JPWO2019039055A1 - Method for manufacturing group 13 element nitride layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress dislocation defects, improve yield of a functional element, and improve characteristics in a group 13 element nitride crystal layer having an upper surface and a lower surface. SOLUTION: An aluminum oxide layer 2 is formed by surface-treating a sapphire substrate 25 (arrow K), and a seed crystal film made of a Group 13 element nitride is formed on the aluminum oxide layer 2 to form a seed crystal. A group 13 element nitride layer composed of a group 13 element nitride selected from gallium nitride, aluminum nitride, indium nitride or a mixed crystal thereof is provided on the film. [Selection diagram] Fig. 1

Description

The present invention relates to a method for producing a Group 13 element nitride layer.

As a light emitting element such as a light emitting diode (LED) using a single crystal substrate, one in which various gallium nitride (GaN) layers are formed on sapphire (α-aluminum oxide single crystal) is known. For example, on a sapphire substrate, an n-type GaN layer, a multiple quantum well layer (MQW) in which a quantum well layer composed of an InGaN layer and a barrier layer composed of a GaN layer are alternately laminated, and a p-type GaN layer are sequentially laminated and formed. Those having a similar structure have been mass-produced.

The gallium nitride layer described in Patent Document 1 is polycrystalline gallium nitride composed of a large number of gallium nitride single crystal particles, and a large number of columnar gallium nitride single crystal particles are arranged in the lateral direction.

The gallium nitride layer described in Patent Document 2 is polycrystalline gallium nitride composed of a large number of gallium nitride single crystal particles, and a large number of columnar gallium nitride single crystal particles are arranged in the lateral direction. Further, the average tilt angle on the surface (the average value of the inclination of the crystal orientation (crystal axis) in the normal direction with respect to the surface) is 1 to 10 °.

In Patent Document 3, a plurality of grain boundaries containing a high concentration of inclusions from the bottom surface to the intermediate position and a low concentration from the intermediate position to the upper surface are formed in an oblique direction from the lower surface. In addition, the grain boundaries extend diagonally in a direction having an angle of 50 to 70 ° with respect to the c-axis.

Patent Document 5 describes that a gallium nitride crystal having a low dislocation density can be obtained by increasing the Ga ratio in the melt.

Patent No. 5770905 Patent No. 6154066 Patent No. 5897790 WO 2011/046203 WO 2010/084682

When a light emitting device is formed on the gallium nitride crystals of Patent Documents 1 and 2, the current path may be blocked and the luminous efficiency may be lowered depending on the balance between the device size and the particle size. It has become clear. The reason for this is not clear, but it is possible that the anisotropy of the orientation between the single crystal particles is involved.

In the gallium nitride crystals of Patent Documents 3 and 4, the larger the diameter, the more difficult it is to control the flow of the melt over the entire surface of the substrate, and voids may remain on the outer periphery of the crystal.

In Patent Document 5, the grain size can be increased and the dislocation density can be reduced by controlling the high Ga ratio and the flow of flux, but voids are likely to be contained between the grains.

An object of the present invention is to suppress dislocation defects in a group 13 element nitride crystal layer having a top surface and a bottom surface, which comprises a group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride or a mixed crystal thereof. It is possible to improve the yield of functional elements and improve their characteristics.

The present invention is a step of forming an aluminum oxide layer by surface-treating a sapphire substrate.
A step of forming a seed crystal film made of a group 13 element nitride on the aluminum oxide layer, and a group 13 selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof on the seed crystal film. The present invention relates to a method for producing a group 13 element nitride layer, which comprises a step of providing a group 13 element nitride layer made of elemental nitride.

According to the present invention, it is possible to provide a group 13 element nitride crystal layer capable of suppressing dislocation defects of the group 13 element nitride crystal layer, improving the yield of functional elements, and improving the characteristics. ..

(A) is a schematic view showing a state in which surface treatment K is applied to the surface 25a of the sapphire substrate 25, and (b) shows a state in which the alnium oxide layer 2 is provided on the surface 1a of the sapphire substrate 1. (A) shows a state in which the aluminum oxide layer 2, the seed crystal layer 3 and the group 13 element nitride crystal layer 13 are provided on the support substrate 1, and (b) is the group 13 element separated from the support substrate. The nitride crystal layer 13 is shown. It is a schematic diagram for demonstrating the cathode luminescence image of the upper surface 13a of the group 13 element nitride crystal layer 13. It is a photograph which shows the cathode luminescence image of the upper surface 13a of the group 13 element nitride crystal layer 13. It is a partially enlarged photograph of FIG. It is a schematic diagram corresponding to the cathode luminescence image of FIG. It is a photograph which shows the cathode luminescence image of the cross section of the group 13 element nitride crystal layer 13. It is a scanning electron micrograph which shows the cross section of the group 13 element nitride crystal layer 13. It is a schematic diagram which shows the functional element 21 which concerns on this invention. It is a photograph taken by a scanning electron microscope on the upper surface of the group 13 element nitride crystal layer. A grayscale histogram generated from the CL image is shown.

Hereinafter, the present invention will be described in more detail.
(Sapphire substrate surface treatment process)
In the present invention, as shown in FIG. 1A, the surface 25a of the sapphire substrate 25 is surface-treated as shown by the arrow K to form the aluminum oxide layer 2 as shown in FIG. 1B.

Here, the surface treatment method of the sapphire substrate is not particularly limited as long as the aluminum oxide layer can be formed, but the methods (1) to (4) described later can be preferably exemplified.
(1) Surface treatment is performed by irradiating the sapphire substrate with an ion beam or a high-speed atomic beam.
(2) Surface treatment is performed by grinding the sapphire substrate.
(3) Surface treatment is performed by subjecting the sapphire substrate to reactive ion etching treatment.
(4) The surface treatment of the sapphire substrate is performed by annealing the sapphire substrate in an atmosphere containing at least hydrogen.

In the method (1), the sapphire substrate is irradiated with an ion beam or a high-speed atomic beam. In this case, examples of the ion species of the ion beam include argon ion, helium ion, neon ion, krypton ion, xenon ion, gallium ion, and hydrogen ion, and examples of the atomic species of the high-speed atomic beam include argon, helium, and neon. Examples include krypton, xenon, and nitrogen.
In the case of ion beam irradiation, the electric power and the gas flow rate are not particularly limited, but the electric power is preferably 5 W or more and 500 W or less, and the gas flow rate is preferably 1 sccm or more and 80 sccm or less.
In the case of high-speed atomic beam irradiation, the electric power, the gas flow rate, and the degree of vacuum before the start of irradiation are not particularly limited, but the electric power is preferably 4 W or more and 500 W or less, and the gas flow rate is preferably 20 sccm or more and 80 sccm or less. The degree of vacuum before the start of irradiation is preferably as low as possible, preferably 1 × 10 ^-5 Pa or less.

In the method (2), the surface treatment is performed by grinding the sapphire substrate. In this method, a work-altered layer is generated by grinding.
Grinding refers to scraping the surface of an object by bringing the fixed abrasive grains, in which the abrasive grains are fixed with a bond, into contact with the object while rotating at high speed. By such grinding, a rough surface is formed, and a work-altered layer is formed on the outermost surface. When grinding a sapphire substrate, fixed abrasive grains formed of high hardness SiC, Al2O3, diamond, CBN (cubic boron nitride, the same shall apply hereinafter), etc., and containing abrasive grains having a particle size of 10 μm or more and 100 μm or less are preferable. Used.

In the method (3), the surface treatment is performed by subjecting the sapphire substrate to reactive ion etching treatment. The gas type used is preferably chlorine, boron trichloride, silicon tetrachloride, or a mixed gas thereof.
In addition to the reactive gas, argon, krypton, and xenon may be mixed.
Examples of the plasma generation source include ICP type, ECR type, and parallel plate type. The electric power, bias power, chamber pressure, and gas flow rate are not particularly limited, but the electric power is 100 W or more and 1000 W or less, the bias power is 50 W or more and 300 W or less, the chamber pressure is 0.1 Pa or more and 10 Pa or less, and the gas flow rate is It is preferably 1 sccm or more and 100 sccm or less.

In the method (4), the surface treatment is performed by annealing the sapphire substrate in an atmosphere containing at least hydrogen. This atmosphere may be hydrogen alone, or may contain ammonia, nitrogen, and argon in addition to hydrogen.
The annealing treatment temperature is preferably 1000 ° C. or higher, more preferably 1200 ° C. or higher. From a practical point of view, the annealing treatment temperature is preferably 1500 ° C. or lower, more preferably 1400 ° C. or lower. The pressure during the annealing treatment may be reduced pressure, atmospheric pressure, or pressurized, and is not particularly limited, but reduced pressure is preferable from the viewpoint of gas usage efficiency.

(Aluminum oxide layer)
In the present invention, an aluminum oxide layer is formed by surface treatment of a sapphire substrate. Here, the composition of the aluminum oxide may be Al ₂ O ₃ , but it may deviate from this composition because it is a thin layer. Specifically, the composition ratio of aluminum _{oxide, Al x O y (x =} 0.15~0.65: y = 0.35~0.85, X + Y = 1) may be. In addition, elements other than aluminum and oxygen used for the surface treatment may be contained in the aluminum oxide layer or may be attached to the surface of the aluminum oxide layer.

The thickness of the aluminum oxide layer is not particularly limited, but from the viewpoint of obtaining a Group 13 element nitride crystal layer capable of reducing the dislocation density and reducing the variation in characteristics throughout, 30 angstroms or more is preferable, and 40 Angstrom or higher is more preferable. From a practical point of view, the thickness of the aluminum oxide layer is preferably 50,000 angstroms or less, and more preferably 20,000 angstroms or less.

The presence of the aluminum oxide layer is confirmed by observation with a transmission electron microscope. H-9000NAR manufactured by Hitachi High-Technologies Corporation is used for this transmission electron microscope device, and the magnification at the time of observation is preferably 2.000,000 times.

Further, when the aluminum oxide layer contains an amorphous phase, the diffraction contrast due to the crystal lattice disappears in the amorphous phase, so that the contrast becomes bright and the image becomes uniform, so that it can be distinguished from the crystal and is an amorphous phase. It can be confirmed that the thickness of the aluminum oxide layer can be measured. Further, when the aluminum oxide layer contains a defect introduction portion, the defect is displayed as a linear dark contrast, so that it can be confirmed that a new defect has been introduced.
When the aluminum oxide layer contains a polycrystalline phase, it can be distinguished from the amorphous phase because different color contrasts are observed in the layer. When the aluminum oxide layer contains a defect introduction portion, it is displayed as a darker linear contrast, so that it can be confirmed that a new defect has been introduced.
In addition, by using a technique called ultrafine electron diffraction, regularly arranged diffraction spots (spots) are observed in single crystals, concentric rings in polycrystals, and broad annular electron diffraction patterns in amorphous phases. Therefore, it is possible to distinguish between a single crystal phase, a polycrystalline phase, and an amorphous phase.

(Seed crystal layer)
For example, as shown in FIG. 2A, the seed crystal layer 3 is provided on the aluminum oxide layer 2. The material constituting the seed crystal layer 3 is one or more nitrides of Group 13 elements specified by IUPAC. The Group 13 element is preferably gallium, aluminum or indium. Specifically, the group 13 element nitride crystals are GaN, AlN, InN, Ga _x Al _1-x N (1>x> 0), Ga _x In _1-x N (1>x> 0). , Ga _x Al _y InN _1-xy (1>x> 0, 1>y> 0) is preferable.

The method for producing the seed crystal layer 3 is not particularly limited, but is MOCVD (organic metal vapor deposition method), MBE (molecular beam epitaxy method), HVPE (hydride vapor phase growth method), vapor phase method such as sputtering, Na flux method. , Amonothermal method, hydrothermal method, liquid phase method such as solgel method, powder method utilizing solid phase growth of powder, and combinations thereof are preferably exemplified.
For example, the seed crystal layer is formed by the MOCVD method by depositing a low temperature growth buffered GaN layer at 450 to 550 ° C. at 20 to 50 nm and then laminating a GaN film having a thickness of 2 to 4 μm at 1000 to 1200 ° C. It is preferable to carry out by.

(Group 13 element nitride crystal layer)
The Group 13 element nitride crystal layer 13 is formed so as to have a crystal orientation substantially following the crystal orientation of the seed crystal layer 3. The method for forming the Group 13 element nitride crystal layer is not particularly limited as long as it has a crystal orientation that roughly follows the crystal orientation of the seed crystal film, and is a vapor phase method such as MOCVD and HVPE, a Na flux method, and an amonothermal method. A liquid phase method such as a hydrothermal method and a solgel method, a powder method utilizing solid phase growth of a powder, and a combination thereof are preferably exemplified, but the Na flux method is particularly preferable.

When forming the Group 13 element nitride crystal layer by the Na flux method, it is preferable to stir the melt strongly and mix the melt sufficiently uniformly. Examples of such a stirring method include vibration, rotation, and vibration method, but the method is not limited.

The formation of the Group 13 element nitride crystal layer by the Na flux method involves forming a Group 13 metal, metal Na, and optionally a dopant (eg, germanium (Ge), silicon (Si), oxygen (O), etc.) in a pit on which a seed crystal substrate is placed. , Or a melt composition containing beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn), cadmium (Cd) and other p-type dopants). It is preferable that the temperature and pressure are raised and pressurized to 830 to 910 ° C. and 3.5 to 4.5 MPa in a nitrogen atmosphere, and then the rotation is performed while maintaining the temperature and pressure. The holding time varies depending on the target film thickness, but may be about 10 to 100 hours.

Further, it is preferable that the gallium nitride crystal thus obtained by the Na flux method is ground with a grindstone to flatten the plate surface, and then the plate surface is smoothed by a lapping process using diamond abrasive grains.

(Group 13 element nitride crystal layer)
In the present invention, a group 13 element nitride crystal layer can be formed on the aluminum oxide layer described above.
The Group 13 element nitride crystal layer is composed of a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof, and has an upper surface and a bottom surface. For example, as shown in FIG. 2B, in the group 13 element nitride crystal layer 13, the upper surface 13a and the bottom surface 13b face each other.

The nitride constituting the group 13 element nitride crystal layer is gallium nitride, aluminum nitride, indium nitride or a mixed crystal thereof. Specifically, GaN, AlN, InN, Ga _x Al _1-x N (1>x> 0), Ga _x In _1-x N (1>x> 0), Ga _x Al _y In _z N (1>x> 0). >X> 0, 1>y> 0, x + y + z = 1).

Particularly preferably, the nitride constituting the Group 13 element nitride crystal layer is a gallium nitride based nitride. Specifically, GaN, Ga _x Al _1-x N (1>x> 0.5), Ga _x In _1-x N (1>x> 0.4), Ga _x Al _y In _z N (1>x> 0.5). 1, 1>y> 0.3, x + y + z = 1).

The group 13 element nitride may be doped with zinc, calcium or other n-type dopant or p-type dopant. In this case, the polycrystalline group 13 element nitride may be doped with a p-type electrode, an n-type electrode, or p. It can be used as a member or layer other than a base material such as a mold layer and an n-type layer. Preferred examples of the p-type dopant include one or more selected from the group consisting of beryllium (Be), magnesium (Mg), strontium (Sr), and cadmium (Cd). Preferred examples of the n-type dopant include one or more selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn) and oxygen (O).

In a preferred embodiment, when the upper surface of the Group 13 element nitride crystal layer is observed by cathodoluminescence, it has a linear high-luminance light emitting portion and a low-luminance light emitting region adjacent to the high-luminance light emitting portion. The high-luminance light emitting portion includes a portion extending along the m-plane of the group 13 element nitride crystal. This is because the linear high-intensity light-emitting part appears on the upper surface, so that the linear high-intensity light-emitting part in which the dopant component and the trace component contained in the group 13 element nitride crystal are dense is generated. Means. At the same time, the fact that the linear high-intensity light-emitting part extends along the m-plane means that the dopants gather along the m-plane during crystal growth, and as a result, the dark linear high-intensity light-emitting part is m. It means that it appears along the surface.

With the group 13 element nitride crystal layer having a novel microstructure like these, even if the size is increased (for example, even if the diameter is 6 inches or more), the dislocation density can be reduced and the variation in characteristics can be reduced as a whole. A group 13 element nitride crystal layer can be provided.
Here, when the upper surface 13a of the Group 13 element nitride crystal layer 13 is observed by cathodoluminescence (CL), as is schematically shown in FIG. 3, a linear high-intensity light emitting unit 5 and a high-intensity light-emitting unit 5 It has a low-luminance light emitting region 6 adjacent to 5.

However, observation by CL shall be performed as follows.
A scanning electron microscope (SEM) equipped with a CL detector is used for CL observation. For example, when a Hitachi High-Technologies S-3400N scanning electron microscope with a Gatan MiniCL system is used, the measurement conditions are an acceleration voltage of 10 kV and a probe current of "90" with the CL detector inserted between the sample and the objective lens. It is preferable to observe at a working distance (WD) of 22.5 mm and a magnification of 50 times.

Further, the high-intensity light emitting portion and the low-intensity light emitting region are distinguished from the observation by cathodoluminescence as follows.
Image analysis software (for example, WinROOF Ver6 manufactured by Mitani Shoji Co., Ltd.) for the brightness of the CL-observed image at an acceleration voltage of 10 kV, a probe current of "90", a working distance (WD) of 22.5 mm, and a magnification of 50 times. Using 1.1.3), a 256-step grayscale histogram is created with the vertical axis representing the frequency and the horizontal axis representing the luminance (GRAY). As shown in FIG. 11, two peaks are confirmed in the histogram, and the high side is defined as the high-intensity light emitting part and the low side is defined as the low-intensity light-emitting region with the brightness at which the frequency is the minimum value between the two peaks as a boundary. To do.

Further, on the upper surface of the Group 13 element nitride crystal layer, a low-luminance light emitting region is adjacent to a linear high-luminance light emitting portion. As a result, the adjacent low-luminance light emitting regions are separated by the linear high-luminance light emitting portion between them. Here, the linear high-luminance light emitting portion indicates a state in which the high-luminance light emitting portion is elongated and forms a boundary line between adjacent low-luminance light emitting regions.

Here, the line formed by the high-luminance light emitting unit may be a straight line, a curved line, or a combination of a straight line and a curved line. The curve may include various forms such as an arc, an ellipse, a parabola, and a hyperbola. Further, the high-luminance light emitting portions having different directions may be continuous, but the end of the high-luminance light emitting portion may be cut off.

On the upper surface of the Group 13 element nitride crystal layer, the low-intensity light emitting region may be an exposed surface of the Group 13 element nitride crystal that has grown beneath it, and extends two-dimensionally in a planar manner. On the other hand, although the high-luminance light emitting portion has a linear shape, it extends unilaterally like a boundary line that divides adjacent low-luminance light emitting regions. This is because, for example, dopant components, trace components, etc. are discharged from Group 13 element nitride crystals that have grown from below, gather between adjacent Group 13 element nitride crystals during the growth process, and emit low-intensity light that is adjacent on the upper surface. It is probable that a portion that emits strong light linearly was generated between the regions.

For example, FIG. 4 shows a photograph of the upper surface of the Group 13 element nitride crystal layer obtained in the examples by CL observation. 5 is a partially enlarged view of FIG. 4, and FIG. 6 is a schematic view corresponding to FIG. The low-intensity light emitting region extends two-dimensionally in a plane shape, and the high-intensity light emitting portion has a linear shape, and extends one-dimensionally like a boundary line that divides adjacent low-intensity light emitting regions. You can see that.

From this, there is no particular limitation on the shape of the low-luminance light emitting region, and it is usually planar and two-dimensionally extended. On the other hand, the line formed by the high-luminance light emitting portion needs to be elongated. From this point of view, the width of the high-luminance light emitting portion is preferably 100 μm or less, more preferably 20 μm or less, and particularly preferably 5 μm or less. Further, the width of the high-luminance light emitting portion is usually 0.01 μm or more.

Further, from the viewpoint of the present invention, the ratio (length / width) of the length and width of the high-luminance light emitting portion is preferably 1 or more, and more preferably 10 or more.

Further, from the viewpoint of the present invention, the ratio of the area of the high-intensity light emitting portion to the area of the low-intensity light emitting region (area of the high-intensity light emitting portion / area of the low-intensity light emitting region) is 0.001 or more on the upper surface. It is preferable, and more preferably 0.01 or more.
Further, from the viewpoint of the present invention, the ratio of the area of the high-intensity light emitting portion to the area of the low-intensity light emitting region (area of the high-intensity light emitting portion / area of the low-intensity light emitting region) on the upper surface is 0.3 or less. It is preferably 0.1 or less, and more preferably 0.1 or less.

In a preferred embodiment, the high-intensity light emitting portion includes a portion extending along the m-plane of the Group 13 element nitride crystal. For example, in the examples of FIGS. 3 and 6, the high-luminance light emitting portion 5 extends in an elongated linear shape, and includes many portions 5a, 5b, and 5c extending along the m-plane. Specifically, the directions along the m-plane of the hexagonal group 13 element nitride crystal are [-2110], [-12-10], [11-20], [2-1-10]. , [1-210], [-1-120], and the high-intensity light emitting unit 5 includes a part of the side of a substantially hexagon reflecting a hexagonal crystal. Further, the fact that the linear high-intensity light-emitting part extends along the m-plane means that the longitudinal direction of the high-intensity light-emitting part is [-2110], [-12-10], [11-20], [2- It means that it extends along one of the directions 1-10], [1-210], and [-1-120]. Specifically, it includes a case where the longitudinal direction of the linear high-luminance light emitting portion is preferably within ± 1 °, more preferably within ± 0.3 ° with respect to the m-plane.

In a preferred embodiment, on the upper surface, a linear high-intensity light emitting portion extends substantially along the m-plane of the Group 13 element nitride crystal. This means that the main portion of the high-luminance light emitting portion extends along the m-plane, and preferably the continuous phase of the high-luminance light-emitting portion extends substantially along the m-plane. At this time, the portion extending in the direction along the m-plane preferably occupies 60% or more, more preferably 80% or more of the total length of the high-luminance light emitting portion, and substantially high-luminance. It may occupy the entire light emitting part.

In a preferred embodiment, on the upper surface of the Group 13 element nitride crystal layer, the high-intensity light emitting portion forms a continuous phase, and the low-intensity light emitting region forms a discontinuous phase partitioned by the high-intensity light emitting portion. ing. For example, in the schematic views of FIGS. 3 and 6, the linear high-luminance light emitting unit 5 forms a continuous phase, and the low-luminance light emitting region 6 forms a discontinuous phase defined by the high-luminance light emitting unit 5. ing.

However, the continuous phase means that the high-luminance light emitting unit 5 is continuous on the upper surface, but it is not essential that all the high-luminance light emitting units 5 are completely continuous, and the whole It is permissible that a small amount of the high-intensity light emitting unit 5 is separated from the other high-intensity light emitting unit 5 within a range that does not affect the pattern.

Further, the dispersed phase means that the low-luminance light emitting region 6 is generally partitioned by the high-luminance light emitting unit 5 and is divided into a large number of regions that are not connected to each other. Further, even if the low-luminance light emitting region 6 is separated by the high-luminance light emitting unit 5 on the upper surface, it is permissible that the low-luminance light emitting region 6 is continuous inside the group 13 element nitride crystal layer.

In a preferred embodiment, the half width of the (0002) plane reflection of the X-ray locking curve on the upper surface of the Group 13 element nitride crystal layer is 3000 seconds or less and 20 seconds or more. This indicates that the surface tilt angle is small on the upper surface, and the crystal orientation is highly oriented like a single crystal as a whole. In addition to having the cathodoluminescence distribution as described above, if the microstructure has a highly oriented crystal orientation on the surface as a whole, the characteristic distribution on the upper surface of the group 13 element nitride crystal layer. Can be made smaller, the characteristics of various functional elements provided on the functional elements can be made uniform, and the yield of the functional elements can be improved.

From this point of view, the half width of the (0002) plane reflection of the X-ray locking curve on the upper surface of the Group 13 element nitride crystal layer is preferably 1000 seconds or less and 20 seconds or more, and 500 seconds or less and 20 seconds or more. It is even more preferable to have. It is practically difficult to reduce the half width of the (0002) plane reflection of the X-ray locking curve on the upper surface of the Group 13 element nitride crystal layer to less than 20 seconds.

However, the X-ray locking curve (0002) surface reflection is measured as follows. Using an XRD device (for example, D8-DISCOVER manufactured by Bruker-AXS), the measurement conditions are tube voltage 40 kV, tube current 40 mA, collimator diameter 0.1 mm, anti-scattering slit 3 mm, and ω = peak position angle ± 0.3 °. The range, the ω step width of 0.003 °, and the counting time of 1 second may be set. In this measurement, it is preferable to convert CuKα rays into parallel monochromatic light (half-value width 28 seconds) with a Ge (022) asymmetric reflection monochromator, and to perform the measurement after arranging the CuKα line around the tilt angle CHI = 0 °. The half-value width of the X-ray locking curve (0002) surface reflection can be calculated by performing a peak search using XRD analysis software (manufactured by Bruker-AXS, LEPTOS 4.03). The peak search conditions are preferably Noise Filter "10", Thrashold "0.30", and Points "10".

When the cross section substantially perpendicular to the upper surface of the Group 13 element nitride crystal layer is observed by CL, a linear high-intensity light emitting portion that emits white light may be observed as shown in FIG. 7. In addition, in FIG. 7, the low-luminance light emitting region extends two-dimensionally in a plane shape, and the high-luminance light emitting portion has a linear shape, and extends like a boundary line for dividing adjacent low-luminance light emitting regions. You can see that. The method of observing the high-intensity light emitting unit and the low-intensity light emitting region is the same as the observation method of the high-intensity light-emitting part and the low-intensity light-emitting region on the upper surface.

The shape of the low-luminance light emitting region in the cross section of the Group 13 element nitride crystal layer is not particularly limited, and is usually planar and two-dimensionally extended. On the other hand, the line formed by the high-luminance light emitting portion needs to be elongated. From this point of view, the width of the high-luminance light emitting portion is preferably 100 μm or less, and more preferably 20 μm or less. Further, the width of the high-luminance light emitting portion is usually 0.01 μm or more.

From the viewpoint of the present invention, the ratio (length / width) of the length and width of the light emitting portion in the cross section of the group 13 element nitride crystal layer is preferably 1 or more, and more preferably 10 or more.

In a preferred embodiment, in the cross section substantially perpendicular to the upper surface of the Group 13 element nitride crystal layer, the linear high-intensity light-emitting portion forms a continuous phase, and the low-intensity light-emitting region is formed by the high-intensity light-emitting portion. It forms a partitioned discontinuous phase. For example, in the CL photograph of FIG. 7, the linear high-luminance light emitting portion forms a continuous phase, and the low-luminance light emitting region forms a discontinuous phase defined by the high-luminance light emitting portion.

However, the continuous phase means that the high-luminance light emitting parts are continuous in the cross section, but it is not essential that all the high-luminance light emitting parts are completely continuous, and the entire pattern is not required. It is permissible that a small amount of high-intensity light-emitting part is separated from other high-intensity light-emitting parts within a range that does not affect the above.

Further, the dispersed phase means that the low-luminance light emitting region is generally partitioned by the high-luminance light emitting portion and is divided into a large number of regions that are not connected to each other.

In a preferred embodiment, no voids are observed in a cross section substantially perpendicular to the top surface of the Group 13 element nitride crystal layer. That is, in the SEM photograph shown in FIG. 8, which has the same field of view as the CL photograph of FIG. 7, no different crystal phase other than voids (voids) and Group 13 element nitride crystals is observed. However, voids are observed as follows.

Voids are observed when a cross section substantially perpendicular to the upper surface of the Group 13 element nitride crystal layer is observed with a scanning electron microscope (SEM), and voids having a maximum width of 1 μm to 500 μm are defined as “voids”. .. For this SEM observation, for example, an S-3400N scanning electron microscope manufactured by Hitachi High-Technologies Corporation is used. The measurement conditions are preferably an acceleration voltage of 15 kV, a probe current of "60", a working distance (WD) of 6.5 mm, and a magnification of 100 times.

In addition, when observing a cross section substantially perpendicular to the upper surface of the Group 13 element nitride crystal layer with a scanning electron microscope (observation conditions described above), obvious grain boundaries such as voids accompanied by structural macro defects are observed. Not observed. With such a microstructure, it is considered that when a functional element such as a light emitting element is formed on a group 13 element nitride crystal layer, it is possible to suppress an increase in resistance and variation in characteristics caused by a clear grain boundary. Be done.

Further, in a preferred embodiment, the dislocation density on the upper surface of the Group 13 element nitride crystal layer is 1 × 10 ² / cm ² or more and 1 × 10 ⁶ / cm ² or less. It is particularly preferable that the dislocation density is 1 × 10 ⁶ / cm ² or less from the viewpoint of improving the characteristics of the functional element. From this point of view, it is more preferable that the dislocation density is 1 × 10 ⁴ / cm ² or less. This dislocation density shall be measured as follows.

A scanning electron microscope (SEM) equipped with a CL detector can be used for measuring the dislocation density. For example, when CL observation is performed using an S-3400N scanning electron microscope manufactured by Hitachi High-Technologies Corporation equipped with a MiniCL system manufactured by Gatan, the dislocation portion is observed as a black spot (dark spot) without emitting light. The dislocation density is calculated by measuring the dark spot density. The measurement conditions are that the CL detector is inserted between the sample and the objective lens, and the observation is performed at an accelerating voltage of 10 kV, a probe current of "90", a working distance (WD) of 22.5 mm, and a magnification of 1200 times. preferable.

Further, in a preferred embodiment, the half width of the (0002) plane reflection of the X-ray locking curve on the upper surface of the Group 13 element nitride crystal layer is 3000 seconds or less, 20 seconds or more, and half of the (1000) plane reflection. The price range is 10,000 seconds or less and 20 seconds or more. This indicates that both the surface tilt angle and the surface twist angle on the upper surface are small, and the crystal orientation as a whole is more highly oriented like a single crystal. With such a microstructure in which the crystal orientation on the surface is more highly oriented as a whole, the characteristic distribution on the upper surface of the Group 13 element nitride crystal layer can be reduced, and the characteristics of various functional elements provided on the microstructure can be reduced. Can be uniformly aligned, and the yield of functional elements is also improved.

Further, in a preferred embodiment, the half width of the (1000) plane reflection of the X-ray locking curve on the upper surface of the Group 13 element nitride crystal layer is 10,000 seconds or less and 20 seconds or more. This means that the surface twist angle on the top surface is very low. It shows that the crystal orientation is highly oriented like a single crystal as a whole. In addition to having the cathodoluminescence distribution as described above, if the microstructure has a highly oriented crystal orientation on the surface as a whole, the characteristic distribution on the upper surface of the group 13 element nitride crystal layer. Can be made smaller, the characteristics of various functional elements provided on the functional elements can be made uniform, and the yield of the functional elements can be improved.

From this point of view, the half width of the (1000) plane reflection of the X-ray locking curve on the upper surface of the Group 13 element nitride crystal layer is preferably 5000 seconds or less, more preferably 1000 seconds or less, and further 20 seconds or more. Is more preferable. Moreover, it is practically difficult to reduce this half width to less than 20 seconds.

However, the X-ray locking curve (1000) surface reflection is measured as follows. Using an XRD device (for example, D8-DISCOVER manufactured by Bruker-AXS), the measurement conditions are tube voltage 40 kV, tube current 40 mA, no collimator, anti-scattering slit 3 mm, ω = peak position angle ± 0.3 ° range, The ω step width may be set to 0.003 ° and the counting time may be set to 4 seconds. In this measurement, it is preferable to convert CuKα rays into parallel monochromatic light (half width 28 seconds) with a Ge (022) asymmetrical reflection monochromator, and to perform the measurement after axially tilting the tilt angle at around CHI = 88 °. Then, the full width at half maximum of the X-ray locking curve (1000) surface reflection can be calculated by performing a peak search using XRD analysis software (manufactured by Bruker-AXS, LEPTOS 4.03). The peak search conditions are preferably Noise Filter "10", Thrashold "0.30", and Points "10".

(Method for separating Group 13 element nitride crystal layer)
By separating the Group 13 element nitride crystal layer from the sapphire substrate, a self-supporting substrate containing the Group 13 element nitride crystal layer can be obtained.

Here, the method for separating the Group 13 element nitride crystal layer from the sapphire substrate is not limited. In a preferred embodiment, the group 13 element nitride crystal layer is naturally peeled from the single crystal substrate in the temperature lowering step after the group 13 element nitride crystal layer is grown.

Alternatively, the Group 13 element nitride crystal layer can be separated from the sapphire substrate by chemical etching.
As the etchant for chemical etching, a strong acid such as sulfuric acid or hydrochloric acid, a mixed solution of sulfuric acid and phosphoric acid, or a strong alkali such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable. The temperature at which chemical etching is performed is preferably 70 ° C. or higher.

Alternatively, the Group 13 element nitride crystal layer can be peeled off from the sapphire substrate by a laser lift-off method.
Alternatively, the Group 13 element nitride crystal layer can be peeled off from the sapphire substrate by grinding.
Alternatively, the Group 13 element nitride crystal layer can be peeled off from the sapphire substrate with a wire saw.

(Self-supporting board)
A self-supporting substrate can be obtained by separating the Group 13 element nitride crystal layer from the sapphire substrate. In the present invention, the "self-supporting substrate" means a substrate that can be handled as a solid substance without being deformed or damaged by its own weight when handled. The self-supporting substrate of the present invention can be used as a substrate for various semiconductor devices such as light emitting elements, but other than that, electrodes (which can be p-type electrodes or n-type electrodes), p-type layers, n-type layers, etc. It can be used as a member or layer other than the base material. The free-standing substrate may be further provided with other layers than one layer.

When the group 13 element nitride crystal layer constitutes a self-supporting substrate, the thickness of the self-supporting substrate needs to be able to impart independence to the substrate, and is preferably 20 μm or more, more preferably 100 μm or more, and further preferably 100 μm or more. It is 300 μm or more. An upper limit should not be specified for the thickness of the free-standing substrate, but from the viewpoint of manufacturing cost, 3000 μm or less is realistic.

(Composite board)
With the Group 13 element nitride crystal layer provided on the sapphire substrate, it can be used as a template substrate for forming another functional layer without separating the Group 13 element nitride crystal layer.

(Functional element)
The functional element structure provided on the Group 13 element nitride crystal layer of the present invention is not particularly limited, and examples thereof include a light emitting function, a rectifying function, and a power control function.

The structure of the light emitting device using the group 13 element nitride crystal layer of the present invention and the method for producing the same are not particularly limited. Typically, the light emitting device is manufactured by providing a light emitting functional layer on a group 13 element nitride crystal layer. However, a light emitting element is produced by using the Group 13 element nitride crystal layer as a member or layer other than the base material such as an electrode (which may be a p-type electrode or an n-type electrode), a p-type layer, and an n-type layer. May be good.

FIG. 9 schematically shows the layer structure of the light emitting device according to one aspect of the present invention. The light emitting element 21 shown in FIG. 9 includes a self-standing substrate 13 and a light emitting functional layer 18 formed on the substrate. The light emitting functional layer 18 brings about light emission based on the principle of a light emitting element such as an LED by appropriately providing an electrode or the like and applying a voltage.

The light emitting functional layer 18 is formed on the substrate 13. The light emitting functional layer 18 may be provided on the entire surface or a part of the substrate 13, or may be provided on the entire surface or a part of the buffer layer when the buffer layer described later is formed on the substrate 13. Good. The light emitting functional layer 18 can adopt various known layer configurations that bring about light emission based on the principle of a light emitting element represented by an LED by appropriately providing an electrode and / or a phosphor and applying a voltage. Therefore, the light emitting functional layer 18 may emit visible light such as blue or red, or may emit ultraviolet light without or together with visible light. The light emitting functional layer 18 preferably constitutes at least a part of a light emitting element using a pn junction, and the pn junction forms the p-type layer 18a and the n-type layer 18c as shown in FIG. The active layer 18b may be included between the two. At this time, a double heterojunction or a single heterojunction (hereinafter collectively referred to as heterojunction) may be performed using a layer having a bandgap smaller than that of the p-type layer and / or the n-type layer as the active layer. Further, as one form of the p-type layer-active layer-n-type layer, a quantum well structure in which the thickness of the active layer is thinned can be adopted. Needless to say, in order to obtain a quantum well, a double heterojunction in which the band gap of the active layer is smaller than that of the p-type layer and the n-type layer should be adopted. Further, a multiple quantum well structure (MQW) in which a large number of these quantum well structures are stacked may be used. By adopting these structures, the luminous efficiency can be improved as compared with the pn junction. As described above, the light emitting functional layer 18 preferably includes a pn junction and / or a hetero junction and / or a quantum well junction having a light emitting function. In addition, 20 and 22 are examples of electrodes.

Therefore, at least one or more layers constituting the light emitting functional layer 18 are selected from the group consisting of an n-type layer doped with an n-type dopant, a p-type layer doped with a p-type dopant, and an active layer. It can include one or more. The n-type layer, the p-type layer and the active layer (if present) may be composed of materials having the same main component or materials having different main components from each other.

The material of each layer constituting the light emitting functional layer 18 is not particularly limited as long as it grows roughly according to the crystal orientation of the group 13 element nitride crystal layer and has a light emitting function, but is a gallium nitride (GaN) -based material. It is preferable that the material is composed of at least one main component selected from zinc oxide (ZnO) -based material and aluminum nitride (AlN) -based material, and a dopant for controlling the p-type to n-type is appropriately used. It may include. A particularly preferable material is a gallium nitride (GaN) -based material. Further, the material constituting the light emitting functional layer 18 may be a mixed crystal in which AlN, InN or the like is dissolved in GaN in order to control the band gap thereof. Further, as described in the preceding paragraph, the light emitting functional layer 18 may be a heterojunction composed of a plurality of types of material systems. For example, a gallium nitride (GaN) -based material may be used for the p-type layer, and a zinc oxide (ZnO) -based material may be used for the n-type layer. Further, zinc oxide (ZnO) -based material may be used for the p-type layer, and gallium nitride (GaN) -based material may be used for the active layer and the n-type layer, and the combination of materials is not particularly limited.

The method for forming the light emitting functional layer 18 and the buffer layer is not particularly limited as long as it grows in accordance with the crystal orientation of the group 13 element nitride crystal layer, but is a vapor phase method such as MOCVD, MBE, HVPE, and sputtering. , Na flux method, amonothermal method, hydrothermal method, liquid phase method such as solgel method, powder method utilizing solid phase growth of powder, and a combination thereof are preferably exemplified.

(Example 1-1)
A gallium nitride crystal layer was grown on the sapphire substrate according to the method described with reference to FIGS. 1 and 2.
Specifically, an Ar ion beam was scanned on the surface 25a of the sapphire substrate 25. At this time, an ion trimming device manufactured by AM Systems was used, the gas type was Ar, the ion beam irradiation power was 120 W, and the gas flow rate was 6 sccm.
When the obtained aluminum oxide layer was observed with a transmission electron microscope, it had an amorphous structure and a thickness of 40 angstroms.

Next, a buffer layer made of gallium nitride was formed on the aluminum oxide layer at 500 ° C. by the MOCVD method, and then a seed crystal film 3 made of gallium nitride having a thickness of 3 μm was formed to obtain a seed crystal substrate.

This seed crystal substrate was placed in an aluminum oxide crucible in a glove box with a nitrogen atmosphere. Next, metallic gallium and metallic sodium were filled in the crucible so that Ga / Ga + Na (mol%) = 15 mol%, and the crucible was covered with an aluminum oxide plate. The crucible was placed in a stainless steel inner container, then placed in a stainless steel outer container that could hold it, and closed with a container lid with a nitrogen introduction pipe. This outer container was placed on a turntable installed in a heating section in a crystal manufacturing apparatus that had been vacuum-baked in advance, and the pressure-resistant container was covered and sealed.

Next, the inside of the pressure-resistant container was evacuated to 0.1 Pa or less with a vacuum pump. Then, while adjusting the upper heater, middle heater and lower heater so that the temperature of the heating space becomes 870 ° C, nitrogen gas is introduced from the nitrogen gas cylinder up to 4.0 MPa, and the outer container is placed around the central axis. It was rotated clockwise and counterclockwise at a constant cycle at a speed of 20 rpm. Acceleration time = 12 seconds, holding time = 600 seconds, deceleration time = 12 seconds, stop time = 0.5 seconds. Then, it was held in this state for 40 hours. Then, after naturally cooling to room temperature and reducing the pressure to atmospheric pressure, the lid of the pressure-resistant container was opened and the crucible was taken out from the inside. The solidified metallic sodium in the crucible was removed.
Next, the sapphire substrate was removed from the gallium nitride crystal layer by a laser lift-off method to obtain a self-supporting substrate composed of a gallium nitride crystal layer having a thickness of 600 μm.

(Evaluation)
The upper surface of the gallium nitride self-supporting substrate was polished and CL was observed with a scanning electron microscope (SEM) equipped with a CL detector. As a result, as shown in FIG. 4, in the CL photograph, a high-intensity light emitting portion that emits white light was confirmed inside the gallium nitride crystal. However, at the same time, as shown in FIG. 10, when the same field of view was observed by SEM, voids and the like were not confirmed, and it was confirmed that homogeneous gallium nitride crystals were growing.

Further, the gallium nitride self-supporting substrate was cut into a cross section perpendicular to the upper surface thereof, the cut surface was polished, and CL observation was performed with a scanning electron microscope (SEM) equipped with a CL detector. As a result, as shown in FIG. 7, in the CL image, a high-luminance light emitting portion that emits white light was confirmed inside the gallium nitride crystal. However, at the same time, as shown in FIG. 8, when the same field of view was observed by SEM, voids and the like were not confirmed, and it was confirmed that homogeneous gallium nitride crystals were growing. That is, in the cross section of the Group 13 element nitride crystal layer, as in the upper surface, the high-intensity light-emitting part is present in the CL observation, but in the SEM, the same shape as the high-intensity light-emitting part seen in the CL photograph in the same field of view. Or a similar microstructure did not exist.

(Measurement of dark spot)
Then, the dislocation density was measured on the upper surface of the Group 13 element nitride crystal layer. The dislocation density was calculated by observing CL and measuring the density of dark spots, which are dislocation sites. As a result of CL observation of an 80 μm × 105 μm field of view, it was 5 × 10 ⁴ / cm ² .

(Measurement of surface tilt angle)
The half width of the (0002) plane reflection of the X-ray locking curve on the upper surface of the gallium nitride crystal layer was measured and found to be 86 seconds.

(Measurement of surface twist angle)
The half width of the (1000) plane reflection of the X-ray locking curve on the upper surface of the gallium nitride crystal layer was measured and found to be 89 seconds.

(Formation of light emitting functional layer by MOCVD method)
Using the MOCVD method, 1 μm of an n-GaN layer doped so that the Si atom concentration was 5 × 10 ¹⁸ / cm ³ was deposited as an n-type layer on the upper surface of the gallium nitride self-supporting substrate at 1050 ° C. Next, a multiple quantum well layer was deposited as a light emitting layer at 750 ° C. Specifically, five 2.5 nm well layers made of InGaN and six 10 nm barrier layers made of GaN were alternately laminated. Next, as a p-type layer, 200 nm of p-GaN doped so that the Mg atom concentration was 1 × 10 ¹⁹ / cm ³ was deposited at 950 ° C. Then, it was taken out from the MOCVD apparatus and heat-treated at 800 ° C. for 10 minutes in a nitrogen atmosphere as a treatment for activating Mg ions in the p-type layer.

(Manufacturing of light emitting element)
Using a photolithography process and a vacuum vapor deposition method, Ti / Al / Ni / Au films as cathode electrodes were placed on the surfaces of the gallium nitride self-supporting substrate opposite to the n-GaN layer and the p-GaN layer at 15 nm and 70 nm, respectively. , 12 nm and 60 nm were patterned. Then, in order to improve the ohm-like contact characteristics, a heat treatment at 700 ° C. in a nitrogen atmosphere was performed for 30 seconds. Further, a photolithography process and a vacuum vapor deposition method were used to pattern a Ni / Au film as a translucent anode electrode on the p-type layer to a thickness of 6 nm and 12 nm, respectively. Then, in order to improve the ohm-like contact characteristics, a heat treatment at 500 ° C. was performed for 30 seconds in a nitrogen atmosphere. Furthermore, using a photolithography process and a vacuum vapor deposition method, the Ni / Au film used as the anode electrode pad has a thickness of 5 nm and 60 nm, respectively, in a part of the upper surface of the Ni / Au film as the translucent anode electrode. Patterned. The substrate thus obtained was cut into chips and further mounted on a lead frame to obtain a light emitting element having a vertical structure.

(Evaluation of light emitting element)
When the 100 elements produced were energized between the cathode electrode and the anode electrode and IV measurement was performed, rectification was confirmed for 91 elements. That is, the yield was 91%. Further, when a forward current was applied, light emission with a wavelength of 460 nm was confirmed. The emission intensity was 0.96 (relative value when the emission intensity of Example 2-2 was 1.0).

(Example 1-2)
An aluminum oxide layer and a group 13 element nitride crystal layer were formed on the sapphire substrate in the same manner as in Example 1-1, and the group 13 element nitride crystal layer was peeled off from the sapphire substrate to obtain a self-supporting substrate.
However, in this example, unlike Example 1-1, an ion trimming device manufactured by AM Systems was used, the gas type was He, the ion beam irradiation power was 120 W, and the gas flow rate was 12 sccm. As a result, an aluminum oxide layer having an amorphous structure with a thickness of 200 angstroms was obtained. A gallium nitride crystal layer was prepared on this in the same manner as in Example 1-1.

The number of dark spots on the upper surface of the obtained Group 13 element nitride crystal layer was observed with CL in a field of view of 80 μm × 105 μm, and the dislocation density was calculated to be 2 × 10 ⁴ / cm ² . Further, using the obtained self-supporting substrate, a light emitting diode was produced in the same manner as in Example 1-1, and the light emitting intensity and the yield were measured. The measurement results are shown in Table 1. In addition, the CL observation results on the upper surface and cross section of the obtained self-supporting substrate, and the observation results of the surface twist angle and surface tilt angle of the upper surface were also the same as those in Example 1-1.

(Example 1-3)
An aluminum oxide layer and a group 13 element nitride crystal layer were formed on the sapphire substrate in the same manner as in Example 1-1, and the group 13 element nitride crystal layer was peeled off from the sapphire substrate to obtain a self-supporting substrate.
However, in this example, unlike Example 1-1, a high-speed Ar atom beam was scanned on the sapphire substrate.
The ultimate vacuum in the chamber before the start of scanning was set to ^10-6 Pa. A saddle field type high-speed atomic beam source was used as the beam source. Ar gas was introduced into the chamber, and a high voltage was applied to the electrodes from a DC power supply. The current value was 200 mA, the voltage was 1.8 kV, the argon flow rate was 80 sccm, and the irradiation time was 900 seconds.
As a result, an aluminum oxide layer having an amorphous structure with a thickness of 60 angstroms was obtained. A gallium nitride crystal layer was prepared on this in the same manner as in Example 1-1.

The number of dark spots on the upper surface of the obtained Group 13 element nitride crystal layer was observed by CL, and the dislocation density was calculated. As a result, it was 7 × 10 ⁴ / cm ² . Further, using the obtained self-supporting substrate, a light emitting diode was produced in the same manner as in Example 1-1, and the light emitting intensity and the yield were measured. The measurement results are shown in Table 1. In addition, the CL observation results on the upper surface and cross section of the obtained self-supporting substrate, and the observation results of the surface twist angle and surface tilt angle of the upper surface were also the same as those in Example 1-1.

(Example 2-1)
An aluminum oxide layer and a group 13 element nitride crystal layer were formed on the sapphire substrate in the same manner as in Example 1-1, and the group 13 element nitride crystal layer was peeled off from the sapphire substrate to obtain a self-supporting substrate.
However, in this example, unlike Example 1-1, the surface of the sapphire substrate was ground with a grindstone having a count of # 2000. As a result, a processed alteration layer having a thickness of 0.2 μm was obtained.
In the processed altered layer, an amorphous phase, a polycrystalline phase, and a crystal defect were observed in the aluminum oxide layer in the TEM photograph. These were observable as described above by the contrast change with respect to the sapphire single crystal.

A gallium nitride crystal layer was prepared on this in the same manner as in Example 1-1. The number of dark spots on the upper surface of the obtained Group 13 element nitride crystal layer was observed by CL, and the dislocation density was calculated. As a result, it was 5 × 10 ⁴ / cm ² . Further, using the obtained self-supporting substrate, a light emitting diode was produced in the same manner as in Example 1-1, and the light emitting intensity and the yield were measured. The measurement results are shown in Table 1. In addition, the CL observation results on the upper surface and cross section of the obtained self-supporting substrate, and the observation results of the surface twist angle and surface tilt angle of the upper surface were also the same as those in Example 1-1.

(Example 2-2)
An aluminum oxide layer and a group 13 element nitride crystal layer were formed on the sapphire substrate in the same manner as in Example 2-1 and the group 13 element nitride crystal layer was peeled off from the sapphire substrate to obtain a self-supporting substrate.
However, in this example, unlike Example 2-1 the surface of the sapphire substrate was ground with a grindstone having a count of # 325. As a result, a processed alteration layer having a thickness of 1.5 μm was obtained.

A gallium nitride crystal layer was prepared on this in the same manner as in Example 1-1. The number of dark spots on the upper surface of the obtained Group 13 element nitride crystal layer was observed by CL, and the dislocation density was calculated. As a result, it was 2 × 10 ⁴ / cm ² . Further, using the obtained self-supporting substrate, a light emitting diode was produced in the same manner as in Example 1-1, and the light emitting intensity and the yield were measured. The measurement results are shown in Table 1. In addition, the CL observation results on the upper surface and cross section of the obtained self-supporting substrate, and the observation results of the surface twist angle and surface tilt angle of the upper surface were also the same as those in Example 1-1.

(Example 3)
An aluminum oxide layer and a group 13 element nitride crystal layer were formed on the sapphire substrate in the same manner as in Example 1-1, and the group 13 element nitride crystal layer was peeled off from the sapphire substrate to obtain a self-supporting substrate.
However, in this example, unlike Example 1-1, the surface of the sapphire substrate was etched by the reactive ion etching method. Specifically, using the Panasonic RIE device "model number E640", the RF power is 400 W, the bias voltage is 200 W, the gas used is chlorine (flow rate 40 sccm), the pressure is 1 Pa, and the RIE time is 20 minutes. did. As a result, an aluminum oxide layer having a thickness of 40 angstroms was obtained.

A gallium nitride crystal layer was prepared on this in the same manner as in Example 1-1. The upper surface of the resultant Group 13 element nitride crystal layer was observed the number of dark spots in CL, result of calculating the dislocation density was 7 × 10 ⁵ / cm ^2. Further, using the obtained self-supporting substrate, a light emitting diode was produced in the same manner as in Example 1-1, and the light emitting intensity and the yield were measured. The measurement results are shown in Table 1. In addition, the CL observation results on the upper surface and cross section of the obtained self-supporting substrate, and the observation results of the surface twist angle and surface tilt angle of the upper surface were also the same as those in Example 1-1.

(Example 4-1)
An aluminum oxide layer and a group 13 element nitride crystal layer were formed on the sapphire substrate in the same manner as in Example 1-1, and the group 13 element nitride crystal layer was peeled off from the sapphire substrate to obtain a self-supporting substrate.
However, in this example, unlike Example 1-1, the surface of the sapphire substrate was annealed under hydrogen gas. Specifically, a MOCVD apparatus was used to raise the temperature to 1200 ° C. in a hydrogen atmosphere and a heating rate of 120 ° C./min. Then, the hydrogen atmosphere was kept unchanged for 30 minutes for annealing. After that, the heater set value was lowered at a temperature lowering rate of 120 ° C./min, and when the actual temperature fell below 500 ° C., the temperature was switched to a nitrogen atmosphere and the temperature was lowered to room temperature.
As a result, an aluminum oxide layer having a thickness of 80 angstroms was obtained.

A gallium nitride crystal layer was prepared on this in the same manner as in Example 1-1. The upper surface of the resultant Group 13 element nitride crystal layer was observed the number of dark spots in CL, result of calculating the dislocation density was 5 × 10 5 ^/ cm ^2. Further, using the obtained self-supporting substrate, a light emitting diode was produced in the same manner as in Example 1-1, and the light emitting intensity and the yield were measured. The measurement results are shown in Table 1. In addition, the CL observation results on the upper surface and cross section of the obtained self-supporting substrate, and the observation results of the surface twist angle and surface tilt angle of the upper surface were also the same as those in Example 1-1.

(Example 4-2)
An aluminum oxide layer and a group 13 element nitride crystal layer were formed on the sapphire substrate in the same manner as in Example 4-1 and the group 13 element nitride crystal layer was peeled off from the sapphire substrate to obtain a self-supporting substrate.
However, in this example, unlike Example 4-1 the surface of the sapphire substrate was annealed under a mixed gas of hydrogen, ammonia, and nitrogen. Specifically, a MOCVD apparatus was used to raise the temperature to 1200 ° C. in a hydrogen atmosphere and a heating rate of 120 ° C./min. After that, the hydrogen atmosphere was maintained for 15 minutes without change and annealed, and then the atmosphere was changed to a mixed gas of hydrogen, ammonia and nitrogen, and the atmosphere was maintained for 15 minutes for annealing. After that, the heater set value was lowered at a temperature lowering rate of 120 ° C./min, and when the actual temperature fell below 500 ° C., the temperature was switched to a nitrogen atmosphere and the temperature was lowered to room temperature.
As a result, an aluminum oxide layer having a thickness of 60 angstroms was obtained.

A gallium nitride crystal layer was prepared on this in the same manner as in Example 1-1. The number of dark spots on the upper surface of the obtained Group 13 element nitride crystal layer was observed by CL, and the dislocation density was calculated. As a result, it was 3 × 10 ⁵ / cm ² . Further, using the obtained self-supporting substrate, a light emitting diode was produced in the same manner as in Example 1-1, and the light emitting intensity and the yield were measured. The measurement results are shown in Table 1. In addition, the CL observation results on the upper surface and cross section of the obtained self-supporting substrate, and the observation results of the surface twist angle and surface tilt angle of the upper surface were also the same as those in Example 1-1.

(Comparison example)
A seed crystal film made of gallium nitride was grown on the sapphire substrate by the MOCVD method in the same manner as in Example 1-1. Next, a gallium nitride crystal layer was grown (thickness 600 μm) in the same manner as in Example 1-1 by the Na flux method. Next, the sapphire substrate was removed by the laser lift-off method in the same manner as in Example 1-1, and the upper surface and the bottom surface of the obtained self-supporting substrate made of the group 13 element nitride crystal layer were polished.

The number of dark spots on the upper surface of the obtained Group 13 element nitride crystal layer was observed by CL, and the dislocation density was calculated. As a result, it was 7 × 10 ⁶ / cm ² . Further, using the obtained self-supporting substrate, a light emitting diode was produced in the same manner as in Example 1-1, and the light emitting intensity and the yield were measured. The measurement results are shown in Table 1.

(Creation of rectifying function element)
A functional element having a rectifying function was manufactured.
That is, a Schottky barrier diode structure was formed on the upper surface of the self-supporting substrate obtained in Example 1-1 and an electrode was formed as follows to obtain a diode and confirm its characteristics.

(Formation of rectifying function layer by MOCVD method)
Using the MOCVD (organometallic chemical vapor deposition) method, an n-GaN layer doped as an n-type layer at 1050 ° C. so that the Si atom concentration is 1 × 10 ¹⁶ / cm ³ is formed in 5 μm. Filmed.
Using a photolithography process and a vacuum vapor deposition method, Ti / Al / Ni / Au films as ohmic electrodes were placed on the surface of the self-supporting substrate opposite to the n-GaN layer at thicknesses of 15 nm, 70 nm, 12 nm, and 60 nm, respectively. Patterned. Then, in order to improve the ohm-like contact characteristics, a heat treatment at 700 ° C. in a nitrogen atmosphere was performed for 30 seconds. Further, using a photolithography process and a vacuum vapor deposition method, Ni / Au films were patterned as shotkey electrodes on the n-GaN layer formed by the MOCVD method with thicknesses of 6 nm and 80 nm, respectively. The substrate thus obtained was cut into chips and further mounted on a lead frame to obtain a rectifying element.

(Evaluation of rectifying element)
When the IV measurement was performed, the rectification characteristics were confirmed.

(Creation of power control element)
A functional element having a power control function was manufactured.
A self-supporting substrate was produced in the same manner as in Example 1-1. However, unlike Example 1, when the gallium nitride crystal was formed by the Na flux method, impurities were not doped. An Al _0.25 Ga _0.75 / GaN HEMT structure was formed on the upper surface of the self-standing substrate thus obtained by the MOCVD method as follows, electrodes were formed, and transistor characteristics were confirmed.

Using the MOCVD (organometallic chemical vapor deposition) method, a 3 μm film of a GaN layer without impurity doping was formed as an i-type layer at 1050 ° C. on a self-supporting substrate. Next, an Al _0.25 Ga _0.75 N layer was formed at 25 nm as a functional layer at the same 1050 ° C. As a result, an Al _0.25 Ga _0.75 N / GaN HEMT structure was obtained.

Using a photolithography process and a vacuum vapor deposition method, Ti / Al / Ni / Au films as source and drain electrodes were patterned with thicknesses of 15 nm, 70 nm, 12 nm and 60 nm, respectively. Then, in order to improve the ohm-like contact characteristics, a heat treatment at 700 ° C. in a nitrogen atmosphere was performed for 30 seconds. Further, using a photolithography process and a vacuum vapor deposition method, Ni / Au films as gate electrodes were formed by Schottky junction with thicknesses of 6 nm and 80 nm, respectively, and patterned. The substrate thus obtained was cut into chips and further mounted on a lead frame to obtain a power control element.

(Evaluation of power control element)
When the IV characteristics were measured, good pinch-off characteristics were confirmed, and a maximum drain current of 760 mA / mm and a maximum transconductance of 240 mS / mm were obtained.

Claims (16)

A process of forming an aluminum oxide layer by surface-treating a sapphire substrate,
A step of forming a seed crystal film made of a group 13 element nitride on the aluminum oxide layer, and a group 13 selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof on the seed crystal film. A method for producing a group 13 element nitride layer, which comprises a step of providing a group 13 element nitride layer made of elemental nitride. The method according to claim 1, wherein the surface treatment is performed by irradiating the sapphire substrate with an ion beam or a high-speed atomic beam. The method according to claim 1, wherein the surface treatment is performed by grinding the sapphire substrate. The method according to claim 1, wherein the surface treatment is performed by subjecting the sapphire substrate to reactive ion etching treatment. The method according to claim 1, wherein the surface treatment is performed by annealing the sapphire substrate in an atmosphere containing at least hydrogen. The method according to any one of claims 1 to 5, wherein the aluminum oxide layer contains an amorphous phase, a polycrystalline phase, or a defect introduction portion. The method according to claim 3, wherein the aluminum oxide layer is a processed alteration layer. The Group 13 element nitride crystal layer has a linear high-intensity light emitting portion and a low-intensity light-emitting region adjacent to the high-intensity light-emitting portion when the upper surface is observed by cathodoluminescence.
The method according to any one of claims 1 to 7, wherein the high-luminance light emitting portion includes a portion extending along the m-plane of the group 13 element nitride crystal. The method according to claim 8, wherein the high-luminance light emitting portion extends substantially along the m-plane of the group 13 element nitride crystal. The method according to claim 8 or 9, wherein the half width of the (0002) surface reflection of the X-ray locking curve on the upper surface is 3000 seconds or less and 20 seconds or more. The method according to any one of claims 8 to 10, wherein no void is observed in a cross section substantially perpendicular to the upper surface of the group 13 element nitride crystal layer. The method according to any one of claims 8 to 11, wherein the dislocation density on the upper surface of the group 13 element nitride crystal layer is 1 × 10 ⁶ / cm ² or less. Any of claims 8 to 12, characterized in that the high-luminance light emitting portion forms a continuous phase, and the low-luminance light emitting region forms a discontinuous phase partitioned by the high-luminance light emitting portion. The method described in one claim. The method according to any one of claims 8 to 13, wherein the half width of the (1000) surface reflection of the X-ray locking curve on the upper surface is 10000 seconds or less and 20 seconds or more. The method according to any one of claims 1 to 14, wherein the group 13 elemental nitride is a gallium nitride based nitride. The method according to any one of claims 1 to 15, wherein the group 13 element nitride layer is formed into a film by a sodium flux method.

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