JP4984557B2 - Method for manufacturing vertical gallium nitride semiconductor device, method for manufacturing epitaxial substrate - Google Patents

Description

  The present invention relates to a vertical gallium nitride semiconductor device and an epitaxial substrate.

  Patent Document 1 describes a method for growing a gallium nitride single crystal. According to this method, a method for growing a gallium nitride single crystal capable of incorporating oxygen as an n-type dopant is provided. In this method, a seed crystal having a surface other than the C plane on the surface (upper surface) is used to supply a source gas containing a gallium source material, a nitrogen source material, and oxygen to be doped, while maintaining the surface other than the C surface and gallium nitride. Oxygen is doped into the gallium nitride crystal through the surface by vapor growth of the crystal. Alternatively, using a seed crystal having a C-plane as a surface, a gallium nitride crystal is produced while supplying a gallium source material, a nitrogen source material, and a source gas containing oxygen to be doped while generating a facet surface other than the C-plane and maintaining the facet surface. Oxygen is doped into the gallium nitride crystal through the facet surface by performing vapor phase growth in the c-axis direction.

Non-Patent Document 1 describes the characteristics of a pin diode. This diode comprises a gallium nitride epitaxial film (undoped, n to ³ × 10 ¹⁶ cm ⁻³ , 3 μm) and a gallium nitride epitaxial film (Mgdoped, p to 1 × 10 ¹⁷ cm ⁻³ , 0.3 μm). In addition to being produced on the gallium nitride free-standing substrate by metal organic vapor phase epitaxy, an n-type ohmic electrode was produced on the back surface of the gallium nitride free-standing substrate, and a p-type ohmic electrode was produced on the epitaxial film surface.
JP 2002-373864 JP Irokawa et al. APPLIED PHYSICS LETTERS Vol. 83 15 September 2003 pp2271-2273

In a gallium nitride vertical electronic device, an n ⁻ -type gallium nitride film is epitaxially grown on an n-type gallium nitride substrate. According to experiments by the inventors, it has been found that unintended impurities such as magnesium (Mg) and iron (Fe) accumulate in the vicinity of the gallium nitride substrate / epitaxial film interface (about 1 μm width). The peak concentration of these impurities reaches about 10 ¹⁷ cm ⁻³ , and due to this impurity peak, it is not easy to provide a gallium nitride film having a low carrier concentration as designed in the region near the interface. Magnesium (Mg), beryllium (Be), calcium (Ca), zinc (Zn), cadmium (Cd), iron (Fe), titanium (Ti), cobalt (Co), nickel (Ni), vanadium (V), Impurities such as chromium (Cr) or manganese (Mn) reduce carriers near the gallium nitride substrate / epitaxial film interface and increase the resistance near the interface. That is, what is required is to provide an epitaxial film having a low carrier concentration on an n-type gallium nitride substrate.

The present invention has been made in consideration of the above matters, n having a desired low carrier concentration ^- a vertical gallium nitride semiconductor device having a structure capable of realizing a type GaN film n-type gallium nitride substrate and its object is to provide a method and a method of making an epitaxial substrate for the vertical gallium nitride semiconductor device is manufactured.

The present invention is a method of manufacturing a vertical gallium nitride semiconductor device, in which an n-conductivity type gallium nitride free-standing substrate is prepared, and a gallium nitride epitaxial film is grown on the main surface of the gallium nitride free-standing substrate. A layered region having a donor impurity concentration of 1 × 10 ¹⁸ cm ⁻³ or more is formed by adding the donor impurity to the main surface of the gallium nitride free-standing substrate, or in the growth of the gallium nitride epitaxial film, A layered region having a concentration of 1 × 10 ¹⁸ cm ⁻³ or more is grown on the main surface of the gallium nitride free-standing substrate while adding the donor impurity, and after the formation of the layered region, the gallium nitride epitaxial film is grown. In the growth, an n ^- conductivity type gallium nitride epitaxial film is grown, and the donor impurity in the layered region is at least one of silicon and germanium, and the gallium nitride epitaxial film forms an interface with the gallium nitride free-standing substrate. In the layered region, magnesium, beryllium, calcium, zinc, There is located the peak of the concentration profile of cadmium.
In this method of manufacturing a vertical gallium nitride semiconductor device, a Schottky electrode is formed on the gallium nitride epitaxial film, and the vertical gallium nitride semiconductor device includes a Schottky diode.
In this method of manufacturing a vertical gallium nitride semiconductor device, a p-conductivity-type gallium nitride epitaxial film is grown on the gallium nitride epitaxial film, an ohmic electrode is formed on the p-conductivity-type gallium nitride epitaxial film, and the vertical type The gallium nitride semiconductor device includes a pn junction diode.
In the method of manufacturing the vertical gallium nitride semiconductor device, the n ⁻ conductivity type gallium nitride epitaxial film has a donor concentration of 5 × 10 ¹⁷ cm ⁻³ or less, and the donor impurity of the gallium nitride free-standing substrate is oxygen or silicon. Including.
In the method of manufacturing the vertical gallium nitride semiconductor device, the peak of the concentration profile of iron, titanium, cobalt, nickel, vanadium, chromium, or manganese is located in the layered region.
The present invention provides a method for producing an epitaxial substrate for a vertical gallium nitride semiconductor device, comprising preparing an n-conductivity-type gallium nitride free-standing substrate and growing a gallium nitride epitaxial film on the main surface of the gallium nitride free-standing substrate. In the growth of the gallium nitride epitaxial film, a layered region having a donor impurity concentration of 1 × 10 ¹⁸ cm ⁻³ or more is formed by adding the donor impurity to the main surface of the gallium nitride free-standing substrate. A layered region having a donor impurity concentration of 1 × 10 ¹⁸ cm ⁻³ or higher is grown on the main surface of the gallium nitride free-standing substrate while adding the donor impurity, and after the formation of the layered region, the gallium nitride in the growth of the epitaxial film, n ^- conductivity type gallium nitride epitaxial layer is grown, the donor of the layered area The pure material is at least one of silicon and germanium, the gallium nitride epitaxial film forms an interface with the gallium nitride free-standing substrate, and the concentration profile of magnesium, beryllium, calcium, zinc, or cadmium in the layered region The peak is located.
In the method for producing an epitaxial substrate, a p-conductivity-type gallium nitride epitaxial film is grown on the gallium nitride epitaxial film.
In the method of manufacturing an epitaxial substrate, the n ⁻ conductivity type gallium nitride epitaxial film has a donor concentration of 5 × 10 ¹⁷ cm ⁻³ or less, and the donor impurity of the gallium nitride free-standing substrate contains oxygen or silicon.
In the method for producing an epitaxial substrate, the peak of the concentration profile of iron, titanium, cobalt, nickel, vanadium, chromium, or manganese is located in the layered region.
A vertical gallium nitride semiconductor device according to one aspect of the present invention includes: (a) an n ⁺ conductivity type gallium nitride support base; and (b) an n ⁻ conductivity type provided on the main surface of the gallium nitride support base. (C) a gate insulating film provided on the gallium nitride epitaxial film, (d) a gate electrode provided on the gate insulating film, and (e) the gallium nitride epitaxial film. A p-conductivity type region provided in the n-type semiconductor layer; (f) an n-conductivity type region provided in the p-conductivity type region; and (g) a source provided on the n-conductivity type region of the gallium nitride epitaxial film. An electrode; and (h) a drain electrode provided on the back surface of the gallium nitride support substrate, and is arranged along an axis extending from the gallium nitride support substrate to the gallium nitride epitaxial film. Layered region the concentration of the donor impurity is 1 × 10 ¹⁸ cm ^-3 or higher, the provided on the gallium nitride support base surface and the GaN epi layer, said donor impurity, silicon and germanium, at least Either. The gallium nitride epitaxial film forms an interface with the gallium nitride supporting substrate, and the peak of the concentration profile of magnesium, beryllium, calcium, zinc, or cadmium is located in the layered region.

Vertical gallium nitride semiconductor device according to another aspect of the present invention, (a) and n conductivity type gallium nitride support base, (b) the is provided on the gallium nitride support base on the main surface n ^- type conductivity A gallium nitride epitaxial film comprising: (c) a Schottky electrode provided on the gallium nitride epitaxial film; and (d) an ohmic electrode provided on the back surface of the gallium nitride support base. A layered region having a donor impurity concentration of 1 × 10 ¹⁸ cm ⁻³ or more along an axis from the substrate toward the gallium nitride epitaxial film is provided on the surface of the gallium nitride supporting substrate and in the gallium nitride epitaxial film. The donor impurity is at least one of silicon and germanium. The gallium nitride epitaxial film forms an interface with the gallium nitride supporting substrate, and the peak of the concentration profile of magnesium, beryllium, calcium, zinc, or cadmium is located in the layered region.

Vertical gallium nitride semiconductor device according to a further another aspect of the present invention, (a) and n conductivity type gallium nitride support base of, is provided on the main surface of the (b) the gallium nitride support base n ^- conductivity type gallium nitride epitaxial layer, (c) the n ^- provided over the conductive type gallium nitride epitaxial film is provided on the p conductivity type gallium nitride epitaxial layer, (d) the p conductivity type gallium nitride epitaxial layer A first ohmic electrode and (e) a second ohmic electrode provided on the back surface of the gallium nitride supporting base, and an axis from the gallium nitride supporting base toward the n ⁻ conductivity type gallium nitride epitaxial film layered region the concentration of the donor impurity is 1 × 10 ¹⁸ cm ^-3 or more along the the surface of the gallium nitride support base and the n ^- conductive It is provided in the gallium nitride epitaxial film, wherein the donor impurity is at least one of silicon and germanium. The gallium nitride epitaxial film forms an interface with the gallium nitride supporting substrate, and the peak of the concentration profile of magnesium, beryllium, calcium, zinc, or cadmium is located in the layered region.
According to the above vertical gallium nitride semiconductor device, since the donor impurity concentration profile in the layered region is 1 × 10 ¹⁸ cm ⁻³ or more, magnesium (Mg), iron (Fe) in the vicinity of the gallium nitride substrate / epitaxial film interface. Thus, the decrease in carrier concentration due to such impurities can be reduced.

In the vertical gallium nitride semiconductor device according to the present invention, the donor concentration of the gallium nitride epitaxial film may be 5 × 10 ¹⁷ cm ⁻³ or less, and the donor impurity of the gallium nitride substrate may include oxygen or silicon.

  According to the vertical gallium nitride semiconductor device, a depletion layer is sufficiently formed in the gallium nitride epitaxial film, and the decrease in carriers near the gallium nitride substrate / epitaxial film interface can be reduced.

  In the vertical gallium nitride semiconductor device according to the present invention, the peak of the concentration profile of magnesium, beryllium, calcium, zinc, or cadmium is located in the layered region. According to this vertical gallium nitride semiconductor device, the decrease in carriers due to magnesium, beryllium, calcium, zinc, or cadmium acting as a p-type dopant can be reduced in the vicinity of the gallium nitride substrate / epitaxial film interface.

  In the vertical gallium nitride semiconductor device according to the present invention, the peak of the concentration profile of iron, titanium, cobalt, nickel, vanadium, chromium, or manganese is located in the layered region. According to this vertical gallium nitride semiconductor device, the decrease in carriers due to iron, titanium, cobalt, nickel, vanadium, chromium, or manganese acting as a lifetime killer can be reduced in the vicinity of the gallium nitride substrate / epitaxial film interface.

An epitaxial substrate according to still another aspect of the present invention is an epitaxial substrate for a vertical gallium nitride semiconductor device, comprising: (a) an n-type gallium nitride substrate; and (b) on the gallium nitride substrate. And a n ^- conductivity-type gallium nitride epitaxial film, and a donor impurity concentration along the axis from the gallium nitride substrate toward the gallium nitride epitaxial film is 1 × 10 ¹⁸ cm ⁻³ or more A region is provided in the surface of the gallium nitride substrate and in the gallium nitride epitaxial film, and the donor impurity is at least one of silicon and germanium. The gallium nitride epitaxial film forms an interface with the gallium nitride substrate, and the peak of the concentration profile of magnesium, beryllium, calcium, zinc, or cadmium is located in the layered region.
An epitaxial substrate according to still another aspect of the present invention is an epitaxial substrate for a vertical gallium nitride semiconductor device, comprising: (a) an n-type gallium nitride substrate; and (b) on the gallium nitride substrate. An n ⁻ conductivity type gallium nitride epitaxial film, and (c) a p conductivity type gallium nitride epitaxial film provided on the n ⁻ conductivity type gallium nitride epitaxial film. ^A layered region having a donor impurity concentration of 1 × 10 ¹⁸ cm ⁻³ or more along the axis toward the conductive gallium nitride epitaxial film is provided on the surface of the gallium nitride substrate and in the gallium nitride epitaxial film; The donor impurity is at least one of silicon and germanium. The n ^- conductivity-type gallium nitride epitaxial film forms an interface with the gallium nitride substrate, and the peak of the concentration profile of magnesium, beryllium, calcium, zinc, or cadmium is located in the layered region.

According to this epitaxial substrate, since the donor impurity concentration profile in the layered region is 1 × 10 ¹⁸ cm ⁻³ or more, the carrier concentration due to impurities such as magnesium (Mg) and iron (Fe) in the vicinity of the gallium nitride substrate / epitaxial film interface. Can be reduced. Accordingly, an epitaxial substrate for a vertical gallium nitride semiconductor device is provided.

In the epitaxial substrate according to the present invention, the gallium nitride epitaxial film has a donor concentration of 5 × 10 ¹⁷ cm ⁻³ or less, and the gallium nitride substrate contains oxygen or silicon as a donor impurity.

  According to this epitaxial substrate, a depletion layer is sufficiently formed in the gallium nitride epitaxial film, and a decrease in carrier concentration in the vicinity of the gallium nitride substrate / epitaxial film interface can be reduced.

  In the epitaxial substrate according to the present invention, a peak of a concentration profile of magnesium, beryllium, calcium, zinc or cadmium is located in the layered region. According to this epitaxial substrate, the decrease in carrier concentration due to magnesium, beryllium, calcium, zinc, or cadmium acting as a p-type dopant can be reduced in the vicinity of the gallium nitride substrate / epitaxial film interface.

  In the epitaxial substrate according to the present invention, a peak of a concentration profile of iron, titanium, cobalt, nickel, vanadium, chromium, or manganese is located in the layered region. According to this epitaxial substrate, the decrease in carrier concentration due to iron, titanium, cobalt, nickel, vanadium, chromium, or manganese acting as a lifetime killer can be reduced in the vicinity of the gallium nitride substrate / epitaxial film interface.

  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, there is provided a method for manufacturing a vertical gallium nitride semiconductor device having a structure capable of realizing an n ⁻ -type gallium nitride film having a desired low carrier concentration on an n ^- type gallium nitride substrate. Is done. Further, according to the present invention, there is provided a method for producing an epitaxial substrate for this vertical gallium nitride semiconductor device.

  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 vertical gallium nitride semiconductor device and epitaxial substrate 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.

(First embodiment)
FIG. 1 shows a Schottky diode. The Schottky diode 11 includes an n ⁺ conductivity type gallium nitride support base 13, an n ⁻ conductivity type gallium nitride epitaxial film 15, a Schottky electrode 17, and an ohmic electrode 19. The gallium nitride epitaxial film 15 is provided on the main surface of the gallium nitride support base 13. The Schottky electrode 17 is provided on the gallium nitride epitaxial film 15. The ohmic electrode 19 is provided on the back surface 13 a of the gallium nitride support base 13. The layered region 21 is provided in the gallium nitride support base 13 and the gallium nitride epitaxial film 15. The interface between the gallium nitride support base 13 and the gallium nitride epitaxial film 15 is located in the layered region 21. In the layered region 21, the donor impurity along the axis from the gallium nitride support base 13 toward the gallium nitride epitaxial film 15 is 1 × 10 ¹⁸ cm ⁻³ or more. The donor impurity is at least one of silicon and germanium.

According to the Schottky diode 11, since the concentration profile of the donor impurity in the layered region 21 has a peak value of 1 × 10 ¹⁸ cm ⁻³ or more, magnesium (Mg), iron (Fe ) Can reduce the decrease in carrier concentration due to impurities.

The donor concentration of the gallium nitride epitaxial film 15 is 5 × 10 ¹⁷ cm ⁻³ or less, and the gallium nitride supporting base 13 may contain oxygen as a donor impurity. Alternatively, the gallium nitride support base 13 may contain silicon as a donor impurity. According to this Schottky diode, a depletion layer is sufficiently formed in the gallium nitride epitaxial film 15, and a decrease in carrier concentration in the vicinity of the gallium nitride supporting substrate / epitaxial film interface can be reduced.

Example 1
An epitaxial substrate was fabricated according to the following procedure. A gallium nitride (GaN) free-standing substrate manufactured by the HVPE method is prepared. This GaN free-standing substrate has a (0001) plane main surface, exhibits n ⁺ conductivity type, has a carrier concentration of 3 × 10 ¹⁸ cm ⁻³ , and a thickness of 400 μm. The average dislocation density in this substrate is 1 × 10 ⁶ cm ⁻² or less. A GaN epitaxial film is grown on the main surface of this free-standing substrate by metal organic vapor phase epitaxy. The epitaxial film has an n ⁻ conductivity type, a carrier concentration of 5 × 10 ¹⁵ cm ⁻³ , and a thickness of 3.3 μm. There is an n ⁺ GaN layered region containing 5 × 10 ¹⁸ cm ⁻³ of silicon (Si) at the interface between the GaN free-standing substrate and the GaN epitaxial film. In order to form a layered region, silicon can be added to the surface layer or epitaxial film of the substrate.

  Next, using this epitaxial substrate, a Schottky diode was fabricated according to the following procedure. After organic cleaning of this sample, an ohmic electrode was formed on the entire back surface of the GaN free-standing substrate. The ohmic electrode is made of Ti / Al / Ti / Au (20 nm / 100 nm / 20 nm / 300 nm). To form the ohmic electrode, an alloying treatment (600 degrees Celsius, 1 minute) was performed after depositing a metal laminated film by EB vapor deposition. A Schottky electrode was formed on the surface of the epitaxial film. The Schottky electrode is made of, for example, an Au film having a diameter of 200 μm. For the formation of the Schottky electrode, a metal film was deposited by resistance heating vapor deposition. Prior to vapor deposition, both the Schottky electrode and the ohmic electrode were subjected to sample pretreatment (for example, at room temperature for 1 minute) using an aqueous HCl solution (hydrochloric acid for semiconductor: pure water = 1: 1).

FIG. 2 is a graph showing the magnesium (Mg) concentration in the epitaxial substrate by secondary ion mass spectrometry. The peak of the concentration curve C _Mg is located in the vicinity of the gallium nitride substrate / epitaxial film interface. The peak concentration is 1 × 10 ¹⁶ cm ⁻³ or less.

FIG. 3 is a graph showing the iron (Fe) concentration in the epitaxial substrate by secondary ion mass spectrometry. The peak of the concentration curve C _Fe is located in the vicinity of the gallium nitride substrate / epitaxial film interface. The peak concentration is 1 × 10 ¹⁷ cm ⁻³ or less.

FIG. 4 is a graph showing the donor concentration (silicon) in the layered region of the epitaxial substrate by secondary ion mass spectrometry. The peak of the concentration curve C _Si is located in the vicinity of the gallium nitride substrate / epitaxial film interface. Since the donor impurity concentration profile in the layered region has a peak value of 1 × 10 ¹⁸ cm ⁻³ or more, the decrease in carrier concentration due to impurities such as magnesium (Mg) and iron (Fe) in the vicinity of the gallium nitride substrate / epitaxial film interface is reduced. it can. The thickness of the layered region is larger than the above impurity distribution width, but is, for example, 1 μm or less. Further, not limited to magnesium (Mg) and iron (Fe), beryllium (Be), calcium (Ca), zinc (Zn), cadmium (Cd), titanium (Ti), cobalt (Co), nickel (Ni), The decrease in carrier concentration due to impurities such as vanadium (V), chromium (Cr), or manganese (Mn) can also be reduced.

(Second Embodiment)
FIG. 5 shows a vertical transistor. The vertical transistor 41 includes an n ⁺ conductivity type gallium nitride support base 43, an n ⁻ conductivity type gallium nitride epitaxial film 45, a gate electrode 47, a p conductivity type region 49, an n conductivity type region 51, and a source. An electrode 53 and a drain electrode 55 are provided. The gallium nitride epitaxial film 45 is provided on the main surface of the gallium nitride support base 43. The gate electrode 47 is provided on the gallium nitride epitaxial film 45. Under the gate electrode 47, an extension 49b of the p conductivity type region 49 is provided. The p conductivity type region 49 is provided in the gallium nitride epitaxial film 45. The n conductivity type region 51 is provided in the p conductivity type region 49. The source electrode 53 is provided on the n conductivity type region 51 in the gallium nitride epitaxial film 45. The drain electrode 55 is provided on the back surface 43 a of the gallium nitride support base 43. A gate insulating film 59 is provided between the gallium nitride epitaxial film 45 and the gate electrode 47. As a material of the gate insulating film 59, a silicon oxide film, a silicon oxynitride film, a silicon nitride film, alumina, aluminum nitride, AlGaN, or the like can be used.

A layered region 57 is provided in the gallium nitride support base 43 and the gallium nitride epitaxial film 45. The interface between the gallium nitride support base 43 and the gallium nitride epitaxial film 45 is located in the layered region 57. In the layered region 57, the donor impurity along the axis from the gallium nitride support base 43 to the gallium nitride epitaxial film 45 is 1 × 10 ¹⁸ cm ⁻³ or more. The donor impurity is at least one of silicon and germanium.

According to the vertical transistor 41, since the concentration profile of the donor impurity in the layered region 57 has a peak value of 1 × 10 ¹⁸ cm ⁻³ or more, magnesium (Mg), iron in the vicinity of the gallium nitride supporting substrate / epitaxial film interface Reduction of carriers due to impurities such as (Fe) can be reduced. Further, not limited to magnesium (Mg) and iron (Fe), beryllium (Be), calcium (Ca), zinc (Zn), cadmium (Cd), titanium (Ti), cobalt (Co), nickel (Ni), The decrease in carrier concentration due to impurities such as vanadium (V), chromium (Cr), or manganese (Mn) can also be reduced.

  As described above, the gallium nitride vertical devices 11 and 41 include the low-concentration homoepitaxial films 15 and 45 on the gallium nitride substrates 13 and 43. However, since impurities such as magnesium and iron tend to accumulate near the interface between the gallium nitride substrate and the homoepitaxial film, it is difficult to control the carrier concentration near the low concentration interface. Therefore, by using a relatively high concentration layered region provided in the vicinity of the interface, the influence of the impurities can be reduced, and the carrier concentration in the epitaxial film away from the interface can be maintained at a desired low concentration. Except for the electrical influence due to the influence of the impurities, the forward resistance or on-resistance of the gallium nitride based vertical devices 11 and 41 can be reduced and the reverse breakdown voltage can be improved.

(Third embodiment)
FIG. 6 is a drawing showing an epitaxial substrate. The epitaxial substrate 61 is manufactured as follows. The epitaxial substrate 61 includes an n ⁺ conductivity type gallium nitride substrate 63, an n ⁻ conductivity type gallium nitride epitaxial film and 65. The gallium nitride epitaxial film 65 is provided on the gallium nitride substrate 63. A layered region 67 is provided in the gallium nitride substrate 63 and the gallium nitride epitaxial film 65. The interface between the gallium nitride substrate 43 and the gallium nitride epitaxial film 65 is located in the layered region 67. In the layered region 67, the donor impurity along the axis from the gallium nitride substrate 63 to the gallium nitride epitaxial film 65 has a peak value of 1 × 10 ¹⁸ cm ⁻³ or more. The donor impurity is at least one of silicon and germanium.

According to this epitaxial substrate 61, since the concentration profile of the donor impurity in the layered region 67 has a peak value of 1 × 10 ¹⁸ cm ⁻³ or more, magnesium (Mg), iron (Fe ) Can reduce the decrease in carrier concentration due to impurities. Further, not limited to magnesium (Mg) and iron (Fe), beryllium (Be), calcium (Ca), zinc (Zn), cadmium (Cd), titanium (Ti), cobalt (Co), nickel (Ni), The decrease in carrier concentration due to impurities such as vanadium (V), chromium (Cr), or manganese (Mn) can also be reduced.

The donor concentration of the gallium nitride epitaxial film 65 is 5 × 10 ¹⁷ cm ⁻³ or less, and the donor impurity of the gallium nitride substrate 63 may contain oxygen. Alternatively, the donor impurity of the gallium nitride substrate 63 may include silicon. According to this epitaxial substrate 61, a sufficient depletion layer is formed in the gallium nitride epitaxial film 65, and the decrease in carrier concentration in the vicinity of the gallium nitride substrate / epitaxial film interface can be reduced. It is suitable for a gallium nitride vertical semiconductor device.

(Fourth embodiment)
FIG. 7 shows a pn junction diode. The pn junction diode 71 includes an n-conductivity-type gallium nitride support base 13, a p-conductivity-type gallium nitride epitaxial film 73, an n ^- conductivity-type gallium nitride epitaxial film 75, a first ohmic electrode 77, and a second ohmic electrode. And an electrode 79. The n ⁻ conductivity type gallium nitride epitaxial film 75 is provided on the main surface of the gallium nitride support base 13. The p conductivity type gallium nitride epitaxial film 73 is provided on the n ⁻ conductivity type gallium nitride epitaxial film 75. The first ohmic electrode 77 is provided on the p conductivity type gallium nitride epitaxial film 73. The second ohmic electrode 79 is provided on the back surface 13 a of the gallium nitride support base 13. The p conductivity type gallium nitride epitaxial film 73 and the n ⁻ conductivity type gallium nitride epitaxial film 75 form a pn junction 76. The layered region 81 having a donor impurity concentration of 1 × 10 ¹⁸ cm ⁻³ or more along the axis from the gallium nitride supporting base 13 toward the gallium nitride epitaxial film 73 is formed on the surface of the gallium nitride supporting base 13 and the n ⁻ conductivity type nitriding. It is provided in the gallium epitaxial film 75. The donor impurity is at least one of silicon and germanium.

According to the pn junction diode 71 described above, since the donor impurity concentration profile of the layered region 81 is 1 × 10 ¹⁸ cm ⁻³ or more, magnesium (Mg), iron (Fe) in the vicinity of the gallium nitride supporting substrate / epitaxial film interface. Thus, the decrease in carrier concentration due to such impurities can be reduced. Further, the donor concentration of the gallium nitride epitaxial film 75 may be 5 × 10 ¹⁷ cm ⁻³ or less.

(Example)
An epitaxial substrate was fabricated according to the following procedure. A gallium nitride (GaN) free-standing substrate manufactured using the HVPE method is prepared. This GaN substrate has a principal surface with a plane orientation (0001) plane. The GaN substrate exhibits n ⁺ conductivity type, its carrier concentration is 3 × 10 ¹⁸ cm ⁻³ , and its thickness is 400 micrometers. The average dislocation density in this substrate is 1 × 10 ⁶ cm ⁻² or less. A GaN epitaxial film is grown on the main surface of this free-standing substrate by metal organic vapor phase epitaxy. The epitaxial film has n ⁻ conductivity, its carrier concentration is 5 × 10 ¹⁵ cm ⁻³ , and its thickness is 10 μm. A first p-conductivity-type gallium nitride epitaxial film is provided on the GaN epitaxial film. The first p-conductivity-type gallium nitride epitaxial film has a magnesium concentration of 1 × 10 ¹⁸ cm ⁻³ and a thickness of 0.5 μm. If necessary, a second p-conductivity-type gallium nitride-based epitaxial film is provided on the second p-conductivity-type gallium nitride-based epitaxial film. The second p-conductivity-type gallium nitride epitaxial film has a magnesium concentration of 5 × 10 ¹⁹ cm ⁻³ and a thickness of 0.05 μm. At the interface between the GaN free-standing substrate and the GaN epitaxial layer, there is an n ⁺ GaN layered region containing silicon of 5 × 10 ¹⁸ cm ⁻³ or more. In order to form the layered region, silicon can be added to the surface of the substrate or the epitaxial film.

  Then, using this epitaxial substrate, a pn diode was formed according to the following procedure. After this sample was organically cleaned, an ohmic electrode was formed on the entire back surface of the GaN free-standing substrate. For the formation of the ohmic electrode, an alloying treatment was performed after depositing a metal deposition film by EB vapor deposition. The alloying process is performed, for example, at 600 degrees Celsius for 1 minute. An ohmic electrode was produced on the epitaxial film. The shape of the ohmic electrode is, for example, a radius of 200 micrometers. For the production of the ohmic electrode, an alloying treatment was performed after depositing a metal deposition film by EB vapor deposition. The alloying process is performed, for example, at 600 degrees Celsius for 1 minute. Prior to the production of both ohmic electrodes, the sample was pretreated with an HCl solution (hydrochloric acid for semiconductor: ultrapure water = 1: 1).

Mg and Fe peaks were detected near the interface between the epitaxial layer and the substrate by the SIMS method. The peak concentration of magnesium was 1 × 10 ¹⁶ cm ⁻³ or less, and the peak concentration of iron was 1 × 10 ¹⁷ cm ⁻³ or less. Thus, since the effect of carrier compensation by magnesium, iron, etc. in the vicinity of the interface can be suppressed, the on-resistance of the pn diode as described above can be reduced, and the forward rising voltage can be reduced. In addition, the breakdown voltage can be improved.

  As described above, the gallium nitride vertical device such as the gallium nitride pn junction diode 71 includes the low-concentration homoepitaxial film 75 on the gallium nitride substrate 13. However, since impurities such as magnesium and iron tend to accumulate near the interface between the gallium nitride substrate and the homoepitaxial film, it is difficult to control the carrier concentration near the low concentration interface. Therefore, by using a relatively high concentration layered region provided in the vicinity of the interface, the influence of the impurities can be reduced, and the carrier concentration in the epitaxial film away from the interface can be maintained at a desired low concentration. Except for the electrical influence due to the influence of the impurities, the forward resistance or on-resistance of the gallium nitride pn junction diode 71 can be reduced and the reverse breakdown voltage can be improved.

The present embodiment is a method of manufacturing a vertical gallium nitride semiconductor device in which an n-conductivity-type gallium nitride free-standing substrate is prepared, and a gallium nitride epitaxial film is grown on the main surface of the gallium nitride free-standing substrate. A layered region having a concentration of 1 × 10 ¹⁸ cm ⁻³ or more is formed by adding a donor impurity to the main surface of the gallium nitride free-standing substrate, or the concentration of the donor impurity is 1 × 10 ^{18 in} the growth of the gallium nitride epitaxial film. A layered region of cm ⁻³ or more is grown on the main surface of the gallium nitride free-standing substrate while adding donor impurities. After the formation of the layered region, an n ⁻ conductivity type gallium nitride epitaxial film is grown in the growth of the gallium nitride epitaxial film. The donor impurity in the layered region is at least one of silicon and germanium, the gallium nitride epitaxial film forms an interface with the gallium nitride free-standing substrate, and the concentration profile of magnesium, beryllium, calcium, zinc, or cadmium in the layered region The peak is located.
In this method of manufacturing a vertical gallium nitride semiconductor device, a Schottky electrode is formed on a gallium nitride epitaxial film, and the vertical gallium nitride semiconductor device includes a Schottky diode.
In this method of manufacturing a vertical gallium nitride semiconductor device, a p-type gallium nitride epitaxial film is grown on a gallium nitride epitaxial film, an ohmic electrode is formed on the p-type gallium nitride epitaxial film, and a vertical gallium nitride semiconductor is formed. The device includes a pn junction diode.
In this method for manufacturing a vertical gallium nitride semiconductor device, the n ⁻ conductivity type gallium nitride epitaxial film has a donor concentration of 5 × 10 ¹⁷ cm ⁻³ or less, and the donor impurity of the gallium nitride free-standing substrate contains oxygen or silicon.
In the method for manufacturing the vertical gallium nitride semiconductor device, the peak of the concentration profile of iron, titanium, cobalt, nickel, vanadium, chromium, or manganese is located in the layered region.
This embodiment is a method for producing an epitaxial substrate for a vertical gallium nitride semiconductor device, in which an n-conductivity-type gallium nitride free-standing substrate is prepared and a gallium nitride epitaxial film is grown on the main surface of the gallium nitride free-standing substrate. A layered region having a donor impurity concentration of 1 × 10 ¹⁸ cm ⁻³ or more is formed by adding a donor impurity to the main surface of the gallium nitride free-standing substrate, or a donor impurity concentration in the growth of a gallium nitride epitaxial film A layered region having a thickness of 1 × 10 ¹⁸ cm ⁻³ or more is grown on the main surface of the gallium nitride free-standing substrate while adding donor impurities. After the formation of the layered region, an n ⁻ conductivity type gallium nitride epitaxial film is grown in the growth of the gallium nitride epitaxial film. The donor impurity in the layered region is at least one of silicon and germanium, the gallium nitride epitaxial film forms an interface with the gallium nitride free-standing substrate, and the magnesium, beryllium, calcium, zinc, or cadmium concentration in the layered region The peak of the profile is located.
In the method for producing an epitaxial substrate, a p-conductivity-type gallium nitride epitaxial film is grown on a gallium nitride epitaxial film.
In the method of manufacturing an epitaxial substrate, the n ⁻ conductivity type gallium nitride epitaxial film has a donor concentration of 5 × 10 ¹⁷ cm ⁻³ or less, and the donor impurity of the gallium nitride free-standing substrate contains oxygen or silicon.
In the method of manufacturing an epitaxial substrate, the peak of the concentration profile of iron, titanium, cobalt, nickel, vanadium, chromium, or manganese is located in the layered region.
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. In the present embodiment, the n-type donor impurity can be added during the growth, but it may be present in the substrate (surface and / or inside) prior to the epitaxial growth. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

FIG. 1 shows a Schottky diode. FIG. 2 is a graph showing the magnesium (Mg) concentration in the epitaxial substrate by secondary ion mass spectrometry. FIG. 3 is a graph showing the iron (Fe) concentration in the epitaxial substrate by secondary ion mass spectrometry. FIG. 4 is a graph showing the donor concentration (silicon) in the layered region of the epitaxial substrate by secondary ion mass spectrometry. FIG. 5 shows a vertical transistor. FIG. 6 is a drawing showing an epitaxial substrate. FIG. 7 shows a pn junction diode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Schottky diode, 13 ... n conductivity type gallium nitride support base, 15 ... n ^- conductivity type gallium nitride epitaxial film, 17 ... Schottky electrode, 19 ... ohmic electrode, 17 ... Schottky electrode, 19 ... ohmic electrode, 21 ... layered region 4 1 ... Vertical transistor, 43 ... n-conductivity-type gallium nitride support base, 45 ... n ^- conductivity-type gallium nitride epitaxial film, 47 ... Gate electrode, 49 ... p-conductivity type region, 51 ... n-conductivity type region, 53 ... Source electrode, 55 ... Drain electrode, 57 ... Layered region, 59 ... Insulating film, 61 ... Epitaxial substrate, 63 ... n conductive gallium nitride substrate, 65 ... n ^- conductive gallium nitride epitaxial film, 67 ... Layered region, 71 ... pn junction diode, 73 ... p conductivity type gallium nitride epitaxial layer, 75 ... n ^- conductivity type gallium nitride Epitaxial film 77 ... first ohmic electrode, 79 ... second ohmic electrode, 76 ... pn junction

Claims (9)

preparing an n-type gallium nitride free-standing substrate;
A method for producing a vertical gallium nitride semiconductor device, wherein a gallium nitride epitaxial film is grown on a main surface of the gallium nitride free-standing substrate,
Donor impurity concentration is 1 × 10 ¹⁸ cm ^-3 The layered region as described above is formed by adding the donor impurity to the main surface of the gallium nitride free-standing substrate, or the concentration of the donor impurity is 1 × 10 in the growth of the gallium nitride epitaxial film. ¹⁸ cm ^-3 A layered region that is the above is grown on the main surface of the gallium nitride free-standing substrate while adding the donor impurity,
In the growth of the gallium nitride epitaxial film after the formation of the layered region, n ⁻ Growing a conductive gallium nitride epitaxial film,
The donor impurity in the layered region is at least one of silicon and germanium;
The gallium nitride epitaxial film forms an interface with the gallium nitride free-standing substrate,
A method of manufacturing a vertical gallium nitride semiconductor device in which a peak of a concentration profile of magnesium, beryllium, calcium, zinc, or cadmium is located in the layered region. In the method of manufacturing a vertical gallium nitride semiconductor device, a Schottky electrode is formed on the gallium nitride epitaxial film,
The method for manufacturing a vertical gallium nitride semiconductor device according to claim 1, wherein the vertical gallium nitride semiconductor device includes a Schottky diode. In the method of manufacturing a vertical gallium nitride semiconductor device, a p-conductivity-type gallium nitride epitaxial film is grown on the gallium nitride epitaxial film, an ohmic electrode is formed on the p-conductivity-type gallium nitride epitaxial film,
The method for manufacturing a vertical gallium nitride semiconductor device according to claim 1, wherein the vertical gallium nitride semiconductor device includes a pn junction diode. N ⁻ The conductivity type gallium nitride epitaxial film has a donor concentration of 5 × 10 ¹⁷ cm ^-3 And
The method for producing a vertical gallium nitride semiconductor device according to any one of claims 1 to 3, wherein the donor impurity of the gallium nitride free-standing substrate contains oxygen or silicon. The peak of the concentration profile of iron, titanium, cobalt, nickel, vanadium, chromium, or manganese is located in the layered region, according to any one of claims 1 to 4. A method of manufacturing a vertical gallium nitride semiconductor device. preparing an n-type gallium nitride free-standing substrate;
A method for producing an epitaxial substrate for a vertical gallium nitride semiconductor device, wherein a gallium nitride epitaxial film is grown on a main surface of the gallium nitride free-standing substrate,
Donor impurity concentration is 1 × 10 ¹⁸ cm ^-3 The layered region as described above is formed by adding the donor impurity to the main surface of the gallium nitride free-standing substrate, or the concentration of the donor impurity is 1 × 10 in the growth of the gallium nitride epitaxial film. ¹⁸ cm ^-3 A layered region that is the above is grown on the main surface of the gallium nitride free-standing substrate while adding the donor impurity,
In the growth of the gallium nitride epitaxial film after the formation of the layered region, n ⁻ Growing a conductive gallium nitride epitaxial film,
The donor impurity in the layered region is at least one of silicon and germanium;
The gallium nitride epitaxial film forms an interface with the gallium nitride free-standing substrate,
A method for producing an epitaxial substrate, wherein a peak of a concentration profile of magnesium, beryllium, calcium, zinc, or cadmium is located in the layered region. The method for producing an epitaxial substrate according to claim 6, wherein a p-conductivity-type gallium nitride epitaxial film is grown on the gallium nitride epitaxial film. N ⁻ The conductivity type gallium nitride epitaxial film has a donor concentration of 5 × 10 ¹⁷ cm ^-3 And
The method for producing an epitaxial substrate according to claim 6 or 7, wherein the donor impurity of the gallium nitride free-standing substrate includes oxygen or silicon. The epitaxial substrate according to any one of claims 6 to 8, wherein a peak of a concentration profile of iron, titanium, cobalt, nickel, vanadium, chromium, or manganese is located in the layered region. Method.

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