Nitride semiconductor substrate, semiconductor device, and method for manufacturing nitride semiconductor substrate

Abstract

This nitride semiconductor substrate (11, 21) is provided with a substrate (2) and an AlN-containing film (100, 200) that is provided above the substrate (2). The film thickness of the AlN-containing film (100, 200) is 10,000 nm or less; and the threading dislocation density of the AlN-containing film (100, 200) is 2 × 108 cm-2 or less.

Description

Technical Field

[0001] The present invention relates to a nitride semiconductor substrate, a semiconductor device, and a method for manufacturing a nitride semiconductor substrate.

Background Art

[0002] Group III nitride semiconductors such as aluminum nitride (AlN), aluminum gallium nitride (AlGaN), and aluminum gallium indium nitride (AlGaInN) have attracted attention as materials for optoelectronic semiconductor devices such as ultraviolet light-emitting devices.

[0003] For example, AlN has a very wide bandgap among semiconductor materials and can efficiently extract ultraviolet light to the outside, so it is expected to be a high-efficiency light-emitting device substrate. However, bulk AlN single crystal substrates are expensive and difficult to fabricate large-area substrates, so there are significant cost issues as a substrate material for ultraviolet light-emitting devices.

[0004] In view of such a situation, for example, a nitride semiconductor substrate on which a high-quality AlN thin film is formed on an inexpensive sapphire substrate is expected.

[0005] However, since AlN has a large lattice mismatch with sapphire, a large number of threading dislocations exist in the AlN thin film grown on the sapphire substrate. Therefore, it is difficult to obtain a flat surface for the AlN thin film formed on the sapphire substrate, and there is also a problem of increasing crystal defects.

[0006] As a method for obtaining a nitride semiconductor substrate on which a high-quality AlN thin film with a low defect density of AlN crystals is formed, for example, there is the technique described in Patent Document 1.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Non-Patent Document

[0008]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] In Patent Document 1, a method for manufacturing a nitride semiconductor substrate is disclosed in which a substrate on which a nitride semiconductor is formed is annealed in an airtight state in which a main surface of the nitride semiconductor is covered with a cover member for suppressing dissociation of components of the nitride semiconductor from the main surface.

[0010] However, Patent Document 1 discloses that the full width at half maximum of the X-ray diffraction rocking curve on the (10-12) plane of the nitride semiconductor substrate manufactured by the above manufacturing method is 300 arcsec, and further high crystallization is required.

[0011] The present invention aims to solve the above-described problems and provides a high-quality nitride semiconductor substrate and the like.

Means for Solving the Problems

[0012] In order to achieve the above object, a nitride semiconductor substrate according to one aspect of the present invention includes a substrate and an AlN-containing film provided above the substrate, the thickness of the AlN-containing film is 10000 nm or less, and the threading dislocation density of the AlN-containing film is 2×10 8 cm -2 or less.

[0013] Also, a nitride semiconductor substrate according to one aspect of the present invention includes a substrate and an AlN-containing film provided above the substrate, the thickness of the AlN-containing film is 300 nm or more and 10000 nm or less, and the oxygen concentration of the AlN-containing film is 10 18 cm-3 10 or more 21 cm -3 or less, and the hydrogen concentration of the AlN-containing film is 10 16 cm -3 or more and 2×10 17 cm -3 or less.

[0014] In addition, a semiconductor device according to one aspect of the present invention includes the above nitride semiconductor substrate.

[0015] In addition, a method for manufacturing a nitride semiconductor substrate according to one aspect of the present invention includes a preparation step of preparing a substrate, a film formation step of forming an AlN film having a film thickness of 100 nm or more and 900 nm or less above the substrate, and an annealing step of annealing the AlN film formed in the film formation step at 1500 °C or more. At least one of the film formation step and the annealing step is performed a plurality of times, and the threading dislocation density of the formed AlN film is 2×10 8 cm -2 or less.

Advantages of the Invention

[0016] According to the present invention, a high-quality nitride semiconductor substrate or the like can be realized.

Brief Description of the Drawings

[0017]

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Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0019] Note that all of the embodiments described below show comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement positions and connection forms of the components, steps, order of steps, etc. shown in the following embodiments are merely examples and are not intended to limit the present invention.

[0020] Note that each figure is a schematic diagram and is not necessarily drawn precisely. Also, in each figure, substantially the same configuration is denoted by the same reference numeral, and duplicate descriptions may be omitted or simplified.

[0021] In the following embodiments, the terms “upper” and “lower” do not refer to the upward (vertically upward) and downward (vertically downward) directions in an absolute spatial recognition. Also, the terms “upper” and “lower” are applicable not only when two components are arranged at intervals and another component exists between the two components, but also when two components are arranged in close contact with each other and the two components are in contact.

[0022] In the following description, aluminum may be denoted as Al, gallium as Ga, indium as In, nitrogen as N, aluminum nitride as AlN, aluminum gallium nitride as AlGaN, aluminum gallium indium nitride as AlGaInN, boron aluminum nitride as BAlN, boron aluminum gallium nitride as BAlGaN, and scandium aluminum magnesium oxide as ScAlMgO4.

[0023] (Embodiment) [Configuration of Nitride Semiconductor Substrate] First, a configuration example of the nitride semiconductor substrate 11 of the first example, the nitride semiconductor substrate 21 of the second example, and the nitride semiconductor substrate 31 of the third example according to the present embodiment will be described with reference to FIGS. 1, 2, and 3.

[0024] FIG. 1 is a diagram showing a configuration example of the nitride semiconductor substrate 11 of the first example according to the present embodiment. FIG. 2 is a diagram showing a configuration example of the nitride semiconductor substrate 21 of the second example according to the present embodiment. FIG. 3 is a diagram showing a configuration example of the nitride semiconductor substrate 31 of the third example according to the present embodiment.

[0025] The nitride semiconductor substrate 11 of the first example includes a substrate 2 and an AlN-containing film 100. The nitride semiconductor substrate 21 of the second example includes a substrate 2 and an AlN-containing film 200. The nitride semiconductor substrate 31 of the third example includes a substrate 2 and an AlN-containing film 300. The AlN-containing film 100, the AlN-containing film 200, and the AlN-containing film 300 are films containing AlN such as AlGaN. In the first to third examples according to the embodiment, they are described as films composed of AlN.

[0026] The substrate 2 is, for example, a substrate made of sapphire. The material constituting the substrate 2 is not limited to sapphire, and the substrate 2 may be a substrate composed of one of sapphire, silicon carbide, and ScAlMgO4. Note that each of the substrates 2 in the first, second, and third examples may be composed of different materials.

[0027] The AlN-containing film 100, the AlN-containing film 200, and the AlN-containing film 300 are thin films provided above the substrate 2. Note that the AlN-containing film 100 of the first example is composed of a first AlN film 10. The AlN-containing film 200 of the second example is composed of a first AlN film 10 and a second AlN film 20. The AlN-containing film 300 of the third example is composed of a first AlN film 10, a second AlN film 20, and a third AlN film 30.

[0028] The first AlN film 10, the second AlN film 20, and the third AlN film 30 are hexagonal and are thin films composed of an aggregate of crystal grains. The first AlN film 10, the second AlN film 20, and the third AlN film 30 are composed of one of AlN, Al x Ga y In 1-x-y N (0.5 ≤ x ≤ 1, 0 ≤ y ≤ 0.5, x + y ≤ 1) and B z Al w Ga 1-z-w N (0 ≤ z ≤ 0.5, 0.5 ≤ w ≤ 1, z + w ≤ 1). That is, the first AlN film 10, the second AlN film 20, and the third AlN film 30 may be AlN, AlGaN, AlGaInN, BAlN, or BAlGaN.

[0029] In addition, when the first AlN film 10, the second AlN film 20, and the third AlN film 30 are composed of Al x Ga y In 1-x-y N, the number of Al elements is 50% or more compared to the total number of elements of Al, Ga, and In. Also, when the first AlN film 10, the second AlN film 20, and the third AlN film 30 are composed of B z Al w Ga 1-z-w N, the number of Al elements is 50% or more compared to the total number of elements of B, Al, and Ga.

[0030] In addition, each of the first AlN film 10, the second AlN film 20, and the third AlN film 30 may be composed of the same material composition or different material compositions.

[0031] The film thicknesses of the AlN-containing films 100, 200, and 300 are 10000 nm or less. The film thicknesses of the AlN-containing films 100, 200, and 300 may be 300 nm or more. Also, the film thicknesses of the AlN-containing films 100, 200, and 300 are more preferably 450 nm or more and 3000 nm or less, and even more preferably 600 nm or more and 2000 nm or less.

[0032] [Method and Apparatus for Manufacturing a Nitride Semiconductor Substrate] Next, a manufacturing apparatus and a manufacturing method for the nitride semiconductor substrate 11 of the first example, the nitride semiconductor substrate 21 of the second example, and the nitride semiconductor substrate 31 of the third example will be described. The manufacturing apparatus is commonly used in the first example, the second example, and the third example.

[0033] Note that the nitride semiconductor substrate 11 of the first example is manufactured by the manufacturing method of the first example, the nitride semiconductor substrate 21 of the second example is manufactured by the manufacturing method of the second example, and the nitride semiconductor substrate 31 of the third example is manufactured by the manufacturing method of the third example.

[0034] <Manufacturing Method of the First Example> First, the manufacturing method of the first example for manufacturing the nitride semiconductor substrate 11 of the first example will be described.

[0035] FIG. 4 is a schematic diagram showing a configuration example of a sputtering apparatus 1000 according to the present embodiment. FIG. 5 is a flowchart showing an example of a manufacturing method of the nitride semiconductor substrate 11 according to the first example of the present embodiment.

[0036] First, the configuration example of the sputtering apparatus 1000 shown in FIG. 4 will be described. As shown in the figure, the sputtering apparatus 1000 includes a chamber 110, an intake pipe 101, an exhaust pipe 102, a valve 103, an exhaust pump 104, a substrate holder 105, a permanent magnet 108, and a high-voltage power supply 109.

[0037] The chamber 110 is a substantially sealed room that holds the substrate 2 and the target 107 that is a raw material for the first AlN film 10 in opposition to each other, and can arbitrarily set the pressure and temperature of the gas inside the chamber 110. Hereinafter, the gas pressure inside the chamber 110 during sputtering is referred to as the sputtering pressure.

[0038] The intake pipe 101 is an intake pipe for introducing an inert gas supplied from the outside into the chamber 110. The inert gas is helium (He) gas, nitrogen (N2) gas, argon (Ar) gas, or the like. The intake pipe 101 may supply a plurality of types of gases simultaneously from one intake pipe.

[0039] Also, a configuration in which a plurality of intake pipes 101 are connected to the chamber 110 may be adopted. Further, it may be possible to introduce a gas other than the inert gas from the intake pipe 101. Examples of the gas other than the inert gas include hydrogen (H2) gas, oxygen (O2) gas, ammonia (NH3) gas, etc. The intake pipe 101 may be provided with a mechanism for precisely controlling the flow rate of the supplied gas.

[0040] The exhaust pipe 102 is an exhaust pipe for exhausting the gas inside the chamber 110 to the outside.

[0041] The valve 103 adjusts the exhaust flow rate of the exhaust pipe 102.

[0042] The exhaust pump 104 is a pump for exhausting the gas inside the chamber 110 to the outside through the exhaust pipe 102 and the valve 103.

[0043] The substrate holder 105 holds the substrate 2 in the state of a wafer substrate. Note that the substrate holder 105 may hold a plurality of substrates 2 to be film-formed simultaneously. The substrate holder 105 has a heating mechanism, and it may be possible to heat and hold the substrate 2 in the range of 500°C or higher and 650°C or lower, for example, at 600°C.

[0044] The substrate holder 105 may have a mechanism capable of arbitrarily controlling the angle at which the substrate 2 is viewed from the target 107. It may also be possible to rotate or revolve the substrate during sputtering film formation.

[0045] The target 107 is held by the target holder. Note that the target holder may hold a plurality of types of targets 107 made of different materials, and it may be possible to switch the target 107 to be sputtered. In this case, it becomes a configuration in which a plurality of different materials can be continuously sputtered while keeping the chamber 110 under high vacuum.

[0046] Also, a configuration that enables simultaneous sputtering of a plurality of different materials may be used. The shape of the target 107 is, for example, a circle with a diameter of 10 cm. The target 107 may be rectangular or have other shapes.

[0047] The high-voltage power supply 109 applies a high-frequency voltage between the substrate 2 and the target 107. The high-frequency voltage is, for example, an RF (Radio Frequency) voltage. The RF voltage component of the high-frequency voltage plasmaizes the gas supplied from the intake pipe 101 between the substrate 2 and the target 107.

[0048] The plasmaized gas collides with the target 107 due to an electric field generated by a self-bias or a DC voltage component applied by an external power supply, ejecting (sputtering) the atoms on the surface of the target 107. The ejected atoms fly toward the substrate 2 and adhere thereto according to the kinetic energy imparted by sputtering.

[0049] As a result, a film made of the target 107 as a raw material or a film made of a compound of the material constituting the target 107 and the gas supplied from the intake pipe 101 is formed on the substrate 2. The voltage of the high-frequency voltage may be, for example, 0 V or more and 5000 V or less, and the frequency of the high-frequency voltage may be 13.56 MHz. The DC voltage component can be set to 0 V or more and 2000 V or less.

[0050] In the sputtering apparatus 1000 of FIG. 4, an example of so-called RF sputtering using a high-frequency voltage is shown, but DC sputtering using a DC voltage may also be used. Further, the voltage may be applied in a pulsed manner having a certain time width. In the case of DC sputtering, it is necessary to use a conductive material for the target 107.

[0051] The permanent magnet 108 forms a magnetic field for confining electrons in the plasma near the target 107. Thereby, the plasma density near the target 107 is increased and the sputtering rate is raised. Also, by distancing the plasma from the substrate 2, it is possible to prevent the substrate 2 from being irradiated with electrons and charged particles and the crystal quality of the first AlN film 10 from deteriorating.

[0052] Note that the sputtering apparatus 1000 may not include the permanent magnet 108. It may also be possible to arbitrarily move the permanent magnet 108 during sputter film formation. The vicinity of the target 107 and the permanent magnet 108 is cooled by cooling water, and the temperature rise of the target 107 is suppressed.

[0053] Also, in the sputtering apparatus 1000 of FIG. 4, a configuration example of a sputter-up type (or face-down type) in which the substrate 2 is disposed to face upward with respect to the target 107 has been described. However, it is not limited to this. A sputter-down type (face-up type) in which the substrate 2 is disposed to face downward with respect to the target 107 may be used, or a side sputter type (side face type) in which the substrate 2 is disposed to face the side of the target 107 may be used.

[0054] In FIG. 4, the distance between the substrate 2 and the target 107 is, for example, 14 cm.

[0055] Next, a method for manufacturing a nitride semiconductor substrate 11 will be described using the flowchart of FIG. 5.

[0056] As shown in FIG. 5, the method for manufacturing a nitride semiconductor substrate 11 broadly includes a first step S21, a second step S22, a third step S23, and a fourth step S24.

[0057] The first step S21 is a preparation step of preparing the substrate 2. Specifically, in the first step S21, the substrate 2 is prepared on the substrate holder 105 in the sputtering apparatus 1000. As described above, this substrate 2 is, for example, a sapphire substrate. This sapphire substrate may have, for example, a surface inclined by 0.1° or more and 1.0° or less with respect to the [1-100] direction (m-axis direction) or [11-20] direction (a-axis direction) of sapphire from the (0001) plane.

[0058] The surface of this sapphire substrate may have a step-terrace structure composed of a single atomic layer or a single molecular layer. The back surface of this sapphire substrate may be polished to be optically mirror-like, or may be subjected to roughening treatment.

[0059] A layer made of AlN or a material other than AlN may be formed on the back surface of this sapphire substrate. The substrate holder 105 may be configured to hold, for example, four or more 2-inch wafer substrates. The substrate holder 105 may be configured to hold a substrate having a size of 2 inches or more.

[0060] As a step before the first step S21, the following steps may be performed.

[0061] First, although not shown in FIG. 4, the substrate 2 is placed in a load lock chamber provided adjacent to the chamber 110 and capable of being independently opened to the atmosphere and evacuated to a vacuum. After evacuating to a sufficiently high vacuum inside the load lock chamber, the substrate 2 is transferred from the load lock chamber to the sputtering chamber under vacuum, and the substrate 2 may be installed on the substrate holder 105 inside the chamber 110.

[0062] Thereby, when the substrate 2 is placed on the substrate holder 105, the chamber 110 is not exposed to the atmosphere, so that the inside of the chamber 110 can always be maintained at a high vacuum. Therefore, it becomes possible to stably control the crystal quality of the sputter-deposited AlN. Before the substrate 2 is transferred into the chamber 110, the pressure inside the load lock chamber is, for example, 1×10-4 It is preferable to reduce it to below Pa.

[0063] In the second step S22, the target 107 which is a film-forming material is prepared in the sputtering apparatus 1000. The preparation step may include the first step S21 and the second step S22. The target 107 is, for example, a sintered body of AlN.

[0064] In the first step S21 and the second step S22, after the substrate 2 and the target 107 are arranged, it is preferable to evacuate the chamber 110 for a sufficient time and reduce the pressure of the chamber 110 until the sputtering film formation is started in the third step S23. At this time, it is preferable to reduce the pressure of the chamber 110 while the temperature of the substrate 2 is maintained at the same temperature as or higher than the temperature during the sputtering film formation.

[0065] Thereby, the residual gas concentration in the chamber 110 can be reduced, and the crystal quality of the sputtered AlN can be stably controlled. Further, by evacuating the chamber 110 while heating the substrate 2, the moisture adsorbed on the surface of the substrate 2 can be effectively removed before the substrate 2 is arranged inside the chamber 110. Therefore, the crystal quality of the sputtered AlN can be stably controlled. Before the third step S23 is started, the pressure inside the chamber 110 is, for example, 6×10 -5 It is preferable to reduce it to below Pa.

[0066] The third step S23 is a film-forming step for forming an AlN film (first AlN film 10). Specifically, in the third step S23, the first AlN film 10 including the composition of the target material is formed on the substrate 2 by sputtering the target 107 at a sputtering pressure smaller than 0.5 Pa. The third step S23 is also called a sputtering process.

[0067] More specifically, the sputtering pressure in the chamber 110 is adjusted by the flow rate of the gas supplied from the intake pipe, the exhaust speed of the exhaust pump 104, and the opening degree of the valve 103 so as to reach a desired pressure of 0.5 Pa or less. The surface temperature of the substrate 2 is maintained at a temperature in the range of about 500°C or higher and 650°C or lower, for example, about 600°C, by the heating mechanism of the substrate holder 105.

[0068] For example, nitrogen gas is supplied from the intake pipe 101 as an inert gas. The flow rate of the nitrogen gas is, for example, 10 sccm (Standard Cubic Centimeter per Minute) or more and 100 sccm. The unit sccm is a unit standardized at 0°C and 1 atm.

[0069] The high-frequency voltage of the high-voltage power supply 109 is several hundred V, and the frequency of the high-frequency voltage is, for example, 13.56 MHz. The power supplied from the high-voltage power supply 109 to the target 107 is, for example, 200 W or more and 1000 W or less. The sputtering time may be determined according to the desired film thickness of the first AlN film 10 to be formed and the power supplied to the target.

[0070] Note that, before the formation of the first AlN film 10 on the substrate 2 is started, a process may be provided in which plasma is generated between the target 107 and the shutter with the shutter disposed between the substrate 2 and the target 107, and the target 107 is sputtered.

[0071] In this way, by sputtering the target 107 in a state where the atoms sputtered from the target 107 are blocked by the shutter and do not reach the substrate 2, it is possible to remove the impurities adhering to the surface of the target 107.

[0072] After sputtering the surface of the target 107 for a sufficient time, the shutter disposed between the substrate 2 and the target 107 may be removed, and the formation of the first AlN film 10 on the substrate 2 may be started. Thereby, it becomes possible to stably control the crystal quality of the first AlN film 10 formed by sputtering thereafter.

[0073] The film thickness of the first AlN film 10 included in the nitride semiconductor substrate 11 of the first example may be, for example, 300 nm or more and 1200 nm or less. Further, in order to suppress the introduction of cracks into the first AlN film 10 due to the annealing treatment described later, the larger the film thickness of the first AlN film 10, the smaller the sputtering pressure of the chamber 110 may be. For example, the sputtering pressure of the chamber 110 may be 0.05 Pa or less.

[0074] More specifically, in order to suppress cracks, when the sputtering pressure of the chamber 110 is P (Pa) or less and the film thickness of the nitride layer is T (nm) or less, the combination of (P, T) may satisfy at least one of (0.05, 640), (0.1, 480), and (0.2, 320). Alternatively, the sputtering pressure P and the film thickness T of the nitride layer may be selected so as to be included in the following ranges.

[0075] That is, (1.1) P ≤ 31117 × T -2.06 and 300 ≤ T ≤ 640, and it may be selected from the ranges included in any one of (1.1) or (1.2) of (1.2) P ≤ 0.05 and T ≥ 640.

[0076] The combination of (P, T) is more preferably such that it satisfies at least one of (0.05, 560) and (0.1, 400). In this case, when the sputtering pressure and the film thickness are values other than the above, the sputtering pressure P and the film thickness T of the nitride layer may be selected so as to be included in the following ranges.

[0077] That is, (2.1) P ≤ 1436 × T -1.61 and 300 ≤ T ≤ 560, and it may be selected from the ranges included in any one of (2.1) or (2.2) of (2.2) P ≤ 0.05 and T ≥ 560.

[0078] The combination of (P, T) is preferably such that it satisfies at least one of (0.03, 850), (0.05, 480), and (0.1, 320). In this case, when the sputtering pressure and the film thickness are other than the above values, the sputtering pressure P and the film thickness T of the nitride layer may be selected so as to be within the following ranges.

[0079] That is, (3.1) P ≤ 76.6 × T -1.17 and 300 ≤ T ≤ 850, and it may be selected from the ranges included in any one of (3.1) or (3.2) where P ≤ 0.03 and T ≥ 850. The numerical ranges of the above P and T are valid within ±10%.

[0080] The fourth step S24 is an annealing step of annealing the AlN film (the first AlN film 10) formed in the film formation step (the third step S23) at 1500 °C or higher. Specifically, in the fourth step S24, the substrate 2 on which the first AlN film 10 is formed is heat-treated at 1500 °C or higher, more preferably 1650 °C or higher and 1750 °C or lower. The fourth step S24 is also referred to as an annealing treatment.

[0081] More specifically, first, the substrate 2 on which the first AlN film 10 is formed by the third step S23 is placed inside the annealing apparatus. The annealing apparatus may be any apparatus capable of performing an annealing treatment, and may be a different apparatus from the sputtering apparatus 1000, or may be the sputtering apparatus 1000. The substrate 2 is placed inside the annealing apparatus as follows.

[0082] That is, the main surface of the first AlN film 10 is covered with a cover member for suppressing the dissociation of the components of the material constituting the first AlN film 10 from the main surface of the first AlN film 10 to form an airtight state. Here, "dissociation" means that the components (nitrogen, aluminum, gallium, indium, boron, etc.) of the first AlN film 10 escape from the main surface thereof, and includes sublimation, evaporation, and diffusion. Also, the "main surface" of the first AlN film 10 (or the substrate 2) refers to the surface on the side where another material is laminated (or formed) when another material is laminated (formed) thereon.

[0083] In addition, when the installation of the cover member or the like is not performed in an inert gas atmosphere between the film formation step (third step S23) and the annealing step (fourth step S24), the substrate 2 on which the first AlN film 10 is formed is exposed to the atmosphere.

[0084] Next, in order to discharge impurities inside the annealing apparatus, after evacuating the inside of the annealing apparatus to a vacuum, gas replacement is performed by flowing an inert gas or a mixed gas. Thereafter, while maintaining the first AlN film 10 in the above-described airtight state, the temperature of the substrate 2 on which the first AlN film 10 is formed is increased. The rate of increasing the temperature is referred to as the heating rate. The heating rate may be, for example, 18.9 ° C per minute.

[0085] After the temperature of the substrate 2 on which the first AlN film 10 is formed reaches a predetermined temperature (for example, 1650 ° C or higher and 1750 ° C or lower), the first AlN film 10 is annealed by holding the temperature of the substrate 2 on which the first AlN film 10 is formed at the predetermined temperature for a predetermined time. The temperature of the substrate 2 on which the first AlN film 10 is formed during annealing is referred to as the annealing temperature, and the time for holding at the annealing temperature is referred to as the annealing time.

[0086] In order to reduce the threading dislocation density of the first AlN film 10 after annealing, annealing may be performed at a higher annealing temperature. The annealing temperature is preferably 1700 ° C or higher and 1750 ° C or lower, and more preferably 1725 ° C or higher and 1750 ° C or lower.

[0087] The annealing time may be, for example, 3 hours or more and 12 hours or less. In addition, in order to reduce the threading dislocation density of the first AlN film 10, the annealing time may be made longer as the film thickness of the first AlN film 10 is thicker. Further, when the annealing temperature is excessively high or the annealing time is excessively long, the surface flatness of the first AlN film 10 after the annealing treatment may be deteriorated. In order to reduce the threading dislocation density without impairing the surface flatness of the first AlN film 10, the annealing temperature may be increased and the annealing time may be made longer within a range where the surface flatness is not impaired.

[0088] After the substrate 2 on which the first AlN film 10 has been formed has been held at the annealing temperature for the annealing time, the temperature of the substrate 2 on which the first AlN film 10 has been formed is lowered to 100°C or lower. Then, the substrate 2 on which the first AlN film 10 has been formed is taken out from the annealing apparatus. The rate of temperature decrease is referred to as the cooling rate. The cooling rate may be, for example, 1°C or more and 100°C or less per minute. Also, the cooling rate may be constant or may change with time.

[0089] At this time, the substrate 2 on which the first AlN film 10 has been formed is annealed in an atmosphere of an inert gas such as nitrogen gas, argon gas, helium gas, or a mixed gas in which ammonia gas or carbon monoxide gas is added to the inert gas.

[0090] Also, the pressure of the inert gas or mixed gas in the annealing apparatus is in the range of 0.1 atm or more and 10 atm or less (76 Torr or more and 7600 Torr or less), which is a range where an annealing effect can be expected. However, due to factors such as the explosion-proof strength at high temperatures, it is set to about 0.5 atm or more and 2 atm or less. In principle, a higher nitrogen partial pressure in these gases can be expected to improve the crystallinity of the first AlN film 10 and suppress surface roughness, but the gas pressure may be set around 1 atm. Here, the relationship between pressure units is 1 atm = 101,325 Pa (Pascal) = 760 Torr.

[0091] By such annealing, the threading dislocation density of the first AlN film 10 can be reduced and the crystallinity can be improved.

[0092] Note that the annealing apparatus may be a heating container having a certain volume and having functions of controlling the substrate temperature within the range of 500°C or more and 1800°C or less, and functions of controlling the pressure and flow rate of the inert gas and mixed gas introduced into and replaced in the apparatus.

[0093] The annealing apparatus may be configured such that a cover member covers the substrate 2 on which the first AlN film 10 is formed inside the apparatus, or the cover member is disposed upward, and the substrate 2 on which the first AlN film 10 is formed is placed upside down such that the first AlN film 10 contacts the cover member. Further, a mechanism for applying an arbitrary pressure between the cover member and the substrate may be provided. The annealing apparatus may be capable of simultaneously heat-treating a plurality of substrates 2 on which the first AlN films 10 are formed.

[0094] Next, the airtight state in the fourth step S24 will be described.

[0095] The airtight state is a state realized inside the annealing apparatus, in which the main surface of the first AlN film 10 is covered with a cover member to suppress the dissociation of its components (such as nitrogen, aluminum, gallium, indium, etc.) from the main surface. That is, in the airtight state, the dissociation of the components from the main surface of the first AlN film 10 is suppressed by a physical method. In this state, the gas between the cover member and the main surface of the first AlN film 10 is in a substantially stagnant state where it does not flow.

[0096] In such an airtight state, when the nitride semiconductor substrate 11 is annealed, the roughening of the main surface due to the dissociation of the components from the main surface of the first AlN film 10 is suppressed. Further, annealing at a higher temperature becomes possible, and a nitride semiconductor substrate 11 with a flat and high-quality first AlN film 10 formed thereon is realized.

[0097] Further, the target 107 prepared in the second step S22 is not limited to a sintered body of AlN, and may be Al, AlGaN, AlNGaIn, BAlN, or BAlGaN.

[0098] Note that the inert gas in the sputtering in the third step S23 is not limited to nitrogen gas, and may be argon gas, helium gas, or a mixed gas of nitrogen gas and argon gas or helium gas.

[0099] Note that the airtight state during annealing is carried out for the purpose of easily obtaining a surface of the nitride layer with a flat surface. Therefore, annealing conditions that do not cause roughness due to substantially desorption from the surface, or in the case of intentionally creating an uneven structure on the surface of the first AlN film 10, it is not necessary to cover the surface.

[0100] <Manufacturing method of the second example> Next, a second example of a manufacturing method for manufacturing the nitride semiconductor substrate 21 of the second example will be described. FIG. 6 is a flowchart showing an example of a manufacturing method of the nitride semiconductor substrate 21 according to the second example of the present embodiment.

[0101] As shown in FIG. 6, the manufacturing method of the nitride semiconductor substrate 21 mainly includes a first step S31, a second step S32, a third step S33, a fourth step S34, a fifth step S35, and a sixth step S36. Here, the first step S31 and the second step S32 are the same as the first step S21 and the second step S22 of the manufacturing method of the first example.

[0102] The third step S33 in the second example is a film forming step of forming an AlN film (first AlN film 10). Specifically, in the third step S33, the target 107 is sputtered at a sputtering pressure lower than 0.5 Pa, whereby the first AlN film 10 containing the composition of the target material is formed on the substrate 2. That is, the third step S33 is the first sputtering process.

[0103] More specifically, the sputtering pressure in the chamber 110 is adjusted by the flow rate of the gas supplied from the intake pipe, the exhaust speed of the exhaust pump 104, and the opening degree of the valve 103 so as to reach a desired pressure of 0.5 Pa or less. The surface temperature of the substrate 2 is maintained at a temperature in the range of about 500°C or more and 650°C or less, for example, about 600°C, by the heating mechanism of the substrate holder 105.

[0104] For example, nitrogen gas is supplied from the intake pipe 101 as an inert gas. The flow rate of the nitrogen gas is, for example, 10 sccm or more and 100 sccm or less.

[0105] The high-frequency voltage of the high-voltage power supply 109 is several hundred volts, and the frequency of the high-frequency voltage is, for example, 13.56 MHz. The power supplied from the high-voltage power supply 109 to the target 107 is, for example, 200 W or more and 1000 W or less. The sputtering time may be determined according to the desired film thickness of the first AlN film 10 to be formed and the power supplied to the target.

[0106] Note that before the formation of the first AlN film 10 on the substrate 2 is started, a step of generating plasma between the target 107 and the shutter with the shutter disposed between the substrate 2 and the target 107 and sputtering the target 107 may be provided.

[0107] In this way, by sputtering the target 107 in a state where the atoms sputtered from the target 107 are blocked by the shutter and do not reach the substrate 2, it becomes possible to remove the impurities adhering to the surface of the target 107. After sputtering the surface of the target 107 for a sufficient time, the shutter disposed between the substrate 2 and the target 107 may be removed, and the formation of the first AlN film 10 on the substrate 2 may be started. Thereby, it becomes possible to stably control the crystal quality of the first AlN film 10 formed by sputtering thereafter.

[0108] The film thickness of the first AlN film 10 provided in the nitride semiconductor substrate 11 of the second example is preferably, for example, 100 nm or more and 900 nm or less. Further, the film thickness of the first AlN film 10 provided in the nitride semiconductor substrate 11 of the second example is more preferably 150 nm or more and 750 nm or less, and even more preferably 200 nm or more and 600 nm or less.

[0109] In addition, in order to suppress the introduction of cracks into the first AlN film 10 due to the annealing treatment described later, the sputtering pressure in the chamber 110 may be reduced as the film thickness of the first AlN film 10 increases. For example, the sputtering pressure in the chamber 110 may be 0.05 Pa or less.

[0110] More specifically, for crack suppression, when the sputtering pressure in the chamber 110 is P (Pa) or less and the film thickness of the nitride layer is T (nm) or less, the combination of (P, T) may satisfy at least one of (0.05, 640), (0.1, 480), and (0.2, 320). Alternatively, the sputtering pressure P and the film thickness T of the nitride layer may be selected so as to be included in the following ranges.

[0111] That is, (1.1) P ≤ 31117 × T -2.06 and 300 ≤ T ≤ 640, and it may be selected from the ranges included in either (1.1) or (1.2) of (1.2) P ≤ 0.05 and T ≥ 640.

[0112] It is better if the combination of (P, T) satisfies at least one of (0.05, 560) and (0.1, 400). In this case, when the sputtering pressure and the film thickness are values other than the above, the sputtering pressure P and the film thickness T of the nitride layer may be selected so as to be included in the following ranges.

[0113] That is, (2.1) P ≤ 1436 × T -1.61 and 300 ≤ T ≤ 560, and it may be selected from the ranges included in either (2.1) or (2.2) of (2.2) P ≤ 0.05 and T ≥ 560.

[0114] It is even better if the combination of (P, T) satisfies at least one of (0.03, 850), (0.05, 480), and (0.1, 320). In this case, when the sputtering pressure and the film thickness are values other than the above, the sputtering pressure P and the film thickness T of the nitride layer may be selected so as to be included in the following ranges.

[0115] That is, (3.1) P ≤ 76.6 × T -1.17 and 300 ≤ T ≤ 850, and it may be selected from the ranges included in either (3.1) or (3.2) of (3.2) P ≤ 0.03 and T ≥ 850.

[0116] The fourth step S34 is an annealing step of annealing the AlN film (first AlN film 10) formed in the film formation step (third step S33) at 1500°C or higher. Specifically, in the fourth step S34, the substrate 2 on which the first AlN film 10 is formed is annealed at 1500°C or higher, more preferably at 1650°C or higher and 1750°C or lower. That is, the fourth step S34 is the first annealing treatment.

[0117] More specifically, first, the substrate 2 on which the first AlN film 10 is formed by the third step S33 is placed inside the annealing apparatus. The substrate 2 is placed inside the annealing apparatus as follows.

[0118] That is, as in the first example, also in the second example, in order to suppress the dissociation of the components of the nitride semiconductor from the main surface of the formed first AlN film 10, the main surface of the first AlN film 10 is covered with a cover member to form an airtight state.

[0119] Next, in order to discharge the impurities inside the annealing apparatus, after evacuating the inside of the annealing apparatus to a vacuum, gas replacement is performed by flowing an inert gas or a mixed gas. Then, while maintaining the first AlN film 10 in the above-mentioned airtight state, the temperature of the substrate 2 on which the first AlN film 10 is formed is raised. At this time, the heating rate may be, for example, 18.9°C per minute.

[0120] After the temperature of the substrate 2 on which the first AlN film 10 is formed reaches a predetermined temperature (for example, 1650°C or higher and 1750°C or lower), for example, the first AlN film 10 is annealed by holding the temperature of the substrate 2 on which the first AlN film 10 is formed for a predetermined time for a predetermined time.

[0121] In the second example, the annealing temperature and annealing time for reducing the threading dislocation density of the first AlN film 10 are the same as those in the fourth step S24 of the first example.

[0122] Also, in the second example, the pressure of the inert gas or mixed gas in the annealing apparatus may be set the same as in the fourth step S24 of the first example.

[0123] Subsequently, a fifth step S35 and a sixth step S36 are performed.

[0124] The fifth step S35 is a film formation step of forming an AlN film (second AlN film 20). That is, the fifth step S35 is the same step as the third step S33, and the fifth step S35 is a second sputtering process.

[0125] The sixth step S36 is an annealing step of annealing the AlN film (second AlN film 20) formed in the film formation step (fifth step S35) at 1500 °C or higher. That is, the sixth step S36 is the same step as the fourth step S34, and the sixth step S36 is a second annealing process.

[0126] Therefore, in the manufacturing method according to the second example of the present embodiment, the film formation step and the annealing step are performed multiple times.

[0127] Here, the fifth step S35 will be briefly described focusing on the differences from the third step S33.

[0128] In the fifth step S35, the second AlN film 20 is formed above the first AlN film 10 that has been annealed in the fourth step S34. Specifically, in the fifth step S35, the target 107 is sputtered at a sputtering pressure less than 0.5 Pa, whereby the second AlN film 20 containing the composition of the target material is formed.

[0129] In the fifth step S35, the procedure until the shutter is removed and the film formation of the second AlN film 20 on the first AlN film 10 is started is the same as that of the third step S33. However, the sputtering conditions such as the surface temperature of the substrate 2, the sputtering pressure, the RF output, the supply gas type, the supply gas flow rate, and the target material may be the same as or different from the conditions when the first AlN film 10 is formed (third step S33). For example, the sputtering pressure when the second AlN film 20 is formed may be set higher than the sputtering pressure when the first AlN film 10 is formed.

[0130] The film thickness of the second AlN film 20 may be, for example, 100 nm or more and 900 nm or less. Further, the film thickness of the second AlN film 20 is more preferably 150 nm or more and 750 nm or less, and even more preferably 200 nm or more and 600 nm or less. Note that the film thicknesses of the first AlN film 10 and the second AlN film 20 may be the same or different. For example, the film thickness of the second AlN film 20 may be greater than the film thickness of the first AlN film 10.

[0131] In addition, in order to suppress the generation of cracks in the first AlN film 10 and the second AlN film 20 due to the annealing treatment in the sixth step S36, the sputtering pressure in the chamber 110 may be reduced as the film thicknesses of the first AlN film 10 and the second AlN film 20 increase. For example, the sputtering pressure in the chamber 110 in the third step S33 and the fifth step S35 may be 0.05 Pa or less.

[0132] Next, the sixth step S36 will be briefly described, focusing on the differences from the fourth step S34.

[0133] In the sixth step S36, the substrate 2 on which the first AlN film 10 and the second AlN film 20 are formed is annealed at 1500 °C or higher, more preferably 1650 °C or higher and 1750 °C or lower.

[0134] In the sixth step S36, the procedure until the start of the temperature increase of the annealing treatment is the same as that of the fourth step S34. However, the annealing treatment conditions such as the temperature increase rate, the temperature decrease rate, the annealing temperature, and the annealing time may be the same as or different from the annealing treatment of the fourth step S34.

[0135] For example, the annealing time of the annealing treatment in the sixth step S36 may be longer than the annealing time of the annealing treatment in the fourth step S34. Also, the annealing temperature of the annealing treatment in the sixth step S36 may be higher than the annealing temperature of the annealing treatment in the fourth step S34.

[0136] After the substrate 2 on which the first AlN film 10 and the second AlN film 20 are formed has been annealed at the annealing temperature for the annealing time, the temperature of the substrate 2 on which the first AlN film 10 and the second AlN film 20 are formed is lowered to 100°C or lower and taken out from the annealing apparatus. The temperature reduction rate may be, for example, 1°C or more and 100°C or less per minute. Also, the temperature reduction rate may be constant or may change with time.

[0137] Here, Non-Patent Document 1 will be described. For example, in the nitride semiconductor substrate in this document, the first AlN layer and the second AlN layer formed on the substrate are each manufactured by a manufacturing method in which the targets are Al and AlN. Therefore, in the nitride semiconductor substrate in this document, the polarities of the first AlN layer and the second AlN layer are inverted.

[0138] On the other hand, in this example, in the third step S33 and the fifth step S35, AlN was used as the target 107. Also, although Al may be used as the target 107, in the third step S33 and the fifth step S35, the material constituting the target 107 is preferably the same material.

[0139] Thereby, in this example, the polarities of the first AlN film 10 and the second AlN film 20 are the same and have an Al polarity. Note that, in the nitride semiconductor substrate 21 in this example, a plurality of layers with different polarities may be formed, but most of the first AlN film 10 and the second AlN film 20 have an Al polarity, and the film thickness of the layer having an N polarity is 200 nm or less.

[0140] <Manufacturing method of the third example> Next, a manufacturing method of the third example for manufacturing the nitride semiconductor substrate 31 of the third example will be described. FIG. 7 is a flowchart showing an example of the manufacturing method of the nitride semiconductor substrate 31 according to the third example of the present embodiment.

[0141] As shown in FIG. 7, the method for manufacturing the nitride semiconductor substrate 31 is roughly divided into a first step S41, a second step S42, a third step S43, a fourth step S44, a fifth step S45, a sixth step S46, a seventh step S47, and an eighth step S48. Here, the first step S41 to the sixth step S46 of the method for manufacturing the nitride semiconductor substrate 31 of the third example are the same as the first step S31 to the sixth step S36 of the method for manufacturing the nitride semiconductor substrate 21 of the second example.

[0142] Further, the seventh step S47 is a film forming step of forming an AlN film (the third AlN film 30). That is, the seventh step S47 is the same step as the third step S43 and the fifth step S45, and the seventh step S47 is the third sputtering process.

[0143] The eighth step S48 is an annealing step of annealing the AlN film (the third AlN film 30) formed in the film forming step (the seventh step S47) at 1500 ° C or higher. That is, the eighth step S48 is the same step as the fourth step S44 and the sixth step S46, and the eighth step S48 is the third annealing process.

[0144] Therefore, in the manufacturing method according to the third example of the present embodiment, the film forming step and the annealing step are performed a plurality of times.

[0145] Here, the seventh step S47 will be briefly described centering on the difference from the fifth step S45 (that is, the fifth step S35 of the second example).

[0146] In the seventh step S47, the third AlN film 30 is formed above the second AlN film 20 that has been annealed in the fifth step S45.

[0147] In the seventh step S47, the procedure until the shutter is removed and the film formation of the second AlN film 20 on the second AlN film 20 is started is the same as that in the fifth step S45. However, the sputtering conditions such as the surface temperature of the substrate 2, the sputtering pressure, the RF output, the supply gas type, the supply gas flow rate, and the target material may be the same as or different from the conditions when the first AlN film 10 and the second AlN film 20 are formed.

[0148] The film thickness of the third AlN film 30 may be, for example, 100 nm or more and 900 nm or less. Further, the film thickness of the third AlN film 30 is preferably 150 nm or more and 750 nm or less, and more preferably 200 nm or more and 600 nm or less.

[0149] Note that the film thicknesses of the first AlN film 10, the second AlN film 20, and the third AlN film 30 may be the same or different. Also, the film formation method may be a sputtering method or other film formation methods such as MOVPE (Metal Organic Vapor Phase Epitaxy), or they may be used in combination. Further, different sputtering apparatuses may be used for each film formation, and it is also possible to arrange the film formation apparatus and the annealing apparatus in a line during production and use them.

[0150] Next, regarding the eighth step S48, a brief explanation will be given centering on the differences from the sixth step S46 (that is, the sixth step S36 of the second example).

[0151] In the eighth step S48, the substrate 2 on which the first AlN film 10, the second AlN film 20, and the third AlN film 30 are formed is annealed at 1500 °C or higher, more preferably 1650 °C or higher and 1750 °C or lower.

[0152] In the eighth step S48, the procedure until the start of temperature increase of the annealing treatment is the same as that of the sixth step S46. However, the annealing treatment conditions such as the temperature increase rate, the temperature decrease rate, the annealing temperature, and the annealing time may be the same as or different from the annealing treatments of the fourth step S44 and the sixth step S46.

[0153] After the substrate 2 on which the first AlN film 10, the second AlN film 20, and the third AlN film 30 are formed is held at the annealing temperature for the annealing time, the temperature of the substrate 2 is lowered to 100 °C or lower and taken out from the annealing apparatus. The temperature decrease rate may be, for example, 1 °C or more and 100 °C or less per minute. Also, the temperature decrease rate may be constant or may change with time.

[0154] Although not shown in FIG. 7, after the eighth step S48, a film forming step and an annealing step may be further performed. For example, after the eighth step S48, the film forming step and the annealing step may each be performed one or more times, but preferably four or less times for the sake of simplicity of the manufacturing method.

[0155] Also, in this example as well, the polarities of the first AlN film 10, the second AlN film 20, and the third AlN film 30 are the same and have an Al polarity. Note that, in the nitride semiconductor substrate 31 in this example, a plurality of layers with different polarities may be formed, but most of the first AlN film 10, the second AlN film 20, and the third AlN film 30 have an Al polarity, and the film thickness of the layer having an N polarity is 200 nm or less.

[0156] Summarizing the above, the manufacturing method according to this embodiment includes a preparation step of preparing the substrate 2, a film forming step, and an annealing step. The film forming step is a step of forming an AlN film (the first AlN film 10, the second AlN film 20, and the third AlN film 30) having a film thickness of 100 nm or more and 900 nm or less as an example above the substrate 2. The annealing step is a step of annealing the AlN film formed in the film forming step at 1500° C. or higher.

[0157] Note that the film forming step and the annealing step are performed a plurality of times. That is, as shown in the manufacturing methods of the second example and the third example, the film forming step is performed a plurality of times and the annealing step is performed a plurality of times. Also, not limited to this, at least one of the film forming step and the annealing step may be performed a plurality of times. That is, for example, the film forming step may be performed once and the annealing step may be performed a plurality of times, and further, for example, the film forming step may be performed a plurality of times and the annealing step may be performed once.

[0158] [Evaluation 1 of Nitride Semiconductor Substrate] Next, the results of evaluating the threading dislocation density of the AlN-containing film 100, the AlN-containing film 200, and the AlN-containing film 300 by changing the manufacturing conditions in the manufacturing methods of the first example, the second example, and the third example of this embodiment will be described.

[0159] FIG. 8 is a diagram showing an example of a table representing the crystallinity of the nitride semiconductor substrates 11, 21, and 31 according to the present embodiment. More specifically, FIG. 8 shows the results of measurements of the nitride semiconductor substrates 11, 21, and 31 by an X-ray diffractometer (XRD).

[0160] The sample substrates (substrate numbers) shown in FIG. 8 correspond to the nitride semiconductor substrates 11, 21, and 31 according to the present embodiment. FIG. 8 shows the full widths at half maximum (FWHM) of the X-ray rocking curves (XRC) of the AlN-containing films 100, 200, and 300 with respect to the film thickness, annealing temperature, and annealing time of the first AlN film 10, second AlN film 20, and third AlN film 30 according to the present embodiment. Specifically, the FWHM of the XRC of the (0002) plane and the FWHM of the XRC of the (10-12) plane of the AlN-containing films 100, 200, and 300 are shown.

[0161] The crystallinity of the AlN-containing films 100, 200, and 300 corresponds to the value of the full width at half maximum (FWHM) of the diffraction peaks obtained by XRC measurement of the (0002) plane and the (10-12) plane. The smaller the FWHM of this XRC, that is, the sharper the obtained diffraction peak, the better the crystallinity. The unit of the FWHM of the XRC is arcsec (") representing an angle.

[0162] Also, the surface states of the AlN-containing films 100, 200, and 300 are represented by flat, pits, and rough. Flat represents the state with the highest surface flatness, rough represents the state with a rough surface, and pits represents an intermediate state between flat and rough.

[0163] The sample substrates with substrate numbers shown in FIG. 8 correspond to the nitride semiconductor substrates 11, 21, and 31 manufactured by the manufacturing method according to the present embodiment. Hereinafter, the sample substrates with substrate numbers are denoted by substrate numbers, for example, like substrate number A1.

[0164] In FIG. 8, the fact that the film thickness of the second AlN film 20 is 0 nm means that after the first annealing treatment, the second annealing treatment was performed without forming the second AlN film 20 by the second sputtering treatment. Note that between this first annealing treatment and the second annealing treatment, the sample substrate was exposed to the atmosphere.

[0165] Similarly, the fact that the film thickness of the third AlN film 30 is 0 nm means that after the second annealing treatment, the third annealing treatment was performed without forming the third AlN film 30 by the third sputtering treatment. Note that between this second annealing treatment and the third sputtering, the sample substrate was exposed to the atmosphere.

[0166] As described above, since the films of the second AlN film 20 and the third AlN film 30 are not formed by the second and third sputtering treatments, the sample with a film thickness of 0 nm for the second AlN film 20 and the third AlN film 30 corresponds to the nitride semiconductor substrate 11 manufactured by the manufacturing method according to the first example of the present embodiment.

[0167] Specifically, substrate numbers A1, A2, A3, B1, B2, B3, C1, C2, D1, and D2 correspond to the nitride semiconductor substrate 11.

[0168] Also, when the film thickness of the second AlN film 20 is greater than 0 nm, the sample substrate was exposed to the atmosphere between the first annealing treatment and the second sputtering.

[0169] Therefore, as described above, the sample with a film thickness of the second AlN film 20 greater than 0 nm corresponds to the nitride semiconductor substrate 21 manufactured by the manufacturing method according to the second example of the present embodiment.

[0170] Specifically, substrate numbers F1, F2, F3, F4, G1, H1, H2, and H3 correspond to the nitride semiconductor substrate 21.

[0171] Note that, since the annealing temperature in the second annealing process for the substrate number F1 is less than 1500°C, a nitride semiconductor substrate of the comparative example is used.

[0172] Also, when the film thickness of the third AlN film 30 is greater than 0 nm, the sample substrate is exposed to the atmosphere between the second annealing process and the third sputtering.

[0173] Therefore, as described above, a sample with a film thickness of the third AlN film 30 greater than 0 nm corresponds to the nitride semiconductor substrate 31 manufactured by the manufacturing method according to the third example of the present embodiment.

[0174] Specifically, the substrate numbers G2 and H4 correspond to the nitride semiconductor substrate 31.

[0175] Here, the full width at half maximum of XRC with respect to the film thickness, annealing temperature, and annealing time of the first AlN film 10, the second AlN film 20, and the third AlN film 30 will be described. Hereinafter, it is described that the higher the crystallinity, the smaller the full width at half maximum of XRC of the (10-12) plane.

[0176] As shown by the substrate numbers A1, A2, and A3, when the film thickness of the first AlN film 10 is 480 nm, the crystallinity is about the same even if the annealing time is prolonged.

[0177] However, as shown by the substrate numbers A1, A2, A3, B1, B2, B3, C1, and C2, when the film thickness of the first AlN film 10 increases from 480 nm to 600 nm and 900 nm, the crystallinity improves as the annealing time is prolonged.

[0178] That is, the greater the film thickness of the first AlN film 10, the more the crystallinity improves as the annealing time is prolonged.

[0179] Similarly, as shown by the substrate numbers A1, G1, and G2, the greater the film thickness of the AlN-containing film 100, the AlN-containing film 200, and the AlN-containing film 300, the more the crystallinity improves as the annealing time is prolonged.

[0180] Also, similar tendencies are confirmed also in substrate numbers B1, H1, and H4.

[0181] As described above, the film thicknesses of the AlN-containing film 100, the AlN-containing film 200, and the AlN-containing film 300 according to the present embodiment are 300 nm or more and 10,000 nm or less. That is, in the present embodiment, the AlN-containing film 100, the AlN-containing film 200, and the AlN-containing film 300 can have a sufficiently large film thickness, and the nitride semiconductor substrates 11 and 21 according to the present embodiment have high crystallinity. That is, high-quality nitride semiconductor substrates 11, 21, and 31 are realized. As shown in FIG. 8, by performing annealing treatment at a sufficient annealing temperature and annealing time, higher-quality nitride semiconductor substrates 11, 21, and 31 are realized.

[0182] Also, as described above, as shown by substrate numbers B1, B2, B3, C1, and C2, the crystallinity is improved by increasing the annealing time (that is, performing the film formation step once and performing the annealing step a plurality of times).

[0183] That is, the nitride semiconductor substrate 11 manufactured by a manufacturing method including a preparation step, a film formation step, and an annealing step, and in which at least one of the film formation step and the annealing step is performed a plurality of times, has high crystallinity. Therefore, by using the manufacturing method according to the present embodiment, the crystallinity of the high-quality nitride semiconductor substrate 11 is realized.

[0184] Also, as shown by substrate numbers D1 and H1, the film thickness of the first AlN film 10 of substrate number D1 and the total film thickness of the first AlN film 10 and the second AlN film 20 of substrate number H1 are the same at 1200 nm, and the total annealing time is the same at 6 hours. However, the crystallinity of the nitride semiconductor substrate 21 (substrate number H1) manufactured by the manufacturing method of the second example is higher than the crystallinity of the nitride semiconductor substrate 11 (substrate number D1) manufactured by the manufacturing method of the first example.

[0185] Therefore, by using the second manufacturing method including a preparation process, a film formation process, and an annealing process, and performing the film formation process and the annealing process a plurality of times, the crystallinity of the nitride semiconductor substrate 21 can be further enhanced. That is, by using the manufacturing method according to the present embodiment, a high-quality nitride semiconductor substrate 21 can be realized. In addition, the generation of cracks can be effectively suppressed. Further, the decrease in surface flatness can be effectively suppressed.

[0186] Note that the same tendency is also confirmed in the substrate numbers D2 and H2.

[0187] Also, as shown by the substrate numbers F1, F2, F3, and F4, the crystallinity improves as the annealing temperature of the first AlN film 10 increases.

[0188] As shown in FIG. 8, the full width at half maximum of XRC in the (10-12) plane of the AlN-containing film 100, AlN-containing film 200, and AlN-containing film 300 according to the present embodiment is 120 arcsec or less.

[0189] Therefore, the nitride semiconductor substrates 11, 21, and 31 according to the present embodiment have high crystallinity. That is, high-quality nitride semiconductor substrates 11, 21, and 31 are realized.

[0190] Furthermore, the full width at half maximum of XRC in the (0002) plane of the AlN-containing film 100, AlN-containing film 200, and AlN-containing film 300 according to the present embodiment is 120 arcsec or less.

[0191] Therefore, the nitride semiconductor substrates 11, 21, and 31 according to the present embodiment have high crystallinity. That is, high-quality nitride semiconductor substrates 11, 21, and 31 are realized.

[0192] Further, the substrate 2 according to the present embodiment is made of sapphire, but is not limited thereto, and may be a substrate made of silicon carbide, ScAlMgO4, or the like. The materials constituting these substrates 2 have high durability at high temperatures as exemplified in FIG. 8. Therefore, the AlN-containing film 100, the AlN-containing film 200, and the AlN-containing film 300 laminated above the substrate 2 can be annealed at high temperatures. As a result, as shown in FIG. 8, high-quality nitride semiconductor substrates 11, 21, and 31 are realized.

[0193] Also, as described above, the first AlN film 10, the second AlN film 20, and the third AlN film 30 are made of one of AlN, Al x Ga y In 1-x-y N and B z Al w Ga 1-z-w N. In the present embodiment, the first AlN film 10, the second AlN film 20, and the third AlN film 30 are made of AlN. As a result, as shown in FIG. 8, high-quality nitride semiconductor substrates 11, 21, and 31 are realized.

[0194] Here, an image of the nitride semiconductor substrate 11 and the nitride semiconductor substrate 21 according to the present embodiment observed by a scanning transmission electron microscope (STEM) will be described.

[0195] FIG. 9A is a diagram showing a planar STEM image of the nitride semiconductor substrate 11 (substrate number D2) and the nitride semiconductor substrate 21 (substrate numbers H2 and H3) according to the present embodiment. More specifically, (a) in FIG. 9A shows the planar STEM image of substrate number D2, (b) in FIG. 9A shows the planar STEM image of substrate number H2, and (c) in FIG. 9A shows the planar STEM image of substrate number H3.

[0196] The values listed in Fig. 9A are the through - dislocation densities of nitride semiconductor substrate 11 and nitride semiconductor substrate 21. The through - dislocation density is a value derived by counting the number of dark spots (the dark spots correspond to through - dislocations) that appear in the image and calculating the density of dark spots per unit area.

[0197] Fig. 9B is a diagram of another example showing a table representing the crystallinity of nitride semiconductor substrates 11 and 21 according to this embodiment. Specifically, it is the value obtained by calculating the through - dislocation densities of nitride semiconductor substrate 11 (substrate number D2) and nitride semiconductor substrates 21 (substrate numbers H2 and H3) from the plane STEM image shown in Fig. 9A.

[0198] As shown in Fig. 9B, the through - dislocation densities of the AlN - containing film 100 of nitride semiconductor substrate 11 and the AlN - containing film 200 of nitride semiconductor substrate 21 in this embodiment are well within 8 cm -2 the following. More specifically, the through - dislocation densities of the AlN - containing film 100 and the AlN - containing film 200 are within 1.5×10 8 cm -2 the following, and more specifically, within 1×10 8 cm -2 the following.

[0199] That is, the nitride semiconductor substrates 11 and 21 according to this embodiment include substrate 2 and an AlN - containing film (AlN - containing film 100 and AlN - containing film 200) provided above substrate 2. The film thickness of this AlN - containing film is 10000 nm or less, and the through - dislocation density of this AlN - containing film realizes 8 cm -2 the following.

[0200] Thus, by being fabricated using the manufacturing method according to this embodiment, the nitride semiconductor substrates 11 and 21 according to this embodiment can have a sufficiently low through - dislocation density and high crystallinity. That is, high - quality nitride semiconductor substrates 11 and 21 are realized.

[0201] FIG. 9C is a diagram showing a cross-sectional STEM image of the nitride semiconductor substrate 21 (substrate number H2) according to the present embodiment. For this analysis, an AlN film is formed above the substrate number H2 by MOVPE (described as MOVPE-AlN in FIG. 9C).

[0202] (a) of FIG. 9C is a cross-sectional observation image including from the interface between the sapphire substrate and the first AlN film 10 to the surface of the MOVPE-AlN. (b) and (c) of FIG. 9C are enlarged cross-sectional observation images of the regions (b) and (c) marked in FIG. 9C(a).

[0203] As shown in FIG. 9C, most of the first AlN film 10 and the second AlN film 20 are AlN films having Al polarity. However, in the vicinity of the interface between the first AlN film 10 and the substrate 2 within the first AlN film 10, and in the vicinity of the interface between the second AlN film 20 and the first AlN film 10 within the second AlN film 20, layers of AlN films having N polarity are formed. At this time, the film thickness of the layer of the AlN film having N polarity is 200 nm or less.

[0204] At the interface between the second AlN film 20 and the first AlN film 10, and in the vicinity of the interface between the second AlN film 20 and the first AlN film 10 within the second AlN film 20, two dark lines are observed in the cross-sectional STEM image. The region surrounded by the two dark lines is defined as the interface region. The polarity of the AlN film may be inverted with the interface region or the dark lines as a boundary, or the AlN films adjacent to the interface region may have the same Al polarity. In the present embodiment, the interface region is the N-polarity region in the second AlN film 20 shown in FIG. 9C.

[0205] As shown in FIG. 9C(a), the through dislocations generated at the interface between the first AlN film 10 and the substrate 2 and propagating through the first AlN film 10 are bent or terminated in the interface region formed at the interface between the second AlN film 20 and the first AlN film 10, and do not propagate into the second AlN film 20. From this, it is presumed that the above-mentioned interface region may function to inhibit the propagation of through dislocations and reduce the density of through dislocations reaching the outermost surface of the nitride semiconductor substrate 21.

[0206] Next, the impurity concentration distributions of the nitride semiconductor substrates 11 and 21 will be described.

[0207] FIG. 10 is a diagram showing the results of analyzing the impurity concentrations of the nitride semiconductor substrates 11 and 21 according to this embodiment.

[0208] More specifically, (a) in FIG. 10 shows the results for substrate number D2, (b) in FIG. 10 shows the results for substrate number H2, and (c) in FIG. 10 shows the results for substrate number H3. Also, in FIG. 10, the impurity concentration analysis is performed by SIMS (Secondary Ion Mass Spectrometry). Further, for this analysis, an AlN film is formed by MOVPE above substrate numbers D2, H2, and H3 (described as MOVPE - AlN in FIG. 10).

[0209] Also, the horizontal axis of the diagram showing the impurity concentration distribution in FIG. 10, Depth (μm), indicates the distance in the direction proceeding from the MOVPE - AlN toward the substrate 2.

[0210] As described above, substrate number D2 is the nitride semiconductor substrate 11 of the first example, and substrate numbers H2 and H3 are the nitride semiconductor substrates 21 of the second example. Therefore, in substrate number D2, the AlN - containing film 100 is composed of the first AlN film 10, and in substrate numbers H2 and H3, the AlN - containing film 200 is composed of the first AlN film 10 and the second AlN film 20.

[0211] As shown in FIG. 10, the oxygen concentration of the AlN - containing film 100 and the AlN - containing film 200 is 10 18 cm -3 or more and 10 21 cm -3 or less. More specifically, the oxygen concentration is 10 19 cm -3 or more and 10 21 cm -3 or less, and even more specifically, 10 20 cm -3 or more and 10 21 cm -3It is as follows. Also, the hydrogen concentration of the AlN-containing film 100 and the AlN-containing film 200 is 10 16 cm -3 or more and 2×10 17 cm -3 or less. More specifically, the hydrogen concentration is 10 16 cm -3 or more and 10 17 cm -3 or less.

[0212] Note that the oxygen concentration and the hydrogen concentration do not necessarily need to be in the above concentration ranges throughout the entire regions of the AlN-containing film 100 and the AlN-containing film 200. For example, the regions where the oxygen concentration and the hydrogen concentration are in the above concentration ranges may be regions that are a predetermined ratio or more of the entire regions of the AlN-containing film 100 and the AlN-containing film 200. The predetermined ratio may be, for example, 30%, 50%, or 70%. Also, for example, the regions where the oxygen concentration and the hydrogen concentration are in the above concentration ranges may be predetermined regions based on the interface between the substrate 2 and the AlN-containing film 100 or the AlN-containing film 200. This predetermined region may be, for example, a region from a position 100 nm away from the interface as a reference to a position 1000 nm away from the interface as a reference.

[0213] Also, the AlN-containing film 200 has a first layer 201 and a second layer 202 different from the first layer 201.

[0214] Note that the first layer 201 is also an interface layer. The first layer 201 (interface layer) is a layer having a maximum in elemental concentration. For example, the first layer 201 (interface layer) is a layer having a maximum in oxygen concentration, carbon concentration, and silicon (Si) concentration. Note that the first layer 201 (interface layer) is a layer having a maximum in at least one of the oxygen concentration, carbon (C) concentration, and silicon (Si) concentration. As shown in FIG. 10, the first layer 201 (interface layer) is located in the middle between the substrate 2. Also, the middle between the substrate 2 means between the interface between the AlN-containing film 200 and the substrate 2 and the surface of the AlN-containing film 200 on the side opposite to the substrate 2 (that is, in FIG. 10, the interface between the AlN-containing film 200 and the MOVPE-AlN).

[0215] Further, the second layer 202 is a layer located around the first layer 201 (interface layer).

[0216] The first layer 201 is, for example, as shown in FIG. 10, a region located at the interface between the first AlN film 10 and the second AlN film 20, and the film thickness of the first layer 201 is 10 nm or more and 200 nm or less.

[0217] Further, the second layer 202 is, for example, as shown in FIG. 10, a region located in the second AlN film 20, but is not limited thereto as long as it is a region different from the first layer 201.

[0218] As shown in FIG. 10, the element concentration of the first layer 201 is higher than that of the second layer 202. For example, the oxygen concentration of the first layer 201 is higher than that of the second layer 202. In other words, the first layer 201 (interface layer) has a maximum oxygen concentration. In substrate numbers H2 and H3, which are the nitride semiconductor substrates 21 of the second example, there is an air exposure between the first annealing treatment and the second sputtering. The reason why the oxygen concentration of the first layer 201 is higher than that of the second layer 202 is considered to be air exposure, and this air exposure causes the first layer 201 to have a peak point (maximum point) in the oxygen concentration.

[0219] That is, as shown in the present embodiment, it is presumed that the nitride semiconductor substrate in which there is a region (for example, the first layer 201) having a higher element concentration than the surrounding region (for example, the second layer 202) is the nitride semiconductor substrate 21 manufactured by the manufacturing method according to the second example.

[0220] By using the manufacturing method of the second example, the crystallinity of the nitride semiconductor substrate 21 can be further enhanced. Therefore, the fact that the element concentration (for example, oxygen concentration) of the first layer 201 is higher than that of the second layer 202 means that the nitride semiconductor substrate 21 has high crystallinity.

[0221] As shown in FIG. 10, the silicon concentration of the first layer 201 is higher than that of the second layer 202, and the carbon concentration of the first layer 201 is higher than that of the second layer 202. Similarly to the above, it is considered that the reason why the silicon or carbon concentration of the first layer 201 is higher than that of the second layer 202 is atmospheric exposure.

[0222] In the present embodiment, in the first layer 201, the oxygen concentration or the silicon concentration is more than twice as high as that of the second layer 202. Thus, a similar effect is expected. In the first layer 201, the oxygen concentration or the silicon concentration may be 1.5 times or more higher than that of the second layer 202, or may be 1.2 times or more higher.

[0223] As described above, in the nitride semiconductor substrates 11 and 21 according to the present embodiment, the threading dislocation density of the AlN-containing film (AlN-containing film 100 and AlN-containing film 200) is 2×10 8 cm -2 or less, and the full width at half maximum of XRC on the (10-12) plane of this AlN-containing film is 120 arcsec or less. The full width at half maximum of XRC on the (10-12) plane of this AlN-containing film is 90 arcsec or less for substrate numbers H2 and H3, and 80 arcsec or less for substrate number H2. Further, as shown in FIG. 10, the oxygen concentration of this AlN-containing film is 10 18 cm -3 or more and 10 21 cm -3 or less, and the hydrogen concentration is 10 16 cm -3 or more and 2×10 17 cm -3 or less.

[0224] Thus, the nitride semiconductor substrates 11 and 21 according to the present embodiment, in which the oxygen concentration and the hydrogen concentration of the AlN-containing film are in the above ranges, show that the threading dislocation density is sufficiently low, the full width at half maximum of XRC is sufficiently low, and the crystallinity is high. That is, high-quality nitride semiconductor substrates 11 and 21 are realized.

[0225] In addition, the nitride semiconductor substrates 11 and 21 according to this embodiment include a substrate 2 and an AlN-containing film (AlN-containing film 100 and AlN-containing film 200) provided above the substrate 2. The film thickness of this AlN-containing film is 300 nm or more and 10000 nm or less. Further, as shown in FIG. 10, the oxygen concentration of this AlN-containing film is 10 18 cm -3 or more and 10 21 cm -3 or less, and the hydrogen concentration is 10 16 cm -3 or more and 2×10 17 cm -3 or less.

[0226] As described above, by applying the manufacturing method of this embodiment, this AlN-containing film of the nitride semiconductor substrates 11 and 21 according to this embodiment has a film thickness large enough as a substrate of a semiconductor element, has high crystallinity, and high-quality nitride semiconductor substrates 11 and 21 are realized.

[0227] In addition, in this embodiment, the film thicknesses of the AlN-containing films 100, 200, and 300 are preferably 2000 nm or less. As shown in FIG. 8, the AlN-containing films 100, 200, and 300 with the above film thickness have high crystallinity. That is, high-quality nitride semiconductor substrates 11, 21, and 31 are realized.

[0228] [Evaluation 2 of Nitride Semiconductor Substrate] Furthermore, here, the results of evaluating the crystallinity of the AlN-containing film 100 included in the nitride semiconductor substrate 11 manufactured by changing the manufacturing conditions in the manufacturing method of the second example of this embodiment will be described. Also, in [Evaluation 2 of Nitride Semiconductor Substrate], descriptions overlapping with [Evaluation 1 of Nitride Semiconductor Substrate] may be omitted or simplified.

[0229] Note that, compared with the nitride semiconductor substrates 11, 21, and 31 described in [Evaluation 1 of Nitride Semiconductor Substrate], the nitride semiconductor substrate 11 described in [Evaluation 2 of Nitride Semiconductor Substrate] mainly has the following two characteristics. Specifically, one of the two characteristics is that the second annealing process is performed without forming the second AlN film 20 in the second sputtering process. Another one of the two characteristics is that the substrate 2 on which the first AlN film 10 (that is, the AlN-containing film 100) is formed is not exposed to the atmosphere and is held at a predetermined temperature (T mid ) (described later) in the chamber 110 or the annealing apparatus.

[0230] First, the influence of controlling the temperature of the substrate 2 on which the first AlN film 10 is formed during the period between the first annealing process and the second annealing process will be described with reference to FIGS. 11 and 12.

[0231] FIG. 11 is another example of a diagram showing a table representing the crystallinity of the nitride semiconductor substrate 11 according to the present embodiment. More specifically, FIG. 11 shows the results measured by XRD for the nitride semiconductor substrate 11. Similarly, in FIGS. 13 and 15 described later, the results measured by XRD are also shown.

[0232] The crystallinity of the AlN-containing film 100 corresponds to the value of the full width at half maximum of the diffraction peak obtained by XRC measurement of the (0002) plane and the (10-12) plane. The smaller the full width at half maximum of this XRC, that is, the sharper the obtained diffraction peak, the better the crystallinity. Note that the unit of the full width at half maximum of XRC is arcsec (") representing an angle. Similarly, in FIGS. 13 and 15 described later.

[0233] The sample substrate with the substrate number shown in FIG. 11 corresponds to the nitride semiconductor substrate 11 manufactured by the manufacturing method according to the present embodiment. Similarly, in FIGS. 13 and 15 described later.

[0234] Hereinafter, in [Evaluation 2 of Nitride Semiconductor Substrate], the sample substrates with substrate numbers are denoted by the substrate numbers, for example, like substrate number 51.

[0235] Also, FIG. 12 is a schematic diagram showing an example of temperature change in the manufacturing method of the second example. More specifically, FIG. 12 shows the temperature change in the manufacturing method of the second example for manufacturing the nitride semiconductor substrate 11 (substrate numbers 51 to 55) shown in FIG. 11. Note that in FIG. 12, the horizontal axis represents the processing time and the vertical axis represents the processing temperature. Similarly, in FIGS. 14 and 16 described later, the horizontal axis represents the processing time and the vertical axis represents the processing temperature.

[0236] Using FIG. 12, the temperature change in the annealing process (the first annealing process (the fourth step S34) and the second annealing process (the sixth step S36)) of the manufacturing method of the second example, which is the manufacturing method for substrate numbers 51 to 55, will be described.

[0237] In the manufacturing method of the second example, which is the manufacturing method for substrate numbers 51 to 55, as shown in FIG. 12, in the first annealing process (the fourth step S34), the substrate 2 on which the first AlN film 10 is formed is annealed at 1700°C for 3 hours. Further, the temperature of the substrate 2 on which the first AlN film 10 is formed is reduced until it reaches T mid becomes.

[0238] Also, as described above, in the second sputtering process, the second AlN film 20 is not formed.

[0239] Next, as shown in FIG. 12, in the second annealing process (the sixth step S36), the substrate 2 on which the first AlN film 10 is formed is annealed at 1700°C for 6 hours. Further, the substrate 2 on which the first AlN film 10 is formed is taken out from the annealing apparatus. Thereby, substrate numbers 51 to 55 are manufactured.

[0240] That is, in the manufacturing method of the second example shown in FIG. 12, during the period between the first annealing process and the second annealing process, the substrate 2 on which the first AlN film 10 is formed is not exposed to the atmosphere and is maintained at a predetermined temperature T in the chamber 110 or in the annealing apparatus. mid It is held at.

[0241] As shown in FIG. 11, in substrate numbers 51 to 55, the film thickness of the first AlN film 10 is 784 nm or 793 nm, and the film thicknesses are substantially the same. Each of substrate numbers 51 to 55 is manufactured by the same manufacturing method except that the predetermined temperature (T mid ) during the period between the first annealing process and the second annealing process is different.

[0242] Also, as shown in FIG. 11, in the order of substrate numbers 51, 52, 53, 54, and 55, the value of T mid decreases. Further, as shown in FIG. 11, in the order of substrate numbers 51, 52, 53, 54, and 55, the full width at half maximum of the XRC of the (10-12) plane tends to decrease, that is, in this order, the crystallinity is improved.

[0243] From the above, it is better that the predetermined temperature (T mid ) during the period when the annealing process is temporarily suspended between the first annealing process and the second annealing process is lower, so that the crystallinity of the first AlN film 10 (that is, the AlN-containing film 100) becomes higher, and a high-quality nitride semiconductor substrate 11 is realized. Specifically, in FIG. 11, the values of T mid of 400 ° C and 150 ° C (that is, substrate numbers 54 and 55) achieve a more suitable full width at half maximum of XRC. The time to maintain the predetermined temperature (T mid ) is selected in the range of 0 seconds or more and 120 minutes or less. By lowering the temperature during the period when the annealing process is temporarily suspended during the annealing process in this way, the strain based on the thermal expansion coefficients of sapphire and AlN moves the threading dislocations. Moving the threading dislocations is effective in reducing the threading dislocation density.

[0244] Furthermore, the influence of the total processing time of the first annealing process and the second annealing process will be described with reference to FIGS. 13 and 14.

[0245] FIG. 13 is another example diagram showing a table representing the crystallinity of the nitride semiconductor substrate 11 according to the present embodiment.

[0246] Further, FIG. 14 is another example schematic diagram showing the temperature change in the manufacturing method of the second example. More specifically, in FIG. 14(a), the temperature change in the manufacturing method of the second example for manufacturing the nitride semiconductor substrate 11 (substrate number 56) shown in FIG. 13 is shown, and in FIG. 14(b), the temperature change in the manufacturing method of the second example for manufacturing the nitride semiconductor substrate 11 (substrate number 57) shown in FIG. 13 is shown.

[0247] Using FIG. 14, the temperature change in the annealing process (the first annealing treatment (step S34) and the second annealing treatment (step S36)) of the manufacturing method of the second example, which is the manufacturing method for substrate numbers 56 and 57, will be described.

[0248] In the manufacturing method of the second example, which is the manufacturing method for substrate numbers 56 and 57, as shown in FIG. 14, in the first annealing process (step S34), the substrate 2 on which the first AlN film 10 is formed is annealed at 1650° C. for 3 hours and then annealed at 1700° C. for 3 hours. Further, the temperature of the substrate 2 on which the first AlN film 10 is formed is lowered until it reaches 150° C.

[0249] Also, in the manufacturing method of the second example in [Evaluation 2 of nitride semiconductor substrate], in the second sputtering process (step S35) in FIG. 6, the second AlN film 20 is not formed.

[0250] Next, as shown in FIG. 14, in the second annealing process (step S36), the substrate 2 on which the first AlN film 10 is formed is annealed at 1700° C. for a predetermined time. Further, the substrate 2 on which the first AlN film 10 is formed is taken out from the annealing apparatus. Thereby, substrate numbers 56 and 57 are manufactured.

[0251] As shown in FIG. 13, for substrate numbers 56 and 57, the film thickness of the first AlN film 10 is 784 nm or 793 nm, which is almost the same. Each of substrate numbers 56 and 57 is manufactured by the same manufacturing method except that the annealing time in the second annealing process is different.

[0252] As shown in FIG. 14, the annealing times in the second annealing process for substrate numbers 56 and 57 are 9 hours and 6 hours, respectively. Therefore, as shown in FIG. 13, the annealing times at 1700 °C for substrate numbers 56 and 57 are 12 hours and 9 hours, respectively. Further, as shown in FIG. 13, in the order of substrate numbers 56 and 57, the full width at half maximum of XRC of the (10-12) plane tends to increase. That is, substrate number 57 with a longer annealing time at 1700 °C has improved crystallinity compared to substrate number 56.

[0253] Furthermore, the influence of the flow rate of nitrogen gas in the first sputtering process will be described with reference to FIGS. 15 and 16.

[0254] FIG. 15 is a diagram showing another example of a table representing the crystallinity of the nitride semiconductor substrate 11 according to the present embodiment.

[0255] A second example of the manufacturing method for manufacturing substrate numbers 58 to 60 shown in FIG. 15 will be described.

[0256] First, the first sputtering process in which the first AlN film 10 is formed will be described. Note that "N2Flow (sccm) During SP" shown in FIG. 15 indicates the flow rate of nitrogen gas in the first sputtering process.

[0257] In the second manufacturing method for manufacturing substrate numbers 58 to 60, the flow rate of nitrogen gas in the first sputtering process is different for each of substrate numbers 58 to 60. For substrate number 58, the flow rate is constant during the first sputtering process and is 24 sccm. For substrate numbers 59 and 60, the flow rate is controlled to increase during the first sputtering process. More specifically, for substrate number 59, the flow rate is controlled to increase from 19 sccm to 28 sccm, and for substrate number 60, the flow rate is controlled to increase from 19 sccm to 32 sccm.

[0258] Next, the annealing process (the first annealing process (step S34) and the second annealing process (step S36)) will be described with reference to FIG. 16. FIG. 16 is another schematic diagram showing the temperature change in the second manufacturing method. More specifically, FIG. 16 shows the temperature change in the second manufacturing method for manufacturing the nitride semiconductor substrate 11 (substrate numbers 58 to 60) shown in FIG. 15.

[0259] In the first annealing process (step S34), the substrate 2 on which the first AlN film 10 is formed is annealed at 1650 °C for 3 hours and then annealed at 1700 °C for 3 hours. Further, the temperature of the substrate 2 on which the first AlN film 10 is formed is lowered until it reaches 150 °C.

[0260] Also, as described above, in the second sputtering process, the second AlN film 20 is not formed.

[0261] Next, as shown in FIG. 16, in the second annealing process (step S36), the substrate 2 on which the first AlN film 10 is formed is annealed at 1700 °C for 6 hours. Further, the substrate 2 on which the first AlN film 10 is formed is taken out from the annealing apparatus. Thereby, substrate numbers 58 to 60 are manufactured.

[0262] As shown in FIG. 15, for substrate numbers 58 to 60, the film thickness of the first AlN film 10 is 778 nm, 791 nm, or 798 nm, and the film thicknesses are substantially the same. Each of substrate numbers 58 to 60 is manufactured by the same manufacturing method except that the above flow rates are different.

[0263] As shown in FIG. 15, compared with substrate number 58, the full width at half maximum of XRC of the (10-12) plane of substrate numbers 59 and 60 tends to be smaller. That is, as the above flow rate increases, the crystallinity is improved. Further, compared with substrate number 59, the full width at half maximum of XRC of the (10-12) plane of substrate number 60 is smaller. That is, as the above flow rate increases to a value higher than 24 sccm, the crystallinity is improved.

[0264] FIG. 17 is a diagram showing another example of the result of analyzing the impurity concentration of the nitride semiconductor substrate 11 according to the present embodiment. More specifically, FIG. 17(a) shows the result of analyzing the impurity concentration of the nitride semiconductor substrate 11 before the first annealing treatment, and FIG. 17(b) shows the result of analyzing the impurity concentration of the nitride semiconductor substrate 11 after the first annealing treatment.

[0265] Note that the nitride semiconductor substrate 11 used in FIG. 17 has the same configuration as the above substrate number A1 except that the film thickness of the first AlN film 10 (AlN-containing film 100) is 320 nm, the annealing temperature in the first annealing treatment is 1700° C., and the annealing time is 3 hours.

[0266] As shown in FIGS. 17(a) and (b), the impurity concentration changes by performing the first annealing treatment. In particular, the hydrogen concentration changes more significantly than other elements. Further, by performing the first annealing treatment, the hydrogen concentration of the first AlN film 10 (AlN-containing film 100) is 10 16 cm -3 above 2×10 17 cm -3It is as follows. As shown in FIG. 17(b), the region where the hydrogen concentration of the first AlN film 10 (AlN-containing film 100) is within the above range is a region that is a predetermined ratio (for example, 50% here) or more of the entire region of the AlN-containing film 100. Further, the oxygen concentration of the first AlN film 10 (AlN-containing film 100) is 10 18 cm -3 or more and 10 21 cm -3 or less.

[0267] That is, the nitride semiconductor substrate 11 used in FIG. 17 includes the substrate 2 and the AlN-containing film 100 provided above the substrate 2. The film thickness of this AlN-containing film 100 is 300 nm or more and 10000 nm or less. Further, as shown in FIG. 17, the oxygen concentration of this AlN-containing film 100 is 10 18 cm -3 or more and 10 21 cm -3 or less, and the hydrogen concentration is 10 16 cm -3 or more and 2×10 17 cm -3 or less.

[0268] As described above, by applying the manufacturing method of the present embodiment, the AlN-containing film 100 of the nitride semiconductor substrate 11 has a sufficiently large film thickness as a substrate of a semiconductor element, has high crystallinity, and a high-quality nitride semiconductor substrate 11 is realized.

[0269] [Evaluation 3 of Nitride Semiconductor Substrate] Furthermore, here, the results of evaluating the crystallinity of the AlN-containing film 100 provided in the manufactured nitride semiconductor substrate 11 by changing the manufacturing conditions in the manufacturing method of the first example of the present embodiment will be described. Also, in [Evaluation 3 of Nitride Semiconductor Substrate], descriptions overlapping with [Evaluation 1 of Nitride Semiconductor Substrate] may be omitted or simplified.

[0270] [Evaluation 3 of Nitride Semiconductor Substrate] mainly evaluates the nitride semiconductor substrate 11 having the same configuration as the substrate number A1 except for the following two points. Specifically, the two points are that the film thickness of the first AlN film 10 (AlN-containing film 100) is 100, 200, 300, 400, 500, 600, 700, 1000 or 1100 nm, and the annealing temperature is 1700 °C and the annealing time is 1, 3, 6, 9 or 12 hours in the first annealing treatment.

[0271] FIG. 18 is a diagram showing the relationship among the film thickness, annealing time, and threading dislocation density of the AlN-containing film 100 according to the present embodiment. As shown in FIG. 18, here, each of the substrates 2 on which the AlN-containing film 100 having a film thickness of 100, 200, 300, 400, 500, 600, 700, 1000 or 1100 nm is formed is annealed for 1, 3, 6, 9 or 12 hours, and a plurality of nitride semiconductor substrates 11 are manufactured.

[0272] In addition, the threading dislocation density of each of the plurality of nitride semiconductor substrates 11 is calculated. The threading dislocation density is calculated from the full width at half maximum of the XRC of the (0002) plane and the (10-12) plane.

[0273] The longer the annealing time, the lower the threading dislocation density. Also, the thicker the film thickness of the AlN-containing film 100, the lower the threading dislocation density. However, as shown in FIG. 18, when the film thickness of the AlN-containing film 100 exceeds a predetermined film thickness, the threading dislocation density becomes high. That is, when the film thickness of the AlN-containing film 100 exceeds the upper limit, the threading dislocation density deteriorates. This is because when the film thickness of the AlN-containing film 100 increases, the full width at half maximum of the XRC of the (0002) plane increases, that is, the axial fluctuation of the c-axis of the crystal grains increases.

[0274] Further, as shown in FIG. 18, when the film thickness of the AlN-containing film 100 is 2000 nm or less, more specifically 1500 nm or less, and even more specifically 1000 nm or less, the threading dislocation density can be made sufficiently low, indicating that the nitride semiconductor substrate 11 according to the present embodiment can have high crystallinity. That is, a high-quality nitride semiconductor substrate 11 is realized. In FIG. 18, it can be read that the threading dislocation density can be 2×10 8 cm -2 or less in the range where the film thickness of the AlN-containing film 100 is 500 nm or more and 1500 nm or less.

[0275] [Semiconductor Device] Furthermore, here, a semiconductor device including the nitride semiconductor substrates 11, 21, and 31 according to the present embodiment will be described. The semiconductor device may be, for example, a high electron mobility transistor (HEMT: High Electron Mobility Transistor), but here, it is an ultraviolet light emitting device or the like. In particular, it can be used as a deep ultraviolet LED having a wavelength of 200 nm or more and 280 nm or less.

[0276] With reference to FIG. 19, the configuration of the ultraviolet light emitting device 400 according to the present embodiment will be described.

[0277] FIG. 19 is a schematic diagram of the stacked structure of the ultraviolet light emitting device 400 according to the present embodiment.

[0278] The ultraviolet light emitting device 400 includes, as an example, a nitride semiconductor substrate 11, a planarization layer 3, a buffer layer 4, an electron injection layer 5, a light emitting layer 6, an electron blocking layer 7, a hole injection layer 8, and an electrode contact layer 9, which are formed in this order.

[0279] The planarization layer 3 uses AlN, but is not limited thereto. For example, the planarization layer 3 may be AlN, AlGaN, or AlGaInN. The planarization layer 3 is used to planarize the surface of the nitride semiconductor substrate 11. Further, the planarization layer 3 also plays a role in matching the lattice constants.

[0280] Also, the buffer layer 4 uses AlGaN, but it is not limited to this. Similar to the planarization layer 3, the buffer layer 4 may be, for example, AlN, AlGaN, or AlGaInN. The buffer layer 4 functions as a layer that matches the lattice constant, similar to the planarization layer 3.

[0281] Also, the electron injection layer 5 uses n-AlGaN, but it is not limited to this. Similar to the planarization layer 3 and the buffer layer 4, it may be, for example, AlN, AlGaN, or AlGaInN. Furthermore, the electron injection layer 5 is desirably an n-type semiconductor for the purpose of exerting the function of injecting electrons.

[0282] Also, the electron injection layer 5 may also exert the function of transporting electrons. In order for the electron injection layer 5 to function as an n-type semiconductor, for example, Si (silicon), Ge (germanium), Sn (tin), O (oxygen), S (sulfur), Se (selenium), Te (tellurium) can be used as the doping material, but in this embodiment, Si is used.

[0283] Also, in the light-emitting layer 6, a MQW (Multiple Quantum Well) layer formed of a plurality of AlGaN layers having different Al compositions is used. MQW is a structure of multiple quantum wells with multiple quantum wells stacked.

[0284] Electrons and holes are injected into this light-emitting layer 6 from the electron injection layer 5 and the hole injection layer 8. In this light-emitting layer 6, electrons and holes recombine to emit light. That is, the larger the band gap, which is the energy difference between the conduction band and the valence band of this light-emitting layer 6, the shorter the wavelength of the light that can be emitted.

[0285] Since the composition ratio of Al and Ga in AlGaN can be controlled, it can have an arbitrary band gap from 3.4 eV (GaN) to 6.0 eV (AlN), which are their respective band gaps. Since this region is the ultraviolet light emission region, AlGaN is suitable as a light-emitting material for devices that emit ultraviolet light.

[0286] The electron blocking layer 7 uses AlN, but is not limited thereto. Similar to the planarization layer 3, the buffer layer 4, and the electron injection layer 5, for example, it may be AlN, AlGaN, or AlGaInN. The electron blocking layer 7 is used to prevent electrons injected from the electron injection layer 5 from leaking out from the light emitting layer 6 to the hole injection layer 8 side. Therefore, the electron blocking layer 7 functions effectively by being composed of a material having a larger bandgap than the light emitting layer 6.

[0287] The electron blocking layer 7 may have a structure in which a plurality of materials having different bandgaps are stacked. The electron blocking layer 7 may have a structure in which the bandgap continuously changes in the stacking direction within the electron blocking layer 7. The electron blocking layer 7 may be doped with an element other than Al, Ga, In, and N as an impurity in order to be p-type semiconductorized.

[0288] The hole injection layer 8 uses p-AlGaN, but is not limited thereto. The hole injection layer 8 may be, for example, AlN, AlGaN, or AlGaInN, similar to the planarization layer 3, the buffer layer 4, the electron injection layer 5, and the electron blocking layer 7. This hole injection layer 8 has a function of injecting holes into the light emitting layer, and may further have a function of transporting holes. Also, for the hole injection layer 8 to be p-type semiconductorized, Mg (magnesium), Be (beryllium), C (carbon), or Zn (zinc) can be used as a doping material, but in this embodiment, Mg is used.

[0289] As the electrode contact layer 9, p-AlGaN with an increased doping material compared to the hole injection layer 8 is used, but is not limited thereto. The electrode contact layer 9 may be, for example, AlN, AlGaN, or AlGaInN, similar to the planarization layer 3, the buffer layer 4, the electron injection layer 5, the electron blocking layer 7, and the hole injection layer 8. The electrode contact layer 9 is connected to an electrode that supplies holes.

[0290] As described above, since the nitride semiconductor substrate 11 according to the present embodiment has high crystallinity, the semiconductor device according to the present embodiment exhibits high performance. For example, when the semiconductor device is the ultraviolet light emitting device 400, since the deterioration of the light emission characteristics due to threading dislocations or the like in the nitride semiconductor substrate 11 is suppressed, the ultraviolet light emitting device 400 has high luminous efficiency. Note that the same effect can be obtained even when the nitride semiconductor substrates 21 and 31 are used.

[0291] In this way, by providing the semiconductor device with the nitride semiconductor substrates 11, 21, and 31 according to the present embodiment, a semiconductor device having high characteristics is realized.

[0292] (Others) As described above, the nitride semiconductor substrate and the like according to the embodiment have been described. However, the present invention is not limited to the above embodiment.

[0293] For example, in the present embodiment, the AlN-containing films 100, 200, and 300 are formed by a sputtering method, but the present invention is not limited to this. For example, a MOVPE method, a hydride vapor phase epitaxy (HVPE) method, a molecular beam epitaxy (MBE) method, or the like may be used.

[0294] In addition, forms obtained by applying various modifications conceivable by those skilled in the art to the above embodiments or forms realized by arbitrarily combining the components and functions in the embodiments without departing from the spirit of the present invention are also included in the present invention.

Industrial Applicability

[0295] The present invention can be used as a high-quality nitride semiconductor substrate and as an optical semiconductor device such as an ultraviolet light emitting device.

Explanation of Signs

[0296] 2 Substrate 3 Planarization layer 4 Buffer layer 5 Electron injection layer 6 Light-emitting layer 7 Electron blocking layer 8 Hole injection layer 9 Electrode contact layer 10 First AlN film 11, 21, 31 Nitride semiconductor substrate 20 Second AlN film 30 Third AlN film 100, 200, 300 AlN-containing film 101 Intake pipe 102 Exhaust pipe 103 Valve 104 Exhaust pump 105 Substrate holder 107 Target 108 Permanent magnet 109 High-voltage power supply 110 Chamber 400 Ultraviolet light-emitting element 1000 Sputtering apparatus S21, S31, S41 First process S22, S32, S42 Second process S23, S33, S43 Third process S24, S34, S44 Fourth process S35, S45 Fifth process S36, S46 Sixth process S47 Seventh process S48 Eighth process

Claims

1. A substrate, an AlN-containing film provided above the substrate, comprising: the film thickness of the AlN-containing film is 10,000 nm or less, The threading dislocation density of the AlN-containing film is 1.5 × 10 ８ cm －２ or less, the full width at half maximum of the X-ray diffraction rocking curve on the (10-12) plane of the AlN-containing film is 120 arcsec or less, The substrate is composed of one of sapphire, silicon carbide, and ScAlMgO ４ and the AlN-containing film has a first AlN film provided above the substrate and a second AlN film provided above the first AlN film, the film thickness of the first AlN film is 100 nm or more and 900 nm or less, the film thickness of the second AlN film is 100 nm or more and 900 nm or less A nitride semiconductor substrate.

2. The oxygen concentration of the AlN-containing film is 10 １８ cm －３ or more and 10 ２１ cm －３ or less, and The hydrogen concentration of the AlN-containing film is 10 １６ cm －３ or more and 2×10 １７ cm －３ or less The nitride semiconductor substrate according to Claim 1.

3. The through dislocation density is 1.0×10 ８ cm －２ or less The nitride semiconductor substrate according to Claim 1 or 2.

4. the AlN-containing film has at least one interface layer having a maximum elemental concentration in the middle between the AlN-containing film and the substrate, The nitride semiconductor substrate according to any one of Claims 1 to 3.

5. the film thickness of the interface layer is 10 nm or more and 200 nm or less, in the interface layer, the oxygen concentration or the silicon concentration is 2 times or more higher than that of the layer located around the interface layer, The nitride semiconductor substrate according to Claim 4.

6. The AlN-containing film is composed of one of AlN, Al ｘ Ga ｙ In １－ｘ－ｙ N (0.5 ≤ x ≤ 1, 0 ≤ y ≤ 0.5, x + y ≤ 1) and B ｚ Al ｗ Ga １－ｚ－ｗ N (0 ≤ z ≤ 0.5, 0.5 ≤ w ≤ 1, z + w ≤ 1). The nitride semiconductor substrate according to any one of Claims 1 to 5.

7. the film thickness of the AlN-containing film is 2,000 nm or less The nitride semiconductor substrate according to any one of Claims 1 to 6.

8. A semiconductor device comprising the nitride semiconductor substrate according to any one of Claims 1 to 7 A semiconductor device.

9. A preparation step of preparing a substrate, a film formation step of forming an AlN film having a film thickness of 100 nm or more and 900 nm or less above the substrate, an annealing step of annealing the AlN film formed in the film formation step at 1,500 °C or higher, including: at least one of the film formation step and the annealing step is performed a plurality of times, The threading dislocation density of the formed AlN film is 1.5×10 ８ cm －２ or less, the full width at half maximum of the X-ray diffraction rocking curve on the (10-12) plane of the AlN-containing film constituted by the AlN film is 120 arcsec or less, in the annealing step, the main surface of the AlN film is covered with a cover member for suppressing dissociation of the components of the material constituting the AlN film, and the AlN film formed in the film formation step is annealed in an airtight state, the film formation step forms the AlN film by sputtering treatment, the annealing step anneals the AlN film at 1,500 °C or higher and 1,750 °C or lower, the annealing step is performed a plurality of times, During the annealing process performed a plurality of times, the substrate is held at a temperature lower than the temperature at which the AlN film is annealed. Method for manufacturing a nitride semiconductor substrate.

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