JP2016069205A - Manufacturing method of nitride semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently manufacturing a GaN substrate having a damage layer removed from a backside plane while avoiding a breakdown of the substrate to the utmost in a process.SOLUTION: A manufacturing method of a nitride semiconductor substrate which has a front-side plane as a primary plane and a backside plane as another primary plane and of which the front-side plane is used for epitaxial growth of a nitride semiconductor includes the following steps: (1) a substrate preparation step for preparing a start substrate of which two primary planes are as-sliced planes formed by slicing a single crystal of a bulk nitride semiconductor, and (2) a backside plane etching step for removing by dry etching at least part of a damage layer formed on the backside primary plane of the nitride semiconductor substrate of the two primary planes of the start substrate.SELECTED DRAWING: Figure 1

Description

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

Nitride semiconductors are also referred to as group III nitride compound semiconductors, nitride group III-V compound semiconductors, GaN semiconductors, etc. In addition to containing GaN, some or all of Ga in GaN is in other periodic tables. Including compounds replaced with group 13 elements (B, Al, In, etc.). For example, AlN, InN, AlGaN, AlInN, GaInN, AlGaInN and the like. Nitride semiconductors have a wurtzite crystal structure belonging to the hexagonal system. A nitride semiconductor substrate refers to a free-standing substrate composed of only a single crystal of a nitride semiconductor, and typical examples thereof are a GaN substrate and an AlN substrate.
Hereinafter, the present invention will be described using a GaN substrate as an example.

  In the GaN crystal, the crystal axis parallel to [0001] is called c-axis, the crystal axis parallel to [10-10] is called m-axis, and the crystal axis parallel to [11-20] is called a-axis. The crystal plane orthogonal to the c-axis is referred to as C-plane, the crystal plane orthogonal to the m-axis is referred to as M-plane, and the crystal plane orthogonal to the a-axis is referred to as A-plane. Hereinafter, in this specification, when referring to crystal axes, crystal planes, crystal orientations, etc., unless otherwise specified, the crystal axes, crystal planes, crystal orientations, etc. of GaN crystals are meant.

  The name of the crystal plane or the Miller index attached to the name of the GaN substrate is that of the low index plane that is parallel or closest to the front side surface of the substrate. The front side surface is a surface intended to be used for the formation of a semiconductor device or the epitaxial growth of a crystal among the two main surfaces of the substrate. The main surface that is not the front side is called the back side. For example, a GaN substrate having a low index plane parallel or closest to the front side surface that is an M plane, ie, (10-10), is called an M plane substrate or a (10-10) substrate. Usually, a crystal plane in which the absolute values of integers h, k, m, and l in the Miller index (hkml) are all 3 or less is defined as a low index plane.

  Various nitride semiconductor devices such as light emitting diodes are formed using a GaN substrate.

  Improvement of nitride semiconductor devices by using a nonpolar or semipolar GaN substrate is expected (Non-Patent Document 1).

  Of particular interest among nonpolar GaN substrates are (10-10) substrates, ie, M-plane substrates. Of particular interest among the semipolar GaN substrates are the (20-21) substrate, the (20-2-1) substrate, the (30-31) substrate, and the (30-3-1) substrate.

  A tiling method has been devised as a method for obtaining a large-area nonpolar or semipolar GaN substrate such as a 2-inch substrate (a disk-shaped substrate having a diameter of 2 inches). In the tiling method, a plurality of seed substrates are densely arranged in the lateral direction so that the crystal orientations are aligned, and a bulk GaN crystal forming one continuous layer is vapor-phase epitaxially grown on the plurality of seed substrates (Patent Document 1). .

  In a GaN substrate, it is desirable that the warpage be as small as possible. In general, the warpage in which the front side becomes a convex surface is permissible as long as it is slight. Warpage with a convex rear surface may be allowed, but is usually not preferred. In order to reduce the warpage generated in the GaN substrate, the damaged main surface is mechanically polished to introduce a damaged layer, or the mechanically polished damaged layer existing on the convex main surface is removed by etching. A method is known (Patent Document 2).

  In the C-plane GaN substrate, in order to improve the adhesion between the substrate holder of the vapor phase growth furnace and the back side surface (N surface) of the substrate, the back side surface is mechanically polished and flattened, and then wet etched and roughened. A method has been proposed (Patent Document 3).

  After the mechanical polishing of the back side of the GaN substrate obtained by slicing the ingot, a part of the damaged layer formed by the mechanical polishing is removed by etching. Manufacturing of the GaN substrate with the damaged layer remaining on the back side A method is known (Patent Document 4).

JP 2006-315947 A JP 2005-136167 A JP 2007-153712 A JP 2007-250766 A

Po Shan Hsu, Matthew T. Hardy, Erin C. Young, Alexey E. Romanov, Steven P. DenBaars, Shuji Nakamura, and James S. Speck, Applied Physics Letters 100, 171917 (2012)

  The GaN substrate is used as a substrate for forming a nitride semiconductor device or a seed substrate for growing a bulk nitride semiconductor crystal. Therefore, the damage layer on the front side surface, which is the main surface on the side on which the nitride semiconductor is epitaxially grown, is removed at the stage of finishing.

  For example, epitaxial growth in forming a nitride semiconductor device is generally performed by MOCVD, and the substrate is heated to a temperature close to 1000 ° C. or higher than 1000 ° C. in a growth furnace. At this time, the GaN substrate having the damaged layer on the back side, which is the main surface opposite to the front side, is greatly deformed. This is because the crystal defects contained in the damaged layer on the back side surface are removed by the action of heat, and the damaged layer thickness is substantially reduced.

  Since such deformation is not preferable, it is desirable to remove the damaged layer as much as possible from the back side surface of the GaN substrate.

  In the prior art, the back side surface of the GaN substrate is generally mechanically polished and then etched to remove the damaged layer.

  An object of the present invention is to provide a method for efficiently producing a GaN substrate from which a damaged layer on the back side surface has been removed while avoiding damage to the substrate during the process as much as possible.

  In addition, an object of the present invention is to provide a method for efficiently producing a GaN substrate having a smoothness suitable for epitaxial growth of a nitride semiconductor, with the damage layer on the back side surface removed, and the front side surface.

(1) A method of manufacturing a nitride semiconductor substrate having a front side surface that is one main surface and a back side surface that is the other main surface, wherein the front side surface is used for epitaxial growth of a nitride semiconductor,
(1) A substrate preparation step of slicing a bulk nitride semiconductor single crystal to prepare a starting substrate whose two main surfaces are as-sliced surfaces;
(2) a back side etching step of removing at least a part of the damaged layer formed on the main surface of the two main surfaces of the starting substrate to be the back side of the nitride semiconductor substrate by dry etching;
A method for manufacturing a nitride semiconductor substrate, comprising:
(2) After the substrate preparation step and before the back side surface etching step, at least a part of the damaged layer formed on the main surface of the starting substrate to be the front side surface of the nitride semiconductor substrate is removed by dry etching. The manufacturing method according to (1), further comprising a front side etching step.
(3) further includes a mechanical polishing step of subjecting the substrate obtained by the back side etching step (hereinafter referred to as a first work-in-process substrate) to mechanical polishing;
The mechanical polishing is performed on the main surface to be the front side surface of the nitride semiconductor substrate of the first processed substrate, from which at least a part of the damaged layer has been removed by dry etching in the front side etching step. The manufacturing method according to (2).
(4) A table in which at least part of the damaged layer formed on the main surface of the substrate subjected to the back side etching after the back side etching is to be the front side of the nitride semiconductor substrate is removed by dry etching. The manufacturing method according to (1), further comprising a side surface etching step.
(5) It further includes a mechanical polishing step for subjecting the substrate obtained by the front side surface etching step (hereinafter referred to as a second work-in-process substrate) to mechanical polishing,
The mechanical polishing is performed on the main surface to be the front side surface of the nitride semiconductor substrate of the second processed substrate, in which at least a part of the damaged layer has been removed by dry etching in the front side etching step. The manufacturing method according to (4).
(6) The manufacturing method according to any one of (1) to (5), wherein the nitride semiconductor substrate is a nonpolar substrate or a semipolar substrate.
(7) The manufacturing method according to (6), wherein an angle formed between a front side surface of the nitride semiconductor substrate and a (10-10) plane is 0 ° or more and 20 ° or less.
(8) The manufacturing method according to any one of (1) to (7), wherein the nitride semiconductor substrate is a GaN substrate.

  According to the method of the present invention, a GaN substrate from which the damage layer on the back side surface has been removed can be efficiently manufactured while avoiding damage to the substrate during the process as much as possible.

  According to the method of one embodiment of the present invention, the damaged layer on the back side surface is removed, and a GaN substrate having smoothness suitable for epitaxial growth of the nitride semiconductor on the front side surface can be efficiently manufactured.

  According to the method of one embodiment of the present invention, a nonpolar or semipolar GaN substrate from which the damage layer on the back side surface has been removed can be efficiently manufactured while avoiding damage to the substrate in the process as much as possible. .

  According to the method of one embodiment of the present invention, a nonpolar or semipolar GaN substrate having a smoothness suitable for epitaxial growth of a nitride semiconductor is efficiently produced by removing the damaged layer on the back side surface. be able to.

It is a plot of the relationship between the etching time and the warp when one of the main surfaces of the M-plane GaN substrate whose both main surfaces are as-sliced surfaces is dry-etched under certain conditions.

The method for manufacturing a nitride semiconductor substrate according to the present invention includes the following steps.
(1) A substrate preparation step of slicing a bulk nitride semiconductor single crystal to prepare a starting substrate in which two main surfaces are as-sliced surfaces.
(2) A back side etching process in which at least a part of a damaged layer formed on the main surface of the two main surfaces of the starting substrate, which should be the back side of the nitride semiconductor substrate, is removed by dry etching.

  The embodiment of the present invention will be described by taking a GaN substrate manufacturing method as an example.

<Board preparation process>
In the substrate preparation step, a bulk GaN single crystal is sliced to prepare a starting substrate whose two main surfaces are as-sliced surfaces.

  The bulk GaN single crystal may be manufactured by any method. Typically, a bulk GaN single crystal is manufactured by a method of epitaxially growing GaN on a seed substrate using an HVPE method, a flux method, an ammonothermal method, or the like.

  When the seed substrate includes a different composition substrate (a substrate having a chemical composition different from that of GaN), it is common to slice the bulk GaN single crystal after removing the seed substrate. When the seed substrate is a GaN single crystal substrate, removal of the seed substrate is not essential.

  In many cases, the outer shape of the bulk GaN crystal is prepared by machining such as grinding and core drilling before being sliced. A flat portion that becomes an orientation flat in the substrate after slicing may be provided in the bulk GaN single crystal before slicing.

  The slicing of the bulk GaN single crystal can be performed using, for example, a wire saw. Although the damage layer caused by slicing is removed by the method of the present invention, it is preferable that the damage layer is thinner in order to reduce the amount of the damage layer that needs to be removed. From this point of view, the bulk GaN single crystal is preferably sliced using a wire saw.

  For the bulk GaN single crystal slicing with a wire saw, there are a free abrasive grain method while supplying a slurry containing abrasive grains and a fixed abrasive grain method using a fixed abrasive wire (a wire having abrasive grains fixed on the surface). is there. Any of them can be adopted, but the fixed abrasive method is more preferable. The reason why the slice by the fixed abrasive method is preferable is that the cutting speed is higher than that of the free abrasive method and the cost is low because the slurry is unnecessary.

  In the fixed abrasive wire, electrodeposition is preferably used to fix the abrasive to the wire surface. The material of the abrasive grains is, for example, alundum (A), white alundum (WA), pink alundum (PA), disassembled alumina (HA), artificial emery (AE), alumina zirconia (AZ), carborundum ( C), green carborundum (GC), cubic boron nitride (CBN), diamond and the like.

  The average grain size of the abrasive grains used for the fixed abrasive wire is preferably 5 μm or more, more preferably 10 μm or more, and 60 μm or less, further 40 μm or less, further 30 μm or less, and further 20 μm or less. Is preferred. In terms of particle size indication of generally available fixed abrasive wire, it is preferably 3000 mesh or less, more preferably 1500 mesh or less, 230 mesh or more, further 325 mesh or more, further 400 mesh or more, and further 600 mesh or more. Furthermore, 800 mesh or more is preferable.

  The wire diameter of the wire used for the fixed abrasive wire is 70 μm or more, more preferably 120 μm or more, further 140 μm or more, further 160 μm or more, more preferably 170 μm or more, and further preferably 180 μm or more, and 200 μm. Hereinafter, it is further preferably 190 μm or less.

  In the slice of the bulk GaN single crystal by the wire saw, the traveling direction of the wire may be one direction or both forward and reverse directions. In any case, the traveling speed of the wire is preferably 100 m / min or more, more preferably 300 m / min or more, and further preferably 400 m / min or more, and is preferably 1500 m / min or less, more preferably 1000 m / min or less.

  After slicing, it is possible to perform machining for adjusting the outer peripheral shape of the substrate.

  There are no particular restrictions on the shape and dimensions of the starting substrate.

<Back side etching process>
In the back side etching step, at least a damage layer formed on the main surface to be the back side out of the two main surfaces (both are as-sliced surfaces) of the starting substrate prepared in the above-described substrate preparation step A part is removed by dry etching.

The type of dry etching is not limited, but is preferably plasma etching or reactive ion etching (RIE). In RIE, it is preferable to use an etching gas containing one or more compounds containing chlorine or fluorine. Examples of compounds containing chlorine include chlorine gas (Cl ₂ ), chloromethanes (CH _x Cl _4-x ; x is an integer from 0 to 3), BCl ₃ , chlorosilanes (SiH _x Cl _4-x ; x is 1 to 3). Examples of the compound containing fluorine are fluoromethanes (CH _x F _4-x ; x is an integer of 0 to 3), SiF ₄ , SF _{6 and the} like.

  Dry etching is desirably performed until the damaged layer is completely removed. The degree of removal of the damaged layer can be known, for example, by measuring how the warpage of the substrate to be processed changes with the etching time.

  FIG. 1 is a plot of the relationship between the etching time and the warp when one of the main surfaces of the M-plane GaN substrate whose main surfaces are as-sliced surfaces is dry-etched under certain conditions. As shown in the graph of FIG. 1, the warpage of the substrate greatly changes with the etching time for a while from the start of etching, but saturates at a certain point and becomes constant regardless of the etching time. It is considered that the damaged layer was completely removed when saturated.

The etching time in the back side etching step can be set based on the minimum time T _min required for complete removal of the damaged layer, which is obtained by this method.

  In the case of a nonpolar or semipolar GaN substrate, it is particularly advantageous to use dry etching instead of wet etching for removing the damaged layer for the following reason.

  In the case of a nonpolar or semipolar GaN substrate (in the case of a semipolar GaN substrate, in particular, a GaN substrate whose angle between the front side surface and the (10-10) plane is 20 ° or less), the wet resistance of the back side surface Etchability is comparable to the gallium polar face of C-plane GaN substrates. That is, the wet etching resistance is very high. For this reason, it is difficult to completely remove the damaged layer on the as-sliced surface within a short time by wet etching. For example, when using a KOH aqueous solution, an etching time of 24 hours is required even at 100 ° C. .

  Further, in wet etching, not only the processing time is long, but also there is a problem that cracks are generated in the substrate due to thermal stress when the substrate is immersed in a high temperature etching solution. This problem becomes more serious when the substrate is thick or when the size of the main surface is large.

  On the other hand, in dry etching, it is possible to remove the damaged layer at a high rate without heating the substrate with a heater, and it is possible to remove the damaged layer while avoiding the occurrence of cracks in the substrate. Therefore, it is advantageous. Therefore, the GaN substrate from which the damaged layer on the back side surface has been removed can be efficiently manufactured while avoiding damage to the substrate during the process as much as possible.

<Front side etching process>
The manufacturing method of the present invention can include a front side etching step in addition to the substrate preparation step and the back side etching step. The front side surface etching step is a step of dry etching the main surface to be the front side surface of the substrate.

  The front side etching process may be performed before or after the back side etching process.

  The front side surface of the GaN substrate is usually flattened by mechanical polishing (grinding, lapping, polishing) and, if necessary, subsequent chemical mechanical polishing. When performing mechanical polishing, it is necessary to attach the substrate to be processed to a flat plate. At this time, the GaN substrate in which only the damaged layer on the back side surface or only the damaged layer on the front side surface is removed from the starting substrate is broken. This is because such a GaN substrate is often greatly warped due to a damaged layer remaining only on one of the front and back sides. Since GaN is a hard and brittle material, it can be easily cracked when trying to correct the warpage.

  On the other hand, the GaN substrate from which the damaged layer has been removed by etching from both the back side and the front side has a small warp, and can be attached to a flat plate so as not to break.

  In dry etching processing, the substrate to be processed only needs to be placed on the sample stage, and does not need to be fixed. This is a big difference between dry etching and mechanical polishing. Even if a GaN substrate in which only one damaged layer on the front side surface or the back side surface is removed from the starting substrate, that is, a GaN substrate having a large warp is a substrate to be processed, dry etching is performed without forcibly correcting the warp. be able to. That is, in dry etching, there is no fear that the GaN substrate breaks.

  The manufacturing method according to the embodiment includes the following two aspects in which the back-and-forth relationship between the back side surface etching step and the front side surface etching step is different.

  In the first embodiment, after the substrate preparation step and before the back side surface etching step, at least a part of the damaged layer formed on the main surface of the starting substrate which should be the front side surface of the nitride semiconductor substrate is removed by dry etching. Including a front side etching step. In this aspect, after that, the substrate (first work-in-process substrate) obtained by the back side etching step is subjected to mechanical polishing (mechanical polishing step described later).

  In the second aspect, after being subjected to the back side etching step, at least part of the damaged layer formed on the main surface to be the front side of the nitride semiconductor substrate of the substrate subjected to the back side etching is dry-etched. A front side etching process to be removed is included. In this aspect, after that, the substrate (second processed work substrate) obtained by the front side surface etching step is subjected to mechanical polishing (a mechanical polishing step described later).

  The dry etching method and conditions in the back side etching step can be appropriately determined in consideration of the back side etching with reference to the dry etching methods and conditions in the front side etching step.

<Mechanical polishing process>
The mechanical polishing process is intended to flatten the main surface of the GaN substrate that should be the front side surface.
The mechanical polishing performed in the mechanical polishing step usually includes at least one process selected from grinding, lapping and polishing.
The mechanical polishing process may be performed before or after the back side etching process.

  The mechanical polishing step is preferably performed after removing the damaged layer from both the front and back sides of the starting substrate by dry etching. That is, it is preferable to carry out after the back side surface etching step and the front side surface etching step.

  After the mechanical polishing step, if necessary, chemical mechanical polishing may be further performed to smooth the main surface (surface to be the front side surface) flattened in the mechanical polishing step. Existing methods and conditions for mechanical polishing and chemical mechanical polishing can be used as they are.

  Further, in addition to processing the front side surface and the back side surface, the outer peripheral portion of the substrate may be processed. For example, chamfering using a rubber grindstone, a tape grindstone, or the like.

<GaN substrate>
The type of GaN substrate manufactured using the manufacturing method of the present invention is not limited, and may be a C-plane substrate, a nonpolar substrate (M-plane substrate or A-plane substrate), or a semipolar substrate.

  The production method of the present invention is particularly useful when used for the production of a nonpolar or semipolar GaN substrate, particularly a GaN substrate in which the angle between the normal of the front side surface and the m-axis is not less than 0 degrees and not more than 20 degrees. It is. Since the main surface of such a GaN substrate is highly resistant to alkalis and acids, it is necessary to perform a long-time treatment under severe conditions in order to completely remove the damaged layer by wet etching. Then, the [000-1] side surface having a lower chemical resistance than that of the main surface is vigorously etched to form a rough surface having significantly unevenness, so that it needs to be repaired.

  Furthermore, in a GaN substrate where the angle between the normal on the front side and the m-axis is 0 degree or more and 20 degrees or less, if the damaged layer is removed by wet etching, a hole penetrating from the front side to the back side is formed. There is a case. This is because the (000-1) plane is exposed inside fine cracks that may be formed in the slicing step. The (000-1) plane has low resistance to alkalis and acids and is easily etched. In addition, as the crack expands due to etching, the fresh etching solution becomes more likely to penetrate into the crack, so that the fine crack easily develops to the through hole. On the other hand, in the dry etching, since the etching proceeds in the thickness direction of the substrate, it is difficult for the cracks to expand.

  In other words, a GaN substrate in which the angle between the normal on the front side and the m-axis is not less than 0 degrees and not more than 20 degrees is a GaN substrate having an inclination angle of 0 to 20 degrees with respect to the M plane on the front side. is there. [10-10], [20-21], [20-2-1], [30-31], and [30-3-1] have an angle of 0 ° or more and 20 ° or less with respect to the m-axis. (10-10) substrate, (20-21) substrate, (20-2-1) substrate, (30-31) substrate, and (30-3-1) substrate are The angle between the normal and the m-axis is included in a GaN substrate having an angle between 0 degrees and 20 degrees.

Example 1
A plurality of M-plane GaN substrates having a main surface of a rectangle, a long side parallel to the a-axis, and a short side parallel to the c-axis were prepared. The plurality of M-plane GaN substrates are arranged closely in the c-axis direction with the front side facing upward, thereby forming a collective seed having an upper surface size of 55 mm × 55 mm.

  A bulk GaN crystal layer having a thickness of about 7 mm was grown on the aggregate seed using the HVPE method to obtain a composite of the aggregate seed and the bulk GaN crystal layer.

  Next, the GaN crystal layer portion contained in this composite is sliced in parallel with the M-plane using a wire saw, so that a GaN substrate (starting substrate) having a thickness of about 450 μm whose both main surfaces are as-sliced surfaces. Got. The saw wire used for slicing was a fixed abrasive wire in which abrasive grains having an average particle size of less than 60 μm were fixed to the wire by electrodeposition.

Next, the damaged layer formed on one of the main surfaces of the starting substrate (the side to be used as the back side surface) was removed by RIE using Cl ₂ as an etching gas. The conditions were an etching gas supply rate of 50 sccm, an etching power of 140 W / 50 W (antenna / bias), a chamber pressure of 0.3 Pa, and an etching time of 17 minutes. This time was determined based on the etching time T _min required for complete removal of the damaged layer obtained by the above-described method. While avoiding breakage of the substrate, the damaged layer formed on the back side should be completely removed.

  Next, the other main surface (side to be the front side) of this substrate was planarized by sequentially applying grinding and lapping, and further smoothed by chemical mechanical polishing (CMP). Through the above procedure, an M-plane GaN substrate having a diameter of 2 inches was obtained.

Example 2
In the same manner as in Example 1, a substrate from which the damaged layer formed on the side to be the back side surface was removed by dry etching was obtained. Before this substrate was ground, dry etching for removing the damaged layer was performed on the main surface that should be the front side. The dry etching conditions are the same as the dry etching conditions applied to the main surface on the side to be the back side surface in Example 1. After the dry etching, grinding, lapping and CMP were sequentially performed on the same main surface (the side to be the front side). The conditions are the same as in Example 1.

  Through the above procedure, an M-plane GaN substrate having a diameter of 2 inches was obtained.

  In Example 1, when the GaN substrate was attached to a flat plate for mechanical polishing, cracks occurred at a frequency of one in four. On the other hand, in Example 2, the crack generation rate of the GaN substrate in the same process was substantially zero.

Comparative Example 1
Instead of RIE processing the as-sliced surface, the entire GaN substrate was immersed in a 48 wt% KOH aqueous solution for etching. Under the condition of an etching temperature of about 100 ° C., the time required for removing the damaged layer was 1440 minutes. In some substrates, cracks occurred when immersed in an etchant heated to about 100 ° C.

  A through-hole that was thought to be caused by expansion of fine cracks was observed in the substrate after etching for 1440 minutes. Further, the side surface on the [000-1] side of the substrate is remarkably rough, and an end surface polishing process for removing this rough surface is required.

Test example 1
The relationship between the etching time and warpage when one main surface of the M-plane GaN substrate having both main surfaces as-sliced planes prepared by the same method as described in Example 1 is dry-etched under certain conditions. Asked. The conditions for dry etching are the same as in Example 1. The results are plotted and shown in FIG.

  The present invention is useful in the field relating to the manufacture of nitride semiconductor substrates.

Claims (8)

A method for producing a nitride semiconductor substrate having a front side surface that is one main surface and a back side surface that is the other main surface, wherein the front side surface is used for epitaxial growth of a nitride semiconductor,
(1) A substrate preparation step of slicing a bulk nitride semiconductor single crystal to prepare a starting substrate whose two main surfaces are as-sliced surfaces;
(2) a back side etching step of removing at least a part of the damaged layer formed on the main surface of the two main surfaces of the starting substrate to be the back side of the nitride semiconductor substrate by dry etching;
A method for manufacturing a nitride semiconductor substrate, comprising: After the substrate preparation step and before the back side surface etching step, front side etching for removing at least a part of the damaged layer formed on the main surface of the starting substrate to be the front side surface of the nitride semiconductor substrate by dry etching The manufacturing method according to claim 1, further comprising a step. It further includes a mechanical polishing step for subjecting the substrate obtained by the back side etching step (hereinafter referred to as a first work-in-process substrate) to mechanical polishing,
The mechanical polishing is performed on the main surface to be the front side surface of the nitride semiconductor substrate of the first processed substrate, from which at least a part of the damaged layer has been removed by dry etching in the front side etching step. The manufacturing method according to claim 2. The front side surface etching step of removing at least a part of the damaged layer formed on the main surface of the substrate subjected to the back side surface etching and to be the front side surface of the nitride semiconductor substrate after being subjected to the back side surface etching step by dry etching The manufacturing method according to claim 1, further comprising: Further including a mechanical polishing step for subjecting the substrate obtained by the front side surface etching step (hereinafter referred to as a second work-in-process substrate) to mechanical polishing;
The mechanical polishing is performed on the main surface to be the front side surface of the nitride semiconductor substrate of the second processed substrate, in which at least a part of the damaged layer has been removed by dry etching in the front side etching step. The manufacturing method according to claim 4. The manufacturing method according to claim 1, wherein the nitride semiconductor substrate is a nonpolar substrate or a semipolar substrate. The manufacturing method according to claim 6, wherein an angle formed between a front side surface of the nitride semiconductor substrate and a (10-10) plane is not less than 0 ° and not more than 20 °. The manufacturing method according to claim 1, wherein the nitride semiconductor substrate is a GaN substrate.