JP2012006830A - Ground substrate for growing group iii nitride semiconductor, and method for growing group iii nitride semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground substrate which grows a thick-film crystal of a group III nitride semiconductor whose surface state and cross section shape are excellent.SOLUTION: The ground substrate includes a first crystal growing-plane and a second crystal growing-plane which faces the same direction as the first crystal growing-plane. The second crystal growing-plane links to 50% or more of a periphery of the first crystal growing-plane through a downward step whose height is 0.1-5 mm.

Description

  The present invention relates to a base substrate for group III nitride semiconductor growth and a method for growing a group III nitride semiconductor using the base substrate. More specifically, the present invention relates to a base substrate capable of growing a group III nitride semiconductor having a good crystal surface state and cross-sectional shape, and a method for growing a group III nitride semiconductor using the base substrate. .

  Group III nitride semiconductors have a high melting point, and since the dissociation pressure of nitrogen near the melting point is high, bulk growth from the melt is difficult. On the other hand, it is known that a group III nitride semiconductor substrate can be manufactured by using a vapor phase growth method such as a hydride vapor phase growth method (HVPE) or a metal organic chemical vapor deposition method (MOCVD). When manufacturing a gallium nitride semiconductor substrate, for example, a base substrate such as sapphire is set in a growth chamber (reactor) of a vapor phase growth apparatus, and a gas containing a gallium compound and a nitrogen compound is contained in the reactor. By supplying a gas for forming a group III nitride semiconductor consisting of gallium nitride, a gallium nitride semiconductor is grown to a thickness of several μm to several cm on the base substrate. Then, a desired group III nitride semiconductor substrate can be obtained by removing portions such as the base substrate using a method of polishing or laser irradiation. Among the above-mentioned vapor phase growth methods, the HVPE method has a feature that can realize a higher growth rate than other growth methods, and therefore, when a thick film growth of a group III nitride semiconductor is necessary or a sufficient thickness is required. This is effective as a method for obtaining a group III nitride semiconductor substrate having the same.

  Conventionally, a single crystal gallium nitride having a thickness of about 500 μm to 1 mm is grown on one base substrate, the base substrate is removed, and a single gallium nitride single crystal substrate is obtained by processing and polishing. This is very inefficient in manufacturing, and an inexpensive single crystal gallium nitride substrate cannot be supplied. Therefore, a technique for obtaining a plurality of gallium nitride single crystal substrates from a single base substrate by growing a single crystal having a thickness of several mm to several cm on the base substrate and slicing the single crystal bulk is drawing attention. ing.

  However, a new problem occurs in growing a thick film of several mm or more. When a thick film of several mm or more is grown, the crystal grows abnormally at the peripheral edge of the substrate, so that the gas flow at the center of the substrate is disturbed and a good crystal cannot be obtained. In addition, the abnormal growth of the crystal at the peripheral edge of the substrate is accelerated and the film thickness at the center of the substrate is hardly increased, and surface roughness is considered to be caused by the etching action of hydrochloric acid gas generated with the formation of GaN.

  In order to prevent such abnormal crystal growth at the edge of the substrate, a technique of covering the edge with a cover has been proposed (see Patent Document 1). Specifically, it is proposed to cover a portion of 1 mm or more from the outer periphery of the growth surface toward the inside in the radial direction with a cover.

JP 2005-200250 A

  However, if the end is covered with a cover, there is a problem that the flow of gas on the crystal growth surface is hindered and it is difficult to uniformly grow a crystal having excellent surface properties. In addition, since a part of the crystal growth surface is covered, the growth surface cannot be used efficiently, which is disadvantageous for growing a large crystal.

  In order to solve the problems of the prior art, the present inventors have developed a thick group III nitride semiconductor crystal having a good surface state and cross-sectional shape without hindering the gas flow on the crystal growth surface. It was set as an object of the present invention to provide a base substrate that can be grown. It was also set as an object of the present invention to provide a method for growing a group III nitride semiconductor having a good surface state and cross-sectional shape using such a base substrate.

  As a result of intensive studies, the present inventors have found that the problem of the prior art can be solved by providing another crystal growth surface with a step on the periphery of the crystal growth surface. That is, the following present invention has been provided as means for solving the problems.

[1] A base substrate having a first crystal growth surface and a second crystal growth surface facing in the same direction as the first crystal growth surface, and facing down to 50% or more of the periphery of the first crystal growth surface A base substrate for growing a group III nitride semiconductor, characterized in that the second crystal growth surface is connected through a step.
[2] The base for growing a group III nitride semiconductor according to [1], wherein the second crystal growth surface is connected to the entire periphery of the first crystal growth surface through a downward step. substrate.
[3] The base substrate for group III nitride semiconductor growth according to [1] or [2], wherein the first crystal growth surface is circular.
[4] The base substrate for group III nitride semiconductor growth according to [3], wherein the second crystal growth surface is annular and concentric with the circular first crystal growth surface.
[5] The base substrate for group III nitride semiconductor growth according to any one of [1] to [4], wherein a width of the second crystal growth surface is 0.5 mm or more.
[6] The base substrate for group III nitride semiconductor growth according to any one of [1] to [5], wherein a height of the step is 0.1 to 5 mm.
[7] The group III according to any one of [1] to [6], wherein the first crystal growth surface and the second crystal growth surface are present in a continuous single member. Base substrate for nitride semiconductor growth.
[8] The group III according to any one of [1] to [6], wherein a member constituting the first crystal growth surface and a member constituting the second crystal growth surface are different. Base substrate for nitride semiconductor growth.
[9] The materials according to [1] to [8], wherein the material constituting the first crystal growth surface and the material constituting the second crystal growth surface are each made of a group III nitride semiconductor single crystal. The base substrate for group III nitride semiconductor growth as described in any one.
[10] The member according to any one of [1] to [9], wherein members constituting the first crystal growth surface and the second crystal growth surface are formed on a base substrate. A base substrate for group nitride semiconductor growth.
[11] The base substrate for group III nitride semiconductor growth according to [10], wherein the basic substrate is a sapphire single crystal substrate or a SiC single crystal substrate.

[12] A step of crystal-growing a group III nitride semiconductor on the base substrate by supplying a gas for forming a group III nitride semiconductor onto the base substrate according to any one of [1] to [11] A method for growing a group III nitride semiconductor, comprising:
[13] The method for growing a group III nitride semiconductor according to [12], wherein the base substrate is made of a single crystal of the same kind as the group III nitride semiconductor to be crystal-grown.
[14] The group III nitride semiconductor growth method according to [12] or [13], wherein the group III nitride semiconductor is crystal-grown with a thickness of 5 mm or more.
[15] The method for growing a group III nitride semiconductor according to any one of [12] to [14], wherein the crystal growth is performed by a hydride vapor phase epitaxy (HVPE method).
[16] The method for growing a group III nitride semiconductor according to any one of [12] to [15], further including a step of separating the second crystal growth surface from the base substrate.

In particular, the present invention having the following configuration is provided as means for solving the above-described problems.
(1) A base substrate having a first crystal growth surface and a second crystal growth surface facing in the same direction as the first crystal growth surface,
The second crystal growth surface is connected to 50% or more of the periphery of the first crystal growth surface through a downward step;
A base substrate for growing a group III nitride semiconductor, wherein the height of the step is 0.1 to 5 mm.
(2) The group III according to (1), wherein both the material constituting the first crystal growth surface and the material constituting the second crystal growth surface are made of a single crystal of a group III nitride semiconductor. Base substrate for nitride semiconductor growth.
(3) A base substrate having a first crystal growth surface and a second crystal growth surface facing in the same direction as the first crystal growth surface,
The second crystal growth surface is connected to 50% or more of the periphery of the first crystal growth surface through a downward step;
Both the material constituting the first crystal growth surface and the material constituting the second crystal growth surface are made of a single crystal of a group III nitride semiconductor,
A base substrate for growing a group III nitride semiconductor, wherein the first crystal growth surface is a (0001) plane.
(4) The base substrate for group III nitride semiconductor growth according to (3), wherein the height of the step is 0.1 to 5 mm.
(5) In any one of (1) to (4), the second crystal growth surface is connected to the entire periphery of the first crystal growth surface through a downward step. Base substrate for group III nitride semiconductor growth.
(6) The base substrate for growing a group III nitride semiconductor according to any one of (1) to (5), wherein the first crystal growth surface is circular.
(7) The base substrate for group III nitride semiconductor growth according to (6), wherein the second crystal growth surface is annular and concentric with the circular first crystal growth surface.
(8) The group III according to any one of (1) to (7), wherein the first crystal growth surface and the second crystal growth surface are present in a continuous single member. Base substrate for nitride semiconductor growth.
(9) The group III according to any one of (1) to (7), wherein a member constituting the first crystal growth surface and a member constituting the second crystal growth surface are different. Base substrate for nitride semiconductor growth.
(10) The member constituting the first crystal growth surface and the second crystal growth surface is formed on a base substrate, and the III according to any one of (1) to (9) A base substrate for group nitride semiconductor growth.
(11) The base substrate for group III nitride semiconductor growth according to (10), wherein the basic substrate is a sapphire single crystal substrate or a SiC single crystal substrate.
(12) A step of crystal growth of a group III nitride semiconductor on the base substrate by supplying a group III nitride semiconductor forming gas onto the base substrate according to any one of (1) to (11) A method for growing a group III nitride semiconductor, comprising:
(13) The method for growing a group III nitride semiconductor according to (12), wherein the base substrate is made of the same type of single crystal as the group III nitride semiconductor to be crystal-grown.
(14) The method for growing a group III nitride semiconductor according to (12) or (13), wherein the group III nitride semiconductor is crystal-grown with a thickness of 5 mm or more.
(15) The method for growing a group III nitride semiconductor according to any one of (12) to (14), wherein the crystal growth is performed by a hydride vapor phase growth method.
(16) The method for growing a group III nitride semiconductor according to any one of (12) to (15), further including a step of separating the second crystal growth surface from the base substrate.
(17) A Group III nitride semiconductor crystal grown on an underlying substrate, wherein the Group III nitride semiconductor crystal has a growth thickness of 2 mm or more, and a surface after crystal growth is a mirror surface Group III nitride semiconductor crystal.
(18) The group III nitride semiconductor crystal according to (17), wherein the surface has a surface roughness of 1 nm or less.

  In the base substrate of the present invention, since the second crystal growth surface is provided with a step on the periphery of the first crystal growth surface, the group III nitride semiconductor crystal grows abnormally at the peripheral portion of the first crystal growth surface. Can be suppressed. As a result, a group III nitride semiconductor having a good surface state and cross-sectional shape can be grown on the first crystal growth surface. In addition, according to the method for growing a group III nitride semiconductor of the present invention, it is possible to produce a flat and uniform thick film crystal.

It is a schematic sectional drawing of the HVPE apparatus used by the Example and the comparative example. It is a schematic sectional drawing of the base substrate installed on the substrate holder (Examples 1 and 2). (Example 3) which is the upper side figure and side sectional drawing of a seed crystal substrate which gave the level | step difference process to the outer periphery. (Example 3) which is a schematic sectional drawing of the seed crystal board | substrate which gave the level | step difference process to the outer periphery installed on the board | substrate holder. It is a schematic sectional drawing of the seed crystal substrate installed on the substrate holder (comparative example 1). It is a schematic sectional drawing of the seed crystal substrate installed on the substrate holder (comparative example 2).

  Hereinafter, the growth method of the base substrate and the group III nitride semiconductor of the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

(Under substrate for group III nitride semiconductor growth)
The base substrate of the present invention is a base substrate having a first crystal growth surface and a second crystal growth surface facing in the same direction as the first crystal growth surface, and has a peripheral 50 of the first crystal growth surface. It is characterized in that the second crystal growth surface is connected via a step that is downwardly more than%.

  The base substrate of the present invention has at least a first crystal growth surface and a second crystal growth surface. The first crystal growth surface and the second crystal growth surface face each other in the same direction. Here, “facing in the same direction” means normal line of the first crystal growth surface and second crystal growth surface. It means that the angle of the surface normal is within 20 °. The angle between the normal line of the first crystal growth surface and the normal line of the second crystal growth surface is preferably within 10 °, more preferably within 5 °, even more preferably within 3 °. It is particularly preferable that the angle is within the range of °.

  The first crystal growth surface is a surface on which a group III nitride semiconductor crystal having a good surface state and cross-sectional shape is grown. The shape of the first crystal growth surface is not particularly limited, and the shape can be determined according to the shape of the group III nitride semiconductor crystal to be obtained. Usually, it is circular, elliptical or rectangular, preferably circular. The size of the first crystal growth surface can also be determined according to the size of the group III nitride semiconductor to be obtained. The diameter when the first crystal growth surface is circular and the maximum diameter when the first crystal growth surface is rectangular are usually 10 to 300 mm, preferably 20 to 150 mm, and preferably 50 to 100 mm. Is more preferable.

  The second crystal growth surface is a surface on which the group III nitride semiconductor crystal is grown at a position lower than the first crystal growth surface, and the first crystal is grown by growing the group III nitride semiconductor crystal on the second crystal growth surface. It is a surface having a function of suppressing abnormal growth of crystals at the peripheral edge of the growth surface. By growing a group III nitride semiconductor crystal on the second crystal growth surface, a group III nitride semiconductor crystal having a good surface state and cross-sectional shape can be grown on the first crystal growth surface.

  The second crystal growth surface is connected to 50% or more of the periphery of the first crystal growth surface via a downward step. That is, 50% or more of the peripheral length of the first crystal growth surface is connected to the second crystal growth surface through a downward step. Preferably 70% or more, more preferably 90% or more, more preferably 95% or more, particularly preferably 100% of the periphery of the first crystal growth surface is connected to the second crystal growth surface via a downward step. It is desirable. When the peripheral edge connected to the second crystal growth surface through a downward step is referred to as a connected peripheral edge, and the non-connected peripheral edge is referred to as a non-connected peripheral edge, the peripheral edge of the first crystal growth surface is not connected to the connected peripheral edge. The connected peripheral edge portions may appear alternately. Preferred is an aspect in which the connecting peripheral edge and the non-connecting peripheral edge appear alternately with regularity, and more preferably, the base substrate is circular and the connecting peripheral edge and the non-connecting peripheral edge alternately with regularity. It is an aspect that appears, more preferably an aspect having rotational symmetry, and an aspect in which all the peripheral edges are connected peripheral edges. By adopting the preferred embodiment, a more uniform crystal can be grown on the first crystal growth surface.

  Since the second crystal growth surface is connected to the periphery of the first crystal growth surface via a downward step, the second crystal growth surface is preferably annular when the first crystal growth surface is circular. . At this time, the annular second crystal growth surface is more preferably concentric with the circular first crystal growth surface. The width of the second crystal growth surface is usually 0.5 to 20 mm, preferably 1 to 15 mm, and more preferably 2 to 15 mm. The width of the second crystal growth surface may be constant over the entire base substrate of the present invention, or a wide portion and a narrow portion may be mixed. If the width is constant over the entire substrate, it is preferable because a more uniform group III nitride semiconductor crystal can be grown on the first crystal growth surface.

  The level difference between the first crystal growth surface and the second crystal growth surface is usually 0.1 to 5 mm in height difference, preferably 0.2 to 2 mm, and preferably 0.3 to 1 mm. Is more preferable. The height difference between the first crystal growth surface and the second crystal growth surface may not necessarily be constant over the entire base substrate of the present invention, but is preferably constant over the entire base substrate. If it is constant over the entire base substrate, a more uniform group III nitride semiconductor crystal can be grown on the first crystal growth surface.

  The first crystal growth surface and the second crystal growth surface may be made of the same crystal or different crystals. In any case, the group III nitride semiconductor must be capable of growing. Preferred is an embodiment in which the growth rates of the group III nitride semiconductor crystals on the first crystal growth surface and the second crystal growth surface are substantially the same. Accordingly, the first crystal growth surface and the second crystal growth surface are preferably made of the same crystal. The first crystal growth surface and the second crystal growth surface are both preferably a single crystal of a group III nitride semiconductor. The single crystal of the same type as the group III nitride semiconductor to be crystal-grown on the base substrate is used. More preferably.

  The first crystal growth surface and the second crystal growth surface may exist in a continuous single member, or may exist in different members. As an aspect that exists in a continuous single member, for example, a case where a first crystal growth surface and a second crystal growth surface are provided in one single crystal can be exemplified. Further, as an aspect in which each exists in different members, a case where the single crystal having the first crystal growth surface and the single crystal having the second crystal growth surface are in contact with each other and integrated is illustrated. Can do. In the latter case, the two members may be firmly connected to each other, or one member may simply be mounted on the other member. In the latter case, the mounting timing is not particularly limited. For example, the upper member (the member having the first crystal growth surface) may be mounted on the lower member (the member having the second crystal growth surface) in the reaction vessel.

  The base substrate of the present invention may be formed on a base substrate. The basic substrate here is generally called a substrate and refers to a thick film material on which a compound semiconductor can be grown. Examples of the basic substrate include a sapphire single crystal substrate, a SiC single crystal substrate, and a Si substrate. A sapphire single crystal substrate or a SiC single crystal substrate is preferable. The base substrate of the present invention may be used for growing a group III nitride semiconductor crystal with such a base substrate, or may be used for growing a group III nitride semiconductor crystal after removing the base substrate. Good. Which one is selected can be appropriately determined according to the stability and workability of the base substrate, the shape and use of the group III nitride semiconductor to be grown, and the like.

(Group III nitride semiconductor growth method)
A method for growing a group III nitride semiconductor according to the present invention includes a step of crystal growth of a group III nitride semiconductor on a base substrate by supplying a gas for forming a group III nitride semiconductor onto the base substrate according to the present invention. It is characterized by including. The type of group III nitride semiconductor to be crystal-grown is not particularly limited. For example, GaN, InN,
AlN, InGaN, AlGaN, AlInGaN, etc. can be mentioned. Preferred is GaN, AlN, AlGaN, and more preferred is GaN.

  The group III nitride semiconductor forming gas is supplied to the first crystal growth surface of the base substrate of the present invention. Specifically, it is preferable to supply from the direction of 0 to 45 ° with respect to the normal direction of the first crystal growth surface, more preferable to supply from the direction of 0 to 30 °, and the direction of 0 to 10 °. It is more preferable to supply from The group III nitride semiconductor forming gas may be supplied directly to the second crystal growth surface or may be supplied via the first crystal growth surface. Preference is given to the case where it is supplied via the first crystal growth surface.

  Examples of the crystal growth method used in the group III nitride semiconductor growth method of the present invention include HVPE method, MOCVD method, MBE method, and sublimation method. The HVPE method and the MOCVD method are preferable, and the HVPE method is most preferable.

Next, a process for growing a group III nitride semiconductor crystal using the base substrate of the present invention will be described.
Details of the apparatus used for crystal growth are not particularly limited. For example, an HVPE apparatus as shown in FIG. 1 can be used. The HVPE apparatus in FIG. 1 includes a substrate holder (susceptor) 107 on which a base substrate 112 is placed and a reservoir 105 into which a group III nitride semiconductor material to be grown is placed. In addition, introduction pipes 101 to 104 for introducing gas into the reactor 100 and an exhaust pipe 108 for exhausting are installed. Further, a heater 106 for heating the reactor 100 from the side surface is installed.

As a material of the reactor 100, quartz, polycrystalline BN, stainless steel or the like is used. A preferred material is quartz. The reactor 100 is filled with atmospheric gas in advance before starting the reaction. Examples of the atmospheric gas include H ₂ gas, N ₂ gas, inert gas such as He, Ne, and Ar. These gases may be mixed and used.

  Carbon is preferable as the material of the substrate holder 107, and a material whose surface is coated with SiC is more preferable. The shape of the substrate holder 107 is not particularly limited as long as the base substrate 112 of the present invention can be installed, but there is no structure on the upstream side of the growing crystal when the crystal is grown. It is preferable. If there is a structure in which a crystal may grow on the upstream side, a polycrystal adheres to the structure, and HCl gas is generated as a product, which adversely affects the crystal to be grown. The size of the base substrate mounting surface of the substrate holder 107 is preferably smaller than the base substrate 112 to be mounted. That is, it is more preferable that the size of the base substrate 112 is such that the substrate holder 107 is hidden when viewed from the gas upstream side.

  When placing the base substrate 112 on the substrate holder 107, it is preferable to place the first crystal growth surface of the base substrate 112 so as to face the upstream side of the gas flow (above the reactor in FIG. 1). That is, it is preferable to mount the gas so that it flows toward the first crystal growth surface, and it is more preferable that the gas flow from a direction perpendicular to the first crystal growth surface. By placing the base substrate 112 in this way, a group III nitride semiconductor crystal having more uniform and excellent crystallinity can be obtained.

  The reservoir 105 is charged with a raw material to be a group III source. Examples of the raw material to be a group III source include Ga, Al, and In.

A gas that reacts with the raw material put in the reservoir 105 is supplied from an introduction pipe 103 for introducing the gas into the reservoir 105. For example, when a raw material that is a group III source is put in the reservoir 105, HCl gas can be supplied from the introduction pipe 103. At this time, the carrier gas may be supplied from the introduction pipe 103 together with the HCl gas. Examples of the carrier gas include H ₂ gas, N ₂ gas, inert gas such as He, Ne, and Ar. These gases may be mixed and used. The carrier gas may be the same as or different from the atmospheric gas, but is preferably the same.

From the introduction pipe 101, a source gas serving as a nitrogen source is supplied. Normally, NH ₃ gas is supplied. A carrier gas is supplied from the introduction pipe 102. As the carrier gas, the same carrier gas supplied from the introduction pipe 103 can be exemplified. The carrier gas supplied from the introduction pipe 102 and the carrier gas supplied from the introduction pipe 103 are preferably the same. A dopant gas can also be supplied from the introduction pipe 102. For example, an n-type dopant gas such as SiH ₄ or SiH ₂ Cl ₂ can be supplied.

  An etching gas can be supplied from the introduction pipe 104. As an etching gas, a chlorine-based gas can be used, and HCl gas is preferably used. Etching can be performed by setting the flow rate of the etching gas to about 0.1% to 3% with respect to the total flow rate. A preferable flow rate is about 1% with respect to the total flow rate. The gas flow rate can be controlled by a mass flow controller (MFC) or the like, and the individual gas flow rates are preferably always monitored by MFC.

  The gases supplied from the introduction pipes 101, 102, and 104 may be exchanged with each other and supplied from different introduction pipes. Further, the source gas and the carrier gas that are the group V source may be mixed and supplied from the same introduction pipe. Further, a carrier gas may be mixed from another introduction pipe. These supply modes can be appropriately determined according to the size and shape of the reactor 100, the reactivity of the raw materials, the target crystal growth rate, and the like.

  The gas discharge pipe 108 is generally installed so that it can be discharged from the reactor inner wall on the opposite side to the introduction pipes 101 to 104 for gas introduction. In FIG. 1, a gas discharge pipe 108 is installed on the bottom surface of the reactor located opposite to the top surface of the reactor where the introduction pipes 101 to 104 for gas introduction are installed. When the introduction pipe for introducing gas is installed on the right side of the reactor, the gas discharge pipe is preferably installed on the left side of the reactor. By adopting such an aspect, a gas flow can be stably formed in a certain direction.

  Crystal growth by the HVPE method is usually performed at 900 ° C. to 1070 ° C., preferably at 925 ° C. to 1050 ° C., more preferably at 950 ° C. to 1030 ° C., and further at 975 ° C. to 1000 ° C. preferable. The pressure in the reactor is preferably 10 kPa to 200 kPa, more preferably 30 kPa to 150 kPa, and even more preferably 50 kPa to 120 kPa. The etching temperature and pressure at the time of etching may be the same as or different from the crystal growth temperature and pressure.

  A group III nitride semiconductor crystal obtained after crystal growth may have a polycrystal at the boundary of crystal planes. The polycrystal here means, for example, a crystal in which a hexagonal crystal lattice cannot be formed and there is no atom at an appropriate position. That is, it refers to a collection of minute crystals with disordered crystal orientation, meaning a collection of very small single crystal grains. In the case of having such a polycrystalline body, after performing the step of removing the polycrystalline body, a step of growing a group III nitride semiconductor crystal on the surface of the crystal from which the polycrystalline body has been removed is further performed. When the group III nitride semiconductor crystal thus obtained still has a polycrystal at the boundary of the crystal plane, a step of removing the polycrystal is performed again, and a group III nitride semiconductor crystal is further formed on the surface. Perform growth process. By repeating such an operation, a group III nitride semiconductor crystal having no polycrystal can be obtained.

  The crystal system of the group III nitride semiconductor obtained by the production method of the present invention is preferably a hexagonal system. Further, the obtained group III nitride semiconductor crystal is preferably a single crystal. The thickness of the group III nitride semiconductor crystal grown on the base substrate is preferably 2 mm to 10 cm. When performing grinding, polishing, laser irradiation, etc. after crystal growth, a crystal of a certain size is required. Therefore, the thickness of the group III nitride semiconductor crystal grown on the base substrate is preferably 5 mm to 10 cm. 1 cm to 10 cm is more preferable.

  The group III nitride semiconductor crystal obtained by the production method of the present invention may be used as it is or after being subjected to processing such as grinding or slicing. Here, slicing is (1) processing to make the quality of the C-plane surface uniform so that the grown crystal can be used as a base substrate, and (2) there is stress generated from dislocations inherent in the initial growth portion. This is a process that is performed to cut off the portion in consideration of the above. Specifically, the slicing can be performed using an inner peripheral slicer, a wire source slicer, or the like. In the present invention, it is preferable to produce a crystal having substantially the same shape, lower dislocation density, and fewer surface defects by slicing.

  According to the production method of the present invention, a group III nitride semiconductor crystal having a C-plane or M-plane with a surface roughness of 1 nm or less can be obtained. In particular, a group III nitride semiconductor crystal having a C-plane or M-plane with a surface roughness of 1 nm or less can be produced without polishing after crystal growth. In addition, the surface roughness (Rms) in this invention is calculated | required by calculating with a root mean square from the data which measured the surface roughness of 10 micrometers square using atomic force microscope (AFM).

  The group III nitride semiconductor crystal produced by the production method of the present invention can be used for various applications. In particular, it is useful as a substrate for semiconductor devices such as light emitting diodes of ultraviolet, blue or green, etc., light emitting elements having relatively short wavelengths such as semiconductor lasers, and electronic devices. It is also possible to obtain a larger group III nitride semiconductor crystal by using the group III nitride semiconductor crystal manufactured by the manufacturing method of the present invention as a base substrate.

The features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.
In the following examples and comparative examples, crystal growth was performed using the HVPE apparatus shown in FIG.

(Example 1)
A GaN layer having a thickness of 4 μm was grown on a sapphire substrate having a surface of (0001) plane and a thickness of 430 μm and a diameter of 76.2 mm (3 inches) using an MOCVD apparatus. This is placed on a SiC-coated carbon substrate holder with a diameter of 80 mm and a thickness of 20 mm, and a GaN free-standing substrate with a thickness of 400 μm and a diameter of 54 mm having a (0001) surface is mounted on the GaN layer. (FIG. 2), placed in the reactor 100 of the HVPE apparatus as shown in FIG.
After raising the temperature to 1050 ° C., H ₂ carrier gas G1 and N The GaN layer was grown for 26 hours while supplying the carrier gas G2, the GaCl gas G3, which is a reaction product of Ga and HCl, and the NH ₃ gas G4 from the introduction pipes 101 to 104, respectively. In this GaN layer growth step, the growth pressure is 1.01 × 10 ⁵ Pa, the partial pressure of the GaCl gas G3 is 3.07 × 10 ² Pa, and the partial pressure of the NH ₃ gas G4 is 1.27 × 10 ⁴ Pa. It was. After completion of the GaN layer growth step, the temperature was lowered to room temperature to obtain a GaN single crystal thick film having a thickness of about 3.8 mm.

(Example 2)
A GaN layer having a thickness of 4 μm was grown on a sapphire substrate having a thickness of 430 μm and a diameter of 60 mm having a (0001) plane by a MOCVD apparatus. This is placed on a SiC-coated carbon substrate holder having a diameter of 75 mm and a thickness of 20 mm, and a GaN free-standing substrate having a thickness of 400 μm and a diameter of 54 mm is mounted on the GaN layer. (FIG. 2), placed in the reactor 100 of the HVPE apparatus as shown in FIG.
The temperature, gas partial pressure, and growth time in the GaN layer growth step were the same as those in Example 1. After completion of the GaN layer growth step, the temperature was lowered to room temperature to obtain a thick GaN single crystal film having a thickness of about 4.0 mm.

(Example 3)
Processing was performed to provide a step of about 3 mm in width and 400 μm in height over the entire outer periphery of a GaN free-standing substrate having a thickness of 600 μm and a diameter of 60 mm with a (0001) surface (FIG. 3). This was placed on a SiC-coated carbon substrate holder having a diameter of 75 mm and a thickness of 20 mm (FIG. 4), and placed in the reactor 100 of the HVPE apparatus as shown in FIG.
The temperature, gas partial pressure, and growth time in the GaN layer growth step were the same as those in Example 1. After completion of the GaN layer growth step, the temperature was lowered to room temperature to obtain a thick GaN single crystal film having a thickness of about 4.0 mm.

(Comparative Example 1)
A GaN free-standing substrate having a surface of (0001) thickness of 400 μm and a diameter of 50.8 mm (2 inches) is placed on a SiC-coated carbon substrate holder having a diameter of 75 mm (FIG. 5), and the reactor 100 of the HVPE apparatus. As shown in FIG.
The temperature, gas partial pressure, and growth time in the GaN layer growth step were the same as those in Example 1. After completing the GaN layer growth step, the temperature was lowered to room temperature to obtain a GaN single crystal thick film.

(Comparative Example 2)
A GaN free-standing substrate having a surface of (0001) thickness of 400 μm and a diameter of 50.8 mm (2 inches) is placed on a SiC-coated carbon substrate holder having a diameter of 30 mm (FIG. 6), and the reactor 100 of the HVPE apparatus. As shown in FIG.
The temperature, gas partial pressure, and growth time in the GaN layer growth step were the same as those in Example 1. After completion of the GaN layer growth step, the temperature was lowered to room temperature to obtain a GaN single crystal thick film.

(Test example)
The surface states of the GaN crystals obtained in Examples 1 to 3 and Comparative Examples 1 and 2 were observed visually and with an optical microscope. Further, the crystal cross-sectional shape was visually confirmed after cutting with a slicer. Furthermore, the thickness of the crystal center was measured with a micrometer. The results are shown in the table below.

In Example 1 and Example 2, a high-quality GaN single crystal thick film having a good cross-sectional shape without abnormal growth in the peripheral portion or surface roughness was obtained.
In Example 3, abnormal growth of the crystal was observed on the outermost periphery, but the height of the abnormally grown crystal was low, and there was no abnormal growth or surface roughness in the range of about 54 mm in diameter at the center. A membrane was obtained.
In Comparative Example 1, abnormal growth was observed at the edge of the substrate, and surface roughness was severe. The film thickness at the center was about 2.5 mm, which was about 1.3 to 1.5 mm thinner than the crystals of Examples 1 to 3 grown at the same gas flow rate and growth time.
Also in Comparative Example 2, abnormal growth was observed at the edge of the substrate, and surface roughness was severe. The film thickness at the center was about 2.2 mm, which was about 1.6 to 1.8 mm thinner than the crystals of Examples 1 to 3 grown at the same gas flow rate and growth time.

  When the group III nitride semiconductor crystal is grown using the base substrate of the present invention, it is possible to suppress the group III nitride semiconductor crystal from growing abnormally at the peripheral portion of the first crystal growth surface. As a result, a group III nitride semiconductor having a good surface state and cross-sectional shape can be grown on the first crystal growth surface. Further, according to the method for growing a group III nitride semiconductor of the present invention, a flat and uniform thick film crystal can be produced at a low cost. The obtained crystal is useful as a substrate for semiconductor light emitting devices such as light emitting diodes and semiconductor lasers, and semiconductor devices such as electronic devices. Therefore, the present invention has high industrial applicability.

DESCRIPTION OF SYMBOLS 100 Reactor 101-104 Introducing pipe 105 Reservoir 106 Heater 107 Substrate holder 108 Exhaust pipe 109 Crystal with the second crystal growth surface 110 Crystal with the first crystal growth surface 111 Seed crystal substrate with step processing on the outer periphery 112 Base Substrate G1 H ₂ carrier gas G2 N ₂ carrier gas G3 Group III source gas G4 Group V source gas

Claims (18)

A base substrate having a first crystal growth surface and a second crystal growth surface facing in the same direction as the first crystal growth surface,
The second crystal growth surface is connected to 50% or more of the periphery of the first crystal growth surface through a downward step;
A base substrate for growing a group III nitride semiconductor, wherein the height of the step is 0.1 to 5 mm.   2. The group III nitride semiconductor according to claim 1, wherein both the material constituting the first crystal growth surface and the material constituting the second crystal growth surface are made of a single crystal of a group III nitride semiconductor. Base substrate for growth. A base substrate having a first crystal growth surface and a second crystal growth surface facing in the same direction as the first crystal growth surface,
The second crystal growth surface is connected to 50% or more of the periphery of the first crystal growth surface through a downward step;
Both the material constituting the first crystal growth surface and the material constituting the second crystal growth surface are made of a single crystal of a group III nitride semiconductor,
A base substrate for growing a group III nitride semiconductor, wherein the first crystal growth surface is a (0001) plane.   4. The base substrate for growing a group III nitride semiconductor according to claim 3, wherein the height of the step is 0.1 to 5 mm.   5. The group III nitride semiconductor according to claim 1, wherein the second crystal growth surface is connected to the entire periphery of the first crystal growth surface via a downward step. Base substrate for growth.   The base substrate for growing a group III nitride semiconductor according to any one of claims 1 to 5, wherein the first crystal growth surface is circular.   The base substrate for growing a group III nitride semiconductor according to claim 6, wherein the second crystal growth surface is annular and concentric with the circular first crystal growth surface.   The group III nitride semiconductor growth according to claim 1, wherein the first crystal growth surface and the second crystal growth surface are present in a single continuous member. Base substrate.   8. The group III nitride semiconductor growth according to claim 1, wherein a member constituting the first crystal growth surface is different from a member constituting the second crystal growth surface. 9. Base substrate.   The group III nitride semiconductor growth according to any one of claims 1 to 9, wherein a member constituting the first crystal growth surface and the second crystal growth surface is formed on a base substrate. Substrate for use.   The base substrate for group III nitride semiconductor growth according to claim 10, wherein the base substrate is a sapphire single crystal substrate or a SiC single crystal substrate.   A step of crystal-growing a group III nitride semiconductor on the base substrate by supplying a gas for forming a group III nitride semiconductor on the base substrate according to claim 1. A method for growing a group III nitride semiconductor.   13. The method for growing a group III nitride semiconductor according to claim 12, wherein the base substrate is made of the same type of single crystal as the group III nitride semiconductor for crystal growth.   14. The method for growing a group III nitride semiconductor according to claim 12, wherein the group III nitride semiconductor is crystal-grown with a thickness of 5 mm or more.   The method for growing a group III nitride semiconductor according to any one of claims 12 to 14, wherein the crystal growth is performed by a hydride vapor phase growth method.   16. The method for growing a group III nitride semiconductor according to claim 12, further comprising a step of separating the second crystal growth surface from the base substrate.   A group III nitride semiconductor crystal grown on a base substrate, wherein the group III nitride semiconductor crystal has a growth thickness of 2 mm or more and a surface after crystal growth is a mirror surface. Semiconductor crystals.   The group III nitride semiconductor crystal according to claim 17, wherein the surface has a surface roughness of 1 nm or less.