JP2009298626A - Hexagonal boron nitride structure and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hexagonal boron nitride structure which is economically cheap and capable of having a large area and cleavage, and its manufacturing method. <P>SOLUTION: The hexagonal boron nitride structure has a sapphire single crystal substrate 41 and single crystal hexagonal boron nitride 42 formed on the substrate 41. Single crystal hexagonal boron nitride 42 is formed on the sapphire single crystal substrate 41 by a vapor growth method using ammonia which is a group V raw material, and triethyl boron, trimethyl boron, diborane, boron trichloride or boron trifluoride which are group III raw materials. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a boron nitride semiconductor structure and a manufacturing method thereof, and more particularly to a hexagonal boron nitride structure on a sapphire substrate and a manufacturing method thereof.

  Light emitting diodes and semiconductor lasers that emit light in the ultraviolet region are expected to be widely applied to light sources for high-density recording media, photocatalysts, sterilization, and nanosurgery. Further, boron nitride is expected as a light emitting material of the optical device.

  Boron nitride includes cubic boron nitride that is a high-pressure stable phase, hexagonal boron nitride that is a normal-pressure stable phase, and wurtzite boron nitride that is a high-pressure stable phase and a metastable phase due to the difference in crystal structure. Cubic boron nitride, which is a high-pressure stable phase, has been reported for n-type and p-type doping, and a cubic boron nitride light-emitting diode is realized by using a high-temperature high-pressure method. On the other hand, hexagonal boron nitride, which is an atmospheric pressure stable phase, has not been realized for a long time as an optical device due to problems in crystal growth, but recently, a single crystal bulk crystal has been realized by a high-temperature high-pressure method, and light emission. Characteristics have been reported (for example, see Non-Patent Document 1).

  However, there are many unexplained parts regarding the basic physical properties of hexagonal boron nitride, such as the band structure, light emission characteristics, and conductivity. By establishing crystal growth technology for hexagonal boron nitride, the basic physical properties can be clarified. It is strongly desired. In consideration of future applications, it is desired to grow single crystal hexagonal boron nitride on an appropriate substrate.

  As described above, it is currently most important to elucidate the basic physical properties of hexagonal boron nitride and to realize a single crystal hexagonal boron nitride structure on a suitable substrate from the viewpoint of future application. It is a problem.

As the single crystal hexagonal boron nitride structure on various substrates, the following three structures are conceivable.
(1) Hexagonal boron nitride structure on a single crystal hexagonal boron nitride bulk substrate (2) Hexagonal boron nitride structure on a substrate that is lattice-matched with hexagonal boron nitride (or has a small lattice mismatch) (3) Hexagonal crystal Hexagonal Boron Nitride Structure on Substrate Mismatched with Boron Nitride For high-quality hexagonal boron nitride growth, the single crystal hexagonal boron nitride structure on the single crystal hexagonal boron nitride bulk substrate of (1) is used. The method of homoepitaxial growth is the place where the most cravings are desired. However, the size of the single crystal hexagonal boron nitride substrate currently realized is about 0.5-1 mm at the maximum, and it is very difficult to grow it with good reproducibility. Furthermore, single crystal hexagonal boron nitride bulk substrates are not commercially available and are not available.

  Regarding (2), a hexagonal boron nitride structure on a single crystal Ni (111) substrate is promising. The in-plane lattice mismatch between hexagonal boron nitride and Ni (111) is about 0.5%, which is very small. Actually, a single crystal hexagonal boron nitride structure on a single crystal Ni (111) substrate grown at a substrate temperature of 1020 ° C. by a flow modulation epitaxy method using triethylboron and ammonia has been reported (for example, non-patent) Reference 2).

  FIG. 1 is a transmission electron microscope image of a heterointerface of a hexagonal boron nitride structure grown on a Ni (111) substrate by the prior art relating to (2). As shown in the figure, the hetero interface between Ni (111) and hexagonal boron nitride is steep and flat at the atomic level, and a layered hexagonal boron nitride structure due to sp2 bonds is observed in the hexagonal boron nitride crystal. It was. Moreover, since the obtained lattice constant was 6.66Å, it was confirmed that a boron nitride structure was formed on the Ni (111) substrate.

  However, the hexagonal boron nitride structure on the Ni (111) substrate has several problems. First, a single crystal Ni (111) substrate is extremely expensive compared to a commercially available Si substrate, 6H—SiC substrate, sapphire substrate, and the like. Next, it is difficult to obtain a Ni (111) substrate having a large area of 2 inches or the like, and furthermore, cleavage is impossible. Finally, the Ni (111) substrate is inferior in crystallinity as compared with commercially available Si substrates, 6H-SiC substrates, sapphire substrates, and the like. Thus, the Ni (111) substrate has some problems in versatility.

  Regarding (3), a boron nitride structure on a sapphire substrate is promising. The sapphire substrate has a hexagonal crystal structure and is extremely inexpensive as compared with the Ni (111) substrate. In addition, the sapphire substrate can have a large area of 2 inches or the like, and has excellent versatility compared to the Ni (111) substrate, such as having high crystallinity. Furthermore, the sapphire substrate has excellent characteristics, for example, excellent heat resistance, a wide light transmission region, and high insulation and mechanical strength.

  However, there is a big problem that the boron nitride structure on the sapphire substrate becomes a disordered layer boron nitride structure. The lattice constants of the sapphire substrate and the hexagonal boron nitride are greatly different, and there is a lattice mismatch of 47%. Due to this large lattice mismatch, formation of single crystal hexagonal boron nitride is hindered, and disordered boron nitride or amorphous boron nitride is formed on the sapphire substrate.

  Hereinafter, a turbulent boron nitride structure formed on a 6H—SiC substrate will be described. FIG. 2 is a transmission electron microscope image of a heterointerface of a single-crystal turbulent boron nitride structure on a single-crystal 6H-SiC substrate grown at a substrate temperature of 1020 ° C. by flow modulation epitaxy using triethylboron and ammonia. is there. As shown, the 19% large lattice mismatch between the 6H-SiC substrate and the hexagonal boron nitride results in the formation of amorphous boron nitride at the heterointerface, on the amorphous boron nitride, several millimeters in size. The sp2-bonded boron nitride having the structure is formed in a random direction. Hexagonal boron nitride is a crystal structure having a three-dimensional order, and the structure in which the three-dimensional order structure is disturbed and the degree of disorder is increased is the disordered layer boron nitride. It has been reported that the lattice constant of the disordered layer boron nitride structure is larger than the lattice constant of the hexagonal boron nitride structure because the degree of disorder increases. Thus, it can be seen that a turbulent boron nitride structure is formed on a substrate having a large lattice mismatch.

  Similarly, boron nitride on a sapphire substrate also has a large lattice mismatch, so that in the prior art a turbostratic boron nitride structure is formed. Hereinafter, a turbulent boron nitride structure on a sapphire substrate formed using a conventional technique will be described (for example, see Non-Patent Document 3). The boron nitride described here is grown on a sapphire substrate by metal organic vapor phase epitaxy using ammonia and triethylboron as raw materials.

  FIG. 3 is a graph showing the growth temperature dependence of the lattice constant of boron nitride grown on a sapphire substrate using the prior art. The vertical axis represents the c-axis lattice constant (Å), and the horizontal axis represents the substrate temperature (° C.). The lattice constant was measured by X-ray diffraction measurement.

  As shown in the figure, the lattice constant of each boron nitride grown on the sapphire substrate at a substrate temperature of 900 ° C. to 1200 ° C. was 6.72 to 7.15 °. These lattice constants are larger than the c-axis lattice constant of 6.66Å of hexagonal boron nitride. That is, this result indicates that the crystal structure of boron nitride grown on the sapphire substrate by the conventional technique is a turbostratic boron nitride structure.

  Thus, in the prior art, there is a problem that the crystal structure of boron nitride grown on the sapphire substrate is turbostratic boron nitride. Turbulent boron nitride has a structure with increased disorder and reduced crystallinity compared to hexagonal boron nitride, so it is not suitable for elucidating the basic physical properties of hexagonal boron nitride. It also has a big problem from the viewpoint.

K. Wanatabe, T. Taniguchi, and H. Kanda, “Direct-bandgap properties and evidence for ultraviolet lasing of hexagonal boron nitride single crystal” Nature Materials, vol.3, pp.404, 2004. Y. Kobayashi, T. Nakamura, T. Akasaka, T. Makimoto, and N. Matumoto, “Hexagonal boron nitride on Ni (111) substrate grown by flow-rate modulation epitaxy” Journal of Crystal Growth, vol.298, pp. 325, 2007. K. Nakamura, “Preparation and Properties of Boron Nitride Films by Metal Organic Chemical Vapor Deposition” Journal of Electrochemical Society, vol.133, No.6, pp.1120, 1986.

  As described above, in the hexagonal boron nitride structure on the single crystal Ni (111) substrate, the Ni (111) substrate is extremely expensive, it is difficult to increase the area of 2 inches or the like, and it cannot be cleaved. There was a problem. Moreover, the disordered boron nitride structure on the sapphire substrate is a structure in which the three-dimensional ordered structure is disturbed and the degree of disorder increases, and there are many defects, dislocations, etc., to elucidate the basic physical properties of hexagonal boron nitride. There was a problem that it was not suitable.

  The present invention has been made in view of such problems, and the object of the present invention is economically inexpensive, suitable for elucidating the basic physical properties of hexagonal boron nitride that can be enlarged and cleaved. Another object is to provide a hexagonal boron nitride structure and a method for manufacturing the same.

  In order to achieve such an object, the hexagonal boron nitride structure according to claims 1 to 5 is characterized in that single crystal hexagonal boron nitride is formed on a sapphire single crystal substrate.

  Since the hexagonal boron nitride structure according to any one of claims 1 to 5 is formed on a sapphire single crystal substrate, the hexagonal boron nitride structure is formed at a lower cost than the hexagonal boron nitride structure on the Ni (111) substrate. It becomes possible to form. Further, the area can be increased to 2 inches, 3 inches, etc., and the hexagonal boron nitride structure can be cleaved.

  Further, the method for producing hexagonal boron nitride according to claims 6 and 7 includes a molar flow rate of ammonia as a group V raw material and triethylboron, trimethylboron, diborane, boron trichloride, or trifluoride as a group III raw material. The V / III ratio with respect to the molar flow rate of boron is 1000 or more.

  By doing so, it is possible to grow single crystal hexagonal boron nitride on the sapphire single crystal substrate while suppressing the growth of the turbulent boron nitride structure on the sapphire single crystal substrate.

  According to the present invention, hexagonal boron nitride can be grown on a sapphire substrate, and a hexagonal boron nitride structure on the sapphire substrate can be realized. As a result, it is possible to provide a hexagonal boron nitride structure on a sapphire substrate that is economically inexpensive and can be enlarged and cleaved.

  Hereinafter, a hexagonal boron nitride structure and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 4 is a view showing a hexagonal boron nitride structure on a sapphire substrate according to an embodiment of the present invention. As shown in the drawing, a (0001) single crystal hexagonal boron nitride 42 is formed on a (0001) sapphire single crystal substrate 41.

  FIG. 5 is a diagram showing an apparatus for manufacturing a hexagonal boron nitride structure according to an embodiment of the present invention. The apparatus for producing a hexagonal boron nitride structure according to an embodiment of the present invention includes a storage container 56 that stores triethylboron that is an organic metal, and a storage container 57 that stores ammonia that is a nitrogen source gas. In the storage container 56, triethylboron is stored in a liquid state, and is supplied to the organometallic gas line 51 by bubbling. The valve 54 a and the valve 54 b control the flow of triethylboron supplied from the storage container 56 to the vent line 53 and the organometallic gas line 51, respectively. The valve 54c and the valve 54d control the flow of ammonia supplied from the storage container 57 to the vent line 53 and the ammonia gas line 52, respectively.

  Triethylboron supplied from the storage container 56 and ammonia supplied from the storage container 57 are flowed by the hydrogen carrier gas 55 through the organometallic gas line 51 and the ammonia gas line 52, respectively, to the reaction furnace 58. Supplied. The organometallic triethylboron is set to about 0 ° C. by a thermostat (not shown). In the reaction furnace 58, single crystal hexagonal boron nitride grows on the (0001) sapphire single crystal substrate 41 placed on the substrate heater 59. When the hexagonal boron nitride is not grown, the organometallic triethylboron and ammonia are exhausted through the vent line 53.

  The procedure for forming a single crystal boron nitride structure on the sapphire single crystal substrate 41 using the manufacturing apparatus illustrated in FIG. 5 will be described below.

  First, the (0001) sapphire single crystal substrate 41 was set on the substrate heater 59 in the reaction furnace 58. Next, the substrate heater 59 was heated while flowing the hydrogen carrier gas 55 to raise the substrate surface temperature to 1080 ° C. Thereafter, the (0001) sapphire single crystal substrate 41 was thermally cleaned at 1080 ° C. for 10 minutes while flowing the hydrogen carrier gas 55. Next, organometallic triethylboron and ammonia were supplied onto the heated sapphire single crystal substrate 41 through the organometallic gas line 51 and the ammonia gas line 52, respectively. Here, the V / III ratio is defined as the ratio of the molar flow rate of triethylboron as a group III material to the molar flow rate of ammonia as a group V material. By changing the molar flow rate of ammonia and the molar flow rate of triethylboron, the V / III ratio was changed from 100 to 2000, and boron nitride was grown on the sapphire single crystal substrate. The film thickness of boron nitride formed on the sapphire single crystal substrate 41 was 0.3 μm.

  FIG. 6 shows the result of 2θ-ω X-ray diffraction measurement of boron nitride grown on the sapphire single crystal substrate 41 under the condition of V / III ratio 630. A (0006) diffraction peak of the sapphire single crystal substrate 41 was clearly observed at 2θ = 41.6 °, and a weak diffraction peak from boron nitride was observed at 2θ = 26.2 °. The c-axis lattice constant determined from the diffraction peak angle is 6.78Å, which is larger than the c-axis lattice constant of 6.66Å of hexagonal boron nitride. From this, it was found that the crystal structure of boron nitride grown under the condition of V / III ratio 630 was turbostratic boron nitride.

  On the other hand, FIG. 7 shows 2θ-ω X-ray diffraction measurement results of boron nitride grown under the condition of V / III ratio 1250 with increasing V / III ratio. In FIG. 7, as in FIG. 6, the (0006) diffraction peak of the sapphire single crystal substrate 41 was clearly observed at 2θ = 41.6 °. However, unlike the weak diffraction peak from the turbulent boron nitride observed in FIG. 6, a sharp diffraction peak and a weak diffraction peak from the boron nitride are observed at 2θ = 26.7 ° and 2θ = 55.0 °. It was. The lattice constant determined from the diffraction peak was 6.66Å, and it was found that the sharp diffraction peak and the weak diffraction peak were diffractions from (0002) and (0004) of hexagonal boron nitride, respectively. From this, it was found that hexagonal boron nitride was grown on the sapphire single crystal substrate by growing boron nitride under conditions where the V / III ratio was 1250 and the V / III ratio was larger.

  FIG. 8 is a graph showing the c-axis lattice constant determined by X-ray diffraction for each boron nitride grown with the V / III ratio varied from 100 to 2000. The vertical axis represents the c-axis lattice constant, and the horizontal axis represents the V / III ratio. The c-axis lattice constant of boron nitride grown under the condition where the V / III ratio is 1000 or less is 6.78 to 6.96Å, which is larger than the c-axis lattice constant of hexagonal boron nitride. This indicates that the boron nitride grown under these conditions has a turbostratic boron nitride structure. In contrast, the c-axis lattice constant of boron nitride grown under conditions where the V / III ratio was 1000 or more was 6.66 to 6.96. This indicates that the boron nitride grown under these conditions has a hexagonal boron nitride structure. Thus, a hexagonal boron nitride structure could be realized on a sapphire single crystal substrate by growing boron nitride under conditions where the V / III ratio was 1000 or more.

  FIG. 9 is a transmission electron microscope image of a heterointerface of a hexagonal boron nitride structure on a (0001) sapphire single crystal substrate grown under the condition of a V / III ratio of 1250. As shown in the drawing, (0001) hexagonal boron nitride is grown on a (0001) sapphire single crystal substrate. In the hexagonal boron nitride region, the structure was confirmed to grow in layers by sp2 bonding, and the lattice constant determined from the spacing between the layers was 6.66６. Therefore, from FIG. 9, it was confirmed that a hexagonal boron nitride structure was formed.

  Similarly, even when trimethylboron, diborane, boron trichloride, or boron trifluoride is used as the group III material in the vapor phase growth, the molar flow rate of the ammonia that is the group V material and the molar flow rate of the group III material A hexagonal boron nitride structure was formed on the (0001) sapphire single crystal substrate by vapor-phase growth of boron nitride under the condition that the V / III ratio was 1000 or more.

  The embodiment described above relates to a (0001) hexagonal boron nitride structure on a (0001) sapphire single crystal substrate. As described above, the lattice mismatch in the a-axis direction between the (0001) sapphire single crystal substrate and the (0001) hexagonal boron nitride is as large as 47%. In crystal growth, if the lattice mismatch between the substrate and the thin film on the substrate is small, a higher quality thin film structure is grown. The lattice mismatch in the a-axis direction between the (11-20) plane sapphire single crystal substrate and the hexagonal boron nitride is 5%, and the lattice mismatch in the a-axis direction between the (0001) plane sapphire single crystal substrate and the hexagonal boron nitride. Very small compared to 47%. Similar to the (0001) sapphire single crystal substrate, in the (11-20) plane sapphire single crystal substrate, triethylboron, trimethylboron, diborane, boron trichloride, or boron trifluoride is used as a group III material in vapor phase growth. When used, (11-20) sapphire is obtained by vapor-phase-growing boron nitride under the condition that the V / III ratio between the molar flow rate of ammonia as a group V raw material and the molar flow rate of the group III raw material is 1000 or more. A hexagonal boron nitride structure was formed on the single crystal substrate.

  Similarly, the lattice mismatch in the a-axis direction between the (1-102) plane sapphire single crystal substrate and the hexagonal boron nitride is 9%, and the (0001) plane sapphire single crystal substrate and the hexagonal boron nitride in the a-axis direction. Compared with the lattice mismatch of 47%, it is extremely small. Similar to the (0001) sapphire single crystal substrate, in the (1-102) plane sapphire single crystal substrate, triethylboron, trimethylboron, diborane, boron trichloride, or boron trifluoride is used as a group III material in vapor phase growth. When used, the vapor phase growth of boron nitride under the condition that the V / III ratio between the molar flow rate of ammonia, which is a Group V raw material, and the molar flow rate of the Group III raw material is 1000 or more, results in (1-102) plane. A hexagonal boron nitride structure was formed on the sapphire single crystal substrate.

  Thus, according to the present invention, a hexagonal boron nitride structure can also be formed on a (11-20) plane sapphire single crystal substrate and a (1-102) plane sapphire single crystal substrate.

It is an electron microscope image of a hexagonal boron nitride structure grown on a Ni (111) substrate by a conventional technique. It is an electron microscope image of the turbulent boron nitride structure grown on the 6H-SiC substrate by a conventional technique. It is a graph which shows the growth temperature dependence of the c-axis lattice constant of the turbostratic boron nitride grown on the sapphire substrate by the prior art. It is a figure which shows the hexagonal boron nitride structure on the sapphire single crystal substrate which concerns on one Embodiment of this invention. It is a figure which shows the manufacturing apparatus of the hexagonal boron nitride structure which concerns on one Embodiment of this invention. It is a figure which shows the X-ray-diffraction measurement result of the turbulent layer boron nitride grown by the V / III ratio 630 on the sapphire single-crystal board | substrate which concerns on one Embodiment of this invention. It is a figure which shows the X-ray-diffraction measurement result of the hexagonal boron nitride grown by the V / III ratio 1250 on the sapphire single crystal substrate which concerns on one Embodiment of this invention. It is a graph which shows the V / III ratio dependence of the c-axis lattice constant of the boron nitride grown on the sapphire single crystal substrate which concerns on one Embodiment of this invention. 4 is an electron microscopic image of a hexagonal boron nitride structure on a sapphire single crystal substrate according to an embodiment of the present invention.

Explanation of symbols

41 Sapphire substrate 42 Hexagonal boron nitride 51 Organometallic gas line 52 Ammonia gas line 53 Vent line 54a, 54b, 54c, 54d Valve 55 Hydrogen carrier gas 56, 57 Storage vessel 58 Reactor 59 Substrate heater

Claims (7)

  A hexagonal boron nitride structure comprising a sapphire single crystal substrate and a single crystal hexagonal boron nitride formed on the substrate.   The hexagonal boron nitride structure according to claim 1, wherein a main orientation plane of the substrate is a (0001) plane.   The hexagonal boron nitride structure according to claim 1, wherein a main orientation plane of the substrate is a (11-20) plane.   The hexagonal boron nitride structure according to claim 1, wherein a main orientation plane of the substrate is a (1-102) plane.   The hexagonal boron nitride structure according to claim 1, wherein a main orientation plane of the single crystal hexagonal boron nitride is a (0001) plane.   Single crystal hexagonal nitridation on a sapphire single crystal substrate by vapor phase growth method using group V source ammonia and group III source triethyl boron, trimethyl boron, dilabone, boron trichloride, or boron trifluoride A method for producing hexagonal boron nitride, characterized by forming boron.   The V / III ratio between the molar flow rate of the group V raw material ammonia and the molar flow rate of the group III raw material triethylboron, trimethylboron, diborane, boron trichloride, or boron trifluoride is 1000 or more. The method for producing hexagonal boron nitride according to claim 6.