JP5082392B2 - Schottky barrier diode - Google Patents

Description

  The present invention relates to a Schottky barrier diode having a field plate.

Non-Patent Document 1 reports a simulation of a gallium nitride rectifier. According to this simulation result, the withstand voltage of the rectifier using the field plate structure using SiO ₂ , SiN, AlN, MgO, Sc ₂ O ₃ is improved as compared with the rectifier not using the field plate structure. In particular, in the rectifier using the SiO ₂ field plate, the breakdown voltage is most improved.

Non-Patent Document 2 describes a Schottky barrier photodetector using a low-temperature grown GaN cap layer. The Schottky barrier photodetector uses a sapphire substrate, and the Schottky electrode is formed on the low-temperature grown GaN cap layer. Although the leakage current of this Schottky barrier photodetector is small, its time constant is large due to the high resistance of low-temperature grown GaN.
KH Balk et al. J. Vac. Sci. Technol. B 20 (5), Sep / Oct. 2002, 2169 Applied physics letters. Vol.82, 2913

As shown in Non-Patent Document 1, in the simulation, by using SiN and SiO ₂ for the field plate, the electric field from the Schottky electrode is relaxed and the breakdown voltage of the Schottky barrier diode is improved. However, in reality, a Schottky barrier diode using a field plate made of SiN or SiO ₂ has a large leakage current and a small improvement in breakdown voltage. The reason for this is considered that group III nitrides are not compatible with silicon compounds such as SiN and SiO ₂ . Since a leak path is formed at the SiO ₂ / GaN interface or SiN / GaN interface, it is considered that the breakdown voltage of the Schottky barrier diode is lowered.

  As described in Non-Patent Document 2, when low-temperature grown gallium nitride is used as a cap for the gallium nitride drift layer, the leakage current of the Schottky barrier diode is reduced. However, on the contrary, the on-resistance of the Schottky barrier diode becomes extremely high, so that it cannot be used for a Schottky barrier diode with low on-resistance and high withstand voltage.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a Schottky barrier diode having a low on-resistance and a high breakdown voltage and using a group III nitride semiconductor.

  A Schottky barrier diode according to the present invention includes (a) a group III nitride semiconductor drift region having a main surface including a first area and a second area, and (b) an electrode including a Schottky conductive portion and an overlap conductive portion. And (c) a gallium nitride field plate layer that covers the first area of the III-nitride semiconductor drift region and has an opening in the second area, and wherein the Schottky conductive portion includes the gallium nitride field A Schottky junction is formed in the second area of the group III nitride semiconductor drift region in the opening of the plate layer, and the overlap conductive portion is provided on the gallium nitride field plate layer.

  According to this Schottky barrier diode, since the gallium nitride field plate layer covers the first area of the group III nitride semiconductor drift region, the Schottky barrier diode has a field plate insulator different from gallium nitride and a group III nitride semiconductor drift. Does not include the interface with the region. Therefore, this Schottky barrier diode does not include a leakage path due to the interface between the field plate insulator and the group III nitride semiconductor drift region. In addition, since the Schottky conductive portion forms a Schottky junction in the second area of the group III nitride semiconductor drift region, the on-resistance is not increased.

  A Schottky barrier diode according to the present invention includes (a) a group III nitride semiconductor drift region having a main surface including a first area and a second area, and (b) an electrode including a Schottky conductive portion and an overlap conductive portion. And (c) a gallium nitride field plate layer that is provided between the first area of the group III nitride semiconductor drift region and the overlap conductive portion and has an opening in the second area. The Schottky conductive portion forms a Schottky junction with the second area of the group III nitride semiconductor drift region through the opening of the gallium nitride field plate layer.

  According to this Schottky barrier diode, since the gallium nitride field plate layer is provided between the first area of the group III nitride semiconductor drift region and the overlapping conductive part, leakage due to the interface of the group III nitride semiconductor is caused. Path formation can be avoided. Further, since the Schottky conductive portion forms a Schottky junction in the second area of the group III nitride semiconductor drift region, the on-resistance is not increased.

  The Schottky barrier diode according to the present invention may further include an insulating layer. The insulating layer has an opening aligned with the opening of the gallium nitride field plate layer and is provided on the gallium nitride field plate layer. The overlapping conductive portion is provided on the gallium nitride field plate layer and the insulating layer. The insulating layer is made of a material different from the gallium nitride material.

  In this Schottky barrier diode, since an insulating layer is also provided between the gallium nitride field plate layer covering the group III nitride semiconductor drift region and the overlapping conductive portion, the resistance due to the electric conduction at the interface can be increased. Further, since the thickness of the insulating layer for the field plate is added to the thickness of the gallium nitride field plate layer, the withstand voltage can be improved.

  In the Schottky barrier diode according to the present invention, the gallium nitride field plate layer is preferably made of undoped GaN. The gallium nitride field plate layer becomes gallium nitride having a high specific resistance, the leakage current in the field plate portion can be reduced, and the dielectric strength of the Schottky barrier diode can be improved.

In the Schottky barrier diode according to the present invention, the carbon concentration of the gallium nitride field plate layer is preferably greater than 3 × 10 ¹⁷ cm ⁻³ . By containing carbon, the specific resistance of the gallium nitride field plate layer can be increased, the leakage current of the Schottky barrier diode is reduced, and the withstand voltage of the Schottky barrier diode is also improved.

  In the Schottky barrier diode according to the present invention, the gallium nitride field plate layer is preferably made of amorphous GaN. The specific resistance of the gallium nitride field plate layer can be increased, the leakage current is reduced, and the withstand voltage is improved.

  In the Schottky barrier diode according to the present invention, the gallium nitride field plate layer is preferably made of polycrystalline GaN. The specific resistance of the gallium nitride field plate layer can be increased, the leakage current is reduced, and the withstand voltage is improved.

In the Schottky barrier diode according to the present invention, the gallium nitride field plate layer is preferably made of an epitaxial GaN film. By improving the crystallinity of the gallium nitride field plate layer, it is possible to increase the specific resistance and the breakdown voltage, reduce the leakage current, and improve the breakdown voltage.
In the Schottky barrier diode according to the present invention, the gallium nitride field plate layer is preferably made of GaN doped with a p-type acceptor impurity. This is because the gallium nitride field plate layer becomes p-type and forms a pn junction with the n-type drift layer, so that the leakage current in the field plate portion is reduced and the breakdown voltage is improved.

The Schottky barrier diode according to the present invention may further include a group III nitride semiconductor substrate having a dislocation density of less than 1 × 10 ⁸ cm ⁻² . The group III nitride semiconductor drift region is provided on the group III nitride semiconductor substrate. According to this Schottky barrier diode, since a low dislocation group III nitride semiconductor substrate is used, the number of threading dislocations extending from the group III nitride semiconductor substrate to the group III nitride semiconductor drift region is reduced. The current that reaches the back surface of the substrate through interfacial conduction and conduction through threading dislocations can be reduced. Further, the breakdown voltage of the Schottky barrier diode can be improved as the leakage current decreases.

In the Schottky barrier diode according to the present invention, the group III nitride semiconductor substrate preferably includes a gallium nitride region having a dislocation density of less than 1 × 10 ⁸ cm ⁻² . According to this Schottky barrier diode, since the low dislocation gallium nitride substrate is used, the number of threading dislocations extending to the group III nitride semiconductor drift region and the gallium nitride semiconductor substrate is reduced. The leakage current of conduction due to interfacial conduction and threading dislocation can be reduced. Moreover, since it is homoepitaxial growth, there is almost no warpage of the wafer for the group III nitride semiconductor substrate.

  In the Schottky barrier diode according to the present invention, the group III nitride semiconductor substrate may be made of aluminum nitride. According to this Schottky barrier diode, the aluminum nitride substrate has high thermal conductivity, which is advantageous for power devices.

  In the Schottky barrier diode according to the present invention, the group III nitride semiconductor substrate may be made of AlGaN. According to this Schottky barrier diode, since the AlGaN substrate is used, the warpage of the wafer can be reduced as compared with a substrate made of a material different from the gallium nitride material (for example, aluminum nitride), and higher than that of the gallium nitride substrate. It has thermal conductivity.

  In the Schottky barrier diode according to the present invention, the group III nitride semiconductor drift region is preferably made of gallium nitride. According to this Schottky barrier diode, since gallium nitride has a relatively large band gap and good controllability of electrical conductivity, both high breakdown voltage and low on-resistance can be achieved.

  In the Schottky barrier diode according to the present invention, the group III nitride semiconductor drift region is preferably made of aluminum nitride. According to this Schottky barrier diode, since aluminum nitride has a large band gap, it has a high dielectric breakdown electric field, which is suitable for a high breakdown voltage.

  In the Schottky barrier diode according to the present invention, the group III nitride semiconductor drift region is preferably made of AlGaN. According to this Schottky barrier diode, AlGaN has a relatively large band gap and a relatively good controllability of electrical conductivity, so that both high breakdown voltage and low on-resistance can be achieved.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to the present invention, a Schottky barrier diode having a low on-resistance and a high breakdown voltage and using a group III nitride semiconductor is provided.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, embodiments of the Schottky barrier diode of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

  FIG. 1 is a drawing showing an example of the structure of a Schottky barrier diode according to the present embodiment. The Schottky barrier diode 11 includes a group III nitride semiconductor drift region 13, a Schottky electrode 15, and a gallium nitride field plate layer 17. Group III nitride semiconductor drift region 13 has a main surface 13a, and main surface 13a includes a first area 13b and a second area 13c. The Schottky electrode 15 includes a Schottky conductive portion 15a and an overlap conductive portion 15b. The gallium nitride field plate layer 17 is provided between the first area 13b of the group III nitride semiconductor drift region 13 and the overlapping conductive portion 15b. The gallium nitride field plate layer 17 has an opening 19 in the second area 13c. The Schottky conductive portion 15 a forms a Schottky junction 21 in the second area 13 c of the group III nitride semiconductor drift region 13 in the opening 19. The overlapping conductive portion 15 b is provided on the gallium nitride field plate layer 17.

According to the Schottky barrier diode 11, the gallium nitride field plate layer 17 is provided between the first area 13b of the group III nitride semiconductor drift region 13 and the overlapping conductive portion 15b. It is possible to avoid formation of a leakage path due to an interface between an insulator made of a different material (for example, a silicon inorganic compound, specifically, SiO _x , SiN, SiON, etc.) and a group III nitride semiconductor. In addition, since the Schottky conductive portion 15a forms a Schottky junction in the second area 13c of the group III nitride semiconductor drift region 13, the on-resistance is not increased.

  The gallium nitride field plate layer 17 covers the first area 13 b of the group III nitride semiconductor drift region 13. According to this Schottky barrier diode, an interface between the field plate insulator different from gallium nitride and the group III nitride semiconductor drift region 13 is not formed. Therefore, the Schottky barrier diode 11 does not include a leak path due to this interface. In the vicinity of the Schottky junction 21, the interface between the drift region 13 and the insulator is not formed, but the interface 23 between the drift region 13 and the field plate layer 17 is formed.

  Further, since the Schottky conductive portion 15a forms the Schottky junction 21 in the second area 13c of the group III nitride semiconductor drift region 13, the on-resistance is not increased. For example, the thickness of the gallium nitride field plate layer 17 is preferably about 0.1 micrometers or more, for example, in order to obtain a good interface and field plate effect.

  On the other hand, the interface 23 between the group III nitride semiconductor drift region 13 and the field plate layer 17 contributes to interface conduction as compared with the interface between the field plate insulator different from gallium nitride and the group III nitride semiconductor drift region 13. Since there are few dangling bonds etc., the electrical conduction of the interface 23 can be made small.

  In the Schottky barrier diode 11, the gallium nitride field plate layer 17 is preferably made of undoped GaN. The interface 23 is formed of the group III nitride semiconductor drift region 13 and the undoped GaN field plate layer 17. The gallium nitride field plate layer 17 is made of high resistivity gallium nitride.

The carbon concentration of the gallium nitride field plate layer 17 is preferably greater than 3 × 10 ¹⁷ cm ⁻³ . The interface 23 is formed by the group III nitride semiconductor drift region 13 and the carbon-containing GaN field plate layer 17. Inclusion of carbon increases the specific resistance of gallium nitride and also improves the withstand voltage of the Schottky barrier diode 11.

  The gallium nitride field plate layer 17 is preferably made of amorphous GaN. The interface 23 is formed of the group III nitride semiconductor drift region 13 and the amorphous GaN field plate layer 17. By using amorphous, a high resistivity gallium nitride field plate layer can be easily obtained. Amorphous GaN is formed, for example, by growing gallium nitride at a low temperature (for example, 550 degrees Celsius) in a metal organic vapor phase growth furnace.

  The gallium nitride field plate layer 17 is preferably made of polycrystalline GaN. The interface 23 is formed of the group III nitride semiconductor drift region 13 and the polycrystalline GaN field plate layer 17. By using polycrystal, a gallium nitride field plate layer having a high specific resistance can be easily obtained. Polycrystalline GaN is formed, for example, by growing gallium nitride at a low temperature (for example, about 700 degrees Celsius) in a metal organic chemical vapor deposition reactor.

  The gallium nitride field plate layer 17 is preferably made of an epitaxial GaN film. This is because the breakdown voltage can be increased by improving the crystallinity of the gallium nitride field plate layer. The interface 23 is formed of the group III nitride semiconductor drift region 13 and the epitaxial GaN field plate layer 17. Epitaxial GaN is formed under normal crystal growth conditions, for example, in a metal organic vapor phase growth furnace. In a preferred embodiment, the group III nitride semiconductor drift region 13 is preferably made of an n-type semiconductor that can provide high carrier mobility. The gallium nitride field plate layer 17 is preferably made of p-type GaN having a majority carrier different from the majority carrier of the group III nitride semiconductor drift region 13. The interface 23 is formed of a group III nitride semiconductor drift region 13 exhibiting n-type conductivity and a p-GaN field plate layer exhibiting p-type conductivity. Since the interface 23 is a pn junction, the leakage current in the field plate portion can be greatly reduced as compared with the Schottky junction portion, and the breakdown voltage is improved.

The Schottky barrier diode 11 can include a group III nitride semiconductor substrate 25. The group III nitride semiconductor substrate 25 has a dislocation density of, for example, less than 1 × 10 ⁸ cm ⁻² . Group III nitride semiconductor drift region 13 is provided on main surface 25 a of group III nitride semiconductor substrate 25. An ohmic electrode 27 is provided on the back surface 25 b of the group III nitride semiconductor substrate 25. According to the Schottky barrier diode 11, since the low dislocation group III nitride semiconductor substrate 25 is used, the number of threading dislocations extending from the group III nitride semiconductor substrate 25 to the group III nitride semiconductor drift region 13 is reduced. The current reaching the back surface of the substrate 25 can be reduced through interfacial conduction and conduction through threading dislocations. In addition, this contributes to higher breakdown voltage of the Schottky barrier diode. If necessary, another group III nitride semiconductor layer such as a GaN buffer layer may be included between the group III nitride semiconductor substrate 25 and the group III nitride semiconductor drift region 13.

The group III nitride semiconductor substrate 25 can be a gallium nitride substrate. The gallium nitride substrate preferably includes a low dislocation gallium nitride region having a dislocation density of less than 1 × 10 ⁸ cm ⁻² . The low dislocation gallium nitride region preferably includes a gallium nitride region having a dislocation density of less than 1 × 10 ⁶ cm ⁻² . Since a low dislocation gallium nitride substrate is used, the number of threading dislocations extending to the group III nitride semiconductor drift region 13 and the gallium nitride semiconductor substrate is reduced. The current reaching the back surface 25b of the substrate 25 can be reduced through interfacial conduction and conduction through threading dislocations. In addition, since the epitaxial growth is homoepitaxial, the wafer used for manufacturing the Schottky barrier diode hardly warps.

The group III nitride semiconductor substrate 25 can be made of aluminum nitride. The aluminum nitride substrate preferably includes an aluminum nitride region having a dislocation density of less than 1 × 10 ⁸ cm ⁻² . Since a low dislocation substrate is used, the crystallinity of the group III nitride semiconductor drift region 13 is improved. For this reason, the number of threading dislocations extending to the low dislocation group III nitride semiconductor drift region 13 is reduced. The current that reaches the back surface 25b of the substrate 25 through interfacial conduction and conduction through threading dislocations can be reduced. Aluminum nitride has high thermal conductivity and is advantageous for power devices.

The group III nitride semiconductor substrate 25 can be made of AlGaN. The AlGaN substrate preferably includes an AlGaN region having a dislocation density of less than 1 × 10 ⁸ cm ⁻² . Since a low dislocation substrate is used, the crystallinity of the group III nitride semiconductor drift region 13 is improved. For this reason, the number of threading dislocations extending to the low dislocation group III nitride semiconductor drift region 13 is reduced. The current reaching the back surface 25b of the substrate 25 can be reduced through interfacial conduction and conduction through threading dislocations. In addition, AlGaN can reduce the warpage of the wafer as compared with aluminum nitride, and has a higher thermal conductivity than that of gallium nitride.

  In the Schottky barrier diode 11, the group III nitride semiconductor drift region 13 is preferably made of gallium nitride. According to this gallium nitride drift region, good electrical conductivity can be controlled, and both low on-resistance and high breakdown voltage can be achieved. In a preferred embodiment, the group III nitride semiconductor drift region 13 and the group III nitride semiconductor substrate 25 are preferably made of gallium nitride. The junction between the gallium nitride field plate layer 17 and the gallium nitride drift region is a homojunction, and electrical conduction at this interface is small. The group III nitride semiconductor drift region 13 is preferably made of aluminum nitride. Interfacial conduction between the gallium nitride field plate layer 17 and the aluminum nitride drift region is small. According to this aluminum nitride drift region, since aluminum nitride has a high dielectric breakdown electric field, it is advantageous for increasing the breakdown voltage. Furthermore, in the Schottky barrier diode according to the present invention, the group III nitride semiconductor drift region is preferably made of AlGaN. Interfacial conduction between the gallium nitride field plate layer 17 and the AlGaN drift region is small. According to this AlGaN drift region, a dielectric breakdown electric field can be increased by a relatively large band gap, and good electrical conductivity can be controlled.

  FIG. 2 is a drawing showing another example of the structure of the Schottky barrier diode according to the present embodiment. The Schottky barrier diode 11 a includes a group III nitride semiconductor drift region 13, a Schottky electrode 15, a gallium nitride field plate layer 17, and can further include an insulating layer 31. The insulating layer 31 has an opening 33 aligned with the opening 19 of the gallium nitride field plate layer 17. The insulating layer 31 is provided on the gallium nitride field plate layer 17. Overlap conductive portion 17 b is provided on gallium nitride field plate layer 17 and insulating layer 31.

  In this Schottky barrier diode 11a, since the insulating layer 31 is also provided between the gallium nitride field plate layer 17 covering the group III nitride semiconductor drift region 13 and the overlapping conductive portion 15b, the resistance caused by the electric conduction at the interface is reduced. Can be big. Moreover, since the thickness of the insulating layer 31 for the field plate is added to the thickness of the gallium nitride field plate layer 17, the withstand voltage can be improved. In the preferred embodiment, the resistivity of the material of the insulating layer 31 is greater than the resistivity of gallium nitride for the field plate layer 17.

As a material of the insulating layer 31, the insulating layer 31 is made of a material different from the gallium nitride material. As a material of the insulating layer 31, an insulating silicon inorganic compound (specifically, SiO _x , SiN, SiON), Al ₂ O ₃ or the like can be used. These materials are deposited by, for example, chemical vapor deposition or plasma CVD (p-CVD). In order to obtain a good interface and field plate effect, the thickness of the insulating layer 31 is preferably about 0.2 micrometers or more, for example. In order to prevent the tunnel effect and the like, the thickness of the gallium nitride field plate layer 17 is preferably about 0.01 micrometers or more, for example. In addition, within this thickness range, a good interface and field plate effect can be obtained.

Next, the main steps of the method for manufacturing a Schottky barrier diode will be described with reference to FIG. A gallium nitride substrate 41 is prepared. The dislocation density of the gallium nitride substrate 41 is, for example, less than 1 × 10 ⁶ cm ⁻² . As shown in FIG. 3A, a gallium nitride drift layer 43 is grown on the main surface 41 a of the gallium nitride substrate 41. This growth is performed using, for example, a metal organic chemical vapor deposition furnace. For the gallium nitride drift layer 43, for example, undoped GaN or GaN to which an n-type dopant is added is used. The gallium nitride drift layer 43 exhibits n conductivity. In one example, the gallium nitride drift layer 43 has 1 × 10 ¹⁶ cm ⁻³ and its film thickness is about 10 micrometers.

  As shown in FIG. 3B, the gallium nitride field plate layer 45 is grown on the main surface 43 a of the gallium nitride drift layer 43. By this growth, a semiconductor interface 44 between the gallium nitride drift layer 43 and the gallium nitride field plate layer 45 is obtained. In this example, since the interface 44 is homozygous, a very good interface can be obtained. If necessary, an insulating film 47 is grown on the gallium nitride field plate layer 45 as shown in FIG.

  As shown in FIG. 3D, a Schottky electrode 49 and an ohmic electrode 51 are formed. After the openings are formed in the gallium nitride field plate layer 45 and the insulating film 47, the Schottky electrode 49 is formed. The ohmic electrode 51 is formed on the back surface 41 b of the substrate 41. The Schottky electrode 49 includes a Schottky conductive portion 49a and an overlap conductive portion 49b. The Schottky conductive portion 49a forms a Schottky junction with the gallium nitride drift layer 43 in the opening. The overlap conductive part 49 b is provided on the insulating film 47. Between the edge 49c of the overlapping conductive portion 49b and the gallium nitride drift layer 43, a gallium nitride field plate layer 45 (an insulating film 47 if necessary) is provided.

  Next, some experimental examples of the Schottky barrier diode (SBD) will be described.

(Experiment 1) SBD without field plate structure
A low dislocation GaN substrate having a dislocation density of 1 × 10 ⁶ cm ⁻² or less and GaN substrates S _A and S _B having a dislocation density of 1 × 10 ⁸ cm ⁻² are prepared. After growing an n ⁺ GaN layer (2 micrometers) with an Si concentration of 2 × 10 ¹⁸ cm ⁻³ on these substrates S _A and S _B , an n-type GaN drift layer with an Si concentration of 1 × 10 ¹⁶ cm ^−3. Grow (10 micrometers). Thereby, epitaxial substrates A and B are formed.

Next, ohmic electrodes are formed on the back surfaces of the epitaxial substrates A and B. A gold (Au) electrode having a diameter of 200 micrometers is formed on the surface of the n-type GaN drift layer by an evaporation method using resistance heating. When the characteristics of these SBDs are measured,
SBD-A1 using substrate A1: withstand voltage of 800 volts, on-resistance of 4 mΩcm ²
SBD-B1 using substrate B: Withstand voltage of 340 volts, on-resistance of 4 mΩcm ²
It is.

(Experimental Example 2) Silicon oxide field plate structure A silicon oxide film is formed on epitaxial substrates A and B. After a 1 micrometer SiN film is grown using plasma CVD, the SiN film is selectively etched using buffered hydrofluoric acid BHF (110) to form an opening with a diameter of 200 micrometers in the SiN film. Form. Thereafter, a gold (Au) electrode of 220 micrometers is formed by the same method as in Experimental Example 1. The gold electrode has a Schottky junction having a diameter of 200 μm and a strip-shaped overlapping conductor having a width of 10 μm. When the characteristics of these SBDs are measured,
SBD-A2 using substrate A: withstand voltage of 310 volts, on-resistance of 4 mΩcm ²
SBD-B2 using substrate B: withstand voltage of 260 volts, on-resistance of 4 mΩcm ²
It is.

(Experimental example 3) Silicon nitride field plate structure A silicon nitride film is formed on epitaxial substrates A and B. After a 1 micrometer SiN film is grown using plasma CVD, the SiN film is selectively etched using buffered hydrofluoric acid BHF (110) to form an opening with a diameter of 200 micrometers in the SiN film. Form. Thereafter, a gold (Au) electrode of 220 micrometers is formed by the same method as in Experimental Example 1. The gold electrode has a Schottky junction having a diameter of 200 μm and a strip-shaped overlapping conductor having a width of 10 μm. When the characteristics of these SBDs are measured,
SBD-A3 using substrate A: 420 volt withstand voltage, 4 mΩcm ² on-resistance
SBD-B3 using substrate B: withstand voltage of 280 volts, on-resistance of 4 mΩcm ²
It is.

(Experimental example 4) A silicon nitride film is formed on the epitaxial substrates A and B of the undoped GaN field plate structure. After growing a 1-micrometer SiN film using plasma CVD, the SiN film is selectively etched using buffered hydrofluoric acid BHF (110) to form an area for forming a feel plate GaN layer. Expose. Next, undoped GaN is selectively grown on the exposed areas using metal organic vapor phase epitaxy. Undoped GaN has a high resistance, and the undoped GaN thickness is 1 micrometer. Thereafter, the remaining SiN film is removed using buffered hydrofluoric acid BHF (110), and then a 220 μm gold (Au) electrode is formed by the same method as in Experimental Example 1. The gold electrode has a Schottky junction having a diameter of 200 μm and a strip-shaped overlapping conductor having a width of 10 μm. When the characteristics of these SBDs are measured,
SBD-A4 using substrate A: withstand voltage 1010 volts, on-resistance 4 mΩcm ²
SBD-B4 using substrate B: withstand voltage 440 volts, on-resistance 4 mΩcm ²
It is.

Experimental Example 5 Silicon nitride films are formed on carbon-containing GaN field plate structure epitaxial substrates A and B. After growing a 1-micrometer SiN film using plasma CVD, the SiN film is selectively etched using buffered hydrofluoric acid BHF (110) to form an area for forming a feel plate GaN layer. Expose. Next, carbon (C) -doped GaN is selectively grown on the exposed area using metalorganic vapor phase epitaxy (if the An3 flow rate is reduced from 5 slm to 2 slm, the carbon concentration becomes 3 × 10 ¹⁷ cm ^{− 3} ). C-doped GaN has a high resistance, and the C-doped GaN thickness is 1 micrometer. Thereafter, the remaining SiN film is removed using buffered hydrofluoric acid BHF (110), and then a 220 μm gold (Au) electrode is formed by the same method as in Experimental Example 1. The gold electrode has a Schottky junction having a diameter of 200 μm and a strip-shaped overlapping conductor having a width of 10 μm. When the characteristics of these SBDs are measured,
SBD-A5 using substrate A: withstand voltage 1080 volts, on-resistance 4 mΩcm ²
SBD-B5 using substrate B: withstand voltage of 480 volts, on-resistance of 4 mΩcm ²
It is.

Experimental Example 6 Silicon nitride films are formed on low-temperature grown GaN field plate structure epitaxial substrates A and B. After growing a 1-micrometer SiN film using plasma CVD, the SiN film is selectively etched using buffered hydrofluoric acid BHF (110) to form an area for forming a feel plate GaN layer. Expose. Then, low temperature growth (LT) GaN is selectively grown on the exposed area using metal organic vapor phase epitaxy (growth temperature is set to about 550 Celsius degrees). LT-GaN is high resistance and the LT-GaN thickness is 1 micrometer. Thereafter, the remaining SiN film is removed using buffered hydrofluoric acid BHF (110), and then a 220 μm gold (Au) electrode is formed by the same method as in Experimental Example 1. The gold electrode has a Schottky junction having a diameter of 200 μm and a strip-shaped overlapping conductor having a width of 10 μm. When the characteristics of these SBDs are measured,
SBD-A6 using substrate A: withstand voltage of 1060 volts, on-resistance of 4 mΩcm ²
SBD-B6 using substrate B: withstand voltage of 470 volts, on-resistance of 4 mΩcm ²
It is.

(Experimental Example 7) Silicon nitride films are formed on p-type dopant-added GaN field plate structure epitaxial substrates A and B. After growing a 1-micrometer SiN film using plasma CVD, the SiN film is selectively etched using buffered hydrofluoric acid BHF (110) to form an area for forming a feel plate GaN layer. Expose. Next, using metalorganic vapor phase epitaxy, p-type GaN is grown on the exposed area selectively while adding a p-type dopant (eg, magnesium, zinc, beryllium) (Mg concentration: 1 × 10 ¹⁸ cm ⁻³ ). No special activation treatment is performed after the growth of p-type GaN. The p-type GaN has a high resistance, and the p-type GaN thickness is 1 micrometer. Thereafter, the remaining SiN film is removed using buffered hydrofluoric acid BHF (110), and then a 220 μm gold (Au) electrode is formed by the same method as in Experimental Example 1. The gold electrode has a Schottky junction having a diameter of 200 μm and a strip-shaped overlapping conductor having a width of 10 μm. When the characteristics of these SBDs are measured,
SBD-A7 using substrate A: withstand voltage 1120 volts, on-resistance 4 mΩcm ²
SBD-B7 using substrate B: withstand voltage of 490 volts, on-resistance of 4 mΩcm ²
It is.

  As understood from some experimental examples, when a gallium nitride field plate is used, the withstand voltage is improved without increasing the on-resistance (rising voltage in the voltage-current characteristic of the diode). In any of the experimental examples, by using a gallium nitride field plate (undoped GaN, C-doped GaN, LT-GaN, p-dopant doped GaN), the withstand voltage is increased without increasing the on-resistance. In addition, the withstand voltage is further increased by using a substrate having a low dislocation density. Furthermore, not only the GaN drift region but also the Schottky barrier diode using the AlGaN drift region and the AlN drift region has a technical contribution by the GaN film for the field plate.

Further, according to a further experiment, a Schottky barrier diode in which the gallium nitride field plate in the above experiment is provided between the GaN drift layer and the silicon-based compound (insulator) film is manufactured. The silicon-based compound contains silicon, at least one element of nitrogen, and oxygen. Examples of the silicon-based compound include SiO _x , SiN, and SiON.

(Experimental example 8) SBD-A8 using field plate structure substrate A of undoped GaN + silicon compound: withstand voltage 1190 volts, on-resistance 4 mΩcm ²
SBD-B8 using substrate B: withstand voltage of 560 volts, on-resistance of 4 mΩcm ²
It is.

(Experimental example 9) SBD-A9 using field plate structure substrate A of carbon-containing GaN + silicon compound: withstand voltage 1240 volts, on-resistance 4 mΩcm ²
SBD-B9 using substrate B: withstand voltage of 580 volts, on-resistance of 4 mΩcm ²
It is.

(Experimental example 10) SBD-A10 using a low-temperature grown GaN + silicon compound field plate structure substrate A: withstand voltage 1310 volts, on-resistance 4 mΩcm ²
SBD-B10 using substrate B: withstand voltage of 620 volts, on-resistance of 4 mΩcm ²
It is.

(Experimental example 11) SBD-A11 using field plate structure substrate A of p-type dopant added GaN + silicon compound: withstand voltage 1290 volts, on-resistance 4 mΩcm ²
SBD-B11 using substrate B: withstand voltage 610 volts, on-resistance 4 mΩcm ²
It is.

In Experimental Examples 8 to 11, SiO ₂ having a thickness of 0.8 micrometers is used as the silicon compound. The GaN film for the field plate has a thickness of 0.2 micrometers. Further, not only the GaN drift region but also the Schottky barrier diode using the AlGaN drift region and the AlN drift region has a technical contribution due to the GaN film for the field plate. Therefore, by providing a GaN (undoped GaN, C-doped GaN, LT-GaN, p-dopant doped GaN) film for a field plate between the group III nitride drift region and the silicon-based insulator, a high field plate effect is achieved. At the same time, it is possible to manufacture a Schottky barrier diode having an excellent withstand voltage and showing reduced interface leakage. Also,

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

FIG. 1 is a drawing showing an example of the structure of a Schottky barrier diode according to the present embodiment. FIG. 2 is a drawing showing another example of the structure of the Schottky barrier diode according to the present embodiment. FIG. 3A to FIG. 3D are drawings showing main steps of a method for manufacturing a Schottky barrier diode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11, 11a ... Schottky barrier diode, 13 ... Group III nitride semiconductor drift region, 13b, 13c ... Group III nitride semiconductor drift region area, 15 ... Schottky electrode, 15a ... Schottky conductive part, 15b ... Overlap conductive part, DESCRIPTION OF SYMBOLS 17 ... Gallium nitride field plate layer, 19 ... Opening of gallium nitride field plate layer, 21 ... Schottky junction, 23 ... Interface between drift region and field plate layer, 25 ... Group III nitride semiconductor substrate, 27 ... Ohmic electrode, 31 Insulating layer, 33 ... Insulating layer opening, 41 ... Gallium nitride substrate, 43 ... Gallium nitride drift layer, 45 ... Gallium nitride field plate layer, 44 ... Semiconductor interface, 47 ... Insulating film, 49 ... Schottky electrode, 49a ... Schottky Conductive part, 49b ... overlap conductive part, 49c ... Burlap conductive portion of the edge, 51 ... ohmic electrode

Claims (11)

A group III nitride semiconductor drift region having a major surface including a first area and a second area;
An electrode including a Schottky conductive portion and an overlapping conductive portion;
A gallium nitride field plate layer covering the first area of the group III nitride semiconductor drift region and having an opening in the second area;
A group III nitride semiconductor substrate comprising a gallium nitride region having a dislocation density of less than 1 × 10 ⁸ cm ⁻² ;
An ohmic electrode provided on the back surface of the group III nitride semiconductor substrate;
With
The Schottky conductive portion forms a Schottky junction with the second area of the group III nitride semiconductor drift region in the opening of the gallium nitride field plate layer,
The overlap conductive part is provided on the gallium nitride field plate layer,
The group III nitride semiconductor drift region is made of gallium nitride,
The group III nitride semiconductor drift region is homoepitaxially grown so as to be provided on the group III nitride semiconductor substrate, and threading dislocations extending to the group III nitride semiconductor drift region are dislocations of the group III nitride semiconductor substrate. Less than density ,
The gallium nitride field plate layer is epitaxially grown on the group III nitride semiconductor drift region to form a homojunction with the group III nitride semiconductor drift region,
A Schottky barrier diode characterized by that. A group III nitride semiconductor drift region having a major surface including a first area and a second area;
An electrode including a Schottky conductive portion and an overlapping conductive portion;
A gallium nitride field plate layer provided between the first area of the group III nitride semiconductor drift region and the overlapping conductive portion and having an opening in the second area;
A group III nitride semiconductor substrate comprising a gallium nitride region having a dislocation density of less than 1 × 10 ⁸ cm ⁻² ;
An ohmic electrode provided on the back surface of the group III nitride semiconductor substrate;
With
The group III nitride semiconductor drift region is made of gallium nitride,
The Schottky conductive portion forms a Schottky junction with the second area of the group III nitride semiconductor drift region through the opening of the gallium nitride field plate layer,
The group III nitride semiconductor drift region is homoepitaxially grown so as to be provided on the group III nitride semiconductor substrate, and threading dislocations extending to the group III nitride semiconductor drift region are dislocations of the group III nitride semiconductor substrate. Less than density ,
The gallium nitride field plate layer is epitaxially grown on the group III nitride semiconductor drift region to form a homojunction with the group III nitride semiconductor drift region,
A Schottky barrier diode characterized by that. And having an opening aligned with the opening of the gallium nitride field plate layer, and further comprising an insulating layer provided on the gallium nitride field plate layer,
The overlap conductive portion is provided on the gallium nitride field plate layer and the insulating layer,
The Schottky barrier diode according to claim 1, wherein the insulating layer is made of a material different from a gallium nitride-based material.   4. The Schottky barrier diode according to claim 1, wherein the gallium nitride field plate layer is made of undoped GaN. 5. 4. The Schottky barrier diode according to claim 1, wherein a carbon concentration of the gallium nitride field plate layer is greater than 3 × 10 ¹⁷ cm ⁻³ . 6. The Schottky barrier according to claim 1, wherein the group III nitride semiconductor substrate is a GaN substrate having a dislocation density of less than 1 × 10 ⁶ cm ^−2. diode.   The Schottky barrier diode according to any one of claims 1 to 6, wherein the gallium nitride field plate layer is formed by selective growth.   4. The Schottky barrier diode according to claim 1, wherein the gallium nitride field plate layer is made of a GaN film containing a p-type dopant. 5.   9. The Schottky barrier diode according to claim 8, wherein the GaN of the gallium nitride field plate layer is grown by metal organic vapor phase epitaxy, and the GaN is not activated.   9. The Schottky barrier diode according to claim 8, wherein the GaN of the gallium nitride field plate layer forms a pn junction with GaN of the group III nitride semiconductor drift region. The group III nitride semiconductor drift region is homoepitaxially grown on the group III nitride semiconductor substrate and has an epitaxial crystal surface,
11. The Schottky barrier diode according to claim 1, wherein the Schottky conductive portion forms a Schottky junction with the surface of the epitaxial crystal.

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