JP2019147726A - Method of manufacturing nitride crystal substrate, nitride crystal substrate, and substrate for crystal growth - Google Patents

Abstract

To manufacture a nitride crystal substrate which has good crystallinity by making a substrate for crystal growth larger in diameter and then using the same.SOLUTION: The process of preparing the substrate for crystal growth comprises the processes of: arranging a plurality of seed crystal substrates each made of a single crystal of group III nitride; epitaxially growing a first layer made of the single crystal of group III nitride on a principal face and a side face of each of the plurality of seed crystal substrates, and joining side faces of adjacent seed crystal substrates together by the first layer under a first growth condition such that a growing rate in a direction along a normal of the principal face of the seed crystal substrate is higher than a growing rate in a direction along the principal face of the seed crystal substrate; and epitaxially growing a second layer made of a single crystal of group III nitride on the first layer under a second growth condition such that the growing rate in the direction along the normal of the principal face of the seed crystal substrate is equal to or less than the growing rate in the direction along the principal face of the seed crystal substrate. The process of growing the crystal film comprises growing a crystal film made of a single crystal of group III nitride on the substrate for crystal growth.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for manufacturing a nitride crystal substrate, a nitride crystal substrate, and a crystal growth substrate.

  When manufacturing a semiconductor device such as a light emitting element or a high-speed transistor, a substrate made of a nitride crystal such as gallium nitride (hereinafter referred to as a nitride crystal substrate) is used. The nitride crystal substrate can be manufactured through a step of growing a nitride crystal on a sapphire substrate or a crystal growth substrate produced using the sapphire substrate. In recent years, in order to obtain a large-diameter nitride crystal substrate having a diameter exceeding, for example, 2 inches, there is an increasing need to increase the diameter of a crystal growth substrate (see, for example, Patent Document 1).

JP 2006-290676 A

  An object of the present invention is to provide a technique capable of increasing the diameter of a crystal growth substrate and manufacturing a nitride crystal substrate having good crystallinity using the substrate.

According to one aspect of the invention,
Producing a substrate for crystal growth;
Growing a crystal film made of a single crystal on the crystal growth substrate;
A method for producing a nitride crystal substrate having
The step of producing the crystal growth substrate includes:
Arranging a plurality of seed crystal substrates made of a group III nitride single crystal so that their principal surfaces are parallel to each other and adjacent side surfaces face each other;
The plurality of seed crystal substrates under a first growth condition in which a growth rate in a direction along a normal line of the main surface of the seed crystal substrate is higher than a growth rate in a direction along the main surface of the seed crystal substrate. A step of epitaxially growing a first layer made of a group III nitride single crystal on each of the main surface and the side surface of the substrate, and bonding side surfaces of adjacent seed crystal substrates with the first layer;
On the first layer under a second growth condition in which a growth rate in a direction along a normal line of the main surface of the seed crystal substrate is equal to or lower than a growth rate in a direction along the main surface of the seed crystal substrate. Epitaxially growing a second layer comprising a group III nitride single crystal;
Have
In the step of growing the crystal film,
Manufacturing a nitride crystal substrate by heating the crystal growth substrate, supplying a group III material and a nitriding agent on the heated crystal growth substrate, and growing the crystal film made of a group III nitride single crystal Methods and related techniques are provided.

  According to the present invention, it is possible to increase the diameter of a crystal growth substrate, and to use this to manufacture a nitride crystal substrate having good crystallinity.

3 is a flowchart showing a method for manufacturing a nitride crystal substrate 30 according to an embodiment of the present invention. It is a flowchart which shows substrate production process S100 for crystal growth. (A) is a top view of the material board | substrate 7 used when producing the seed crystal substrate 10, (b) is sectional drawing which shows a mode that a ditch | groove (scribe groove | channel) is formed in the back surface of the material board | substrate 7. (C) is a schematic diagram which shows a mode that the peripheral part is removed by cleaving the material board | substrate 7 along a ditch | groove, (d) is the seed | species obtained by removing the peripheral part of the material board | substrate 7. 2 is a plan view of the crystal substrate 10, and FIG. 3E is a side view of the seed crystal substrate 10. (A) is a top view which shows an example of the arrangement pattern of the seed crystal board | substrate 10, (b) is B-B 'sectional drawing of the seed crystal board | substrate group shown to Fig.4 (a). It is the schematic of the vapor phase growth apparatus used when growing the crystal film 14 or 21. (A) is a schematic sectional drawing which shows 1st layer growth process S132, (b) is a schematic sectional drawing which shows 2nd layer growth process S134. (A) is a schematic diagram showing a state in which a crystal film 14 has been grown on a seed crystal substrate 10, and (b) is a method in which the sacrificial layer 12 a is peeled off from the surface of the holding plate 12 to make the crystal growth substrate 20 self-supporting. It is a schematic diagram which shows a mode, (c) is a schematic diagram of the board | substrate 20 for crystal growth after back surface washing | cleaning. (A) is a schematic diagram showing how the crystal film 21 is grown thickly on the crystal growth substrate 20, and (b) is a diagram showing a plurality of nitride crystal substrates 30 by slicing the thickly grown crystal film 21. It is a schematic diagram which shows a mode that it acquires. (A) is a cross-sectional view showing a state in which the crystal film 14 is grown thickly on the seed crystal substrate 10, and (b) is a diagram showing a plurality of nitride crystal substrates 30 by slicing the thick crystal film 14. It is a schematic diagram which shows a mode that it acquires. 2 is a schematic view illustrating a planar configuration of a crystal growth substrate 20 and a nitride crystal substrate 30 produced using the same. FIG. (A) is an image observed by an optical microscope on the main surface side of the crystal growth substrate in Experiment 1, and (b) is an image observed by an optical microscope on the back surface side of the crystal growth substrate in Experiment 1. (A) is an image observed by a scanning electron microscope on the main surface side of the crystal growth substrate in Experiment 2, and (b) is an image observed by a scanning electron microscope in a cross section of the crystal growth substrate in Experiment 2. And (b) is a cathodoluminescence image of a cross section of the crystal growth substrate of Experiment 2 using a scanning electron microscope. It is an enlarged view of the X section of the cathode luminescence image by the scanning electron microscope of the cross section of the substrate for crystal growth of Experiment 2.

<Knowledge obtained by the inventor>
First, the knowledge obtained by the inventors will be described.

  Arranging a plurality of seed crystal substrates made of group III nitride single crystals so that their principal surfaces are parallel to each other and adjacent side surfaces are opposed to each other, and producing a crystal growth substrate; A large-diameter nitride crystal substrate may be manufactured by performing a step of growing a crystal film on the substrate for use.

  In this method, a predetermined crystal film is grown under growth conditions in which the growth rate in the direction along the normal line of the main surface of the seed crystal substrate is equal to or lower than the growth rate in the direction along the main surface of the seed crystal substrate. Consider a case where seed crystal substrates are bonded together. In this case, the growth (lateral growth) of the crystal film in the direction along the main surface of the seed crystal substrate is promoted. By promoting the lateral growth of the crystal film, the upper part of the gap between the side surfaces of the adjacent seed crystal substrates is blocked at an early stage. For this reason, during the growth of the crystal film, the film forming gas such as the group III source gas and the nitriding agent cannot be allowed to reach the gap between the side surfaces of the adjacent seed crystal substrates. If the deposition gas does not reach the gap, the crystal films on the side surfaces of the adjacent seed crystal substrates cannot be grown, and the side surfaces of the adjacent seed crystal substrates cannot be bonded to each other by the crystal film. .

  As a result, the bonding between the seed crystal substrates depends only on the crystal film grown on the main surface of the seed crystal substrate, and the bonding strength between the seed crystal substrates may not be sufficiently improved. In a state where the seed crystal substrates are joined only with the crystal film grown on the main surface of the seed crystal substrate, the crystal film is broken in various post processes (for example, a self-supporting process, a slicing process, etc.), and the seed crystal There is a possibility that the bonding between the substrates breaks.

  The present invention is based on the above-described new problem found by the inventors.

<One Embodiment of the Present Invention>
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

(1) Method for Manufacturing Nitride Crystal Substrate A method for manufacturing a nitride crystal substrate according to the present embodiment will be described with reference to FIGS. In this embodiment, by performing S100 to S400 shown below, a nitride crystal substrate (nitride semiconductor substrate, nitride free-standing substrate) is used as a substrate made of gallium nitride (GaN) crystal (hereinafter also referred to as a GaN substrate). An example of manufacturing the above will be described. Step is abbreviated as “S”.

  Hereinafter, in a group III nitride crystal having a wurtzite structure, the <0001> axis (for example, the [0001] axis) is referred to as “c-axis”, and the (0001) plane is referred to as “c-plane”. The (0001) plane may be referred to as “+ c plane (group III element polar plane)”, and the (000-1) plane may be referred to as “−c plane (nitrogen (N) polar plane)”. The <1-100> axis (for example, the [1-100] axis) is referred to as the “m axis”, and the {1-100} plane is referred to as the “m plane”. The m-axis may be expressed as the <10-10> axis. The <11-20> axis (for example, the [11-20] axis) is referred to as “a axis”, and the {11-20} plane is referred to as “a plane”.

  In the following, the angle formed by the main axis (c-axis) of the crystal with respect to the normal line of the main surface of the predetermined substrate is referred to as “off angle”.

  As shown in FIG. 1, the method for manufacturing a nitride crystal substrate according to this embodiment includes, for example, a crystal growth substrate manufacturing step S100, a crystal film growth step S200, a slicing step S300, and a polishing step S400. Have.

(S100: substrate growth process for crystal growth)
First, in the crystal growth substrate manufacturing step S100 according to the present embodiment, for example, a plurality of seed crystal substrates 10 (hereinafter sometimes abbreviated as “substrates 10”) made of GaN single crystals, and their main surfaces 10ms are mutually connected. A crystal growth substrate 20 (hereinafter, may be abbreviated as “substrate 20”) is manufactured by arranging the side surfaces 10ss so as to face each other in parallel.

  As shown in FIG. 2, specifically, the crystal growth substrate manufacturing step S100 includes, for example, a seed crystal substrate preparation step S110, an arrangement step S120, a bonding step S130, and a self-supporting step S140. Yes.

(S110: seed crystal substrate preparation step)
In the seed crystal substrate preparation step S110, a plurality of substrates 10 are prepared.

  First, a plurality of material substrates (crystal substrates, small-diameter seed substrates) 7 (hereinafter abbreviated as substrates 7) made of GaN crystals are prepared as base materials used when the substrate 10 is manufactured. Here, for example, the substrate 7 is manufactured by a so-called VAS (Void-Assisted Separation) method.

The planar shape of the substrate 7 is, for example, a circle, and the diameter of the substrate 7 is larger than that of the substrate 10 to be manufactured, for example, 1 inch or more. The thickness of the substrate 7 is, for example, 200 μm or more and 1 mm or less. Although the conductivity type of the board | substrate 7 is not specifically limited, For example, it is n type. The n-type impurity in the substrate 7 is, for example, silicon (Si) or germanium (Ge). The n-type impurity concentration in the substrate 7 is, for example, 1.0 × 10 ¹⁸ cm ⁻³ or more and 1.0 × 10 ²⁰ cm ⁻³ or less. Note that the conductivity type of the substrate 7 may be, for example, a p-type or a semi-insulating type.

  The main surface 7s of the substrate 7 is, for example, a mirror surface. The surface roughness (arithmetic mean roughness Ra) of the main surface 7s of the substrate 7 is, for example, 10 nm or less, preferably 5 nm or less.

  The closest low-index crystal plane to the main surface 7s of the substrate 7 is, for example, the c-plane. The c-plane is, for example, a Ga polar plane. Further, the c-axis of the GaN crystal constituting the substrate 7 may have a predetermined off angle with respect to the normal line of the center of the main surface 7 s of the substrate 7. In the present embodiment, the c-plane of the substrate 7 is curved in a concave spherical shape with respect to the main surface 7s due to the VAS method. The off angle formed by the c-axis with respect to the normal line of the center of the main surface 7s of the substrate 7 has a predetermined distribution (variation). The variation of the off angle (difference between the maximum value and the minimum value of the off angle) is, for example, within 0.3 °, preferably within 0.15 °.

The dislocation density (average dislocation density) in the main surface 7s of the substrate 7 is, for example, 2 × 10 ⁶ cm ⁻² or more and less than 6 × 10 ⁶ cm ⁻² .

  When the substrate 7 is prepared, as shown in FIG. 3B, a concave groove on the back surface (-c surface) that is the surface opposite to the main surface 7s that is the crystal growth surface (+ c surface) of the substrate 7, A scribe groove is formed. The concave groove can be formed by using a known method such as a laser processing method or a machining method. After forming the concave groove, as shown in FIG. 3C, the substrate 10 is cleaved along the concave groove and the peripheral portion thereof is removed, whereby the substrate 10 is obtained. FIG. 3D shows a planar configuration of the substrate 10.

  The planar shape of the substrate 10 is preferably a shape in which when a plurality of the substrates 10 are arranged on the same plane, these can be planarly filled, that is, can be spread without gaps.

  In this case, for the reason described later, of the side surfaces 10ss of the substrate 10, all the surfaces facing the side surface 10ss of the other adjacent substrate 10, that is, all the surfaces facing the side surface 10ss of the other adjacent substrate 10 are all. It is preferable that the plane is a plane excluding the m plane and is equivalent to each other. For example, when the main surface 10 ms (crystal growth surface) of the substrate 10 is the c-plane as in the present embodiment, all the surfaces of the side surface 10 ss of the substrate 10 that face the side surface 10 ss of another adjacent substrate 10 are defined. The a-plane is preferable.

  Since the GaN crystal has a hexagonal crystal structure, in order to satisfy the above-described requirements, the planar shape of the substrate 10 constituting at least the peripheral portion (arc portion) of the substrate 20 is an equilateral triangle. A parallelogram (inner angles 60 ° and 120 °), a trapezoid (inner angles 60 ° and 120 °), a regular hexagon, and a parallelogram are preferable. When the planar shape of the substrate 10 is a square or a rectangle, when any one of the side surfaces 10ss of the substrate 10 is an a surface, the side surface orthogonal to the surface is necessarily an m surface. Further, if the planar shape of the substrate 10 is a circle or an ellipse, it cannot be filled with a plane, and the side surface 10ss of the substrate 10 cannot be an equivalent surface excluding the m-plane.

  Of the several types of shapes described above, the planar shape of the substrate 10 constituting at least a portion other than the peripheral portion of the substrate 20 is particularly preferably a regular hexagon as shown in FIG. In this case, it is possible to efficiently obtain the substrate 10 with the maximum size, that is, take the material from the substrate 7 having a circular planar shape. In addition, when the substrates 10 are filled in the same plane in S120 described later, the arrangement forms a honeycomb pattern, and the plurality of substrates 10 are arranged so as to mesh with each other in plan view. . Accordingly, when an external force is applied along the in-plane direction to the plurality of arranged substrates 10, it is possible to suppress the displacement of the substrates 10 regardless of the direction. On the other hand, when the planar shape of the substrate 10 is a regular triangle, a parallelogram, a trapezoid, a square, a rectangle, or the like, the external force from a specific direction is compared to the case where the planar shape of the substrate 10 is a regular hexagon. And the displacement of the substrate 10 is likely to occur. In the present embodiment, the case where the planar shape of the substrate 10 is a regular hexagon is described. In addition, the planar shape of the board | substrate 10 which comprises the peripheral part of the below-mentioned board | substrate 20 is circular arc shape so that a part of regular hexagon may follow the outer periphery of the disk-shaped board | substrate 20, as shown to Fig.4 (a). The shape is cut out. Regarding the substrate 10 constituting the peripheral portion of the substrate 20, that is, the substrate 10 having a small area, it is preferable to obtain one or more, preferably two or more together from one substrate 7. When a plurality of substrates 10 are acquired from one substrate 7, waste of the substrate 7 can be reduced and the quality of the substrate 10 can be easily aligned.

  Of the plane orientations that can be taken by the GaN crystal, the m plane can be easily cleaved because the bond density per unit area is low (bonds between atoms are weak). On the other hand, for a plane orientation other than the m-plane to be employed in the present embodiment (for example, a-plane), the bond density per unit area is larger than the bond density in the m-plane (the bond between atoms is strong). ) Etc., it is relatively difficult to cleave. In order to deal with such a problem, in this embodiment, as described above, the cleaving operation is performed after forming the concave groove (scribe groove) on the back surface (−c surface) of the substrate 7. As a result, the substrate 7 can be cleaved accurately in the direction of a weakly cleaved surface other than the m-plane (a surface that is difficult to cleave).

  FIG. 3E shows a side view of the substrate 10 obtained by the above method. As shown in FIG. 3 (e), on the side surface 10ss of the substrate 10, a melting surface (laser processing surface) or cutting surface (machining surface) generated by forming a concave groove on the back surface of the substrate 7, and a concave surface are formed. A cleavage plane generated by cleaving the substrate 7 along the groove is formed. The melting surface here is, for example, a surface including an amorphous surface formed by rapidly solidifying the crystal once melted. Moreover, the cutting surface here is a surface having a relatively large surface roughness including, for example, a cleavage surface. As shown in FIG. 3E, by arranging the cleavage plane closer to the crystal growth surface, the bonding strength between adjacent substrates 10 is increased or formed around the bonding portion of the substrates 10 in S130 described later. It is possible to improve the quality of the crystal film.

  In order to accurately control the cleavage position, the cross-sectional shape of the groove is preferably V-shaped (tapered with a wide opening) as shown in FIG. In addition, although there is no restriction | limiting in particular about the opening width of a ditch | groove, For example, 0.2-1.8 mm is illustrated. By controlling the size and shape of the grooves in this way, the controllability when the substrate 7 is cleaved is improved, and the width of the cleavage plane formed when the substrate 7 is cleaved (width in the thickness direction). It is possible to ensure sufficient. This makes it possible to increase the bonding strength between adjacent substrates 10 and improve the quality of the crystal film formed around the bonding portion of the substrates 10 in S130 described later.

When the above-described processing is performed, a large amount of chips of the substrate 7 are generated and adhere to the substrate 10, which may adversely affect crystal growth described later. Therefore, a cleaning process for removing chips is performed. As the method, for example, bubbling cleaning using a chemical obtained by mixing hydrogen chloride (HCl) and hydrogen peroxide solution (H ₂ O ₂ ) on a one-to-one basis can be mentioned.

(S120: Arrangement process)
When a plurality of substrates 10 are acquired, an arrangement step S120 is performed. In this step, a plurality of substrates 10 made of GaN crystals are arranged such that their main surfaces 10 ms are parallel to each other and their side surfaces 10 ss are opposed to each other. That is, the plurality of substrates 10 are arranged in a planar shape and in a disk shape (planar filling) so that the side surfaces 10ss of the adjacent substrates 10 face each other.

  FIG. 4A is a plan view showing an example of the arrangement pattern of the substrates 10. When the substrate 10 having a regular hexagonal plan shape is used as in this embodiment, a honeycomb pattern (honeycomb pattern) is formed by filling the substrate 10 with a plane. Of the plurality of substrates 10, a substrate constituting at least a portion other than the peripheral portion of the substrate 20 has a main surface 10 ms whose planar shape is a regular hexagon. As shown in this figure, the honeycomb pattern in which the main surface 10 ms of the substrate 10 is combined is obtained when the substrate 20 is rotated once around the axis passing through the center of the main surface of the substrate 20 and orthogonal to the main surface. More than once, the arrangement is arranged so as to have six-fold rotational symmetry in this arrangement example.

  Here, “arranging a plurality of substrates 10 so that their principal surfaces 10 ms are parallel to each other” means that the principal surfaces 10 ms of adjacent substrates 10 are completely arranged on the same plane. In addition, the case where there is a slight difference in the heights of these surfaces and the case where these surfaces are arranged with a slight inclination are included. That is, it means that the plurality of substrates 10 are arranged such that their main surfaces 10 ms are as high as possible and as parallel as possible. However, even when there is a difference in the height of the main surface 10 ms of the adjacent substrates 10, the size thereof is, for example, 20 μm or less, preferably 10 μm or less in the largest case. Further, even when an inclination occurs between the main surfaces 10 ms of the adjacent substrates 10, the magnitude is desirably 1 ° or less, preferably 0.5 ° or less, on the largest surface. Further, when arranging a plurality of substrates 10, variation in the off angle in the main surface of the substrate group obtained by arranging them (difference between the maximum value and the minimum value of the off angle in all main surfaces) is determined. For example, it is desirable that the angle is within 0.3 °, preferably within 0.15 °. This is because if these are too large, the crystallinity of the crystal film grown in S130 and S200 described later may be deteriorated (good surface morphology cannot be obtained).

  Further, “arranging the plurality of substrates 10 so that their side surfaces 10ss face each other” means here that the side surfaces 10ss of adjacent substrates 10 are completely in contact with each other, that is, in contact with no gap. In addition, the case where a slight gap exists between them is included. That is, it means that a plurality of substrates 10 are opposed to each other so that a gap is not generated as much as possible between side surfaces 10ss of adjacent substrates 10. However, even when a gap is generated between the side surfaces 10ss of the adjacent substrates 10, the size in the room temperature condition is, for example, 100 μm or less, preferably 50 μm or less at the largest place. This is because if the gap is too large, the adjacent substrates 10 may not be joined to each other or the strength may be insufficient even if they are joined when performing S130 described later. Further, in order to increase the bonding strength between the adjacent substrates 10 after performing S130, it is preferable to arrange the adjacent substrates 10 so that at least the cleavage surfaces of the side surfaces 10ss face each other.

  In order to facilitate handling in S <b> 130, the plurality of substrates 10 are preferably fixed on a holding plate (support plate) 12 configured as a flat plate, for example. FIG. 4B shows a cross-sectional configuration of an assembly substrate 13 in which a plurality of substrates 10 are bonded onto a disc-shaped holding plate 12. As shown in the figure, the substrate 10 is placed on the holding plate 12 via a layer made of an adhesive 11 so that its main surface 10 ms (c-plane which is a crystal growth surface) is the upper surface. In other words, a layer made of the adhesive 11 is provided between the substrate 10 and the holding plate 12.

The material of the holding plate 12 includes a film forming temperature in S130, which will be described later, heat resistance and corrosion resistance that can withstand the film forming atmosphere, and crystals constituting the GaN crystal film 14 formed in the substrate 10 and S130. It is preferable to use a material having a linear expansion coefficient equivalent or smaller. By using such a material as the material of the holding plate 12, it is possible to suppress the formation of a gap between the substrates 10 in S130 and the spread of the gap formed between the substrates 10. The linear expansion coefficient here refers to a linear expansion coefficient in a direction parallel to the main surface 10 ms (c-plane) of the substrate 10, that is, in the a-axis direction of the GaN crystal constituting the substrate 10. The linear expansion coefficient in the a-axis direction of the GaN crystal is 5.59 × 10 ⁻⁶ / K. As a material that has a linear expansion coefficient that is equal to or smaller than that of this, is inexpensive and easily available, and exhibits a certain degree of rigidity, for example, isotropic graphite, anisotropic graphite (pyrolytic graphite, etc.), silicon (Si ), Quartz, silicon carbide (SiC), and the like. Among these, pyrolytic graphite (hereinafter, also referred to as PG) that can easily peel off the surface layer can be particularly preferably used for the reasons described later. In addition, a composite material obtained by coating (coating) the surface of a flat base material such as isotropic graphite, Si, quartz, or SiC with a material that is easy to peel off, such as PG, is excellent in corrosion resistance. it can.

  The material of the adhesive 11 is a material that solidifies by being held for a predetermined time under a temperature condition much lower than the film forming temperature in S130, for example, a temperature condition within a range of room temperature to 300 ° C. A material that can be solidified by being dried for several minutes to several tens of hours underneath can be suitably used. By using such a material as the material of the adhesive 11, the position, height, inclination, etc. of the substrate 10 arranged on the holding plate 12 can be finely adjusted until the adhesive 11 is solidified. It becomes possible. Moreover, the solidification of the adhesive 11 (fixation of the substrate 10) can be completed under a relatively low temperature condition before the start of S130, whereby the S130 is started in a state in which the displacement of the substrate 10 is suppressed. It becomes possible to do. As a result, the quality of the GaN crystal film 14 grown in S130 can be improved, and the bonding strength between the substrates 10 can be increased. Further, the bonding operation of the substrate 10 can be performed manually, for example, and the simplicity of the bonding operation can be remarkably improved, and the equipment required for the bonding operation can be simplified.

  Further, as the material of the adhesive 11, it is preferable to use a material having heat resistance and corrosion resistance that can withstand a film forming temperature in S 130 described later, a film forming atmosphere. By using such a material as the material of the adhesive 11, it is possible to avoid that the adhesive 11 is thermally decomposed during the temperature increase in S <b> 130 and the fixing of the substrate 10 is released. Further, it is possible to avoid warping of the finally obtained substrate 20 due to the growth of the GaN crystal film 14 while the substrate 10 is not sufficiently fixed. Further, contamination of the growth atmosphere due to the thermal decomposition of the adhesive 11 can be avoided, thereby preventing the quality of the GaN crystal film 14 and the bonding strength between the substrates 10 from decreasing.

  Further, as the material of the adhesive 11, it is preferable to use a material having a linear expansion coefficient close to that of the crystal constituting the GaN crystal film 14 formed by the substrate 10 or S 130. Note that “the linear expansion coefficient is close” means that the linear expansion coefficient of the adhesive 11 and the linear expansion coefficient of the crystal constituting the GaN crystal film 14 are substantially equal. It means within 10%. By using such a material as the material of the adhesive 11, the stress applied in the in-plane direction of the substrate 10 due to the difference in linear expansion coefficient with the adhesive 11 can be relaxed when performing S130 described later. It is possible to avoid warpage, cracks, and the like in the substrate 10.

  As a material of the adhesive 11 satisfying these requirements, for example, a heat-resistant inorganic adhesive mainly composed of heat-resistant (fire-resistant) ceramics and an inorganic polymer can be used, and zirconia, silica, etc. are mainly used. Materials used as components can be preferably used. Examples of such an adhesive include commercially available Aron ceramic C agent and E agent (Aron ceramic is a registered trademark of Toagosei Co., Ltd.). These adhesives, for example, form a cured product that can withstand a high temperature of 1100 to 1200 ° C. by being dried and solidified at a temperature in the range of room temperature to 300 ° C., and have high corrosion resistance against the film forming atmosphere in S130. It has been confirmed that it exhibits high adhesive strength that does not cause misalignment of the substrate 10 and the like. It has also been confirmed that the crystal grown on the substrate 10 is not affected. In addition, since it exhibits an appropriate viscosity of, for example, about 40,000 to 80,000 mPa · s at room temperature before solidification, it is extremely difficult to temporarily fix or align the substrate 10 on the holding plate 12. It has also been confirmed that it is suitable.

  When adhering the substrate 10 onto the holding plate 12, it is preferable to apply the adhesive 11 to a region excluding at least the peripheral portion of the substrate 10 so that the adhesive 11 does not run around the side surface 10ss side of the substrate 10. For example, it is preferable to apply the adhesive 11 only in a region that is a predetermined width away from the peripheral edge of the substrate 10 and preferably near the center. If the adhesive 11 wraps around the side surface 10ss, the growth of the first layer 50 described later is hindered at the wraparound portion and the periphery thereof, and the bonding strength between the substrates 10 by the first layer 50 may be reduced. is there.

  The substrate 10 is disposed on the holding plate 12 via the adhesive 11 and the adhesive 11 is solidified, whereby the fabrication of the assembly substrate 13 is completed. The adhesive 11 is solidified until the adhesive 11 is solidified so that the main surfaces 10 ms of the plurality of substrates 10 are parallel to each other and the side surfaces 10 ss of the adjacent substrates 10 face each other. The position, inclination, and height of the substrate 10 are preferably adjusted as necessary. The solidification of the adhesive 11 is preferably completed before the start of S130. By doing in this way, it becomes possible to perform the introduction | transduction of the assembly board | substrate 13 to the HVPE apparatus 200 mentioned later, and each of the crystal growth in the state in which the position shift of the some board | substrate 10 was suppressed.

(S130: Joining process)
When the adhesive 11 is solidified and the fabrication of the assembly substrate 13 is completed, a GaN crystal film 14 as a bonding film is formed on the surfaces of the plurality of substrates 10 arranged in a plane using the HVPE apparatus 200 shown in FIG. Grow.

The HVPE apparatus 200 includes an airtight container 203 made of a heat resistant material such as quartz and having a film forming chamber 201 formed therein. A susceptor 208 that holds the assembly substrate 13 and the substrate 20 is provided in the film formation chamber 201. The susceptor 208 is connected to a rotation shaft 215 included in the rotation mechanism 216, and is configured to be rotatable. Gas supply pipes 232 a to 232 c for supplying HCl gas, ammonia (NH ₃ ) gas as a nitriding agent, and nitrogen (N ₂ ) gas into the film forming chamber 201 are connected to one end of the airtight container 203. A gas supply pipe 232d for supplying hydrogen (H ₂ ) gas is connected to the gas supply pipe 232c. The gas supply pipes 232a to 232d are respectively provided with flow rate controllers 241a to 241d and valves 243a to 243d in order from the upstream side. A gas generator 233a for storing Ga melt as a raw material is provided downstream of the gas supply pipe 232a. In the gas generator 233a, an assembled substrate 13 on which gallium chloride (GaCl) gas, which is a group III source gas (raw material halide) generated by the reaction between HCl gas and Ga melt, is held on the susceptor 208. A nozzle 249a that supplies the liquid to the surface is connected. On the downstream side of the gas supply pipes 232b and 232c, nozzles 249b and 249c for supplying various gases supplied from these gas supply pipes toward the assembly substrate 13 and the like held on the susceptor 208 are connected, respectively. . An exhaust pipe 230 that exhausts the inside of the film forming chamber 201 is provided at the other end of the hermetic container 203. The exhaust pipe 230 is provided with a pump 231. A zone heater 207 for heating the assembly substrate 13 held in the gas generator 233a or on the susceptor 208 to a desired temperature is provided on the outer periphery of the hermetic container 203, and the temperature in the film forming chamber 201 is set in the hermetic container 203. A temperature sensor 209 for measurement is provided. Each member included in the HVPE apparatus 200 is connected to a controller 280 configured as a computer, and is configured such that processing procedures and processing conditions described later are controlled by a program executed on the controller 280.

S130 can be implemented by the following processing procedure, for example, using the above-described HVPE apparatus 200. First, Ga polycrystal is accommodated as a raw material in the gas generator 233 a, and the assembly substrate 13 is loaded (loaded) into the hermetic container 203 and held on the susceptor 208. Then, H ₂ gas (or a mixed gas of H ₂ gas and N ₂ gas) is supplied into the film forming chamber 201 while heating and exhausting the film forming chamber 201. Then, gas supply from the gas supply pipes 232a and 232b is performed in a state in which the inside of the film formation chamber 201 reaches a desired film formation temperature and film formation pressure, and the atmosphere in the film formation chamber 201 is a desired atmosphere. Then, GaCl gas and NH ₃ gas are supplied as film forming gases to the main surface of the assembly substrate 13 (substrate 10).

  As a result, as shown in FIGS. 6A, 6B, and 7A, a GaN crystal is epitaxially grown on the surface of the substrate 10, and a GaN crystal film 14 is formed. By forming the GaN crystal film 14, the adjacent substrates 10 are joined to each other by the GaN crystal film 14 and become an integrated state. As a result, a substrate 20 obtained by bonding adjacent substrates 10 is obtained.

In order to prevent decomposition of crystals constituting the substrate 10 during the film formation process, NH ₃ gas is supplied prior to HCl gas, for example, before heating in the film formation chamber 201. preferable. Further, in order to improve the in-plane film thickness uniformity of the GaN crystal film 14 and to improve the bonding strength of the adjacent substrates 10 uniformly in the plane, it is preferable to perform S130 while the susceptor 208 is rotated.

  Further, when the substrate 10 is bonded by the GaN crystal film 14, all of the side surfaces of the substrate 10 that are in contact with the side surfaces of the other substrate 10 are surfaces other than the m surface and are equivalent to each other. As a result, it is possible to increase their bonding strength. When the film thickness of the GaN crystal film 14 is the same, the bonding of the substrate 10 is more effective when the adjacent substrates 10 are bonded to each other than the m surfaces are bonded to each other. The strength can be increased.

  Here, the bonding step S130 of the present embodiment is classified into two steps based on, for example, growth conditions. Specifically, the bonding step S130 of the present embodiment includes, for example, a first layer growth step S132 and a second layer growth step S134. Through these steps, the GaN crystal film 14 has, for example, the first layer 50 and the second layer 60.

(S132: First layer growth step)
In S132, as shown in FIG. 6A, the first growth condition in which the growth rate in the direction along the normal of the main surface 10ms of the substrate 10 is higher than the growth rate in the direction along the main surface 10ms of the substrate 10. Below, the 1st layer 50 which consists of a single crystal of GaN is epitaxially grown on each main surface 10ms and side 10ss of a plurality of substrates 10.

  The “growth rate in the direction along the normal of the main surface 10 ms of the substrate 10” as used herein is not only the normal direction of the main surface 10 ms of the substrate 10 but also slightly inclined from the normal of the main surface 10 ms of the substrate 10. Including the direction. Further, the “growth rate in the direction along the normal line of the main surface 10 ms of the substrate 10” here can be rephrased as “growth rate in the direction along the c-axis”, for example.

  Further, the “growth rate in the direction along the main surface 10 ms of the substrate 10” here is not only a direction completely parallel to the main surface 10 ms of the substrate 10 but also a direction slightly inclined from the main surface 10 ms of the substrate 10. Is included. In addition, the “growth rate in the direction along the main surface 10 ms of the substrate 10” here can be paraphrased as a growth rate in the direction along the direction (a axis or m axis) perpendicular to the c axis, for example. .

  By growing the first layer 50 under a first growth condition in which the growth rate in the direction along the normal of the main surface 10 ms of the substrate 10 is higher than the growth rate in the direction along the main surface 10 ms of the substrate 10, The growth (lateral growth) of the first layer 50 in the direction along the main surface 10 ms of the substrate 10 can be suppressed. By suppressing the lateral growth of the first layer 50, it is possible to suppress the upper portion of the gap between the side surfaces 10ss of the adjacent substrates 10 from being blocked. Thereby, during the growth of the first layer 50, a film forming gas such as a group III source gas and a nitriding agent can be allowed to reach the gap between the side surfaces 10ss of the adjacent substrates 10. The first layer 50 can be grown on each of the side surfaces 10ss of the adjacent substrates 10 by allowing the deposition gas to reach the gap. As the first layer 50 is grown, the first layer 50 grown on the side surface 10ss of one of the pair of substrates 10 and the first layer 50 grown on the side surface 10ss of the other substrate 10; Meet. As a result, the gap between the side surfaces 10 ss of the substrate 10 can be filled with the first layer 50. As a result, the side surfaces 10 ss of the adjacent substrates 10 can be joined by the first layer 50.

  Further, the first layer 50 is grown under the first growth condition in which the growth rate in the direction along the normal line of the main surface 10 ms of the substrate 10 is higher than the growth rate in the direction along the main surface 10 ms of the substrate 10. Thus, as the first layer 50, a continuous layer exposing facets other than the c-plane is formed on the main surface 10 ms of the substrate 10. That is, in S132, the first layer 50 is three-dimensionally grown so as to roughen the main surface 10ms of the mirror-finished substrate 10.

  At this time, in the growth process of the first layer 50, at least a part of the plurality of dislocations extending in the direction along the c-axis in the substrate 10 is transferred from the substrate 10 to the c-axis of the first layer 50. Propagates along the direction. The dislocation propagated in the direction along the c-axis of the first layer 50 propagates by bending in a direction substantially perpendicular to the facet at a position where the facet other than the c-plane of the first layer 50 is exposed. To do. That is, the dislocation propagates by bending in a direction inclined with respect to the c-axis. Thereby, in the second layer growth step S134 described later, dislocations are locally collected on the facet meeting portion other than the c-plane.

  As the first growth condition of the present embodiment, for example, the growth temperature in the first layer growth step S132 is set lower than the growth temperature in the second layer growth step S134 described later. Specifically, the growth temperature in the first layer growth step S132 is, for example, 900 ° C. or higher and 970 ° C. or lower, preferably 940 ° C. or higher and 960 ° C. or lower. If the growth temperature in the first layer growth step S132 is less than 900 ° C., the first layer 50 may not be a single crystal but may be polycrystalline. On the other hand, the 1st layer 50 can be made into a single crystal by making the growth temperature in 1st layer growth process S132 into 900 degreeC or more. Furthermore, it can suppress that a crack arises in the 1st layer 50 by making the growth temperature in 1st layer growth process S132 into 940 degreeC or more. On the other hand, when the growth temperature in the first layer growth step S132 exceeds 970 ° C., the growth rate in the direction along the normal line of the main surface 10 ms of the substrate 10 is in the direction along the main surface 10 ms of the substrate 10. There is a possibility that it will be below the growth rate. For this reason, the upper part of the gap between the side surfaces 10ss of the adjacent substrates 10 may be blocked. On the other hand, by setting the growth temperature in the first layer growth step S132 to 970 ° C. or less, the growth rate in the direction along the normal line of the main surface 10 ms of the substrate 10 is changed to the direction along the main surface 10 ms of the substrate 10. The growth rate can be stably increased. Thereby, it is possible to suppress the upper portion of the gap between the side surfaces 10ss of the adjacent substrates 10 from being blocked. Further, by setting the growth temperature in the first layer growth step S132 to 960 ° C. or lower, it is possible to stably prevent the upper portion of the gap between the side surfaces 10ss of the adjacent substrates 10 from being blocked, and The side surfaces 10ss can be joined by the first layer 50 over a wide range in the thickness direction.

Further, as the first growth condition of the present embodiment, for example, the ratio of the partial pressure of the flow rate of NH ₃ gas as the nitriding agent gas to the partial pressure of GaCl gas as the group III source gas in the first layer growth step S132 (Hereinafter also referred to as “V / III ratio”) may be adjusted. For example, you may make V / III ratio in 1st layer growth process S132 larger than V / III ratio in 2nd layer growth process S134 mentioned later. Specifically, the V / III ratio in the first layer growth step S132 is, for example, 1 or more and 4 or less.

Moreover, other conditions among the first growth conditions of the present embodiment are as follows, for example.
Growth pressure: 90-105 kPa, preferably 90-95 kPa
GaCl gas partial pressure: 1.5 to 15 kPa
N ₂ gas flow rate / H ₂ gas flow rate: 0 to 1

  In the present embodiment, the thickness of the first layer 50 on the main surface 10 ms of the substrate 10 is, for example, at least 1.5 times the maximum gap between the adjacent substrates 10. Specifically, the thickness of the first layer 50 on the main surface 10 ms of the substrate 10 is, for example, 15 μm or more and 200 μm or less. If the thickness of the first layer 50 is less than 15 μm, the side surfaces 10ss of the adjacent substrates 10 may not be sufficiently bonded to each other. On the other hand, when the thickness of the first layer 50 is 15 μm or more, the side surfaces 10ss of the adjacent substrates 10 can be sufficiently bonded to each other. On the other hand, from the viewpoint of the bonding strength by the first layer 50, the thicker the first layer 50, the better. However, since the surface of the first layer 50 is rough as will be described later, if the thickness of the first layer 50 exceeds 200 μm, the thickness until the second layer 60 of the GaN crystal film 14 is flattened is large. May be thicker. In contrast, by setting the thickness of the first layer 50 to 200 μm or less, the thickness of the GaN crystal film 14 until the second layer 60 is planarized can be reduced.

  In the present embodiment, in the above-described arrangement step S120, the adjacent substrates 10 are arranged so that at least the cleaved surfaces of the side surfaces 10ss face each other, thereby narrowing the interval between the side surfaces 10ss of the adjacent substrates 10. be able to. Thereby, in 1st layer growth process S132, the thickness of the 1st layer 50 which joins the side surfaces 10ss of the adjacent board | substrate 10 can be made thin. Further, in the first layer growth step S132, the cleavage surfaces of adjacent substrates 10 are bonded to each other by the first layer 50, whereby the substrates 10 can be bonded in a balanced manner so that the main surface 10ms is flat. .

(S134: Second layer growth step)
In S134, as shown in FIG. 6B, the second growth condition in which the growth rate in the direction along the normal line of the main surface 10ms of the substrate 10 is equal to or lower than the growth rate in the direction along the main surface 10ms of the substrate 10. Below, a mirror-finished second layer 60 made of a single crystal of GaN is epitaxially grown on the first layer 50.

  By growing the second layer 60 under a second growth condition in which the growth rate in the direction along the normal of the main surface 10 ms of the substrate 10 is equal to or lower than the growth rate in the direction along the main surface 10 ms of the substrate 10, The growth (lateral growth) of the second layer 60 in the direction along the main surface 10 ms of the substrate 10 can be promoted. By promoting the lateral growth of the second layer 60, the second layer 60 can be formed on the first layer 50 in which the side surfaces 10 ss of the adjacent substrates 10 are joined together. That is, the second layer 60 can fill the groove (not shown) of the V-shaped first layer 50 formed above the gap between the side surfaces 10 ss of the adjacent substrates 10. Thereby, the second layer 60 can be continuously formed on the main surface 10 ms of the plurality of substrates 10 over the entire main surface 10 ms. As a result, the substrates 10 can be bonded to each other by both the first layer 50 and the second layer 60. That is, the bonding between the substrates 10 by the first layer 50 can be reinforced by the second layer 60.

  By growing the second layer 60 under a second growth condition in which the growth rate in the direction along the normal of the main surface 10 ms of the substrate 10 is equal to or lower than the growth rate in the direction along the main surface 10 ms of the substrate 10, As the second layer 60, a layer having a mirror-finished surface in which facets other than the c-plane have disappeared above the main surface 10 ms of the substrate 10 is formed. Specifically, the surface roughness (arithmetic average roughness Ra) of the main surface of the second layer 60 is, for example, 10 nm or less, preferably 5 nm or less.

  At this time, in the growth process of the second layer 60, the dislocations are locally collected above the main surface 10 ms of the substrate 10, thereby overlapping the main surface 10 ms of the substrate 10 in plan view among the main surfaces of the second layer 60. The dislocation density in the hexagonal region (hereinafter also referred to as “species corresponding region”) can be reduced. Specifically, dislocations propagated toward the direction inclined with respect to the c-axis in the first layer 50 described above continue to propagate in the same direction also in the second layer 60. Dislocations propagated in the second layer 60 toward the direction inclined with respect to the c-axis are collected at the meeting portion of the adjacent facets. Among the plurality of dislocations collected at the meeting portion of the adjacent facets in the second layer 60, dislocations whose Burgers vectors are opposite to each other disappear at the time of the association. On the other hand, the other part of the plurality of dislocations collected at the meeting portion of the adjacent facet in the second layer 60 changes its propagation direction again from the direction inclined with respect to the c axis to the direction along the c axis. And propagates to the main surface of the second layer 60. In this way, by eliminating some of the plurality of dislocations, the dislocation density in the seed corresponding region of the second layer 60 can be reduced. In addition, by collecting dislocations locally, in the seed corresponding region of the second layer 60, when compared in the seed corresponding region, a sparse part with relatively few dislocations and a relatively large number of dislocations. A dense part is formed. At least the dislocation density of the sparse part is 30% or less of the dislocation density in the main surface 10 ms of the substrate 10.

  As the second growth condition of the present embodiment, the growth temperature in the second layer growth step S134 is, for example, 990 ° C. or higher and 1100 ° C. or lower, preferably 1050 ° C. or higher and 1100 ° C. or lower. If the growth temperature in the second layer growth step S134 is less than 990 ° C., the growth rate in the direction along the c-axis may not be lower than the growth rate in the direction other than the method along the c-axis. There is. On the other hand, by setting the growth temperature in the second layer growth step S134 to 990 ° C. or higher, the growth rate in the direction along the c-axis can be stably increased in the direction other than the method along the c-axis. It can be as follows. Furthermore, the 2nd layer 60 with favorable crystallinity can be stably obtained by making the growth temperature in 2nd layer growth process S134 into 1050 degreeC or more. On the other hand, if the growth temperature in the second layer growth step S134 is higher than 1100 ° C., the Ga polar surface as the group III polar surface is likely to be thermally etched, and the flat second layer 60 may not be obtained. There is. Further, the quartz airtight container 203 in the HVPE apparatus 200 may be damaged. In contrast, by setting the growth temperature in the second layer growth step S134 to 1100 ° C. or lower, it is possible to suppress excessive thermal etching of the Ga polar surface as the group III polar surface, and the second flat surface. Layer 60 can be obtained. Further, damage to the quartz airtight container 203 in the HVPE apparatus 200 can be suppressed.

  In addition, as 2nd growth conditions of this embodiment, you may adjust V / III ratio in 2nd layer growth process S134, for example. For example, the V / III ratio in the second layer growth step S134 may be made smaller than the V / III ratio in the first layer growth step S132.

Further, other conditions among the second growth conditions of the present embodiment are as follows, for example.
Growth pressure: 90-105 kPa, preferably 90-95 kPa
GaCl gas partial pressure: 1.5 to 15 kPa
N ₂ gas flow rate / H ₂ gas flow rate: 1 to 20

  In the present embodiment, the thickness of the second layer 60 above the main surface 10 ms of the substrate 10 is, for example, 6 Dμm or more when the outer diameter of the substrate 20 is D (cm). If the thickness of the second layer 60 is less than 6 Dμm, the bonding force between the substrates 10 by the second layer 60 may be insufficient, and the self-standing state of the substrate 20 may not be maintained. On the other hand, by setting the thickness of the second layer 60 to 6 D μm or more, a sufficient bonding force between the substrates 10 by the second layer 60 can be obtained, and the self-standing state of the substrate 20 can be maintained.

  Although there is no particular upper limit on the thickness of the second layer 60, the crystal growth of the second layer 60 performed here is limited to the purpose of joining a plurality of substrates 10 so as to be in a self-supporting state. May be. In other words, the thickness of the second layer 60 is equal to the adjacent substrate even in a state where the substrate 20 composed of the substrates 10 bonded to each other is removed from the holding plate 12 and washed or the like in the self-standing process S140 described later. It is also possible to keep the thickness as small as necessary to maintain the ten bonded states, that is, the self-standing state of the substrate 20. If S200 is separately performed as a full-fledged crystal growth step as in this embodiment, the thickness of the second layer 60 may be set to, for example, 100 Dμm or less from the viewpoint of improving productivity.

  Therefore, in this embodiment, when the outer diameter of the substrate 10 is 2 inches and the outer diameter of the substrate 20 is 6 to 8 inches, the thickness of the second layer 60 is, for example, 100 μm or more and 2 mm or less. be able to.

  The steps from the first layer growth step S132 to the second layer growth step S134 are continuously performed in the film forming chamber 201 of the same HVPE apparatus 200 without exposing the assembly substrate 13 (substrate 20) to the atmosphere. . This suppresses the formation of an unintended oxide layer (a layer having an oxygen concentration excessively higher than that of the high oxygen concentration layer 40) at the interface between the first layer 50 and the second layer 60. it can.

(S140: Free standing substrate)
When the growth of the GaN crystal film 14 is completed and the adjacent substrates 10 are joined to each other, NH ₃ gas and N ₂ gas are supplied into the film forming chamber 201 and the film forming chamber 201 is evacuated. Thus, supply of HCl gas into the gas generator 233a, supply of H ₂ gas into the film formation chamber 201, and heating by the heater 207 are stopped. Then, when the temperature in the film formation chamber 201 becomes 500 ° C. or lower, the supply of NH ₃ gas is stopped, and then the atmosphere in the film formation chamber 201 is replaced with N ₂ gas to return to atmospheric pressure. After the temperature in the film chamber 201 is lowered to a temperature at which the film chamber 201 can be unloaded, the substrate 20 is unloaded from the film forming chamber 201.

  Thereafter, the substrate 20 formed by bonding the adjacent substrates 10 is peeled off from the holding plate 12 and separated (the substrate 20 is self-supported).

  When a material such as PG (a material whose surface layer is easier to peel off than the substrate 10) is used as the material of the holding plate 12, the surface layer of the holding plate 12 is a sacrificial layer (peeling) as shown in FIG. Layer) 12a and peeled thinly, the substrate 20 from the holding plate 12 can be easily self-supported. The same effect can be obtained when a composite material obtained by coating the surface of a flat substrate made of isotropic graphite or the like with PG or the like is used as the material of the holding plate 12. Although it is more expensive than PG, the same effect can be obtained when pyrolytic boron nitride (PBN) is used as the material of the holding plate 12. Further, even when the material of the holding plate 12 is, for example, a material such as isotropic graphite, Si, quartz, or SiC, that is, a material that cannot act as a sacrificial layer, the adhesive 11 If the amount is extremely small, the solidified adhesive 11 can be broken or peeled off at an appropriate timing. Thereby, the substrate 20 can be easily self-supported from the holding plate 12.

  The adhesive 11 and the sacrificial layer 12a adhering to the back surface of the self-supporting substrate 20 (the back surface of the substrate 10) are removed using a cleaning agent such as a hydrogen fluoride (HF) aqueous solution. Thereby, the substrate 20 in a self-supporting state as shown in FIG. 7C is obtained. The substrate 20 has a main surface (the surface of the GaN crystal film 14) used as a ground for crystal growth, and is distributed in the market in this state as a large-diameter substrate exceeding 100 mm, further 150 mm (6 inches). There is. It should be noted that until the back surface of the substrate 20 is polished, traces of residual components of the adhesive 11 and the sacrificial layer 12a may remain on the back surface of the substrate 10 even after the cleaning. .

(Substrate 20)
The substrate 20 manufactured by the above S110 to S140 has, for example, the following characteristics.

  As shown in FIG. 10, the main surface 64s of the substrate 20 has, for example, a high dislocation density region HD and a low dislocation density region LD. The high dislocation density region HD has a relatively high dislocation density due to the influence of the joint portion between the adjacent substrates 10. The high dislocation density region HD is continuously formed in the main surface 64 s of the substrate 20. In the present embodiment, the high dislocation density region HD constitutes a honeycomb pattern in which, for example, a contour shape having a regular hexagonal plan shape is combined. The honeycomb pattern has two or more rotational symmetries when the substrate 20 is rotated once about the axis passing through the center of the main surface of the substrate 20 and orthogonal to the main surface. For example, it has 6-fold rotational symmetry.

  On the other hand, the dislocation density in the low dislocation density region LD is relatively low. The low dislocation density region LD corresponds to the above-described species corresponding region, and is divided by the high dislocation density region HD. The dislocation density in the low dislocation density region LD is one digit or more lower than the dislocation density in the high dislocation density region HD.

Here, as described above, the dislocations are locally collected in the growth process of the first layer 50 and the second layer 60, so that the low dislocation density region LD has a dislocation when compared in the region LD. It has a relatively small sparse part and a dense part with a relatively large number of dislocations. The sparse part and the dense part are irregularly distributed. In the dense part of the low dislocation density region LD of the present embodiment, the dislocation density can be made equal to or less than the dislocation density in the main surface of the substrate 10 even if the number of dislocations is relatively large. Specifically, the dislocation density in the dense part can be set to, for example, less than 4 × 10 ⁶ cm ⁻² . On the other hand, in the sparse part of the substrate 20 of the present embodiment, the dislocation density can be 30% or less of the dislocation density in the main surface of the substrate 10. Specifically, the dislocation density of the sparse part can be, for example, 9 × 10 ⁵ cm ⁻² or less.

(S200: Crystal film growth step)
In S200, the HVPE apparatus 200 shown in FIG. 5 is used, and the GaN crystal film 21 as a full-scale growth film is grown on the main surface of the substrate 20 in a self-supporting state by the same processing procedure as S130. FIG. 8A shows a state in which the GaN crystal film 21 is formed thick on the main surface of the substrate 20, that is, on the surface of the GaN crystal film 14 by vapor phase growth.

  The processing procedure of this step is almost the same as that of S130. However, as shown in FIG. 8A, this step is performed with the substrate 20 configured to be self-supporting placed directly on the susceptor 208. Is called. That is, this step is performed in a state where the holding plate 12 and the adhesive 11 are not present between the substrate 20 and the susceptor 208. For this reason, heat transfer between the susceptor 208 and the substrate 20 is efficiently performed, and the time required for raising and lowering the temperature of the substrate 20 can be shortened. Further, since the entire back surface of the substrate 20 is in contact with the susceptor 208, the substrate 20 is heated evenly over the entire surface. As a result, the temperature condition on the main surface of the substrate 20, that is, the crystal growth surface can be made uniform over the entire in-plane. In addition, since the heat treatment is performed in a state where the adjacent substrates 10 are integrally joined, direct heat transfer (heat exchange) between the adjacent substrates 10, that is, heat conduction in the substrate 20 is quickly performed. It will be. As a result, the temperature condition on the crystal growth surface can be made more uniform over the entire in-plane region. That is, in this step, crystal growth is performed using the substrate 20 that is configured to be self-supporting, so that the productivity of crystal growth is improved, and the in-plane uniformity of the crystal grown on the substrate 20 is improved. It becomes possible.

  On the other hand, a plurality of seed crystal substrates are aligned and bonded on the holding plate via an adhesive, and then a crystal is grown on each of the plurality of seed crystal substrates. An alternative method of integration is also conceivable. However, this method may make it difficult to obtain some of the various effects described above. This is because, in this method, heat transfer from the susceptor to the seed crystal substrate may be hindered by a holding plate or an adhesive interposed therebetween, which may reduce the heating efficiency of the substrate. In addition, since the efficiency of heat transfer from the susceptor to the substrate is greatly affected by the amount of adhesive applied, the position of application, and the like, this alternative method may result in uneven heating efficiency between the substrates. As a result, in this alternative method, the productivity of crystal growth may be reduced or the in-plane uniformity of the finally obtained crystal may be reduced as compared with the method of the present embodiment.

  As described above, it can be said that the crystal growth method of the present embodiment using the substrate 20 configured to be capable of self-supporting has a great advantage in improving productivity and crystal quality as compared with the above-described alternative method.

  The growth conditions in the crystal film growth step S200 can be the same conditions as the second growth conditions in the second layer growth step S134 described above. The growth conditions in the crystal film growth step S200 may be different from the second growth conditions as long as facets other than the c-plane are not exposed on the main surface of the GaN crystal film 21.

Examples of the growth conditions for performing S200 include the following.
Growth temperature: 990-1100 ° C, preferably 1050-1100 ° C
Growth pressure: 90-105 kPa, preferably 90-95 kPa
GaCl gas partial pressure: 1.5 to 15 kPa
N ₂ gas flow rate / H ₂ gas flow rate: 0 to 20

  After the GaN crystal film 21 having a desired film thickness is grown, the film forming process is stopped by the same processing procedure as that at the end of S130, and the substrate 20 on which the GaN crystal film 21 is formed is carried out from the film forming chamber 201. .

(S300: Slicing step)
Next, as shown in FIG. 8B, for example, the GaN crystal film 21 is sliced by guiding a wire saw to a cut surface substantially parallel to the main surface of the GaN crystal film 21. Thereby, the substrate 30 as an as-sliced substrate is formed. At this time, the thickness of the substrate 30 is set to be 300 μm or more and 700 μm or less, for example.

(S400: Polishing process)
Next, both surfaces of the substrate 30 are polished by a polishing apparatus. At this time, the final thickness of the substrate 30 is, for example, not less than 250 μm and not more than 650 μm.

  As a result, one or more GaN substrates 30 having a disk-shaped outer shape can be obtained. The GaN substrate 30 is also a large-diameter circular substrate of 100 mm or more, and more than 150 mm (6 inches). When the substrate 20 is cut out from the GaN crystal film 21, S200 can be performed again using the cut out substrate 20, that is, the cut out substrate 20 can be reused.

(GaN substrate 30)
The GaN substrate 30 produced by the above S200 to 400 has the following features, for example.

(Dislocation)
Dislocations in the GaN substrate 30 have the same characteristics as the dislocations in the GaN crystal film 14 of the substrate 20.

  That is, as shown in FIG. 10, the main surface of the GaN substrate 30 has, for example, a high dislocation density region HD and a low dislocation density region LD. The high dislocation density region HD on the main surface of the GaN substrate 30 constitutes a honeycomb pattern similar to the high dislocation density region HD on the main surface of the substrate 20, for example.

  However, the honeycomb pattern formed by the high dislocation density region HD on the main surface of the GaN substrate 30 is compared with the honeycomb pattern formed by the high dislocation density region HD on the main surface 64s of the substrate 20 described above. Depending on the thickness, film forming conditions, etc., the image may be blurred (outlined) or deformed. In particular, when a plurality of GaN substrates 30 are obtained by slicing the GaN crystal film 21, the above-described tendency becomes strong in the GaN substrate 30 obtained from the surface side of the GaN crystal film 21.

  The low dislocation density region LD on the main surface of the GaN substrate 30 is divided by the high dislocation density region HD. The dislocation density in the low dislocation density region LD is one digit or more lower than the dislocation density in the high dislocation density region HD.

  The low dislocation density region LD has a sparse portion with relatively few dislocations and a dense portion with relatively little dislocation when compared in the region LD. The dislocation density in the dense portion is, for example, equal to or less than the dislocation density in the main surface of the substrate 10. On the other hand, the dislocation density in the sparse part is 30% or less of the dislocation density in the main surface of the substrate 10.

  However, since dislocations may be dispersed in the process of growing the thick GaN crystal film 21, the dislocation densities of the sparse part and the dense part in the low dislocation density region LD of the GaN substrate 30 are the sparse part and the dense part in the substrate 20, respectively. It may be averaged compared to the dislocation density of each dense part. Even in this case, the dislocation density (average dislocation density) of the low dislocation density region LD is, for example, lower than the dislocation density in the main surface of the substrate 10.

  The dense portion of the high dislocation density region HD and the low dislocation density region LD in the GaN substrate 30 may be visually confirmed, but if the impurity concentration (especially oxygen concentration) in the region is high, fluorescence It can also be easily confirmed by observation using a microscope or observation of a cathodoluminescence (CL) image using a scanning electron microscope (SEM).

  When a semiconductor device is manufactured using the GaN substrate 30, the high dislocation density region HD is an unusable area (non-use region), and the low dislocation density is a usable area (use region) in which the semiconductor device can be manufactured. The region LD can be selectively used.

(Polarity reversal zone)
The main surface of the GaN substrate 30 of this embodiment does not include an inversion domain as a polarity reversal zone regardless of the difference between the high dislocation density region HD and the low dislocation density region LD. Here, the “inversion domain” means a region whose polarity is reversed from the surrounding crystal. When the main surface is a Ga polar surface as in this embodiment, the region where the N polar surface exists is an inversion domain.

Here, in the growth of a GaN crystal, for example, when a mask made of SiO ₂ or the like is formed on a GaN thin film as a seed crystal layer, the mask has no polarity. When this occurs, it is difficult to control the polarity of the GaN crystal formed on the nucleus so as to align in a certain direction. Therefore, in such a case, an inversion domain is inevitably generated from the front surface to the back surface of the substrate constituted by the GaN crystal.

  On the other hand, in the GaN substrate 30 of the present embodiment, a plurality of substrates 10 with suppressed variation in off-angle are arranged, the substrate 20 is formed thereon, and the GaN crystal film 21 is further formed on the substrate 20. The GaN substrate 30 is obtained by slicing the GaN crystal film 21. That is, the GaN crystals constituting the GaN substrate 30 are controlled so that their polarities are aligned in a certain direction.

  Therefore, the main surface of the GaN substrate 30 of this embodiment does not include an inversion domain. That is, the polarities of the GaN crystals constituting the GaN substrate 30 are aligned in a certain direction.

  If the inversion domain is not included in the main surface, the main surface is very high quality as a region for manufacturing a semiconductor device. For example, if an inversion domain is included, abnormal growth may occur on the area where the inversion domain exists, but if the inversion domain is not included, the possibility of abnormal growth can be eliminated. is there.

  The presence or absence of such an inversion domain determines the polarity of the surface of the GaN crystal using, for example, a convergent beam electron diffraction (CBED) method using a transmission electron microscope (TEM). Can be judged.

(Surface roughness)
The main surface of the GaN substrate 30 is mirror-finished by the above-described polishing, and the surface roughness (arithmetic average roughness Ra) of the main surface is, for example, 10 nm or less, preferably 5 nm or less.

(2) Effects Obtained by the Present Embodiment According to the present embodiment, one or more effects shown below can be obtained.

(A) In the first layer growth step S132 of the present embodiment, the first growth rate in the direction along the normal line of the main surface 10ms of the substrate 10 is higher than the growth rate in the direction along the main surface 10ms of the substrate 10. Under the growth conditions, the first layer 50 made of a single crystal of GaN is epitaxially grown on the main surface 10 ms and the side surface 10 ss of each of the plurality of substrates 10. Thereby, the growth (lateral growth) of the first layer 50 in the direction along the main surface 10 ms of the substrate 10 can be suppressed. By suppressing the lateral growth of the first layer 50, it is possible to suppress the upper portion of the gap between the side surfaces 10ss of the adjacent substrates 10 from being blocked. By suppressing the upper blockade of the gap between the side surfaces 10ss of the adjacent substrates 10, during the growth of the first layer 50, the group III source gas and nitridation are introduced into the gap between the side surfaces 10 ss of the adjacent substrates 10. A film forming gas such as an agent can be made to reach. The first layer 50 can be grown on each of the side surfaces 10ss of the adjacent substrates 10 by allowing the deposition gas to reach the gap. As the first layer 50 grows, the first layer 50 grown on the side surface 10 ss of one of the pair of substrates 10, the first layer 50 grown on the side surface 10 ss of the other substrate 10, Meet. As a result, the gap between the side surfaces 10 ss of the substrate 10 can be filled with the first layer 50. As a result, the side surfaces 10 ss of the adjacent substrates 10 can be joined by the first layer 50.

  Thus, the bonding strength between the substrates 10 can be improved by bonding the side surfaces 10ss of the adjacent substrates 10 with the first layer 50. Thereby, the board | substrate 20 with which the board | substrates 10 were joined by the 1st layer 50 can be made to stand stably. As a result, the substrate 20 can be easily increased in diameter.

(B) In the second layer growth step S134 of the present embodiment, the growth rate in the direction along the normal line of the main surface 10 ms of the substrate 10 is equal to or lower than the growth rate in the direction along the main surface 10 ms of the substrate 10. Under the growth conditions, the second layer 60 made of GaN single crystal is epitaxially grown on the first layer 50. By growing the second layer 60 under the second growth condition, growth in the direction along the main surface 10 ms of the substrate 10 (lateral growth) can be promoted. By promoting the lateral growth of the second layer 60, the second layer 60 can be formed on the first layer 50 in which the side surfaces 10 ss of the adjacent substrates 10 are joined together. That is, the second layer 60 can fill the groove (not shown) of the V-shaped first layer 50 formed above the gap between the side surfaces 10 ss of the adjacent substrates 10. Thereby, the second layer 60 can be continuously formed on the main surface 10 ms of the plurality of substrates 10 over the entire main surface 10 ms. As a result, the substrates 10 can be bonded to each other by both the first layer 50 and the second layer 60. That is, the bonding between the substrates 10 by the first layer 50 can be reinforced by the second layer 60.

(C) In the manufacturing method of the present embodiment, dislocations are locally collected during the growth process of the first layer 50 and the second layer 60, whereby some of the collected dislocations can be eliminated. it can. Thereby, the dislocation density in the low dislocation density region LD of the substrate 20 can be reduced. As a result, the substrate 20 having the low dislocation density region LD in which the dislocation density is further reduced as compared with the substrate 10 can be obtained.

  Here, in the case where a semiconductor layer made of a single crystal of a group III nitride semiconductor is epitaxially grown using the substrate 10 without exposing facets other than the c-plane, the dislocation density is inversely proportional to the thickness of the semiconductor layer. Tends to be reduced.

  On the other hand, according to the present embodiment, in the growth process of the first layer 50, at the position where the facet other than the c-plane is exposed, the dislocation is bent and propagated in a direction substantially perpendicular to the facet. Can be made. Thereby, the local set of dislocations can be accelerated. By eliminating some of the plurality of dislocations collected in this way, the dislocation density can be reduced more rapidly than the tendency inversely proportional to the thickness of the semiconductor layer. As a result, it is possible to efficiently obtain a low dislocation density region LD in which the dislocation density is further reduced as compared with the substrate 10.

<Other embodiments>
The embodiment of the present invention has been specifically described above. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

  In the above-described embodiment, the case where a substrate manufactured by the VAS method is used as the substrate 10 has been described, but a substrate manufactured by a method other than the VAS method may be used as the substrate 10.

  In the above-described embodiment, when the honeycomb pattern formed by combining the substrates 10 rotates the substrate 20 about the axis passing through the center of the main surface of the substrate 20 and orthogonal to the main surface, the symmetry is 6 times. The case where it has was explained. However, the present invention is not limited to such an embodiment. For example, the honeycomb pattern in which the substrates 10 are combined may have two or three times rotational symmetry.

  In the above-described embodiment, a case has been described in which all of the side surfaces of the substrate 10 that are in contact with the side surfaces of the other substrate 10 are a-planes. However, the present invention is not limited to such an embodiment, and may be joined on a surface other than the a-plane. For example, of the side surfaces of the substrate 10, all surfaces that abut on the side surfaces of the other substrate 10 may be m-planes. Since the m-plane is a surface that can be easily cleaved, the substrates 7 to 10 can be efficiently manufactured at low cost.

  In the above-described embodiment, the case where the HVPE method is used as the crystal growth method in S130 and S200 has been described, but the present invention is not limited to such a mode. For example, a crystal growth method other than the HVPE method such as the MOVPE method may be used in one or both of S130 and S200. Even in this case, the same effect as the above-described embodiment can be obtained.

  In the above-described embodiment, a case has been described in which the GaN substrate 30 is manufactured by preparing the substrate 20 that is self-supported by being peeled off from the holding plate 12 and growing the GaN crystal film 21 using the substrate 20. However, the present invention is not limited to such an embodiment. That is, after the assembly substrate 13 is prepared, the GaN crystal film 14 is grown thick on the substrate 10 as shown in FIG. 9A, and then the GaN crystal film 14 is sliced as shown in FIG. 9B. Thus, one or more GaN substrates 30 may be obtained. That is, the process from the preparation of the assembly substrate 13 to the manufacture of the GaN substrate 30 may be performed consistently without going through the process of making the substrate 20 self-supporting. In this case, unlike the above-described embodiment, the heating of the substrate 10 is performed via the holding plate 12 and the adhesive 11, so that the heating efficiency is lowered. However, in other respects, substantially the same effect as the above-described embodiment can be obtained. Note that when the GaN crystal film 14 is sliced, the adhesive 11 or the like attached to the back side of the substrate 10 may be removed in advance.

  In the above-described embodiment, the case where adjacent substrates 10 are joined and used as the substrate 20, that is, the case where the substrate 20 includes the substrate 10 has been described. However, the present invention is not limited to such an embodiment. That is, each of one or more substrates obtained by slicing the GaN crystal film 14 grown thick as described above may be used as the substrate 20. Even in this case, the same effect as the above-described embodiment can be obtained.

  In the above-described embodiment, when the first layer growth step S132 and the second layer growth step S134 are performed in the bonding step S130 of the crystal growth substrate manufacturing step S100 (that is, the substrates 10 are combined with each other in the first layer 50 and the second layer growth step S134). The case of bonding by the second layer 60 has been described. However, the present invention is not limited to such an embodiment. For example, if the bonding strength between the substrates 10 can be sufficiently secured only by the first layer 50, even if only the first layer growth step S132 is performed in the bonding step S130 of the crystal growth substrate manufacturing step S100. Good. In this case, in the subsequent self-supporting step S <b> 140, the substrate 20 in which the plurality of substrates 10 are bonded only by the first layer 50 is made self-standing. After the substrate 20 is self-supported, in the crystal film growth step S200, the second layer is formed as at least one layer constituting the GaN crystal film 21 under the second growth conditions similar to the second layer growth step S134 of the above-described embodiment. A layer 60 is grown on the first layer 50. Even in such a case, the same effect as the above-described embodiment can be obtained.

The present invention is not limited to GaN, for example, nitride crystals such as aluminum nitride (AlN), aluminum gallium nitride (AlGaN), indium nitride (InN), indium gallium nitride (InGaN), aluminum indium gallium nitride (AlInGaN), That is, a substrate made of a group III nitride crystal represented by a composition formula of Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) is manufactured. In this case, it can be suitably applied.

  Hereinafter, various experimental results supporting the effects of the present invention will be described.

(1) Experiment 1
(1-1) Production of Crystal Growth Substrate In the bonding step S130 of the above-described embodiment, only the first layer growth step S132 was performed, and a crystal growth substrate was produced under the following conditions.

(Seed crystal substrate)
Material: GaN
Fabrication method: VAS method Diameter: 1 inch Thickness: 400 μm
Low-index crystal plane closest to the main surface: c-plane (first layer)
Material: GaN
Film formation method: HVPE method First layer thickness (on the main surface of the seed crystal substrate): about 131 μm
Growth temperature: 947 ° C
Growth rate of the first layer: 262 μm / h

(1-2) Evaluation Using an optical microscope, the surface side and the back side of the crystal growth substrate were observed.

(1-3) Result As shown in FIG. 11A, when the surface side of the crystal growth substrate was observed, a gap was formed between adjacent seed crystal substrates. From this, during the growth of the first layer, the first growth condition in which the growth rate in the direction along the normal line of the main surface of the seed crystal substrate is higher than the growth rate in the direction along the main surface of the seed crystal substrate. Thus, it was confirmed that the upper portion of the gap between the side surfaces of the adjacent seed crystal substrates could be suppressed by growing the first layer.

  On the other hand, as shown in FIG. 11B, when the back surface side of the crystal growth substrate was observed, the adjacent seed crystal substrates were bonded via the first layer. Therefore, during the growth of the first layer, the upper portion of the gap between the side surfaces of the adjacent seed crystal substrates is prevented from being blocked, thereby forming a film in the gap between the side surfaces of the adjacent seed crystal substrates. It was confirmed that the gas could be managed. As a result, it was confirmed that the side surfaces of adjacent seed crystal substrates could be joined by the first layer.

(2) Experiment 2
(2-1) Production of Crystal Growth Substrate The bonding step S130 of the above-described embodiment was performed, and a crystal growth substrate was produced under the following conditions.

(Seed crystal substrate)
Same as Experiment 1. The side on which the scribe groove by laser was formed was defined as the main surface side.
(First layer)
Same as Experiment 1 (second layer)
Material: GaN
Film formation method: HVPE method Second layer thickness: about 307 μm
Growth temperature: 1065 ° C

(2-2) Evaluation (SEM observation)
The surface and cross section of the crystal growth substrate were observed using a scanning electron microscope (SEM). In observation of the cross section of the crystal growth substrate, cathodoluminescence (CL) images were also observed.

(Measurement of dislocation density)
Using SEM, the CL image on the main surface of the above-mentioned crystal growth substrate was observed, and the dislocation density (average dislocation density) on the main surface of the second layer was measured.

(2-3) Results (SEM observation: bonding mode)
As shown in FIG. 12 (c) and FIG. 13 in which the portion X in FIG. 12 (c) is enlarged, among the side surfaces of the adjacent seed crystal substrates, the cleavage planes close to the back side are formed by the first layer. It was joined. From this, it was confirmed that the deposition gas was able to reach the deep part of the gap between the side surfaces of the adjacent seed crystal substrates. As a result, it was confirmed from the SEM image that the side surfaces of the adjacent seed crystal substrates could be joined by the first layer.

  As shown in FIGS. 12A to 12C, when viewed from the surface side of the crystal growth substrate, adjacent seed crystal substrates were bonded via the second layer. Therefore, the second layer is laterally moved under the second growth condition in which the growth rate in the direction along the normal line of the main surface of the seed crystal substrate is equal to or lower than the growth rate in the direction along the main surface of the seed crystal substrate. It was confirmed that the second layer could be formed on the first layer in which the side surfaces of the adjacent seed crystal substrates were joined by growing. As a result, it was confirmed that the bonding between the seed crystal substrates by the first layer could be reinforced by the second layer.

(Dislocation density)
When the CL image on the main surface of the crystal growth substrate was observed, the main surface of the crystal growth substrate had a high dislocation density region and a low dislocation density region. It was confirmed that the high dislocation density region overlaps with the junction of the seed crystal substrate in plan view, and the low dislocation density region is formed in the seed corresponding region. Further, it was confirmed that the dislocation density in the low dislocation density region was lower by one digit or more than the dislocation density in the high dislocation density region.

  Further, in the low dislocation density region in the main surface of the crystal growth substrate, there are a sparse portion with relatively few dislocations and a dense portion with relatively little dislocation when compared in the region. It was confirmed that it was formed.

Further, in the low dislocation density region, the dislocation density in the dense part was 3.11 × 10 ⁶ cm ⁻² . Since the dislocation density in the main surface of the seed crystal substrate was about 4 × 10 ⁶ cm ⁻² , the dislocation density was reduced in the dense portion of the low dislocation density region even though the dislocation density was relatively large. It was confirmed that the dislocation density on the main surface could be equal to or less than the dislocation density. On the other hand, the dislocation density in the sparse part was 7.96 × 10 ⁵ cm ⁻² . In the sparse part of the low dislocation density region, it was confirmed that the dislocation density could be 30% or less of the dislocation density in the main surface of the seed crystal substrate. From these results, in the crystal growth substrate, dislocation density in the main surface of the second layer can be reduced by eliminating some of the plurality of dislocations collected locally in the second layer. I confirmed that.

<Preferred embodiment of the present invention>
Hereinafter, preferred embodiments of the present invention will be additionally described.

(Appendix 1)
Producing a substrate for crystal growth;
Growing a crystal film made of a single crystal on the crystal growth substrate;
A method for producing a nitride crystal substrate having
The step of producing the crystal growth substrate includes:
Arranging a plurality of seed crystal substrates made of a group III nitride single crystal so that their principal surfaces are parallel to each other and adjacent side surfaces face each other;
The plurality of seed crystal substrates under a first growth condition in which a growth rate in a direction along a normal line of the main surface of the seed crystal substrate is higher than a growth rate in a direction along the main surface of the seed crystal substrate. A step of epitaxially growing a first layer made of a group III nitride single crystal on each of the main surface and the side surface of the substrate, and bonding side surfaces of adjacent seed crystal substrates with the first layer;
On the first layer under a second growth condition in which a growth rate in a direction along a normal line of the main surface of the seed crystal substrate is equal to or lower than a growth rate in a direction along the main surface of the seed crystal substrate. Epitaxially growing a second layer comprising a group III nitride single crystal;
Have
In the step of growing the crystal film,
Manufacturing a nitride crystal substrate by heating the crystal growth substrate, supplying a group III material and a nitriding agent on the heated crystal growth substrate, and growing the crystal film made of a group III nitride single crystal Method.

(Appendix 2)
In the step of arranging the plurality of seed crystal substrates,
Bonding the plurality of seed crystal substrates on a holding plate via an adhesive;
In the step of epitaxially growing the first layer,
Epitaxially growing the first layer on the plurality of seed crystal substrates bonded on the holding plate;
The step of producing the crystal growth substrate includes:
The nitride according to claim 1, further comprising a step of, after the step of epitaxially growing the second layer, the step of making the crystal growth substrate formed by bonding the plurality of seed crystal substrates joined by the first layer and the second layer self-supporting. A method for producing a crystal substrate.

(Appendix 3)
Producing a substrate for crystal growth;
Growing a crystal film made of a single crystal on the crystal growth substrate;
A method for producing a nitride crystal substrate having
The step of producing the crystal growth substrate includes:
Arranging a plurality of seed crystal substrates made of a group III nitride single crystal so that their principal surfaces are parallel to each other and adjacent side surfaces face each other;
The plurality of seed crystal substrates under a first growth condition in which a growth rate in a direction along a normal line of the main surface of the seed crystal substrate is higher than a growth rate in a direction along the main surface of the seed crystal substrate. A step of epitaxially growing a first layer made of a group III nitride single crystal on each of the main surface and the side surface of the substrate, and bonding side surfaces of adjacent seed crystal substrates with the first layer;
Have
The step of growing the crystal film includes:
On the first layer under a second growth condition in which a growth rate in a direction along a normal line of the main surface of the seed crystal substrate is equal to or lower than a growth rate in a direction along the main surface of the seed crystal substrate. A method for manufacturing a nitride crystal substrate, comprising the step of epitaxially growing a second layer made of a group III nitride single crystal.

(Appendix 4)
In the step of arranging the plurality of seed crystal substrates,
Bonding the plurality of seed crystal substrates on a holding plate via an adhesive;
In the step of epitaxially growing the first layer,
Epitaxially growing the first layer on the plurality of seed crystal substrates bonded on the holding plate;
The step of producing the crystal growth substrate includes:
The manufacture of the nitride crystal substrate according to appendix 3, further comprising a step of, after the step of epitaxially growing the first layer, causing the crystal growth substrate formed by bonding the plurality of seed crystal substrates only by the first layer. Method.

(Appendix 5)
In the step of epitaxially growing the first layer,
Any one of Supplementary notes 1 to 4 for keeping the group III raw material and the nitriding agent in the gap between the side surfaces while preventing the upper part of the gap between the side surfaces of the adjacent seed crystal substrates from being blocked. A method for producing a nitride crystal substrate as described in 1).

(Appendix 6)
In the step of epitaxially growing the second layer,
The second layer is formed on the first layer obtained by bonding the side surfaces of the adjacent seed crystal substrates, and the second layer is formed over the main surface of the plurality of seed crystal substrates. The method for producing a nitride crystal substrate according to any one of appendices 1 to 5, wherein the substrate is continuously formed.

(Appendix 7)
In the step of epitaxially growing the second layer,
The nitriding according to any one of appendices 1 to 6, wherein a continuous high dislocation density region and a plurality of low dislocation density regions separated by the high dislocation density region are formed on the main surface of the second layer. A method for manufacturing a physical crystal substrate.

(Appendix 8)
In the step of epitaxially growing the second layer,
In the low dislocation density region, a sparse part with relatively few dislocations and a dense part with relatively many dislocations are formed,
The method for producing a nitride crystal substrate according to appendix 7, wherein at least the dislocation density of the sparse part is 30% or less of the dislocation density in the main surface of the seed crystal substrate.

(Appendix 9)
The method for manufacturing a nitride crystal substrate according to any one of appendices 1 to 8, wherein a growth temperature in the step of epitaxially growing the first layer is lower than a growth temperature in the step of epitaxially growing the second layer.

(Appendix 10)
The growth temperature in the step of epitaxially growing the first layer is 900 ° C. or higher and 970 ° C. or lower,
The method for manufacturing a nitride crystal substrate according to appendix 9, wherein a growth temperature in the step of epitaxially growing the second layer is 990 ° C. or higher and 1100 ° C. or lower.

(Appendix 11)
Any one of Supplementary notes 1 to 10 in which the steps from the step of epitaxially growing the first layer to the step of epitaxially growing the second layer are continuously performed in the same chamber without exposing the plurality of seed crystal substrates to the atmosphere. A method for producing a nitride crystal substrate according to claim 1.

(Appendix 12)
The step of producing the crystal growth substrate includes:
A step of preparing the plurality of seed crystal substrates before the step of arranging the plurality of seed crystal substrates;
In the step of preparing the plurality of seed crystal substrates,
A scribe groove is formed on the back surface side of the material substrate by irradiating the material substrate from which the seed crystal substrate is materialized with a laser beam from the back surface side opposite to the main surface side of the seed crystal substrate. Process,
Separating the seed crystal substrate from the material substrate by cleavage so that a cleavage plane is disposed on the side surface on the main surface side;
The method for producing a nitride crystal substrate according to any one of appendices 1 to 11, wherein:

(Appendix 13)
In the step of epitaxially growing the first layer,
The manufacturing method of the nitride crystal substrate according to appendix 12, wherein the cleavage planes of the side surfaces of the adjacent seed crystal substrates are bonded to each other by the first layer.

(Appendix 14)
A nitride crystal substrate obtained by the method for manufacturing a nitride crystal substrate according to any one of appendices 1 to 13.

(Appendix 15)
A plurality of seed crystal substrates made of a single crystal of group III nitride, arranged so that main surfaces are parallel to each other and adjacent side surfaces are opposed to each other;
A first layer made of a group III nitride single crystal, epitaxially grown on the main surface and the side surface of each of the plurality of seed crystal substrates, and joining the side surfaces of adjacent seed crystal substrates;
A second layer made of a single crystal of group III nitride and epitaxially grown on the first layer;
A substrate for crystal growth.

10 seed crystal substrate 20 crystal growth substrate 30 GaN substrate (nitride crystal substrate)

Claims (10)

Producing a substrate for crystal growth;
Growing a crystal film made of a single crystal on the crystal growth substrate;
A method for producing a nitride crystal substrate having
The step of producing the crystal growth substrate includes:
Arranging a plurality of seed crystal substrates made of a group III nitride single crystal so that their principal surfaces are parallel to each other and adjacent side surfaces face each other;
The plurality of seed crystal substrates under a first growth condition in which a growth rate in a direction along a normal line of the main surface of the seed crystal substrate is higher than a growth rate in a direction along the main surface of the seed crystal substrate. A step of epitaxially growing a first layer made of a group III nitride single crystal on each of the main surface and the side surface of the substrate, and bonding side surfaces of adjacent seed crystal substrates with the first layer;
On the first layer under a second growth condition in which a growth rate in a direction along a normal line of the main surface of the seed crystal substrate is equal to or lower than a growth rate in a direction along the main surface of the seed crystal substrate. Epitaxially growing a second layer comprising a group III nitride single crystal;
Have
In the step of growing the crystal film,
Manufacturing a nitride crystal substrate by heating the crystal growth substrate, supplying a group III material and a nitriding agent on the heated crystal growth substrate, and growing the crystal film made of a group III nitride single crystal Method. Producing a substrate for crystal growth;
Growing a crystal film made of a single crystal on the crystal growth substrate;
A method for producing a nitride crystal substrate having
The step of producing the crystal growth substrate includes:
Arranging a plurality of seed crystal substrates made of a group III nitride single crystal so that their principal surfaces are parallel to each other and adjacent side surfaces face each other;
The plurality of seed crystal substrates under a first growth condition in which a growth rate in a direction along a normal line of the main surface of the seed crystal substrate is higher than a growth rate in a direction along the main surface of the seed crystal substrate. A step of epitaxially growing a first layer made of a group III nitride single crystal on each of the main surface and the side surface of the substrate, and bonding side surfaces of adjacent seed crystal substrates with the first layer;
Have
The step of growing the crystal film includes:
On the first layer under a second growth condition in which a growth rate in a direction along a normal line of the main surface of the seed crystal substrate is equal to or lower than a growth rate in a direction along the main surface of the seed crystal substrate. A method for manufacturing a nitride crystal substrate, comprising the step of epitaxially growing a second layer made of a group III nitride single crystal. In the step of epitaxially growing the first layer,
3. The nitriding according to claim 1, wherein the group III raw material and the nitriding agent are allowed to reach the gap between the side surfaces while preventing the upper part of the gap between the side surfaces of the adjacent seed crystal substrates from being blocked. A method for manufacturing a physical crystal substrate. In the step of epitaxially growing the second layer,
The second layer is formed on the first layer obtained by bonding the side surfaces of the adjacent seed crystal substrates, and the second layer is formed over the main surface of the plurality of seed crystal substrates. The method for manufacturing a nitride crystal substrate according to any one of claims 1 to 3, wherein the substrate is formed continuously. The method for producing a nitride crystal substrate according to claim 1, wherein a growth temperature in the step of epitaxially growing the first layer is lower than a growth temperature in the step of epitaxially growing the second layer. . The growth temperature in the step of epitaxially growing the first layer is 900 ° C. or higher and 970 ° C. or lower,
The method for manufacturing a nitride crystal substrate according to claim 5, wherein a growth temperature in the step of epitaxially growing the second layer is 990 ° C. or higher and 1100 ° C. or lower. The step of producing the crystal growth substrate includes:
A step of preparing the plurality of seed crystal substrates before the step of arranging the plurality of seed crystal substrates;
In the step of preparing the plurality of seed crystal substrates,
A scribe groove is formed on the back surface side of the material substrate by irradiating the material substrate from which the seed crystal substrate is materialized with a laser beam from the back surface side opposite to the main surface side of the seed crystal substrate. Process,
Separating the seed crystal substrate from the material substrate by cleavage so that a cleavage plane is disposed on the side surface on the main surface side;
The manufacturing method of the nitride crystal substrate of any one of Claims 1-6 which have these. In the step of epitaxially growing the first layer,
The method for manufacturing a nitride crystal substrate according to claim 7, wherein the cleavage surfaces of the side surfaces of the adjacent seed crystal substrates are bonded to each other by the first layer. A nitride crystal substrate obtained by the method for manufacturing a nitride crystal substrate according to claim 1. A plurality of seed crystal substrates made of a single crystal of group III nitride, arranged so that main surfaces are parallel to each other and adjacent side surfaces are opposed to each other;
A first layer made of a group III nitride single crystal, epitaxially grown on the main surface and the side surface of each of the plurality of seed crystal substrates, and joining the side surfaces of adjacent seed crystal substrates;
A second layer made of a single crystal of group III nitride and epitaxially grown on the first layer;
A substrate for crystal growth.