JP4860665B2 - Single crystal thin film structure of boron nitride and manufacturing method thereof - Google Patents

Description

  The present invention relates to a single crystal thin film structure and manufacturing method of boron nitride, and more particularly to a single crystal thin film structure of boron nitride having a metastable wurtzite crystal structure and a manufacturing method thereof.

  Boron nitride has a wide band gap of about 6 electron volts or more, and n-type doping and p-type doping are possible, so it is promising as a material for light-emitting diodes and laser diodes in the deep ultraviolet region. FIG. 1 shows a phase diagram of boron nitride. At low pressure including normal pressure, hexagonal boron nitride is a stable phase, and at high pressure zinc blende type boron nitride is a stable phase. In addition, wurtzite boron nitride that is a metastable phase may be produced under non-equilibrium and high pressure (several GPa). Wurtzite-type boron nitride is expected to have a wider band gap and superior mechanical strength than hexagonal and zinc-blende boron nitride as physical properties. Since nitride semiconductors GaN, AlN, InN and mixed crystals of these are wurtzite types are stable phases, fabrication of heterostructures of these nitride semiconductors and wurtzite type boron nitrides, and new functional devices The possibilities of application will also expand.

FIG. 2 shows a schematic diagram of the crystal structure of wurtzite and hexagonal boron nitride. In the wurtzite type, nitrogen atoms and boron atoms are three-dimensionally bonded by sp ³ hybrid orbitals, and nitrogen atoms and boron atoms are also bonded by a strong covalent bond in the c-axis direction. On the other hand, in the hexagonal crystal type, a nitrogen atom and a boron atom are two-dimensionally bonded by sp ² hybrid orbital to form a sheet-like hexagonal network structure. In the c-axis direction (between sheets), the upper and lower nitrogen atoms and boron atoms are connected by a weak intermolecular force.

A. Sawaoka, T. Soma, and S. Saito, “Structure determination of boron nitride transformed by shock compression,” Japan Journal of Applied Physics, vol.13, No.5, pp. 891, 1974. F. R. Corrigan and F. P. Bundy, “Direct transitions among the allotropic forms of boron nitride at high pressures and temperatures,” The Journal of Chemical Physics, vol. 63, No. 9, pp. 3812, 1975. edited by James H. Edgar, “Properties of Group III nitrides,” (London), INSPEC, 1994, p. 11.

  Hexagonal and zinc blende boron nitrides have a bulk crystal and thin film structure, respectively. However, wurtzite boron nitride is a metastable phase and is extremely difficult to produce. Although formation of powdered wurtzite boron nitride by thermal shock method (see Non-Patent Document 1) or high-temperature and high-pressure annealing method (see Non-Patent Document 2) has been reported, single crystal thin films and large bulk crystals are currently available It is not obtained until. In particular, it is difficult to produce a single crystal thin film that is essential for using wurtzite boron nitride as a material for a light emitting diode or a laser diode. Single crystal thin films such as semiconductors are often obtained by epitaxial growth by vapor phase epitaxy performed under a pressure below atmospheric pressure, but wurtzite boron nitride is a metastable phase under a high pressure of several GPa. Because there is.

  The present invention has been made in view of such problems, and an object thereof is to provide a single crystal thin film structure of wurtzite boron nitride and a method for manufacturing the same.

  In order to achieve such an object, the invention described in claim 1 is a substrate having a wurtzite type crystal structure having a c-axis lattice constant of less than 6.66 angstroms, wherein the principal orientation plane is ( An amorphous structure having an off angle within ± 10 degrees from the (0001) plane and having a plurality of holes on the main azimuth plane of the substrate and a portion excluding the plurality of holes on the main azimuth plane of the substrate And a single crystal thin film of wurtzite boron nitride on the mask, the single crystal thin film filling the plurality of holes of the substrate. It is a thin film structure.

According to a second aspect of the present invention, in the first aspect, the substrate is any one of Al _{x Gal x} N (0 ≦ x ≦ 1), ZnO, or BeO.

  The invention according to claim 3 is characterized in that, in claim 1 or 2, the plurality of holes have a diameter of 10 microns or less and a depth of 1/10 or more of the diameter.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the mask is any one of silicon oxide, aluminum oxide, and silicon nitride.

  The invention according to claim 5 is a substrate having a wurtzite type crystal structure in which the c-axis lattice constant is less than 6.66 angstroms, and the main orientation plane is within ± 10 degrees from the (0001) plane. Providing an off-angle substrate, forming a mask having an amorphous structure on the main orientation surface of the substrate, etching the mask and the substrate, and forming a plurality of on the main orientation surface of the substrate. Forming a wurtzite-type boron nitride single crystal by vapor deposition in the plurality of holes, and growing the wurtzite-type boron nitride single crystal. The wurtzite boron nitride single crystal fills the plurality of holes, grows laterally on the mask, and combines with the wurtzite boron nitride grown laterally from adjacent holes to form a single crystal thin film A method for producing a single crystal thin film structure of wurtzite boron nitride, characterized in that continues until the formation.

According to a sixth aspect of the present invention, in the fifth aspect, the substrate is any one of Al _{x Gal x} N (0 ≦ x ≦ 1), ZnO, or BeO.

  The invention according to claim 7 is characterized in that, in claim 5 or 6, the plurality of holes have a diameter of 10 microns or less and a depth of 1/10 or more of the diameter.

  The invention described in claim 8 is characterized in that, in any one of claims 5 to 7, the mask is any one of silicon oxide, aluminum oxide, and silicon nitride.

  The invention according to claim 9 is characterized in that, in any one of claims 5 to 8, the vapor phase growth method is performed under conditions of 0.1 to 1 atm and 1100 to 1600K. To do.

  The present invention is a substrate having a wurtzite type crystal structure having a c-axis lattice constant of less than 6.66 angstroms, wherein the main orientation plane is an off angle within ± 10 degrees from the (0001) plane, By growing a single crystal of boron nitride on a substrate having a plurality of holes on the main orientation plane of the substrate, a single crystal thin film structure of wurtzite boron nitride and a method for manufacturing the same can be provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 3 shows a single crystal thin film structure of wurtzite boron nitride according to the present invention. The wurtzite-type boron nitride single crystal thin film structure 300 is a substrate 301 having a wurtzite-type crystal structure with a c-axis lattice constant of less than 6.66 angstroms, and the main orientation plane 301A is from the (0001) plane. A mask having an off-angle within ± 10 degrees and having a plurality of holes 301B on the main orientation surface 301A of the substrate 301 and an amorphous structure covering a portion excluding the plurality of holes 301B on the main orientation surface 301A of the substrate 301 302 and a single crystal thin film 303 of wurtzite boron nitride on the mask 302, which fills the plurality of holes 301B of the substrate 301.

  A method for producing a single crystal thin film structure of wurtzite boron nitride according to the present invention will be described. First, a substrate having a wurtzite crystal structure with a c-axis lattice constant of less than 6.66 angstroms and having a main orientation plane with an off angle within ± 10 degrees from the (0001) plane is provided. Next, a mask having an amorphous structure is formed on the main orientation plane of the substrate. Next, a resist pattern 400 in which a plurality of holes 401 are arranged is formed on the surface of the mask 302 by lithography (see FIG. 4). Next, the mask 302 and the substrate 301 are etched by a dry etching method or the like using the resist pattern 400 to form a plurality of holes 301B on the main orientation surface 301A of the substrate (see FIG. 5). Thereafter, the resist is removed with an organic solvent. Then, a single crystal of wurtzite boron nitride is grown inside the plurality of holes 301B by vapor phase growth. A single crystal of wurtzite boron nitride is grown by vapor phase epitaxy. A single crystal of wurtzite boron nitride fills the plurality of holes 301B, grows laterally on the mask, and grows laterally from adjacent holes. Continue until the wurtzite boron nitride coalesces to form a single crystal thin film.

Here, the mechanism by which wurtzite boron nitride is formed inside the plurality of holes 301B when a boron nitride single crystal is grown by the vapor phase growth method will be described. First, there is a “pulling effect” on the crystal structure of the substrate. The “drawing effect” on the crystal structure of the substrate is not a stable phase wurtzite gallium nitride on a zinc blende GaAs substrate, for example, when a gallium nitride thin film is produced by the MBE method. This refers to a phenomenon in which a metastable phase zincblende gallium nitride single crystal thin film grows taking over the crystal structure of the substrate. In the present invention, by using the substrate 301 having a wurtzite crystal structure whose c-axis lattice constant is less than 6.66 angstroms, there is an effect of drawing into the wurtzite crystal structure. Secondly, generation of compressive stress in the c-axis direction can be mentioned. As shown in the phase diagram of FIG. 1, hexagonal boron nitride is a stable phase under conditions such as 0.1 to 1 atm and 1100 to 1600 K. Hexagonal boron nitride has a lattice constant of a ₀ = 2.50 angstroms and c ₀ = 6.66 angstroms, and a substrate having a wurtzite crystal structure with a c-axis lattice constant of less than 6.66 angstroms When 301 is used, a compressive stress in the c-axis direction is applied to hexagonal boron nitride nucleated inside a plurality of minute holes 301B so as to match the crystal structure of the substrate 301 surrounding the bottom and side surfaces. Occurs (see FIG. 6). When a large compressive stress of several GPa is applied in the c-axis direction of hexagonal boron nitride, upper and lower nitrogen atoms and boron atoms form a covalent bond, causing a phase transition in the wurtzite type (see Non-Patent Document 2). This corresponds well with the phase diagram of FIG. With these two mechanisms, when a boron nitride single crystal is grown by the vapor phase growth method, wurtzite boron nitride is formed inside the plurality of holes 301B.

For example, when wurtzite BeO is used as the substrate 301, the lattice constants are a _s = 2.70 angstroms and c _s = 4.38 angstroms, so the strain in the [1-100] direction (m-axis) is reduced. ε _xx , where the strain in the [11-20] direction (a axis) is ε _yy and the strain in the [0001] direction (c axis) is ε _zz ,
_{ε xx = (a s -a 0} ) / a 0 = (2.70-2.50) /2.50=0.08 (1)
ε _yy = (a _s −a ₀ ) / a ₀ = (2.70−2.50) /2.50=0.08 (2)
ε _zz = (c _s −c ₀ ) / c ₀ = (4.38−6.66) /6.66=−0.34 (3)
It is. Here, plus and minus of strain indicate a tensile state and a compressed state, respectively. The stress σ _zz in the [0001] direction (c-axis) is obtained from the following relational expression.
σ _zz = c ₁₃ * ε _xx + c ₁₃ * ε _yy + c ₃₃ * ε _zz (4)
Here, c ₁₃ and c ₃₃ are elastic constants, and c ₁₃ = 6.2 GPa and c ₃₃ = 35.6 GPa in the case of hexagonal boron nitride (see Non-Patent Document 3). Therefore, from equations (1) to (4), σ _zz = 6.2 * 0.08 + 6.2 * 0.08 + 35.6 * (− 0.34) = − 11.1 GPa
Thus, a large compressive stress (11.1 GPa) is applied to the hexagonal boron nitride in the c-axis direction. Similarly, even when wurtzite type Al _{x Gal x} N (0 ≦ x ≦ 1) or ZnO is used, a compressive force of at least 4 GPa or more is applied in the c-axis direction of the boron nitride generation nucleus, and wurtzite type nitriding is performed. A boron thin film is formed. Note that the substrate 301 is not limited thereto. It should be noted that the substrate 301 can obtain the same effect if the main azimuth plane has an off angle within about ± 10 degrees from the (0001) plane.

  Since the mask 302 has an amorphous structure, it does not affect the growth of the wurtzite boron nitride when the wurtzite boron nitride single crystal fills the plurality of holes 301B and grows laterally on the mask. . The material of the mask 302 is desirably an amorphous substance having heat resistance, and for example, silicon oxide, aluminum oxide, silicon nitride, or the like is suitable. The thickness of the mask 302 can be about 10 nanometers to about 2 microns. Further, as a method for forming the mask 302, there are a vapor deposition method, a vacuum deposition method, a sputtering method, and the like.

  The plurality of holes 301B in the substrate 301 preferably have a diameter of 10 microns or less and a depth of 1/10 or more of the diameter. It is considered that the smaller the diameter, the higher the effect can be obtained. Therefore, it is more preferable that the diameter is as small as possible in the present technical range, for example, the range of 0.1 to 0.5 microns. The shape of the hole may be a perfect circle or a regular hexagon. The regular hexagonal diameter is defined as the length of a diagonal line passing through the center. Since the wurtzite type is six-fold symmetric, a regular hexagonal hole is more preferable. The space | interval of the center of a micro hole can be set to 50 times or less of the diameter of a hole. This is because if it exceeds 50 times, boron nitride is deposited on the mask and the selectivity is lowered.

  Chemical vapor deposition (CVD), metal organic chemical vapor deposition (MOCVD), plasma-assisted chemical vapor deposition (PECVD), molecular beam epitaxy (MBE), or the like is used as the vapor deposition method. However, the diffraction intensity and full width at half maximum of X-ray diffraction are improved particularly by MOCVD, and good crystallinity is obtained. The growth procedure in MOCVD will be specifically described. A substrate 301 is introduced into a reactor of a MOCVD apparatus and heated while flowing hydrogen as a carrier gas. The pressure in the reactor is preferably about 0.1 to 1 atmosphere. When the temperature of the substrate 301 reaches 1100 to 1600 K, ammonia and triethyl boron as source gases are introduced. At this time, growth does not occur on the surface of the mask 302 due to poor wettability of boron nitride, and boron nitride grows only in minute holes in the substrate 301.

It is a figure which shows the phase diagram of boron nitride. It is a figure which shows the schematic diagram of the crystal structure of a wurtzite type and a hexagonal type boron nitride. It is a figure which shows the single crystal thin film structure of wurtzite type boron nitride concerning the present invention. It is a figure for demonstrating the manufacturing method of the single crystal thin film structure of wurtzite type boron nitride based on this invention. It is a figure for demonstrating the manufacturing method of the single crystal thin film structure of wurtzite type boron nitride based on this invention. It is a figure for demonstrating generation | occurrence | production of the compressive stress of a c-axis direction.

Explanation of symbols

300 Wurtzite Boron Nitride Single Crystal Thin Film Structure 301 Substrate 301A Main Orientation Surface 301B Hole 302 Mask 303 Wurtzite Boron Nitride Single Crystal Thin Film 400 Resist Pattern 401 Resist Pattern Hole

Claims (9)

a substrate having a wurtzite crystal structure with a c-axis lattice constant of less than 6.66 angstroms, wherein a main orientation plane is an off angle within ± 10 degrees from a (0001) plane, A substrate having a plurality of holes on an orientation plane;
A mask having an amorphous structure covering a portion of the main orientation surface of the substrate excluding the plurality of holes;
A wurtzite boron nitride single crystal thin film on the mask, the single crystal thin film filling the plurality of holes of the substrate. 2. The single crystal thin film structure according to claim 1, wherein the substrate is made of any one of Al _{x Gal x} N (0 ≦ x ≦ 1), ZnO, or BeO.   The single crystal thin film structure according to claim 1 or 2, wherein the plurality of holes have a diameter of 10 microns or less and a depth of 1/10 or more of the diameter.   4. The single crystal thin film structure according to claim 1, wherein the mask is any one of silicon oxide, aluminum oxide, and silicon nitride. providing a substrate having a wurtzite crystal structure with a c-axis lattice constant of less than 6.66 angstroms, the main orientation plane having an off angle within ± 10 degrees from the (0001) plane;
Forming an amorphous structure mask on the principal orientation surface of the substrate;
Etching the mask and the substrate to form a plurality of holes on the principal orientation surface of the substrate;
Growing a wurtzite-type boron nitride single crystal inside the plurality of holes by vapor deposition,
The step of growing the single crystal of the wurtzite boron nitride includes the single crystal of the wurtzite boron nitride filling the plurality of holes and laterally growing on the mask and laterally growing from adjacent holes. A process for producing a single crystal thin film structure of wurtzite boron nitride, which is continued until it is united with wurtzite boron nitride to form a single crystal thin film. The manufacturing method according to claim 5, wherein the substrate is any one of Al _{x Gal x} N (0 ≦ x ≦ 1), ZnO, or BeO.   The manufacturing method according to claim 5 or 6, wherein the plurality of holes have a diameter of 10 microns or less and a depth of 1/10 or more of the diameter.   The manufacturing method according to claim 5, wherein the mask is any one of silicon oxide, aluminum oxide, and silicon nitride.   9. The manufacturing method according to claim 5, wherein the vapor phase growth method is performed under conditions of 0.1 to 1 atm and 1100 to 1600K.

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