JP2008044842A - Group iii-v nitride-based semiconductor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a self-standing group III-V nitride-based semiconductor substrate almost free from warp. <P>SOLUTION: A GaN layer 33 is epitaxially grown on a sapphire substrate 31 through a GaN low-temperature buffer layer 32. Then the substrate is taken out of a reaction tube, and a self-standing GaN substrate 35 is obtained by removing the sapphire substrate 31, the GaN low-temperature buffer layer 32 and a portion of the GaN layer 33. Thereafter, the self-standing GaN substrate 35 is put in an electric furnace and heat-treated at 1,200°C for 24 h in an NH<SB>3</SB>atmosphere. Thereby, a self-standing GaN substrate having surface dislocation density of 4×10<SP>7</SP>cm<SP>-2</SP>, rear surface dislocation density of 8×10<SP>5</SP>cm<SP>-2</SP>, and a dislocation density ratio of 50 can be obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a group III-V nitride semiconductor substrate.

  Nitride semiconductor materials have a sufficiently large forbidden band width and a direct transition type between band transitions. Therefore, application to a short wavelength light emitting element has been actively studied. In addition, application to electronic devices is also expected due to the high saturation drift velocity of electrons and the use of two-dimensional carrier gas by heterojunction.

  The nitride semiconductor layers constituting these elements are formed using a vapor phase growth method such as metal organic vapor phase epitaxy (MOVPE), molecular beam vapor phase epitaxy (MBE), or hydride vapor phase epitaxy (HVPE). It is obtained by performing epitaxial growth on the substrate. However, since there is no underlying substrate having a lattice constant matching with this nitride semiconductor layer, it is difficult to obtain a high-quality growth layer, and the obtained nitride semiconductor layer contains many crystal defects. . Since this crystal defect becomes a factor that hinders improvement in device characteristics, so far, studies have been actively conducted to reduce the crystal defect in the nitride semiconductor layer.

  As a method for obtaining Group III element nitride-based crystals with relatively few crystal defects, a method is known in which a low temperature deposition buffer layer (buffer layer) is formed on a dissimilar substrate such as sapphire and an epitaxial growth layer is formed thereon. It has been. In the crystal growth method using the low temperature deposition buffer layer, first, AlN or GaN is deposited on a substrate such as sapphire at around 500 ° C. to form an amorphous film or a continuous film partially including polycrystal. This is heated to around 1000 ° C. to partially evaporate and crystallize to form high-density crystal nuclei. Using this as a growth nucleus, a GaN film with relatively good crystallinity can be obtained. However, even if a method for forming a low temperature deposition buffer layer is used, there are considerable crystal defects such as threading dislocations and hole pipes, and it is not sufficient to obtain a high-performance device that is currently desired. It was.

  Therefore, a method of using a GaN substrate as a substrate for crystal growth and forming a semiconductor multilayer film constituting an element portion thereon has been actively studied. Hereinafter, such a GaN substrate for crystal growth is referred to as a free-standing GaN substrate. An ELO (Epitaxial Lateral Overgrowth) technique is known as a technique for obtaining a self-standing GaN substrate. ELO is a technique for obtaining a GaN layer with few dislocations by forming a mask having a stripe-shaped opening on a base substrate and laterally growing from the opening. Japanese Laid-Open Patent Publication No. 11-251253 proposes that a GaN layer is formed on a sapphire substrate using this ELO technique, and then the sapphire substrate is removed by etching or the like to obtain a self-standing GaN substrate.

  On the other hand, the FELLO (Facet-Initiated Epitaxial Lateral Overgrowth) technology (A. Usui et al., Jpn. J. Appl. Phys. Vol. 36 (1997) pp. L. 899-) L.902)) has been developed. This technique is common to ELO in that selective growth is performed using a silicon oxide mask, but differs in that facets are formed in the mask opening. By forming facets, the propagation direction of dislocations is changed, and threading dislocations reaching the upper part of the epitaxial growth layer are reduced. By using this method, a high-quality free-standing GaN substrate with relatively few crystal defects can be obtained by growing a thick GaN layer on a base substrate such as sapphire and then removing the base substrate.

  However, problems to be solved still remain in the self-standing GaN substrate manufactured by such a method. The biggest problem is the generation of warpage. For example, it is known that a self-standing GaN substrate from which a sapphire substrate is removed is warped concavely with the growth surface facing upward. The curvature radius of this warp reaches about several tens of centimeters. If this warpage is large, when a layer structure for a device is grown with a MOVPE apparatus or the like using this as a substrate, the substrate cannot be brought into close contact with the substrate holder, resulting in a temperature distribution and a uniform composition and impurity distribution cannot be obtained. In addition, since uniform lithography becomes difficult, the device yield is greatly impaired. Of course, the smaller the warp, the better, but it is desirable that the radius of curvature be 1 m or more.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a group III-V nitride semiconductor free-standing substrate having a small warpage.

  According to the study by the present inventors, the warpage of the free-standing substrate is due to the fact that the average dislocation density (particularly the edge dislocation) differs between the front surface and the back surface of the substrate and has a distribution in the substrate. It turned out to be the cause. That is, the greater the difference in dislocation density between one surface and the other surface of the substrate, the greater the warpage. Therefore, it is extremely important to control the dislocation density distribution in order to reduce warpage.

The difference in the edge dislocation density between one surface and the other surface can be considered as follows that the dislocation gradient causes the substrate to warp. In hexagonal GaN, crystal grains exist at a high density, and there is a slight rotational shift between the crystal grains due to lattice mismatch with different substrates, so that there are many edge dislocations at the boundaries. Will exist. A substantially linear relationship is recognized between the edge dislocation density and the crystal grain size. The crystal grain size d ₀ and the strain accumulated in the substrate (ε) are:
ε = Δ / d ₀ (1)
The following relational expression holds. Here, Δ is approximately equal to the Burgers vector of edge dislocations. Therefore, when a substrate having different dislocation densities exists on one surface and the other surface, the magnitude of this strain differs inside the substrate, which causes warpage.

Actually, when a self-standing GaN substrate is produced by epitaxially growing a GaN layer on a heterogeneous substrate and then removing the heterogeneous substrate, 10 ⁹ to 10 due to lattice mismatch at the interface between the substrate and the GaN layer. A high edge dislocation density of ¹¹ cm ⁻² is obtained. Even in such a crystal, the dislocation density is reduced to about 10 ⁵ to 10 ⁷ cm ^{−2 on the} surface of the GaN layer by various low-dislocation technologies including lateral growth and thick film growth. Such warpage of the substrate usually has an edge dislocation density on one side of about 10 ⁹ cm ^{−2 and} an edge dislocation density on the other side of about 10 ⁶ cm ⁻² . In the case of a self-supporting GaN substrate having a thickness of 200 μm, the curvature radius of warpage is as large as about 20 cm, and it is difficult to use it for device application as it is. On the other hand, if the value is reduced to about 10 ⁷ cm ⁻² on the surface having the higher edge dislocation density, the curvature radius of warpage is about 10 m, and the warpage is greatly improved, and a substrate suitable for device application can be obtained. it can.

  The reason why the warpage of the substrate can be suppressed by controlling the edge dislocation density has been described above. Similarly, the warpage of the substrate can be effectively suppressed by controlling the total dislocation density including the edge dislocation density.

  The present invention has been made based on the above viewpoint, and suppresses the warpage of the substrate by controlling the total dislocation density, particularly the edge dislocation density.

According to the present invention, in a self-supporting group III-V nitride semiconductor substrate, the dislocation density on the lower edge dislocation density side is m ₁ , and the dislocation density on the higher edge dislocation density side is m _2. In this case, a group III-V nitride-based semiconductor substrate having a m ₂ / m ₁ value of less than 1000 is provided.

  According to the present invention, the warpage of the substrate is remarkably improved. Since the effect of reducing warpage can be stably obtained, the manufacturing stability is also excellent.

In this group III-V nitride semiconductor substrate, m ₁ can be preferably 5 × 10 ⁷ cm ⁻² or less, more preferably 5 × 10 ⁶ cm ⁻² or less. By doing so, it is possible to effectively suppress warping while realizing good crystal quality.

  In the present invention, the dislocation density and the edge dislocation density refer to an in-plane average density. For example, in the case of a group III-V nitride semiconductor substrate manufactured by mask growth, the dislocation density may be different in the substrate plane depending on the manufacturing method. When such an in-plane dislocation density distribution exists, the warpage of the substrate can be effectively reduced by configuring the average dislocation density and the average edge dislocation density to be values within the above range.

  As described above, according to the present invention, since the dislocation density in the substrate, particularly the edge dislocation density, is controlled, an independent III-V group nitride semiconductor substrate with small warpage can be stably obtained.

  The “self-supporting” substrate in the present invention refers to a substrate having a strength that can retain its shape and does not cause inconvenience in handling. In order to have such strength, the thickness of the self-supporting substrate is preferably 30 μm or more, more preferably 50 μm or more. In consideration of easiness of cleavage after element formation, the thickness of the self-supporting substrate is preferably 1 mm or less, more preferably 300 μm or less. If the thickness is too thick, it will be difficult to cleave, and the cleaved surface will be uneven. As a result, when applied to, for example, a semiconductor laser, deterioration of device characteristics due to loss of reflection becomes a problem.

The III-V nitride semiconductor in the present _invention, a semiconductor is represented by _{In x Ga y Al 1-x} -y N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ x + y ≦ 1) Can be mentioned. Of these, semiconductors such as GaN and AlGaN are preferably used. This is because the properties required for the substrate material such as strength and manufacturing stability are satisfied.

  The present invention suppresses the warpage of the substrate by reducing the dislocation density of the self-standing substrate, particularly the edge dislocation density. In general, names such as “edge” and “screw” are used as dislocation characters. The edge dislocations and the screw dislocations indicate cases where the Burgers vector b is perpendicular and parallel to the direction in which the dislocation line runs. When the blade-shaped and spiral characters are mixed, that is, when the Burgers vector b is oblique with respect to the dislocation line, this is called “mixed” dislocation. Here, the dislocation line direction may change with respect to the direction of the Burgers vector b within one dislocation. Dislocations do not always run straight, but are often bent. Considering the case where dislocation lines are formed in a ring shape as an extreme example, a portion that runs parallel to Burgers vector b is a spiral dislocation, and a portion that runs perpendicular to Burgers vector b is an edge dislocation. The “edge dislocation” in the present invention includes such a case where a part of the dislocation is an edge dislocation.

  The dislocation character can be identified by, for example, a transmission electron microscope (TEM). When the normal vector (referred to as “diffraction vector”) g of the diffraction grating surface selected during TEM observation and the Burgers vector b of the dislocation line are perpendicular, that is, the inner product of each vector is zero (diffraction vector) In the case of g · Burgers vector b = 0), the dislocation contrast disappears. By utilizing this, an unknown dislocation character (blade, spiral, mixed) can be determined.

  The dislocation character can also be discriminated from the observation result of the shape and depth of the depression (etch pit) formed as a result of selective etching with a chemical solution.

The self-supporting group III-V nitride semiconductor substrate according to the present invention can be formed by forming a heterogeneous substrate by FIELO or pendio epitaxy and then removing the heterogeneous substrate. When produced by such a method, a substrate having a low surface dislocation density can be stably produced. FIELO is a method in which a GaN layer is vapor-phase grown while forming a mask having a plurality of openings and forming a facet structure with the openings as growth regions. GaN crystals grown from adjacent openings merge to change the propagation direction of the transition in a direction parallel to the substrate, thereby obtaining a GaN layer having a low surface transition density. By separating the GaN layer and the heterogeneous substrate, a high-quality free-standing GaN substrate can be obtained. On the other hand, in pendioepitaxy, first, a low-temperature buffer layer made of Al _x Ga _1-x N (0 ≦ x ≦ 1) is formed on a heterogeneous substrate, and then Al _y Ga _1-y N (0 ≦ x) is formed thereon. A first crystal layer composed of y ≦ 1) is formed. A mask having a plurality of stripe openings is formed on the crystal layer, and then etching is performed to form a stripe-shaped first Al _y Ga _1-y N layer. Then, starting from this, an Al _z Ga _1-z N (0 ≦ z ≦ 1) crystal is vapor-phase grown to form a second single crystal layer made of thick Al _z Ga _1-z N. Then, a high-quality free-standing substrate can be obtained by separating the second single crystal layer and the dissimilar substrate.

  However, when a substrate is produced by such a method, dislocation is reduced and good crystal quality can be obtained, but warping tends to be further promoted. While dislocations are effectively reduced on the element formation surface, a large amount of dislocations remain on the surface opposite to the element formation surface. This is because the ratio of dislocation density increases more than usual. When the present invention is applied to such a low dislocation substrate, the present invention exhibits a remarkable effect and can effectively suppress warpage while realizing good crystal quality.

  Hereinafter, the present invention will be described in more detail with reference to examples. In the examples, “total dislocation density” and “edge dislocation density” mean the average densities of the substrate surface and the back surface of the substrate.

Example 1
In this example, a GaN epitaxial layer was grown on the sapphire substrate using the above-described FIELO, and then the sapphire substrate was removed to produce and evaluate a self-standing GaN substrate. Hereinafter, a method of manufacturing a self-standing GaN substrate according to this example will be described with reference to FIG.

First, a GaN epitaxial layer 12 is grown using a sapphire substrate 11 as shown in FIG. 1A, and a silicon oxide mask 13 having a stripe-shaped opening is formed thereon, and the HVPE growth shown in FIG. Set in the device. In this apparatus, GaCl, which is a halide of a group III element, can be transported to the substrate. GaCl is a reaction of HCl and Ga metal 21 supplied together with a carrier gas such as H ₂ or N ₂ from the introduction tube 22. Generated. In the substrate region, GaCl and NH ₃ supplied from the introduction tube 23 are mixed, and GaN is vapor-grown on the substrate 24 while these are reacted. The temperature of the substrate region was set to 1000 ° C. in the electric furnace 25. The raw material GaCl partial pressure and NH ₃ partial pressure were set to 5 × 10 ⁻³ atm and 0.3 atm in the substrate region, respectively. Under this condition, the growth rate is about 50 μm / h. Doping was performed by supplying SiH ₂ Cl _{2 as} a doping source gas to the substrate region from the introduction tube 26, and a GaN layer 14 doped with about 350 μm thick Si as shown in FIG. 1B was grown.

  The substrate was taken out from the reaction tube, and a sapphire substrate and a GaN layer of about several μm were removed from the substrate as shown in FIG. As a method for removing the sapphire substrate, for example, it is possible to perform etching by mechanical polishing or strong alkali or strong acid chemicals. Further, physical etching may be performed by a charged beam or a neutral beam. Furthermore, although the sapphire substrate transmits, GaN can be irradiated with an ultraviolet laser beam that is absorbed to melt and remove the vicinity of the interface.

As a result of investigating the dislocation density of the self-standing GaN substrate 15, the surface on which the sapphire substrate is removed is 5 × 10 ⁹ cm ⁻² , while the growth surface has a value of 1 × 10 ⁶ cm ^−2. It was. Of these, values of 4.5 × 10 ⁹ cm ⁻² and 3.5 × 10 ⁵ cm ⁻² were obtained for the edge dislocations, respectively. Here, when measuring the dislocation density, particularly when the dislocation density exceeds 10 ⁸ cm ⁻² as in the back surface of the substrate, the transmission electron microscope (TEM) observation of the plane and the cross section is performed, and the dislocation density lower than that is observed. In this case, the etching was selectively performed with a chemical solution, and the number of depressions (etch pits) formed as a result was counted using an optical microscope or a scanning electron microscope. There are two main types of etch pits, with relatively shallow pits corresponding to edge dislocations. In this verification, a dark field image is taken using a cross-sectional transmission electron microscope of a sample having an etch pit, and the Burgers vector of dislocation can be determined from the relationship between the g vector of the electron beam and the direction of the dislocation line. The type of dislocation can be determined.

When the warpage of the obtained freestanding GaN substrate 15 was measured, a value of 30 cm was obtained as the radius of curvature. As a method for measuring this warp, for example, a simple and accurate result can be obtained from X-ray rocking curve measurement. That is, by examining the Bragg angle change θ _B when the warped sample is moved by X in the lateral direction, the radius of curvature ρ is
(1 / ρ) = dθ _B / dx
The following relational expression can be obtained.

Next, as shown in FIG. 1 (d), the region 16 over about 150 μm was removed from the surface on which the sapphire substrate was removed to obtain a self-standing GaN substrate 17. For this removal, molten KOH was used. Since this etching solution can selectively etch only the N surface, it is particularly convenient for etching the back surface of the GaN layer (the side opposite to the growth surface). In addition, even if there is no etching selectivity, it is possible to perform chemical etching of the back surface by forming a protective film such as SiO _{2 on} the GaN surface, and it can also be removed by mechanical polishing.

As a result, the total dislocation density on the surface of the free-standing GaN substrate 17 from which the sapphire substrate was removed was as low as 5 × 10 ⁷ cm ⁻² and the edge dislocation density was as low as 3 × 10 ⁷ cm ⁻² . When the warpage of this substrate was measured, the curvature radius was 5 m, and the warpage was greatly improved. An InGaN-based laser structure was grown on this and a laser was prototyped. However, due to the influence of warping during lithography, non-uniform exposure did not occur and the yield was greatly improved.

Example 2
In this example, a GaN epitaxial layer was grown on a sapphire substrate using the above-mentioned ELO technique (S. Nakamura, et al., Jpn. J. Appl. Phys., Vol 36 (1997) p. L1130). Then, the self-standing GaN substrate was produced by removing the sapphire substrate and evaluated. Hereinafter, a method for manufacturing a self-standing GaN substrate according to this example will be described with reference to FIG.

First, a thin GaN layer 42 is epitaxially grown using a sapphire substrate 41, and a silicon oxide mask 43 having a stripe-shaped opening in the [1-100] direction of GaN is formed thereon, and trimethylgallium (TMGa) and NH _A flat GaN layer 44 was grown to a thickness of 10 μm by MOVPE using ₃ as the main raw material as shown in FIG.

Next, this substrate was set in the HVPE growth apparatus shown in FIG. The temperature of the substrate region was set to 1000 ° C. in the electric furnace 25. The raw material GaCl partial pressure and NH ₃ partial pressure were set to 5 × 10 ⁻³ atm and 0.3 atm in the substrate region, respectively. Under this condition, the growth rate is about 50 μm / h. Further, doping was performed by supplying SiH ₂ Cl _{2 as} a doping source gas from the introduction tube 26 to the substrate region. As a result, a GaN layer 45 doped with Si having a thickness of about 350 μm was grown on the substrate as shown in FIG. Thereafter, the substrate was taken out from the reaction tube, and the sapphire substrate and a GaN layer of about several μm were removed from the substrate in the same manner as shown in FIG. 1C to obtain a GaN layer 45 having a self-standing substrate form. As a method for removing the sapphire substrate, for example, it is possible to perform etching by mechanical polishing or strong alkali or strong acid chemicals. Further, physical etching may be performed by a charged beam or a neutral beam. Furthermore, although the sapphire substrate transmits, GaN can be irradiated with an ultraviolet laser beam that is absorbed to melt and remove the vicinity of the interface. As a result of examining the dislocation density of the free-standing GaN layer 45, the surface on which the sapphire substrate is removed is 1.5 × 10 ⁹ cm ⁻² , while the growth surface has a value of 2 × 10 ⁶ cm ^−2. Obtained. Among these, values of 1 × 10 ⁹ cm ⁻² and 1 × 10 ⁶ cm ⁻² were obtained for edge dislocations, respectively.

  When the warpage of the obtained free-standing GaN layer 45 (free-standing GaN substrate) was measured, a value of 1 m was obtained as the radius of curvature.

Next, as shown in FIG. 1D, a region extending about 150 μm was removed from the surface on which the sapphire substrate was removed. For this removal, molten KOH was used. Since this etching solution can selectively etch only the N surface, it is particularly convenient for etching the back surface of the GaN substrate (the side opposite to the growth surface). In addition, even if there is no etching selectivity, it is possible to perform chemical etching of the back surface by forming a protective film such as SiO _{2 on} the GaN surface, and it can also be removed by mechanical polishing.

As a result, the total dislocation density on the surface of the free-standing GaN layer 45 from which the sapphire substrate was removed was as low as 5 × 10 ⁸ cm ⁻² and the edge dislocation density was as low as 2.5 × 10 ⁸ cm ⁻² . When the warpage of this substrate was measured, the curvature radius was 3 m, and the warpage was greatly improved. An InGaN-based laser structure was grown on this and a laser was prototyped. However, due to the influence of warping during lithography, non-uniform exposure did not occur and the yield was greatly improved.

Example 3
In this embodiment, a GaN epitaxial layer is grown on a sapphire substrate using a technique called PENDEO (TSZheleva, MRS Internet J. Nitride Semicond. Res., 4S11, G3.38 (1999)), and then a sapphire substrate. A self-standing GaN substrate was fabricated and evaluated by removing. Hereinafter, a method for manufacturing a self-standing GaN substrate according to this example will be described with reference to FIG.

First, a silicon oxide mask 53 having a stripe-shaped opening in the [1-100] direction of GaN is formed on a thin GaN epitaxial layer 52 using a sapphire substrate 51, and then a dry etching method or the like is used to form FIG. As in b), a part of the GaN epitaxial layer 52 and a part 54 of the sapphire substrate are etched. Next, a flat GaN layer 55 is grown to a thickness of 10 μm by MOVPE using trimethylgallium (TMGa) and NH ₃ as main raw materials as shown in FIG. A part of the dry etching portion remains as a void.

This substrate was set in the HVPE growth apparatus shown in FIG. The temperature of the substrate region in the apparatus was set to 1000 ° C. in the electric furnace 25. The raw material GaCl partial pressure and NH ₃ partial pressure were set to 5 × 10 ⁻³ atm and 0.3 atm in the substrate region, respectively. Under this condition, the growth rate is about 50 μm / h. Further, doping was performed by supplying SiH ₂ Cl _{2 as} a doping source gas from the introduction tube 26 to the substrate region. Thus, a Si-doped GaN layer 56 having a thickness of about 350 μm was grown as shown in FIG.

This substrate was taken out from the reaction tube, and the sapphire substrate and a GaN layer of about several μm were removed from the substrate in the same manner as in FIG. 1C to obtain a GaN layer 56 having a form as a free-standing substrate. As a method for removing the sapphire substrate, for example, it is possible to perform etching by mechanical polishing or strong alkali or strong acid chemicals. Further, physical etching may be performed by a charged beam or a neutral beam. Furthermore, although the sapphire substrate transmits, GaN can be irradiated with an ultraviolet laser beam that is absorbed to melt and remove the vicinity of the interface. As a result of investigating the dislocation density of the free-standing GaN layer 56, the average value is 3 × 10 ⁹ cm ⁻² on the surface from which the sapphire substrate is removed, and 3 × 10 ⁶ cm ^{−2 on} the growth surface. was gotten. Among these, regarding edge dislocations, values of 2.4 × 10 ⁹ cm ⁻² and 1.2 × 10 ⁶ cm ⁻² were obtained, respectively.

  When the warpage of the obtained GaN layer 56 having a form as a free-standing substrate was measured, a value of 80 cm was obtained as the radius of curvature.

Next, in the same manner as in FIG. 1D, a region extending about 150 μm was removed from the surface on which the sapphire substrate was removed. For this removal, molten KOH was used. Since this etching solution can selectively etch only the N surface, it is particularly convenient for etching the back surface of the GaN substrate (the side opposite to the growth surface). In addition, even if there is no etching selectivity, it is possible to perform chemical etching of the back surface by forming a protective film such as SiO _{2 on} the GaN surface, and it can also be removed by mechanical polishing.

As a result, the total dislocation density on the surface of the free-standing GaN layer 56 on the side where the substrate was removed was as low as 3.5 × 10 ⁸ cm ⁻² and the edge dislocation density was as low as 1 × 10 ⁸ cm ⁻² . When the warpage of this substrate was measured, the curvature radius was 4 m, and the warpage was greatly improved.

  An InGaN-based laser structure was grown on this and a laser was prototyped. However, due to the influence of warping during lithography, non-uniform exposure did not occur and the yield was greatly improved.

Example 4
In this example, the dislocation density on the surface of the free-standing GaN substrate is controlled by heat treatment. Hereinafter, a method for manufacturing a self-standing GaN substrate according to this example will be described with reference to FIG.

First, using the sapphire substrate 31, a GaN layer 33 was grown on the GaN low-temperature buffer layer 32 using the HVPE growth apparatus shown in FIG. 2 (FIG. 3A). In the substrate region in the apparatus, GaCl and NH ₃ supplied from the introduction tube 23 are mixed, and GaN vapor-phase grows on the substrate 24 while reacting. The temperature of the substrate region was set to 1000 ° C. in the electric furnace 25. The raw material GaCl partial pressure and NH ₃ partial pressure were set to 5 × 10 ⁻³ atm and 0.3 atm in the substrate region, respectively. Under this condition, the growth rate is about 50 μm / h. Further, doping was performed by supplying SiH ₂ Cl _{2 as} a doping source gas from the introduction tube 26 to the substrate region. As a result, a GaN layer 33 doped with Si having a thickness of about 200 μm was epitaxially grown.

  Thereafter, the substrate was taken out of the reaction tube, and a part of the sapphire substrate 31, the GaN low-temperature buffer layer 32, and the GaN layer 33 was removed (FIG. 3B). 3A is divided into a self-standing GaN substrate 35 and a GaN layer 34 removed from the self-standing GaN substrate in FIG. 3B. The GaN layer 34 is about several tens of μm.

  As a method for removing the sapphire substrate 31, for example, mechanical polishing or etching with strong alkali or strong acid chemicals can be performed. Further, physical etching may be performed by a charged beam or a neutral beam. Furthermore, although the sapphire substrate transmits, GaN can be irradiated with an ultraviolet laser beam that is absorbed to melt and remove the vicinity of the interface.

As a result of examining the dislocation density of the free-standing GaN substrate 35 obtained as described above, the surface on the side from which the sapphire substrate was removed was 9 × 10 ⁹ cm ⁻² , while the growth surface was 1 × 10 ⁷ cm. A value of ^-2 was obtained. Among these, values of 7 × 10 ⁹ cm ⁻² and 5 × 10 ⁶ cm ⁻² were obtained for the edge dislocations, respectively. When the warpage of the self-standing GaN substrate 35 was measured, the curvature radius was as large as 90 cm.

This self-standing GaN substrate 35 was placed in an electric furnace and heat-treated at 1200 ° C. for 24 hours in an NH ₃ atmosphere. The NH ₃ atmosphere is used to prevent decomposition during the heat treatment, but it is not necessary to supply NH ₃ in particular if the sample can be sealed. As a result of examining the dislocation density after the heat treatment, the surface on which the sapphire substrate was removed was 4 × 10 ⁷ cm ⁻² , while the growth surface was 8 × 10 ⁵ cm ⁻² and the dislocation density was greatly improved. It was observed. Of these, values of 1 × 10 ⁷ cm ⁻² and 3 × 10 ⁵ cm ⁻² were obtained for edge dislocations, respectively. When the warpage of the free-standing GaN substrate 35 after the heat treatment was measured, the curvature radius was 6 m, and the warpage was greatly improved.

  An InGaN-based laser structure was grown on this and a laser was prototyped. However, due to the influence of warping during lithography, non-uniform exposure did not occur and the yield was greatly improved.

Example 5
In this embodiment, the dislocation density on the surface of the free-standing GaN substrate is controlled by inserting a heat treatment process during epitaxial growth. Hereinafter, a method for manufacturing a self-standing GaN substrate according to this example will be described.

In this example, a sapphire C-plane substrate was used, and the HVPE apparatus shown in FIG. 2 was used to grow a GaN layer by the process shown in FIG. At this time, the GaN layer 33 was grown and heat-treated according to a temperature sequence as shown in FIG. During the growth, the GaCl partial pressure was 5 × 10 ⁻³ atm, and the NH ₃ partial pressure was 0.3 atm.

First, the furnace temperature was set to 1200 ° C., and the sapphire substrate was thermally cleaned in an H ₂ gas stream. Next, the furnace temperature was lowered to 500 ° C., and a GaN low-temperature buffer layer 32 was deposited. Thereafter, the furnace temperature was raised to 1000 ° C., and a GaN layer was grown by 50 μm. Here, the raw material supply was temporarily stopped and heat treatment was performed. That is, the furnace temperature was raised to 1400 ° C. in an NH ₃ atmosphere and held there for 10 minutes. Furthermore, the furnace temperature was lowered to 500 ° C. and held there for 5 minutes. After this series of heat treatments, the furnace temperature was raised again to 1000 ° C. Subsequently, a GaN layer was further grown by 150 μm, and a GaN layer 33 having a total film thickness of 200 μm was obtained.

  Thereafter, the substrate was taken out from the reaction tube, and a part of the sapphire substrate 31, the GaN low-temperature buffer 32, and the GaN layer 33 was removed (FIG. 3B). 3A is divided into a self-standing GaN substrate 35 and a GaN layer 34 removed from the self-standing GaN substrate in FIG. 3B. The GaN layer 34 is about several tens of μm. As a method for removing the sapphire substrate 31, the method described above can be employed.

As a result of examining the dislocation density of the free-standing GaN substrate 35 obtained as described above, the surface on the side from which the sapphire substrate was removed was 4 × 10 ⁷ cm ⁻² and the growth surface was 5 × 10 ⁶ cm ^−. A value of ² was obtained. Among these, values of 1.5 × 10 ⁷ cm ⁻² and 2 × 10 ⁶ cm ⁻² were obtained for the edge dislocations, respectively. When the warpage of the GaN layer was measured, the radius of curvature was 7 m. When grown without performing the heat treatment process, the surface on the side from which the sapphire substrate was removed was 9 × 10 ⁹ cm ⁻² , while the growth surface was 1 × 10 ⁷ cm ⁻² . Of these, the edge dislocations were 7 × 10 ⁹ cm ⁻² and 5 × 10 ⁶ cm ⁻² , respectively. When the warpage of this GaN layer was measured, the curvature radius was 90 cm and the substrate was a large warp. Therefore, the warpage could be greatly improved by inserting a heat treatment process during growth.

Example 6
In this embodiment, the dislocation density on the surface of the free-standing GaN substrate is controlled with higher accuracy by inserting a plurality of heat treatment processes during the epitaxial growth. Hereinafter, a method for manufacturing a self-standing GaN substrate according to this example will be described.

In this example, a sapphire C-plane substrate was used, and the HVPE apparatus shown in FIG. 2 was used to grow a GaN layer by the process shown in FIG. At this time, the GaN layer 33 was grown and heat-treated according to a temperature sequence as shown in FIG. During the growth, the GaCl partial pressure was 5 × 10 ⁻³ atm, and the NH ₃ partial pressure was 0.3 atm.

First, the furnace temperature was set to 1200 ° C., and the sapphire substrate was thermally cleaned in an H ₂ atmosphere. Next, the furnace temperature was lowered to 500 ° C., and a low temperature buffer layer 33 was deposited. Thereafter, the furnace temperature was raised to 1000 ° C., and a GaN layer was grown to 25 μm. Here, the raw material supply was temporarily stopped and heat treatment was performed. That is, the furnace temperature was raised to 1400 ° C. in an NH ₃ atmosphere and held there for 10 minutes. Furthermore, the furnace temperature was lowered to 500 ° C. and held there for 5 minutes. After this series of heat treatments, the furnace temperature was raised again to 1000 ° C. Thereafter, the same growth interruption and heat treatment were performed every time the GaN layer was grown to 25 μm, and the GaN layer 33 having a total film thickness of 200 μm was obtained.

  Thereafter, the substrate was taken out of the reaction tube, and a part of the sapphire substrate 31, the GaN low-temperature buffer layer 32, and the GaN layer 33 was removed (FIG. 3B). 3A is divided into a self-standing GaN substrate 35 and a GaN layer 34 removed from the self-standing GaN substrate in FIG. 3B. The GaN layer 34 is about several tens of μm. In addition, as a removal method of the sapphire substrate 31, the method mentioned above is employable.

As a result of examining the dislocation density of the free-standing GaN substrate 35 obtained as described above, the surface on the side from which the sapphire substrate was removed was 2 × 10 ⁷ cm ⁻² , while the growth surface was 4 × 10 ⁶ cm. A value of ^-2 was obtained. Of these, values of 9 × 10 ⁶ cm ⁻² and 1.5 × 10 ⁶ cm ⁻² were obtained for the edge dislocations, respectively. When the warpage of the GaN substrate was measured, the radius of curvature was 10 m. When grown without performing the heat treatment process, the surface on the side from which the sapphire substrate was removed was 9 × 10 ⁹ cm ⁻² , while the growth surface was 1 × 10 ⁷ cm ⁻² . Of these, the edge dislocations were 7 × 10 ⁹ cm ⁻² and 5 × 10 ⁶ cm ⁻² , respectively. When the warpage of the GaN substrate was measured, the curvature radius was 90 cm and the substrate was a large warp. Therefore, the warpage could be greatly improved by inserting a heat treatment process during the growth.

Example 7
In this embodiment, the dislocation density on the surface of the free-standing GaN substrate is controlled by performing heat treatment, and a method of covering the element formation surface with a mask when heat-treating the free-standing substrate is employed. Hereinafter, a method for manufacturing a self-standing GaN substrate according to this example will be described.

In this example, a sapphire C-plane substrate was used, and the HVPE apparatus shown in FIG. 2 was used to grow a GaN layer by the process shown in FIG. First, a GaN low-temperature buffer layer 32 was formed on the sapphire substrate 31. Subsequently, the GaN layer 33 was grown as follows. First, the temperature of the substrate region in the apparatus of FIG. 2 is set to 1000 ° C. in the electric furnace 25, and the GaCl partial pressure and NH ₃ partial pressure as raw materials are 5 × 10 ⁻³ atm and 0.3 atm, respectively, in the substrate region. did. Under this condition, the growth rate is about 50 μm / h. Further, doping was performed by supplying SiH ₂ Cl _{2 as} a doping source gas from the introduction tube 26 to the substrate region. As described above, the Si-doped GaN layer 33 having a thickness of about 200 μm was grown.

  Thereafter, the substrate was taken out of the reaction tube, and a part of the sapphire substrate 31, the GaN low-temperature buffer layer 32, and the GaN layer 33 was removed (FIG. 3B). 3A is divided into a self-standing GaN substrate 35 and a GaN layer 34 removed from the self-standing GaN substrate in FIG. 3B. The GaN layer 34 is about several tens of μm. In addition, as a removal method of the sapphire substrate 31, the method mentioned above is employable.

As a result of examining the dislocation density of the free-standing GaN substrate 35 obtained as described above, the surface on the side from which the sapphire substrate was removed was 9 × 10 ⁹ cm ⁻² , and the growth surface was 1 × 10 ⁷ cm ^−. A value of ² was obtained. Among these, values of 7 × 10 ⁹ cm ⁻² and 5 × 10 ⁶ cm ⁻² were obtained for the edge dislocations, respectively. When the warpage of the GaN layer was measured, the curvature radius was 90 cm, and the substrate was a large warp.

Next, the entire surface of the self-standing GaN substrate 35 was covered with a SiO ₂ film. Film formation was performed by CVD. As a result, the GaN substrate can be prevented from being decomposed even when heat treatment is performed at a high temperature. Subsequently, the self-standing GaN substrate 35 was placed in an electric furnace and heat-treated at 1600 ° C. for 2 hours in the atmosphere. As a result of examining the dislocation density after the heat treatment, the surface on which the sapphire substrate is removed is 6 × 10 ⁷ cm ⁻² , while the growth surface is 9 × 10 ⁵ cm ⁻² , which is a significant improvement in the dislocation density. It was observed. Among these, regarding edge dislocations, values of 4 × 10 ⁷ cm ⁻² and 3.5 × 10 ⁵ cm ⁻² were obtained, respectively. When the warpage of this GaN substrate was measured, the curvature radius was 3.5 m, the warpage was greatly improved, an InGaN-based laser structure was grown, and a laser was prototyped. Due to the warpage during lithography, There was no unevenness in exposure, and the yield was greatly improved.

  The results of the above examples are summarized in Tables 1 and 2. 8 and 9 show the relationship between the dislocation density ratio between the front and back surfaces of the obtained free-standing GaN substrate and the radius of curvature of the substrate. As can be seen from the results of FIGS. 8 and 9, when the total dislocation density ratio is less than 750 (the line of the total dislocation density ratio 750 is shown in FIG. 8), and when the edge dislocation density ratio is less than 1000. (A line having an edge dislocation density ratio of 1000 is shown in FIG. 9). It can be seen that the radius of curvature is remarkably increased and the warpage is reduced.

The present invention has been described above based on the embodiments. However, these are exemplifications, and various modifications can be made to combinations of the respective processes, and such modifications are also within the scope of the present invention. It will be understood by those skilled in the art. For example, in Example 5 and Example 6, after removing the sapphire substrate, a process for reducing dislocation may be performed. For example, you may implement the process of removing the area | region over 100 micrometers from the side which isolate | separated the dissimilar board | substrate. Moreover, you may implement the process which heat-processes a self-supporting GaN board | substrate at the temperature of 1150 degreeC or more.
Moreover, although the manufacturing method of the self-supporting GaN substrate has been described as an example in the embodiment, it can be applied to a self-supporting AlGaN substrate.

  By using the substrate of the present invention, it is possible to manufacture light-emitting elements and electronic elements as designed with high yield.

It is process sectional drawing for demonstrating an example of the manufacturing process of the self-supporting GaN substrate which concerns on this invention. It is a schematic diagram of the hydride vapor phase growth apparatus used for GaN growth shown in an Example. It is process sectional drawing for demonstrating an example of the manufacturing process of the self-supporting GaN substrate which concerns on this invention. It is process sectional drawing for demonstrating an example of the manufacturing process of the self-supporting GaN substrate which concerns on this invention. It is process sectional drawing for demonstrating an example of the manufacturing process of the self-supporting GaN substrate which concerns on this invention. It is process sectional drawing for demonstrating the example of the temperature profile in the manufacturing process of the self-supporting GaN substrate which concerns on this invention. It is process sectional drawing for demonstrating the example of the temperature profile in the manufacturing process of the self-supporting GaN substrate which concerns on this invention. It is a figure which shows the relationship between the total dislocation density ratio of the surface of a self-supporting GaN substrate, and a back surface, and a substrate curvature radius. It is a figure which shows the relationship between the edge dislocation density ratio of the surface of a self-standing GaN substrate, and a back surface, and a substrate curvature radius.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Sapphire substrate 12 GaN epitaxial layer 13 Silicon oxide mask 14 GaN layer 15 Free standing GaN substrate 16 Area | region 17 Free standing GaN substrate 21 Ga metal 22 Introducing tube 23 Introducing tube 24 Substrate 25 Electric furnace 26 Doping gas introducing tube 31 Sapphire substrate 32 GaN low temperature buffer Layer 33 GaN layer 34 GaN layer 35 freestanding GaN substrate 41 sapphire substrate 42 GaN layer 43 silicon oxide mask 44 GaN layer 45 GaN layer 51 sapphire substrate 52 GaN epitaxial layer 53 silicon oxide mask 54 part of sapphire substrate 55 GaN layer 56 GaN layer

Claims (4)

In a self-supporting group III-V nitride semiconductor substrate, when the dislocation density on the surface with the lower edge dislocation density is m ₁ and the dislocation density on the surface with the higher edge dislocation density is m ₂ , m ₂ III-V nitride semiconductor substrate, wherein the value of / m ₁ is less than 1000. 2. The group III-V nitride semiconductor substrate according to claim 1, wherein m ₁ is 5 × 10 ⁷ cm ⁻² or less. 3.   3. The group III-V nitride semiconductor substrate according to claim 1, wherein the group has a thickness of 30 μm or more and 1 mm or less. 4.   The group III-V nitride semiconductor substrate according to any one of claims 1 to 3, further comprising a layer made of GaN or AlGaN.

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