WO2019039055A1 - Method for producing group 13 element nitride layer - Google Patents

Abstract

[Problem] To provide a group 13 element nitride crystal layer having a top surface and a bottom surface, wherein dislocation defects can be suppressed, the yield of a functional element can be improved, and characteristics of the functional element can be enhanced. [Solution] An aluminum oxide layer 2 is formed by subjecting a sapphire substrate 25 to a surface treatment (shown by the arrow K), a seed crystal film comprising a group 13 element nitride is formed on the aluminum oxide layer 2, and a group 13 element nitride layer comprising a group 13 element nitride selected from among gallium nitride, aluminum nitride, indium nitride and mixed crystals of these is provided on the seed crystal film.

Description

Method of manufacturing Group 13 element nitride layer

The present invention relates to a method of manufacturing 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 quantum well layers composed of InGaN layers and barrier layers composed of GaN layers are alternately stacked, and p-type GaN layers are sequentially deposited. Those having a different structure are 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. In addition, the average tilt angle (average value of the inclination of crystal orientation (crystal axis) in the direction normal to the surface) on the surface is 1 to 10 °.

In Patent Document 3, a large number of inclusions are included from the bottom to an intermediate position, and a plurality of grain boundaries including only a low concentration are formed diagonally from the lower surface from the intermediate position to the upper surface. In addition, the grain boundaries extend obliquely in the 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 is 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 light emitting devices are fabricated on gallium nitride crystals described in Patent Documents 1 and 2, the current path may be interrupted to cause a decrease in light emission efficiency depending on the balance between the device size and the particle diameter. It turned out. Although the reason for this is not clear, anisotropy in orientation between single crystal grains may be 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 in some cases voids may remain around the crystal.

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

An object of the present invention is to suppress dislocation defects in a Group 13 element nitride crystal layer comprising a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride or mixed crystals thereof and having a top surface and a bottom surface. To improve the yield of functional devices and improve their characteristics.

The present invention provides a process of forming an aluminum oxide layer by surface treating a sapphire substrate,
Forming a seed crystal film of Group 13 element nitride on the aluminum oxide layer; and Group 13 selected from gallium nitride, aluminum nitride, indium nitride, or mixed crystals thereof on the seed crystal film. The present invention relates to a method for producing a Group 13 element nitride layer, including the step of providing a Group 13 element nitride layer comprising an element nitride.

According to the present invention, dislocation defects in a Group 13 element nitride crystal layer can be suppressed, the yield of functional devices can be improved, and a Group 13 element nitride crystal layer capable of improving characteristics can be provided. .

(A) is a schematic view showing the surface 25 a of the sapphire substrate 25 subjected to the surface treatment K, and (b) shows the surface 1 a of the sapphire substrate 1 provided with the aluminum oxide layer 2. (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) shows the group 13 element separated from the support substrate The nitride crystal layer 13 is shown. FIG. 6 is a schematic view for explaining a cathode luminescence image of the upper surface 13 a of the group 13 element nitride crystal layer 13. It is a photograph which shows the cathode luminescence image of upper surface 13a of 13 group element nitride crystal layer 13. FIG. It is a partial 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 section of 13 group element nitride crystal layer 13. 7 is a scanning electron micrograph showing a cross section of a 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 photography picture with a scanning electron microscope of the upper surface of 13 group element nitride crystal layer. 2 shows a gray scale histogram generated from a CL image.

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

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

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

In the method of (2), surface treatment is performed by grinding the sapphire substrate. In this method, a damaged layer is generated by grinding.
Grinding (grinding) refers to scraping off the surface of an object by bringing the fixed abrasive in which the abrasive is fixed by bonding into contact with the object while rotating at high speed. By such grinding, a rough surface is formed, and a process-altered layer is formed on the outermost surface. In the case of grinding a sapphire substrate, it is preferable to use a fixed abrasive including abrasive grains having a particle diameter of about 10 μm to 100 μm which is formed of SiC, Al 2 O 3, diamond and CBN (cubic boron nitride, the same applies hereinafter) having high hardness. Used.

In the method (3), the sapphire substrate is subjected to reactive ion etching to perform surface 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.
As a plasma generation source, an ICP type, an ECR type, and a parallel plate type can be exemplified. The power, bias power, pressure in the chamber, and flow rate of the used gas are not particularly limited, but the power is 100 W or more and 1000 W or less, bias power is 50 W or more and 300 W or less, the pressure in the chamber is 0.1 Pa or more and 10 Pa or less, the used gas flow rate It is preferable to be 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. The atmosphere may be hydrogen alone or may contain ammonia, nitrogen and argon in addition to hydrogen.
The annealing temperature is preferably 1000 ° C. or more, more preferably 1200 ° C. or more. From a practical viewpoint, the annealing temperature is preferably 1500 ° C. or less, more preferably 1400 ° C. or less. The pressure at the time of the annealing treatment may be any of reduced pressure, atmospheric pressure and increased pressure, and is not particularly limited, but reduced pressure is preferable from the viewpoint of gas use efficiency.

(Aluminum oxide layer)
In the present invention, the aluminum oxide layer is formed by surface treatment of the sapphire substrate. Here, the composition of the aluminum oxide may be Al ₂ O ₃ but may deviate from this composition because it is a thin layer. Specifically, the composition ratio of the aluminum oxide may be Al _x O _y (x = 0.15 to 0.65: y = 0.35 to 0.85, X + Y = 1). In addition, elements other than aluminum and oxygen used for 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 is preferably 30 angstroms or more, from the viewpoint of obtaining a Group 13 element nitride crystal layer which can lower dislocation density and reduce variation in characteristics throughout. More than angstroms are more preferred. Further, from the practical viewpoint, the thickness of the aluminum oxide layer is preferably 50,000 angstroms or less, more preferably 20,000 angstroms or less.

The presence of the aluminum oxide layer is confirmed by transmission electron microscopy. For this transmission electron microscope apparatus, H-9000NAR manufactured by Hitachi High-Technologies Corporation is used, and the magnification during observation is preferably 2,000,000 times.

In addition, when the aluminum oxide layer contains an amorphous phase, the diffraction contrast due to the crystal lattice disappears in the amorphous phase, so that a bright contrast is obtained and a uniform image can be obtained. It can be confirmed and the thickness of the aluminum oxide layer can be measured. In addition, when the aluminum oxide layer includes a defect-introduced portion, the defect is displayed as a linear dark contrast, so it can be confirmed that a defect is newly introduced.
When the aluminum oxide layer contains a polycrystalline phase, it can be distinguished from the amorphous phase because different color contrasts can be seen in the layer. When the aluminum oxide layer contains a defect-introduced portion, it is displayed as a darker line-like contrast, so it can be confirmed that a defect is newly introduced.
In addition, by using a technique called ultra-fine electron beam diffraction, diffraction spots (spots) aligned regularly in a single crystal, concentric circular rings in a polycrystal, and broad circular ring electron beam diffraction patterns in an amorphous phase are observed. Therefore, the single crystal phase, the polycrystalline phase, and the amorphous phase can be distinguished.

(Seed crystal layer)
For example, as shown in FIG. 2A, a seed crystal layer 3 is provided on the aluminum oxide layer 2. The material constituting the seed crystal layer 3 is a nitride of one or two or more kinds of Group 13 elements specified by IUPAC. The group 13 element is preferably gallium, aluminum or indium. Further, specifically, 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) And Ga _x Al _y InN _{1 -x-y} (1>x> 0, 1>y> 0).

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

(Group 13 element nitride crystal layer)
Group 13 element nitride crystal layer 13 is formed to have a crystal orientation substantially conforming to the crystal orientation of seed crystal layer 3. The method of forming the group 13 element nitride crystal layer is not particularly limited as long as it has a crystal orientation substantially following the crystal orientation of the seed crystal film, and a vapor phase method such as MOCVD or HVPE, Na flux method, ammonothermal method, A hydrothermal method, a liquid phase method such as a sol-gel method, a powder method utilizing solid phase growth of powder, and a combination thereof are preferably exemplified, but the Na flux method is particularly preferable.

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

Formation of Group 13 element nitride crystal layer by Na flux method, Group 13 metal, metal Na and optionally dopant (for example, germanium (Ge), silicon (Si), oxygen (O), etc., etc. in place of the seed crystal substrate) Filled with a melt composition containing n-type dopants or p-type dopants such as beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn) and cadmium (Cd) After heating to 830 ° C. to 910 ° C. and 3.5 to 4.5 MPa in a nitrogen atmosphere, it is preferable to carry out rotation 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 to flatten the plate surface by grinding the gallium nitride crystal thus obtained by the Na flux method with a grindstone, and then to smooth the plate surface by lapping using diamond abrasive grains.

(Group 13 element nitride crystal layer)
In the present invention, the Group 13 element nitride crystal layer can be formed on the above-described aluminum oxide layer.
The group 13 element nitride crystal layer is made of group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride or mixed crystals thereof, and has top and bottom surfaces. For example, as shown in FIG. 2B, in the group 13 element nitride crystal layer 13, the top 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 mixed crystals 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, 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>y> 0.3, x + y + z = 1).

Group 13 element nitrides may be doped with zinc, calcium or other n-type dopants or p-type dopants, in which case polycrystalline group 13 element nitrides may be p-type electrodes, n-type electrodes, p It can be used as a member or layer other than a substrate 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 top 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. And the high brightness light emitting portion includes a portion extending along the m-plane of the Group 13 element nitride crystal. This is because a linear high-intensity light emitting portion appears on the upper surface, so that a linear high-intensity light emitting portion in which a dopant component, a trace amount component, and the like contained in a Group 13 element nitride crystal are dark 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 dopant is gathered along the m-plane during crystal growth, and as a result, the dark linear high-intensity light emitting part is m It means to appear along the face.

Group 13 element nitride crystal layers having such novel microstructures can reduce dislocation density even if the size is increased (for example, even if the diameter is 6 inches or more), and the variation in characteristics can be reduced overall It is possible to provide a group 13 element nitride crystal layer.
Here, when the upper surface 13a of the group 13 element nitride crystal layer 13 is observed by cathode luminescence (CL), as schematically shown in FIG. 3, a linear high-intensity light emitting portion 5 and a high-intensity light emitting portion And a low luminance light emitting region 6 adjacent to the fifth one.

However, observation by CL shall be performed as follows.
For CL observation, a scanning electron microscope (SEM) with a CL detector is used. For example, when using Hitachi High-Technologies S-3400N scanning electron microscope with Gatan MiniCL system, measurement conditions are: acceleration voltage 10 kV, probe current “90” with CL detector inserted between sample and objective lens The working distance (W.D.) is preferably 22.5 mm and observed at a magnification of 50 times.

Further, the high luminance light emitting portion and the low luminance light emitting region are distinguished as follows from the observation by cathode luminescence.
Image analysis software (for example, Mitani Shoji Co., Ltd. WinROOF Ver. 6) against the luminance of the image observed with CL at a magnification of 50 × with an acceleration voltage of 10 kV, a probe current of “90”, a working distance (W.D.) of 22.5 mm. Using .1.3), create a 256-step gray scale histogram with the vertical axis as frequency and the horizontal axis as luminance (GRAY). In the histogram, as shown in FIG. 11, two peaks are confirmed, and the high side is defined as a high brightness light emitting portion and the low side as a low brightness light emitting area with the brightness at which the frequency is minimum between the two peaks as a boundary. Do.

Further, on the top surface of the group 13 element nitride crystal layer, the low luminance light emitting region is adjacent to the linear high luminance light emitting portion. By this, adjacent low-intensity light emission areas are divided by the linear high-intensity light emission parts located between them. Here, that the high brightness light emitting portion is linear means that the high brightness light emitting portion is elongated and elongated between adjacent low brightness light emitting regions to form a boundary line.

Here, the line made by the high-intensity light emitting portion 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 arc, ellipse, parabola, hyperbola and the like. Moreover, although the high-intensity light emission part from which a direction mutually differs may be continuous, the terminal of the high-intensity light emission part may be cut off.

In the upper surface of the group 13 element nitride crystal layer, the low luminance light emitting region may be an exposed surface of the group 13 element nitride crystal grown therebelow, and is two-dimensionally spread in a planar manner. On the other hand, the high brightness light emitting portion is linear, but extends in a one-dimensional manner as a boundary that divides adjacent low brightness light emitting regions. This is because, for example, a dopant component and a trace component are discharged from a Group 13 element nitride crystal grown from below, and are gathered between adjacent Group 13 element nitride crystals in the growth process, and the low luminance emission is adjacent on the top surface It is considered that linear bright light-emitting portions were generated between the regions.

For example, FIG. 4 shows a photograph by CL observation of the top surface of the Group 13 element nitride crystal layer obtained in the example. FIG. 5 is a partial enlarged view of FIG. 4 and FIG. 6 is a schematic view corresponding to FIG. The low brightness light emitting area is two-dimensionally spread in a plane, and the high brightness light emitting portion is linear, and is one-dimensionally stretched like a boundary dividing the adjacent low brightness light emitting areas. I understand that.

From this, the shape of the low luminance light emitting region is not particularly limited, and usually extends two-dimensionally in a planar shape. On the other hand, the line formed by the high luminance light emitting portion needs to be elongated. From such a viewpoint, the width of the high brightness light emitting portion is preferably 100 μm or less, more preferably 20 μm or less, and particularly preferably 5 μm or less. In addition, the width of the high brightness light emitting portion is usually 0.01 μm or more.

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

From the viewpoint of the present invention, the ratio of the area of the high luminance light emitting portion to the area of the low luminance light emitting region on the upper surface (area of high luminance light emitting portion / area of low luminance light emitting region) is 0.001 or more Is more preferably 0.01 or more.
From the viewpoint of the present invention, the ratio of the area of the high luminance light emitting portion to the area of the low luminance light emitting region on the upper surface (area of high luminance light emitting portion / area of low luminance light emitting region) is 0.3 or less Is more preferably 0.1 or less.

In a preferred embodiment, the high brightness light emitting portion includes a portion extending along the m-plane of the Group 13 element nitride crystal. For example, in the example of FIG. 3, FIG. 6, the high-intensity light emission part 5 is extended in elongate linear form, and includes many parts 5a, 5b, 5c extended along m surface. Specifically, the directions along the m-plane of Group 13 element nitride crystal, which is a hexagonal crystal, are [-2110], [-12-10], [11-20], and [2-1-10]. The high-intensity light emitting unit 5 includes a part of the side of a substantially hexagonal shape reflecting the hexagonal crystal, which is a [1-210], [-1-120] direction. The linear high-intensity light emitting portion extending along the m-plane means that the longitudinal direction of the high-intensity light emitting portion is [-2110], [-12-10], [11-20], [2- It means extending along one of 1-10 directions, [1-210] and [-1-120] directions. Specifically, the case where the longitudinal direction of the linear high luminance light emitting part is preferably within ± 1 °, more preferably within ± 0.3 ° with respect to the m-plane is included.

In a preferred embodiment, at the top surface, linear high-intensity light emitting portions extend generally along the m-plane of the Group 13 element nitride crystal. This means that the main part of the high luminance light emitting part extends along the m plane, and preferably the continuous phase of the high luminance light emitting part extends along substantially 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 brightness light emitting portion, and substantially high brightness It may occupy the whole of the light emitting part.

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

However, the continuous phase means that the high brightness light emitting portion 5 is continuous on the upper surface, but it is not essential that all the high brightness light emitting portions 5 are completely continuous, and the whole It is to be allowed that a small amount of the high luminance light emitting portion 5 is separated from the other high luminance light emitting portions 5 without affecting the pattern.

Further, the dispersed phase means that the low brightness light emitting region 6 is divided by the high brightness light emitting portion 5 and divided into a large number of regions which are not connected to each other. In addition, even if the low brightness light emitting region 6 is separated by the high brightness light emitting portion 5 on the upper surface, it is acceptable that the low brightness light emitting region 6 is continuous inside the group 13 element nitride crystal layer.

In a preferred embodiment, the half width of (0002) plane reflection of the X-ray rocking curve on the top surface of the group 13 element nitride crystal layer is 3000 seconds or less and 20 seconds or more. This indicates that the top surface has a small surface tilt angle, and the crystal orientation as a whole is highly oriented like a single crystal. A characteristic distribution on the upper surface of a Group 13 element nitride crystal layer as having a microstructure in which the crystal orientation on the surface as a whole is highly oriented while having the cathode luminescence distribution as described above It is possible to make the characteristics of the various functional elements provided thereon uniform, and to improve the yield of the functional elements.

From such a viewpoint, the half value width of (0002) plane reflection of the X-ray rocking curve on the top 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 that there be. In addition, it is practically difficult to reduce the half width of (0002) plane reflection of the X-ray rocking curve on the upper surface of the group 13 element nitride crystal layer to less than 20 seconds.

However, X-ray rocking curve (0002) surface reflection is measured as follows. Measurement conditions are: tube voltage 40 kV, tube current 40 mA, collimator diameter 0.1 mm, anti-scattering slit 3 mm, using an XRD apparatus (for example, D8-DISCOVER manufactured by Bruker-AXS), ω = peak position angle ± 0.3 ° And the ω step width of 0.003 ° and the counting time of 1 second. In this measurement, it is preferable to parallelize CuKα rays (half-width 28 seconds) with a Ge (022) asymmetric reflection monochromator and measure the axis after setting the axis at a tilt angle CHI of about 0 °. The half width of the X-ray rocking curve (0002) surface reflection can be calculated by performing peak search using XRD analysis software (LEPTOS 4.03 manufactured by Bruker-AXS). The peak search conditions are preferably Noise Filter “10”, Threshold “0.30”, and Points “10”.

When a cross section substantially perpendicular to the top surface of the group 13 element nitride crystal layer is observed by CL, as shown in FIG. 7, a linear high-intensity light emitting portion emitting white may be observed. Note that in FIG. 7, the low luminance light emitting region is spread in a two-dimensional manner in a planar manner, and the high luminance light emitting portion is linear and extends like a boundary dividing the adjacent low luminance light emitting regions. Know that The observation method of such a high luminance light emitting portion and the low luminance light emitting region is the same as the observation method of the high luminance light emitting portion and the low luminance light emitting region on the upper surface.

There is no particular limitation on the shape of the low luminance light emitting region in the cross section of the Group 13 element nitride crystal layer, and usually it is two-dimensionally extended in a planar shape. On the other hand, the line formed by the high luminance light emitting portion needs to be elongated. From such a viewpoint, the width of the high brightness light emitting portion is preferably 100 μm or less, and more preferably 20 μm or less. In addition, the width of the high brightness light emitting portion is usually 0.01 μm or more.

Further, from the viewpoint of the present invention, the ratio (length / width) of length to 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 top surface of the Group 13 element nitride crystal layer, the linear high luminance light emitting portion forms a continuous phase, and the low luminance light emitting region is formed by the high luminance light emitting portion. It forms a partitioned discontinuous phase. For example, in the CL photograph of FIG. 7, the linear 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.

However, the continuous phase means that the high brightness light emitting portion is continuous in the cross section, but it is not essential that all the high brightness light emitting portions are completely continuous, and the whole pattern It is acceptable that a small amount of high-intensity light emitting portions are separated from other high-intensity light emitting portions without affecting the above.

Further, the dispersed phase means that the low brightness light emitting region is divided by the high brightness light emitting portion and divided into many regions which are not connected to each other.

In a preferred embodiment, no void is 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 is the same field of view as the CL photograph in FIG. 7, different crystal phases other than voids (voids) and group 13 element nitride crystals are not observed. However, observation of void is performed as follows.

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

Also, in the scanning electron microscope (the observation conditions described above), when observing a cross section substantially perpendicular to the top surface of the Group 13 element nitride crystal layer, apparent grain boundaries accompanied by structural macro defects such as voids are Not observed. With such a microstructure, it is believed that when a functional element such as a light emitting element is fabricated on a Group 13 element nitride crystal layer, it is possible to suppress an increase in resistance and characteristic variations caused by apparent grain boundaries. Be

In a preferred embodiment, the dislocation density on the top 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 to set the dislocation density to 1 × 10 ⁶ / cm ² or less from the viewpoint of improving the characteristics of the functional element. From this viewpoint, it is more preferable to set the dislocation density to 1 × 10 ⁴ / cm ² or less. The dislocation density is measured as follows.

For measurement of dislocation density, a scanning electron microscope (SEM) with a CL detector can be used. For example, when CL observation is carried out using a Hitachi High-Technologies S-3400N scanning electron microscope with a MiniCL system manufactured by Gatan, dislocation sites are observed as black spots (dark spots) without light emission. Dislocation density is calculated by measuring the dark spot density. As the measurement conditions, while the CL detector is inserted between the sample and the objective lens, it is preferable to observe at an acceleration voltage of 10 kV, a probe current of "90", a working distance (W.D.) 22.5 mm, and a magnification of 1200 times. preferable.

In a preferred embodiment, the half width of (0002) plane reflection of the X-ray rocking curve on the top surface of the group 13 element nitride crystal layer is 3,000 seconds or less, 20 seconds or more, and half of (1000) plane reflection. The value range is 10000 seconds or less and 20 seconds or more. This indicates that both the surface tilt angle and the surface twist angle at the upper surface are small, and the crystal orientation is highly oriented as a whole, like a single crystal. With such a fine structure in which the crystal orientation at the surface as a whole is more highly oriented, 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 thereon Can be made uniform, and the yield of functional devices is also improved.

In a preferred embodiment, the half value width of (1000) plane reflection of the X-ray rocking curve on the upper surface of the group 13 element nitride crystal layer is 10000 seconds or less and 20 seconds or more. This means that the surface twist angle at the top surface is very low. It indicates that the crystal orientation as a whole is highly oriented like a single crystal. A characteristic distribution on the upper surface of a Group 13 element nitride crystal layer as having a microstructure in which the crystal orientation on the surface as a whole is highly oriented while having the cathode luminescence distribution as described above It is possible to make the characteristics of the various functional elements provided thereon uniform, and to improve the yield of the functional elements.

From such a viewpoint, the half value width of (1000) plane reflection of the X-ray rocking 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, further 20 seconds or more It is more preferable that In addition, it is practically difficult to reduce this half-width to less than 20 seconds.

However, X-ray rocking curve (1000) surface reflection is measured as follows. Measurement conditions are: tube voltage 40 kV, tube current 40 mA, no collimator, anti-scattering slit 3 mm, range of ω = peak position angle ± 0.3 °, using an XRD apparatus (for example, D8-DISCOVER manufactured by Bruker-AXS) The ω step width may be set to 0.003 ° and the counting time to 4 seconds. In this measurement, it is preferable to measure CuKα rays in parallel monochromatization (half-width 28 seconds) with a Ge (022) asymmetric reflection monochromator and centering around a tilt angle CHI = 88 °. And the half value width of X-ray rocking curve (1000) surface reflection can be calculated by performing peak search using XRD analysis software (manufactured by Bruker-AXS, LEPTOS 4.03). The peak search conditions are preferably Noise Filter “10”, Threshold “0.30”, and Points “10”.

(Separation method of Group 13 element nitride crystal layer)
By separating the group 13 element nitride crystal layer from the sapphire substrate, it is possible to obtain a freestanding substrate including the group 13 element nitride crystal layer.

Here, the method of 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 exfoliated 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 an etchant at the time of 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 sodium hydroxide aqueous solution or potassium hydroxide aqueous solution is preferable. Moreover, as for the temperature at the time of performing chemical etching, 70 degreeC or more is preferable.

Alternatively, the group 13 element nitride crystal layer can be separated 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-standing substrate)
A freestanding substrate can be obtained by separating the group 13 element nitride crystal layer from the sapphire substrate. In the present invention, the term "self-supporting substrate" means a substrate which can be handled as a solid without deformation or breakage under its own weight. The self-supporting substrate of the present invention can be used as a substrate for various semiconductor devices such as light emitting elements, but in addition to that, it can be an electrode (may be a p-type electrode or an n-type electrode), a p-type layer, an n-type layer, etc. It can be used as a member or layer other than the base material. This freestanding substrate may further be provided with one or more other layers.

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 self-supporting properties to the substrate, preferably 20 μm or more, more preferably 100 μm or more, and still more preferably It is 300 μm or more. The upper limit of the thickness of the free-standing substrate should not be defined, but 3000 μm or less is realistic in terms of manufacturing cost.

(Composite substrate)
When a group 13 element nitride crystal layer is provided on a 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)
Although the functional element structure provided on the Group 13 element nitride crystal layer of the present invention is not particularly limited, the light emitting function, the rectifying function or the power control function can be exemplified.

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, a light emitting element is manufactured by providing a light emitting functional layer in a Group 13 element nitride crystal layer. However, a light emitting element is manufactured 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, or an n-type layer. It is also good.

FIG. 9 schematically shows a layer configuration of a light emitting element according to one embodiment of the present invention. A light emitting element 21 shown in FIG. 9 includes a self-supporting substrate 13 and a light emitting functional layer 18 formed on the substrate. The light emitting functional layer 18 provides 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 provide 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 and red, or may emit ultraviolet light without visible light or together with visible light. The light emitting functional layer 18 preferably constitutes at least a part of a light emitting element utilizing a pn junction, and the pn junction includes a p-type layer 18a and an n-type layer 18c as shown in FIG. The active layer 18 b may be included between At this time, a double hetero junction or a single hetero junction (hereinafter collectively referred to as a hetero junction) using a layer having a smaller band gap than the p-type layer and / or the n-type layer may be used as the active layer. In addition, a quantum well structure in which the thickness of the active layer is reduced can be employed as one mode of the p-type layer-active layer-n-type layer. It goes without saying that in order to obtain a quantum well, a double hetero junction 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 employed. Further, a multiple quantum well structure (MQW) in which a large number of these quantum well structures are stacked may be used. With these structures, the light emission efficiency can be enhanced as compared to a pn junction. Thus, the light emitting functional layer 18 is preferably provided with a pn junction and / or hetero junction and / or quantum well junction having a light emitting function. 20 and 22 are examples of electrodes.

Therefore, at least one layer constituting the light emitting functional layer 18 is at least 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 be one or more. The n-type layer, the p-type layer and the active layer (if present) may be composed of the same material as the main component or may be composed of materials different from each other in the main component.

The material of each layer constituting the light emitting functional layer 18 is not particularly limited as long as it grows substantially in accordance with the crystal orientation of the group 13 element nitride crystal layer and has a light emitting function, but a gallium nitride (GaN) based material It is preferable to be composed of a material mainly composed of at least one or more selected from zinc oxide (ZnO) based materials and aluminum nitride (AlN) based materials, and a dopant for controlling p type to n type is suitably selected It may be included. Particularly preferred materials are gallium nitride (GaN) based materials. Further, the material constituting the light emitting functional layer 18 may be, for example, a mixed crystal in which AlN, InN or the like is solid-solved in GaN in order to control the band gap. In addition, as described in the immediately preceding paragraph, the light emitting functional layer 18 may be a heterojunction made of a plurality 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, a zinc oxide (ZnO) based material may be used for the p-type layer, and a 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 film formation method of the light emitting functional layer 18 and the buffer layer is not particularly limited as long as it is a method of growing substantially in accordance with the crystal orientation of the Group 13 element nitride crystal layer, but a vapor phase method such as MOCVD, MBE, HVPE, sputtering, etc. Preferred examples thereof include liquid phase methods such as Na flux method, ammonothermal method, hydrothermal method and sol-gel method, powder method utilizing solid phase growth of powder, and combinations thereof.

Example 1-1
A gallium nitride crystal layer was grown on a sapphire substrate according to the method described with reference to FIGS. 1 and 2.
Specifically, an Ar ion beam was scanned on the surface 25 a of the sapphire substrate 25. At this time, an ion trimming apparatus manufactured by AM Systems, Inc. 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 was an amorphous structure and had a thickness of 40 angstrom.

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

The seed crystal substrate was placed in an aluminum oxide crucible in a nitrogen atmosphere glove box. Next, metallic gallium and metallic sodium were filled in the crucible so that Ga / Ga + Na (mol%) = 15 mol%, and a lid was covered with an aluminum oxide plate. The crucible was placed in a stainless steel inner container, further placed in a stainless steel outer container capable of containing it, and closed with a container lid with a nitrogen introduction pipe. The outer container was placed on a rotary table installed in a heating unit in a crystal manufacturing apparatus which has been vacuum baked in advance, and the pressure resistant container was covered and sealed.

Subsequently, the inside of the pressure resistant container was evacuated to 0.1 Pa or less by a vacuum pump. Subsequently, nitrogen gas is introduced from a nitrogen gas cylinder to 4.0 MPa while heating the temperature of the heating space to 870 ° C. by adjusting the upper heater, middle heater and lower heater, and the outer container around the central axis It was rotated at a speed of 20 rpm in a constant cycle clockwise and counterclockwise. The acceleration time was 12 seconds, the holding time was 600 seconds, the deceleration time was 12 seconds, and the stop time was 0.5 seconds. And it hold | maintained in this state for 40 hours. Thereafter, the vessel was naturally cooled to room temperature and depressurized to the atmospheric pressure, and then the lid of the pressure container was opened and the bale 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 freestanding substrate made of a gallium nitride crystal layer having a thickness of 600 μm.

(Evaluation)
The upper surface of the gallium nitride free-standing 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, a high luminance light emitting portion emitting white light was confirmed inside the gallium nitride crystal in the CL photograph. However, at the same time, as shown in FIG. 10, when the same field of view was observed by SEM, no void etc. were confirmed, and it was confirmed that a homogeneous gallium nitride crystal was grown.

In addition, the gallium nitride free-standing substrate was cut into a cross section perpendicular to the upper surface, and the cut surface was polished and subjected to CL observation 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-intensity light emitting portion emitting 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, no void etc. were confirmed, and it was confirmed that a homogeneous gallium nitride crystal was grown. That is, even in the cross section of the group 13 element nitride crystal layer, the high brightness light emitting portion exists in CL observation as in the upper surface, but the same shape as the high brightness light emitting portion seen in the same field of view in the SEM There was no microstructure similar to it or that.

(Dark spot measurement)
Then, the dislocation density was measured on the top surface of the group 13 element nitride crystal layer. The dislocation density was calculated by performing CL observation and measuring the density of dark spots as dislocation sites. As a result of CL observation of an 80 μm × 105 μm field, it was 5 × 10 ⁴ / cm ² .

(Measurement of surface tilt angle)
It was 86 seconds as a result of measuring the half value width of (0002) plane reflection of the X ray rocking curve in the upper surface of a gallium nitride crystal layer.

(Measurement of surface twist angle)
It was 89 seconds when the half value width of (1000) plane reflection of the X-ray rocking curve in the upper surface of the gallium nitride crystal layer was measured.

(Deposition of light emitting functional layer by MOCVD method)
Using an MOCVD method, an n-type n-type layer was deposited 1 μm as an n-type layer at 1050 ° C. to have a Si atomic concentration of 5 × 10 ¹⁸ / cm ³ as the n-type layer. Next, a multiple quantum well layer was deposited at 750 ° C. as a light emitting layer. Specifically, five layers of 2.5 nm well layers of InGaN and six layers of 10 nm of barrier layers of GaN were alternately stacked. Next, as a p-type layer, 200 nm of p-GaN doped at a temperature of 950 ° C. so that the Mg atom concentration is 1 × 10 ¹⁹ / cm ³ was deposited. Thereafter, it was taken out of the MOCVD apparatus, and heat treatment at 800 ° C. in a nitrogen atmosphere was performed for 10 minutes as activation treatment of Mg ions in the p-type layer.

(Fabrication of light emitting element)
15 nm and 70 nm Ti / Al / Ni / Au film as cathode electrode on the opposite side of n-GaN layer and p-GaN layer of gallium nitride freestanding substrate by photolithography process and vacuum evaporation method It patterned in thickness of 12 nm and 60 nm. Thereafter, heat treatment at 700 ° C. in a nitrogen atmosphere was performed for 30 seconds in order to improve ohmic contact characteristics. Further, a Ni / Au film was patterned to a thickness of 6 nm and 12 nm as a light transmitting anode electrode in the p-type layer using a photolithography process and a vacuum evaporation method. Thereafter, a heat treatment at 500 ° C. was performed for 30 seconds in a nitrogen atmosphere in order to improve ohmic contact characteristics. Furthermore, using a photolithography process and a vacuum evaporation method, the Ni / Au film to be the anode electrode pad has a thickness of 5 nm and 60 nm, respectively, on a partial region of the upper surface of the Ni / Au film as the translucent anode electrode. Patterned. The substrate thus obtained was cut into chips, and then mounted on lead frames to obtain light emitting elements of a vertical structure.

(Evaluation of light emitting element)
When current was applied between the cathode electrode and the anode electrode and IV measurement was performed for 100 elements produced, rectification was confirmed for 91 elements. That is, the yield was 91%. In addition, when forward current flowed, emission of wavelength 460 nm was confirmed. The light emission intensity was 0.96 (a relative value when the light 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 a 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 freestanding substrate.
However, in this example, unlike Example 1-1, the ion trimming apparatus manufactured by AM Systems, Inc. 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 of amorphous structure with a thickness of 200 angstroms was obtained. A gallium nitride crystal layer was formed thereon in the same manner as in Example 1-1.

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

(Example 1-3)
An aluminum oxide layer and a group 13 element nitride crystal layer were formed on a 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 freestanding substrate.
However, in this example, unlike the example 1-1, a high-speed Ar atom beam was scanned on the sapphire substrate.
The degree of vacuum reached in the chamber before the start of scanning was set to 10 ^-6 Pa or so. As a beam source, a saddle field type high-speed atomic beam source was used. Ar gas was introduced into the chamber, and a high voltage was applied to the electrode 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 of amorphous structure with a thickness of 60 angstroms was obtained. A gallium nitride crystal layer was formed thereon in the same manner as in Example 1-1.

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

(Example 2-1)
An aluminum oxide layer and a group 13 element nitride crystal layer were formed on a 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 freestanding substrate.
However, in this example, unlike the example 1-1, the surface of the sapphire substrate was ground with a whetstone # 2000. As a result, a 0.2 μm thick process-altered layer was obtained.
In the work-affected layer, an amorphous phase, a polycrystalline phase, and crystal defects were observed in the aluminum oxide layer in the TEM photograph. These were observable as described above by the change in contrast to the sapphire single crystal.

A gallium nitride crystal layer was formed thereon in the same manner as in Example 1-1. The number of dark spots was observed by CL on the upper surface of the obtained Group 13 element nitride crystal layer, and the dislocation density was calculated to be 5 × 10 ⁴ / cm ² . Further, using the obtained free standing substrate, a light emitting diode was produced in the same manner as in Example 1-1, and the light emission intensity and the yield were measured. The measurement results are shown in Table 1. Further, as a result of CL observation on the upper surface and the cross section of the obtained free-standing substrate, observation results of the surface twist angle and the surface tilt angle of the upper surface were also equivalent to Example 1-1.

(Example 2-2)
In the same manner as in Example 2-1, an aluminum oxide layer and a group 13 element nitride crystal layer were formed on a sapphire substrate, and the group 13 element nitride crystal layer was peeled off from the sapphire substrate to obtain a freestanding substrate.
However, in the present example, unlike the example 2-1, the surface of the sapphire substrate was ground with a whetstone # 325. As a result, a 1.5 μm thick process-altered layer was obtained.

A gallium nitride crystal layer was formed thereon in the same manner as in Example 1-1. The number of dark spots was observed by CL on the top surface of the obtained Group 13 element nitride crystal layer, and the dislocation density was calculated to be 2 × 10 ⁴ / cm ² . Further, using the obtained free standing substrate, a light emitting diode was produced in the same manner as in Example 1-1, and the light emission intensity and the yield were measured. The measurement results are shown in Table 1. Further, as a result of CL observation on the upper surface and the cross section of the obtained free-standing substrate, observation results of the surface twist angle and the surface tilt angle of the upper surface were also equivalent to Example 1-1.

(Example 3)
An aluminum oxide layer and a group 13 element nitride crystal layer were formed on a 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 freestanding substrate.
However, in this example, unlike the example 1-1, the sapphire substrate surface was etched by reactive ion etching. Specifically, using a RIE apparatus "Model E640" manufactured by Panasonic Corporation, RF power is 400 W, bias voltage is 200 W, working gas is chlorine (flow rate 40 sccm), pressure is 1 Pa, RIE time is 20 minutes. did. As a result, a 40 angstrom thick aluminum oxide layer was obtained.

A gallium nitride crystal layer was formed thereon in the same manner as in Example 1-1. The number of dark spots was observed by CL on the upper surface of the obtained Group 13 element nitride crystal layer, and the dislocation density was calculated to be 7 × 10 ⁵ / cm ² . Further, using the obtained free standing substrate, a light emitting diode was produced in the same manner as in Example 1-1, and the light emission intensity and the yield were measured. The measurement results are shown in Table 1. Further, as a result of CL observation on the upper surface and the cross section of the obtained free-standing substrate, observation results of the surface twist angle and the surface tilt angle of the upper surface were also equivalent to Example 1-1.

Example 4-1
An aluminum oxide layer and a group 13 element nitride crystal layer were formed on a 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 freestanding substrate.
However, in this example, unlike Example 1-1, the sapphire substrate surface was annealed under hydrogen gas. Specifically, using a MOCVD apparatus, the temperature was raised to 1200 ° C. at a heating rate of 120 ° C./min under a hydrogen atmosphere. Then, it hold | maintained and annealed for 30 minutes, without changing hydrogen atmosphere. Thereafter, the heater setting value was lowered at a temperature lowering rate of 120 ° C./min, and when the actual temperature fell below 500 ° C., the atmosphere was switched to a nitrogen atmosphere and the temperature was lowered to room temperature.
As a result, an aluminum oxide layer with a thickness of 80 angstroms was obtained.

A gallium nitride crystal layer was formed thereon in the same manner as in Example 1-1. The number of dark spots was observed by CL on the upper surface of the obtained Group 13 element nitride crystal layer, and the dislocation density was calculated to be 5 × 10 ⁵ / cm ² . Further, using the obtained free standing substrate, a light emitting diode was produced in the same manner as in Example 1-1, and the light emission intensity and the yield were measured. The measurement results are shown in Table 1. Further, as a result of CL observation on the upper surface and the cross section of the obtained free-standing substrate, observation results of the surface twist angle and the surface tilt angle of the upper surface were also equivalent to Example 1-1.

(Example 4-2)
In the same manner as in Example 4-1, an aluminum oxide layer and a Group 13 element nitride crystal layer were formed on a sapphire substrate, and the Group 13 element nitride crystal layer was peeled from the sapphire substrate to obtain a freestanding substrate.
However, in this example, unlike Example 4-1, the sapphire substrate surface was annealed under a mixed gas of hydrogen, ammonia and nitrogen. Specifically, using a MOCVD apparatus, the temperature was raised to 1200 ° C. at a heating rate of 120 ° C./min under a hydrogen atmosphere. Then, after holding and annealing for 15 minutes without changing the hydrogen atmosphere, the atmosphere was changed to a mixed gas of hydrogen, ammonia and nitrogen, and was held for 15 minutes for annealing. Thereafter, the heater setting value was lowered at a temperature lowering rate of 120 ° C./min, and when the actual temperature fell below 500 ° C., the atmosphere 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 formed thereon in the same manner as in Example 1-1. The number of dark spots was observed by CL on the top surface of the obtained Group 13 element nitride crystal layer, and the dislocation density was calculated to be 3 × 10 ⁵ / cm ² . Further, using the obtained free standing substrate, a light emitting diode was produced in the same manner as in Example 1-1, and the light emission intensity and the yield were measured. The measurement results are shown in Table 1. Further, as a result of CL observation on the upper surface and the cross section of the obtained free-standing substrate, observation results of the surface twist angle and the surface tilt angle of the upper surface were also equivalent to Example 1-1.

(Comparative example)
On a sapphire substrate, a seed crystal film made of gallium nitride was grown by MOCVD in the same manner as in Example 1-1. Then, a gallium nitride crystal layer was grown by the Na flux method in the same manner as in Example 1-1 (thickness 600 μm). Then, in the same manner as in Example 1-1, the sapphire substrate was removed by a laser lift-off method, and the top and bottom surfaces of the obtained freestanding substrate composed of a Group 13 element nitride crystal layer were polished.

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

 

(Creation of rectification function element)
A functional element having a rectifying function was produced.
That is, a Schottky barrier diode structure was formed on the upper surface of the freestanding substrate obtained in Example 1-1 as follows, and an electrode was formed to obtain a diode, and the characteristics were confirmed.

(Deposition of rectifying function layer by MOCVD method)
A 5 μm thick n-GaN layer doped as an n-type layer at 1050 ° C. and having a Si atomic concentration of 1 × 10 ¹⁶ / cm ³ on a free-standing substrate using MOCVD (metal organic chemical vapor deposition) method I made a film.
Ti / Al / Ni / Au films with a thickness of 15 nm, 70 nm, 12 nm, and 60 nm as ohmic electrodes on the surface of the free-standing substrate opposite to the n-GaN layer using photolithography process and vacuum evaporation method Patterned. Thereafter, heat treatment at 700 ° C. in a nitrogen atmosphere was performed for 30 seconds in order to improve ohmic contact characteristics. Further, a Ni / Au film was patterned as a Schottky electrode to a thickness of 6 nm and 80 nm, respectively, on the n-GaN layer formed by the MOCVD method using a photolithography process and a vacuum evaporation method. The substrate obtained in this manner was cut into chips, and then mounted on lead frames to obtain rectifying devices.

(Evaluation of rectifier)
When the IV measurement was performed, the rectification characteristic was confirmed.

(Creating a power control element)
A functional element having a power control function was produced.
A self-supporting substrate was produced in the same manner as in Example 1-1. However, unlike Example 1, when forming a gallium nitride crystal film by Na flux method, doping of impurities was not performed. The upper surface of the free-standing substrate obtained in this manner, in the following manner, forming a _Al 0.25 _Ga 0.75 / GaN HEMT structure by MOCVD to form the electrodes was confirmed transistor characteristics.

Using an MOCVD (metal organic chemical vapor deposition) method, a 3 μm-thick GaN layer was formed as an i-type layer at 1050 ° C. as an i-type layer on a free-standing substrate. Next, a 25 nm Al _0.25 Ga _0.75 N layer was deposited at 1050 ° C. as a functional layer. This resulted in an Al _0.25 Ga _0.75 N / GaN HEMT structure.

Ti / Al / Ni / Au films as source and drain electrodes were patterned to thicknesses of 15 nm, 70 nm, 12 nm, and 60 nm, respectively, using a photolithography process and a vacuum evaporation method. Thereafter, heat treatment at 700 ° C. in a nitrogen atmosphere was performed for 30 seconds in order to improve ohmic contact characteristics. Furthermore, using a photolithography process and a vacuum evaporation method, a Ni / Au film as a gate electrode was formed by Schottky junction with a thickness of 6 nm and 80 nm, respectively, and patterned. The substrate thus obtained was cut into chips, and then mounted on lead frames to obtain power control elements.

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

Claims (16)

1. Forming an aluminum oxide layer by surface treating a sapphire substrate;
   Forming a seed crystal film of Group 13 element nitride on the aluminum oxide layer; and Group 13 selected from gallium nitride, aluminum nitride, indium nitride, or mixed crystals thereof on the seed crystal film. A method for producing a Group 13 element nitride layer, comprising the step of providing a Group 13 element nitride layer comprising an element nitride.
2. 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.
3. The method according to claim 1, wherein the surface treatment is performed by grinding the sapphire substrate.
4. The method according to claim 1, wherein the surface treatment is performed by reactive ion etching of the sapphire substrate.
5. The method according to claim 1, wherein the surface treatment is performed by annealing the sapphire substrate in an atmosphere containing at least hydrogen.
6. The method according to any one of the preceding claims, wherein the aluminum oxide layer comprises an amorphous phase, a polycrystalline phase or a defect induced part.
7. The method according to claim 3, wherein the aluminum oxide layer is a processing-altered layer.
8. The group 13 element nitride crystal layer has a linear high luminance light emitting portion and a low luminance light emitting region adjacent to the high luminance light emitting portion when the upper surface is observed by cathode luminescence.
   The method according to any one of claims 1 to 7, wherein the high brightness light emitting portion includes a portion extending along the m-plane of the group 13 element nitride crystal.
9. 9. The method of claim 8, wherein the high brightness light emitting portion extends substantially along the m-plane of the Group 13 element nitride crystal.
10. 10. The method according to claim 8, wherein the half width of (0002) plane reflection of the X-ray rocking curve on the upper surface is 3000 seconds or less and 20 seconds or more.
11. 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.
12. The method according to any one of claims 8 to 11, characterized in that the dislocation density on the top surface of the group 13 element nitride crystal layer is 1 x 10 ⁶ / cm ² or less.
13. 13. 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. Method according to any one of the claims.
14. The method according to any one of claims 8 to 13, characterized in that the half value width of (1000) plane reflection of the X-ray rocking curve on the upper surface is 10000 seconds or less and 20 seconds or more.
15. The method according to any one of claims 1 to 14, wherein the Group 13 element nitride is a gallium nitride based nitride.
16. The method according to any one of the preceding claims, characterized in that the Group 13 element nitride layer is deposited by a sodium flux method.

Images