conductor 13 depends on the internal shape of the trench 3. It is not preferable because it is not restrained and becomes an irregular shape.

Thus, by setting the height h of the conductor 13 to 30% or more and 95% or less of the depth d of the trench 3, the shape of the conductor 13 becomes the same as the internal shape of the trench 3, and the conductor 3 can be prevented from being deformed.
Further, by preventing the conductor 3 from being deformed, the electrical characteristics as the conductor 13 can be maintained, and therefore the electrical function of the conductor 13 can be sufficiently exhibited. it can.

On the other hand, as shown in FIG. 2, the uppermost surface 12 a of the insulating film 12 is an inclined surface 22 that connects the side wall upper surface 3 a of the trench 3 and the uppermost end portion 21 a of the peripheral surface of the concave surface 21 of the conductor 13. .
The inclination angle θ formed by the inclined surface 22 and the surface 2a of the silicon substrate 2, in other words, the inclination angle θ of the inclined surface 22 with respect to the plane parallel to the surface 2a of the silicon substrate 2 is preferably 30 ° or more and 60 ° or less. More preferably, it is 40 ° or more and 50 ° or less.

Here, the reason why the range of the inclination angle θ is 30 ° or more and 60 ° or less is that the range is a smooth surface from the side wall upper surface 3a of the trench 3 to the concave surface 21 of the conductor 13. It is because it is a range where
When this inclination angle θ is out of the above range, a corner is easily formed at the contact portion between the barrier metal layer 14 and the side wall upper surface 3a of the trench 3, and as a result, the coverage of the barrier metal layer 14 may be reduced. This is not preferable.

As described above, the uppermost surface 12a of the insulating film 12 is the inclined surface 22 that connects the sidewall upper surface 3a of the trench 3 and the uppermost end portion 21a of the concave surface 21 of the conductor 13, so that the sidewall upper surface 3a of the trench 3 is removed. The portion up to the concave surface 21 of the conductor 13 is a smooth surface. Therefore, in the barrier metal layer 14 formed on the insulating film 12, a corner portion is formed at the contact portion with the side wall upper surface 3a of the trench 3. Therefore, the coverage of the barrier metal layer 14 is improved.
Note that the uppermost surface 12a of the insulating film 12 may have a smooth surface from the side wall upper surface 3a of the trench 3 to the concave surface 21 of the conductor 13, or may be a curved surface.

  In this SBD 11, since the barrier metal layer 14 is formed on the conductor 13 made of polycrystalline silicon embedded in the trench 3, an excessive stress due to the expansion and contraction of the barrier metal layer 14 is applied to the conductor 13. Even in this case, the excessive external stress is relaxed by the anchor effect, and the external stress is prevented from being concentrated locally at a specific location of the conductor 13. Thus, by preventing local concentration of external stress in the conductor 13, the reverse current (IR), which is an important characteristic of the SBD 11, becomes extremely small, and the leakage current of the SBD 11 is improved. .

Next, the manufacturing method of SBD11 is demonstrated based on FIG.
First, as shown in FIG. 3A, the surface 2a of the silicon substrate 2 is thermally oxidized to form a silicon oxide film 31 serving as a trench formation mask.
Next, a resist 32 is applied on the silicon oxide film 31, and exposure and development are performed to form an opening 32 a at a position corresponding to the trench of the resist 32.
Next, the silicon oxide film 31 is anisotropically etched using hydrofluoric acid using the resist 32 in which the opening 32a is formed as a mask, and the opening 31a is formed at a position corresponding to the trench of the silicon oxide film 31.

  Next, the resist 32 is removed, and a mixed gas obtained by adding oxygen gas to argon gas is applied to the surface 2a of the silicon substrate 2 using the silicon oxide film 31 with the openings 31a formed as a mask, as shown in FIG. The used anisotropic etching is performed to form a trench 3 having a rectangular cross section on the surface 2 a of the silicon substrate 2. Thereafter, the silicon oxide film 31 is removed using hydrofluoric acid.

Next, as shown in FIG. 3C, the entire surface 2 a of the silicon substrate 2 including the inside of the trench 3 is thermally oxidized to form a silicon oxide film 33 on the surface 2 a of the silicon substrate 2 and the inner surface of the trench 3.
Next, polycrystalline silicon is deposited on the silicon oxide film 33 by thermal CVD. As a result, the conductor 34 made of polycrystalline silicon is deposited on the entire surface of the silicon oxide film 33 including the inside of the trench 3.

  Next, as shown in FIG. 3D, the conductor 34 is etched by anisotropic etching using plasma, and a portion of the conductor 34 except for the inside of the trench 3 is removed. In this process, by adjusting the etching conditions, the silicon oxide film 33 outside the trench 3 is exposed, the upper surface of the conductor 34 in the trench 3 is positioned below the side wall upper surface 3a of the trench 3, and The height h of the conductor 34 is set to 30% to 95% of the depth d of the trench 3.

As a result, the upper surface of the conductor 34 remaining in the trench 3 is the concave surface 21, and the uppermost end 21 a of the concave surface 21 becomes the conductor 13 positioned below the side wall upper surface 3 a of the trench 3.
Thereafter, the silicon oxide film 33 except for the trench 3 is removed using hydrofluoric acid.

Next, as shown in FIG. 3E, anisotropic etching using plasma and isotropic etching using hydrofluoric acid are sequentially performed on the silicon oxide film 33 in the trench 3, and the silicon oxide film 33 is finally etched. The upper surface 33 a is etched to the uppermost end portion 21 a of the concave surface 21 of the conductor 13. As a result, the silicon oxide film 33 remaining in the trench 3 has an insulating film 12 whose uppermost surface is an inclined surface 22 that connects the side wall upper surface 3a of the trench 3 and the uppermost end portion 21a of the concave surface 21 of the conductor 13. It becomes.
As described above, the surface from the surface 2a of the silicon substrate 2 to the concave surface 21 of the conductor 13 via the side wall upper surface 3a of the trench 3 becomes a smooth surface.

Next, as shown in FIG. 3F, a barrier metal such as chromium is deposited by vapor deposition so as to cover the surface 2a of the silicon substrate 2, the insulating film 12, and the conductor 13, thereby forming the barrier metal layer. .
Next, an electrode metal such as aluminum is deposited on the barrier metal layer 14 by vapor deposition to form the electrode metal layer 15.
As described above, the trench structure type SBD 11 of this embodiment can be manufactured.

According to the trench structure type SBD 11 of the present embodiment, the concave surface 21 of the conductor 13 is positioned below the sidewall upper surface 3a of the trench 3, and the uppermost surface 12a of the insulating film 12 is connected to the sidewall upper surface 3a of the trench 3 and the conductor. Since the inclined surface 22 is connected to the 13 concave surfaces 21, a portion from the side wall upper surface 3 a of the trench 3 to the concave surface 22 of the conductor 13 can be made smooth. Therefore, the coverage of the barrier metal layer 14 can be improved.
Further, since the upper surface of the conductor 13 is the concave surface 22, the external stress applied to the conductor 13 can be further relaxed, and the external stress can be prevented from being concentrated locally on a part of the conductor 13. it can. Therefore, the reverse current (leakage current) can be further reduced.

  In addition, the conductor 13 can be prevented from being deformed, and the stress caused by the barrier metal layer 14 can be prevented from being concentrated locally on the conductor 13. Therefore, the reverse current (leakage current) can be reduced.

  According to the method for manufacturing the trench structure type SBD 11 of the present embodiment, the silicon oxide film 33 in the mesa portion is exposed by etching the conductor 34 made of polycrystalline silicon, and the conductor 34 in the trench 3 is exposed. Since the upper surface is positioned below the side wall upper surface 3a of the trench 3, and the uppermost surface 33a of the silicon oxide film 33 in the trench 3 is etched to the vicinity of the upper surface of the conductor 34, the coverage of the barrier metal layer 14 is improved. In addition, the trench structure type SBD 11 having excellent reverse current (IR) characteristics can be easily and inexpensively manufactured.

11 Schottky barrier diode (SBD)
2 Silicon substrate (semiconductor substrate)
2a Surface (one main surface)
3 trench 3a side wall upper surface 12 insulating film 12a uppermost surface 13 conductor 14 barrier metal layer 15 electrode metal layer 21 concave surface 21a uppermost end 22 inclined surface 31 silicon oxide film 31a opening 32 resist 32a opening 33 silicon oxide film 33a uppermost surface 34 conductive body

Claims (4)

A Schottky barrier in which a trench is formed on one main surface of a semiconductor substrate, an insulating film is formed on the inner surface of the trench, a conductor is embedded in the trench, and a barrier metal layer is formed on the conductor In the diode,
The upper surface of the conductor is located below the upper surface of the trench sidewall;
The uppermost surface of the insulating film is a curved surface or an inclined surface connecting the upper surface of the sidewall of the trench and the upper surface of the conductor.   2. The Schottky barrier diode according to claim 1, wherein an upper surface of the conductor is a concave surface.   3. The Schottky barrier diode according to claim 1, wherein a height of the conductor is 30% to 95% of a depth of the trench.   A trench is formed on one main surface of the semiconductor substrate, an insulating film is formed on the inner surface of the trench, a conductor is embedded in the trench in which the insulating film is formed, and an upper surface of the conductor and an uppermost surface of the insulating film By selectively removing the upper surface of the conductor, the upper surface of the conductor is positioned below the upper surface of the trench sidewall, and the uppermost surface of the insulating film is a curved surface or inclined surface connecting the upper surface of the sidewall of the trench and the upper surface of the conductor. A method of manufacturing a Schottky barrier diode, characterized in that a barrier metal layer is formed on the conductor.

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