Gallium nitride heating method, gallium nitride semiconductor manufacturing method, and gallium nitride semiconductor device manufacturing method

Abstract

To provide a heating method of gallium nitride which can uniformly, highly efficiently and stably apply a desired high-temperature treatment to gallium nitride with microwave irradiation.SOLUTION: In a microwave heating device 10, a sample plate 50 on which gallium nitride 51 is placed is arranged along a magnetic field vector of a standing wave of a microwave, and the magnetic field heating is applied to the gallium nitride by irradiating the gallium nitride with the standing wave of the microwave from a microwave supply port 14 with the c axial direction of the gallium nitride as the vertical direction with respect to the surface of the sample plate.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for heating gallium nitride, a method for manufacturing a gallium nitride semiconductor, and a method for manufacturing a semiconductor device including gallium nitride. [Background technology]

[0002] The semiconductor properties of gallium nitride (GaN) can be controlled by introducing other elements into the GaN crystal. To control GaN to have n-type conductivity, for example, ionized Si is introduced into the GaN crystal. To control GaN to have p-type conductivity, ionized Mg is generally introduced into the GaN crystal. After ion implantation into GaN, annealing is usually performed using an electric furnace or similar. Annealing is a heat treatment necessary to restore the crystalline structure of GaN in the areas that have become amorphous due to ion implantation. This annealing is said to require heating in excess of 1000°C. However, when GaN is exposed to temperatures exceeding 1000°C, nitrogen is desorbed from the GaN crystal. To prevent this nitrogen desorption, high-temperature annealing is performed under fairly high-pressure conditions (e.g., 1 GPa).

[0003] Microwaves have spread from household appliances such as microwave ovens to industrial heating systems. Microwave irradiation generates heat directly on the object being heated without contact, which has the advantage of allowing heating in a short time. Another advantage is that only materials that absorb microwaves well can be selectively heated. Microwaves are electromagnetic waves whose energy intensity changes periodically with wavelength, which makes them prone to uneven heating. Patent Document 1, for example, describes a microwave heating device that uses a cavity resonator to address this issue. This technology uses a TM (Metal Microwave Oxide) in a rectangular parallelepiped cavity resonator. 110 Patent Document 2 also describes a method for generating a standing wave of a TM mode and uniformly heating a sheet containing a conductive or magnetic thin film with high efficiency. 110Patent Document 2 describes a microwave heating device and a microwave heating method that forms a standing wave of a mode and magnetically heats an object to be heated in a magnetic field irradiation space where the magnetic field strength is maximized and uniform. Patent Document 2 describes that a gallium nitride substrate was heated to 300°C by this microwave heating method with a microwave irradiation power of 100 W and an irradiation time of 25 seconds. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-221958 [Patent Document 1] Japanese Patent Application Publication No. 2019-140103 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, annealing of ion-implanted GaN requires high-temperature treatment under ultrahigh-pressure conditions of approximately 1 GPa. However, such severe high-pressure and high-temperature conditions may impose limitations on versatility and practical application in terms of energy costs and equipment. Therefore, it is desirable to perform this annealing treatment using simpler equipment. High-temperature treatment of GaN is also expected to be applied to purposes other than annealing after ion implantation. For example, AlGaN (aluminum gallium nitride) / GaN heterojunction field-effect transistors are known to exhibit high carrier mobility by using a high-density two-dimensional electron gas formed at the AlGaN / GaN interface as channel charge due to the piezoelectric polarization effect associated with lattice strain. Furthermore, exposing the GaN at this interface to high temperatures, such as above 1000°C, is expected to increase electron mobility and lead to higher transistor performance. However, it is not possible to expose the entire semiconductor device, such as an AlGaN / GaN heterojunction field-effect transistor, to the harsh high-pressure and high-temperature conditions described above. Therefore, a high-temperature treatment that can be applied to such semiconductor devices, can selectively heat the GaN within the device, can suppress nitrogen desorption, and causes minimal damage to the device, is desired.

[0006] Microwave heating allows rapid switching between rapid heating and non-rapid heating by turning irradiation on and off, and pulsed heating is also possible. Furthermore, by utilizing standing microwave waves, it is possible to instantly and uniformly heat the entire GaN. Therefore, if a technology could be established to apply microwave heating to high-temperature processes such as annealing of GaN, it would be possible to precisely control the amount of energy imparted to GaN, for example, to further suppress nitrogen desorption and modify GaN to desired physical properties. However, as described in Patent Document 2, microwave heating of GaN has not yet reached a temperature high enough for annealing. Furthermore, if the microwave output were simply increased to heat GaN to temperatures above 1000 °C, there would be concerns about high-power electromagnetic waves leaking from the resonator, posing a safety issue for the process.

[0007] An object of the present invention is to provide a GaN heating method that can uniformly, efficiently, and stably subject GaN to a desired high-temperature treatment by microwave irradiation. Another object of the present invention is to provide a GaN semiconductor manufacturing method that can transform ion-implanted GaN into a high-quality GaN semiconductor. Another object of the present invention is to provide a semiconductor device manufacturing method that includes selectively subjecting a GaN semiconductor to a high-temperature treatment by microwave irradiation to modify the GaN semiconductor in a semiconductor device incorporating the GaN semiconductor. [Means for solving the problem]

[0008] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that, when heating GaN using a standing microwave wave, by arranging the sample plate on which the GaN is placed along the magnetic field vector (magnetic field oscillation direction) of the standing microwave wave and orienting the c-axis direction (polarity direction, spontaneous polarization direction) of the GaN perpendicular to the surface of the sample plate, the GaN can be magnetically heated efficiently and stably to a desired high temperature range with low power (for example, 400 W or less) without thermal runaway. The present invention was completed after further research based on this finding.

[0009] The above-mentioned object of the present invention is achieved by the following means. [1] A method for heating gallium nitride, comprising: placing a sample plate carrying gallium nitride along the magnetic field vector of the standing microwave wave, and irradiating the sample plate with the standing microwave wave so that the c-axis direction of the gallium nitride is perpendicular to the surface of the sample plate, thereby magnetically heating the gallium nitride. [2] The standing microwave is TM n10 (n is an integer greater than or equal to 1) mode or TE 10n The method for heating gallium nitride according to [1], wherein the heating mode is (n is an integer of 1 or more). [3] The method for heating gallium nitride described in [2], wherein the sample plate is placed in a cylindrical cavity resonator with the cross section of the sample plate corresponding to the diameter of the cross section of the cavity resonator, and a standing wave of the microwave is formed in the cavity resonator. [4] The method for heating gallium nitride according to any one of [1] to [3], wherein the gallium nitride is in the form of a plate with its thickness direction as the c-axis direction. [5] The method for heating gallium nitride according to any one of [1] to [4], wherein the gallium nitride is heated to 900° C. or higher. [6] The method for heating gallium nitride according to [5], wherein the microwave irradiation is pulsed irradiation. [7] The method for heating gallium nitride according to any one of [1] to [6], wherein the gallium nitride has been subjected to an ion implantation process, and the gallium nitride has been partially amorphized by the ion implantation process. [8] The method for heating gallium nitride according to [7], wherein the method for heating gallium nitride restores a crystalline structure to an amorphous portion of the gallium nitride. [9] The method for heating gallium nitride according to any one of [1] to [8], wherein the gallium nitride is mounted on the sample plate in a state where it is incorporated into a semiconductor device.

[10] A method for producing a gallium nitride semiconductor, comprising obtaining an n-type or p-type gallium nitride semiconductor by the method for heating gallium nitride according to [8].

[11] A method for manufacturing a semiconductor device, comprising obtaining a semiconductor device in which gallium nitride has been modified by the method for heating gallium nitride according to [9].

[12] The method for manufacturing a semiconductor device according to

[11] , wherein the semiconductor device is an aluminum gallium nitride / gallium nitride heterojunction field effect transistor.

[0010] In the present invention, when the term "gallium nitride" is used simply, it is meant to encompass both undoped and doped gallium nitride, unless otherwise specified. [Effects of the Invention]

[0011] According to the GaN heating method of the present invention, GaN can be uniformly, efficiently, and stably subjected to a desired high-temperature treatment by microwave irradiation. Furthermore, according to the GaN semiconductor manufacturing method of the present invention, ion-implanted GaN can be transformed into a high-quality GaN semiconductor. Furthermore, according to the semiconductor device manufacturing method of the present invention, in a semiconductor device incorporating GaN, GaN can be selectively subjected to a high-temperature treatment using microwaves to modify the GaN or the interface between GaN and AlGaN. [Brief explanation of the drawings]

[0012] [Figure 1] Figure 1 shows the magnetic field vectors when a standing wave of the TM110 mode is formed in a cylindrical cavity resonator. The "sample" indicates the object to be heated (e.g., GaN). [Figure 2] Figure 2 shows a configuration in which a sample plate is arranged so that its cross section (thickness direction cross section, vertical cross section) corresponds to (matches) the diameter in one direction of the cross section of a cylindrical cavity resonator. [Figure 3] Figure 3 shows a configuration in which the cross section of the sample plate is not perfectly aligned with the cross-sectional diameter of the cavity resonator, but the cross section (longitudinal or transverse section) of the sample plate is shifted approximately parallel to the cross-sectional diameter of the cavity resonator. [Figure 4] FIG. 4 is an explanatory diagram that schematically illustrates an outline of one embodiment of a microwave heating device. [Figure 5] FIG. 5 shows the relationship between the magnetic field vector (magnetic field oscillation direction) along the in-plane direction of the sample plate and the crystal axis of GaN (four patterns (i) to (iv)). [Figure 6]FIG. 6 is a graph showing the temperatures reached by GaN when the GaN is magnetically heated by a standing wave at microwave outputs of 50 W, 100 W, and 150 W in the four patterns shown in FIG. [Figure 7] Figure 7 shows the photoluminescence profile of ideal p-type GaN obtained by epitaxial growth. [Figure 8] FIG. 8 shows the photoluminescence profile of GaN implanted with Mg ions when it was subjected to a conventional high-pressure annealing process using an electric furnace. [Figure 9] FIG. 9 shows the photoluminescence profile when GaN implanted with Mg ions is heated to approximately 1500° C. by the heating method of the present invention. [Figure 10] FIG. 10 shows the photoluminescence profile when GaN implanted with Mg ions is heated to approximately 700° C. by the heating method of the present invention. [Figure 11] 1 shows a photoluminescence profile when GaN implanted with Mg ions is heated to approximately 1050° C. by the heating method of the present invention. [Figure 12] 1 shows a photoluminescence profile when GaN implanted with Mg ions is heated to approximately 1100° C. by the heating method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Gallium nitride heating method] The gallium nitride heating method of the present invention includes arranging a sample plate carrying GaN along the magnetic field vector of the microwave standing wave, and irradiating the GaN with the microwave standing wave while aligning the c-axis of the GaN perpendicular to the surface of the sample plate. By aligning the c-axis of the GaN perpendicular to the surface of the sample plate, the c-axis of the GaN is also oriented perpendicular to the magnetic field vector.

[0014] In the present invention, "the sample plate on which GaN is mounted is arranged along the magnetic field vector of the standing wave of the microwave" means that the sample plate is arranged so that the in-plane direction (planar direction) of the sample plate is parallel to the magnetic field vector of the microwave. For example, as shown in Figure 1, 110 When a standing wave of a microwave mode is formed, the magnetic field vector is aligned with the diameter in one direction (the horizontal direction in Fig. 1) in the cross section of the cavity resonator, and the magnetic field vector with the strongest vector strength coincides with the diameter in the cross section of the cavity resonator. Therefore, for example, as shown in Fig. 2, a configuration in which the sample plate is arranged so that its cross section (the cross section in the thickness direction or the vertical cross section of the sample plate) corresponds to the diameter in one direction in the cross section of the cavity resonator is one configuration in which the sample plate is arranged along the magnetic field vector of the microwave standing wave. The above phrase "the in-plane direction (planar direction) of the sample plate is parallel to the magnetic field vector of the microwave" means that the in-plane direction of the sample plate and the magnetic field vector of the microwave are approximately parallel. In other words, the in-plane direction of the sample plate and the magnetic field vector of the microwave do not have to be completely parallel as long as the effects of the present invention are not impaired. In addition, in the present invention, "arranging the sample plate with gallium nitride placed along the magnetic field vector of the standing wave of the microwave" means that the plane or cross section from the front to the back of the sample plate (the plane or cross section perpendicular to the thickness of the sample plate) coincides with the magnetic field vector of the microwave with the strongest vector strength. In addition, a gap may be provided between the plane or cross section from the front to the back of the sample plate and the magnetic field vector of the microwave with the strongest vector strength, as long as the effect of the present invention is not impaired. For example, TM 110 In the case of forming a standing wave of the mode, in the arrangement of the sample plate shown in Fig. 2, the cross section of the sample plate is not perfectly aligned with the cross-sectional diameter of the cavity resonator, but the cross section (longitudinal cross section) of the sample plate is shifted approximately parallel to the cross-sectional diameter of the cavity resonator (Fig. 3) is also an embodiment of the present invention. However, in this case, it is assumed that the sample plate or the GaN placed thereon can be heated by a magnetic field. The sample plate is preferably arranged parallel to the central axis of the cavity resonator, as shown in FIGS. In the present invention, the term "sample plate" is used in a broader sense than usual. That is, as long as it functions as a stage on which a sample can be placed, its shape is not limited to a plate. For example, a sample plate can be formed by combining multiple rod-shaped objects whose longitudinal direction is aligned with the magnetic field vector. Furthermore, there may be gaps between the rod-shaped objects as long as a sample can be placed thereon. When referring to a sample plate made up of multiple rod-shaped objects, the term "surface" refers to a single plane that is in contact with the surface on which the sample is placed, of all the rod-shaped objects. Furthermore, when referring to a sample plate made up of multiple rod-shaped objects, the term "cross section" refers to a cross section of the plate defined by a plane that is in contact with the surface on which the sample is placed and another plane that is in contact with the surface on the opposite side from the surface on which the sample is placed. Furthermore, the term "rod-shaped" is not limited to a round rod with a circular cross section. For example, it may be a polygonal cross section, a semicircular half-section rod, or a hollow rod. That is, the shape of the "sample plate" is not particularly limited as long as it functions as a sample stage without impairing the effects of the present invention.

[0015] In this way, by arranging the sample plate carrying the GaN along the magnetic field vector of the microwave standing wave and orienting the c-axis direction (polarity direction, spontaneous polarization direction) of the GaN perpendicular to the surface of the sample plate, the GaN can be stably heated by the action of the magnetic field, for example, to a high temperature range sufficient for restoring crystallinity. Here, "orienting the c-axis direction of the GaN perpendicular to the surface of the sample plate" means that the c-axis direction of the GaN is approximately perpendicular to the surface of the sample plate. In other words, the c-axis direction of the GaN does not have to be completely perpendicular to the surface of the sample plate, as long as the effects of the present invention are not impaired.

[0016] The material of the sample plate used in the present invention is preferably a material that can withstand high temperatures of 1000°C or higher, and can be, for example, alumina, quartz glass, silicon nitride, carbon nitride, calcium oxide (calcia), magnesium oxide (magnesia), tantalum, etc. The thickness of the sample plate is preferably 100 to 10,000 μm, more preferably 500 to 3,000 μm.The sample plate is usually a plate that is substantially not curved and has a straight cross section.

[0017] In the present invention, the GaN placed on the sample plate is preferably a plate (approximately rectangular parallelepiped) with its thickness direction along the c-axis. The size of the GaN placed on the sample plate is not particularly limited as long as it can be heated by the magnetic field generated in the cavity resonator.

[0018] In the present invention, the GaN placed on the sample plate can be one that has been subjected to ion implantation to impart n-type or p-type conductivity. That is, GaN in which a portion of the GaN crystal structure has been destroyed and amorphized by ion implantation is preferably used. By treating such amorphous GaN using the heating method of the present invention, the GaN can be annealed at high temperatures with high efficiency and instantaneously, thereby efficiently restoring the GaN crystal structure and enabling the desired semiconductor performance to be achieved. Furthermore, microwave heating allows for pulsed microwave irradiation, enabling precise temperature control and avoiding the application of excessive energy. As a result, nitrogen desorption can be further suppressed even at high temperatures, such as approximately 1500°C. In this way, GaN that has been subjected to ion implantation processing and has been partially amorphized by this ion implantation processing is used as the object to be heated, and an n-type or p-type GaN semiconductor can be obtained. For example, to control GaN to have n-type conductivity, Si is ionized and introduced into the GaN crystal, while to control GaN to have p-type conductivity, Mg is generally ionized and introduced into the GaN crystal.

[0019] In the present invention, the GaN to be placed on the sample plate may be mounted in a state where it is incorporated into a semiconductor device. One example of this configuration is a configuration in which an AlGaN / GaN heterojunction field-effect transistor is mounted on the sample plate. In this configuration, the c-axis of the GaN is oriented perpendicular to the surface of the sample plate, and the GaN is selectively heated, thereby modifying the GaN or the heterojunction while minimizing damage to the entire semiconductor device. In this way, by incorporating GaN into a semiconductor device and then magnetically heating it with a standing microwave, with the c-axis of the GaN perpendicular to the surface of the sample plate, the GaN can be modified to obtain a semiconductor device that exhibits the desired performance.

[0020] In the present invention, the standing microwave wave is TM n10 (n is an integer greater than or equal to 1) mode or TE 10n (n is an integer of 1 or more) mode standing waves can be suitably used. Such single-mode standing waves can be formed by irradiating microwaves in a cavity resonator of a predetermined shape while controlling the frequency. The shape of the cavity resonator and the types of standing waves that can be formed are already known. TM n10 (n is an integer greater than or equal to 1) mode or TE 10n By forming a standing wave in the (n is an integer of 1 or more) mode, a uniform magnetic field with maximum magnetic field strength can be formed parallel to the central axis of the cavity resonator. When the above "n" is an odd number, the central axis of the cavity resonator and the part where the magnetic field strength is maximum coincide with each other, so it is possible to form a desired magnetic field vector by matching it with the diameter in one direction of the cross section of the cavity resonator. The microwave standing wave used in the present invention is TM 110 Mode, TM 210 Mode, TM 310 Mode or TM 410 Mode is preferred, TM 110 Mode is more preferable.

[0021] By the GaN heating method of the present invention, GaN is preferably heated to 900°C or higher, more preferably 950°C or higher, and even more preferably 1000°C or higher. The heating temperature is usually 1800°C or lower, preferably 1700°C or lower, also preferably 1600°C or lower, also preferably 1500°C or lower, and also preferably 1400°C or lower. Specifically, a preferred heating temperature range is 900 to 1800°C, more preferably 950 to 1700°C, even more preferably 950 to 1600°C, still more preferably 950 to 1500°C, and also preferably 1000 to 1400°C.

[0022] As described above, the GaN heating method of the present invention can be performed using a microwave heating device having a cavity resonator. Figure 4 shows a preferred embodiment of the microwave heating device. Figure 4 is an explanatory diagram that schematically shows an overview of the microwave heating device. Therefore, for the sake of convenience, some components may be omitted from Figure 4. As shown in Fig. 4, the microwave heating device 10 has a cavity resonator (hereinafter also referred to as a (cylindrical) cavity resonator) 11 having a microwave irradiation space. The cavity resonator 11 may be cylindrical or may be a polygonal cylinder with two parallel faces facing each other about the central axis of the cylinder. In other words, it is sufficient if it can form a standing wave in which a magnetic field vector is formed along a straight line passing through the central axis CE of the cavity resonator 11 (a straight line in the A direction in Fig. 4). Hereinafter, a cylindrical cavity resonator will be used to form a TM 110 The case where a standing wave of a mode is formed will be described.

[0023] The cylindrical cavity resonator 11 shown in FIG. 4 is a TM cavity resonator in which the magnetic field intensity is maximized and uniform along the cylindrical central axis (hereinafter also referred to as the central axis) CE. 110 A standing wave of the mode is formed. In this case, the magnetic field vector (magnetic field oscillation direction) is oriented in the same direction as the diameter of the cross section of the cavity resonator. Hereinafter, the central axis of the cavity resonator 11 and the central axis of the microwave irradiation space will be used interchangeably.

[0024] The cavity resonator 11 has an inlet 12 provided in a body wall 11SA of the cavity resonator 11, and an outlet 13 provided in a body wall 11SB opposite the body wall 11SA, which are opposite each other across the cylindrical central axis CE of the cavity resonator. The inlet 12 and outlet 13 are preferably slit-shaped with a width sufficient to allow a sample plate 50 carrying GaN 51 to pass through. The cavity resonator 11 also includes a transport mechanism 31 for transporting GaN 51 to a magnetic field region 52 where the electric field is minimized and the magnetic field strength is maximized and uniform. The magnetic field strength of the magnetic field region 52 weakens from the cylindrical central axis CE outward. In the drawing, the region where the magnetic field strength is more than three-quarters of its maximum value is schematically shown by a two-dot chain line as an example. The above-mentioned transport mechanism 31 transports the GaN 51 on the sample plate 50 into the microwave irradiation space from the entrance 12, and since the c-axis of the GaN 51 is perpendicular to the surface of the sample plate, at least the GaN 51 is magnetically heated with high efficiency, and the annealed GaN is transported out from the exit 13. For example, TM 110 In the case of a cylindrical cavity resonator 11 in which a standing wave of the mode is generated, the magnetic field region 52 is a space in which the electric field strength is minimum at the central axis CE, the magnetic field strength is maximum at the central axis CE, and the magnetic field strength is uniform along the central axis CE.

[0025] A microwave generator 21 is disposed in the cavity resonator 11, and microwaves are supplied to the cavity resonator 11. Generally, the frequency of the microwave is 0.3 to 300 GHz, and the S band of 2 to 4 GHz is often used. Alternatively, frequencies of 900 to 930 MHz, 5.725 to 5.875 GHz, etc. can also be used. However, the present invention does not exclude the use of frequencies other than these.

[0026] In the microwave heating device 10, microwaves generated by the microwave generator 21 are supplied from the microwave supply port 14 to the microwave irradiation space within the cavity resonator 11, forming a standing wave within the microwave irradiation space. It is preferable that the microwaves supplied from the microwave generator 21 be supplied with an adjusted frequency. By adjusting the frequency, it is possible to stably control the magnetic field strength distribution of the standing wave formed in the cavity resonator 11 to a desired distribution state. In addition, the strength of the standing wave can be adjusted by the microwave output. The configuration of the microwave heating device 10 of the present invention will be described in order.

[0027] <Cavity resonator> The cylindrical cavity 11 used in the microwave heating device 10 has one microwave supply port 14 and is not particularly limited as long as it forms a desired standing wave when microwaves are supplied thereto. The microwave irradiation space of the cavity resonator used in the present invention is not limited to the cylindrical shape shown in the drawings. That is, it may be a polygonal cylindrical cavity resonator having two parallel faces facing each other about a central axis. For example, the cross section perpendicular to the central axis may be a cylindrical shape having a regular even polygon, such as a square, regular hexagon, regular octagon, regular dodecagon, or regular hexagon. Alternatively, it may be a polygonal cylindrical shape in which the two opposing faces are flattened relative to the central axis of a regular even polygon. In the case of the polygonal cylindrical cavity resonator, the corners inside the cavity resonator may be rounded. Furthermore, the microwave irradiation space may be a cylindrical cavity resonator having a space with a large roundness, such as an ellipsoid. Even with such a polygonal shape, it is possible to achieve the same effect as with a cylindrical shape (that is, it is possible to form a standing wave with a uniform and maximum magnetic field strength at the central axis). The size of the cavity resonator 11 can also be designed appropriately depending on the purpose. It is desirable that the cavity resonator 11 has a low electrical resistivity. It is usually made of metal, and examples of materials that can be used include aluminum, copper, iron, magnesium, or alloys thereof, or alloys such as brass and stainless steel. Alternatively, the surface of resin, ceramic, or metal may be coated with a substance having a low electrical resistivity by plating, vapor deposition, or the like. Materials containing silver, copper, gold, tin, or rhodium can be used for the coating. The size of the cavity resonator is not particularly limited as long as it can form the desired standing wave.

[0028] <Transport mechanism> The conveying mechanism 31 preferably has a supply-side conveying section 31A, a delivery-side conveying section 31B, or both. Alternatively, the transport mechanism 31, supply port 12, and discharge port 13 may not be installed. In this case, the GaN 51 is placed in advance at a position where the magnetic field inside the cavity resonator is maximized. Then, after processing for a suitable time, the microwave is stopped. After that, part of the cavity resonator is opened, and the GaN 51 can be extracted. Alternatively, the cavity resonator itself may be moved without using a special transport mechanism as the transport mechanism 31.

[0029] <Microwave supply> For supplying the microwave, it is preferable to use a microwave generator 21, a microwave amplifier 22, an isolator 23, a matching box 24, and an antenna 25.

[0030] A microwave supply port 14 is provided on or near a wall surface (inner surface of the cylinder) parallel to the central axis C of the cavity resonator 11. In one embodiment, the microwave supply port 14 has an antenna 25 to which microwaves can be applied. FIG. 4 shows a microwave supply port 14 using a coaxial-waveguide converter. In this case, the antenna 25 is an electric field excitation type monopole antenna. In this case, to effectively form a standing wave, an iris (not shown) may be used as an appropriate opening between the microwave supply port 14 and the cavity resonator 11. Alternatively, an antenna may be installed directly on the cavity resonator 11 without using the waveguide 14. In this case, a loop antenna (not shown) serving as a magnetic field excitation antenna may be installed near the side wall of the cavity resonator. Alternatively, a monopole antenna serving as an electric field excitation may be installed on the top or bottom surface of the cavity resonator. Antenna 25 receives a supply of microwaves from microwave generator 21. Specifically, it is preferable that microwave amplifier 22, isolator 23, matching box 24, and antenna 25 are connected to microwave generator 21 in this order. Cables 26 (26A, 26B, 26C, 26D) are used for each connection. For example, a coaxial cable is used for each cable 26. In this configuration, microwaves emitted from microwave generator 21 are supplied via each cable 26 by antenna 25 from microwave supply port 14 to the microwave irradiation space within cavity resonator 11.

[0031] (microwave generator) The microwave generator 21 used in the microwave heating device 10 of the present invention may be, for example, a microwave generator such as a magnetron or a microwave generator using a semiconductor solid-state element. From the viewpoint of being able to finely adjust the microwave frequency, it is preferable to use a VCO (Voltage Controlled Oscillator), VCXO (Voltage Controlled Crystal Oscillator), or PLL (Phase Locked Loop) oscillator.

[0032] (microwave amplifier) The microwave heating device 10 includes a microwave amplifier 22. The microwave amplifier 22 has a function of amplifying the output of the microwaves generated by the microwave generator 21. There are no particular limitations on the configuration thereof. For example, it is preferable to use a semiconductor solid-state element formed of a high-frequency transistor circuit.

[0033] (Isolator) The microwave heating device 10 includes an isolator 23. The isolator 23 is intended to protect the microwave generator 21 by suppressing the influence of reflected waves generated within the cavity resonator 11. In other words, it ensures that microwaves are supplied in one direction (toward the antenna 25). If there is no risk of the microwave amplifier 22 or the microwave generator 21 being damaged by reflected waves, an isolator need not be installed.

[0034] (matching box) The microwave heating device 10 includes a matching box 24. The matching box 24 is for matching (matching) the impedance of the microwave generator 21 to the isolator 23 with the impedance of the antenna 25. If there is no risk that the microwave amplifier 22 or the microwave generator 21 may be damaged even if a reflected wave occurs due to mismatching, or if adjustments can be made to prevent mismatching, a matching box need not be installed.

[0035] <Control system> The microwave heating device 10 is preferably provided with a thermal image measuring device (thermoviewer) 41 for measuring temperature or a radiation thermometer (not shown). The cavity resonator 11 is preferably provided with a window 15 for measuring the temperature distribution in the cavity resonator 11 by the thermal image measuring device 41 or the radiation thermometer (not shown). The measurement image of the temperature distribution measured by the thermal image measuring device 41 or the temperature information measured by the radiation thermometer is transmitted to a control unit 43 via a cable 42. Furthermore, an electromagnetic wave sensor 44 is preferably disposed on the body wall 11S of the cavity resonator 11. A signal corresponding to the electromagnetic field energy inside the resonator 11 detected by the electromagnetic wave sensor 44 is transmitted to the control unit 43 via a cable 45. Based on the signal from the electromagnetic wave sensor 44, the control unit 43 can detect the formation state (resonance state) of a standing wave generated in the microwave irradiation space of the cavity resonator 11. When a standing wave is formed, that is, when resonance occurs, the output of the electromagnetic wave sensor 44 increases. By adjusting the oscillation frequency of the microwave generator so that the output of the electromagnetic wave sensor 44 is maximized, the microwave frequency can be controlled to match the resonance frequency of the cavity resonator 11.

[0036] Based on the detected frequency, the control unit 43 can feed back to the microwave generator 21 via the cable 46 the frequency of the microwaves that will cause a standing wave of a constant frequency to occur within the cavity resonator 11. Based on this feedback, the control unit 43 can precisely control the frequency of the microwaves supplied from the microwave generator 21. In this way, a desired standing wave can be stably generated within the cavity resonator 11. The control unit 43 can also instruct the microwave amplifier 22 to adjust the microwave output so that a constant microwave output can be supplied to the antenna 25. Alternatively, the control unit 43 can adjust the attenuation factor of an attenuator (not shown) installed between the microwave generator 21 and the microwave amplifier 22 without changing the gain of the microwave amplifier 22. The microwave output may be feedback-controlled based on the readings of the thermal image measuring device 41 or a radiation thermometer so that the object to be heated reaches a target temperature.

[0037] As a control method without using the electromagnetic wave sensor 44, the magnitude of the reflected wave from the cavity resonator 11 may be measured and the measured value may be used. The reflected wave can be measured using the isolation amount obtained from the isolator 23. By adjusting the frequency of the microwave generator so that the reflected wave signal becomes minimum, microwave energy can be efficiently supplied to the cavity resonator 11. [Example]

[0038] The present invention will be described in more detail below by showing experimental examples. These experimental examples are provided to facilitate understanding of the present invention, and the present invention is not limited to these examples.

[0039] [Experimental Example 1] <Relationship between the sample plate (magnetic field vector) and the GaN crystal axis, and the heating efficiency of GaN> Using a microwave heating device similar to that shown in Figure 4, a TM was placed in a cavity resonator (size: 146cmΦ x 5cm). 110A standing wave (frequency 2.5 GHz) of the GaN mode was formed and a magnetic field heating test was carried out. The GaN used was a plate-shaped GaN (GaN size: width × length × thickness = 10 mm × 10 mm × 0.4 mm) that was doped with Si by Si ion implantation to control it to n-type. In this experimental example, the relationship between the magnetic field vector (magnetic field oscillation direction) along the in-plane direction of the sample plate and the crystal axis of GaN was tested in four patterns, as shown in Figure 5. In Figure 5, (i) and (ii) are the configurations specified in the present invention. That is, "the sample plate with GaN mounted thereon is oriented along the magnetic field vector of the standing microwave wave, and the c-axis of the GaN is perpendicular to the surface of the sample plate." In (i) and (ii), the thickness direction of the GaN plate (not shown) is the c-axis direction. On the other hand, (iii) and (iv) in Figure 5 are configurations "the sample plate with GaN mounted thereon is oriented along the magnetic field vector of the standing microwave wave, and the m-axis of the gallium nitride is perpendicular to the surface of the sample plate." In (iii) and (iv), the thickness direction of the GaN plate (not shown) is the m-axis direction. The temperatures achieved by GaN when the microwave (frequency 2.5 Hz) output was set to 50 W, 100 W, and 150 W are shown in Figure 6. As shown in Figure 6, in the heating methods (i) and (ii) of the present invention, GaN is magnetically heated with high efficiency, approximately in proportion to the microwave output.

[0040] In addition, TM 110 Change to TM mode 010 When a standing wave of the mode (a mode in which the electric field strength at the central axis of the cavity is maximized) was formed in the cavity and GaN was heated by an electric field, the heating efficiency was higher in (iii) and (iv) than in (i) and (ii). However, thermal runaway (sparking) occurred during electric field heating, making stable temperature control difficult. Therefore, it was considered that heating GaN by magnetic field heating, with the c-axis direction of GaN perpendicular to the surface of the sample plate, would be more suitable for achieving stable high-temperature heating.

[0041] [Experimental Example 2] <Crystalline recovery test after ion implantation> The Mg ion-implanted p-type GaN was subjected to magnetic field heating (annealing) using a standing microwave, and the degree of recovery of the GaN crystallinity, which had been partially amorphized by the ion implantation, was examined by photoluminescence analysis. Photoluminescence analysis was carried out as follows. The excitation light source was a He-Cd laser (wavelength 325 nm, model IK5751I-G, manufactured by Kimmon Koha Co., Ltd.) and the detector was a multi-fiber channel spectrometer (USB2000, manufactured by OceanOptics). Measurements were performed with the sample cooled (77 K) and the excitation light intensity set to 30 kW / cm. 2 The measurement was performed under the condition that the detector energy range was 2 to 3.6 eV.

[0042] (Experimental Example 2-1: p-type GaN obtained by epitaxial growth) Figure 7 shows the photoluminescence profile of ideal p-type GaN (p-GaN, size: 10mm x 10mm x 0.4mm) obtained by epitaxial growth. No GL (Green Luminescence) due to crystal defects was detected, but a DAP (Donor Acceptor Pair, 3.28eV) peak due to p-type conversion and an NBE (Near Band Edge, 3.47eV) peak due to normal crystals were detected.

[0043] (Experimental Example 2-2: High-pressure, high-temperature treatment of Mg-implanted GaN using an electric furnace) Figure 8 shows the photoluminescence profile of GaN implanted with Mg ions (Mg-implanted GaN, size: 7.5 mm x 7.5 mm x 0.344 mm) after conventional high-pressure annealing using an electric furnace (1 GPa, 1300°C, 3 minutes). Although a GL peak is observed, DAP and NBE peaks are also clearly detectable. This indicates that the crystal defects have been repaired and the material operates as a p-type GaN semiconductor.

[0044] (Experimental Example 2-3: Magnetic field heating of Mg-implanted GaN using non-pulsed microwaves) 9 shows the photoluminescence profile when the same Mg-implanted GaN as used in Experimental Example 2-2 was heated by the heating method of the present invention. That is, an apparatus having the same configuration as the microwave heating apparatus (cavity size: 146 cmΦ×5 cm) shown in FIG. 4 was constructed, and a sample plate (material: alumina, made by combining two rod-shaped stages with a cross-sectional diameter of 1 mmΦ) on which the Mg-implanted GaN was placed was placed in the same position as the sample plate shown in FIG. 2, and microwave standing waves (TM 110 The sample plate was placed along the magnetic field vector of the cavity resonator (the longitudinal section of the sample plate was made to correspond to the diameter of the cavity resonator cross section, and the sample plate was placed parallel to the central axis of the cavity resonator and along the magnetic field vector). At this time, the c-axis direction of the Mg-implanted GaN was set perpendicular to the surface of the sample plate, and the microwave standing wave (TM 110 The Mg-implanted GaN was magnetically heated by irradiation with a 200 W laser (mode, frequency 2.5 Hz, output: 200 W, irradiation time: 1 minute, temperature reached: approximately 1500°C). As shown in Figure 9, the DAP and NBE peaks were clearly detected. This indicates that the crystal defects were repaired and the GaN functioned as a p-type semiconductor.

[0045] (Experimental Example 2-4: Magnetic field heating of Mg-implanted GaN by pulsed microwaves -1) Figure 10 shows the photoluminescence profile of Experimental Example 2-3, where pulsed microwave irradiation (200 W for 2 seconds, then 50 W for 3 seconds, repeated, irradiation time: 1 minute) was used to heat the Mg-implanted GaN in a magnetic field. In Experimental Example 2-4, the average temperature reached by the Mg-implanted GaN during pulsed irradiation was a low temperature of approximately 700°C. As shown in Figure 10, the DAP and NBE peaks were not detected, and only the GL peak was detected. This indicates that the crystal defects were not repaired. As with conventional knowledge, this indicates that if the GaN reaches a low temperature, the annealing of the GaN is insufficient.

[0046] (Experimental Example 2-5: Magnetic field heating of Mg-implanted GaN by pulsed microwaves -2) Figure 11 shows the photoluminescence profile of Mg-implanted GaN when magnetic field heating was performed in the same manner as in Experimental Example 2-4, except that the microwave irradiation pulse conditions were alternating between 0.5 seconds at 350 W and 3 seconds at 200 W. In Experimental Example 2-5, the average temperature reached by the Mg-implanted GaN during pulse irradiation was approximately 1050°C. As shown in Figure 11, the DAP and NBE peaks were clearly detected. This indicates that the crystal defects were repaired and the GaN functioned as a p-type GaN semiconductor.

[0047] (Experimental Example 2-6: Magnetic field heating of Mg-implanted GaN by pulsed microwaves -3) Figure 12 shows the photoluminescence profile of Mg-implanted GaN when magnetic field heating was performed in the same manner as in Experimental Example 2-5, except that the microwave irradiation pulse conditions were alternating between 1 second at 350 W and 3 seconds at 200 W. In Experimental Example 2-6, the average temperature reached by the Mg-implanted GaN during pulse irradiation was approximately 1100°C. As shown in Figure 12, the DAP and NBE peaks were clearly detected. This indicates that the crystal defects were repaired and the GaN functioned as a p-type GaN semiconductor.

[0048] Furthermore, in Experimental Examples 2-5 and 2-6, in which the Mg-implanted GaN was heated to 1000°C or higher by microwave pulse irradiation and crystallinity was restored, nitrogen desorption was more suppressed than in Experimental Example 2-3, in which the Mg-implanted GaN was heated to 1000°C or higher by non-pulse irradiation. [Explanation of symbols]

[0049] 10 Microwave heating device 11 Cavity resonator 12 Entrance 13 Exit 14 Microwave supply port 15. Window 21 Microwave Generator 22 Microwave Amplifier 23 Isolator 24 Matching box 25 Antenna 26, 42, 45, 46 cables 31 Transport mechanism 31A Supply side conveying section 31B Sending side conveying section 41 Thermal image measuring device 43 Control Unit 44 Electromagnetic wave sensor 50 sample plates 51 GaN board 52 Magnetic Field Region A Conveying direction CE Cavity center axis (center axis)

Claims

1. A method for heating gallium nitride, comprising: placing a sample plate carrying gallium nitride along the magnetic field vector of a standing microwave wave; irradiating the sample plate with the standing microwave wave so that the c-axis direction of the gallium nitride is perpendicular to the surface of the sample plate, thereby magnetically heating the gallium nitride.

2. The standing wave of the microwave is TM ｎ１０ (n is an integer of 1 or more) mode or TE １０ｎ The method for heating gallium nitride according to claim 1 , wherein the heating mode is (n is an integer of 1 or more).

3. 3. The method for heating gallium nitride according to claim 2, wherein the sample plate is placed in a cylindrical cavity resonator with the cross section of the sample plate corresponding to the diameter of the cross section of the cavity resonator, and a standing wave of the microwave is formed in the cavity resonator.

4. The method for heating gallium nitride according to any one of claims 1 to 3, wherein the gallium nitride is in the form of a plate with its thickness direction being the c-axis direction.

5. The method for heating gallium nitride according to any one of claims 1 to 3, wherein the gallium nitride is heated to 900°C or higher.

6. The method for heating gallium nitride according to claim 5 , wherein the microwave irradiation is pulsed.

7. 4. The method for heating gallium nitride according to claim 1, wherein the gallium nitride has been subjected to an ion implantation process, and the gallium nitride has been partially amorphized by the ion implantation process.

8. 8. The method for heating gallium nitride according to claim 7, wherein the method for heating gallium nitride restores a crystalline structure to an amorphous portion of the gallium nitride.

9. 4. The method for heating gallium nitride according to claim 1, wherein the gallium nitride is mounted on the sample plate in a state where it is incorporated into a semiconductor device.

10. A method for producing a gallium nitride semiconductor, comprising obtaining an n-type or p-type gallium nitride semiconductor by the gallium nitride heating method according to claim 8.

11. A method for manufacturing a semiconductor device, comprising obtaining a semiconductor device in which the gallium nitride has been modified by the gallium nitride heating method according to claim 9.

12. The method for manufacturing a semiconductor device according to claim 11, wherein the semiconductor device is an aluminum gallium nitride / gallium nitride heterojunction field effect transistor.

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