JP6579951B2 - Aluminum nitride single crystal laminate, method for producing the laminate, and method for producing a semiconductor device using the laminate - Google Patents

Description

  The present invention relates to a novel aluminum nitride single crystal laminate, a method for producing the laminate, and a novel method for producing a semiconductor element using the laminate.

  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, an active layer or the like is provided between an n-type semiconductor layer electrically bonded to an n-type electrode and a p-type semiconductor layer electrically bonded to a p-type 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, few crystal dislocations and point defects. For these reasons, the above structure is generally formed on a single crystal substrate with high crystallinity (single crystal free-standing substrate) having sufficient mechanical strength to exist independently.

  The single crystal substrate 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) formed on the single crystal substrate, and a viewpoint of preventing deterioration of the device. Therefore, high thermal conductivity is required. Therefore, in order to manufacture a semiconductor element containing aluminum nitride, it is advantageous to form the above layer structure on an Al-based group III nitride single crystal substrate. Among them, as the substrate, in order to reduce the dislocation density, defects, and cracks of the element layer grown on the substrate and improve the light emission efficiency, the crystallinity is high, the impurities are small, and the optical characteristics are excellent. A substrate made of a single crystal of aluminum nitride is considered preferable.

  In general, a c-axis oriented aluminum nitride single crystal has two types of polarity: aluminum polarity and nitrogen polarity. The polarity in the aluminum nitride single crystal indicates the direction of atomic arrangement (see, for example, Patent Document 1). The aluminum nitride single crystal has a hexagonal wurtzite structure. In the wurtzite structure, there is no symmetry plane with respect to the c-axis direction, and the crystal has a front-back relationship. A crystal in which a nitrogen atom is arranged vertically upward from an aluminum atom is called aluminum polarity, and a crystal in which an aluminum atom is arranged vertically upward from a nitrogen atom is called nitrogen polarity. Therefore, normally, in the aluminum nitride single crystal film, the surface opposite to the surface having nitrogen polarity (nitrogen polarity surface) is a surface having aluminum polarity (aluminum polarity surface).

  In the aluminum polar plane of the aluminum nitride single crystal, one nitrogen atom appearing on the surface is bonded to one aluminum atom, and in the nitrogen polar plane, one nitrogen atom appearing on the surface is bonded to three aluminum atoms. ing. When a group III nitride semiconductor is grown on a nitrogen polar surface, the growth rate is slow because there is only one bond of a nitrogen atom to a group III atom flying during the growth, and the bonding force becomes weak. In addition, for the same reason, group III vacancies are easily formed, and the crystal quality may be inferior compared to the case where a group III nitride semiconductor layer is grown on the aluminum polar surface.

  From the above, it may be inappropriate to use the nitrogen polar surface as the growth surface of the semiconductor element layer. Growth of the semiconductor element layer is necessary. Therefore, when an aluminum nitride single crystal substrate is used as a substrate for manufacturing a semiconductor device, a semiconductor device layer is generally formed on the aluminum polar surface, and the nitrogen polar surface, which is the back surface, is exposed. .

  The present inventors have proposed that an aluminum nitride single crystal substrate having a low oxygen concentration can be manufactured by growing a second aluminum nitride single crystal on the nitrogen polar face of the first aluminum nitride single crystal substrate. (See Patent Document 2). Specifically, such a substrate is manufactured as follows. First, a first aluminum nitride single crystal layer is grown on a different substrate (for example, a silicon single crystal substrate). Then, the heterogeneous substrate is separated to obtain a first aluminum nitride single crystal substrate. A second aluminum nitride single crystal layer is further laminated on the nitrogen polar face of the obtained first aluminum nitride single crystal substrate. At this time, the surface (outermost surface) of the second aluminum nitride single crystal layer is an aluminum polar surface. Finally, the first aluminum nitride single crystal substrate is removed to obtain a high-quality aluminum nitride single crystal substrate having a low oxygen concentration and comprising a second aluminum nitride single crystal layer. In the finally obtained substrate, one surface is an aluminum polar surface and the other surface is a nitrogen polar surface.

  The method described in Patent Document 2 succeeded in reducing impurities, particularly impurities derived from the base substrate. However, since the base substrate for growing the first aluminum nitride single crystal layer was a substrate different from aluminum nitride (a heterogeneous substrate), the finally obtained substrate was due to a difference in lattice constant and a difference in thermal expansion coefficient. It has been desired to further increase the crystallinity as a substrate for forming a semiconductor element layer that easily generates cracks, warpage, and dislocations, and has higher output and higher durability.

  In addition, the present inventors have proposed to reduce the warpage of the aluminum nitride substrate. Specifically, the following method is proposed. First, a heterogeneous substrate such as a silicon single crystal substrate is used as a base substrate, an aluminum nitride single crystal layer having a thickness of 10 nm to 1.5 μm is stacked on the base substrate, and the single crystal layer is formed on the single crystal layer. An aluminum nitride non-single-crystal layer having a thickness of 100 times or more of the thickness is stacked. Thereafter, the base substrate is removed to reduce the warpage of the obtained aluminum nitride substrate (single crystal and non-single crystal laminate) (see Patent Document 3). In the method of Patent Document 3, warpage was evaluated from the radius of curvature. The curvature radius of the aluminum nitride substrate with the single crystal surface convex downward was evaluated as a positive curvature radius, and the curvature radius of the aluminum nitride substrate as convex upward was evaluated as a negative curvature radius. For example, when the film thickness is not satisfied, the radius of curvature of −0.1 m becomes −1.8 m or more when the film thickness is satisfied, thereby successfully reducing the warpage of the substrate.

However, more advanced characteristics are required for a substrate for manufacturing a semiconductor element in recent years, and a substrate having higher quality than that obtained in Patent Document 3 is required. Specifically, a substrate having higher crystallinity and a larger radius of curvature is desired. In the method described in Patent Document 3, since a heterogeneous substrate is used, the crystallinity of the substrate (single crystal layer) obtained by any means is lowered, and the improvement of the warp is not sufficient. Therefore, even if an aluminum nitride single crystal layer is formed on the substrate, the substrate made of the aluminum nitride single crystal layer has a warp of about | 4 | m and a dislocation density of 10 ⁷ cm ⁻³ or more. there were. As described above, there is room for improvement in the conventional substrate for manufacturing the semiconductor element.

  A method of laminating an aluminum nitride single crystal layer by an HVPE method on an aluminum polar surface of an aluminum nitride single crystal free-standing substrate having a low dislocation density, for example, an aluminum nitride single crystal substrate manufactured by a sublimation method is also known (non-patent document). 1). According to this method, a decrease in crystallinity can be suppressed, and a high-quality substrate for manufacturing a semiconductor element can be manufactured. This method uses an aluminum nitride single crystal substrate (same substrate) as a base substrate. Therefore, the introduction of impurities derived from the base substrate is less than in the case of using a different substrate, and it is not necessary to stack an aluminum nitride single crystal layer on the nitrogen polar surface as in Patent Document 2 in order to reduce the impurity concentration. In this case, an aluminum nitride single crystal layer is generally laminated on the aluminum polar surface.

  In any of the aluminum nitride single crystal substrates manufactured by these methods, one main surface is an aluminum polar surface and the other surface is a nitrogen polar surface. When the aluminum nitride single crystal substrate is used for manufacturing a semiconductor element, a semiconductor element layer is grown on the aluminum polar face, and the nitrogen polar face as the back face is exposed.

  In the manufacturing process of a semiconductor element, it is known that the electrode characteristics are improved by performing a process of removing a damaged layer on the surface by bringing the element surface into contact with an alkaline solution such as an aqueous potassium hydroxide (KOH) solution. For example, Patent Document 6 proposes the following method in manufacturing a semiconductor element having a sapphire single crystal substrate. First, an n-type semiconductor layer is stacked on a sapphire single crystal substrate, and a p-type semiconductor layer is stacked on the n-type semiconductor layer. Then, the p-type semiconductor layer is dry etched to expose the n-type semiconductor layer. At this time, a damage layer is formed in the n-type semiconductor layer by dry etching. Then, when the damaged layer is removed by bringing it into contact with a KOH aqueous solution, an n-type contact electrode having a good contact resistance value can be formed on the surface of the n-type semiconductor layer.

  When such a method of Patent Document 6 is applied to a semiconductor element having an aluminum nitride single crystal substrate, there are the following problems. For example, when an aluminum nitride single crystal substrate obtained by the methods of Patent Documents 2 and 3 and Non-Patent Document 1 is used, as described above, in order to manufacture a high-quality semiconductor element, on the aluminum polar surface A semiconductor element layer is formed. In this case, when the damaged layer is brought into contact with the KOH aqueous solution, if the entire semiconductor element is brought into contact with the KOH aqueous solution, the exposed back surface (nitrogen polar surface) of the aluminum nitride single crystal substrate is dissolved in the KOH solution. . It is known that the nitrogen polar surface has low chemical resistance and is particularly easily dissolved in an alkaline solution such as an aqueous KOH solution. In order to solve this problem, it is necessary to cover and protect the back surface of the substrate (nitrogen polar surface) with an alkali-resistant metal or the like before bringing the semiconductor element into contact with the alkaline solution. However, if the coating is insufficient due to the influence of fine particles adhering to the nitrogen polar surface, the nitrogen polar surface is dissolved, and the yield of the semiconductor element may be reduced.

  Further, in a substrate having a high dislocation density, even if the surface to be contacted with the KOH aqueous solution is an aluminum polar surface, the contact portion is etched by the contact with the KOH aqueous solution to form pits, which adversely affects the quality of the semiconductor element. There was an effect.

  In order to solve the above problems, a group III nitride single crystal substrate (for example, an aluminum nitride single crystal substrate) that is a group III polar surface (for example, an aluminum polar surface) having a low dislocation density on both the front and back sides. ) Can be solved. A method of manufacturing a semiconductor device using a group III nitride single crystal substrate having such a double-sided group III polar surface is also known. Patent Document 4 proposes that the semiconductor element layer can be formed on both surfaces of the group III nitride substrate by setting both surfaces of the group III nitride substrate to group III polar surfaces.

JP 2006-253462 A JP 2010-89971 A WO2009 / 090821 pamphlet JP 2009-267088 A JP 2010-56459 A WO2011 / 078252 pamphlet JP, 2015-017030, A Japanese Patent Application Laid-Open No. 2015-156383

Applied Physics Express 5 (2012) 0555504

  In the method described in Patent Document 4, light emission including a first main surface showing group III polarity, a second main surface showing nitrogen polarity, and a polarity inversion layer provided on the second main surface. An element manufacturing substrate has been proposed. It is described that the polarity inversion layer may contain polycrystal or amorphous. In general, since the crystallinity of a nitride semiconductor formed on a substrate greatly depends on the crystallinity of the base substrate, when the polarity inversion layer is polycrystalline or amorphous, the crystal of the semiconductor formed on the polarity inversion layer It can be easily imagined that sex will deteriorate. Further, according to the study by the present inventors, even when the polarity inversion layer is a single crystal, when a group III nitride semiconductor is grown on the nitrogen polarity surface, the polarity inversion region does not invert in the substrate surface. It turned out that the area is easy to mix. In order to use the surface of the polarity inversion layer as a substrate for manufacturing a light emitting device, there is room for improvement of crystallinity and in-plane uniformity of polarity.

  Also, in the method described in Patent Document 5, the formation of the polarity inversion layer is described. However, since the polarity inversion layer is formed after the manufacture of the semiconductor element, the contact process with an alkali during the manufacture of the semiconductor element is performed. The back surface is a nitrogen polar surface, and the problems related to the dissolution of the back surface are not solved.

  Accordingly, an object of the present invention is to provide a high-quality aluminum nitride single crystal laminate (substrate). More specifically, an aluminum nitride single crystal laminate (substrate) having a low dislocation density, low warpage, high chemical resistance, and capable of manufacturing a high-quality semiconductor element without covering and protecting the back surface when the semiconductor element is manufactured. ) To provide.

  In order to solve the above problems, the present inventors first examined a polarity inversion layer made of an aluminum nitride single crystal. When a cross section of the laminate of the aluminum nitride single crystal substrate and the aluminum nitride single crystal layer formed on the nitrogen polar surface is observed with a transmission electron microscope (TEM), the polarity inversion is completed within the substrate surface. It was found that the timing of the aluminum polarity was different. If polarity reversal is not completed on the entire surface, nitrogen polarity and aluminum polarity are mixed in the surface. In this state, when a semiconductor element layer (for example, an n-type AlGaN layer) is grown on the aluminum nitride single crystal layer, it tends to grow with non-uniform polarity within the substrate surface or to increase the dislocation density. It was. As a result, chemical resistance could not be improved over the entire surface of the device.

  Based on the above examination, if the aluminum nitride single crystal laminate (substrate) has both the front surface and the back surface are both aluminum polar surfaces and the dislocation density is low, The formed semiconductor element was considered to have high chemical resistance. In other words, the laminate is an aluminum polar surface having a low dislocation density on the growth surface (surface on which the semiconductor element layer is formed) and on the back surface, so that it is difficult to dissolve in an alkaline solution. An alkaline solution can be used without going through a step of coating the back surface with a metal or the like. And while variously examining the growth conditions etc. of the aluminum nitride single crystal layer on the nitrogen polar face, the laminate is manufactured, and the semiconductor element obtained using the laminate is found to have high chemical resistance. The present invention has been completed.

That is, the first aspect of the present invention is an aluminum nitride single crystal laminate having a laminated structure in which an aluminum nitride single crystal layer is directly laminated on a nitrogen polar face of an aluminum nitride single crystal substrate,
Front and back surfaces of the entire surface of the laminate are both aluminum polar plane, front and back surfaces of the dislocation density Ri der both 10 ⁶ cm ^-2 or less, the radius of curvature of the surface shape of the aluminum nitride single crystal laminate | 5 | m or more (5m more or -5m less) aluminum nitride single crystal laminate, characterized in der Rukoto.

The second aspect of the present invention uses a base substrate made of an aluminum nitride single crystal substrate having an aluminum polar face dislocation density of 10 ⁶ cm ⁻² or less, and has a nitrogen temperature of 1400 ° C. to 1900 ° C. A method for producing an aluminum nitride single crystal laminate, comprising growing an aluminum nitride single crystal layer on the nitrogen polar surface by supplying an aluminum source gas and a nitrogen source gas to react on the polar surface. It is.

  According to a third aspect of the present invention, there is provided a step of manufacturing a semiconductor element layer having at least an n-type semiconductor layer on at least one aluminum polar surface of the aluminum nitride single crystal laminate, and bringing the semiconductor element layer into contact with an alkaline solution. It is a manufacturing method of a semiconductor element characterized by including.

  According to the aluminum nitride single crystal laminate of the present invention, since both the front surface and the back surface are both aluminum polar surfaces having a low dislocation density, the quality of the semiconductor element layer formed on the front surface and / or the back surface is improved. Even in the case where a step of contacting an alkaline solution is included in manufacturing the device, the step of protecting the back surface can be omitted.

It is the schematic of the aluminum nitride single crystal laminated body of this invention. It is the photograph (40000 times the photograph) of the cross-section TEM (transmission microscope observation) of the typical aluminum nitride single crystal laminated body of this invention. It is the schematic of the typical semiconductor element containing the laminated body part of this invention. It is a typical example of the apparatus which manufactures the laminated body of this invention.

(Aluminum nitride single crystal laminate)
A first aspect of the present invention is an aluminum nitride single crystal laminate having at least an aluminum nitride single crystal substrate and an aluminum nitride single crystal layer laminated on a nitrogen polar surface of the aluminum nitride single crystal substrate, The aluminum nitride single crystal laminate is characterized in that the entire front and back surfaces of the laminate are both aluminum polar surfaces, and the dislocation density on the front and back surfaces is both 10 ⁶ cm ⁻² or less. FIG. 1 shows a schematic diagram of a typical sectional view of an aluminum nitride single crystal laminate of the present invention, and FIG. 2 shows a TEM photograph of the laminate. Hereinafter, description will be given with reference to the drawings.

  In the present invention, the dislocation density refers to the number of dislocation lines per unit area of the surface reaching the target surface (exposed surface, front surface or back surface). Dislocation lines can be detected by measuring with TEM. In addition, if the measurement surface is an aluminum polar surface, it can be detected by an etch pit (EPD; Etch Pit Density) method. Specifically, by immersing the measurement surface in a mixed solution of heated potassium hydroxide (KOH) and sodium hydroxide (NaOH), an etch pit corresponding to dislocation can be generated and detected. In the present invention, KOH and NaOH are mixed at a weight ratio of 1: 1, and the value of etch pits when immersed in a melt heated to 450 ° C. for 5 minutes is defined as the dislocation density.

  In the present invention, the surface 7 of the aluminum nitride single crystal laminate 1 refers to the exposed c-plane on the aluminum nitride single crystal layer 3 side, and the exposed c-plane (aluminum nitride single crystal on the opposite side of the surface from the back surface 5). Exposed c-plane on the substrate side).

  In the present invention, the determination of the polarity of the surface 7 of the aluminum nitride single crystal laminate 1 was confirmed by the presence or absence of etching when the surface was immersed in a KOH aqueous solution. Specifically, the aluminum nitride single crystal laminate was immersed for 10 minutes in a 45 mass% KOH aqueous solution heated to 50 ° C. on a hot plate. After the immersion, the surface of the substrate was observed with a field emission scanning electron microscope (FE-SEM; Field Emission Scanning Electron Microscope), and the presence or absence of dissolution marks (area where the film thickness was reduced) was confirmed. If there is a dissolution trace on the surface, it is a nitrogen polar plane, and if there is no dissolution trace, it is an aluminum polar plane. In addition, a focused electron diffraction (CBED) method or an annular bright field scanning transmission electron microscope (ABF-STEM; an annular bright field scanning electron microscopic polarity microscopic cross-section microscopic aluminum microscopic method or an aluminum cross-sectional microscopic microscopical aluminum microscopic method is used. Can also be determined.

  Further, it can be confirmed by X-ray diffraction measurement of the aluminum nitride single crystal layer 3 that the aluminum nitride single crystal layer 3 is an aluminum nitride single crystal. When the surface of the aluminum nitride single crystal layer is measured in the θ-2θ mode, and a peak appears only in the diffraction angle of the (002) plane and the equivalent surface, the aluminum nitride single crystal layer 3 has inherited the orientation of the base substrate. , C can be confirmed as a single crystal having a growth surface.

  The aluminum nitride single crystal laminate 1 is suitably used as a semiconductor element manufacturing substrate in which a semiconductor element layer 11 is formed on the front surface 7 and / or the back surface 5 of the laminate. FIG. 3 shows a conceptual diagram of a semiconductor element 10 manufactured by laminating a semiconductor element layer 11 on the surface 7 of the laminate.

  When the semiconductor element layer 11 is formed, if the warp is large, defects may occur due to stress at the time of forming the semiconductor element layer 11 or at the time of raising and lowering the temperature. In addition, after the laminate is installed in an element layer forming apparatus (for example, an MOCVD apparatus), the laminate is prevented from moving from the installation position due to pressure fluctuation, gas flow, and rotation of the laminate installation table. Therefore, it is better that the warpage of the laminate is smaller.

  In the present invention, the warpage was evaluated from the radius of curvature of the surface shape of the aluminum nitride single crystal laminate. Specifically, using a blue-violet laser microscope from the surface side of the substrate, the height information of the substrate is obtained at a magnification of 50 times, and based on the assumption of a spherical approximation from the in-plane height distribution, The curvature radius of the substrate was calculated. The state where the substrate is convex downward is defined as a positive curvature radius, and the state where the substrate is convex upward is defined as a negative curvature radius. Whether the radius of curvature is a positive value or a negative value, it can be determined that the larger the value, the smaller the curvature. The radius of curvature of the surface shape of the aluminum nitride single crystal laminate is preferably | 5 | m or more (5 m or more and −5 m or less), more preferably | 10 | m or more (10 m or more and −10 m or less).

(Aluminum nitride single crystal substrate (base substrate))
The aluminum nitride single crystal substrate 2 used in the present invention has a dislocation density of 10 ⁶ cm ⁻² or less on the aluminum polar surface (the back surface 5 of the aluminum nitride single crystal substrate). By setting the dislocation density of the aluminum polar face to 10 ⁶ cm ⁻² or less, the dislocation density of the front surface 7 and the back surface 5 of the obtained aluminum nitride single crystal laminate 1 can be set to 10 ⁶ cm ⁻² or less. Reduction of the dislocation density of the semiconductor element layer 11 manufactured on the aluminum polar surface (back surface 5 of the aluminum nitride single crystal substrate) on the substrate and / or dislocation density of the aluminum nitride single crystal layer 3 manufactured on the nitrogen polar surface 6 Is preferably 10 ⁵ cm ^-2 or less, and more preferably 10 ⁴ cm ^-2 or less. What is necessary is just to determine the thickness of the board | substrate 2 in the range which does not reduce operativity, and it is preferable that it is specifically 50-1000 micrometers.

(Aluminum nitride single crystal layer)
In the present invention, the aluminum nitride single crystal layer 3 is on the nitrogen polar surface 6 of the aluminum nitride single crystal substrate 2, and the entire surface (surface 7 of the aluminum nitride single crystal laminate) is an aluminum polar surface. The aluminum nitride single crystal layer 3 includes a polarity inversion portion 8. In the present invention, the polarity inversion portion 8 is a portion where the polarity is inverted, and is a portion where the nitrogen polarity and the aluminum polarity are mixed. And it is the part shown by the black dot (line | wire) in the TEM image of FIG. This can be confirmed by comparing the TEM image and the method for determining the polarity described above. In the TEM image of FIG. 2, the portion of the same color as the aluminum nitride single crystal substrate 2 on the polarity inversion portion is an aluminum polar portion 9 that is an aluminum nitride single crystal of aluminum polarity. The TEM image includes information with a depth of about 100 nm.

  According to the study by the present inventors, it has been found that the timing of polarity reversal during the growth of the aluminum nitride single crystal layer 3 is not simultaneous in the plane. The timing at which polarity inversion occurs at a certain point is considered to be affected by the timing at which polarity inversion occurs around the point, the substrate size, the growth conditions, and the like. Then, due to the timing at which the polarity reversal occurs, from the nitrogen polarity surface 6 of the aluminum nitride single crystal substrate 2 to the point where the polarity reversal is completed (the point at the upper end of the polarity reversal part and the aluminum polarity) The thickness varies depending on the position (that is, the surface of the polarity reversing portion 8 has an uneven structure). Therefore, in order for the entire surface 7 of the aluminum nitride single crystal layer 3 to have aluminum polarity, the film thickness of the aluminum nitride single crystal layer 3 should be the same as the maximum thickness of the polarity inversion portion 8 or more. It is necessary to make it thick.

  The film thickness of the aluminum nitride single crystal layer 3 is preferably 2 μm or more, more preferably 5 μm or more, and further preferably 10 μm or more. Further, the film thickness of the aluminum nitride single crystal layer 3 does not need to be larger if the entire surface has aluminum polarity. According to the manufacturing method of the aluminum nitride single crystal layer 3 described in detail below, the maximum thickness of the polarity reversing portion 8 can be less than 2 μm (the thickness of the polarity reversing portion 8 is not particularly limited). However, in order to produce a high-quality laminate 1, it is preferably 0.1 μm or more and less than 2 μm.) Therefore, by setting the thickness of the aluminum nitride single crystal layer 3 to 2 μm or more, the entire surface 7 of the aluminum nitride single crystal laminate 1 can be stably made to have an aluminum polarity. The upper limit of the film thickness of the aluminum nitride single crystal layer 3 is not particularly limited as long as the entire surface is an aluminum polar surface, but is 1000 μm in view of industrial production.

  In the present invention, the thickness of the polarity reversal part 8 can be confirmed by TEM. Specifically, as shown in FIG. 2, the cross section of the interface between the aluminum nitride single crystal substrate 2 and the aluminum nitride single crystal layer 3 of the aluminum nitride single crystal laminate 1 may be observed by TEM. The thickness of the black dot (line) shown in the TEM image of FIG. The maximum thickness of the polarity reversal portion 8 depends on the size of the substrate to be observed, but the position where the thickness of the polarity reversal portion is the maximum while observing any part of the substrate at a magnification of about 10,000 to 50,000 times. Of the thickness.

When the entire surface 7 of the aluminum nitride single crystal layer 3 is aluminum polar and the dislocation density is 10 ⁶ cm ⁻² or less, the aluminum nitride single crystal layer or the semiconductor element layer 11 is formed on the surface. High quality can be manufactured. In particular, in order to form the semiconductor element layer 11 having a low dislocation density, the dislocation density is preferably 10 ⁵ cm ⁻² or less.

  In order to reliably and stably manufacture the aluminum nitride laminate 1 of the present invention, it is preferable to make the film thickness of the aluminum nitride single crystal layer 3 larger than the maximum thickness of the polarity reversal part 8. That is, the aluminum nitride single crystal layer 3 has a structure having the polarity reversing portion 8 and the aluminum polarity portion 9 on the polarity reversing portion 8. The aluminum nitride single crystal layer 3 preferably has an aluminum polar layer 4 whose entire surface is composed only of the aluminum polar portion 9 in a plane parallel to the nitrogen polar plane 6 of the aluminum nitride single crystal substrate 2. . The thickness of the aluminum polar layer 4 is preferably 0.1 μm or more, and more preferably 1 μm or more. In consideration of industrial production of semiconductors, the upper limit of the thickness of the aluminum polar layer 4 is a value obtained by subtracting the maximum thickness of the polarity reversal portion 8 from the maximum thickness of the aluminum nitride single crystal layer 3 and is approximately 1000 μm. Since the maximum thickness of the polarity reversing portion 8 is preferably less than 2 μm, the maximum thickness of the aluminum polar layer 4 is preferably more than 9998 μm and less than 1000 μm (the maximum thickness of the polarity reversing portion 8 is 0.1 μm or more and less than 2 μm). In this case, the maximum thickness of the aluminum polar layer 4 is preferably more than 9998 μm and 9999.9 μm or less).

  By setting the thickness of the aluminum polar layer 4 to 0.1 μm or more, the following effects can also be exhibited. For example, when a semiconductor is stacked on a base substrate in the HVPE method or the MOCVD method, thermal cleaning may be performed to remove an oxide film or polishing scratches on the surface of the base substrate. In some cases, the semiconductor is grown by heating to a growth temperature in an atmosphere containing hydrogen gas and then flowing the source gas after reaching the growth temperature. It is known that the surface of aluminum nitride is etched when it comes into contact with hydrogen gas at high temperatures, particularly at high temperatures. When the thickness of the aluminum nitride single crystal layer 3 is equal to the maximum thickness of the polarity reversal part 8 (when the aluminum polar layer 4 is not present), or when the aluminum polar layer 4 is too thin, the laminate 1 is heated at a high temperature. When exposed to hydrogen gas, the surface is etched, and the nitrogen polar surface may be exposed before growth. In order to prevent this, it is desirable to start the growth of the semiconductor without exposing the nitrogen polar surface even if the surface is etched during the temperature rise and leaving the entire surface as the aluminum polar surface. For this purpose, the thickness of the aluminum polar layer 4 is preferably 0.1 μm or more.

  Further, when the semiconductor element layer 11 is laminated on the surface 7 (aluminum polar layer 4) of the laminate 1 of the present invention and finally the aluminum nitride single crystal substrate 2 is removed, the aluminum nitride single crystal substrate 2 is not present. It is desirable to make the semiconductor device self-supporting. For example, in the case of manufacturing an ultraviolet light emitting diode (semiconductor element) by laminating the semiconductor element layer 11 on the surface of the laminate 1 using the aluminum nitride single crystal substrate 2 having low ultraviolet transmittance, in order to improve the light extraction efficiency. In addition, it is preferable to remove the aluminum nitride single crystal substrate 2 having low ultraviolet transmittance.

  Next, an aluminum nitride laminate of the present invention and a method for forming a semiconductor element layer (multilayer semiconductor) on the laminate will be described.

(Production of aluminum nitride single crystal laminate)
The aluminum nitride single crystal laminate 1 of the present invention uses an aluminum nitride single crystal substrate 2 having a dislocation density of 10 ⁶ cm ⁻² or less as a base substrate, and an aluminum source gas and nitrogen are formed on the nitrogen polar face 6 of the base substrate. The aluminum nitride single crystal layer 3 may be grown on the nitrogen polar face 6 by supplying and reacting with the source gas. At this time, the temperature on the nitrogen polar face 6 is preferably set to 1400 ° C. or higher and 1900 ° C. or lower.

(Preparation of aluminum nitride single crystal substrate (base substrate))
A known method such as a sublimation method or a HVPE (Hydride Vapor Phase Epitaxy) method can be used as a method for manufacturing the base substrate. An aluminum nitride single crystal laminate produced by laminating an aluminum nitride single crystal (HVPE layer) by an HVPE method on an aluminum polar surface of an aluminum nitride single crystal substrate (sublimation method substrate) produced by a sublimation method is used as a base substrate. You can also.

  In the production of the base substrate, the growth surface is not particularly limited, and c-plane (aluminum polar surface or nitrogen polar surface), m-plane, a-plane, r-plane or the like can be used. However, in the present invention, the surface on which the aluminum nitride single crystal layer 3 is grown is the nitrogen polar surface of the base substrate, and the back surface is the aluminum polar surface. Therefore, in manufacturing the base substrate, the aluminum polar surface or the nitrogen polar surface is used. It is preferable to manufacture as a growth surface. In the production of the base substrate, if the growth surface is a nitrogen polar surface, the aluminum nitride single crystal layer 3 can be grown on the nitrogen polar surface. In the production of the base substrate, if the growth surface is an aluminum polar surface, the growth may be started with the nitrogen polar surface of the base substrate as the surface when the aluminum nitride single crystal layer 3 is grown. When the base substrate is manufactured on a surface other than the c-plane, the aluminum polarity surface and the nitrogen polarity surface are exposed on the surface by cutting or the like after the substrate is manufactured, and the polarity inversion layer is formed on the exposed nitrogen polarity surface. Can be grown.

  In any case, in order to reduce cracks, defects, stress and the like of the aluminum nitride single crystal layer, the surface roughness (nitrogen polar surface 6) on which the aluminum nitride single crystal layer is grown is preferably 5 nm or less. Preferably it is 2 nm or less, More preferably, it is 1 nm or less. The surface curvature radius is preferably | 5 | m or more, more preferably | 10 | m or more. The surface roughness and the radius of curvature may be affected by the abrasive used when CMP is performed on the surface. Specifically, polishing can be performed using an alkaline, neutral, or acidic abrasive, but in the present invention, the surface is a nitrogen polar surface and has low alkali resistance, so that it is weakly alkaline. Or acidic abrasive, specifically, an abrasive having a pH of 8 or less is preferably used.

(Formation of aluminum nitride single crystal layer)
As a method for forming the aluminum nitride single crystal layer 3, a known method such as an HVPE method or a MOCVD (Metal Organic Chemical Vapor Deposition) method can be used. In particular, as described in Patent Document 2, it is known that when aluminum nitride is grown on a nitrogen polar surface at a growth temperature of 1400 ° C. or higher and 1900 ° C. or lower in the HVPE method, the polarity is reversed. According to the study by the present inventors, a growth temperature of 1400 ° C. or higher and 1700 ° C. or lower is more preferable from the viewpoint of productivity.

  An HVPE method suitable for forming the aluminum nitride single crystal layer 3 will be described. The HVPE method has a slower growth rate than the sublimation method and is not suitable for manufacturing a bulk single crystal, but has a low impurity concentration that adversely affects the deep ultraviolet light transmittance. It is used suitably for manufacture of. In addition, compared with MBE (Molecular Beam Epitaxy) method and MOCVD method, it is not suitable for precise film thickness control, but it is possible to grow a single crystal with good crystallinity at a high film formation rate. Therefore, it can be said that it is suitable for mass production of single crystal substrates.

  FIG. 4 shows a conceptual diagram of a typical example of a vapor phase growth apparatus (HVPE apparatus) used for the HVPE method. The growth of the aluminum nitride single crystal layer 3 by the HVPE method is performed by supplying a group III source gas (aluminum source gas) and a group V source gas (nitrogen source gas) into the reactor, and both gases are heated. This is done by reacting above. Aluminum halide gas such as aluminum chloride gas is suitably used for the group III source gas, and ammonia gas is suitably used for the group V source gas.

  In the HVPE method, various studies have been conducted in order to obtain a single crystal with good crystallinity. In the present invention, these known methods can be used without any particular limitation. Among these, in the present invention, it is preferable to use an aluminum halide gas (a main component is an aluminum trihalide gas) in which an aluminum monohalide gas is reduced as a raw material gas. If the aluminum trihalide gas contains a large amount of aluminum monohalide gas, the crystal quality may deteriorate.

  For the above reasons, when the aluminum nitride single crystal layer 3 is grown by the HVPE method, in the reaction zone on the nitrogen polar surface, the source gas is an aluminum halide gas (the main component is an aluminum trihalide gas). ) Is preferably supplied at least one halogen-based gas selected from a hydrogen halide gas and a halogen gas. This is because by supplying the halogen-based gas in advance, the equilibrium partial pressure of the aluminum monohalide gas can be reliably lowered, and generation of the aluminum monohalide gas can be suppressed. Moreover, it is not limited to this method, The method of suppressing the production | generation of aluminum monohalide gas can employ | adopt a well-known method. Other conditions are not particularly limited, and for example, the method of Patent Document 7 can be adopted.

  In the aluminum nitride single crystal layer 3, after the entire surface becomes aluminum polarity (after forming a film thickness equal to or larger than the maximum thickness of the polarity reversal part), the method of forming the aluminum polar layer 4 is a nitridation including a polarity reversal part It may be the same as or different from the aluminum single crystal layer. Specifically, it can be formed at a temperature of 1400 ° C. or less by the HVPE method. The aluminum polar layer 4 is continuously formed on the polarity inversion layer portion 8 without taking out the substrate in which the aluminum nitride single crystal layer including the polarity inversion portion 8 is laminated on the aluminum nitride single crystal substrate 2 from the film forming apparatus. It can also be grown to once, or it can be taken out from the apparatus once and then introduced again into the apparatus to grow. For surface stability, continuous growth is preferred.

  By manufacturing the aluminum nitride single crystal layer 3 by the HVPE method, a layer having a high ultraviolet light transmittance can be formed. When the aluminum nitride single crystal substrate 2 which is the base substrate is a substrate having a low ultraviolet light transmittance manufactured by the sublimation method, the substrate manufactured by the sublimation method can be finally removed by the HVPE method. A semiconductor element layer (multilayer semiconductor) is preferably formed on the produced aluminum nitride single crystal layer 3.

  By the method as described above, the aluminum nitride single crystal laminate 1 of the present invention can be manufactured. Next, a method for manufacturing the semiconductor element 10 by growing the semiconductor element layer 11 (multilayer semiconductor) on at least one aluminum polar surface of the laminate 1 of the present invention will be described.

(Semiconductor element manufacturing method)
In the present invention, a semiconductor element layer 11 having at least an n-type semiconductor layer 12 is manufactured on at least one aluminum polar surface of the aluminum nitride single crystal laminate 1, and the semiconductor element layer 11 is brought into contact with an alkaline solution. In particular, it exhibits an excellent effect. The semiconductor element layer 11 may be a multilayer semiconductor having at least an n-type semiconductor layer 12, an active layer 13, and a p-type semiconductor layer 14. When forming a multilayer semiconductor, the p-type semiconductor layer 14 and a part of the active layer 13 are removed to expose the n-type semiconductor layer 12, and then the multilayer semiconductor from which the n-type semiconductor layer 12 is exposed is converted to an alkaline solution. The present invention exhibits particularly excellent effects when it is brought into contact with.

The n-type semiconductor layer 12, active layer 13 and p-type semiconductor layer 14, _{is, Al X Ga Y In Z N} ( where, X, Y, Z is, 0 ≦ X ≦ 1.0,0 ≦ Y ≦ 1. 0, 0 ≦ Z ≦ 1.0, and a rational number satisfying X + Y + Z = 1.0). By forming the semiconductor element layer 11 having the composition on the aluminum nitride single crystal laminate 1 according to the first aspect of the present invention, a high-quality semiconductor element layer 11 having small cracks, strains, and dislocation density can be obtained. it can.

  The method for forming the semiconductor element layer 11 (multilayer semiconductor) is not particularly limited, and can be implemented by, for example, the method of Patent Document 8.

(Formation of semiconductor element layer (multilayer semiconductor))
The n-type semiconductor layer 12, the active layer 13, and the p-type semiconductor layer 14 can be formed by a known method such as MOCVD or MBE. Specifically, it can be formed using, for example, the MOCVD method described in Patent Document 8.

The n-type semiconductor layer 12 is a conductive layer imparted with n-type conductivity by containing a dopant raw material. It is preferably made of an AlGaN single crystal, and as a dopant raw material, a known n-type dopant material such as Si, O, Ge, etc. can be doped, but considering the controllability of the raw material concentration, ionization energy in the n-type layer, etc. Si is preferred. The dislocation density of the n-type semiconductor layer is preferably 10 ⁸ cm ⁻² or less, more preferably 10 ⁶ cm ⁻² or less, and most preferably 10 ⁴ cm ⁻² or less. The dislocation density can be easily achieved by using the aluminum nitride single crystal laminate 1 of the present invention. Further, the thickness of the n-type semiconductor layer 12 is not particularly limited, and is preferably 500 to 5000 nm.

  The active layer 13 is preferably formed on the n-type semiconductor layer 12 and has a quantum well structure in which a quantum well layer and a barrier layer are combined. The quantum well structure may be a structure having a single quantum well layer or a multiple quantum well structure having a plurality of quantum well layers. The thickness of the quantum well layer is not particularly limited, but is preferably 2 to 10 nm, and more preferably 4 to 8 nm, from the viewpoint of improvement in output density and reliability. In order to stably obtain a higher power density, the active layer 13 preferably has three or more quantum well layers. Since the active layer has a multiple quantum well structure having three or more quantum well layers having a thickness of 2 to 10 nm, the effective volume of the quantum well layer can be increased, so that the output characteristics are rapidly deteriorated when the semiconductor element is driven. Can be suppressed. The thickness of the barrier layer is not particularly limited, but is generally in the range of 5 to 30 nm.

The p-type semiconductor layer 14 is a conductive layer imparted with p-type conductivity by containing a known p-type dopant raw material. Among known p-type dopant materials, Mg is preferably used as a dopant. The p-type semiconductor layer may have a single layer structure having a single composition or a multilayer structure in which a plurality of layers having different compositions are stacked. In order to have the effect of confining electrons in the active layer and the effect of reducing the contact resistance with the p-type electrode, a multilayer structure is preferable. For example, two AlGaN layers having different compositions can be stacked, and further an InGaN layer can be stacked. The thickness of the AlGaN layer is not particularly limited, but is preferably in the range of 5 to 50 nm. The thickness of the InGaN layer is not particularly limited, but is preferably 5 to 200 nm. Moreover, it is preferable that the quantity of the dopant contained in each layer of the p-type semiconductor layer 14 exists in the range of 1 * 10 < ¹⁹ > -1 * 10 < ²⁰ > cm < ^-3 > from an electroconductive viewpoint.

  In addition, although not specifically described, an electron blocking layer or the like can be provided.

(Electrode formation)
The n-type electrode 16 is formed on the n-type semiconductor layer 12 (n-type layer 12). Usually, the n-type electrode 16 is formed on the n-type semiconductor layer 12 by the following method. First, for example, by the method of forming the semiconductor element layer 11 (multilayer semiconductor), the aluminum nitride single crystal stacked body 1, the n-type semiconductor layer 12, the active layer 13, and the p-type semiconductor layer 14 (p-type layer 14) are arranged in this order. The laminated body laminated | stacked by is manufactured. Next, the surface of the n-type semiconductor layer 12 is exposed by removing a part of the stacked body from the p-type semiconductor layer 14 side by etching or the like. As the etching method, a known method such as an inductively coupled plasma (ICP) etching method can be used without particular limitation.

  When ICP etching is employed, as described in Patent Document 6, damage is caused by contacting an alkali solution, specifically, an aqueous KOH solution, with the n-type semiconductor layer 12 exposed and damaged by ICP etching. It is preferred to remove the layer. In the present invention, since the back surface is an aluminum polar surface having a low dislocation density, the back surface does not dissolve even if the solution contacts the back surface. Therefore, the step of protecting the nitrogen polar surface, which was necessary when using the conventional aluminum nitride single crystal substrate in which the nitrogen polar surface is exposed, can be omitted and brought into contact with the alkaline solution.

  Subsequently, an n-type electrode 16 is formed on the n-type semiconductor layer 12. The n-type electrode 16 can be formed using a known n-type ohmic electrode material and formation method. The n-type ohmic electrode material is not particularly limited as long as it can reduce the contact resistance value with the n-type semiconductor layer 12. For example, a material containing Ti and Al can be used. Each layer constituting the n-type electrode 16 can be formed by a vacuum deposition method, a sputtering method, or the like. In order to reduce the contact resistance value between the n-type electrode 16 and the n-type semiconductor layer 12, it is preferable to anneal in an inert gas atmosphere such as argon or nitrogen after the n-type electrode 16 is formed. The thickness of the n-type electrode 16 is not particularly limited, and the thickness of each layer constituting the n-type electrode 16 (layer) may be appropriately determined within a range in which the contact resistance value can be reduced. Considering the productivity of the electrode 16 (layer), the total thickness is preferably 50 to 500 nm.

  The p-type electrode 15 is formed on the p-type layer (p-type semiconductor layer 14 in FIG. 3). A known p-type ohmic electrode material can be used for the p-type electrode 15. Specifically, the material is not particularly limited as long as the material can reduce the contact resistance value with the p-type layer. For example, an electrode material containing Ni and Au can be preferably used. These electrode material layers can be formed by vacuum deposition, sputtering, or the like. In addition, after the p-type electrode 15 is formed, it is preferable to perform an annealing process in an atmosphere of nitrogen, oxygen or the like in order to reduce the contact resistance value. The thickness of the p-type electrode 15 (layer) is not particularly limited, but is preferably 5 to 300 nm.

  The arrangement of the n-type electrode 16 and the p-type electrode 15 is not particularly limited, but the distance between the n-type electrode 16 and the p-type electrode 15 is preferably 0.5 to 10 μm, and the semiconductor It is preferable that the n-type electrode 16 surround the p-type electrode 15 substantially uniformly so as to improve the uniformity of the current path when the element is driven.

(Manufacture of semiconductor elements using both surfaces of aluminum nitride single crystal laminate)
In the above method, a semiconductor element layer is formed on one aluminum polar face of the aluminum nitride laminate, and the other aluminum polar face of the laminate is formed by the same method or a different method as the formation of the semiconductor element layer. A semiconductor element layer can also be formed thereon.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

<Example 1>
Back surface 5 (aluminum nitride single crystal) of aluminum nitride single crystal laminate 1 manufactured by forming aluminum nitride single crystal layer 3 by HVPE method on nitrogen polar surface 6 of aluminum nitride single crystal substrate 2 manufactured by sublimation method This is an example of a deep ultraviolet light emitting diode manufactured by laminating the semiconductor element layer 11 on the aluminum polar surface of the substrate.

(Preparation of aluminum nitride single crystal substrate)
A commercially available aluminum nitride single crystal substrate of φ1 inch manufactured by the sublimation method was prepared. The nitrogen polar surface 6 of the substrate was subjected to CMP using a neutral abrasive. The plate thickness after polishing was 450 μm, the RMS of the nitrogen polar face 6 was 0.9 nm, and the radius of curvature of the nitrogen polar face was 12 m.

  Next, the aluminum nitride single crystal substrate was cut into four square shapes of about 7 mm square. One was an aluminum nitride single crystal substrate analysis substrate, two was an aluminum nitride single crystal laminate production / analysis substrate, and one was a semiconductor element (deep ultraviolet light emitting diode) production / analysis substrate.

The dislocation density of the aluminum polar face 5 and the nitrogen polar face 6 of the aluminum nitride single crystal substrate analysis substrate was measured by a cross-sectional TEM. When an area of about 150 μm ² was observed at a magnification of 10,000, no dislocation was observed on both surfaces, and it was found that the dislocation density was 7 × 10 ⁵ cm ⁻² or less on both surfaces. The dislocation density of the aluminum polar face 5 was also measured by the EPD method. Specifically, when KOH and NaOH were mixed at a weight ratio of 1: 1 and immersed in a melt heated to 450 ° C. for 5 minutes, the value of etch pits was defined as a dislocation density of 6 × 10 ⁴ cm ^{−. 2} .

(Lamination of aluminum nitride single crystal layer)
For the growth of the aluminum nitride single crystal layer, the vapor phase growth apparatus (HVPE apparatus) of the embodiment shown in FIG. 4 was used.

  One of the substrates for manufacturing and analyzing the aluminum nitride single crystal laminate was placed on the susceptor 23 as the base substrate 22 so that the nitrogen polar face 6 became the growth face.

  A hydrogen / nitrogen mixed carrier gas 6500 sccm in which hydrogen and nitrogen were mixed at a ratio of 7: 3 was allowed to flow from the extruded gas inlet 24 as a gas for sweeping the entire atmosphere inside the reaction tube. Further, the pressure in the reactor 21 during the growth was maintained at 0.99 atm.

  An ammonia gas of 20 sccm and a hydrogen carrier gas of 160 sccm are supplied from the nitrogen source gas inlet 41, and a hydrogen chloride gas of 20 sccm is supplied from the group V additional halogen-based gas supply nozzle 44. A mixed gas was supplied. At this time, the temperature of the nitrogen source gas supply nozzle 42 was adjusted to 400 ° C. so that ammonia gas and hydrogen chloride gas did not react. Further, 1500 sccm of nitrogen gas was supplied from a barrier gas nozzle (a nozzle arranged so as to be able to supply barrier gas from between the nitrogen source gas supply nozzle 42 and the aluminum halide gas supply nozzle 34 (not shown)). .

  The base substrate 22 was heated to 1450 ° C. under the above gas supply conditions.

  After heating the base substrate 22 to 1450 ° C., hydrogen chloride gas 7 sccm is supplied from the group III additional halogen-based gas supply nozzle 36, and hydrogen nitrogen mixed carrier gas 1793 sccm is supplied from the raw material halogen-based gas introduction nozzle 33, A total of 1800 sccm of gas was supplied from the aluminum fluoride gas supply nozzle 34.

  25 seconds after the supply of hydrogen chloride gas from the group III additional halogen gas supply nozzle 36 is started, 9 sccm of hydrogen chloride gas is introduced from the raw material halogen gas introduction nozzle 33 and heated to 400 ° C. in the raw material reactor 31 in advance. The aluminum chloride gas was generated by reacting with aluminum 32. At the same time, the hydrogen-nitrogen mixed carrier gas was reduced by 9 sccm to 1784 sccm. The aluminum chloride gas was supplied onto the base substrate 22 from the aluminum halide gas supply nozzle 34, and crystal growth was started.

  The aluminum nitride single crystal layer 3 was grown to 12 μm on the base substrate 22 with the gas flow rate and base substrate temperature under the above conditions. Here, the growth film thickness of the aluminum nitride single crystal layer is a film thickness obtained by growing in a growth time such that the growth film thickness becomes 12 μm, based on the growth rate obtained under the same conditions obtained by a preliminary experiment. After the growth of the aluminum nitride single crystal layer 3, the supply of aluminum chloride gas, ammonia gas, and hydrogen chloride gas was stopped and cooled to room temperature.

  By the above method, the aluminum nitride single crystal laminate 1 in which the entire surface 7 and the back surface 5 are aluminum polar surfaces was completed.

  An aluminum nitride single crystal layer is formed on the remaining nitrogen nitride plane 6 of the aluminum nitride single crystal laminate manufacturing / analysis substrate and semiconductor element (deep ultraviolet light emitting diode) manufacturing / analysis substrate under exactly the same conditions as described above. 3 were laminated to produce a total of three aluminum nitride single crystal laminates 1.

(Polishing and analysis of aluminum nitride single crystal laminate)
The surface 7 of the obtained three aluminum nitride single crystal laminates 1 was subjected to CMP using an alkaline abrasive. When the dislocation density was measured on the front and back surfaces of one aluminum nitride single crystal laminate after polishing by the EPD method, they were 7 × 10 ⁴ cm ⁻² and 6 × 10 ⁴ cm ⁻² , respectively. Further, when the radius of curvature of the surface 7 of another single aluminum nitride single crystal laminate 1 was measured, it was 10 m. Further, when the surface of the aluminum nitride single crystal laminate was measured by XRD θ-2θ, a peak appeared only in the diffraction angle of the aluminum nitride (002) plane and its equivalent surface. It was confirmed to be a single crystal. Further, when the three portions of the cross section of the aluminum nitride single crystal laminate 1 were observed with a TEM at a magnification of 12500 times, the aluminum nitride single crystal layer 3 was 5.0 μm, and the maximum thickness of the polarity reversal portion 8 was 1. 3 μm, and the aluminum polar layer 4 was 3.7 μm.

(Formation of semiconductor element layer)
Of the aluminum nitride single crystal laminate 1 after polishing, one that was not used for analysis of the aluminum nitride single crystal layer 3 (aluminum nitride single crystal laminate produced using a substrate for semiconductor element production / analysis), The aluminum nitride single crystal laminate 1 was placed on the susceptor in the MOCVD apparatus so that the back surface 5 of the aluminum nitride single crystal laminate 1 became a growth surface.

At 1080 ° C., an n-type Al _0.65 Ga _0.35 N layer (thickness 1 μm: n-type layer), triplet well layer (Al _0.40 Ga _0.6 N (thickness 4 nm: quantum well layer)) / Al _0.55 Ga _0.45 N layer (thickness 10 nm: barrier layer): active layer), p-type AlN layer (thickness 50 nm: p-type layer), p-type Al _0.75 Ga _0.25 N ( A multilayer semiconductor element layer 11 was formed by sequentially stacking a thickness of 50 nm: p-type layer) and a p-type GaN layer (thickness 20 nm: p-type layer). Impurity doping is performed using tetraethylsilane and biscyclohexane used as dopants so that the Si concentration in the n-type layer is 2 × 10 ¹⁹ cm ⁻³ and the Mg concentration in the p-type layer is 3 × 10 ¹⁹ cm ^−3. The pentadienyl magnesium flow rate was controlled.

Next, a part of the ultraviolet light emitting laminate (part from the p-type layer side) was etched by an ICP etching apparatus until the n-type Al _0.65 Ga _0.35 N layer (n-type layer) was exposed. Thereafter, the laminate was immersed in a 10 wt% KOH aqueous solution at a temperature of 100 ° C. for 15 minutes to perform a surface treatment of the n-type Al _0.65 Ga _0.35 N layer (n-type layer).

  An n-type layer in which a surface-treated n-type layer is made of Ti layer (thickness 20 nm) / Al layer (thickness 100 nm) / Ti layer (thickness 20 nm) / Au layer (thickness 50 nm) by vacuum deposition. An electrode was formed. Thereafter, heat treatment was performed in a nitrogen atmosphere at 950 ° C. for 1 minute.

  Next, a p-type electrode composed of a Ni layer (thickness 20 nm) / Au layer (thickness 50 nm) is formed on the p-type GaN layer by vacuum deposition, and then in an oxygen atmosphere at 500 ° C. for 5 minutes. Heat treatment was performed.

  Finally, the aluminum nitride single crystal layer 3 and the aluminum nitride single crystal substrate 2 were removed by mechanical polishing to complete an ultraviolet light emitting diode wafer.

(Ultraviolet light emitting diode and its analysis)
An ultraviolet light emitting diode chip was produced by cutting the ultraviolet light emitting diode wafer into a square shape of about 0.8 mm square, and the ultraviolet light emitting diode chip was mounted on a polycrystalline AlN carrier to complete the ultraviolet light emitting diode. The emission peak wavelength and emission output (total luminous flux) of the produced ultraviolet light emitting diode were measured using a 2-inch integrating sphere (Zenith coating manufactured by Sphere Optics) and a multichannel spectrometer (USB 4000 manufactured by Ocean Photonics). The emission peak wavelength of the ultraviolet light emitting diode was 280 nm. Luminous output density measured at a driving current value of 100 mA and 25 ° C. (the luminous output (W) of the ultraviolet light-emitting diode determined by the total luminous flux measurement of the above-mentioned emission spectrum is the area (cm ² ) of the active layer 13 of the ultraviolet light-emitting diode) The value divided by the value was 19 W / cm ² .

<Example 2>
Surface 7 (aluminum nitride single crystal) of aluminum nitride single crystal laminate 1 manufactured by forming aluminum nitride single crystal layer 3 by HVPE method on nitrogen polar surface 6 of aluminum nitride single crystal substrate 2 manufactured by sublimation method This is an example of a deep ultraviolet light emitting diode manufactured by laminating the semiconductor element layer 11 on the aluminum polar surface of the layer.

  The aluminum nitride single crystal layer 3 was grown in the same manner as in Example 1 except that the growth film thickness of the aluminum nitride single crystal layer 3 was set to 300 μm, and three aluminum nitride single crystal laminates 1 were manufactured.

The surface 7 of the obtained three aluminum nitride single crystal laminates 1 was subjected to CMP using an alkaline abrasive. The dislocation densities of the front surface 7 and the back surface 3 of the laminate 1 after polishing were 6 × 10 ⁴ cm ⁻² and 9 × 10 ⁴ cm ⁻² , respectively. Further, the radius of curvature of the surface 7 of the laminate 1 was 12 m. The thickness of the aluminum nitride single crystal layer 3 was 282.7 μm, the maximum thickness of the polarity reversing portion 8 was 1.6 μm, and the thickness of the aluminum polar layer 4 was 281.1 μm.

  Then, of the obtained aluminum nitride single crystal laminate, a semiconductor element is formed on the surface 7 of one aluminum nitride single crystal laminate that was not used for the analysis of the aluminum nitride single crystal layer in the same manner as in Example 1. Layer 11 was formed. Finally, the light emitting diode wafer was completed by removing the aluminum nitride single crystal substrate 2 by mechanical polishing.

Thereafter, an ultraviolet light emitting diode was completed in the same manner as in Example 1. The emission peak wavelength of the produced ultraviolet light emitting diode was 281 nm. The light emission output density measured at a drive current value of 100 mA and 25 ° C. was 18 W / cm ² , and it was confirmed to be an ultraviolet light emitting diode equivalent to Example 1.

<Example 3>
The aluminum nitride single crystal layer 3 was grown in the same manner as in Example 1 except that the growth film thickness of the aluminum nitride single crystal layer 3 was 5 μm, and three aluminum nitride single crystal laminates 1 were produced.

The surface 7 of the obtained three aluminum nitride single crystal laminates 1 was subjected to CMP using an alkaline abrasive. The dislocation densities of the front surface 7 and the back surface 3 of the laminate 1 after polishing were 9 × 10 ⁴ cm ⁻² and 7 × 10 ⁴ cm ⁻² , respectively. Further, the radius of curvature of the surface 7 of the laminate 1 was 9 m. The film thickness of the aluminum nitride single crystal layer 3 was 1.3 μm, the maximum thickness of the polarity inversion portion 8 was 1.2 μm, and the film thickness of the aluminum polar layer 4 was 0.1 μm.

  Then, of the obtained aluminum nitride single crystal laminate, a semiconductor element is formed on the surface 7 of one aluminum nitride single crystal laminate that was not used for the analysis of the aluminum nitride single crystal layer in the same manner as in Example 1. Layer 11 was formed to complete the light emitting diode wafer.

The produced ultraviolet light emitting diode had a light emission peak wavelength of 281 nm, a light emission output density of 16 W / cm ² measured at a drive current value of 100 mA and 25 ° C.

<Comparative Example 1>
An aluminum nitride single crystal was grown by 0.3 μm on a silicon single crystal substrate by HVPE, and then an aluminum nitride polycrystal was grown by 230 μm to produce an aluminum nitride polycrystal / aluminum nitride single crystal / silicon single crystal laminate. . The laminate was immersed in an aqueous solution in which hydrofluoric acid: nitric acid: acetic acid: ultra pure water was mixed at a volume ratio of 1: 2: 1: 4 for 12 hours to dissolve and remove silicon as a base substrate. Subsequently, it was washed with ultrapure water to produce an aluminum nitride polycrystal / aluminum nitride single crystal laminate. Furthermore, an aluminum nitride single crystal was grown to 300 μm on the aluminum nitride single crystal of the laminate by HVPE. Then, 350 μm from the aluminum nitride polycrystal side was removed by mechanical polishing. Finally, an aluminum nitride single crystal substrate was manufactured by CMP of the aluminum polar surface of the aluminum nitride single crystal using an alkaline abrasive. The dislocation density of the aluminum polar face of the aluminum nitride single crystal substrate was 4 × 10 ⁸ cm ⁻² , and the radius of curvature of the aluminum polar face was −2.0 m.

  The aluminum nitride substrate was used as an alternative to the aluminum nitride single crystal laminate used in Example 1, and a semiconductor element layer was laminated on the aluminum polar surface of the aluminum nitride substrate. Prior to, an ultraviolet light emitting diode was completed in the same manner as in Example 1 except that the back surface was covered and protected by vapor deposition of Ni on the back surface (nitrogen polar surface) of the substrate.

The produced ultraviolet light emitting diode had a light emission peak wavelength of 281 nm, a light emission output density measured at a drive current value of 100 mA and 25 ° C. was 1 W / cm ² .
Reference example 1
In the same manner as the conditions for growing the aluminum nitride single crystal layer 3 in Example 1, an aluminum nitride single crystal layer is laminated on the aluminum polar surface of the sublimation substrate, and the same as in Example 1 is applied on the aluminum nitride single crystal layer. The semiconductor layer was formed by the method. In the semiconductor manufacturing process, before ICP etching, electrodes are formed in the same manner as in Example 1 except that the back surface is covered and protected by vapor deposition of Ni on the back surface (nitrogen polar surface) of the substrate, and ultraviolet light emission is performed. The diode was completed.

The produced ultraviolet light emitting diode had a light emission peak wavelength of 279 nm, and a light emission output density measured at a drive current value of 100 mA and 25 ° C. was 19 W / cm ² .

1 Aluminum nitride single crystal laminate 2 Aluminum nitride single crystal substrate (nitrogen polarity)
3 Aluminum nitride single crystal layer 4 Aluminum polar layer 5 Back surface (aluminum polar surface of aluminum nitride crystal substrate)
6 Nitrogen polar surface of aluminum nitride single crystal substrate 7 Surface (aluminum polar surface)
DESCRIPTION OF SYMBOLS 8 Polarity inversion part 9 Aluminum polar part 10 Semiconductor element 11 Semiconductor element layer 12 N type semiconductor layer 13 Active layer 14 P type semiconductor layer 15 P type electrode 16 N type electrode 20 Vapor phase growth apparatus (HVPE apparatus)
21 Reactor 22 Base substrate 23 Susceptor
24 Extrusion gas introduction port 25 Exhaust port 26 Raw material part external heating device 27 Growth part external heating device 31 Raw material part reactor 32 Aluminum
33 Raw material halogen-based gas introduction nozzle 34 Aluminum halide gas supply nozzle
36 Group III additional halogen gas supply nozzle
41 Nitrogen source gas inlet 42 Nitrogen source gas supply nozzle
44 Group V additional halogen gas supply nozzle

Claims (9)

An aluminum nitride single crystal laminate having a laminated structure in which an aluminum nitride single crystal layer is directly laminated on a nitrogen polar face of an aluminum nitride single crystal substrate,
Front and back surfaces of the entire surface of the laminate are both aluminum polar plane, front and back surfaces of the dislocation density Ri der both 10 ⁶ cm ^-2 or less, the radius of curvature of the surface shape of the aluminum nitride single crystal laminate | 5 | m or more (5m more or -5m less) aluminum nitride, characterized in der Rukoto single crystal laminate. 2. The aluminum nitride single crystal laminate according to claim 1, wherein the aluminum nitride single crystal layer has a thickness of 2 μm or more. The aluminum nitride single crystal layer has a structure having a polarity reversal portion whose polarity is reversed and an aluminum polarity portion which is an aluminum polarity on the polarity reversal portion,
The aluminum nitride single crystal layer has an aluminum polar layer whose entire surface is composed only of an aluminum polar part in a plane parallel to the nitrogen polar plane of the aluminum nitride single crystal substrate,
The aluminum nitride single crystal laminate according to claim 1 or 2 , wherein the aluminum polar layer has a thickness of 0.1 µm or more. On at least one aluminum-polar surface of the aluminum nitride single crystal laminate according to any one of claims 1 to 3, a semiconductor device including a semiconductor element layer having at least n-type semiconductor layer. The semiconductor element according to claim 4 , wherein the semiconductor element layer is a multilayer semiconductor having at least an n-type semiconductor layer, an active layer, and a p-type semiconductor layer. It is a manufacturing method of the aluminum nitride single-crystal laminated body in any one of Claims 1-3 ,
Using a base substrate made of an aluminum nitride single crystal substrate having a dislocation density of 10 ⁶ cm ⁻² or less on the aluminum polar surface, an aluminum raw material is formed on the nitrogen polar surface of the base substrate at a temperature of 1400 ° C. to 1900 ° C. A method of producing an aluminum nitride single crystal laminate, comprising growing an aluminum nitride single crystal layer on the nitrogen polar face by supplying a gas and a nitrogen source gas to cause a reaction. When the aluminum nitride single crystal layer is grown on the nitrogen polar surface, before supplying the aluminum source gas, at least one halogen-based gas selected from a hydrogen halide gas and a halogen gas is added to the nitrogen polar surface. The method for producing an aluminum nitride single crystal laminate according to claim 6 , wherein: A semiconductor element layer having at least an n-type semiconductor layer is manufactured on at least one aluminum polar surface of the aluminum nitride single crystal laminate according to any one of claims 1 to 3 , and the semiconductor element layer is brought into contact with an alkaline solution. The manufacturing method of the semiconductor element characterized by including the process to make. A multilayer semiconductor element layer having at least an n-type semiconductor layer, an active layer, and a p-type semiconductor layer on at least one aluminum polar surface of the aluminum nitride single crystal laminate according to any one of claims 1 to 3 is manufactured. Then, after removing a part of the p-type semiconductor layer and the active layer to expose the n-type semiconductor layer, the step of bringing the multilayer semiconductor from which the n-type semiconductor layer is exposed into contact with an alkaline solution is included. A method for manufacturing a semiconductor device, characterized in that:

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