JP2013063908A - Method for manufacturing group iii metal nitride single crystal and template substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relatively easily manufacture a group III metal nitride single crystal with high productivity and to prevent melt back of a seed crystal film.SOLUTION: In a substrate body 1 wherein a film forming face 2b and a processed recess portion 8 are formed, base films 4A, 4B and 5 of the group III metal nitride single crystal are formed as films so as to coat the film forming face 2b and the processed recess portion 8. The base film has the seed crystal film on the film forming face and a polycrystal film coating a sidewall face and a bottom face of the processed recess portion. Then, the group III metal nitride single crystal 6 is grown on the base films by a flux method.

Description

  The present invention relates to a method for growing a group III metal nitride single crystal.

  Gallium nitride thin film crystals are attracting attention as an excellent blue light-emitting device, put into practical use in light-emitting diodes, and expected as a blue-violet semiconductor laser device for optical pickups.

  In Patent Document 1, using a template substrate with a concavo-convex shape formed as a seed substrate, GaN is grown by Na flux method, and then a flux growth portion is formed in the vicinity of the void formed in the recess. Separated (peeled) from the template.

  In Patent Document 2, a void is produced in the same manner as Patent Document 1, and after growing GaN by the HVPE method, the grown GaN is separated from the template substrate.

  In Patent Document 3, there is no void, but a mask with the convex portions and side surfaces of the concavo-convex portion masked is used as a template substrate. After GaN is grown by the HVPE method, the grown GaN is separated from the template substrate.

  In Patent Document 4, an island-shaped portion is formed on the surface of the sapphire substrate by processing, a seed crystal film is formed on the surface of the island-shaped portion, and a group III metal nitride single crystal is formed on the seed crystal film by a flux method. It is described to form.

  In the HVPE method, the crystal does not easily grow in the lateral direction, so the period of the unevenness is as small as several tens of microns. For this reason, it is described in Patent Document 1 (0051) that the period can be expanded to about 0.5 mm by using the flux method. Further, according to (0035) (0050) of Patent Document 1, in order to provide a void portion from which the grown crystal can be easily separated, the ratio of the convex portion (the portion with the seed) on the seed substrate is 50% or less, and further 10 % Or less is preferred. Specifically, the period is 5 to 20 microns with respect to the convex portions of 1 to 5 microns. In Example 5, the convex portion is 5 microns, and the period is about 300 microns.

JP2004-247711 JP2004-51415 JP2004-55799 JP2008-239365

  However, according to the method of Patent Document 1, it has been found that when the ratio of the convex portion with the seed crystal film is reduced, the seed crystal film is likely to melt and disappear in the flux.

  The present inventor has studied to increase the thickness of the seed crystal film to several tens of microns in order to prevent the seed crystal from melting back. However, in this case as well, it has been found difficult to prevent meltback. This means that the meltback progresses unexpectedly from the side of the seed crystal film, so that even if the seed crystal film is thickened, the disappearance due to the meltback cannot be prevented. As described in Patent Documents 2 and 3, the flux method was applied by setting the ratio of the width S of the seed crystal to the width W of the non-seeded part (wing) to 1/3 to 1/5. Similarly, the meltback was remarkable.

An object of the present invention is to make the Group III metal nitride single crystal highly productive, relatively easy to manufacture, and to suppress the meltback of the seed crystal film .

The present invention provides a substrate processing step of forming a projection and a processing recess provided with a film formation surface and a side wall surface on a substrate body,
A base film of a group III metal nitride single crystal is formed on the substrate body so as to cover the film formation surface, the side wall surface, and the processing recess, and the base film is formed on the film formation surface. A seed crystal forming step having a seed crystal film and a polycrystalline film covering the side wall surface and the bottom surface of the processed recess ; and a group III metal nitride single crystal is grown on the base film by a flux method. It is characterized by comprising a single crystal growth step of associating a-planes of group III metal nitride single crystals grown from the adjacent protrusions with each other.

The present invention also provides a substrate body provided with a projection provided with a film formation surface and a side wall surface and a processing recess, and a group III metal nitride covering the film formation surface, the side wall surface and the processing recess. A base film made of a single crystal is provided, and the base film includes a seed crystal film on the film formation surface and a polycrystalline film covering the side wall surface and the bottom surface of the processed recess. This relates to the template substrate.

  The present inventor provided a processing recess on the substrate, left the projection provided with the film formation surface and the side wall surface, and then applied the base film made of the group III metal nitride single crystal to the entire film formation surface and the processing recess. The group III metal nitride single crystal was grown on the underlayer. Then, it was found that the base film is well oriented on the film formation surface and functions effectively as a seed crystal. The nitride single crystal grown on the seed crystal grows so as to cover the substrate in the lateral direction. At the same time, it has been found that the base film provided on the processed concave portion is insufficiently oriented in crystals and becomes polycrystallized. For this reason, it was found that the base film does not function as a seed crystal on the processed recess, and the single crystal film does not grow effectively on the base film.

  As a result, it was found that the group III metal nitride single crystal grew well from the seed crystal film on the film formation surface. In addition, it was confirmed that the seed film on the film formation surface can be prevented by the base film on the processed recess, and the present invention has been achieved.

  At this time, the present inventors also examined the orientation of the processed recess, and found that it is important to prepare the recess so that the a-planes of the grown hexagonal nitride single crystal are associated with each other. . As a result of examining all the orientations, the orientation that was not suitable at all was the case where the concave portions were formed so that the m-planes of the hexagonal nitride single crystal were associated with each other. This reason was considered to be due to the orientation dependency of the growth rate. Only when the growth rate of the polycrystal from the processed recess grows beyond the unprocessed portion to the recess, that is, when the growth rate in the associating direction is high, the regions where the single crystals have grown are smoothly associated with each other. It grows as a uniform single crystal, and if the growth rate in the direction of association is slower than the rate at which the polycrystal in the processed recess grows, a mixture in which the polycrystal is sandwiched between the single crystals is created. It is.

  In order to confirm this, the following experiment was conducted. That is, a hexagonal nitride single crystal c-plane free-standing substrate was sliced in various directions and arranged side by side with slight gaps, and a growth experiment was conducted by the flux method. The result shows that when crystals sliced parallel to the a-plane are arranged side-by-side, they are connected smoothly and a uniform bulk single crystal can be grown, whereas when crystals sliced parallel to the m-plane are arranged side-by-side Although it is connected for the time being, there are gaps in some places, and the outermost surface has become an abnormally grown portion that is uneven just above the gap. From the above experiments, it has been found that it is important to make the recess so that the a-planes of the hexagonal nitride single crystal to be grown meet each other.

(A) is the schematic of the board | substrate body 1, (b) is the schematic which shows the state which provided the recessed part 8 by the process to the board | substrate body 1, (c) is the schematic which shows a template board | substrate. is there. 2 is a schematic view showing a state where a nitride single crystal 6 is formed on a template substrate 9. FIG. It is a schematic diagram explaining the association of the group III metal nitride single crystal to be grown. (A), (b) is a schematic diagram which shows the positional relationship of the azimuth | direction of the a axis | shaft of a board | substrate body, and the longitudinal direction A of a protrusion side wall surface, and both are parallel. (A), (b) is a schematic diagram which shows the positional relationship of the azimuth | direction of the a-axis of a board | substrate body, and the longitudinal direction A of a protrusion side wall surface, and both cross | intersect by angle (theta). (A), (b) is a schematic diagram which shows the positional relationship of the azimuth | direction of the a axis | shaft of a base film, and the longitudinal direction A of a protrusion side wall surface, and both crossing angle is 30 degrees. (A), (b) is a schematic diagram which shows the positional relationship of the a-axis direction of a base film, and the longitudinal direction A of a protrusion side wall surface, and the crossing angle of both is smaller than 30 degrees. In Example 1, after detaching the single crystal from the substrate, a fluorescence micrograph of the single crystal associating from the peeled surface side, and confirming that the a surfaces are associated with each other as indicated by the dotted line. did it.

Hereinafter, the present invention will be described in more detail with reference to the drawings.
FIG. 1A shows a substrate body 1 that can be used in the present invention. The film formation surface 1a of the substrate body 1 is processed smoothly, and a well-oriented seed crystal film can be formed on the film formation surface 1a.

  A concave portion 8 having a predetermined shape is formed on the film forming surface 1a of the substrate body 1 as shown in FIG. As a result, the substrate body 1 is formed with a recess 8 and a remaining protrusion 2. On the protrusion 2, the film formation surface 2b remains and a side wall surface 2a is formed. The side wall surface 2a and the recess bottom surface 3 are processed surfaces formed by processing.

  Next, a base film 10 made of a group III metal nitride single crystal is formed on the substrate body 1 to obtain a template substrate 9 shown in FIG. The base film 10 covers the surface side of the substrate 1. At this time, the well-oriented seed crystal film 5 is formed on the film formation surface 2b of the base film 10. However, distortion is introduced into the wall surface 2a of the protrusion 2 facing the recess 8 and the bottom surface 3 of the recess. As a result of this processing distortion, the base films 4A and 4B formed on the wall surface 2a and the recess bottom surface 3 are disordered and become polycrystallized.

  Here, in the prior art, the seed crystal film 5 is formed on the film formation surface 2 b on the protrusion 2, and no attempt is made to form the seed crystal film on the side wall surface of the recess 8. For this reason, even if the seed crystal film 5 is formed thick to prevent melt back of the film, the progress of melt back from the side wall surface 2a is fast, and the film formation on the seed crystal film 5 can be effectively advanced. It was difficult. On the other hand, in the present invention, since the base film 10 covers not only the film formation surface 2b but also the entire side wall surface 2a and the bottom surface 3 of the recess, meltback of the seed crystal film 5 can be prevented.

  Next, a group III metal nitride single crystal 6 is formed on the template substrate 9 shown in FIG. 1C by a flux method to obtain the state shown in FIG. In this step, the single crystals 6 formed on the seed crystal film 5 are connected to cover the substrate. At the same time, the film 6a is also formed on the polycrystalline base films 4A and 4B.

  As schematically shown in FIG. 3, it is necessary that the a-planes of the hexagonal nitride single crystal to be grown meet at the meeting surface 7. That is, single crystals 6A and 6B grow from adjacent seed crystal films 5 as indicated by arrows D, and eventually meet at 7. At this time, when the processed recess 8 is formed so that the m-planes of the single crystals 6A and 6B grown from the adjacent seed crystal film 5 are associated with each other, the associating direction is higher than the rate at which the polycrystal grows from the processed recess. The growth rate of D was slow, the regions where the crystals grew did not associate smoothly, and a mixture in which polycrystals were sandwiched between single crystals was formed.

  It was confirmed with a fluorescence microscope that single crystals grown from the adjacent seed crystal film 5 were associated with the a-axis at the meeting surface 7. An example of a fluorescence microscope image is shown in FIG. When a fluorescence microscope is used, the growth history can be observed from the state of emission of the impurity band. Electrons excited by the ultraviolet light of the mercury lamp emit light from impurity levels in the crystal. At this time, the difference in emission intensity can be observed like a tree ring due to the difference in impurity concentration.

The material of the substrate body is not particularly limited, but perovskite type such as sapphire, silicon single crystal, SiC single crystal, MgO single crystal, spinel (MgAl ₂ O ₄ ), LiAlO ₂ , LiGaO ₂ , LaAlO ₃ , LaGaO ₃ , NdGaO _3, etc. A composite oxide can be illustrated. The composition formula _{[A 1-y (Sr 1-} x Ba x) y ] _{[(Al 1-z Ga z)} 1-u · D u ] _O 3 (A is a rare earth element; D is niobium and One or more elements selected from the group consisting of tantalum; y = 0.3-0.98; x = 0-1; z = 0-1; u = 0.15-0.49; x + z = 0 .1 to 2) cubic perovskite structure composite oxides can also be used. SCAM (ScAlMgO ₄ ) can also be used.

  The formation method of the recessed part to a board | substrate body is not limited. In particular, by grooving a single crystal such as sapphire with a dicer (diamond blade), a deep groove (depth of 10 microns or more) that is difficult to produce by lithography can be produced. Further, it is sufficient that the processed surface is smooth and processing distortion remains and is not epi-ready. For example, laser processing, plasma etching, or sand blasting may be used.

  The depth of the recess is preferably 10 μm or more, and more preferably 20 μm or more, from the viewpoint of allowing the upper portions of the recess to associate faster than the polycrystals from the recess grow. On the other hand, if the recess is too deep, the substrate main body is liable to break during handling. From this viewpoint, 100 μm or less is preferable.

  The group III metal nitride single crystal constituting the base film is a nitride of one or more metals selected from Ga, Al, and In, such as GaN, AlN, GaAlN, and GaAlInN. Of these, GaN, AlN, and GaAlN are preferable.

  The formation method of the base film is preferably the MOCVD method from the viewpoint of controllability of impurity concentration and film thickness uniformity.

  The thickness of the base film is not particularly limited. From the viewpoint of suppressing the meltback of the seed crystal film, the thickness is preferably 1 μm or more, and more preferably 10 μm or more. If the base film is thick, it takes time to form the base film. From this point of view, the thickness of the base film can be 30 μm or less.

  In Patent Document 1, the groove width is 20 to 500 μm, preferably 100 μm or more. In Example 5, the protrusion width is 5 μm, the protrusion period is 300 μm, and the recess width is 295 μm. However, under these conditions, the seed crystal film is likely to melt back.

  In the present invention, the width b of the recess is preferably 400 μm or more, and more preferably 500 μm or more. Moreover, since the grown single crystal becomes difficult to be connected when the width b of the concave portion is increased, the width b of the concave portion is preferably 1000 μm or less and more preferably 700 μm or less from this viewpoint.

  The width a of the protrusion is preferably 100 μm or more, and more preferably 150 μm or more, from the viewpoint of promoting single crystal growth. Moreover, 300 micrometers or less are preferable.

  Preferably, the angle θ formed by the longitudinal direction of the side wall surface of the protrusion and the a-axis of the substrate body is 25 ° or less, more preferably 20 ° or less, and even more preferably 10 ° or less. Most preferably, the longitudinal direction of the side wall surface of the protrusion is parallel to the a-axis of the substrate body.

Here, the a axis indicates (1 1 -2 0) of a hexagonal single crystal. Since both sapphire and gallium nitride are hexagonal, a1, a2, and a3 are equivalent, (2 -1 -1 0), (1 1 -2 0), (-1 2 -1 0), (-2 6 of (1 1 0), (-1 -1 2 0), and (1 -2 1 0) are equivalent.
Of these six, (1 1 -2 0) is often used for the a-axis, and the a-axis in this application means all of these equivalent surfaces and is expressed as (1 1 -2 0) Even when doing so, all of the equivalent axes are included.

  In the examples of FIGS. 4A and 4B, the material of the substrate body is a hexagonal group III metal nitride single crystal. The longitudinal direction A of the side wall surface 2a of the protrusion 2 is parallel to the a-axis of the substrate body.

  In the example of FIGS. 5A and 5B, the longitudinal direction A of the side wall surface 2a of the protrusion 2 intersects with the a axis of the substrate body. And this intersection angle (theta) is 25 degrees or less, More preferably, it is 20 degrees or less, More preferably, it is 10 degrees or less.

  Preferably, the angle θ formed by the longitudinal direction of the side wall surface of the protrusion and the a-axis of the base film is 5 ° or more and 30 ° or less, more preferably 10 to 30 ° or less, and still more preferably 15 to 30 ° or less. Most preferably, the angle formed by the longitudinal direction of the side wall surface of the protrusion and the a-axis of the base film is 30 °.

  That is, in the example of FIGS. 6A and 6B, the material of the base film is a hexagonal group III metal nitride single crystal. The angle formed between the longitudinal direction A of the side wall surface 2a of the protrusion 2 and the a-axis of the base film is 30 °.

  7A and 7B, the angle formed by the longitudinal direction A of the side wall surface 2a of the protrusion 2 and the a-axis of the base film is smaller than 30 °.

  In addition, in the example of FIGS. 1-7, although each protrusion and each recessed part are the stripe shape extended toward the fixed direction, this is not an essential requirement. For example, the protrusions may have a shape such as a triangle or a hexagon instead of an elongated stripe. However, in this case, the angle formed between the longitudinal direction A of the side wall surface of each piece of the protrusion and the a-axis of the substrate body is preferably 30 ° or less as described above. Moreover, it is preferable that the angle formed between the longitudinal direction A of the side wall surface and the a-axis of the base film in each piece of the protrusion is 5 ° to 30 ° as described above.

  It is also possible to form a large number of protrusions on the substrate body at regular intervals. For example, a large number of protrusions having various shapes such as a circular shape, an elliptical shape, a triangular shape, and a polygonal shape such as a quadrilateral shape can be formed on the substrate body vertically and horizontally at regular intervals. Also in this case, the group III metal nitride single crystal to be grown is associated with the a-plane even when the angle formed by the longitudinal direction A of the side wall surface of the protrusion and the a-axis of the substrate body is not 30 ° or less. Design is possible.

  Next, a group III metal nitride single crystal is grown on the base film by a flux method.

  Employing the flux method is preferable in terms of high productivity. In this case, the type of flux is not particularly limited as long as a group III metal nitride single crystal can be produced. In a preferred embodiment, a flux containing at least one of sodium metal and calcium metal is used, and a flux containing sodium metal is particularly preferred.

  In the flux, the raw material of the target group III metal nitride single crystal is mixed and used. This group III metal nitride single crystal is a nitride of one or more metals selected from Ga, Al, In, and B, such as GaN, AlN, GaAlN, GaAlInN, and BN. GaN and GaAlN are preferable.

The raw material constituting the flux is selected according to the target group III metal nitride single crystal.
As the gallium source material, a gallium simple metal, a gallium alloy, and a gallium compound can be applied, but a gallium simple metal is also preferable in terms of handling.

  As the aluminum raw material, an aluminum simple metal, an aluminum alloy, and an aluminum compound can be applied, but an aluminum simple metal is also preferable in terms of handling.

  As the indium raw material, indium simple metal, indium alloy, and indium compound can be applied, but indium simple metal is preferable from the viewpoint of handling.

The growth temperature and holding time during the growth of the group III metal nitride single crystal are not particularly limited, and the target III
It changes suitably according to the kind of group metal nitride single crystal, and the composition of a flux. In one example, when a gallium nitride single crystal is grown using sodium or lithium-containing flux, the growth temperature can be set to 800 to 1000 ° C.

  In a preferred embodiment, the group III metal nitride single crystal is grown in an atmosphere composed of a mixed gas containing nitrogen gas. The total pressure of the atmosphere is not particularly limited, but is preferably 10 atm or more, and more preferably 30 atm or more from the viewpoint of preventing evaporation of the flux. However, since the apparatus becomes large when the pressure is high, the total pressure of the atmosphere is preferably 2000 atmospheres or less, and more preferably 1000 atmospheres or less.

  Also, the nitrogen partial pressure in the atmosphere is not particularly limited, but when growing a gallium nitride single crystal, 10 to 2000 atmospheres is preferable, and 100 to 1000 atmospheres is more preferable. When growing an aluminum nitride single crystal, 0.1 to 50 atm is preferable, and 1 to 10 atm is more preferable.

  A gas other than nitrogen in the atmosphere is not limited, but an inert gas is preferable, and argon, helium, and neon are particularly preferable. The partial pressure of a gas other than nitrogen is a value obtained by subtracting the nitrogen gas partial pressure from the total pressure.

  The actual training method in the present invention is not particularly limited. For example, the template substrate can be immersed in a flux in a crucible, the crucible can be accommodated in a pressure resistant container, and heated while supplying a nitrogen-containing atmosphere in the pressure resistant container. Further, the flux can be brought into contact with the surface of the base film by fixing the template substrate at a predetermined position and raising the crucible containing the flux upward.

Example 1
A gallium nitride single crystal was grown according to the method described with reference to FIGS.
Specifically, a number of grooves 8 having a depth of 25 microns and a width of 0.5 mm were formed on the surface 1a of the c-plane sapphire substrate body 1 having a diameter of 2 inches with a period of 0.7 mm. At this time, the groove direction was parallel to the a-axis (1 1 -2 0) direction of sapphire. The recess was formed by a dicer (diamond blade count # 400). Next, a base film 10 made of gallium nitride single crystal was epitaxially grown on the substrate body 1 to obtain a template substrate 9. That is, the film formation surface 2a was oriented so as to be the a-plane of the GaN seed crystal, that is, the (1 1 -2 0) plane.

  Subsequently, the gallium nitride single crystal 6 was grown on the template substrate by a flux method. Specifically, a cylindrical flat bottom crucible having an inner diameter of 70 mm and a height of 50 mm was used, and the raw materials for growth (metal Ga 60 g, metal Na 60 g, carbon 0.1 g) were melted in a glove box and filled in the crucible. First, Na was filled, and then Ga was filled to shield Na from the atmosphere and prevent oxidation. The melt height of the raw material in the crucible was about 20 mm.

Next, one of the template substrates 9 described above was placed obliquely on a seed substrate holding base installed inside the crucible. The holding table is slightly larger than the template substrate and has a recess for fitting the substrate. The crucible was placed in a refractory metal container and hermetically sealed, and then placed on a table where the crystal growth furnace could swing and rotate. After heating up to 870 ° C and 4.5 MPa, 100
Crystals were grown while stirring by stirring and rotating the solution while maintaining the time. Thereafter, the mixture was gradually cooled to room temperature over 10 hours, and crystals were collected. The grown crystal had a GaN crystal of about 1.5 mm grown on the entire surface of the 2-inch seed substrate. The in-plane thickness variation was small, less than 10%.

(Example 2)
A gallium nitride single crystal was grown in the same manner as in Example 1. However, the width b of the groove 8 was 0.7 mm (period 0.9 mm). Other than this, a single crystal was grown in the same manner as in Example 1.

(Example 3)
A gallium nitride single crystal was grown in the same manner as in Example 1. However, the width b of the groove 8 was set to 0.9 mm (period 1.1 mm). Other than this, a single crystal was grown in the same manner as in Example 1.

Example 4
A template substrate was produced in the same manner as in Example 2. Next, a template substrate was placed on the susceptor of a hydride vapor phase epitaxy (HVPE) apparatus. After heating to 1100 ° C. at normal pressure, gallium chloride (GaCl) and ammonia (NH 3) were flowed over the seed substrate as source gases, and a GaN thick film was formed for 15 hours. Thereafter, the mixture was gradually cooled to room temperature over 5 hours, and crystals were collected. A GaN crystal of about 1.5 mm was grown on the entire surface of the 2-inch seed substrate. The in-plane thickness variation was small, less than 10%. No cracks were confirmed visually.

(Comparative Example 1)
A GaN template was produced in the same manner as in Example 1 of Patent Document 1. Next, using this template substrate, a gallium nitride single crystal was grown by the flux method in the same manner as in Example 1 above. As a result, the seed crystal film by the MOCVD method was completely melted back, and only sapphire was present, and crystal growth was not possible.

(Comparative Example 2)
A gallium nitride single crystal was grown in the same manner as in Example 1. However, unlike Example 1, the film-forming surface 2a was oriented so as to be the m-plane of the GaN seed crystal, that is, the (10-10) plane.
As a result, the gallium nitride single crystal 6 could be grown. However, the upper part of the groove 8 was polycrystallized and was not a uniform single crystal as a whole.

Claims (12)

A substrate processing step for forming a protrusion and a processing recess provided with a film formation surface and a side wall surface on the substrate body;
A base film of a group III metal nitride single crystal is formed on the substrate body so as to cover the film formation surface, the side wall surface, and the processing recess, and the base film is formed on the film formation surface. A seed crystal forming step having a seed crystal film and a polycrystalline film covering the side wall surface and the bottom surface of the processed recess ; and a group III metal nitride single crystal is grown on the base film by a flux method. A method for growing a group III metal nitride single crystal, comprising a step of growing a single crystal in which a-planes of group III metal nitride single crystals grown from adjacent projections are associated with each other.   2. The method according to claim 1, wherein the group III metal nitride single crystal to be grown is a gallium nitride single crystal or an aluminum nitride single crystal.   3. The method according to claim 1, wherein the group III metal nitride single crystal constituting the base film is a gallium nitride single crystal, an aluminum nitride single crystal, or an aluminum nitride-gallium nitride solid solution crystal.   The method according to claim 1, wherein an angle formed by a longitudinal direction of the side wall surface of the protrusion and an a-axis of the substrate body is 25 ° or less. The angle formed by the longitudinal direction of the side wall surface of the protrusion and the a-axis of the group III metal nitride single crystal constituting the seed crystal film is 5 ° or more and 30 ° or less. The method according to any one of claims 1 to 4 . The method according to claim 1, wherein there is a processing strain on the side wall surface and the bottom surface of the processing recess. A substrate body provided with a projection provided with a film formation surface and a side wall surface and a processing recess, and a base film made of a group III metal nitride single crystal covering the film formation surface, the side wall surface and the processing recess The template substrate is characterized in that the base film has a seed crystal film on the film formation surface and a polycrystalline film covering the side wall surface and the bottom surface of the processed recess .   8. The template substrate according to claim 7, wherein the group III metal nitride single crystal constituting the base film is a gallium nitride single crystal, an aluminum nitride single crystal, or an aluminum nitride-gallium nitride solid solution crystal.   The template substrate according to claim 7 or 8, wherein an angle formed by a longitudinal direction of the side wall surface of the protrusion and an a-axis of the substrate body is 25 ° or less. The angle formed by the longitudinal direction of the side wall surface of the protrusion and the a-axis of the group III metal nitride single crystal constituting the seed crystal film is 5 ° or more and 30 ° or less. The template substrate according to any one of claims 7 to 9. 11. The template substrate according to claim 7, wherein the side wall surface and the bottom surface of the processing recess have a processing strain. A composite substrate comprising the template substrate according to any one of claims 7 to 11 and a group III metal nitride single crystal formed on the base film by a flux method.

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