WO2024004576A1

WO2024004576A1 - Group iii nitride substrate and manufacturing method thereof

Info

Publication number: WO2024004576A1
Application number: PCT/JP2023/021470
Authority: WO
Inventors: 勇介森; 政志吉村; 正幸今西; 茂佳宇佐美; 淳一滝野; 雄大旭
Original assignee: パナソニックホールディングス株式会社
Priority date: 2022-06-28
Filing date: 2023-06-09
Publication date: 2024-01-04

Abstract

A group III nitride substrate that comprises a GaN epitaxial layer formed on a GaN substrate and contains oxygen as an impurity element, wherein: the polished surface of the c-plane of the group III nitride substrate includes at least one first region exhibiting a first impurity concentration and a second region exhibiting a second impurity concentration that is lower than the first impurity concentration; the first dislocation density in the first region is lower than the second dislocation density in the second region; and the root mean square surface roughness (RMS) in any 0.2 mm square area within the surface of the group III nitride substrate is 10 nm or less.

Description

Group III nitride substrate and method for manufacturing the same

The present disclosure relates to a group III nitride substrate and a method for manufacturing the same.

Vertical GaN power devices require GaN substrates with low resistance and low dislocation density. For example, when manufacturing an n-type low-resistance GaN substrate, crystal growth has been performed while forming pits to improve the carrier concentration and reduce the dislocation density (for example, see Patent Document 1). ).

JP 2021-50107 Publication

A group III nitride substrate according to one aspect of the present disclosure is a group III nitride substrate including a GaN epitaxial layer formed on a GaN substrate, and includes oxygen as an impurity element, and the c-plane of the group III nitride substrate. at least one first region exhibiting a first impurity concentration and a second region exhibiting a second impurity concentration lower than the first impurity concentration in the polished surface; The first dislocation density of is lower than the second dislocation density of the second region, and the root mean square surface roughness RMS value is 10 nm or less in an arbitrary 0.2 mm square range within the surface of the group III nitride substrate. .

A method for manufacturing a group III nitride substrate according to one aspect of the present disclosure includes the steps of preparing a seed substrate, supplying a group III element oxide gas and a nitrogen element-containing gas, and disposing a group III nitride substrate on the seed substrate. a step of growing a group III nitride crystal, and a step of polishing the group III nitride crystal so that the root mean square surface roughness RMS value is 10 nm or less in an arbitrary 0.2 mm square range within the plane of the group III nitride crystal. and, including.

FIG. 2 is a diagram showing a surface AFM image of a GaN substrate after surface CMP, which was fabricated by an OVPE method. They are (a) a surface optical microscope image and (b) a surface SIMS mapping image of the same location of a GaN substrate after surface CMP produced by the OVPE method. 1 is a flowchart showing a time-series manufacturing method of a group III nitride crystal according to an embodiment of the present disclosure. 2 is a flowchart showing each functional unit as a process from upstream to downstream in a manufacturing apparatus used in a method for manufacturing a group III nitride crystal according to an embodiment of the present disclosure. 1 is a schematic diagram of a manufacturing apparatus used for manufacturing a group III nitride crystal according to an embodiment of the present disclosure. FIG. 3 is a conceptual diagram of a group III nitride crystal grown on a seed substrate before and after slicing. FIG. 3 is a diagram showing the relationship between the double average surface roughness RMS of an OVPE GaN substrate before growth by the MOVPE method and the pit density of the GaN growth layer grown by the MOVPE method. It is a figure which shows the relationship between the CMP time and double average surface roughness RMS of the GaN substrate surface (Ga surface) made from OVPE. This is a photoluminescence image (PL image) of the surface (Ga surface) of the OVPE GaN substrate when the CMP time is 60 minutes.

The planes that form pits (growth pits) exposed by crystal growth are composed of m-plane components and a-plane components, and impurity concentrations such as oxygen and carrier concentrations differ depending on each plane. Therefore, in the polishing step for smoothing the surface, there was a difference in polishing rate within the surface due to the difference in impurity concentration and the difference in carrier concentration between each growth surface. Differences in polishing speeds create irregularities on the surface. The surface unevenness causes deterioration of surface morphology and appearance of pits when a device layer is formed on the substrate surface using a subsequent MOVPE method or the like.

The present disclosure aims to provide a group III nitride substrate with good surface flatness while satisfying high carrier concentration, low resistance, and low dislocation density.

The group III nitride substrate according to the first aspect is a group III nitride substrate consisting of a GaN epitaxial layer formed on a GaN substrate, contains oxygen as an impurity element, and has a structure in which the c-plane of the group III nitride substrate is in the polished surface, at least one first region exhibiting a first impurity concentration and a second region exhibiting a second impurity concentration lower than the first impurity concentration; The first dislocation density is lower than the second dislocation density in the second region, and the root mean square surface roughness RMS value is 10 nm or less in an arbitrary 0.2 mm square range within the surface of the group III nitride substrate.

In the Group III nitride substrate according to the second aspect, in the first aspect, at least one first region is composed of a plurality of first regions, and the plurality of first regions are arranged such that the second region is the center of the group III nitride substrate. They may be arranged so as to surround two areas.

In the Group III nitride substrate according to the third aspect, in the second aspect, further, six third regions are arranged in the surface so as to surround the second region with the second region as the center. , the plurality of first regions consists of six first regions, the six third regions are arranged alternately with the six first regions in the circumferential direction, and the six third regions are composed of six first regions. The first area may be more depressed than the first area.

The Group III nitride substrate according to the fourth aspect has one polishing scratch in any 0.2 mm square range within the surface of the Group III nitride substrate in any one of the first to third aspects. It may be less than

In the Group III nitride substrate according to a fifth aspect, in any one of the first to fourth aspects, the impurity contained in at least one first region is at least one selected from the group of oxygen and silicon. It may be.

In the group III nitride substrate according to the sixth aspect, in any one of the first to fifth aspects, the first impurity concentration may be an oxygen concentration of 1×10 ²⁰ /cm ³ or more.

In the group III nitride substrate according to a seventh aspect, in any one of the first to sixth aspects, at least one first region is composed of an m-plane component, and the third region is composed of an a It may be composed of surface components.

The method for manufacturing a group III nitride crystal according to the eighth aspect includes the steps of preparing a seed substrate, supplying a group III element oxide gas and a nitrogen element-containing gas, and forming a group III nitride crystal on the seed substrate. a step of growing a crystal; and a step of polishing the group III nitride crystal to make the root mean square surface roughness RMS value 10 nm or less in an arbitrary 0.2 mm square range within the plane of the group III nitride crystal. ,including.

In the method for manufacturing a group III nitride substrate according to a ninth aspect, in the eighth aspect, the polishing includes chemical mechanical polishing (CMP), and the chemical mechanical polishing time ranges from 120 minutes to 700 minutes. There may be.

According to the Group III nitride substrate according to the present disclosure, it has high carrier concentration, low resistance, low dislocation density, and good surface flatness, and the generation of pits is suppressed when forming a device layer on the surface of the substrate. can do. Therefore, it is possible to improve the withstand voltage when driving diodes, transistors, and the like.

Hereinafter, a group III nitride substrate according to an embodiment will be described with reference to the accompanying drawings. In the drawings, substantially the same members are designated by the same reference numerals.

(Embodiment 1)
<Group III nitride substrate>
The group III nitride substrate according to the first embodiment is a group III nitride substrate consisting of a GaN epitaxial layer formed on a GaN substrate. The Group III nitride substrate contains oxygen as an impurity element, and in the polished c-plane of the Group III nitride substrate, a first region exhibiting a first impurity concentration and a first region lower than the first impurity concentration. and a second region exhibiting an impurity concentration of 2. The first dislocation density in the first region is lower than the second dislocation density in the second region, and the root mean square surface roughness RMS value (Rq Value: JIS B0601-2001, ISO25178) is 10 nm or less.

In this way, by setting the root mean square surface roughness RMS value to 10 nm or less, the pit density of the growth layer crystal-grown on the Group III nitride substrate can be set to 20 pits/cm ² or less. Furthermore, by setting the root mean square surface roughness RMS value to 8.4 nm or less, the pit density of the growth layer can be reduced to less than 1 pit/cm ² , and therefore, the pit density can be substantially reduced to 0 pits/cm ² . In other words, by using a Group III nitride substrate with a double average surface roughness RMS value of 10 nm or less, it is possible to suppress the occurrence of pits in the device layer grown on it, and when driving diodes, transistors, etc. It is possible to improve the withstand voltage and reduce leakage current.

FIG. 1 is an AFM image of a group III nitride substrate manufactured using the OVPE method according to the first embodiment, observed from the surface.

As shown in FIG. 1, the wafer surface (substrate surface) is composed of regions α and β that can be clearly distinguished in an AFM image. Here, α is the first region, and β is the third region. Further, six first regions and six third regions are arranged alternately in the circumferential direction surrounding the second region. Let the second region be γ. Further, the diameters of the first region and the third region are reduced toward the second region. In other words, the first region and the third region extend radially around the second region. Further, a dislocation exists at the center of the second region. The difference in the unevenness between α and β is due to the fact that the surfaces exposed during the crystal growth process have different surface indices of {30-34} and {11-22}, respectively. Comparing α and β, it can be seen that the surface depression is larger on the surface β. Therefore, a step occurs at the boundary between α and β.

FIGS. 2A and 2B are SIMS mapping images showing the oxygen concentration distribution and silicon concentration distribution on the surface of the group III nitride substrate according to the first embodiment. As can be seen from FIG. 2(a), when α and β are compared, it is found that the oxygen concentration is high on the plane α. In the oxygen concentration distribution in FIG. 2(a), the average oxygen concentration in the high oxygen concentration region is 5.1×10 ²⁰ atoms/cm ³ and the average oxygen concentration in the low oxygen concentration region is 3.2 ×10 ²⁰ atoms/cm ³ . Oxygen in the Group III nitride crystal becomes an n-type dopant. Therefore, a group III nitride crystal to which oxygen is added at a high concentration has a high carrier concentration and exhibits a low electrical resistance. Furthermore, it can be seen that the distribution of oxygen concentration in FIG. 2(a) has a pattern similar to that of the AFM image shown in FIG. 1. Therefore, from the results shown in FIGS. 1 and 2(a), it can be seen that the surface irregularities correspond to the surface oxygen concentration distribution. Furthermore, in the region of high oxygen concentration distribution, the protrusion on the surface is larger than in the region of low oxygen concentration distribution. Moreover, from FIG. 2(b), it can be seen that the silicon concentration is not as high as the oxygen concentration, but has an in-plane distribution.

<Summary of the method for manufacturing group III nitride crystals>
An overview of the method for manufacturing a group III nitride substrate according to the first embodiment will be described with reference to the flowchart of FIG. 3 and FIG. 4. FIG. 3A shows a chronological flowchart of the manufacturing method. FIG. 3B shows each functional unit as a process from upstream to downstream in the group III nitride substrate manufacturing apparatus used in this manufacturing method.

The method for manufacturing a group III nitride substrate according to the first embodiment includes a step of preparing a seed substrate, and supplying a group III element oxide gas and a nitrogen element-containing gas to form a group III nitride crystal on the seed substrate. The method includes a step of growing the crystal, and a step of polishing the extracted Group III nitride crystal.
(1) In the seed substrate preparation step of preparing the seed substrate 116, the seed substrate 116 is placed on the substrate susceptor 117.
(2) In the temperature raising step, the temperature of the growth chamber 111 is raised to 100° C. or higher and lower than 500° C. in an inert gas atmosphere.
(3) Decomposition protection In temperature raising step 1, the temperature of the growth chamber 111 is raised to 500° C. or higher and lower than 1100° C. in an NH ₃ gas atmosphere.
(4) In the decomposition protection temperature raising step 2, the temperature of the growth chamber 111 is raised to 1100° C. or more and less than 1500° C. in a Ga ₂ O gas and NH ₃ gas atmosphere.
(5) In the growth step of growing a group III nitride crystal on the seed substrate 116, a group III element oxide gas is generated in the raw material chamber 100 and supplied to the growth chamber 111, and a nitrogen element-containing gas is supplied to the growth chamber 111. Then, a group III nitride crystal is generated on the seed substrate 116.

The above growth process includes a reactive gas supply process, a group III element oxide gas generation process, a group III element oxide gas supply process, a nitrogen element-containing gas supply process, a group III nitride crystal generation process, and a residual gas exhaust process. have Note that each step included in the growth step may be performed simultaneously within a group III nitride crystal manufacturing apparatus.

(5-1) In the reactive gas supply step, a reactive gas is supplied to the raw material reaction chamber.

(5-2) In the group III element oxide gas generation step, a starting group III element source and a reactive gas (reducing gas when the starting group III element source is an oxide, oxidizing gas when the starting group III element source is a metal) are A reaction is caused to produce a Group III element oxide gas.

(5-3) In the group III element oxide gas supply step, the group III element oxide gas produced in the group III element oxide gas generation step is supplied to the growth chamber.

(5-4) In the nitrogen element-containing gas supply step, a nitrogen element-containing gas is supplied to the growth chamber.

(5-5) In the group III nitride crystal generation step, the group III element oxide gas supplied into the growth chamber in the group III element oxide gas supply step and the group III element oxide gas supplied into the growth chamber in the nitrogen element-containing gas supply step A group III nitride crystal is grown on the seed substrate.

(5-6) In the residual gas exhaust step, unreacted gases that do not contribute to the formation of group III nitride crystals are exhausted to the outside of the chamber.
(6) In the decomposition protection temperature lowering step, in order to suppress the decomposition of the group III nitride crystal grown on the seed substrate 116, the temperature of the raw material chamber 100 and the growth chamber 111 is lowered to 500° C. while supplying NH ₃ gas. do.
(7) In the temperature lowering step, the temperatures of the raw material chamber 100 and the growth chamber 111 are lowered to below 100° C. in an inert gas atmosphere.
(8) In the take-out step, the seed substrate 116 on which the group III nitride crystal has grown is taken out from the growth chamber 111.
(9) In the slicing step, as shown in FIG. 5, the prepared group III nitride crystal and seed substrate are sliced to obtain a plurality of group III nitride substrates. This allows the seed substrate to be reused.
(10) In the polishing step, the front and back surfaces of the prepared Group III nitride substrate are polished and smoothed. Note that a group III nitride substrate made of grown group III nitride crystals may be manufactured by removing the seed substrate in a polishing step without performing the slicing step.

<Overview of Group III nitride crystal manufacturing equipment>
An overview of a group III nitride crystal manufacturing apparatus used in the method for manufacturing a group III nitride crystal according to the first embodiment will be described with reference to FIG. In FIG. 4, the size, ratio, etc. of each component may differ from the actual size.

In the apparatus for producing group III nitride crystals, a raw material reaction chamber 101 is disposed within a raw material chamber 100, and a raw material boat 104 carrying a starting group III element source 105 is disposed within the raw material reaction chamber 101. . A reactive gas supply pipe 103 that supplies a gas that reacts with the starting group III element source 105 is connected to the raw material reaction chamber 101 . The raw material reaction chamber 101 has a group III element oxide gas outlet 107 that discharges the generated group III element oxide gas. When the starting Group III source is an oxide, a reducing gas is used as the reactive gas. When the starting Group III source is a metal, an oxidizing gas is used as the reactive gas. Further, a first carrier gas supply port 102 through which a first carrier gas is supplied is connected to the raw material chamber 100, and the first carrier gas supplied from the first carrier gas supply port 102 and the group III element oxide gas exhaust are connected to the raw material chamber 100. Group III element oxide gas discharged from the outlet 107 passes through the connecting pipe 109 from the gas outlet 108 and flows into the growth chamber 111, and flows into the growth chamber 111 from the gas supply port 118 connected to the growth chamber 111. Supplied. The growth chamber 111 has a gas supply port 118 , a third carrier gas supply port 112 , a nitrogen element-containing gas supply port 113 , a second carrier gas supply port 114 , and an exhaust port 119 . The growth chamber 111 includes a substrate susceptor 117 on which a seed substrate 116 is placed.

<Details of Group III nitride crystal manufacturing method and manufacturing equipment>
A method for manufacturing a group III nitride crystal according to this embodiment will be described in detail with reference to FIGS. 3 and 4.

In this embodiment, metal Ga is used as the starting Group III element source 105, but the material is not limited to this, and for example, Al or In may be used.

<Seed substrate preparation process>
First, a seed substrate 116 is prepared. As the seed substrate 116, for example, gallium nitride, gallium arsenide, silicon, sapphire, silicon carbide, zinc oxide, gallium oxide, or ScAlMgO ₄ can be used. In this embodiment, gallium nitride is used as the seed substrate 116.

<Temperature raising process>
In the temperature raising step, the temperature of the growth chamber is raised in an inert gas atmosphere to a temperature at which the seed substrate 116 does not decompose. In manufacturing a group III nitride crystal by the OVPE method, heating is performed to about 500° C. in an inert gas (for example, N ₂ gas) atmosphere.

<Decomposition protection temperature increase step 1>
In the decomposition protection temperature raising step 1, the temperature is raised in a nitrogen element-containing gas atmosphere while suppressing decomposition of the seed substrate 116. In the production of group III nitride crystals by the OVPE method, heating is performed at a temperature of 500° C. or higher and lower than 1100° C. in a state where an inert gas and a nitrogen element-containing gas NH ₃ gas are mixed. The reason for mixing NH ₃ is to prevent the seed substrate 116 from being decomposed due to desorption of N atoms. Further, heating may be performed in a state in which H ₂ gas is further mixed.

<Decomposition protection temperature increase step 2>
In the decomposition protection temperature raising step 2, the temperature is raised while suppressing the decomposition of the seed substrate 116 in a group III oxide gas and nitrogen element-containing gas atmosphere. In the production of group III nitride crystals by the OVPE method, from 1100°C to less than 1500°C, H ₂ gas, inert gas, group III element oxide gas, and nitrogen element-containing gas NH ₃ gas are mixed. Heating is performed with The reason why group III element oxide gas is mixed is that decomposition cannot be suppressed with nitrogen element-containing gas alone. By providing a driving force for the growth of Group III nitride crystals, it is possible to suppress decomposition.

<Growth process>
In the growth process, a group III element oxide gas is generated in the raw material chamber 100 and supplied to the growth chamber 111, and a nitrogen element-containing gas is supplied to the growth chamber 111 to generate a group III nitride crystal on the seed substrate 116. conduct. Specifically, the growth process includes a reactive gas supply process, a group III element oxide gas generation process, a group III element oxide gas supply process, a nitrogen element-containing gas supply process, a group III nitride crystal generation process, and a process for generating a group III nitride crystal. It has a gas exhaust process.

<Reactive gas supply process>
In the reactive gas supply step, reactive gas is supplied from the reactive gas supply pipe 103 to the raw material reaction chamber 101 in the raw material chamber 100 . As mentioned above, a reducing gas or an oxidizing gas can be used as the reactive gas as necessary. In the first embodiment, since metal Ga is used as the starting group III element source 105, H ₂ O gas is used as the reactive gas.

<Group III element oxide gas generation process>
In the group III element oxide gas generation step, the reactive gas supplied to the raw material reaction chamber 101 in the reactive gas supply step reacts with Ga, which is the starting group III element source 105, to form a group III element oxide gas. Generate Ga ₂ O gas. The generated Ga ₂ O gas is discharged from the raw material reaction chamber 101 to the raw material chamber 100 via the group III element oxide gas outlet 107 . The discharged Ga ₂ O gas is mixed with the first carrier gas supplied from the first carrier gas supply port 102 to the raw material chamber, and is supplied to the gas exhaust port 108 . In the first embodiment, the raw material chamber 100 is heated by the first heater 106. When heating the raw material chamber 100, the temperature of the raw material chamber 100 is preferably set to 800° C. or higher from the viewpoint of the boiling point of Ga ₂ O gas. Further, it is preferable that the temperature of the raw material chamber 100 is lower than that of the growth chamber 111. When the growth chamber is heated by the second heater 115 as described later, it is preferable that the temperature of the raw material chamber 100 is, for example, less than 1800°C. The starting group III element source 105 is placed in a raw material boat 104 disposed within the raw material reaction chamber 101 . The raw material boat 104 preferably has a shape that can increase the contact area between the reactive gas and the starting Group III element source. For example, in order to prevent the starting Group III element source 105 and the reactive gas from passing through the raw material reaction chamber 101 in a non-contact state, the raw material boat 104 is preferably in the shape of a multi-tiered dish.

The methods for producing the group III element oxide gas can be roughly divided into a method of reducing the starting group III element source 105 and a method of oxidizing the starting group III element source 105. For example, in the reducing method, an oxide (e.g., Ga ₂ O ₃ ) is used as the starting group III element source 105, and a reducing gas (e.g., H ₂ gas, CO gas, CH ₄ gas, C ₂ H ₆ gas) is used as the reactive gas. , H ₂ S gas, SO ₂ gas). On the other hand, in the oxidation method, the starting Group III element source 105 is a non-oxide (e.g., liquid Ga), and the reactive gas is an oxidizing gas (e.g., H ₂ O gas, O ₂ gas, CO gas, CO ₂ gas, NO gas, N ₂ O gas, NO ₂ gas) is used.

Further, in addition to the starting group III element source 105, an In source and an Al source can be employed as the starting group III element. As the first carrier gas, an inert gas, _H2 gas, etc. can be used.

<Group III element oxide gas supply process>
In the group III element oxide gas supply step, the Ga ₂ O gas generated in the group III element oxide gas generation step is supplied to the growth chamber 111 via the gas exhaust port 108, the connecting pipe 109, and the gas supply port 118. do. When the temperature of the connecting pipe 109 connecting the raw material chamber 100 and the growth chamber 111 falls below the temperature of the raw material chamber 100, a reverse reaction of the reaction that generates the group III element oxide gas occurs, and the starting group III element source 105 It is deposited in the connecting pipe 109. Therefore, it is preferable that the connecting pipe 109 be heated to a higher temperature than the first heater 106 by the third heater 110 so that the temperature does not drop below the temperature of the raw material chamber 100.

<Nitrogen element-containing gas supply process>
In the nitrogen element-containing gas supply step, a nitrogen element-containing gas is supplied to the growth chamber 111 from the nitrogen element-containing gas supply port 113 . Examples of the nitrogen element-containing gas include, for example, NH ₃ gas, NO gas, NO ₂ gas, N ₂ O gas, N ₂ H ₂ gas, and N ₂ H ₄ gas.

<Group III nitride crystal generation process>
In the group III nitride crystal generation step, the source gases supplied into the growth chamber through each supply step are reacted to grow a group III nitride crystal on the seed substrate 116. The temperature of the growth chamber 111 is preferably raised by the second heater 115 to a temperature at which the group III element oxide gas and the nitrogen element-containing gas react. At this time, the temperature of the growth chamber 111 should be controlled so that it does not fall below the temperature of the raw material chamber 100 in order to prevent the reverse reaction of the reaction that generates the group III element oxide gas from occurring. is preferred. The temperature of the growth chamber 111 heated by the second heater 115 is preferably 1000°C or more and 1800°C or less. Furthermore, in order to suppress temperature fluctuations in the growth chamber 111 due to the Ga ₂ O gas generated in the raw material chamber 100 and the first carrier gas, the temperatures of the second heater 115 and the third heater 110 are set to be the same. is desirable.

The group III element oxide gas supplied to the growth chamber 111 through the group III element oxide supply step, and the nitrogen element-containing gas supplied to the growth chamber 111 through the nitrogen element-containing gas supply step. By mixing upstream of the seed substrate 116, group III nitride crystals can be grown on the seed substrate 116.

Incidentally, the reactive gas supply step, the group III element oxide gas generation step, the group III element oxide gas supply step, the nitrogen element-containing gas supply step, the group III nitride crystal generation step, and the residual gas included in the growth step. The discharge steps may be performed simultaneously.

As the second carrier gas, an inert gas, _H2 gas, or the like can be used. In the residual gas exhausting step, unreacted group III element oxide gas and nitrogen element-containing gas, as well as the first carrier gas, second carrier gas, and third carrier gas are discharged from the exhaust port 119.

<Decomposition protection temperature cooling process>
In the decomposition protection temperature lowering step, the temperature is lowered in a nitrogen element-containing gas atmosphere while suppressing the decomposition of the group III nitride crystal. In the production of group III nitride crystals by the OVPE method, cooling is performed to 500° C. or lower in a mixed state of an inert gas and a nitrogen element-containing gas NH ₃ gas.

<Temperature cooling process>
In the temperature lowering step, the temperature is lowered in an inert gas atmosphere to a temperature at which the group III nitride crystal can be taken out from the growth chamber.

In this embodiment, the seed substrate 116 on which the group III nitride crystal has grown is taken out from the growth chamber 111 after a temperature-lowering step.

<Slicing process>
In the slicing step, the group III nitride crystal produced on the seed substrate 116 is sliced using a wire or a laser. By performing slicing, the Group III nitride crystal and the seed substrate 116 are separated. Further, the produced group III nitride crystal is separated into a plurality of group III nitride substrates. Note that the number of group III nitride substrates obtained by slicing may be one or more.

<Polishing process>
In the polishing step, the front and back surfaces of the group III nitride substrate obtained by slicing are smoothed. From the viewpoint of forming a device layer by MOVPE on a polished Group III nitride substrate, it is important to improve flatness and remove polishing scratches. Note that the polishing process in the present disclosure includes mechanical polishing (MP) and chemical mechanical polishing (CMP). Mechanical polishing MP mainly reduces the overall wafer thickness and thickness distribution. At this time, polishing scratches may occur due to mechanical polishing MP. Polishing scratches are shown, for example, in the form of streaks or lines in the photoluminescence image of FIG. Chemical mechanical polishing (CMP) mainly removes damaged layers and polishing scratches. Among these, CMP is important for Group III nitride substrates manufactured using the OVPE method. By prolonging the CMP polishing time, polishing scratches introduced by MP are removed, but on the other hand, surface irregularities reflecting the α and β regions (growth history) occur. The surface unevenness causes pits to be generated when a device layer is formed on the surface of the substrate by the MOVPE method. Therefore, CMP is performed to remove polishing scratches and minimize unevenness. Note that the pit is, for example, a concave portion in the shape of an inverted polygonal pyramid such as an inverted hexagonal pyramid or an inverted dodecagonal pyramid.

Through the above steps, it is possible to obtain a group III nitride substrate that achieves both removal of polishing scratches and reduction of unevenness on the wafer surface.

(Summary of Examples and Comparative Examples)
Group III nitride crystals were grown using the growth furnace shown in FIG. Here, GaN was grown as a group III nitride crystal. Liquid Ga was used as a starting group III element source, Ga was reacted with H ₂ O gas as a reactive gas, and the generated Ga ₂ O gas was used as a group III element oxide gas. NH ₃ gas was used as the nitrogen element-containing gas, and a mixture of H ₂ gas and N ₂ gas was used as the first carrier gas and the second carrier gas. The growth surface of the grown GaN crystal was covered with numerous pits consisting of planes with plane indices of {30-34} and {11-22}. By using this growth mode, the convergence of dislocations to the center of the pit is promoted, and dislocations coalesce and pair annihilation occurs. Therefore, as the film becomes thicker, the dislocation density is reduced.

A GaN substrate with a thickness of 0.3 to 0.5 mm was prepared from the grown GaN crystal, and the front and back surfaces were flattened in a polishing process. Here, the execution time of chemical mechanical polishing CMP in the polishing process was varied, and the flatness of the surface and the presence or absence of polishing scratches were checked. Chemical mechanical polishing CMP was performed for a period of 200 minutes to 780 minutes. Furthermore, a GaN thin film of about 5 to 10 μm was grown on a polished GaN substrate by MOVPE, and the correlation between the flatness of the GaN substrate before growth and the pit density generated in the growth layer formed by MOVPE was confirmed. . Note that pits with a size of less than 1 μm were not counted. Growth by the MOVPE method was carried out at a wafer surface temperature in the range of 1070 to 1080°C. In addition, to evaluate the surface flatness of the GaN substrate before growth by the MOVPE method, the root mean square surface roughness RMS value (Rq value: JIS B0601-2001, ISO25178) in the range of 200 μm square to 300 μm square in the image taken with a white interference microscope is used. ) was used. Note that in the standards since 2001, the RMS value is the Rq value. Furthermore, the presence or absence of polishing scratches on the surface of the GaN substrate before growth was evaluated using a surface photoluminescence image (PL image).

(Example 1)
A GaN substrate made of OVPE was subjected to chemical mechanical polishing CMP to produce a sample having a root mean square surface roughness RMS value of 8.42 nm. Photoluminescence (PL) observation of the GaN substrate before growth revealed no polishing scratches on the surface. When GaN was grown on an OVPE GaN substrate by the MOVPE method, the pit density was 0/cm ² .

(Example 2)
A GaN substrate made of OVPE was subjected to chemical mechanical polishing CMP to produce a sample having a root mean square surface roughness RMS value of 4.48 nm. Photoluminescence (PL) observation of the GaN substrate before growth revealed no polishing scratches on the surface. When GaN was grown on an OVPE GaN substrate by the MOVPE method, the pit density was 0/cm ² .

(Example 3)
A sample having a root mean square surface roughness RMS value of 2.44 nm was prepared by subjecting an OVPE GaN substrate to chemical mechanical polishing CMP. Photoluminescence (PL) observation of the GaN substrate before growth revealed no polishing scratches on the surface. When GaN was grown on an OVPE GaN substrate by the MOVPE method, the pit density was 0/cm ² .

(Example 4)
A GaN substrate made of OVPE was subjected to chemical mechanical polishing CMP to produce a sample having a root mean square surface roughness RMS value of 9.80 nm. Photoluminescence (PL) observation of the GaN substrate before growth revealed no polishing scratches on the surface. As a result of GaN growth performed on an OVPE GaN substrate by the MOVPE method, the pit density was 9.75 pieces/cm ² .

(Example 5)
A GaN substrate made of OVPE was subjected to chemical mechanical polishing CMP to produce a sample having a root mean square surface roughness RMS value of 8.94 nm. Photoluminescence (PL) observation of the GaN substrate before growth revealed no polishing scratches on the surface. As a result of GaN growth performed on an OVPE GaN substrate by the MOVPE method, the pit density was 0.25 pieces/cm ² .

(Comparative example 1)
A chemical mechanical polishing CMP was applied to an OVPE GaN substrate for less than approximately 780 minutes to produce a sample having a root mean square surface roughness RMS value of 10.7 nm. Photoluminescence (PL) observation of the GaN substrate before growth revealed no polishing scratches on the surface. As a result of GaN growth performed on an OVPE GaN substrate by the MOVPE method, the pit density was 73.5/cm ² .

The above results are summarized in Figure 6. As can be seen from this, by setting the root mean square surface roughness RMS value to 10 nm or less, the pit density of the MOVPE growth layer grown on the OVPE GaN substrate can be set to 20 pits/cm ² or less. Furthermore, by setting the root mean square surface roughness RMS value to 8.4 nm or less, it is possible to reduce the pit density of the MOVPE growth layer to less than 1 pit/cm ² , and therefore to substantially 0 pit density/cm ² . can. In other words, if an OVPE GaN substrate with a double average surface roughness RMS value of 10 nm or less is used, it is possible to suppress the occurrence of pits in the device layer grown on it, and it is possible to suppress the occurrence of pits in the device layer grown on it. It is possible to improve withstand voltage and reduce leakage current.

Further, FIG. 7 shows an example of the relationship between the execution time of chemical mechanical polishing CMP of a GaN substrate and the double average surface roughness RMS value. As shown in FIG. 7, it can be seen that the double average surface roughness RMS value increases as the CMP processing time increases. In other words, from the relationship with Figures 6 and 7, in order to make the double average surface roughness RMS value 10 nm or less, the chemical mechanical polishing CMP execution time should be shorter than the conventional 800 minutes, and approximately 700 minutes or less. I understand that it is necessary. Furthermore, it can be seen that in order to make the root mean square surface roughness RMS value 8.4 nm or less, the chemical mechanical polishing CMP execution time needs to be 600 minutes or less.

In the sample plotted in Figure 7, no polishing scratches were observed on the surface. On the other hand, FIG. 8 shows a surface photoluminescence (PL) image when the chemical mechanical polishing CMP was performed for 60 minutes. As shown by the arrows in FIG. 8, if the chemical mechanical polishing CMP is performed for too short a time, streak-like polishing scratches 120 remain. Polishing scratches are a problem because they cause pits and dislocations to occur during device layer formation. That is, in order to remove polishing scratches, specifically, it is necessary to reduce the number of polishing scratches to less than one in any 0.2 mm square area within the surface of the group III nitride substrate. Therefore, it can be seen that it is necessary to carry out chemical mechanical polishing CMP for a time exceeding 60 minutes, for example, 120 minutes or more, and further, 200 minutes or more.

Therefore, the optimum chemical mechanical polishing CMP condition is the value that removes polishing scratches and gives the smallest double average surface roughness RMS value. Specifically, the chemical mechanical polishing CMP time may be, for example, 120 minutes or more and 700 minutes or less, and further may be 200 minutes or more and 600 minutes or less.

According to the Group III nitride substrate according to the present disclosure, it has high carrier concentration, low resistance, low dislocation density, and good surface flatness, and the generation of pits is suppressed when forming a device layer on the surface of the substrate. can do.

100 Raw material chamber 101 Raw material reaction chamber 102 First carrier gas supply port 103 Reactive gas supply pipe 104 Raw material boat 105 Starting group III element source 106 First heater 107 Group III element oxide gas outlet 108 Gas outlet 109 Connecting pipe 110 Third heater 111 Growth chamber 112 Third carrier gas supply port 113 Nitrogen element-containing gas supply port 114 Second carrier gas supply port 115 Second heater 116 Seed substrate 117 Substrate susceptor 118 Gas supply port 119 Exhaust port 120 Polishing scratch

Claims

A group III nitride substrate consisting of a GaN epitaxial layer formed on a GaN substrate,
Contains oxygen as an impurity element,
At least one first region exhibiting a first impurity concentration within the polished surface of the c-plane of the Group III nitride substrate, and a second region exhibiting a second impurity concentration lower than the first impurity concentration; has
a first dislocation density in the at least one first region is lower than a second dislocation density in the second region;
A group III nitride substrate, wherein the root mean square surface roughness RMS value is 10 nm or less in any 0.2 mm square range within the surface of the group III nitride substrate.
the at least one first region is comprised of a plurality of first regions;
The III-nitride substrate according to claim 1, wherein the plurality of first regions are arranged to surround the second region with the second region as the center.
Furthermore, in the surface, six third regions are arranged surrounding the second region with the second region as the center,
The plurality of first regions include six first regions,
The six third regions are arranged alternately with the six first regions in the circumferential direction,
The III-nitride substrate according to claim 2, wherein the six third regions are more depressed than the six first regions.
The Group III nitride substrate according to any one of claims 1 to 3, wherein there is less than one polishing scratch in any 0.2 mm square area within the surface of the Group III nitride substrate.
The Group III nitride substrate according to any one of claims 1 to 3, wherein the impurity contained in the at least one first region is at least one selected from the group of oxygen and silicon.
The Group III nitride substrate according to claim 1 , wherein the first impurity concentration is an oxygen concentration of 1×10 20 /cm 3 or more.
Group III nitriding according to any one of claims 1 to 3, wherein the at least one first region is composed of an m-plane component, and the third region is composed of an a-plane component. object board.
preparing a seed substrate;
supplying a group III element oxide gas and a nitrogen element-containing gas to grow a group III nitride crystal on the seed substrate;
a step of polishing the Group III nitride crystal to have a root mean square surface roughness RMS value of 10 nm or less in an arbitrary 0.2 mm square range within the plane of the Group III nitride crystal;
A method for manufacturing a group III nitride substrate, comprising:
The method for manufacturing a Group III nitride substrate according to claim 8, wherein the polishing includes chemical mechanical polishing (CMP), and the chemical mechanical polishing time ranges from 120 minutes to 700 minutes.