JP5197283B2 - Aluminum nitride single crystal substrate, laminate, and manufacturing method thereof - Google Patents

Description

  The present invention relates to a novel aluminum nitride single crystal substrate, a laminate, and a production method thereof, and more specifically, an aluminum nitride single crystal substrate having a low impurity concentration and excellent optical characteristics, a laminate including the substrate, And a manufacturing method thereof.

  Aluminum nitride (AlN) has a large forbidden band of 6.2 eV and is a direct transition type semiconductor. Therefore, the same group III nitride as gallium nitride (GaN) and indium nitride (InN) is used. It is expected as an ultraviolet light-emitting device material including mixed crystals of

  In order to form a semiconductor element such as an ultraviolet light emitting element, a cladding layer, an active layer, etc. are provided between an n-type semiconductor layer electrically bonded to the n-electrode and a p-type semiconductor layer electrically bonded to the p-electrode. It is necessary to form a laminated structure including it, and from the viewpoint of light emission efficiency, it is important that any layer has high crystallinity, that is, there are few crystal dislocations and point defects. For these reasons, the above laminated structure is generally formed on a single crystal substrate (single crystal free-standing substrate) having sufficient mechanical strength to exist independently.

  The substrate for forming the laminated structure has a small difference in lattice constant and thermal expansion coefficient from a group III nitride single crystal such as aluminum gallium indium nitride (AlGaInN) forming the laminated structure, and further deterioration of the element. High thermal conductivity is required from the viewpoint of preventing the above. Therefore, in order to produce a semiconductor element containing aluminum nitride, it is advantageous to form the above layer structure using an Al-based group III nitride single crystal substrate as a substrate. Among them, it is considered that the substrate is preferably a substrate made of an aluminum nitride single crystal in order to reduce the dislocation density, defects, and cracks of the growth layer and improve the light emission efficiency.

  At present, the Al group III nitride single crystal substrate (aluminum nitride single crystal substrate) for forming the laminated structure is not commercially available. Therefore, usually by forming an aluminum nitride single crystal layer on a dissimilar single crystal substrate (base substrate) of sapphire, silicon (Si), or silicon carbide (SiC) and separating it from the base substrate, Attempts have been made to produce an aluminum nitride single crystal substrate for forming the laminated structure. As specific methods, a vapor phase growth method, a sublimation recrystallization method, and a growth method via a liquid phase are applicable.

  As the aluminum nitride single crystal substrate for forming the laminated structure, the crystallinity is high, the impurities are small, and the optical properties are excellent in order to reduce the dislocation density, defects and cracks of the growth layer and improve the light emission efficiency. Is required.

As the aluminum nitride single crystal substrate, a substrate obtained by a sublimation method is known (see Non-Patent Document 1). This Non-Patent Document 1 describes a high-purity aluminum nitride single crystal substrate in which the concentration of oxygen as an impurity is very low (the lowest value is 2.7 × 10 ¹⁷ atoms / cm ³ ). . However, the aluminum nitride single crystal substrate has an uneven oxygen concentration in the substrate because the oxygen concentration gradually decreases. Therefore, a more uniform aluminum nitride single crystal substrate is desired for use as a light emitting device. Further, in the sublimation method, aluminum nitride as a raw material has to be sublimated at a high temperature, and coloring problems cannot be avoided. In particular, when an aluminum nitride single crystal substrate for forming the above laminated structure is to be manufactured by a sublimation method, the aluminum nitride single crystal substrate is optically thick when it is thick enough to have a sufficient mechanical strength to exist independently. There was a problem that the characteristics were inferior.

  On the other hand, as a method of manufacturing the aluminum nitride single crystal substrate, a hydride vapor phase epitaxy (HVPE), which is a kind of vapor phase growth method, can be obtained because a single crystal having good crystallinity can be obtained at a high film formation rate. : Hydride Vapor Phase Epitaxy) method is attracting attention. In the HVPE method, an aluminum halide gas and a nitrogen source gas are supplied onto a sapphire, silicon, or silicon carbide base substrate to form an aluminum nitride single crystal layer on the base substrate (Patent Document 1). 2). In this HVPE method, a method of reducing oxygen impurities in an aluminum nitride single crystal to be obtained by bringing an aluminum halide gas as a source gas into contact with metal aluminum and then supplying it to the reaction zone is known ( (See Patent Document 3).

  The aluminum nitride single crystal layer (aluminum nitride single crystal substrate) obtained by these methods has a high growth rate, good crystallinity, and is very useful. However, according to the study by the present inventors, the aluminum nitride single crystal layer obtained by the above method is considered to be due to impurities derived from the base substrate of sapphire, silicon, or silicon carbide, and other factors. It was found that it contains a relatively large amount of atoms and silicon atoms, and there was room for improvement. Moreover, there is room for improvement in the method described in Patent Document 3 in which an aluminum halide gas is brought into contact with metal aluminum.

  In the HVPE method, the surface of the sapphire substrate is reduced and nitrided to form a sapphire substrate having an aluminum nitride single crystal thin film layer, and an aluminum nitride single crystal film is formed on the aluminum nitride single crystal thin film layer. A method of growing sapphire has also been studied (see Patent Documents 4 and 5).

Journal of Crystal Growth (2008), doi: 10.016 / j. jcrysgro. 2008.06032 JP 2006-114845 A JP 2006-253462 A JP 2007-42854 A JP 2006-240895 A JP 2006-240895 A

  According to the methods described in Patent Documents 4 and 5, since the aluminum nitride single crystal layer can be grown on the sapphire substrate via the aluminum nitride single crystal thin film layer, impurities derived from the sapphire substrate are nitrided. It is considered that the transition to the aluminum single crystal layer can be prevented. However, even with these methods, oxygen could not be reduced sufficiently.

  Accordingly, it is an object of the present invention to provide an aluminum nitride single crystal substrate having few impurities such as oxygen and silicon and having excellent optical characteristics, and to provide a method for producing the aluminum nitride single crystal substrate.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies. In particular, the cause of the relatively large amount of impurities such as oxygen atoms in the aluminum nitride single crystal layer (aluminum nitride single crystal substrate) obtained by the conventional HVPE method was examined. Then, the cause is determined to be due to the type of base substrate to be used, crystallinity (polarity), and conditions for growing an aluminum nitride single crystal layer, and by improving them, oxygen atoms that are impurities The present inventors have found that an aluminum nitride single crystal substrate having a very low concentration and the like and excellent optical characteristics can be produced, and the present invention has been completed.

That is, according to the first aspect of the present invention, the oxygen concentration is 2.5 × 10 ¹⁷ atoms / cm ³ or less, the spectral intensity (A) of the emission wavelength in photoluminescence measurement at 23 ° C. is 210 nm, and the spectral intensity of 360 nm ( B) is an aluminum nitride single crystal substrate having a ratio (A / B) of 0.50 or more. The aluminum nitride single crystal substrate can have a silicon concentration of 5.5 × 10 ¹⁷ atoms / cm ³ or less.

The second aspect of the present invention is a laminate having an aluminum nitride single crystal layer to be the aluminum nitride single crystal substrate of the first aspect of the present invention, wherein the oxygen concentration exceeds 2.5 × 10 ¹⁷ atoms / cm ³ and 2 on a surface having a nitrogen polarity .0 × ¹⁰ 19 atom / cm ³ or less of the aluminum nitride single crystal self-supporting substrate, the oxygen concentration is not more 2.5 × ¹⁰ 17 atom / cm ³ or less, the photoluminescence measurement at 23 ° C. Is a laminate in which an aluminum nitride single crystal layer having a ratio (A / B) of a spectral intensity (A) having an emission wavelength of 210 nm and a spectral intensity (B) of 360 nm of 0.50 or more is formed. In the stacked body, the silicon concentration of the aluminum nitride single crystal layer may be 5.5 × 10 ¹⁷ atoms / cm ³ or less.

The third aspect of the present invention is a method for producing the laminate of the second aspect of the present invention,
(1) a step of preparing an aluminum nitride single crystal free-standing substrate having an oxygen concentration exceeding 2.5 × 10 ¹⁷ atoms / cm ³ and not more than 2.0 × 10 ¹⁹ atoms / cm ³ , and (2) the aluminum nitride single crystal The temperature of the free-standing substrate is controlled in the range of 1400 ° C. or more and 1900 ° C. or less, and an aluminum halide gas and a nitrogen source gas are supplied onto the surface of the aluminum nitride single crystal free-standing substrate having a nitrogen polarity, and nitriding is performed. And a step of producing a laminate by vapor phase growth of an aluminum single crystal layer.

  In the third aspect of the present invention, in the step (1), the silicon single crystal base substrate is formed from the first laminate obtained by growing the first aluminum nitride single crystal layer on the silicon single crystal base substrate. The first aluminum nitride single crystal layer obtained by separation is preferably prepared as the aluminum nitride single crystal free-standing substrate. Furthermore, in the third invention, in the step (2), it is preferable to vapor-phase grow the aluminum nitride single crystal layer by supplying the nitrogen source gas first and then supplying the aluminum halide gas. .

  The fourth aspect of the present invention is a method for producing an aluminum nitride single crystal substrate comprising a step of separating at least the aluminum nitride single crystal free-standing substrate portion from the laminate obtained by the third aspect of the invention. Thus, the aluminum nitride single crystal substrate of the first invention can be easily manufactured.

  As described above, the first to fourth aspects of the present invention are related to each other. This relationship is shown in FIG. FIG. 1 shows an outline of the present invention. Referring to FIG. 1, first, a first aluminum nitride single crystal layer 12 is grown on an inorganic base substrate 11 to manufacture a first laminate 15. Next, an aluminum nitride single crystal layer obtained by separating the inorganic base substrate 11 from the first laminate 15 is prepared as an aluminum nitride single crystal free-standing substrate 16. Next, an aluminum nitride single crystal layer 17 is vapor-phase grown on the surface (nitrogen polar surface 14) of the aluminum nitride single crystal free-standing substrate 16 that has been in contact with the inorganic base substrate 11, and a laminated body 18 (second book) Invention). Then, by separating the aluminum nitride single crystal free-standing substrate from the laminate 18, the aluminum nitride single crystal substrate 19 according to the first invention can be obtained.

  According to the present invention, an aluminum nitride single crystal free-standing substrate containing a certain amount of oxygen is controlled to a specific temperature range, and an aluminum nitride single crystal layer is formed on the surface of the aluminum nitride single crystal free-standing substrate having a nitrogen polarity. By performing vapor phase growth, it is possible to manufacture a laminated body in which a uniform aluminum nitride single crystal layer having very high purity and no impurity unevenness is formed in the depth direction. In the present invention, since an aluminum nitride single crystal layer is further grown on the aluminum nitride single crystal free-standing substrate, the aluminum nitride single crystal layer can be stably grown even at a high temperature of 1400 ° C. or higher without cracks. Can be made.

  Then, by separating a portion of the aluminum nitride single crystal free-standing substrate containing oxygen from the laminate obtained by the method of the present invention, a high-purity aluminum nitride single crystal substrate having a very low oxygen and silicon concentration is obtained. Can be manufactured.

  The aluminum nitride single crystal substrate of the present invention is a substrate with extremely reduced concentrations of oxygen atoms and silicon atoms, which are impurities, and is excellent in optical characteristics. Therefore, it is effectively used as a substrate for an ultraviolet light emitting device. be able to.

  Thus, there is no conventional aluminum nitride single crystal substrate having high purity and excellent optical properties, and the laminate of the present invention, the method for producing the laminate, and the aluminum nitride single crystal substrate have industrial utility value. Very expensive.

(Aluminum nitride single crystal substrate)
In the present invention, the oxygen concentration is 2.5 × 10 ¹⁷ atoms / cm ³ or less, and the ratio of the spectral intensity (A) having an emission wavelength of 210 nm and the spectral intensity (B) of 360 nm in photoluminescence measurement at 23 ° C. This is an aluminum nitride single crystal substrate having (A / B) of 0.50 or more. In the aluminum nitride single crystal substrate of the present invention, the oxygen concentration does not change in the depth direction. The aluminum nitride single crystal substrate of the present invention may further have an oxygen concentration of 2.0 × 10 ¹⁷ atoms / cm ³ or less and a spectral intensity ratio (A / B) of 0.80 or more. As described above, the aluminum nitride single crystal substrate of the present invention has a very high purity that satisfies the above ranges for the oxygen concentration and the spectral intensity ratio (A / B), and has excellent optical characteristics. It can be suitably used for applications such as elements. Since the lower limit of the oxygen concentration is better, it is 0 atom / cm ^3. However, in consideration of industrial production, it is 1.0 × 10 ¹⁶ atom / cm ³ . The upper limit of the spectral intensity ratio (A / B) is not particularly limited, but is 20.00 in view of industrial production.

The aluminum nitride single crystal substrate of the present invention preferably has a silicon concentration of 5.5 × 10 ¹⁷ atoms / cm ³ or less, more preferably 5.0 × 10 ¹⁷ atoms / cm ³ or less. Since the lower limit of the silicon concentration is better, the lower limit is 0 atom / cm ³ , but it is 1 × 10 ¹⁶ atom / cm ³ in consideration of industrial production. Although described in detail below, the aluminum nitride single crystal substrate obtained by the method of the present invention has a silicon concentration in the above range even when an inorganic base substrate such as silicon is used or quartz is used as the material of the reactor. Will be reduced.

  Further, the thickness and size of the aluminum nitride single crystal substrate are not particularly limited, and may be determined as appropriate according to the intended use. Considering industrial production and applications, the thickness is usually 100 to 3000 μm, and the diameter of the substrate is 10 to 100 mm.

  An aluminum nitride single crystal substrate having such a high purity and excellent optical properties has not been known so far and has been achieved for the first time by the present invention.

(Laminate)
The laminate of the present invention has an oxygen concentration on a surface having a nitrogen polarity of an aluminum nitride single crystal free-standing substrate having an oxygen concentration of more than 2.5 × 10 ¹⁷ atoms / cm ³ and not more than 2.0 × 10 ¹⁹ atoms / cm ^3. The ratio (A / B) of the spectral intensity (A) having a concentration of 2.5 × 10 ¹⁷ atoms / cm ³ or less and an emission wavelength of 210 nm and a spectral intensity (B) of 360 nm in photoluminescence measurement at 23 ° C. An aluminum nitride single crystal layer having a thickness of 0.50 or more is formed. As will be described later, in the laminated body of the present invention, it is important that the aluminum nitride single crystal layer is formed on the surface having the nitrogen polarity of the aluminum nitride single crystal free-standing substrate.

  The aluminum nitride single crystal substrate of the present invention comprises an aluminum nitride single crystal layer portion obtained by separating the aluminum nitride single crystal free-standing substrate portion from the laminate.

(The aluminum nitride single crystal layer part of the laminate)
In the laminate of the present invention, the aluminum nitride single crystal layer has an oxygen concentration of 2.5 × 10 ¹⁷ atoms / cm ³ or less, preferably 2.0 × 10 ¹⁷ or less. In addition, the ratio (A / B) of the spectral intensity (A) having an emission wavelength of 210 nm and the spectral intensity (B) of 360 nm in photoluminescence measurement at 23 ° C. is 0.50 or more, preferably 0.80 or more. is there. Since the lower limit of the oxygen concentration is better, it is 0 atom / cm ^3. However, in consideration of industrial production, it is 1.0 × 10 ¹⁶ atom / cm ³ . The upper limit of the spectral intensity ratio (A / B) is not particularly limited, but is 20.0 in view of industrial production.

Further, the aluminum nitride single crystal layer preferably has a silicon concentration of 5.5 × 10 ¹⁷ atoms / cm ³ or less, more preferably 5.0 × 10 ¹⁷ atoms / cm ³ or less. The lower limit of the silicon concentration is better as it is lower, so it is 0 atom / cm ^3. However, in consideration of industrial production, it is 1.0 × 10 ¹⁶ atom / cm ³ .

  In addition, the thickness of the aluminum nitride single crystal layer may be determined according to the desired thickness of the aluminum nitride single crystal substrate, and therefore may be a thickness equal to or greater than the desired aluminum nitride single crystal substrate. Considering the industrial productivity of the laminate, the upper limit of the thickness is usually about 1000 μm. The aluminum nitride single crystal layer can be manufactured by the method described in detail below. At this time, the outermost surface of the aluminum nitride single crystal layer is a plane having aluminum polarity.

(The aluminum nitride single crystal free-standing substrate part of the laminate)
In the laminate of the present invention, the aluminum nitride single crystal free-standing substrate has an oxygen concentration of more than 2.5 × 10 ¹⁷ atoms / cm ³ and not more than 2.0 × 10 ¹⁹ atoms / cm ³ . Considering the productivity of the aluminum nitride single crystal free-standing substrate itself, the purity, optical characteristics, crystallinity, etc. of the aluminum nitride single crystal substrate finally obtained, the oxygen concentration is preferably 1.0 × 10 ¹⁸ to 1.0 × 10 ¹⁹ atoms / cm ³ . According to the present invention, even when an aluminum nitride single crystal self-supporting substrate containing the oxygen concentration is used, the resulting aluminum nitride single crystal substrate has few impurities such as oxygen concentration and has excellent optical characteristics.

  The aluminum nitride single crystal self-supporting substrate has a mechanical strength sufficient to exist independently, and its thickness is preferably 50 to 1000 μm. When the thickness of the aluminum nitride single-crystal free-standing substrate satisfies the above range, the aluminum nitride single-crystal free-standing substrate has a corresponding strength, so that it can be easily handled and the productivity of the aluminum nitride single-crystal substrate can be improved. it can. Further, the aluminum nitride single crystal free-standing substrate itself can be easily manufactured. In addition, the aluminum nitride single crystal free-standing substrate is preferably a single layer made of only an aluminum nitride single crystal in consideration of the purity, optical characteristics, etc. of the finally obtained aluminum nitride single crystal substrate. In the present invention, since the aluminum nitride single crystal layer can be stably grown even at a temperature of 1400 ° C. or higher by using the aluminum nitride single crystal free-standing substrate, the nitride is high in purity and excellent in optical characteristics. An aluminum single crystal layer (aluminum nitride single crystal substrate) can be manufactured stably.

(Growth plane of aluminum nitride single crystal layer: plane having nitrogen polarity)
In the laminate of the present invention, it is important that the aluminum nitride single crystal layer is formed on the surface of the aluminum nitride single crystal free-standing substrate having a nitrogen polarity. First, the polarity (nitrogen polarity, aluminum polarity) in an aluminum nitride single crystal will be described.

  The nitrogen polarity in the aluminum nitride single crystal indicates the orientation of the atomic arrangement as described in JP-A-2006-253462. The aluminum nitride single crystal has a hexagonal wurtzite structure. In the wurtzite structure, there is no target surface in the c-axis direction, and the crystal has a front-back relationship. When attention is paid to aluminum atoms, a crystal in which nitrogen atoms are arranged vertically above aluminum atoms is called aluminum polarity. On the other hand, a crystal in which aluminum atoms are arranged vertically above nitrogen atoms is called nitrogen polarity. Therefore, in the aluminum nitride single crystal film, the surface opposite to the surface having nitrogen polarity is a surface having aluminum polarity.

  This polarity can usually be determined by an etching process using an aqueous potassium hydroxide solution. For this determination, see Applied Physics Letter, Vol. 72 (1998) 2480 (Non-Patent Document 2), MRS Internet Journal Semiconductor Research, Vol. 7, no. 4, 1-6 (2002) (Non-Patent Document 3), JP-A-2006-253462 (Patent Document 2), and the like. In other words, in the aluminum nitride single crystal film, the surface having nitrogen polarity is dissolved by etching using an aqueous potassium hydroxide solution, while the opposite surface having aluminum polarity is formed using an aqueous potassium hydroxide solution. Even if it etches, it does not melt | dissolve. Therefore, in the present invention, when one surface is immersed in a 50% strength by weight potassium hydroxide aqueous solution heated to 50 ° C. for 5 minutes and observed with an electron microscope, the surface shape is before and after the immersion in the potassium hydroxide aqueous solution. A surface that has not changed at all is referred to as “a surface having aluminum polarity”, and a surface that has the surface shape changed on the opposite surface is referred to as “a surface having nitrogen polarity”.

  In the laminate of the present invention, both the surface on the aluminum nitride single crystal layer side and the surface on the aluminum nitride single crystal free-standing substrate side are surfaces having aluminum polarity. There is no change on both surfaces. Therefore, it is also possible to confirm whether or not the aluminum nitride single crystal layer is formed on the surface having the nitrogen polarity of the aluminum nitride single crystal free-standing substrate by etching the laminate.

  In the laminate of the present invention, the aluminum nitride single crystal layer is formed on the surface of the aluminum nitride single crystal free-standing substrate having a nitrogen polarity. As will be described in detail below, it is important for the laminate to grow an aluminum nitride single crystal layer on the surface under specific conditions.

(Laminate manufacturing method)
As described above, the aluminum nitride single crystal substrate of the present invention can be manufactured from the above laminated body. Next, a method for manufacturing this laminated body will be described.

In the present invention, the method for producing the laminate is as follows:
(1) a step of preparing an aluminum nitride single crystal free-standing substrate having an oxygen concentration exceeding 2.5 × 10 ¹⁷ atoms / cm ³ and not more than 2.0 × 10 ¹⁹ atoms / cm ³ , and (2) the aluminum nitride single crystal An aluminum nitride gas and a nitrogen source gas are supplied onto the surface of the aluminum nitride single crystal free-standing substrate having a nitrogen polarity, and the temperature of the free-standing substrate is controlled in the range of 1400 ° C. to 1900 ° C. And a step of producing a laminate by vapor-phase-growing a single crystal layer.

  The laminate obtained through the above steps can have an aluminum nitride single crystal layer with very high purity and excellent optical characteristics.

(Process (1) Preparation process of aluminum nitride single crystal free-standing substrate)
In the present invention, the step (1) is a step of preparing an aluminum nitride single crystal free-standing substrate having an oxygen concentration exceeding 2.5 × 10 ¹⁷ atoms / cm ³ and not more than 2.0 × 10 ¹⁹ atoms / cm ³ .

  In the step (1), a known method for producing an aluminum nitride single crystal free-standing substrate is employed. For example, a first laminate in which a first aluminum nitride single crystal layer is grown on an inorganic base substrate such as sapphire, silicon carbide, or silicon is manufactured by sublimation or HVPE, and the first laminate The first aluminum nitride single crystal layer obtained by separating the inorganic base substrate from the body can be an aluminum nitride single crystal free-standing substrate.

The range of the oxygen concentration in the aluminum nitride single crystal free-standing substrate of the present invention is not special, and is a range of a free-standing substrate obtained by a normal method. Therefore, by growing the first aluminum nitride single crystal layer on the inorganic base substrate by a known method, the oxygen concentration exceeds 2.5 × 10 ¹⁷ atoms / cm ³ and is 2.0 × 10 ¹⁹ atoms / cm ^3. An aluminum nitride single crystal self-supporting substrate of cm ³ or less can be manufactured (prepared). Above all, the method of growing the first aluminum nitride single crystal layer on the inorganic base substrate is characterized by the productivity of the first aluminum nitride single crystal layer (aluminum nitride single crystal free-standing substrate) and the finally obtained aluminum nitride single crystal layer. Considering the purity, optical characteristics, crystallinity, etc. of the crystal substrate, it is preferable to adopt the HVPE method. Below, the manufacturing method of the said aluminum nitride single crystal self-supporting board | substrate by HVPE method is demonstrated using FIG.

  The HVPE apparatus includes a main body composed of a cylindrical quartz glass reaction tube 21, an external heating means 22 disposed outside the reaction tube 21, and a support base 23 disposed inside the reaction tube 21. . Then, a carrier gas and a source gas (aluminum halide gas and a nitrogen source gas) are supplied from one end of the reaction tube 21, and the carrier gas and unreacted gas are supplied from an opening provided in the side wall near the other end. It is structured to discharge the reaction gas. The external heating means 22 is not intended to heat the inorganic base substrate 24, but is mainly used to maintain the temperature of the reaction gas in the reaction zone at a predetermined temperature, and is not necessarily essential. Absent. As the external heating means 22, a resistance heating heater, a high frequency heating device, a high frequency induction heating device, a lamp heater, or the like can be used. In this embodiment, a resistance heating heater is used. The support base 23 can hold the inorganic base substrate 24 on the upper surface thereof.

  The carrier gas can be a single gas of hydrogen, nitrogen, helium, or argon, or a mixed gas thereof. Impurity gas components such as oxygen, water vapor, carbon monoxide, or carbon dioxide are previously removed using a purifier. It is desirable to remove it.

  In the reaction tube on the source gas supply side in the apparatus shown in FIG. 2, for example, an aluminum halide gas diluted with a carrier gas is supplied from a nozzle 25, and a carrier is formed using a space between the nozzle 25 and the reaction tube wall as a flow path. Nitrogen source gas diluted with gas is supplied. Examples of the aluminum halide gas include aluminum monochloride gas and aluminum trichloride gas. If quartz glass is used for the reaction tube, aluminum trichloride gas may be used from the viewpoint of low corrosiveness to quartz glass. preferable. On the other hand, the nitrogen source gas is preferably ammonia gas in view of ease of handling. As a matter of course, it is preferable to use these source gases in which impurities such as oxygen are reduced as much as possible.

  The flow path of the aluminum halide gas is connected to an “aluminum halide gas supply source” (not shown) through a pipe. The aluminum halide gas supply source is, for example, a metal aluminum placed in a reaction tube made of quartz glass, heated to 500 ° C. by a resistance heating type electric furnace installed outside the reaction tube, and then a carrier such as hydrogen or nitrogen By supplying hydrogen chloride gas together with the gas and reacting the hydrogen chloride gas and metal aluminum, aluminum trichloride is generated and supplied to the nozzle 25. The generation of this aluminum halide gas can be carried out with reference to the method described in JP-A No. 2003-303774. Moreover, this aluminum halide gas can also reduce oxygen impurities by the method of Unexamined-Japanese-Patent No. 2007-42854.

  On the other hand, the nitrogen source gas flow path is connected to a “nitrogen source gas supply source” (not shown) via a flow rate adjusting means by piping, and the downstream side of the flow rate adjusting means is connected to the piping via the flow rate adjusting means. A pipe connected to the carrier gas supply source is connected so that the nitrogen source gas can be diluted with the carrier gas to a desired dilution factor.

  In the HVPE apparatus shown in FIG. 2, a composite heater in which a carbon heating element is coated with a material having good corrosion resistance such as boron nitride as necessary is used as the support base 23, and the inorganic base substrate 24 is provided on the support base 23. Install and heat. An electrode portion is provided on the end face of the heater, and electric power is applied to the support base from the outside via the electrode (the support base 23 is heated via the substrate support base energizing electrode 26 to thereby form an inorganic base substrate. 24 is controlled to a predetermined temperature).

  In the step (1) of the present invention, when the HVPE apparatus as described above is used, it is preferable to manufacture the first laminate under the following conditions. As specific manufacturing conditions, it is preferable that an aluminum halide gas is first brought into contact with the heated inorganic base substrate 24, and then an aluminum halide gas and a nitrogen source gas are brought into contact with the inorganic base substrate 24. . By doing so, the crystallinity of the first aluminum nitride single crystal layer (aluminum nitride single crystal free-standing substrate) is improved, and the crystallinity of the finally obtained aluminum nitride single crystal substrate can be improved.

  Further, other conditions are not particularly limited as long as aluminum nitride is epitaxially grown on the inorganic base substrate. The temperature of the inorganic base substrate when the first aluminum nitride single crystal layer is grown may be appropriately determined within the range of the decomposition temperature of the material to be used and the melting temperature or lower, preferably 1050 ° C. or higher and 1700 ° C. or lower. Preferably they are 1050 degreeC or more and 1500 degrees C or less, More preferably, they are 1100 degreeC or more and less than 1400 degreeC.

Moreover, the supply ratio of the aluminum halide gas and the nitrogen source gas may be appropriately determined according to the apparatus to be used, but the partial pressure of the aluminum halide gas is 1.0 × 10 ^{−5 to} 1.0 × 10 ^−. was supplied at ¹ atm, it is preferred to supply the partial pressure of the nitrogen source gas at ^{1.0 × 10 -5 ~1.0 × 10 -1} atm.

  Under the above conditions, aluminum nitride is epitaxially grown until the first aluminum nitride single crystal layer having a desired thickness is stacked on the inorganic base substrate. In addition, the thickness of the first aluminum nitride single crystal layer may be appropriately determined according to the desired thickness of the aluminum nitride single crystal free-standing substrate. In this way, the first laminated body can be manufactured. By separating the inorganic base substrate from the first laminated body, the first aluminum nitride single crystal layer that satisfies the oxygen concentration range, that is, An aluminum nitride single crystal free-standing substrate can be manufactured.

  In the present invention, in order to carry out the step (2) described in detail below, the surface having the nitrogen polarity of the aluminum nitride single crystal free-standing substrate (first aluminum nitride single crystal layer) must be exposed on the surface. When a 1st laminated body is manufactured by the sublimation method or the HVPE method by the said method, the surface which has a nitrogen polarity turns into the surface by the side of the inorganic base substrate of a 1st aluminum nitride single crystal layer. Therefore, in the present invention, it is necessary to separate the inorganic base substrate from the first laminate.

  In the present invention, the method for separating the inorganic base substrate from the first laminate may be determined according to the material of the base substrate to be used. Specifically, when a sapphire substrate or a silicon carbide substrate is used, since the substrate has chemical durability, it must be mechanically cut. In addition, in the case of a silicon single crystal substrate, it can be removed by a chemical etching process, for example, an etching process using a mixed acid such as hydrofluoric acid, nitric acid, and acetic acid, in addition to a mechanical cutting method. Relative to the mechanical cutting method, separating the inorganic base substrate by a chemical etching process causes less damage to the first aluminum nitride single crystal layer, and no polishing process is required. Can be put out. Therefore, it is preferable to use a substrate made of silicon single crystal as the inorganic base substrate.

By following the method as described above, the oxygen concentration exceeds 2.5 × 10 ¹⁷ atoms / cm ³ and is 2.0 × 10 ¹⁹ atoms / cm ³ or less, preferably 1.0 × 10 ^{18 to} 1.0 × 10 6. ^An aluminum nitride single crystal free-standing substrate of ¹⁹ atoms / cm ³ can be prepared. Next, process (2) is demonstrated.

(Process (2))
In the present invention, in step (2), the temperature of the aluminum nitride single crystal free-standing substrate is controlled to be in the range of 1400 to 1900 ° C., and the halogenated surface of the aluminum nitride single crystal free-standing substrate has a nitrogen polarity. In this process, an aluminum gas and a nitrogen source gas are supplied, and an aluminum nitride single crystal layer is vapor-phase grown on the surface to produce a laminate. When performing the step (2), the aluminum nitride single crystal free-standing substrate is etched with an aqueous potassium hydroxide solution using the aluminum nitride single crystal free-standing substrate manufactured under the same conditions, and the polar surface is confirmed. Use after.

  In the step (2), an aluminum halide gas and a nitrogen source gas are supplied onto the surface of the aluminum nitride single crystal free-standing substrate obtained in the step (1) having a nitrogen polarity, and the aluminum nitride single crystal layer is gasified. Phase growth is performed to produce a laminate. That is, the aluminum nitride single crystal layer is vapor-phase grown by the HVPE method. The HVPE method in this step (2) can basically be carried out using the apparatus and raw material gas described in step (1). As a matter of course, in the step (2), the aluminum nitride single crystal free-standing substrate obtained in the step (1) is used instead of the inorganic base substrate.

  In step (2), when the aluminum nitride single crystal layer is grown by the HVPE method, the temperature of the aluminum nitride single crystal free-standing substrate on which the aluminum nitride single crystal layer is grown and the surface on which the aluminum nitride single crystal layer is grown are surfaces having nitrogen polarity. This is very important.

  When the aluminum nitride single crystal layer is grown, the temperature of the aluminum nitride single crystal free-standing substrate on which the aluminum nitride single crystal layer is grown must be 1400 ° C. or higher and 1900 ° C. or lower. When the temperature of the aluminum nitride single crystal free-standing substrate is less than 1400 ° C., the oxygen concentration of the resulting aluminum nitride single crystal layer (and thus the aluminum nitride single crystal substrate) cannot be sufficiently reduced, and sufficient optical properties are obtained. There is a tendency not to improve. On the other hand, when it exceeds 1900 ° C., the aluminum nitride single crystal itself may be decomposed, which is not preferable. In order to efficiently produce an aluminum nitride single crystal layer with further reduced oxygen concentration and excellent optical properties, the temperature of the aluminum nitride single crystal free-standing substrate on which the aluminum nitride single crystal layer grows is preferably 1400 ° C. The temperature is 1700 ° C. or lower, more preferably 1450 ° C. or higher and 1600 ° C. or lower.

  When the aluminum nitride single crystal layer is grown at a temperature lower than the temperature of the present invention, the inventors transferred impurities from the aluminum nitride single crystal free-standing substrate, and used the material used for the reaction tube (for example, quartz It is presumed that the grown aluminum nitride single crystal layer contains a large amount of impurities such as oxygen due to oxygen uptake from the like. Therefore, in the methods of Patent Documents 4 and 5 in which an aluminum nitride single crystal layer is grown on a conventional sapphire substrate having an aluminum nitride single crystal thin film layer on the surface, the aluminum nitride single crystal thin film layer is thin, so Since it is affected by the sapphire substrate and the aluminum nitride single crystal layer is grown only at a temperature of 1250 ° C. at most, it is considered that the obtained aluminum nitride single crystal layer contains a large amount of oxygen. In the methods of Patent Documents 4 and 5, an aluminum nitride single crystal thin film layer is laminated on a sapphire substrate. However, since the sapphire substrate is inferior in heat resistance to a substrate made of aluminum nitride, the temperature is 1400 ° C. or higher. Then, the sapphire substrate is decomposed. In the present invention, by using an aluminum nitride single crystal free-standing substrate, an aluminum nitride single crystal layer can be grown at a temperature of 1400 ° C. or higher, which is excellent in terms of heat resistance.

  Furthermore, in step (2), the aluminum nitride single crystal free-standing substrate is controlled to the above temperature range, and an aluminum nitride single crystal layer is not grown on the surface of the aluminum nitride single crystal free-standing substrate having a nitrogen polarity. Don't be. When the temperature of the aluminum nitride single crystal free-standing substrate was controlled within the above range and the aluminum nitride single crystal layer was grown on the aluminum polar surface of the substrate, the aluminum nitride single crystal layer was grown at a temperature lower than the above temperature range Compared to the case, the effect of reducing the oxygen concentration in the aluminum nitride single crystal layer is confirmed. However, it has been found that in order to further reduce the oxygen concentration in the aluminum nitride single crystal layer, the aluminum nitride single crystal layer must be grown on the surface having the nitrogen polarity of the aluminum nitride single crystal free-standing substrate. The reason for this is not clear, but it is thought that the growth of the aluminum nitride single crystal layer on the surface having nitrogen polarity may prevent the migration of oxygen contained in the aluminum nitride single crystal free-standing substrate.

  When an aluminum nitride single crystal free-standing substrate is manufactured once by a known method, as described above, the surface in contact with the inorganic base substrate made of a material different from aluminum nitride such as sapphire, silicon carbide, silicon, etc. has a surface having nitrogen polarity. Become. Therefore, when an aluminum nitride single crystal layer is grown on a surface that is in direct contact with a material different from that of aluminum nitride, it is affected by the material. For sapphire, oxygen, silicon carbide, and silicon can be used. In general, it is considered that silicon may be taken into a single crystal to be grown. However, contrary to this estimation, it is usually unpredictable that the oxygen concentration can be reduced by growing the aluminum nitride single crystal layer on the surface of the aluminum nitride single crystal free-standing substrate having the nitrogen polarity.

  Furthermore, in the present invention, as described in the step (1), it is preferable to manufacture the aluminum nitride single crystal free-standing substrate on the silicon single crystal substrate, but the temperature of the aluminum nitride single crystal free-standing substrate is controlled within the above range. In addition, an aluminum nitride single crystal layer (aluminum nitride single crystal substrate) having a very low silicon concentration is manufactured by growing an aluminum nitride single crystal layer by HVPE on the surface of the substrate having nitrogen polarity. be able to.

In the laminate manufactured under the above conditions, the aluminum nitride single crystal layer portion of the laminate has an oxygen concentration of 2.5 × 10 ¹⁷ atoms / cm ³ or less, preferably 2.0 × 10 ¹⁷ atoms. / Cm ³ or less, and the ratio (A / B) of the spectral intensity (A) of the emission wavelength of 210 nm and the spectral intensity (B) of 360 nm in the photoluminescence measurement at 23 ° C. is 0.50. As mentioned above, Preferably it can be 0.80 or more. Further, even when the first aluminum nitride single crystal layer grown on the silicon single crystal base substrate is used as an aluminum nitride single crystal free-standing substrate, the aluminum nitride single crystal layer has a silicon concentration of 5.5 × 10 ^17. Attom / cm ³ or less, more preferably 5.0 × 10 ¹⁷ atoms / cm ³ or less is satisfied.

In the present invention, other production conditions in the step (2) are not particularly limited as long as the aluminum nitride single crystal layer is grown. In particular, in order to form an aluminum nitride single crystal layer with fewer impurities and excellent optical characteristics, in step (2), the aluminum nitride single crystal self-supported in the temperature range (1400 ° C. to 1900 ° C.) is used. Preferably, the substrate is first brought into contact with a nitrogen source gas, and then an aluminum halide gas and a nitrogen source gas are supplied to the reaction zone. The supply ratio of these raw material gases may be appropriately determined according to the reactor and the like, but the partial pressure of the aluminum halide gas is 1.0 × 10 ^{−5 to} 1.0 × 10 ⁻¹ atm, the nitrogen source It is preferable to supply the gas with a partial pressure of 1.0 × 10 ^{−5 to} 1.0 × 10 ⁻¹ atm. In this case, as a matter of course, the carrier gas can be simultaneously supplied.

  Under the above conditions, the aluminum nitride single crystal layer is grown on the aluminum nitride single crystal free-standing substrate until the desired thickness of the aluminum nitride single crystal layer (the thickness of the aluminum nitride single crystal substrate) is reached. Good.

  In step (2), an aluminum nitride single crystal layer having low oxygen concentration, low silicon concentration, high purity, and excellent optical characteristics was formed on the aluminum nitride single crystal free-standing substrate by the above method. A laminate can be manufactured.

  The aluminum nitride single crystal substrate of the present invention can be obtained by separating the aluminum nitride single crystal self-supporting substrate portion from the laminate. Next, this separation method will be described.

(Step of separating the aluminum nitride single crystal free-standing substrate from the laminate (production of aluminum nitride single crystal substrate))
The aluminum nitride single crystal substrate of the present invention can be obtained through a step of separating at least the aluminum nitride single crystal free-standing substrate portion from the laminate obtained through the step (2). As a method of separating the aluminum nitride single crystal free-standing substrate from the laminate, a known method can be adopted. Specifically, the aluminum nitride substrate can be separated by mechanically polishing the laminate. It is.

  The obtained aluminum nitride single crystal substrate has very few impurities and is excellent in optical characteristics, so that it can be used in various applications such as a substrate for a deep ultraviolet light emitting element.

  EXAMPLES The present invention will be described in detail below using examples, but the present invention is not limited to the following examples.

  First, a method for measuring each physical property will be described.

(1) Measuring method of oxygen concentration and silicon concentration For the measurement of oxygen concentration and silicon concentration, secondary ion mass spectrometry (SIMS) is used because of the feature that elements existing near the surface can be detected with high sensitivity. ) Method. The measuring device used was IMS-4f manufactured by CAMECA. In the measurement, the acceleration voltage was 14.5 kv, and the measurement was performed by irradiating a region of 30 μmφ with an incident angle of 60 ° (in the sample normal direction) with a primary ion beam of cesium ions. The average values of the O ⁺ and Si ⁺ secondary ion intensity profiles in the depth direction obtained at this time were defined as oxygen concentration and silicon concentration.

(2) Calculation method of spectral intensity ratio by photoluminescence measurement at 23 ° C. As a measuring device, HR800 UV (laser light source: ExciStarS-200) manufactured by HORIBA, Ltd. was used. Using a 193 nm ArF laser as an excitation light source, the sample was irradiated to excite the sample. At this time, ArF laser was irradiated perpendicularly to the sample. Luminescence generated from the sample was imaged with a focusing lens and then detected with a spectroscope to obtain spectral intensity with respect to wavelength. The measurement conditions were as follows: measurement temperature was room temperature, irradiation time was 10 seconds, integration was 3 times, hole diameter was 1000 μm, and grating was 300 grooves / mm. The temperature at the time of measurement is 23 ° C.

  Focusing on the spectral intensity (A) of 210 nm, which is the band edge emission of aluminum nitride, and the spectral intensity (B) of 360 nm derived from oxygen as an impurity, normalization was performed using the following formula, and the spectral intensity ratio was calculated. .

  Formula: (spectral intensity ratio (A / B)) = (spectral intensity (A) at 210 nm) / (spectral intensity (B) at 360 nm).

Example 1
As the vapor phase growth apparatus, an HVPE reactor having a structure shown in FIG. 2 was used. In addition, as a source gas serving as an aluminum source, aluminum trichloride gas obtained by reacting metal aluminum and hydrogen chloride gas according to the method described in JP-A-2003-303774 was used. Further, according to the method disclosed in Japanese Patent Application Laid-Open No. 2007-42854, aluminum trichloride gas having a reduced oxygen impurity concentration was used by contacting the aluminum trichloride gas with metal aluminum. In addition to the support base 23 having a heater function, the apparatus includes “a temperature of a region in which aluminum trichloride gas is generated” and “a region in which aluminum nitride is deposited by reacting the generated aluminum trichloride gas with a nitrogen source gas”. A device having a hot wall type resistance heating device capable of simultaneously controlling “temperature” was used.

(Method for producing the first laminate)
After the silicon single crystal (111) base substrate (inorganic base substrate 24) is placed on the support base 23 in the reactor, the atmosphere in the reaction tube 21 is changed to hydrogen (partial pressure: 0.70 atm) and nitrogen ( A mixed gas circulation atmosphere with a partial pressure of 0.30 atm) was used. Electric power was gradually applied to the heater of the support base 23 to gradually heat the silicon single crystal (111) base substrate to 1230 ° C. After heating, first, aluminum trichloride was supplied, and then ammonia gas was supplied to start growth of the aluminum nitride single crystal. At this time, the supply partial pressure of aluminum trichloride gas was 6.0 × 10 ⁻⁴ atm, and the supply partial pressure of ammonia gas was 2.4 × 10 ⁻³ atm. The growth temperature (temperature of the silicon single crystal base substrate) was set to 1230 ° C., and this state was maintained for 420 minutes to grow the first aluminum nitride single crystal layer, thereby manufacturing the first laminate.

  The crystal growth was terminated by stopping the supply of aluminum trichloride after a lapse of a predetermined time, and the cooling of the external and local heating devices was started. At this time, in order to prevent re-decomposition of the first aluminum nitride single crystal layer grown on the silicon single crystal base substrate, ammonia gas was circulated through the reaction tube 21 until the temperature of the silicon single crystal base substrate became 550 ° C. or lower. . After confirming that the heating device had dropped to near room temperature, the first laminate was taken out from the reaction tube 21. When the thickness of the 1st aluminum nitride single-crystal layer was confirmed with the electron microscope, it was 110 micrometers.

(Method of manufacturing aluminum nitride single crystal free-standing substrate)
Next, a solution for chemical etching in which hydrofluoric acid (concentration 49% by weight), nitric acid (concentration 70% by weight), acetic acid (concentration 99% by weight), and ultrapure water were mixed at a volume ratio of 1: 2: 1: 2. The first laminated body was immersed in 200 ml for 12 hours to dissolve and remove silicon as a base substrate. Subsequently, it was washed with ultrapure water to remove the chemical etching solution, and an aluminum nitride single crystal free-standing substrate was obtained.

Here, the oxygen concentration and the silicon concentration of the aluminum nitride single crystal free-standing substrate were measured by SIMS measurement. As a result of measurement, the oxygen concentration was 1.0 × 10 ¹⁹ atoms / cm ³ , and the silicon concentration was 5.0 × 10 ¹⁹ atoms / cm ³ . Further, when the thickness of the aluminum nitride single crystal free-standing substrate was confirmed with an electron microscope, it was 110 μm which was the same as the thickness of the first aluminum nitride single crystal.

(Confirmation of polarity surface)
An aluminum nitride single crystal self-supporting substrate manufactured by the same method was immersed in a 50 mass% potassium hydroxide aqueous solution heated to 50 ° C. for 5 minutes, and the polar surface was confirmed by electron microscope observation of the surface before and after deposition. As a result, on the surface in contact with the silicon single crystal base substrate, it was confirmed that the shape was changed before and after immersion in the aqueous potassium hydroxide solution, and the other surface was confirmed to be unchanged before and after immersion. . In the aluminum nitride single crystal free-standing substrate, it was confirmed that the surface in contact with the silicon single crystal base substrate was a nitrogen polar surface.

(Laminate manufacturing method)
The aluminum nitride single crystal free-standing substrate obtained by the above method was placed on the support base 23 in FIG. After the nitrogen polar face of a 3 × 5 mm rectangular and 110 μm thick aluminum nitride (0001) single crystal free-standing substrate is placed on the upper side (surface), the atmosphere in the reaction tube 21 is hydrogen (partial pressure: 0.70 atm). ) And nitrogen (partial pressure: 0.30 atm). Thereafter, electric power was gradually applied to the heater of the support base 23 to heat the aluminum nitride single crystal free-standing substrate. When the temperature of the aluminum nitride single crystal free-standing substrate reaches 550 ° C., the atmosphere in the reaction tube 21 is changed to hydrogen (partial pressure: 0.7 atm), nitrogen (partial pressure: 0.3 atm), and ammonia gas (partial pressure). : 2.0 × 10 ⁻³ atm). The reason why ammonia gas coexists at the above partial pressure is to prevent decomposition of the single crystal aluminum nitride substrate. In this state, the aluminum nitride single crystal substrate was gradually heated until the temperature reached 1450 ° C. After heating, first, ammonia gas was supplied, and then aluminum trichloride gas was supplied to start growth of the aluminum nitride single crystal. The supply partial pressure of aluminum trichloride gas at this time was 5.0 × 10 ⁻⁴ atm, and the supply partial pressure of ammonia gas was 2.0 × 10 ⁻³ atm. The growth temperature (the temperature of the aluminum nitride single crystal substrate) was set to 1450 ° C., and this state was maintained for 240 minutes to grow the aluminum nitride single crystal layer, thereby producing a laminate.

  The crystal growth was terminated by stopping the supply of aluminum trichloride after a lapse of a predetermined time, and the cooling of the external and local heating devices was started. At this time, in order to prevent re-decomposition of the aluminum nitride single crystal layer grown on the aluminum nitride single crystal free-standing substrate, ammonia gas was circulated through the reaction tube until the temperature of the laminated body became 550 ° C. or lower. After confirming that the heating device had dropped to near room temperature, the laminate was taken out of the reactor. The thickness of this laminate was 190 μm, and the thickness of the grown aluminum nitride single crystal layer was confirmed to be 80 μm.

  Moreover, when this laminated body was evaluated by the same method as the confirmation of the polar surface, it was confirmed that there was no change in shape before and after being immersed in an aqueous potassium hydroxide solution on either the upper surface or the lower surface.

(Production and evaluation of aluminum nitride single crystal substrate)
The aluminum nitride single crystal free-standing substrate portion was separated from the laminate obtained by the above method by mechanical polishing. The obtained aluminum nitride single crystal layer portion was used as an aluminum nitride single crystal substrate, and the following evaluation was performed.
The obtained aluminum nitride single crystal substrate was measured for oxygen concentration and silicon concentration by SIMS measurement. As a result of measurement, the oxygen concentration is constant at 2.0 × 10 ¹⁷ atoms / cm ³ in the depth direction, and the silicon concentration is also 5.0 × 10 ¹⁷ atoms in the depth direction. It was constant at / cm ³ . On the other hand, as a result of calculating the spectral intensity ratio between 210 nm and 360 nm by photoluminescence measurement, it was 1.04.

Comparative Example 1
(Laminate manufacturing method)
The aluminum nitride single crystal free-standing substrate obtained by the method shown in Example 1 was used. Aluminum nitride according to the conditions of Example 1 except that the aluminum polar surface of the aluminum nitride (0001) single crystal free-standing substrate having a rectangle of 3 × 5 mm and a thickness of 110 μm was placed on the support base 23 as the upper side (surface). A single crystal layer was grown to produce a laminate. The thickness of the aluminum nitride single crystal layer in the laminate was 80 μm.
(Production and evaluation of aluminum nitride single crystal substrate)
The aluminum nitride single crystal self-supporting substrate was separated from the obtained laminate in the same manner as in Example 1, and the aluminum nitride single crystal layer was taken out and evaluated as an aluminum nitride single crystal substrate.

The obtained aluminum nitride single crystal substrate was measured for oxygen concentration and silicon concentration by SIMS measurement. As a result of measurement, the oxygen concentration was 4.0 × 10 ¹⁷ atoms / cm ³ , and the silicon concentration was 7.0 × 10 ¹⁷ atoms / cm ³ . On the other hand, as a result of calculating the intensity ratio of the spectra of 210 nm and 360 nm by photoluminescence measurement, it was 0.91.

Comparative Example 2
(Laminate manufacturing method)
In the manufacturing method of the laminated body of Comparative Example 1, the same operation as Comparative Example 1 was performed except that the temperature of the aluminum nitride single crystal free-standing substrate was 1230 ° C. and the laminated body was produced. The thickness of the aluminum nitride single crystal layer in the obtained laminate was 40 μm.
(Production and evaluation of aluminum nitride single crystal substrate)
The aluminum nitride single crystal self-supporting substrate was separated from the obtained laminate in the same manner as in Example 1, and the aluminum nitride single crystal layer was taken out and evaluated as an aluminum nitride single crystal substrate.

The obtained aluminum nitride single crystal substrate was measured for oxygen concentration and silicon concentration by SIMS measurement. As a result of measurement, the oxygen concentration was 1.0 × 10 ¹⁹ atoms / cm ³ , and the silicon concentration was 2.0 × 10 ¹⁸ atoms / cm ³ . Next, the intensity ratio of the spectra of 210 nm and 360 nm was calculated by photoluminescence measurement and found to be 0.29.

Comparative Example 3
An aluminum nitride single crystal layer was grown according to the conditions of Example 1 except that a sapphire (0002) substrate having a 7 × 11 mm rectangle and a thickness of 380 μm was placed on the support base 23. When the laminated body was taken out from the reaction apparatus after completion of the growth, a large number of pits and cracks existed, and an aluminum nitride single crystal could not be grown.

  While the present invention has been described in connection with embodiments that are presently the most practical and preferred, the present invention is not limited to the embodiments disclosed herein. Rather, it can be changed as appropriate without departing from the scope or spirit of the invention that can be read from the claims and the entire specification, and an aluminum nitride single crystal substrate, a laminate, and a method for producing the laminate are also included. Moreover, it should be understood as being included in the technical scope of the present invention.

It is the schematic which shows the outline | summary and manufacturing method of this invention. It is a schematic diagram of the HVPE apparatus used by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Inorganic base substrate 12 1st aluminum nitride single crystal layer 13 Aluminum polar surface 14 Nitrogen polar surface 15 First laminated body 16 Aluminum nitride single crystal free-standing substrate 17 Aluminum nitride single crystal layer 18 Laminated body 19 Aluminum nitride single crystal substrate 21 Reaction tube 22 made of quartz glass External heating device 23 Support base 24 Inorganic base substrate 25 Nozzle 26 Substrate support base energizing electrode

Claims (8)

The ratio (A / B) of the spectral intensity (A) having an oxygen concentration of 2.5 × 10 ¹⁷ atoms / cm ³ or less and an emission wavelength of 210 nm and a spectral intensity (B) of 360 nm in photoluminescence measurement at 23 ° C. ) Is 0.50 or more aluminum nitride single crystal substrate. The aluminum nitride single crystal substrate according to claim 1, wherein the silicon concentration is 5.5 × 10 ¹⁷ atoms / cm ³ or less. The oxygen concentration is 2.5 × ¹⁰ 17 atom / cm ³ and more than 2.0 × ¹⁰ 19 atom / cm ³ surface on having a nitrogen polarity following the aluminum nitride single crystal self-supporting substrate, the oxygen concentration is 2 × ¹⁰ 17 atom / Cm ³ or less, and the ratio (A / B) of the spectral intensity (A) having a light emission wavelength of 210 nm and the spectral intensity (B) of 360 nm in photoluminescence measurement at 23 ° C. is 0.5 or more A laminate in which a single crystal layer is formed. The laminated body according to claim 3, wherein the aluminum nitride single crystal layer has a silicon concentration of 5.5 × 10 ¹⁷ atoms / cm ³ or less. A method for producing the laminate according to claim 3 or 4,
(1) a step of preparing an aluminum nitride single crystal free-standing substrate having an oxygen concentration exceeding 2.5 × 10 ¹⁷ atoms / cm ³ and not more than 2.0 × 10 ¹⁹ atoms / cm ³ , and (2) the aluminum nitride single crystal The temperature of the free-standing substrate is controlled in the range of 1400 ° C. or more and 1900 ° C. or less, and an aluminum halide gas and a nitrogen source gas are supplied onto the surface of the aluminum nitride single crystal free-standing substrate having a nitrogen polarity, and nitriding And a step of producing a laminate by vapor phase growth of an aluminum single crystal layer. 6. The stacked layer according to claim 5, wherein in the step (2), the nitrogen nitride single crystal layer is vapor-phase grown by supplying the nitrogen source gas first and then supplying the aluminum halide gas. Body manufacturing method. In the step (1), a first aluminum nitride obtained by separating the silicon single crystal base substrate from the first laminate obtained by growing the first aluminum nitride single crystal layer on the silicon single crystal base substrate. The method for producing a laminate according to claim 5 or 6, wherein a single crystal layer is prepared as the aluminum nitride single crystal free-standing substrate. The manufacture of an aluminum nitride single crystal substrate comprising a step of separating at least the aluminum nitride single crystal free-standing substrate portion from the obtained laminate after producing the laminate by the method according to claim 5. Method.

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