JP2022087348A - Trench MOS type Schottky diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a trench MOS type Schottky diode with high breakdown voltage and low loss.

SOLUTION: A trench MOS type Schottky diode 1 includes: a first semiconductor layer 10 made of a Ga₂O₃-based single crystal; a second semiconductor layer 11 having a trench 12 opening to a surface 17 and made of the Ga₂O₃-based single crystal; an anode electrode 13 formed on the surface 17; a cathode electrode 14 formed on a surface of the first semiconductor layer 10; an insulating film 15 covering an inner surface of the trench 12 of the second semiconductor layer 11; and a trench MOS gate 16 embedded in the trench 12 of the second semiconductor layer 11 so as to be covered with the insulating film 15 and being in contact with the anode electrode 13. The second semiconductor layer 11 is composed of a lower layer 11b on a side of the first semiconductor layer and an upper layer 11a on a side of the anode electrode 13 having a higher donor concentration than that of the lower layer 11b, and reverse voltage when a leakage current of 1 μA flows is 600 V or more and 1200 V or less.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to a trench MOS type Schottky diode.

Conventionally, a Schottky barrier diode (Schottky diode) using Ga ₂ O ₃ in a semiconductor layer is known (for example, Patent Document 1).

According to Patent Document 1, for example, the withstand voltage of the Schottky diode is 1000 V when the electron carrier concentration and the thickness of the n ^- Ga ₂ O ₃ layer are 9.95 × 10 ¹⁶ cm ^-3 and 3.3 μm, respectively. It is stated that.

Further, a trench MOS type Schottky diode using Si for a semiconductor layer and a trench MOS type Schottky diode using SiC for a semiconductor layer are known (for example, Non-Patent Documents 1 and 2).

In Non-Patent Document 1, when the doping concentration and thickness of the n ^- Si layer are 1 × 10 ¹⁶ cm ^-3 and 9 μm, respectively, the withstand voltage of the trench MOS type Schottky diode using Si for the semiconductor layer is 107 V. It is stated that there is.

From the reverse voltage-reverse current characteristics described in Non-Patent Document 2, SiC is used for the semiconductor layer when the doping concentration and thickness of the n ^- SiC layer are 6 × 10 ¹⁵ cm ^-3 and 4 μm, respectively. It can be read that the withstand voltage of the trench MOS type Schottky diode that was present is about several tens of volts.

Japanese Unexamined Patent Publication No. 2013-102081

T. Shimizu et al., Proceedings of 2001 International Symposium on Power Semiconductor Devices & ICs, Osaka, pp.243-246 (2001). V. Khemka, et al., IEEE ELECTRON DEVICE LETTERS, VOL. 21, NO. 5, MAY 2000, pp.286-288

In Patent Document 1, the withstand voltage of the Schottky diode is defined by the dielectric breakdown electric field strength of Ga ₂ O ₃ . However, in a Schottky diode using a material having a large dielectric breakdown electric current strength such as Ga ₂ O ₃ , when the reverse voltage is increased, the anode electrode and Ga ₂ O are before the Ga ₂ O ₃ layer causes dielectric breakdown. The leakage current between the _three layers becomes extremely large, and the Schottky diode burns out.

Therefore, for Schottky diodes using Ga ₂ O ₃ in the semiconductor layer, it is appropriate to define the reverse voltage when a leak current of a predetermined magnitude (for example, 1 μA) flows as the withstand voltage. The Schottky diode of Patent Document 1 does not have a special structure for suppressing a leak current, and when the carrier concentration of the n ^- Ga ₂ O ₃ layer is 9.95 × 10 ¹⁶ cm ^-3 . The reverse voltage when a leak current of 1 μA flows is estimated to be about 64 V.

An object of the present invention is to provide a trench MOS type Schottky diode having a high withstand voltage and a low loss.

One aspect of the present invention provides the following trench MOS type Schottky diodes [1] to [2] in order to achieve the above object.

[1] A first semiconductor layer made of a β _- type Ga ₂ O3 system single crystal and a layer laminated on the first semiconductor layer, on the surface opposite to the first semiconductor layer. A second semiconductor layer made of a β-type Ga ₂ O ₃ system single crystal having an opening trench, and an anode electrode formed on the surface of the second semiconductor layer opposite to the first semiconductor layer. A cathode electrode formed on a surface of the first semiconductor layer opposite to the second semiconductor layer, an insulating film covering the inner surface of the trench of the second semiconductor layer, and the second. It has a trench MOS gate embedded in the trench of the semiconductor layer so as to be covered with the insulating film and in contact with the anode electrode, and the second semiconductor layer is a lower layer on the side of the first semiconductor layer. A trench MOS type Schottky diode having a donor concentration higher than that of the lower layer and having a reverse voltage of 600 V or more and 1200 V or less when a leak current of 1 μA flows.
[2] The barrier height of the Schottky junction formed between the second semiconductor layer and the anode electrode is 0.7 eV or more, and the donor concentration of the upper layer is 4.5 × 10 ¹⁶ cm ^-3 or more. 2.4 × 10 ¹⁷ cm ^-3 or less, and the mesa-shaped portion of the second semiconductor layer between the adjacent trenches is 1.4 μm depending on the donor concentration of the upper layer of the second semiconductor layer. The trench MOS type Schottky diode according to the above [1], which has the following width. "

According to the present invention, it is possible to provide a trench MOS type Schottky diode having a high withstand voltage and a low loss.

FIG. 1 is a vertical sectional view of a trench MOS type Schottky diode according to the first embodiment. 2 (a) and 2 (b) are top views of the second semiconductor layer showing typical examples of the planar pattern of the trench, respectively. FIG. 3 is a vertical sectional view of a modified example of the trench MOS type Schottky diode according to the first embodiment. FIG. 4 is a vertical sectional view of the trench MOS type Schottky diode according to the second embodiment. FIG. 5 shows a trench MOS type Schottky diode (withstand voltage 1200 V) having a second semiconductor layer having a two-layer structure and a trench MOS type shot as a comparative example having a single semiconductor layer instead of the second semiconductor layer. It is a graph which shows the forward characteristic of a key diode (withstand voltage 1200V). FIG. 6 shows a trench MOS type Schottky diode (withstand voltage 600 V) having a second semiconductor layer having a two-layer structure and a trench MOS type shot as a comparative example having a single semiconductor layer instead of the second semiconductor layer. It is a graph which shows the forward characteristic of a key diode (withstand voltage 600V).

[First Embodiment]
(Structure of trench MOS type Schottky diode)
FIG. 1 is a vertical cross-sectional view of the trench MOS type Schottky diode 1 according to the first embodiment. The trench MOS type Schottky diode 1 is a vertical Schottky diode having a trench MOS region.

The trench MOS type shot key diode 1 is a layer laminated on the first semiconductor layer 10 and the first semiconductor layer 10, and is a trench 12 that opens on a surface 17 opposite to the first semiconductor layer 10. A second semiconductor layer 11 having a semiconductor layer 11, an anode electrode 13 formed on a surface 17 of the second semiconductor layer 11, and a surface of the first semiconductor layer 10 opposite to the second semiconductor layer 11. The cathode electrode 14 was formed, the insulating film 15 covering the inner surface of the trench 12 of the second semiconductor layer 11, and the anode electrode 13 embedded in the trench 12 of the second semiconductor layer 11 so as to be covered with the insulating film 15. Has a trench MOS gate 16 in contact with.

In the trench MOS type Schottky diode 1, the anode electrode 13 seen from the second semiconductor layer 11 is formed by applying a forward voltage (positive potential on the anode electrode 13 side) between the anode electrode 13 and the cathode electrode 14. The energy barrier at the interface between the surface and the second semiconductor layer 11 is lowered, and a current flows from the anode electrode 13 to the cathode electrode 14.

On the other hand, when a reverse voltage (negative potential on the anode electrode 13 side) is applied between the anode electrode 13 and the cathode electrode 14, no current flows due to the Schottky barrier. When a reverse voltage is applied between the anode electrode 13 and the cathode electrode 14, the depletion layer spreads from the interface between the anode electrode 13 and the second semiconductor layer 11 and the interface between the insulating film 15 and the second semiconductor layer 11. ..

Generally, the upper limit of the reverse leakage current of the Schottky diode is 1 μA. In the present embodiment, the reverse voltage when a leak current of 1 μA flows is defined as the withstand voltage.

For example, "Hiroyuki Matsunami, Noboru Otani, Tsunenobu Kimoto, Takashi Nakamura," Semiconductor SiC Technology and Applications, "2nd Edition, Nikkan Kogyo Shimbun, September 30, 2011, p. According to the Schottky interface electric field strength dependence data of the reverse leakage current in the Schottky diode having SiC as the semiconductor layer described in 355 ”, the current density of the reverse leakage current is 0.0001 A / cm ² . The electric field strength immediately below the Schottky electrode is approximately 0.8 MV / cm. Here, 0.0001 A / cm ² is when a current of 1 μA flows through the Schottky electrode having a size of 1 mm × 1 mm. The current density just below the Schottky electrode.

Therefore, even if the dielectric breakdown electric field strength of the semiconductor material itself is several MV / cm, if the electric field strength directly under the shotkey electrode exceeds 0.8 MV / cm, a leak current exceeding 1 μA will flow.

For example, in order to obtain a withstand voltage of 1200 V in a conventional Schottky diode having no special structure for suppressing the electric field strength directly under the Schottky electrode, the electric field strength directly under the Schottky electrode should be 0.8 MV / cm or less. It is necessary to reduce the donor concentration of the semiconductor layer to 10 ¹⁵ cm ^-3 units and make the semiconductor layer very thick. Therefore, the conduction loss becomes very large, and it is difficult to manufacture a Schottky barrier diode having a high withstand voltage and a low loss.

Since the trench MOS type Schottky diode 1 according to the present embodiment has a trench MOS structure, a high withstand voltage can be obtained without increasing the resistance of the semiconductor layer. That is, the trench MOS type Schottky diode 1 is a Schottky diode having a high withstand voltage and a low loss.

A junction barrier Schottky (JBS) diode is known as a high withstand voltage and low loss Schottky diode, but since it is difficult to manufacture the p-type Ga ₂ O ₃ , the Ga ₂ O ₃ is a p-type. Not suitable for JBS diode materials that require regions.

The first semiconductor layer 10 is composed of an n-type Ga ₂ O ₃ system single crystal containing Group IV elements such as Si and Sn as donors. The donor concentration of the first semiconductor layer 10 is, for example, 1.0 × 10 ¹⁸ or more and 1.0 × 10 ²⁰ cm ^-3 or less. The thickness T _s of the first semiconductor layer 10 is, for example, 10 to 600 μm. The first semiconductor layer 10 is, for example, a Ga ₂ O ₃ system single crystal substrate.

Here, the Ga ₂ O ₃ system single crystal means a Ga ₂ O ₃ single crystal or a Ga ₂ O ₃ single crystal to which an element such as Al or In is added. For example, it is a Ga ₂ O ₃ single crystal to which Al and In are added (Ga _x Al _y In _(1-xy) ) ₂ O ₃ (0 <x ≦ 1, 0 ≦ y <1, 0 <x + y). ≦ 1) It may be a single crystal. When Al is added, the bandgap widens, and when In is added, the bandgap narrows. The Ga ₂ O ₃ single crystal described above has, for example, a β-type crystal structure.

The second semiconductor layer 11 is composed of an n-type Ga ₂ O ₃ system single crystal containing Group IV elements such as Si and Sn as donors. The second semiconductor layer 11 is, for example, an epitaxial layer epitaxially grown on the first semiconductor layer 10 which is a Ga ₂ O ₃ system single crystal substrate.

A high-concentration layer containing a high-concentration donor may be formed between the first semiconductor layer 10 and the second semiconductor layer 11. This high donor concentration layer is used, for example, when the second semiconductor layer 11 is epitaxially grown on the first semiconductor layer 10 which is a substrate. At the initial stage of growth of the second semiconductor layer 11, the amount of dopant taken up is unstable and acceptor impurities are diffused from the first semiconductor layer 10 which is a substrate, so that the acceptor impurities are diffused on the first semiconductor layer 10. When the second semiconductor layer 11 is directly grown, the region of the second semiconductor layer 11 near the interface with the first semiconductor layer 10 may have high resistance. To avoid such problems, a high donor concentration layer is used. The concentration of the high donor concentration layer is set, for example, to be higher than that of the second semiconductor layer 11, and more preferably to a concentration higher than that of the first semiconductor layer 10.

The second semiconductor layer 11 is composed of an upper layer 11a on the anode electrode 13 side and a lower layer 11b on the first semiconductor layer 10 side. The upper layer 11a has a higher donor concentration than the lower layer 11b. Further, the donor concentration of the upper layer 11a and the lower layer 11b is lower than the donor concentration of the first semiconductor layer 10.

As the donor concentration of the second semiconductor layer 11 increases, the electric field strength of each part of the trench MOS type Schottky diode 1 increases. Therefore, a large leakage current flows even when a relatively small reverse voltage is applied. That is, the withstand voltage of the trench MOS type Schottky diode 1 decreases.

However, as a result of diligent research, the present inventor has found that the donor concentration of the layer in which the trench 12 is formed in the second semiconductor layer 11 is the second concentration directly under the anode electrode 13 even if it is increased to a specific concentration. It has been found that there is almost no effect on the electric field strength (near the Schottky interface) in the semiconductor layer 11. On the other hand, by increasing the donor concentration of the layer in which the trench 12 is formed in the second semiconductor layer 11, the electric resistance of the second semiconductor layer 11 is lowered and the loss of the trench MOS type Schottky diode 1 is reduced. It will be reduced.

Therefore, the second semiconductor layer 11 is divided into an upper layer 11a and a lower layer 11b, and the donor concentration of the upper layer 11a is made higher than the donor concentration of the lower layer 11b, so that the second semiconductor layer 11 in the second semiconductor layer 11 directly under the anode electrode 13 The loss of the trench MOS type Schottky diode 1 can be reduced while suppressing the electric field strength (near the Schottky interface) to less than 0.8 MV / cm.

When the height of the interface between the upper layer 11a and the lower layer 11b is equal to or higher than the height of the bottom of the trench 12, it is possible to effectively suppress the increase in the electric field strength near the Schottky interface due to the increase in the donor concentration of the upper layer 11a. .. Further, when the height of the interface between the upper layer 11a and the lower layer 11b is equal to or higher than the height of the lowermost portion of the trench MOS gate 16, it is possible to more effectively suppress the increase in the electric field strength in the vicinity of the Schottky interface.

The upper limit of the donor concentration range of the upper layer 11a of the second semiconductor layer 11 that has almost no effect on the withstand voltage of the trench MOS type Schottky diode 1 is the mesa shape of the second semiconductor layer 11 between the adjacent trenches 12. It depends on the width W _m of the part. Therefore, it is preferable to set the width _Wm according to the donor concentration of the upper layer 11a of the second semiconductor layer 11.

In order to keep the maximum electric field strength in the region directly below the anode electrode 13 in the second semiconductor layer 11, the maximum electric field strength in the second semiconductor layer 11, and the maximum electric field strength in the insulating film 15 low, the second It is preferable that the donor concentration of the lower layer 11b of the semiconductor layer 11 of the above is about 6.0 × 10 ¹⁶ cm ^-3 or less. On the other hand, as the donor concentration of the lower layer 11b decreases, the resistance of the second semiconductor layer 11 increases and the forward loss increases. Therefore, for example, in order to obtain a withstand voltage of 1200 V or less, 3.0 × 10 ¹⁶ cm. It is preferably ^-3 or more. Further, in order to obtain a higher pressure resistance, it is preferable to reduce the donor concentration to, for example, about 1.0 × 10 ¹⁶ cm ^-3 .

As the thickness _Te of the second semiconductor layer 11 increases, the maximum electric field strength in the second semiconductor layer 11 and the maximum electric field strength in the insulating film 15 decrease. By setting the thickness _Te of the second semiconductor layer 11 to about 6 μm or more, the maximum electric field strength in the second semiconductor layer 11 and the maximum electric field strength in the insulating film 15 can be effectively reduced. From the viewpoint of reducing the electric field strength and downsizing of the trench MOS type Schottky diode 1, the thickness _Te of the second semiconductor layer 11 is preferably about 5.5 μm or more and 9 μm or less.

The electric field strength of each part of the trench MOS type Schottky diode 1 changes depending on the depth _Dt of the trench 12. In order to keep the maximum electric field strength in the region directly below the anode electrode 13 in the second semiconductor layer 11, the maximum electric field strength in the second semiconductor layer 11, and the maximum electric field strength in the insulating film 15 low, the trench 12 The depth D _t is preferably about 2 μm or more and 6 μm or less, and more preferably about 3 μm or more and 4 μm or less. Further, in the present specification, the width of the trench 12 is defined as _Wt .

As the dielectric constant of the insulating film 15 increases, the maximum electric field strength in the insulating film 15 decreases. Therefore, the insulating film 15 is preferably made of a material having a high dielectric constant. For example, Al ₂ O ₃ (relative permittivity of about 9.3) and HfO ₂ (relative permittivity of about 22) can be used as the material of the insulating film 15, but HfO ₂ having a high dielectric constant can be used. Especially preferable.

Further, as the thickness _Ti of the insulating film 15 increases, the maximum electric field strength in the second semiconductor layer 11 decreases, but the maximum electric field strength in the insulating film 15 and the maximum electric field in the region directly under the anode electrode 13 Increases strength. From the viewpoint of ease of manufacture, the thickness of the insulating film 15 is preferably small, and more preferably 300 nm or less. However, as a matter of course, a thickness such that a direct current hardly flows between the trench MOS gate 16 and the second semiconductor layer 11 is required.

The material of the trench MOS gate 16 is not particularly limited as long as it has conductivity, and for example, polycrystalline Si doped at a high concentration or a metal such as Ni or Au can be used.

As described above, the electric field strength in the trench MOS type Schottky diode 1 is the width of the mesa-shaped portion between two adjacent trenches 12, the depth D _t of the trench 12, the thickness _Ti of the insulating film 15, and the like. However, it is hardly affected by the planar pattern of the trench 12. Therefore, the planar pattern of the trench 12 of the second semiconductor layer 11 is not particularly limited.

2 (a) and 2 (b) are top views of the surface 17 of the second semiconductor layer 11, showing typical examples of the planar pattern of the trench 12, respectively.

The trench 12 shown in FIG. 2A has a linear planar pattern. The trench 12 shown in FIG. 2B has a planar pattern such that the planar pattern of the mesa-shaped portion between two adjacent trenches 12 becomes a dot.

The cross section of the trench MOS type Schottky diode 1 shown in FIG. 1 is a cut surface along the cutting line AA in the trench MOS type Schottky diode 1 shown in FIG. 2 (a), and FIG. 2 (b). In the trench MOS type Schottky diode 1 shown in the above, it corresponds to a cut surface along the cut line BB.

The anode electrode 13 makes Schottky contact with the second semiconductor layer 11. The anode electrode 13 is made of materials such as Pt, Pd, Au, Ni, Ag, Cu, Al, Mo, In, Ti, polycrystalline Si and their oxides, nitrides and alloys. The reverse leakage current at the Schottky interface between the anode electrode 13 and the second semiconductor layer 11 decreases as the height of the barrier at the interface between the anode electrode 13 and the second semiconductor layer 11 (barrier height) increases. On the other hand, when a metal having a high barrier height is used for the anode electrode 13, the rising voltage in the forward direction increases, so that the forward loss increases. Therefore, it is preferable to select a material having a barrier height such that the reverse leakage current is about 1 μA at the maximum. For example, when the reverse withstand voltage is 600 V to 1200 V, by setting the barrier height to about 0.7 eV, the forward loss can be reduced most while keeping the reverse leakage current to about 1 μA. The anode electrode 13 may have a multilayer structure in which different metal films are laminated, for example, Pt / Au, Pt / Al, Pd / Au, Pd / Al, or Pt / Ti / Au and Pd / Ti / Au. ..

The cathode electrode 14 makes ohmic contact with the first semiconductor layer 10. The cathode electrode 14 is made of a metal such as Ti. The cathode electrode 14 may have a multilayer structure in which different metal films are laminated, for example, Ti / Au or Ti / Al. In order to ensure ohmic contact between the cathode electrode 14 and the first semiconductor layer 10, it is preferable that the layer in contact with the first semiconductor layer 10 of the cathode electrode 14 is made of Ti.

FIG. 3 is a vertical sectional view of a modified example of the trench MOS type Schottky diode 1. As shown in FIG. 3, the trench MOS type Schottky diode 1 may have a field plate structure.

In the modification shown in FIG. 3, a dielectric film 18 made of SiO ₂ or the like is provided along the edge of the surface 17 of the second semiconductor layer 11, and the anode electrode 13 is placed on the dielectric film 18. The edge is riding up.

By providing such a field plate structure, it is possible to suppress electric field concentration on the end portion of the anode electrode 13. The dielectric film 18 also functions as a passivation film that suppresses a surface leakage current flowing through the surface 17 of the second semiconductor layer 11. The presence or absence of the field plate structure is determined by each parameter in the structure of the trench MOS type Schottky diode 1 (width W _m of the mesa-shaped portion, depth D _t of the trench 12, thickness _Ti of the insulating film 15, etc.). Does not affect the optimum value of.

[Second Embodiment]
The second embodiment differs from the first embodiment in that an insulator different from the insulator constituting the insulating film 15 is embedded in the bottom of the trench. The same points as in the first embodiment will be omitted or simplified.

(Structure of trench MOS type Schottky diode)
FIG. 4 is a vertical sectional view of the trench MOS type Schottky diode 2 according to the second embodiment.

The second semiconductor layer 11 of the trench MOS type Schottky diode 2 has a trench 21 that opens to the surface 17. An insulator 22 is embedded in the bottom of the trench 21, and the insulating film 15 covers the upper surface of the insulator 22 and the inner side surface of the trench 21. The trench MOS gate 16 is embedded in the trench 21 so as to be covered with the insulating film 15.

For example, after embedding the insulator 22 in the bottom of the trench 21, the upper part of the insulator 22 is cut into a round shape by etching to form the trench 12. Then, the insulating film 15 and the trench MOS gate 16 are formed in the trench 12. The bottom surface of the trench 21 may be flat or may be rounded like the trench 12.

The insulator 22 is made of an insulator having a dielectric constant lower than that of the insulating film 15. Therefore, when a voltage is applied between the anode electrode 13 and the cathode electrode 14, the electric field applied to the insulator 22 is larger than the electric field applied to the insulating film 15.

In the trench MOS type Schottky diode 1 according to the first embodiment, the region where the electric field strength is highest in the insulating film 15 is a region near the bottom of the trench 12. Further, the region having the highest electric field strength in the second semiconductor layer 11 is a region directly below the trench 12.

By providing the insulator 22 according to the second embodiment, the electric field strength in the region near the bottom of the trench 12 in the insulating film 15 and the electric field strength in the region directly below the trench 12 in the second semiconductor layer 11 Can be reduced. That is, the maximum electric field strength in the insulating film 15 and the maximum electric field strength in the second semiconductor layer 11 can be reduced.

As the material of the insulator 22, it is preferable to use a material having a low dielectric constant such as SiO ₂ (relative permittivity is about 4). The thickness T _b of the insulator 22 immediately below the lowermost portion of the insulating film 15 is preferably about 200 nm or more. The insulator 22 has the same planar pattern as the trench 12, typically having a width approximately equal to the width _Wt of the trench 12.

In the trench MOS type Schottky diode 2, when the height of the interface between the upper layer 11a and the lower layer 11b is equal to or higher than the height of the bottom of the trench 21, the electric field strength in the vicinity of the Schottky interface as the donor concentration of the upper layer 11a increases. Can be effectively suppressed. Further, when the height of the interface between the upper layer 11a and the lower layer 11b is equal to or higher than the height of the lowermost portion of the trench MOS gate 16, it is possible to more effectively suppress the increase in the electric field strength in the vicinity of the Schottky interface.

(Effect of embodiment)
According to the first and second embodiments, the semiconductor layer made of Ga ₂ O ₃ in which the trench is formed is divided into an upper layer and a lower layer, and the donor concentration in the upper layer is higher than the donor concentration in the lower layer. It is possible to provide a trench MOS type Schottky diode having a withstand voltage and a low loss.

By simulation, in the structure of the trench MOS type Schottky diode 1 according to the first embodiment, the effect of dividing the second semiconductor layer 11 into an upper layer 11a and a lower layer 11b was investigated.

Below, as an example, the evaluation results when the withstand voltage of the trench MOS type Schottky diode 1 is set to 1200 V and when it is set to 600 V will be described.

(When the withstand voltage is set to 1200V)
When the withstand voltage of the trench MOS type Schottky diode 1 is set to 1200 V, assuming that the barrier height of the Schottky junction formed between the second semiconductor layer 11 and the anode electrode 13 is 0.7 eV, a leak current is generated. In order to suppress this, the electric current strength directly under the anode electrode 13 is required to be 0.4 MV / cm or less.

In order to satisfy this condition, the width _Wm of the mesa-shaped portion of the second semiconductor layer 11 between the adjacent trenches 12 is set according to the donor concentration of the upper layer 11a of the second semiconductor layer 11. For example, when the donor concentration of the upper layer 11a is 4.5 × 10 ¹⁶ cm ^-3 , the width W _m is set to 1.4 μm or less, and when the donor concentration of the upper layer 11a is 6.0 × 10 ¹⁶ cm ^-3 , the width W m is set to 1.4 μm or less. When the width W _m is set to 1.0 μm or less and the donor concentration of the upper layer 11a is 9.0 × 10 ¹⁶ cm ^-3 , the width W _m is set to 0.7 μm or less and the donor concentration of the upper layer 11a is 1. In the case of 2 × 10 ¹⁷ cm ^-3 , set the width W _m to 0.5 μm or less.

Further, the donor concentration and the thickness of the lower layer 11b of the second semiconductor layer 11 at this time may be set to, for example, 3 × 10 ¹⁶ cm ^-3 , 4.0 μm, respectively.

FIG. 5 shows a trench MOS type Schottky diode 1 (hereinafter referred to as Example 1) having the second semiconductor layer 11 having the above-mentioned two-layer structure, and a single-layer semiconductor layer instead of the second semiconductor layer 11. It is a graph which shows the forward direction characteristic of the trench MOS type Schottky diode (hereinafter, referred to as a comparative example 1) as a comparative example which has.

Here, for Example 1, the donor concentration and thickness of the upper layer 11a are 6.0 × 10 ¹⁶ cm ^-3 , 3 μm, respectively, and the donor concentration and thickness of the lower layer 11b are 3.0 × 10 ¹⁶ cm ^-3 , respectively. The width Wt of the trench 12 was set to 4 μm, the width _Wt of the trench 12 was set to 0.5 _μm , and the width Wm of the mesa-shaped portion of the second semiconductor layer 11 was set to 1 μm. Further, in Comparative Example 1, the donor concentration and thickness of the single-layer semiconductor layer instead of the second semiconductor layer 11 were 3.0 × 10 ¹⁶ cm ^-3 , 7 μm, respectively, and the width _Wt of the trench 12 was 1. The width Wm of the mesa-shaped portion of the second semiconductor layer 11 was set to 0 _μm and set to 2 μm. In both Example 1 and Comparative Example 1, the barrier height of the Schottky junction was set to 0.7 eV, the depth _Dt of the trench 12 was set to 3 μm, and the insulating film 15 was set to an HfO ₂ film having a thickness of 50 nm.

FIG. 5 shows that Example 1 has a smaller on-resistance than Comparative Example 1. From this, it was confirmed that the on-resistance was reduced by dividing the second semiconductor layer 11 into the upper layer 11a and the lower layer 11b and making the donor concentration of the upper layer 11a higher than the donor concentration of the lower layer 11b.

(When setting the withstand voltage to 600V)
When the withstand voltage of the trench MOS type Schottky diode 1 is set to 600 V, assuming that the barrier height of the Schottky junction formed between the second semiconductor layer 11 and the anode electrode 13 is 0.7 eV, the withstand voltage is 1200 V. As in the case of designing, the electric field strength directly under the anode electrode 13 is required to be 0.4 MV / cm or less.

In order to satisfy this condition, the width _Wm of the mesa-shaped portion of the second semiconductor layer 11 between the adjacent trenches 12 is set according to the donor concentration of the upper layer 11a of the second semiconductor layer 11. For example, when the donor concentration of the upper layer 11a is 9.0 × 10 ¹⁶ cm ^-3 , the width W _m is set to 1.4 μm or less, and when the donor concentration of the upper layer 11a is 1.2 × 10 ¹⁷ cm ^-3 , the width W m is set to 1.4 μm or less. When the width W _m is set to 1.0 μm or less and the donor concentration of the upper layer 11a is 1.89 × 10 ¹⁷ cm ^-3 , the width W _m is set to 0.67 μm or less and the donor concentration of the upper layer 11a is 2. In the case of 4 × 10 ¹⁷ cm ^-3 , set the width W _m to 0.5 μm or less.

Further, the donor concentration and thickness of the lower layer 11b of the second semiconductor layer 11 at this time may be set to, for example, 3 × 10 ¹⁶ cm ^-3 and 1.5 μm, respectively.

FIG. 6 shows a trench MOS type Schottky diode 1 (hereinafter referred to as Example 2) having the second semiconductor layer 11 having the above-mentioned two-layer structure, and a single-layer semiconductor layer instead of the second semiconductor layer 11. It is a graph which shows the forward direction characteristic of the trench MOS type Schottky diode (hereinafter, referred to as a comparative example 2) as a comparative example which has.

Here, for Example 2, the donor concentration and thickness of the upper layer 11a are 1.2 × 10 ¹⁷ cm ^-3 , 3 μm, respectively, and the donor concentration and thickness of the lower layer 11b are 3.0 × 10 ¹⁶ cm ^-3 , respectively. The width Wt of the trench 12 was set to 1.5 μm, the width _Wt of the trench 12 was set to 0.5 _μm , and the width Wm of the mesa-shaped portion of the second semiconductor layer 11 was set to 1 μm. Further, in Comparative Example 2, the donor concentration and thickness of the single-layer semiconductor layer instead of the second semiconductor layer 11 were 3.0 × 10 ¹⁶ cm ^-3 and 4.5 μm, respectively, and the width _Wt of the trench 12 was set. The width Wm of the mesa-shaped portion of the second semiconductor layer 11 was set to 1.0 _μm and 2 μm. In both Example 2 and Comparative Example 2, the barrier height of the Schottky junction was set to 0.7 eV, the depth _Dt of the trench 12 was set to 3 μm, and the insulating film 15 was set to an HfO ₂ film having a thickness of 50 nm.

FIG. 6 shows that Example 2 has a smaller on-resistance than Comparative Example 2. From this, it was confirmed that the on-resistance was reduced by dividing the second semiconductor layer 11 into the upper layer 11a and the lower layer 11b and making the donor concentration of the upper layer 11a higher than the donor concentration of the lower layer 11b.

Although the embodiments and examples of the present invention have been described above, the present invention is not limited to the above embodiments and examples, and various modifications can be carried out within a range that does not deviate from the gist of the invention.

Further, the embodiments and examples described above do not limit the invention according to the claims. It should also be noted that not all combinations of embodiments and features described in the examples are essential to the means for solving the problems of the invention.

1, 2 ... Trench MOS type Schottky diode, 10 ... First semiconductor layer, 11 ... Second semiconductor layer, 11a ... Upper layer, 11b ... Lower layer, 12, 21 ... Trench, 13 ... Anode electrode, 14 ... Cathode electrode , 15, 22 ... Insulation film, 16 ... Trench MOS gate

Claims (2)

A first semiconductor layer made of β-type Ga ₂ O ₃ series single crystal,
A second layer composed of a β-type Ga ₂ O ₃ system single crystal, which is a layer laminated on the first semiconductor layer and has a plurality of trenches opening on a surface opposite to the first semiconductor layer. Semiconductor layer and
An anode electrode formed on the surface of the second semiconductor layer opposite to the first semiconductor layer,
A cathode electrode formed on a surface of the first semiconductor layer opposite to the second semiconductor layer,
An insulating film covering the inner surface of the trench of the second semiconductor layer and
A trench MOS gate embedded in the trench of the second semiconductor layer so as to be covered with the insulating film and in contact with the anode electrode, and
Have,
The second semiconductor layer is composed of a lower layer on the first semiconductor layer side and an upper layer on the anode electrode side having a higher donor concentration than the lower layer.
The reverse voltage when a leak current of 1 μA flows is 600 V or more and 1200 V or less.
Trench MOS type Schottky diode. The barrier height of the Schottky junction formed between the second semiconductor layer and the anode electrode is 0.7 eV or more.
The donor concentration in the upper layer is 4.5 × 10 ¹⁶ cm ^-3 or more and 2.4 × 10 ¹⁷ cm ^-3 or less.
The mesa-shaped portion of the second semiconductor layer between the adjacent trenches has a width of 1.4 μm or less depending on the donor concentration of the upper layer of the second semiconductor layer.
The trench MOS type Schottky diode according to claim 1.

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