JP2018137432A - Nitride semiconductor substrate and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure which can increase the concentration of two dimensional electron gas without lowering a mobility.SOLUTION: Provided is a nitride semiconductor substrate comprising: a first layer having a composition given by InAlGaN (where 0≤a1≤1, 0≤b1≤1, 0≤c1≤1 and a1+b1+c1=1); a second layer formed on the first layer, having a composition given by InAlGaN (where 0≤a2≤1, 0≤b2≤1, 0≤c2≤1 and a2+b2+c2=1) and having a bandgap different from that of the first layer; and a third layer formed on the second layer, and having a composition given by ABN (where A is an element of Group XIII, B is an element of Group XIII or XIV, A≠B and 0<j<1).SELECTED DRAWING: Figure 1

Description

  The present invention particularly relates to a nitride semiconductor substrate used for a high electron mobility transistor (HEMT) and a method for manufacturing the same.

  In a HEMT made of a nitride semiconductor, a technique for improving electrical characteristics by forming various layers (a protective layer or a cap layer) on an electron supply layer (or a barrier layer) is known.

  Patent Document 1 discloses a III-nitride-based channel layer, a III-nitride-based barrier layer on the channel layer, and a multilayer cap layer on the barrier layer, wherein the nitride layer is nitrided on the barrier layer. A III-nitride layer having a layer containing aluminum (AlN), a multilayer cap layer having a gallium nitride (GaN) layer on the layer containing AlN, and a SiN passivation layer on the GaN layer There is disclosure of an electron mobility transistor (HEMT).

In Patent Document 2, a GaN-based semiconductor layer, a source electrode provided on the GaN-based semiconductor layer, a drain electrode provided on the GaN-based semiconductor layer, and between the source electrode and the drain electrode, A gate electrode provided on the GaN-based semiconductor layer, a first protective film provided in contact with the GaN-based semiconductor layer between the gate electrode and the drain electrode, and on the first protective film And a second protective film having a higher resistivity than the first protective film, wherein the first protective film includes gallium (Ga), iron (Fe), chromium (Cr) as impurities, Alternatively, there is a disclosure of a semiconductor device that is silicon oxide, silicon nitride, silicon oxynitride, or aluminum oxide containing nickel (Ni) at 1 × 10 ¹⁸ cm ⁻³ or more.

JP 2008-227501 A Japanese Patent Laying-Open No. 2015-177069

  In the invention described in Patent Document 1 or 2, silicon nitride (SiN) is formed as a protective film on an electron supply layer (or barrier layer) made of a GaN-based semiconductor via various layers as necessary. We use what we did.

  However, it has been found that when the SiN film is used as a protective layer as described above, the concentration of the two-dimensional electron gas (2DEG) is not sufficiently high. This is considered to be caused by the high insulating property of the protective film.

  In this regard, the semiconductor device described in Patent Document 2 includes a first protective film provided in contact with the GaN-based semiconductor layer and a first protective film provided on the first protective film and having a higher resistance than the first protective film. 2, and the first protective film has a certain level of conductivity, so that charges generated in the GaN-based semiconductor layer can be removed from the GaN-based semiconductor layer or generated in the GaN-based semiconductor layer. The function of suppressing the uneven distribution of the charged charges in the semiconductor device is exhibited, and unnecessary charges in the GaN-based semiconductor layer are released through the first protective film or dispersed in the first protective film. Thus, unintentional localization and uneven distribution of electric charges are prevented. Therefore, fluctuations in transistor characteristics such as current collapse can be suppressed.

  However, even with the above method, it is not always possible to obtain a desirable effect from the viewpoint of sufficiently increasing the concentration of the two-dimensional electron gas.

  In view of such problems, the present invention has an object to provide a nitride semiconductor substrate capable of increasing the concentration of a two-dimensional electron gas while maintaining mobility in a HEMT having a protective film on an electron supply layer. And

The nitride semiconductor substrate of the present invention has a composition of In _a1 Al _b1 Ga _c1 N (0 ≦ a1 ≦ 1, 0 ≦ b1 ≦ 1, 0 ≦ c1 ≦ 1, a1 + b1 + c1 = 1). And a composition of In _a2 Al _b2 Ga _c2 N (0 ≦ a2 ≦ 1, 0 ≦ b2 ≦ 1, 0 ≦ c2 ≦ 1, a2 + b2 + c2 = 1) formed on the first layer. And a second layer having a band gap different from that of the first layer, and formed on the second layer, and A _j B _1-j N (A is an arbitrary group 13 element, B And a third layer having a composition of any group 13 element or group 14 element, A ≠ B, 0 <j <1).

  By having such a configuration, it is possible to further increase the concentration of the two-dimensional electron gas while maintaining the mobility.

  The nitride semiconductor substrate of the present invention preferably has a cap layer made of a group 13 nitride between the second layer and the third layer.

In a preferred aspect of the present invention, the first layer is an electron transit layer made of GaN, and the second layer is In _a2 Al _b2 Ga _c2 N (a2 = 0, 0 <b2 ≦ 1, 0 ≦ an electron supply layer having a composition of c2 <1, b2 + c2 = 1), the cap layer is a GaN layer, and the third layer is a Ga _j Si _1-j N (0 <j <1) layer It is.

The method for producing a nitride semiconductor substrate of the present invention includes a GaN layer that is an electron transit layer as a first layer, and an In _a2 Al _b2 Ga _c2 N (a2 = 0, which is an electron supply layer as a second layer). 0 <b2 ≦ 1, 0 ≦ c2 <1, b2 + c2 = 1), a GaN layer as a cap layer, and a Ga _j Si _1-j N (0 <j <1) layer as a third layer In this order, and a method for producing a nitride semiconductor substrate by metal organic vapor phase epitaxy, wherein the first layer is laminated, and then the second layer is continuously laminated on the first layer. After the first step, the second step of forming the cap layer on the second layer after the first step, and immediately after the end of the second step, the Ga source gas, the Si source gas, and the N source gas are changed for 3 seconds. After the third step of laminating the third layer, and after the third step, the supply of the Ga source gas is stopped and the Si source gas is supplied. Characterized in that it comprises a fourth step of supplying said N source gas and.

  According to the present invention, in a HEMT having a protective film on an electron supply layer, a nitride semiconductor substrate capable of increasing the concentration of a two-dimensional electron gas without reducing the mobility, that is, increasing the electron concentration. And a method for manufacturing the same.

1 is a schematic cross-sectional view showing one embodiment of a nitride semiconductor substrate of the present invention. 1 is a schematic cross-sectional view showing a preferred embodiment of a nitride semiconductor substrate of the present invention. It is the schematic which shows typically the form of Ga composition ratio in the layer in the other one aspect | mode of the nitride semiconductor substrate of this invention. It is the schematic which shows typically the form of Ga composition ratio in the layer in another suitable one aspect | mode of the nitride semiconductor substrate of this invention.

Hereinafter, the present invention will be described in detail with reference to the drawings. The nitride semiconductor substrate of the present invention has a composition of In _a1 Al _b1 Ga _c1 N (0 ≦ a1 ≦ 1, 0 ≦ b1 ≦ 1, 0 ≦ c1 ≦ 1, a1 + b1 + c1 = 1). And a composition of In _a2 Al _b2 Ga _c2 N (0 ≦ a2 ≦ 1, 0 ≦ b2 ≦ 1, 0 ≦ c2 ≦ 1, a2 + b2 + c2 = 1) formed on the first layer. And a second layer having a band gap different from that of the first layer, and formed on the second layer, and A _j B _1-j N (A is an arbitrary group 13 element, B Includes an optional group 13 element or group 14 element, and a third layer having a composition of A ≠ B, 0 <j <1).

FIG. 1 is a schematic cross-sectional view showing one embodiment of a nitride semiconductor substrate Z of the present invention, which is a base substrate 1, a buffer layer 2, a first layer 3, a second layer 4, a third layer X, and an electrode. 5 is included. Specifically, the first layer 3 is an electron transit layer, and the second layer 4 is an electron supply layer.
A nitride semiconductor substrate Z shown in FIG. 2 is a preferred embodiment of the present invention, and includes a base substrate 1, a buffer layer 2, a first layer (electron transit layer) 3, a cap layer C, and a second layer (electrons). Supply layer) 4, third layer X and electrode 5.
Note that all the drawings shown in the present invention are schematically simplified and emphasized for the purpose of explanation, and the shape, size, and ratio of details are different from actual ones. Moreover, description is omitted about the other structure considered unnecessary in order to demonstrate this invention.

  Examples of the base substrate 1 include silicon single crystal, silicon carbide, sapphire, and GaN. In these materials, silicon single crystals tend to be disadvantageous in terms of longitudinal breakdown voltage compared to silicon carbide, sapphire and the like, which have higher insulation properties. Even in the case where is used, the effect is more prominently exhibited, which is particularly preferable.

As the buffer layer 2, for example, the buffer layer structure disclosed in Japanese Patent No. 5159858 or Japanese Patent No. 5188545 can be applied. That is, for example, an AlGaN-based initial buffer layer composed of AlN having a thickness of 50 to 200 nm and a second layer of AlGaN having a thickness of 100 to 300 nm, and GaN having a thickness of 1 to 50 nm. The fourth layer is AlN having a thickness of 1 to 50 nm, the fifth layer is GaN having a thickness of 200 nm or more, the third layer and the fourth layer are repeatedly stacked in this order, and the fifth layer is finally stacked. Or an AlGaN-based multilayer buffer layer in which nitrides are repeatedly stacked 5 to 100 times in total, or an Al _x Ga _1-x N single crystal layer (0.6 ≦ x ≦ 1.0) and a multilayer buffer layer in which 5 to 100 pairs of Al _y Ga _1-y N single crystal layers (0 ≦ y ≦ 0.5) are repeatedly laminated can be applied. Further, under the electron transit layer 3, a high resistance buffer layer, for example, a carbon concentration of 1 × 10 ^{18 to} 3 × 10 ²⁰ atoms / cm ³ , specifically, 1 × 10 ^{18 to} 3 × 10 ¹⁸ atoms. / Cm ³ , when there is a GaN layer having a thickness of 100 nm or more, preferably about 100 to 200 nm, the vertical breakdown voltage improvement effect by this GaN layer and the vertical breakdown voltage improvement effect by the present invention are synergistically exhibited. preferable.

FIG. 1 shows a first layer 3 (electron traveling) having a composition of In _a1 Al _b1 Ga _c1 N (0 ≦ a1 ≦ 1, 0 ≦ b1 ≦ 1, 0 ≦ c1 ≦ 1, a1 + b1 + c1 = 1). Layer) and the first layer 3 have different band gaps, and In _a2 Al _b2 Ga _c2 N (0 ≦ a2 ≦ 1, 0 ≦ b2 ≦ 1, 0 ≦ c2 ≦ 1, a2 + b2 + c2 = 1) shows a structure in which the second layer 4 (electron supply layer) having the composition is laminated in this order.

Specifically, In _a1 Al _b1 Ga _c1 N (0 ≦ a1 ≦ 1, 0 ≦ b1 ≦ 1, 0 ≦ c1 ≦ 1, a1 + b1 + c1 = 1) constituting the electron transit layer is specifically InN, AlN , GaN, InAlN, InGaN, AlGaN, and InAlGaN. Of these nitrides, GaN, AlGaN, InGaN and the like are preferable, and GaN is more preferable. Note that the constituent elements of InAlN, InGaN, AlGaN, and InAlGaN may have various composition ratios.

Specifically, In _a2 Al _b2 Ga _c2 N (0 ≦ a2 ≦ 1, 0 ≦ b2 ≦ 1, 0 ≦ c2 ≦ 1, a2 + b2 + c2 = 1) constituting the electron supply layer includes InN, AlN , GaN, InAlN, InGaN, AlGaN, and InAlGaN. Of these nitrides, AlN, AlGaN, InGaN and the like are preferable, AlN and AlGaN are more preferable, and AlGaN is particularly preferable. Note that the constituent elements of InAlN, InGaN, AlGaN, and InAlGaN may have various composition ratios.

The thickness of the electron transit layer and the electron supply layer is not limited, but usually the electron transit layer is 10 nm or more, preferably 300 to 2500 nm, and the electron supply layer is 1 to 100 nm, preferably 10 to 100 nm.
Further, the allowable amount of impurities contained in the first layer 3 and the second layer 4 is not limited. The impurities are, for example, carbon, phosphorus, magnesium, silicon, iron, oxygen and hydrogen.

  Further, a spacer layer may be interposed between the electron transit layer and the electron supply layer. The spacer layer has a role of suppressing a decrease in mobility due to scattering of two-dimensional electrons formed at the interface with the electron transit layer and the electron supply layer by enhancing the confinement effect of the two-dimensional electrons. The spacer layer has a thickness of about several molecular layers and is formed using a material such as AlN having a large band gap.

The nitride semiconductor substrate Z of the present invention is formed on the second layer 4, and A _j B _1-j N (A is any group 13 element, B is any group 13 element or group 14 element, A ≠ B, including a third layer X having a composition of 0 <j <1).
The third layer X plays a role as a protective layer in a broad sense. In the present invention, in particular, the third layer X has a function of avoiding problems caused by exposure of the electron supply layer to the air atmosphere.

  In general, an insulating film such as SiN has been conventionally used as such a protective layer. However, when there is an insulating film on the electron supply layer, the mobility decreases when the electron concentration is increased. There was a trend.

The present inventors diligently studied the optimum material and structure for such a protective layer, and are basically insulators, but some of them have some conductivity and the conductivity. It has been found that a material having a structure with high crystallinity is suitable. Such a material has a composition of A _j B _1-j N (A is an arbitrary group 13 element, B is an arbitrary group 13 element or group 14 element, A ≠ B, 0 <j <1). is there.

As an example of A _j B _1-j N (A is an arbitrary group 13 element, B is an arbitrary group 13 element or group 14 element, A ≠ B, 0 <j <1) constituting the third layer X, A nitride having a combination in which A is arbitrarily selected from Ga, In, and Al and B is arbitrarily selected from Si and Ge. Among these, specific examples include GaSiN, GaGeN, and AlSiN, but GaSiN is more preferable. According to the present invention, the conventional SiN layer is expressed as A _j B _1-j N (A is a group 13 element, B is a group 14 element Si, A ≠ B, j = 0).

Since the third layer X has a composition of A _j B _1-j N, it retains the same degree of crystallinity as the second layer 4, which is an electron supply layer, rather than a simple insulating film. Therefore, the lattice mismatch at the interface between the second layer 4 and the third layer X is also small. This is because the deterioration of the electronic behavior at the interface can be suppressed as compared with the case where an insulating layer in which both the difference in resistance and the degree of lattice mismatch are large is formed.

In this regard, in the invention described in Japanese Patent Application Laid-Open No. 2015-177069, the first protective film is a silicon nitride film containing Ga as an impurity, and thus the present invention has a composition of A _j B _1-j N. Due to the structure, it can be said that a significant difference in effect is exhibited due to the above-described high crystallinity and stability at the interface.

The thickness of the third layer X is preferably 1 nm or more and 10 nm or less, and more preferably 5 nm or less.
As described above, the third layer X affects the behavior of electrons at the interface with the second layer 4. If the layer itself is too thick, the influence of stress due to the difference in lattice constant cannot be ignored. . However, if it is less than 1 nm, not only the effect of the present invention is not sufficiently obtained, but also the formation itself is difficult.

The effect of the present invention can be obtained if _{j in} A _j B _1-j N of the third layer X is at least 0.01 or more, and the effect is not impaired until 0.95. Preferably, j is 0.3 or more and 0.6.

  In the present invention, a cap layer C made of a group 13 nitride may be provided between the second layer 4 and the third layer X. FIG. 2 is a schematic cross-sectional view showing a preferred embodiment of the nitride semiconductor substrate of the present invention, that is, a structure further having a cap layer C on the second layer 4. For example, the effect of the present invention is not impaired if the cap layer has a thickness of about 1 to 3 nm and is not an insulating layer.

In a preferred embodiment of the present invention, the first layer 3 is GaN as an electron transit layer, and the second layer 4 is In _a2 Al _b2 Ga _c2 N (a2 = 0, 0 <b2 ≦ 1, 0 ≦ c2 <1, b2 + c2 = 1), the cap layer C is GaN, and the third layer X is Ga _j Si _1-j N (0 <j <1). In this case, it can be said that j is more preferably about 0.4 to 0.5.

  FIG. 3 is a schematic view schematically showing the form of the Ga composition ratio in the layer in another embodiment of the present invention. Thus, the SiN protective layer 6 may be formed on the third layer X. FIG. 4 is a schematic view schematically showing the form of the Ga composition ratio in the layer when the cap layer C is inserted, which is a preferred embodiment of the present invention.

  In one embodiment shown in FIG. 3, a mixed crystal nitride compound layer made of Ga and Si, which becomes the third layer X, is provided between the SiN protective film 6 and the second layer 4 (electron supply layer). Thus, it is possible to increase the electron concentration without causing a decrease in mobility, and as a result, it is possible to suppress sheet resistance. Furthermore, as in a preferred embodiment shown in FIG. 4, by providing a cap layer between the second layer 4 (electron supply layer) and the third layer X, the decrease in the Ga composition ratio is less, The effect of the present invention becomes remarkable.

  One aspect of the manufacturing method of the present invention includes a first step of successively laminating a first layer and a second layer using metal organic chemical vapor deposition (MOCVD), followed by a cap. A second step of forming a layer, a third step of supplying Ga source gas, Si source gas, and N source gas for a period of time exceeding 0 seconds and not exceeding 3 seconds immediately after completion of the second step, After the step, there is provided a fourth step of stopping the supply of the Ga source gas and supplying only the Si source gas and the N source gas.

  That is, in the present invention, in particular, in the third step and the fourth step, the source gas of the element A (eg, Ga) in the third layer X is changed to the element B (eg, By supplying together with the source gas of Si) and the nitrogen source gas, a structure having the effect of the present invention can be obtained.

In the MOCVD method, crystal growth occurs with a time lag after the supply of the source gas is stopped. In the present invention, the supply time of the source gas of the element A is suppressed to 3 seconds or less at the longest, thereby forming Ga _j Si _1-j N thin on the second layer 4 and having j of 0.01 or more. It becomes possible to do.

Formation of Ga _j Si _1-j N having a thin thickness and j of 0.01 or more is possible by, for example, molecular beam epitaxy (MBE), but MBE is an MOCVD method. Compared with the case where the first layer 3 and the second layer 4 are produced, the production efficiency is remarkably poor.

  As described above, the nitride semiconductor substrate of the present invention can increase the electron concentration without reducing the mobility by adding Ga to the silicon nitride film, thereby suppressing the sheet resistance. It becomes possible. Therefore, the nitride semiconductor substrate of the present invention is suitable as a nitride semiconductor substrate for HEMT having more excellent electrical characteristics.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not restrict | limited by the following Example.

[Common experimental conditions]
A silicon single crystal substrate having a diameter of 6 inches, a thickness of 675 μm, a p-type, a specific resistance of 0.002 Ωcm, and a plane orientation (111) was prepared. After this is cleaned by a known substrate cleaning method, it is set in an MOCVD apparatus, the temperature is raised, the inside of the apparatus is replaced with a carrier gas, and then heat treatment is performed at 1000 ° C. for 15 minutes in a 100% hydrogen atmosphere. The natural oxide film on the single crystal surface was removed.

Next, trimethylaluminum (TMA) and ammonia (NH ₃ ) were used as source gases, and an initial layer made of an AlN single crystal having a thickness of 70 nm was vapor-phase grown at a growth temperature of 1000 ° C.

On the initial layer, trimethylgallium (TMG), TMA, and NH ₃ are used as source gases, and an Al _0.1 Ga _0.9 N single layer having a carbon concentration of 5 × 10 ¹⁹ atoms / cm ³ and a thickness of 300 nm is vapor-phase grown. It was. Next, at a carbon concentration of 5 × 10 ¹⁹ atoms / cm ³ , an AlN thin layer having a thickness of 5 nm and an Al _0.1 Ga _0.9 N thin layer having a thickness of 30 nm were alternately formed to form a laminate of 8 layers. Then, an Al _0.1 Ga _0.9 N single layer having a carbon concentration of 5 × 10 ¹⁹ atoms / cm ³ was grown to a thickness of 125 nm. The laminate and single layer were repeated four more times in order. Further, a GaN single layer having a carbon concentration of 1 × 10 ¹⁸ atoms / cm ³ and a thickness of 500 nm was stacked, and a series of buffer layers including an initial layer of an Al _0.1 Ga _0.9 N single layer having a thickness of 300 nm was formed. After that, a GaN single layer having a carbon concentration of 1 × 10 ¹⁶ atoms / cm ³ and a thickness of 700 nm is stacked in the same manner as an electron transit layer, and then Al _x Ga _1-x N (x = 1) is 2 nm as an electron supply layer. A film was formed. After the formation of the initial layer, the buffer layer, the electron transit layer, and the electron supply layer were all formed by making fine adjustments in the range of 1 to 15 ° C. with a growth temperature of 1000 ° C. as a reference.

[Example 1]
On the electron supply layer, a GaN layer having a thickness of 1 nm and a third layer having a thickness of 4 nm were formed as a cap layer. In the formation of the third layer, silane (SiH ₄ ), NH ₃ and TMGa are supplied simultaneously for 3 seconds, then only the supply of TMGa is stopped, and SiH ₄ and NH ₃ are supplied for 5 seconds, and Ga _j A Si _1-j N (0 <j <1) layer was formed. The thickness of Ga _j Si _1-j N was about 1 nm, and the j value was about 0.5.

[Comparative Example 1]
TMGa was not supplied, and a cap layer was formed and a SiN layer was formed at a thickness of about 4 nm in the same manner as in Example 1 except that the film formation time of the third layer was adjusted.

[Evaluation]
For the nitride semiconductor substrates of Example 1 and Comparative Example 1, mobility and carrier concentration were evaluated. That is, electrodes were formed on the surfaces of these nitride semiconductor substrates, and the Hall effect was measured. The Hall effect was measured using the Van der Pauw method, and the measuring apparatus was an ACCENT HL5500PC. Moreover, sheet resistance was also measured using this electrode.
The results are shown below.

  From Table 1, the mobility is 1250 sq. In both Example 1 and Comparative Example 1. In the nitride semiconductor substrate of Comparative Example 1, the carrier concentration was 0.92E + 13 / sq. In contrast, in the nitride semiconductor substrate of Example 1, the carrier concentration is 1.45E + 13 / sq. cm. Accordingly, the sheet resistance is 544 Ohm / sq. In Example 1, 345 Ohm / sq. It became.

  From this, it can be seen that the nitride semiconductor substrate of the present invention has improved electron density while having mobility equivalent to that of the conventional spacer layer structure.

DESCRIPTION OF SYMBOLS 1 Base substrate 2 Buffer layer 3 1st layer (electron transit layer)
4 Second layer (electron supply layer)
X Third layer 5 Electrode 6 SiN protective film C Cap layer

Claims (4)

A first layer having a composition of In _a1 Al _b1 Ga _c1 N (0 ≦ a1 ≦ 1, 0 ≦ b1 ≦ 1, 0 ≦ c1 ≦ 1, a1 + b1 + c1 = 1);
Formed on the first layer and having a composition of In _a2 Al _b2 Ga _c2 N (0 ≦ a2 ≦ 1, 0 ≦ b2 ≦ 1, 0 ≦ c2 ≦ 1, a2 + b2 + c2 = 1), And a second layer having a band gap different from that of the first layer;
A third layer formed on the second layer and having a composition of A _j B _1-j N (A is a group 13 element, B is a group 13 element or group 14 element, A ≠ B, 0 <j <1). And a nitride semiconductor substrate characterized by comprising:   The nitride semiconductor substrate according to claim 1, further comprising a cap layer made of a group 13 nitride between the second layer and the third layer. The first layer is an electron transit layer made of GaN;
The second layer is an electron supply layer having a composition of In _a2 Al _b2 Ga _c2 N (a2 = 0, 0 <b2 ≦ 1, 0 ≦ c2 <1, b2 + c2 = 1);
The cap layer is a GaN layer;
The nitride semiconductor substrate according to claim 2, wherein the third layer is a Ga _j Si _1-j N (0 <j <1) layer. As the first layer, a GaN layer that is an electron transit layer,
As the second layer, an In _a2 Al _b2 Ga _c2 N (a2 = 0, 0 <b2 ≦ 1, 0 ≦ c2 <1, b2 + c2 = 1) layer which is an electron supply layer;
A GaN layer as a cap layer;
A third layer having a Ga _j Si _1-j N (0 <j <1) layer in this order, and producing a nitride semiconductor substrate by metal organic vapor phase epitaxy,
After laminating the first layer, a first step of continuously laminating a second layer on the first layer;
A second step of forming a cap layer on the second layer after the first step;
Immediately after the end of the second step, the Ga source gas, the Si source gas, and the N source gas are supplied in a time of 3 seconds or less, and the third step of stacking the third layer;
After the third step, the fourth step of stopping the supply of the Ga source gas and supplying the Si source gas and the N source gas;
A method for producing a nitride semiconductor substrate, comprising:

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