JP2013033887A - Nitride semiconductor substrate manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor substrate manufacturing method which simply and effectively reduces a decrease in breakdown voltage of a nitride semiconductor.SOLUTION: A nitride semiconductor substrate manufacturing method comprises: a process of forming a silicon nitride layer on one principal surface of a silicon single crystal substrate; a process of forming an intermediate layer composed of a nitride semiconductor on the silicon nitride layer; and a process of forming an active layer composed of a nitride semiconductor on the intermediate layer. The process of forming the silicon nitride layer includes: a first step of raising a temperature from a room temperature to an achieving temperature of 900°C or higher to 1000°C or lower in a gas atmosphere containing a nitrogen gas of 90 vol% or more to 100 vol% or less and the rest containing an inert gas other than the nitrogen gas; a second step of keeping the gas atmosphere and the achieving temperature for a predetermined time; and a third step of changing the gas atmosphere to a reducing gas containing atmosphere and keeping the reducing gas containing atmosphere for a predetermined time.

Description

The present invention relates to a method for manufacturing a nitride semiconductor substrate used for a nitride semiconductor for electronic devices.

Forming a nitride semiconductor on a silicon single crystal substrate, which is said to be advantageous for increasing the diameter and cost, as an example of a method for manufacturing a nitride semiconductor such as gallium nitride (GaN), which is expected as a next-generation electronic device material There are several methods for manufacturing the same.

Japanese Patent Application Laid-Open No. 2004-228561 discloses a method for manufacturing a nitride semiconductor device including a substrate, an AlN-based superlattice buffer layer formed on the substrate, and a nitride semiconductor layer formed on the AlN-based superlattice buffer layer. Forming a first buffer layer having a composition of Al _x Ga _1-x N (0.5 ≦ x ≦ 1) on the substrate; and on the first buffer layer. Forming a second buffer layer having a composition of Al _y Ga _1-y N (0.01 ≦ y ≦ 0.2), forming the first buffer layer, and the second buffer And a step of forming the AlN-based superlattice buffer layer by alternately repeating the step of forming the layer, and an invention of a method of manufacturing a nitride semiconductor device, comprising:

Patent Document 2 discloses a step of forming an insulating film on a single crystal silicon substrate, a step of forming a gallium nitride-based compound semiconductor layer on the insulating film to form a buffer layer, and gallium nitride on the buffer layer. A step of sequentially laminating a lower clad layer, an active layer, an upper clad layer and a cap layer made of a compound compound semiconductor, a step of etching perpendicularly to the single crystal silicon substrate to expose the buffer layer, the cap layer and the etching An invention of a method for producing a semiconductor light-emitting device comprising a step of forming an electrode on the buffer layer exposed by the above and a step of separating the chip by dicing or cleaving is disclosed.

JP 2007-067077 A JP-A-8-64913

Patent Document 1 discloses that in a step of forming a first buffer layer having a composition of Al _x Ga _1-x N (0.5 ≦ x ≦ 1) on a silicon substrate, a source gas such as ammonia or hydrogen The silicon substrate surface is etched by the carrier gas, and unevenness is generated on the silicon substrate surface.

However, if a new nitride film is formed in the presence of the irregularities, defects due to the irregularities occur in the nitride film, and an electrode with a wide area on the order of mm is formed on the nitride semiconductor surface. When formed, dielectric breakdown defects frequently occur due to a decrease in dielectric breakdown voltage.

Therefore, when a nitride semiconductor layer is formed on a silicon substrate, a technique of forming a silicon nitride film on the silicon substrate is known. According to this method, a nitride semiconductor is formed by a relatively simple method. It is said that the occurrence of dislocation to the layer can be suppressed and the flatness can be improved.

In Patent Document 2, heat treatment is performed in a nitrogen atmosphere at 500 to 900 ° C., the surface on the single crystal silicon substrate is nitrided, an Si ₃ N ₄ insulating film is formed to a thickness of 1 to 5 nm, and a vapor phase is formed thereon. A manufacturing method of a semiconductor light emitting device is disclosed in which each layer made of a nitride semiconductor is formed by a growth method.

However, the technique disclosed in Patent Document 2 does not specifically disclose the detailed holding time and the type of gas in the holding atmosphere when forming a silicon nitride film on silicon. For this reason, it has been difficult to effectively reduce the dielectric breakdown voltage drop when an electrode having a wide area on the order of mm is formed on the nitride semiconductor surface.

In view of these problems, the present invention can easily and effectively reduce the dielectric breakdown voltage drop of a nitride semiconductor layer caused by unevenness generated when nitride is deposited on a silicon single crystal substrate. Provided is a method for manufacturing a nitride semiconductor substrate.

The method for manufacturing a nitride semiconductor substrate according to the present invention includes a step of forming a silicon nitride layer on one main surface of a silicon single crystal substrate, and a step of forming an intermediate layer made of a nitride semiconductor on the silicon nitride layer. Forming an active layer made of a nitride semiconductor on the intermediate layer, wherein the step of forming the silicon nitride layer includes nitrogen gas of 90 vol% or more and 100 vol% In the following, the remainder is a first step of raising the temperature from room temperature to an ultimate temperature of 900 ° C. to 1000 ° C. in a gas atmosphere composed of an inert gas other than the nitrogen gas, and the gas atmosphere and the ultimate temperature for a predetermined time. It is characterized by comprising the second step of holding and the third step of switching to the reducing gas-containing atmosphere and holding it for a predetermined time.

Thereby, the nitride semiconductor substrate in which the dielectric breakdown voltage drop is reduced can be manufactured easily and effectively.

In the method for manufacturing a nitride semiconductor substrate according to the present invention, it is desirable that the reducing gas-containing atmosphere in the third step is 30 vol% or more and 70 vol% or less of the reducing gas, and the balance is made of an inert gas.

According to the present invention, it is possible to easily and effectively reduce the breakdown voltage drop of a nitride semiconductor layer caused by unevenness generated when depositing nitride on a silicon single crystal substrate. It becomes possible. In particular, when an electrode having a large area is formed in the nitride semiconductor layer, a more remarkable effect is exhibited.

It is a conceptual diagram when the structure of the nitride semiconductor substrate produced with the manufacturing method of the nitride semiconductor substrate which concerns on this invention is seen from a cross-sectional direction. It is a schematic diagram showing an average thickness of a thin film layer made of silicon nitride and a maximum height difference of surface irregularities of the thin film layer of the nitride semiconductor substrate manufactured by the method for manufacturing a nitride semiconductor substrate according to the present invention.

The present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram of a structure of a nitride semiconductor substrate manufactured by the method for manufacturing a nitride semiconductor substrate according to the present invention as viewed from a cross-sectional direction.

The present invention includes a step of forming a silicon nitride layer 2 on one main surface of a silicon single crystal substrate 1, a step of forming an intermediate layer 3 made of a nitride semiconductor on the silicon nitride layer 2, A method of manufacturing a nitride semiconductor substrate W including a step of forming an active layer 4 made of a nitride semiconductor, wherein the step of forming the silicon nitride layer 2 includes nitrogen gas of 90 vol% or more and 100 vol% or less, and the remainder A first step of raising the temperature from room temperature to an ultimate temperature of 900 ° C. to 1000 ° C. in a gas atmosphere composed of an inert gas other than the nitrogen gas; and a second step of maintaining the gas atmosphere and the ultimate temperature for a predetermined time. And a third step of switching to a reducing gas-containing atmosphere and holding for a predetermined time.

A widely known manufacturing method can be applied to the method for manufacturing the nitride semiconductor substrate W, but a metal organic chemical vapor deposition (MOCVD) method is preferable in terms of excellent film formation controllability and ease of handling. Hereinafter, description will be made according to the manufacturing process by the MOCVD method.

First, the silicon single crystal substrate 1 is set in an MOCVD apparatus. At this time, the surface of the silicon single crystal substrate 1 is preferably in a state where no natural oxide film or organic matter remains. For this reason, a known semiconductor substrate cleaning method may be applied to the silicon single crystal substrate 1 in advance before setting the MOCVD apparatus.

The silicon single crystal substrate 1 becomes a base substrate in the nitride semiconductor substrate W. The aperture, thickness, resistance, dopant type, surface orientation, surface finish state of front and back surfaces, defect density, oxygen concentration, etc. may be set as appropriate according to the specifications of the nitride semiconductor substrate W to be designed. . Examples of the method for manufacturing the silicon single crystal substrate 1 include a Czochralski (CZ) method, a floating zone (FZ) method, and a bonding method.

Next, a step of forming the silicon nitride layer 2 is performed. First, as a first step, the temperature is raised from room temperature to an ultimate temperature of 900 ° C. or higher and 1000 ° C. or lower in a gas atmosphere composed of 90 vol% or more and 100 vol% or less of the nitrogen gas and an inert gas other than the nitrogen gas.

The processing atmosphere of the silicon single crystal substrate 1 set in the MOCVD apparatus is switched from the air atmosphere to the nitrogen atmosphere. The switching timing may be at room temperature or during the temperature increase. In the latter case, it is preferable that the replacement with the nitrogen atmosphere is completed before reaching 600 ° C. This is because oxygen and moisture remaining in the reaction chamber react actively with silicon due to the high temperature, and there is a concern that the formation of the silicon nitride layer 2 in the next step may be adversely affected.

As for gas atmosphere, it is desirable for nitrogen gas to be 90 vol% or more and 100 vol% or less, and the remainder to consist of inert gas other than the said nitrogen gas. If the nitrogen gas is less than 90 vol%, the silicon nitride layer 2 may not be formed with a uniform thickness and high quality in the next step. The nitrogen gas concentration is preferably 98 vol% or more, more preferably 100 vol%.

The nitrogen gas is preferably, for example, a high-purity nitrogen gas for semiconductor production having a purity of 99.999% or higher. In addition, the inert gas is preferable as the remainder other than the nitrogen gas when the nitrogen gas concentration is less than 100%, and examples thereof include argon, xenon, and krypton.

Next, the silicon single crystal substrate 1 set in the MOCVD apparatus is heated from room temperature to an ultimate temperature of 900 ° C. to 1000 ° C. At this time, the surface layer portion of the silicon single crystal substrate 1 is nitrided in a nitrogen atmosphere to form the silicon nitride layer 2.

The room temperature is not strictly defined but is in the range of 5 ° C. or more and 35 ° C. or less.

The ultimate temperature is in the range of 900 ° C. or higher and 1000 ° C. or lower, preferably 950 ° C. or higher and 1000 ° C. or lower.

When the ultimate temperature is less than 900 ° C., the required generation of silicon nitride constituting the silicon nitride layer 2 may be insufficient. When the temperature exceeds 1000 ° C., the growth rate becomes unnecessarily high, and silicon nitride is not formed evenly in the planar direction on one main surface of the silicon single crystal substrate 1, and as a result, the silicon nitride layer 2 is not formed. There is a concern that the maximum height difference of the surface irregularities increases.

The surface unevenness of the silicon nitride layer 2 and the maximum height difference thereof will be described with reference to FIG.

Here, it is desirable to spend 10 minutes or more and 200 minutes or less for raising the temperature. Within this range, the silicon atoms and nitrogen molecules in the surface layer portion of the silicon single crystal substrate 1 react with each other, so that the growth rate of silicon nitride is extremely slow, and extremely large surface irregularities are not easily generated.

If the temperature rising time is less than 10 minutes, the temperature rising speed is too high, and the silicon nitride layer 2 is not easily formed with a uniform film thickness on the entire surface of the silicon single crystal substrate 1. As a result, the layer thickness uniformity is reduced. When the temperature rising time is 200 minutes or more, the average thickness of the silicon nitride layer 2 hardly increases in the temperature range of the present invention, which leads to a process loss in the manufacturing process.

Subsequently, the process proceeds to the second step in which the gas atmosphere and the ultimate temperature in the first step are maintained for a predetermined time. This second step is a so-called layer thickness in which the silicon nitride layer 2 generated at a slow growth rate in the temperature raising process is maintained for a sufficient time as necessary so that the silicon nitride layer 2 has a uniform thickness on the silicon single crystal substrate 1. It has the role of equalization.

The holding time of the second step is desirably 1 minute or more and 10 minutes or less. If it is less than 1 minute, the effect of equalizing the layer thickness cannot be sufficiently obtained. If it exceeds 10 minutes, the maximum height difference T2 of the surface irregularities of the silicon nitride layer 2 may increase in the process of forming the silicon nitride layer 2.

Subsequent to the second step, a third step is performed in which the atmosphere is changed to a reducing gas-containing atmosphere and held for a predetermined time. The presence of the reducing gas causes an action of promoting the movement of silicon nitride molecules so as to fill the surface irregularities of the silicon nitride layer 2.

Therefore, the surface layer unevenness is further reduced as compared with the case of forming silicon nitride only in the second step. Further, since the film thickness does not increase more than necessary, the crystal plane orientation information of the silicon single crystal substrate 1 is more accurately transmitted to the nitride semiconductor formed above.

In the reducing gas-containing atmosphere, it is desirable that the reducing gas is 30 vol% or more and 70 vol% or less and the balance is an inert gas. If the reducing gas is less than 30 vol%, there is a concern that the action of promoting the movement of silicon nitride molecules is not sufficiently exhibited due to the lack of reducing gas. On the other hand, when the reducing gas exceeds 70 vol%, the reducing gas becomes excessive, the action of promoting the movement of silicon nitride molecules becomes excessive, and there is a concern that the surface irregularities become large.

The reducing gas is preferably hydrogen because a high-purity product is easily available and handling is well known. For example, high-purity hydrogen gas for semiconductor production having a purity of 99.999% or more can be given. Examples of the inert gas include nitrogen gas, argon, xenon, and krypton.

The holding time in the third step is desirably 1 minute or more and 10 minutes or less. If it is less than 1 minute, uniform film formation is not performed, and if it exceeds 10 minutes, there is a concern about increase in surface irregularities due to the thick film thickness.

Further, the holding temperature in the reducing gas-containing atmosphere may be implemented after changing the temperature within the range of ± 50 ° C. from the temperature reached in the first step. This is because, within this range, the holding effect in the mixed gas atmosphere of the present invention is not likely to be significantly impaired.

Subsequently, at least one intermediate layer 3 made of a nitride semiconductor is formed on one main surface of the silicon single crystal substrate 1 for which the third step has been completed by a vapor deposition method. Then, at least one active layer 4 made of a nitride semiconductor layer is formed on the intermediate layer 3. Here, a nitride semiconductor layer having an arbitrary composition, thickness, and number of layers may be formed in accordance with the specifications of the device to be designed.

A nitride semiconductor substrate W manufactured by the method for manufacturing a nitride semiconductor substrate according to the present invention has a silicon nitride layer 2 formed on one main surface of a silicon single crystal substrate 1, as shown in FIG. Includes an intermediate layer 3 made of at least one nitride semiconductor and an active layer 4 made of at least one nitride semiconductor on the intermediate layer 3. For the intermediate layer 3 and the active layer 4, a well-known configuration of a nitride semiconductor substrate can be applied according to the purpose and specification of the product to be manufactured.

The silicon nitride layer 2 suppresses the occurrence of minute surface irregularities that occur when a nitride semiconductor layer is formed on the main surface of the silicon single crystal substrate 1 by means such as vapor phase growth. If the surface irregularities are large, the breakdown voltage of the nitride semiconductor substrate W is lowered.

The average thickness T1 of the silicon nitride layer 2 is desirably 1 nm or more and 3 nm or less. If it is 1 nm or less, the effect of suppressing the occurrence of surface irregularities is insufficient. However, if the thickness exceeds 3 nm, the crystal information of the silicon single crystal substrate 1 is not accurately propagated to the intermediate layer 3 and the active layer 4, and there is a concern that the crystallinity of the intermediate layer 3 and the active layer 4 is impaired.

The maximum height difference T2 of the surface irregularities of the silicon nitride layer 2 is desirably 0.3 nm or less. In consideration of the fact that a completely flat silicon nitride layer is ideal, but it is difficult to realize it in practice, if the silicon nitride has a single molecular diameter in practical use, the intermediate layer 3 formed thereon is flat. It is assumed that there is no problem in ensuring safety. Still, if T2 exceeds 0.3 nm, the dielectric breakdown voltage may decrease significantly.

Note that the maximum height difference T2 of the surface unevenness of the silicon nitride layer 2 is very sensitive to the dielectric breakdown voltage even though the absolute value is very small as the surface unevenness of around 0.3 nm. Considering this point, the nitride semiconductor substrate W of the present invention is designed with the thickness of the silicon nitride layer 2 and the surface irregularities being kept low.

As described above, according to the method for manufacturing a nitride semiconductor substrate according to the present invention, the dielectric breakdown voltage of the nitride semiconductor layer caused by surface irregularities generated when the nitride semiconductor is deposited on the silicon single crystal substrate. It is possible to suppress the decrease easily and effectively.

Hereinafter, preferred embodiments of the present invention will be described based on examples, but the present invention is not limited to these examples.

[Example 1]
An N-type silicon single crystal substrate 1 having a plane orientation (111), a diameter of 4 inches, a thickness of 625 μm, and a specific resistance of 25 Ωcm, prepared by the CZ method, is prepared. The intermediate layer 3 and the active layer 4 were laminated by the MOCVD method to produce a nitride semiconductor substrate for evaluation.

First, the silicon single crystal substrate 1 was set in a MOCVD apparatus at room temperature and replaced with 100% nitrogen gas. Then, the temperature was increased to 950 ° C. over 30 minutes at a constant temperature increase rate, and 950 ° C. Held for 5 minutes. The nitrogen gas flow rate at this time was 6 liters / minute.

Subsequently, after replacing the nitrogen gas 100% with a mixed gas atmosphere of nitrogen gas 50 vol% and hydrogen gas 50 vol%, the temperature was kept as it was for 5 minutes. Thus, the silicon nitride layer 2 was formed on one main surface of the silicon single crystal substrate 1.

Next, the intermediate layer 3 was formed on the silicon nitride layer 2 with the following contents. Trimethylaluminum (TMA) and ammonia (NH ₃ ) were used as raw materials, and an AlN single crystal layer having a thickness of 5 nm was stacked by vapor phase growth at 1000 ° C. Subsequently, a GaN single crystal layer having a thickness of 20 nm was laminated by vapor phase growth at 1000 ° C. using trimethylgallium (TMG), TMA, and NH ₃ . The AlN single crystal layer and the GaN single crystal layer were alternately repeated in the same process to form a multilayer buffer region with the number of stacked layers set to 50. The multilayer buffer region thus formed was used as the intermediate layer 3.

A GaN single crystal layer having a thickness of 2000 nm was stacked on the intermediate layer 3 by vapor phase growth at 1000 ° C. using TMG and NH ₃ as raw materials. This was designated as active layer 4.

The nitride semiconductor substrate for evaluation of Example 1 was manufactured through the above steps. Note that the thickness of each layer formed by vapor phase growth was adjusted by adjusting the gas flow rate and the supply time.

At one central point of the nitride semiconductor substrate for evaluation of Example 1, immediately after the formation of the silicon nitride layer 2, the average thickness T1 of the silicon nitride layer 2 was measured using ellipsometry.

Here, the average thickness of the silicon nitride layer 2 corresponds to T1 in FIG. 2, and the maximum height difference of the surface irregularities of the silicon nitride layer 2 corresponds to T2 in FIG. As a method for measuring and evaluating T1 and T2, a method of cleaving the nitride semiconductor substrate W in the diameter direction and measuring the cross section with an atomic force microscope (AFM) can be suitably used. The evaluation example is shown below.

A strip-shaped sample having a width of 1 mm in the radial direction is cleaved and cut out from a region including the center point of the main surface of the nitride semiconductor substrate W. Then, the cross section of the sample is observed with an AFM, and the distance in the cross sectional direction of the silicon nitride layer 2 existing at the interface between the silicon single crystal substrate 1 and the intermediate layer 3 is measured.

The measurement location is a location where the measurement location 1 mm width is equally divided into five. The AFM observation range T3 at this time ranges from 500 nm to 2000 nm in the radial direction. In addition, you may change this measurement location, a division | segmentation pitch, and a measurement range timely according to a measurement precision, a sample state, and evaluation specification.

In the AFM observation range T3, a line L1 is drawn at the boundary between the silicon single crystal substrate 1 and the thin film layer 2. Then, in the vicinity of the boundary between the silicon nitride layer 2 and the intermediate layer 3, a line L2 in which surface irregularities are averaged is drawn within a range that can be visually observed. The distance T1 between L1 and L2 obtained in this way is defined as the average thickness of the silicon nitride layer 2 at the central portion and the outer peripheral portion.

Alternatively, the average thickness T1 of the silicon nitride layer 2 may be evaluated by an in-line film thickness measuring device, preferably ellipsometry, in-line with the MOCVD apparatus immediately after the thin film layer 2 is formed.

Further, within the AFM observation range T3, a portion where the thickness of the silicon nitride layer 2 is the maximum and a portion where the thickness is minimum is selected within the limit to be observed, and virtual lines L3 and L4 parallel to L1 are shown in FIG. Set to. Then, among the distance T2 between L3 and L4, the maximum value within the AFM observation range T3 is defined as the maximum height difference of the surface irregularities of the silicon nitride layer 2.

A plurality of arbitrary locations other than the region including the center point of the main surface of the nitride semiconductor substrate W may be selected as the location where the sample is cut out.

From the central point of the nitride semiconductor substrate for evaluation of Example 1, a slice with a width of 1 mm square was cut out, and a section of 2000 nm of the slice of an arbitrary side was observed with AFM, and the maximum surface roughness of the silicon nitride layer 2 was observed. The height difference T2 was measured.

On one main surface of the nitride semiconductor substrate for evaluation, an Au electrode foil having a diameter of 2 mm was deposited on the cross line passing through the center point, one in the center and two in each length and width at a pitch of 3 mm, for a total of nine. . Between the back surface of the nitride semiconductor substrate for evaluation and each electrode foil, a 600 V electric field was applied using a commercially available probe device and a device having an electric field application and measurement circuit to confirm the presence or absence of dielectric breakdown. .

In Example 1, the average thickness T1 was 1.5 nm, and the maximum height difference T2 of the surface irregularities was 0.2 nm. That is, the surface unevenness was reduced by the additional heat treatment containing the reducing gas. Further, no breakdown failure occurred in all nine electrodes.

[Comparative Example 1]
A comparative nitride semiconductor substrate was prepared and evaluated in the same manner as in Example 1 except that the silicon nitride layer 2 was not formed.

As for the nitride semiconductor substrate for evaluation of Comparative Example 1, 8 out of 9 electrodes showed a breakdown failure. From this, it was confirmed that the effect of the silicon nitride layer 2 appeared remarkably.

[Comparative Example 2]
The nitride semiconductor substrate for evaluation, which was prepared and evaluated in the same manner as in Example 1 except that the third step was omitted, was used as Comparative Example 2.

In the nitride semiconductor substrate for evaluation of Comparative Example 2, a breakdown failure occurred with five electrodes. Further, the average thickness T1 was 1.8 nm, the maximum height difference T2 of the surface layer unevenness was 0.3 nm, and the surface layer unevenness was larger than that of Example 1.

[Examples 2 to 9, Comparative Examples 3 to 5] The production conditions were changed in accordance with the contents of Table 1, and other production conditions and evaluation methods were the same as in Example 1.

From Table 1, when the implementation range of the present invention is outside the range, the number of occurrences of dielectric breakdown failure is 5 or more out of 9, or the film thickness uniformity of the silicon nitride layer 2 is decreased and the unevenness is increased. It was inferior to the scope of the invention.

Further, if the concentration of the reducing gas in the third step is outside the more preferable range of the present invention, the number of occurrences of dielectric breakdown defects is 2 out of 9 sheets, which is better than outside the implementation range of the present invention. It was a little inferior.

The present invention is suitable as a nitride semiconductor substrate used for a light emitting diode, a laser light emitting element, an electronic element operable at high speed and high temperature, and the like. Further, it can be applied to a method for improving the flatness of a substrate in heteroepitaxial growth of various materials.

W nitride semiconductor substrate 1 silicon single crystal substrate 2 silicon nitride layer 3 intermediate layer 4 made of nitride semiconductor active layer L1 made of nitride semiconductor boundary line L2 between silicon single crystal substrate 1 and thin film layer 2 unevenness of thin film layer 2 Averaged line L3 Virtual line L4 parallel to L1 hypothesized at the point where the thickness of the thin film layer 2 is maximum The hypothetical line T1 parallel to L1 hypothesized at the point where the thickness of the thin film layer 2 is minimum Average of the thin film layer 2 Thickness T2 Maximum height difference of surface irregularities of thin film layer 2 T3 AFM observation range

Claims (2)

Forming a silicon nitride layer on one principal surface of the silicon single crystal substrate;
Forming an intermediate layer made of a nitride semiconductor on the silicon nitride layer;
Forming an active layer made of a nitride semiconductor on the intermediate layer;
A method for producing a nitride semiconductor substrate comprising:
The step of forming the silicon nitride layer includes:
A first step in which the temperature of the nitrogen gas is 90 vol% or more and 100 vol% or less and the balance is raised from room temperature to an ultimate temperature of 900 ° C or more and 1000 ° C or less in a gas atmosphere composed of an inert gas other than the nitrogen gas;
A second step of maintaining the gas atmosphere and the ultimate temperature for a predetermined time;
A third step of switching to a reducing gas-containing atmosphere and holding for a predetermined time;
A method for producing a nitride semiconductor substrate comprising: 2. The method for manufacturing a nitride semiconductor substrate according to claim 1, wherein the reducing gas-containing atmosphere in the third step is 30 vol% or more and 70 vol% or less of the reducing gas, and the balance is made of an inert gas.