WO2015037232A1 - 窒化物半導体結晶、製造方法および製造装置 - Google Patents
窒化物半導体結晶、製造方法および製造装置 Download PDFInfo
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Definitions
- the present invention relates to a nitride semiconductor crystal, a manufacturing method, and a manufacturing apparatus.
- nitride semiconductor crystals have been used in various fields such as laser diodes (LDs), light emitting diodes (LEDs), solar cells, and power devices.
- LDs laser diodes
- LEDs light emitting diodes
- solar cells solar cells
- power devices power devices
- the trihalide vapor phase growth method (THVPE method, Tri-halide Vapor Phase Epitaxy) can grow a nitride semiconductor crystal at a higher temperature and at a higher speed than the hydride vapor phase growth method (HVPE method, Hydride Vapor Phase Epitaxy).
- Patent Document 1 International Publication No. 2011/142402 Pamphlet
- a step of preparing a substrate a step of supplying a gallium trihalide gas having a partial pressure of 9.0 ⁇ 10 ⁇ 3 atm or more onto the substrate, a GaN layer on the substrate,
- a method for producing a nitride semiconductor crystal comprising a step of growing the crystal in a ⁇ C-axis direction, wherein a growth temperature of the GaN crystal is 1200 ° C. or higher.
- a step of preparing a substrate a step of supplying an aluminum trihalide gas having a partial pressure of 9.0 ⁇ 10 ⁇ 3 atm or more onto the substrate, an AlN layer on the substrate, And a method for producing a nitride semiconductor crystal, wherein the growth temperature of the AlN crystal is 1400 ° C. or higher.
- a nitride semiconductor crystal having a crystal diameter of 4 inches or more, a curvature radius of curvature of 100 m or more, and an impurity concentration of the crystal of 1 ⁇ 10 17 / cm 3 or less.
- An outline of the nitride semiconductor crystal manufacturing apparatus 200 is shown.
- An outline of a conventional nitride semiconductor crystal manufacturing apparatus 250 is shown.
- the manufacturing process of the conventional nitride semiconductor substrate is shown.
- 1 shows a manufacturing process of a GaN substrate according to the present invention.
- a method for determining the polarity of a GaN crystal by KOH etching will be described.
- a comparative example of band diagrams of LEDs created on the ⁇ C plane and the + C plane is shown.
- a comparative example of the magnitude of In incorporation on the ⁇ C plane and the + C plane is shown.
- the partial pressure of GaCl 3 gas shows the relationship between the growth rate of the GaN crystal.
- the cross-sectional photograph and bird's-eye view photograph of the SEM of the GaN crystal layer concerning Example 1 are shown.
- the optical micrograph of the GaN crystal layer concerning Example 4 is shown.
- 2 shows a photoluminescence (PL) spectrum of a GaN crystal layer.
- 7 shows a cross-sectional SEM photograph of a GaN crystal layer according to Example 5.
- the bird's-eye view SEM photograph of the GaN crystal layer concerning comparative example 1 is shown.
- the SEM bird's-eye photograph of the GaN crystal layer concerning the comparative example 2 is shown.
- the SEM bird's-eye view photograph of the GaN crystal layer concerning comparative example 3 is shown.
- the SEM bird's-eye view photograph of the GaN crystal layer concerning comparative example 4 is shown.
- the relationship between the growth temperature and growth rate when growing a nitride semiconductor crystal is shown.
- FIG. 1 shows an outline of a cross section of a laminate in which a nitride semiconductor thin film layer is laminated on an initial substrate.
- the stacked body 300 (left figure) in the case of using the initial substrate 301 of a different material from the nitride semiconductor thin film layer 303 and the initial substrate 101 of the same material as the nitride semiconductor thin film layer 303 are used.
- the laminated body 100 (right figure) is shown.
- an initial substrate 301 made of a different material is used as an initial substrate on which the nitride semiconductor thin film layer 303 is grown.
- sapphire substrates have been used for LED applications
- silicon substrates have been used for horizontal electronic device applications.
- the low temperature buffer layer 302 is provided on the initial substrate 301.
- the low temperature buffer layer 302 is used to relieve the lattice constant difference and the thermal expansion coefficient difference between the initial substrate 301 and the nitride semiconductor thin film layer 303.
- the crystal of the nitride semiconductor thin film layer 303 is grown on different kinds of initial substrates 301 by relaxing the lattice constant difference to some extent.
- the nitride semiconductor thin film layer 303 is epitaxially grown on the low temperature buffer layer 302 by using the MOVPE method or the like. Even when the low-temperature buffer layer 302 is used, the influence of the lattice constant difference cannot be completely mitigated, so that a large number of defects 304 due to the lattice constant difference are generated in the nitride semiconductor thin film layer 303. For example, dislocations with a high density of about 10 9 cm ⁇ 2 or more occur on the surface of the nitride semiconductor thin film layer 303. Further, when the nitride semiconductor thin film layer 303 is grown at a high temperature, stress strain (warping) due to the difference in thermal expansion coefficient occurs when returning to room temperature.
- stress strain warping
- a crystal layer having a radius of curvature with a warp due to stress of 100 m or more can be put into practical use as a highly reliable nitride semiconductor crystal without distortion.
- a 4-inch GaN crystal layer manufactured using an initial substrate 301 made of a different material currently on sale has a radius of curvature of about 20 m.
- a crystal layer having a curvature radius of 1000 m can be manufactured. However, it is not suitable for increasing the diameter and is about 2 inches. I can only grow.
- the nitride semiconductor thin film layer 303 can be formed by homoepitaxial growth, and the dislocation density is greatly reduced.
- the dislocation density is reduced to 1 ⁇ 10 5 cm ⁇ 2 or less.
- a nitride semiconductor crystal having a diameter of 4 inches and a curvature radius of 300 m or more can be obtained.
- a nitride semiconductor crystal having a radius of curvature of 1000 m or more can be obtained.
- FIG. 2 shows a Drop phenomenon that is a problem in a nitride-based LED.
- FIG. 2 shows a change in external quantum efficiency [%] (vertical axis) with respect to current density [A / cm 2 ] (horizontal axis).
- the external quantum efficiency is a ratio of the number of photons emitted outside the LED to the number of electrons injected into the light emitting layer of the LED.
- LED1 and LED2 are LEDs having different characteristics from each other, and are manufactured by growing a GaN crystal layer on a sapphire substrate.
- the current density exceeds a certain value, the external quantum efficiency of the GaN crystal layer grown by the conventional crystal growth method decreases.
- the GaN crystal layer grown on a substrate made of a different material such as sapphire by the conventional crystal growth method has a problem of a Drop phenomenon in which the light emission efficiency decreases in a large current operation. In order to reduce the Drop phenomenon, a high-quality GaN crystal layer with few defects and impurities is required.
- a conventional nitride semiconductor crystal initial substrate 101 is formed by an HVPE growth method using GaCl as a raw material.
- a high-quality nitride semiconductor crystal is grown by this method, a high-quality crystal cannot be obtained at a growth rate of 500 ⁇ m / h or more because of the upper limit of temperature (1100 ° C.).
- a large-diameter nitride semiconductor crystal can be easily manufactured by stably growing a nitride semiconductor crystal in the ⁇ C axis direction at a high speed.
- FIG. 3 is a flowchart showing an example of a method for manufacturing a nitride semiconductor crystal according to an embodiment of the present invention.
- growth in the ⁇ C axis direction is realized by the THVPE method using a trihalide gas as a source gas and controlling the growth temperature.
- step S100 a high-concentration trihalide gas having a partial pressure of 9.0 ⁇ 10 ⁇ 3 atm or higher is generated.
- the growth rate is improved.
- step S200 the temperature of the nitride semiconductor substrate 101 is controlled.
- the growth temperature is preferably 1200 ° C. or higher, and may be 1300 ° C. or higher and 1400 ° C. or higher depending on the material to be grown.
- the growth temperature refers to the temperature of the nitride semiconductor substrate 101.
- step S300 a trihalide source gas and ammonia (NH 3 ) gas are supplied onto the nitride semiconductor substrate 101. Since the conditions such as the growth temperature are optimized by using the trihalide source gas as the raw material, the crystal can be grown in the ⁇ C-axis direction (step S400). A nitride semiconductor crystal can be easily increased in diameter by -C axis growth.
- the order of each step is not limited to the order shown in FIG. For example, step S100 and step S200 may be performed simultaneously, and step S200 may be performed first.
- FIGS. 4 and 5 are diagrams for explaining that growth in the ⁇ C-axis direction can be realized by selecting a source gas.
- a GaN crystal layer will be mainly described as an example, but the same applies to an AlN crystal.
- FIG. 4 shows the structure and polarity of the GaN crystal layer.
- the crystal structure of GaN generally has a hexagonal crystal structure in which Ga atoms (black circles) and N atoms (white circles) are bonded to each other.
- the polarity of the crystal layer becomes Ga polarity or N polarity depending on which direction is positive or negative in the C-axis direction.
- the C-axis direction is a direction perpendicular to the hexagonal crystal bottom surface.
- the growth surface of the GaN crystal layer is a + C plane (0001).
- the crystal structure with respect to the substrate is a structure opposite to the Ga polarity in the C-axis direction, three of the four bonds of Ga atoms are directed to the surface side, and the remaining one is perpendicular to the substrate side. Suitable for.
- the growth surface of the GaN crystal layer is a -C plane (000-1).
- FIG. 5 shows the relationship between GaN crystal growth and polarity. Reactions in the case of crystal growth using gallium trichloride (GaCl 3 ) gas are shown on the N polar face (left figure) and the Ga polar face (right figure). In the GaCl 3 molecule, chlorine atoms (dark black circles) are bonded to three bonds of Ga atoms.
- GaCl 3 gallium trichloride
- Ga atoms of GaCl 3 gas are difficult to bond with N-bonds, so that they are difficult to be taken into the crystal and epitaxial growth is unlikely to proceed.
- one N atom bond faces the surface side when reacting with GaCl 3 gas. Since Ga atoms of GaCl 3 gas are more likely to be bonded to N atom bonds than the Ga polar plane, they are easily taken into the crystal and promote epitaxial growth.
- GaN crystal growth using gallium monochloride (GaCl) gas is less likely to cause steric hindrance than GaCl 3 gas. Therefore, the GaCl gas is adsorbed on both the Ga polar face and the N polar face.
- GaCl gallium monochloride
- the GaCl gas is adsorbed on both the Ga polar face and the N polar face, the growth direction is easily reversed during the crystal growth, and cannot be stably grown in the ⁇ C axis direction.
- GaCl gas it is more difficult to grow a nitride semiconductor crystal in the ⁇ C-axis direction using the initial substrate 301 of a different material.
- GaCl 3 gas is more likely to be adsorbed on the N-polar surface than on the Ga-polar surface, and therefore, using GaCl 3 gas facilitates stable growth in the ⁇ C axis direction. Even when the growth is started in the + C axis direction, the crystal is inverted in the ⁇ C axis direction to grow. Therefore, a nitride semiconductor crystal can be grown in the ⁇ C-axis direction using the initial substrate 301 of a different material. Thus, by selecting the source gas, a nitride semiconductor crystal can be grown in the ⁇ C axis direction. However, even when GaCl 3 gas is used as a raw material, when the growth temperature is low, the ⁇ C axis direction and the + C axis direction may be mixed, so the growth temperature must be increased. Is preferred.
- FIG. 6 shows the shape of the crystal layer when GaN is grown in the ⁇ C axis and + C axis directions.
- the left figure shows the shape of the crystal layer when the crystal is grown in the ⁇ C axis direction
- the right figure shows the crystal layer when the crystal is grown in the + C axis direction.
- the crystal shape shown in FIG. 6 has been verified by first-principles calculations and growth experiments.
- the facet of the (10-11) plane appears as in the growth in the + C axis direction.
- the angle formed between the (0001) plane and the (10-11) plane of the crystal layer grown in the ⁇ C axis direction is an obtuse angle (for example, 118.0 °). Therefore, in the growth in the ⁇ C axis direction, the crystal area of the ⁇ C plane becomes larger than the crystal area of the + C plane. Therefore, a large-diameter nitride semiconductor crystal can be easily manufactured by growth in the ⁇ C axis direction.
- the angle formed by the (0001) plane and the (10-11) plane may be an obtuse angle that is greater than 90 ° and smaller than 180 °.
- the facet is not limited to the (10-11) plane, and may be a plane such that the angle formed with the (0001) plane, such as the (11-22) plane or the (10-12) plane, becomes an obtuse angle.
- FIG. 7 is a table comparing the characteristics of each nitride semiconductor crystal growth method.
- Examples of the method for growing a nitride semiconductor crystal include a THVPE method, an HVPE method, a metal organic vapor phase growth (MOVPE method), a molecular beam epitaxy method (MBE method), and the like.
- ⁇ indicates that a crystal layer satisfying the conditions (i) to (v) shown in FIG. 7 can be obtained.
- “ ⁇ ” indicates that although it may satisfy the conditions (i) to (v), it is actually difficult to obtain a crystal layer.
- “X” indicates that a crystal layer satisfying the conditions (i) to (v) cannot be obtained from the conventional technique.
- the growth temperature is less than 1300 ° C., and the partial pressure of GaCl 3 gas supplied onto the substrate is 8.0 ⁇ 10 ⁇ 3 atm or less.
- the growth temperature is 1200 ° C. or higher and lower than 1300 ° C., and the partial pressure of GaCl 3 gas supplied onto the substrate is 9.0 ⁇ 10 ⁇ 3 atm or higher.
- the growth temperature in the THVPE method of the present invention can be 1300 ° C. or higher.
- each growth method can satisfy
- Conditions (i) to (v) are: (i) -C axis growth, (ii) 4 inches in diameter, dislocation density of 1 ⁇ 10 5 / cm 2 or less, curvature radius of 100 m or more, and (iii) thickness of 100 ⁇ m or more.
- the THVPE method is a method for growing a GaN crystal layer using GaCl 3 gas and NH 3 gas.
- a crystal layer can be grown at high speed and at high speed using GaCl 3 gas.
- the crystal layer can be stably grown in the (i) -C-axis direction by optimizing the growth conditions.
- the concentration of GaCl 3 gas cannot be increased more than 8.0 ⁇ 10 ⁇ 3 atm. Therefore, when the growth temperature is 1200 ° C. or higher, the growth rate decreases rapidly. When the growth temperature is lowered, oxygen (O 2 ) and silicon (Si) are easily taken in during the growth, and (iv) the impurity concentration cannot be reduced to 1 ⁇ 10 17 / cm 3 or less.
- the nitride semiconductor crystal manufacturing apparatus used in the conventional THVPE method has a density of about 180 ⁇ m / h because it is difficult to increase the concentration of GaCl 3 gas.
- the growth rate rapidly decreases at 1200 ° C. or higher.
- there is a problem of deposits reattached to the inside of the growth chamber not limited to the magnitude of the growth rate, so there is a limit to the continuous operation time for crystal growth. That is, when the growth rate is high, the film thickness that can be continuously formed becomes thick, and when the growth rate is slow, the film thickness that can be continuously formed becomes thin. Therefore, in the conventional THVPE method, it was very difficult to grow the (v) GaN crystal layer to a thickness of 5 mm or more.
- the growth temperature is set to 1200 ° C. or higher and lower than 1300 ° C.
- the crystal growth is performed with the partial pressure of GaCl 3 gas supplied onto the substrate being 9.0 ⁇ 10 ⁇ 3 atm or higher.
- a growth rate of 300 ⁇ m / h or more is possible.
- an increase in the partial pressure of GaCl 3 gas enables a growth rate of 1 mm / h or more, and an ultra-thick film (5 mm or more) nitride semiconductor crystal that satisfies the conditions (i) and (v) can be grown.
- the crystal layer is grown at a growth temperature of 1300 ° C. or higher.
- the growth rate can be 0.15 to 1 mm / h or higher.
- the growth temperature is high, a nitride semiconductor crystal with a low transparency and a high transparency can be obtained. Thereby, a nitride semiconductor crystal that satisfies the conditions (i) to (iv) can be grown.
- the THVPE method of this example realized high-temperature growth at 1300 ° C. or higher, so that the impurity concentration can be reduced to 1 ⁇ 10 16 / cm 3 or lower, and further to 1 ⁇ 10 15 / cm 3 or lower.
- GaN crystal growth method by the HVPE method a gallium monochloride-ammonia system (GaCl-NH 3 system) has been used.
- GaCl-NH 3 system gallium monochloride-ammonia system
- (i) stable growth in the ⁇ C axis direction is difficult.
- the HVPE method as described with reference to FIG. 8, when the growth temperature becomes high, the growth driving force decreases and the growth rate decreases, so the growth temperature cannot be increased (1200 ° C. or higher). iv) Impurity concentration increases.
- the MOVPE method uses an organic material such as TMG (trimethylgallium) as a raw material, (iv) the impurity concentration of carbon C increases.
- TMG trimethylgallium
- the MOVPE method can grow a thin film in the ⁇ C-axis direction under certain conditions.
- the MBE method crystals can be grown in the ⁇ C axis direction if the ratio of raw materials is strictly controlled.
- the MBE method has an extremely slow growth rate of about several tens to several hundreds nm / h compared to other growth methods, so it takes several weeks to several months to grow a GaN crystal layer of 100 ⁇ m or more.
- the deposits inside the device and the growth cost caused by starting the device for a long time it is difficult to use the MBE method for GaN thick film crystal growth.
- the material temperature control method is limited to substrate heating and the like, and it is difficult to maintain the material at a high temperature.
- a nitride semiconductor crystal grown by the MBE method has a large oxygen impurity concentration of (iv) 1 ⁇ 10 17 / cm 3 . Furthermore, it takes 57 years to achieve (v) a film thickness of 5 mm or more under typical growth conditions using the MBE method.
- the ammonothermal method and the Na flux method are conceivable, but the current technical common sense is that the diameter is about 2 inches, and the diameter is increased. And unsuitable for thickening. For this reason, even if an ammonothermal method or the like is used, a crystal layer having a thickness of 4 inches or more or a film thickness of 5 mm or more cannot be obtained.
- FIG. 8 is a diagram comparing the growth driving force of the HVPE method (broken line) and the THVPE method (solid line).
- FIG. 8 shows the growth driving force [atm] (vertical axis) with respect to the growth temperature [° C.] (horizontal axis).
- the total pressure ⁇ Pi is 1.0 atm
- the partial pressures (P ° GaCl 3 , P ° GaCl) of the GaCl 3 gas and the GaCl gas are 1.0 ⁇ 10 ⁇ 3 atm, respectively.
- the V / III ratio indicating the ratio of the supply amounts of the Group 5 source gas and the Group 3 source gas is 20, and the ammonia decomposition rate ⁇ is 0.0.
- FIG. 9 is a graph comparing growth rates by changing raw materials in the same apparatus in order to compare the growth rates of the HVPE method and the THVPE method.
- FIG. 9 shows changes in growth rate [ ⁇ m / h] (vertical axis) with respect to the growth temperature [° C.] (horizontal axis).
- the partial pressure of the GaCl 3 gas (P ° GaCl 3 ) and the partial pressure of the GaCl gas (P ° GaCl) supplied to the growth chamber are 1.0 ⁇ 10 ⁇ 3 atm, respectively.
- the partial pressure (P ° NH 3 ) of NH 3 gas supplied to the growth chamber is 2.0 ⁇ 10 ⁇ 2 atm.
- the growth rate decreases when the growth temperature is between 900 ° C. and 1000 ° C.
- the growth rate decreases between 1100 ° C. and 1200 ° C. That is, the THVPE method is less likely to cause a decrease in growth rate due to an increase in growth temperature than the HVPE method.
- the partial pressure of GaCl 3 gas in the THVPE method and the partial pressure of GaCl gas in the HVPE method are the same, the growth rate of the THVPE method is larger than the growth rate of the HVPE method.
- FIG. 10 shows an outline of a nitride semiconductor crystal manufacturing apparatus 200 using the THVPE method.
- the nitride semiconductor crystal manufacturing apparatus 200 of this example includes a first reaction chamber 210, a second reaction chamber 220, and a growth chamber 230.
- the first reaction chamber 210 and the second reaction chamber 220 are an example of a gas supply unit that generates a trihalogenated gas and supplies it to the substrate.
- the first reaction chamber 210 and the second reaction chamber 220 may be provided in different reaction tubes.
- the first reaction chamber 210 and the second reaction chamber 220 are partitioned by a suppression structure 214.
- the first reaction chamber 210 includes a first halogen gas supply port 262 and has a first zone Z1.
- Metal gallium 212 is installed in the first zone Z1.
- the first halogen gas supply port 262 supplies halogen gas to the first zone Z1 where the metal gallium 212 is installed.
- the second reaction chamber 220 includes a second halogen gas supply port 264 and a first exhaust port 266, and has a second zone Z2.
- the gas generated in the first reaction chamber 210 is supplied to the second zone Z2.
- the suppression structure 214 is provided between the first reaction chamber 210 in which the first step is performed and the second reaction chamber 220 in which the second step is performed. Thereby, the suppression structure 214 suppresses that the density
- the suppression structure 214 is a path between the first reaction chamber and the second reaction chamber.
- the cross-sectional area of the path is smaller than the cross-sectional areas of the first reaction chamber 210 and the second reaction chamber 220.
- the nitride semiconductor crystal manufacturing apparatus 200 can increase the pressure in the first zone Z1.
- the partial pressure of chlorine gas (Cl 2 ) may be increased.
- the partial pressure of Cl 2 gas supplied to the first reaction chamber 210 is 1.0 ⁇ 10 ⁇ 3 atm or more.
- the second reaction chamber 220 includes a plurality of partition plates 222 that reduce the flow rate of the GaCl 3 gas. Thereby, the nitride semiconductor crystal manufacturing apparatus 200 can increase the flow rate of the Cl 2 gas at the second halogen gas supply port 264 and the pressure in the second zone Z2.
- the nitride semiconductor crystal manufacturing apparatus 200 of this example adjusts the partial pressure (P ° GaCl 3 ) of gallium trihalide gas supplied on the substrate to 9.0 ⁇ 10 ⁇ 3 atm or more.
- the GaCl 3 gas partial pressure (P ° GaCl 3 ) in this example can be adjusted to a higher value than the conventional value.
- the partial pressure of the gallium trihalide gas supplied onto the substrate is adjusted to 9.0 ⁇ 10 ⁇ 3 atm or more and 1.0 ⁇ 10 ⁇ 1 atm or less. Further, the partial pressure of NH 3 gas (P ° NH 3 ) in the growth chamber 230 is adjusted to 5.0 ⁇ 10 ⁇ 2 atm or more and 2.5 ⁇ 10 ⁇ 1 atm or less.
- gallium monohalide gas is generated by reacting metal gallium 212 with a halogen gas.
- the halogen gas is Cl 2 gas, bromine (Br 2 ) gas, or iodine (I 2 ) gas.
- reaction formula (1) Ga (l) + 1 / 2Cl 2 (g) ⁇ GaCl (g) (1)
- (l) and (g) indicate that the substance is in a liquid and gas state, respectively.
- the Cl 2 gas is supplied together with the carrier gas.
- the carrier gas an inert gas such as nitrogen gas, argon gas, helium gas, or a mixed gas containing at least one of them is used.
- the partial pressure of the Cl 2 gas is adjusted to 1.0 ⁇ 10 ⁇ 3 atm or more, and the total pressure is adjusted to 1 atm.
- gallium chloride gas is generated in addition to GaCl gas.
- Gallium chloride refers to gallium chloride in general such as gallium monochloride, gallium dichloride, gallium trichloride, and dimer (dimer) of gallium trichloride.
- gallium chloride gas containing GaCl gas as a main component is preferably generated.
- the amount of GaCl gas with respect to the total amount of gallium chloride gas produced is preferably 99 mol% or more, and more preferably 99.9 mol% or more.
- External heating means may be provided outside the first reaction chamber 210.
- the external heating means may be a resistance heating heater, a high frequency heating device, a lamp heater, or the like.
- the external heating means heats the first zone Z1 and the second zone Z2 independently.
- the external heating means may be a means capable of heating the first zone Z1 and the second zone Z2 simultaneously.
- the nitride semiconductor crystal manufacturing apparatus 200 may further include a heating unit capable of independently heating the metal gallium 212 in addition to the external heating unit.
- the reaction temperature in the first step is preferably 300 to 1000 ° C, more preferably 500 to 900 ° C, and particularly preferably 700 to 850 ° C.
- generated GaCl gas improves that the reaction temperature in a 1st process is 300 degreeC or more.
- the reaction temperature in the first step is 1000 ° C. or lower, damage to the reaction tube made of quartz or the like can be suppressed.
- reaction formula (2) GaCl (g) + Cl 2 (g) ⁇ GaCl 3 (g) (2)
- the Cl 2 gas is supplied together with the carrier gas.
- the carrier gas for example, an inert gas such as nitrogen gas, argon gas, helium gas, or a mixed gas containing at least one of them is used.
- the partial pressure of Cl 2 gas is adjusted to 2.0 ⁇ 10 ⁇ 3 atm and the total pressure is adjusted to 1 atm.
- the reaction temperature in the second step is preferably 150 to 1000 ° C, more preferably 200 to 900 ° C, and particularly preferably 500 to 700 ° C.
- the reaction temperature in the second step is 150 ° C. or higher, the selectivity of the generated GaCl 3 gas is improved.
- the first exhaust port 266 supplies the growth chamber 230 with the GaCl 3 gas generated in the second step.
- the first exhaust port 266 may be disposed inside the growth chamber 230.
- the growth chamber 230 includes an ammonia gas supply port 236, a susceptor 232, and a second exhaust port 238.
- An initial substrate 234 is installed on the susceptor 232.
- the ammonia gas supply port 236 supplies NH 3 gas to the gas mixing unit M1 together with the carrier gas.
- the carrier gas for example, an inert gas such as nitrogen gas, argon gas, helium gas, or a mixed gas containing at least one of them is used.
- NH 3 gas and GaCl 3 gas are mixed to generate a raw material gas.
- the susceptor 232 is an example of a temperature control unit that holds the initial substrate 234 and controls the initial substrate 234 to a predetermined growth temperature.
- the susceptor 232 is made of, for example, a boron nitride sintered body having heat resistance and corrosion resistance or carbon covered with a boron nitride sintered body.
- the susceptor 232 is provided with a carbon heating element inside and raises the temperature of the initial substrate 234.
- the initial substrate 234 is supplied with a source gas containing NH 3 gas and GaCl 3 gas generated in the gas mixing unit M1. Thereby, a GaN crystal layer is grown on the initial substrate 234 in the crystal growth part G1.
- the initial substrate 234 is a single crystal substrate such as a sapphire (0001) substrate, gallium arsenide, silicon carbide substrate, or gallium nitride substrate.
- the nitride semiconductor crystal manufacturing apparatus 200 may supply a barrier gas from the periphery of the first exhaust port 266 so as to surround the GaCl 3 gas. In this case, GaCl 3 gas and NH 3 gas are mixed in the vicinity of the crystal growth part G 1, so that reattachment inside the growth chamber 230 is prevented. Thereby, the nitride semiconductor crystal manufacturing apparatus 200 of this example can suppress a decrease in growth rate caused by operating for a long time.
- the barrier gas is an inert gas such as nitrogen gas or argon gas.
- the second exhaust port 238 exhausts unnecessary gas generated by GaN crystal growth and unreacted gas to the outside.
- the unnecessary gas generated by the GaN crystal growth is hydrogen chloride HCl, hydrogen H 2 or the like.
- the nitride semiconductor crystal manufacturing apparatus 200 of this example can grow a GaN crystal layer on the nitride semiconductor substrate 101 at a rate of 1 mm / h or more in the ⁇ C axis direction.
- the growth temperature of the GaN crystal layer is 1200 ° C. or higher. Since the nitride semiconductor crystal manufacturing apparatus 200 of this example can grow crystals in the ⁇ C-axis direction, the crystal layer can be enlarged by increasing the growth film thickness.
- the nitride semiconductor crystal manufacturing apparatus 200 of this example can grow a nitride semiconductor crystal having a crystal layer diameter of 3 inches or more and a thickness of 5 mm or more. For example, since a GaN crystal layer manufactured using the nitride semiconductor crystal manufacturing apparatus 200 is grown to 1 cm or 5 cm or more, it is easy to cut out a plurality of GaN substrates.
- the example which used the gallium as a group 3 raw material was shown regarding the manufacturing method
- aluminum can be used as a group III raw material.
- AlN crystal growth by setting the growth temperature to 1400 ° C. or higher, an AlN crystal layer having a crystal layer diameter of 3 inches or more and a thickness of 5 mm or more is obtained as in the case of GaN crystal growth. It is done.
- differences between the method for manufacturing the AlN crystal layer and the method for manufacturing the GaN crystal layer will be described.
- the nitride semiconductor crystal manufacturing apparatus 200 can prevent the quartz in the first reaction chamber 210 from being eroded by the AlCl gas.
- the Cl 2 gas may not be supplied from the second halogen gas supply port 264.
- the AlCl 3 gas may be directly supplied from the first reaction chamber 210 to the growth chamber 230 without using the second reaction chamber 220.
- the nitride semiconductor crystal manufacturing apparatus 200 of this example can grow an AlN crystal layer on the nitride semiconductor substrate 101 at a rate of 1 mm / h or more in the ⁇ C axis direction.
- the growth temperature of the AlN crystal layer is 1400 ° C. or higher.
- the nitride semiconductor crystal manufacturing apparatus 200 of the present embodiment a diameter of 4 inches or more, and warpage of the curvature radius of not less than 100 m, the impurity concentration can be grown 1 ⁇ 10 17 / cm 3 or less of the AlN crystal layer .
- the impurity concentration was reduced to 1 ⁇ 10 16 / cm 3 or lower, and further to 1 ⁇ 10 15 / cm 3 or lower. it can.
- FIG. 11 shows an outline of a conventional nitride semiconductor crystal manufacturing apparatus 250.
- a conventional nitride semiconductor crystal manufacturing apparatus 250 is different from the nitride semiconductor crystal manufacturing apparatus 200 in that it includes a common reaction chamber 260 in which the first reaction chamber 210 and the second reaction chamber 220 serve as a common reaction tube.
- the common reaction chamber 260 includes a first halogen gas supply port 262, a second halogen gas supply port 264, and a first exhaust port 266.
- the common reaction chamber 260 has a first zone Z1 in which the first step is performed and a second zone Z2 in which the second step is performed.
- the conventional nitride semiconductor crystal manufacturing apparatus 250 In the conventional nitride semiconductor crystal manufacturing apparatus 250, the first zone Z1 and the second zone Z2 are not structurally separated in the common reaction chamber 260. Therefore, the conventional nitride semiconductor crystal manufacturing apparatus 250 cannot sufficiently increase the flow rate of the chlorine gas Cl 2 at the first halogen gas supply port 262 and the pressure in the first zone Z1.
- FIG. 12 shows a manufacturing process of a conventional nitride semiconductor substrate.
- a GaN crystal layer is grown on an initial substrate such as GaAs or sapphire by heteroepitaxial growth using the HVPE method. Thereafter, the initial substrate is peeled off to manufacture a GaN free-standing substrate.
- the HVPE method has a slow growth rate and cannot stably grow in the ⁇ C-axis direction. Therefore, it is necessary to grow GaN substrates one by one, which costs several hundred thousand yen per substrate.
- an 18-inch bulk crystal technique has been established for a silicon semiconductor substrate, but a technique for cutting a wafer from a bulk crystal like a silicon wafer has not been established for a GaN substrate. Therefore, a GaN substrate of about 2 inches manufactured by a conventional nitride semiconductor substrate manufacturing process is currently limited to manufacturing blue-violet LDs and high-intensity LEDs, and is used for manufacturing power devices. It has not reached.
- FIG. 13 shows a manufacturing process of the GaN substrate according to the present invention.
- a high-quality GaN substrate is prepared as an initial substrate by Na flux, ammonothermal method, or the like.
- an ultra-thick GaN crystal layer is grown by homoepitaxial growth using the THVPE method of the present invention.
- a GaN wafer is cut out from the grown ultra-thick GaN bulk crystal.
- a step of cutting the upper surface of the nitride semiconductor crystal, and a step of growing a crystal further on the upper surface of the cut nitride semiconductor crystal And may be repeated.
- the dislocation density on the ⁇ C plane can be 1 ⁇ 10 5 cm ⁇ 2 or less, or 1 ⁇ 10 3 cm ⁇ 2 or less.
- the crystal layer without dislocation on the ⁇ C plane Can be manufactured.
- the diameter of the crystal layer is 4 inches or more, the curvature radius of warpage is 100 m or more, and the impurity concentration of the crystal layer is 1 ⁇ 10 17 / cm 3 or less.
- a physical semiconductor crystal is obtained.
- the nitride semiconductor crystal dislocation density -C surface is 1 ⁇ 10 5 cm -2 or less is obtained.
- GaN substrates currently on the market are about 2 inches at most, and those that are less than 1 inch are the mainstream for AlN substrates.
- a GaN bulk thick film crystal can be formed by high-speed crystal growth in the ⁇ C axis direction. That is, since the area can be increased by growth in the ⁇ C axis direction, a plurality of GaN free-standing substrates having large diameters of 4 inches and 6 inches can be cut out from the GaN bulk crystal.
- the nitride semiconductor crystal manufactured according to the present invention can be used as a template substrate integrated with an initial substrate such as sapphire.
- an initial substrate such as sapphire.
- the nitride semiconductor crystal of this example can be thickened, it may be sold in a state separated from the initial substrate.
- nitride semiconductor crystals can be grown at high speed.
- a nitride semiconductor crystal for a light emitting element, a power device, etc. with high quality and high efficiency can be manufactured at low cost.
- due to the realization of large diameter and low cost it is significant to be used for power devices that have never been used.
- FIG. 14 shows a method of determining the polarity of the GaN crystal layer by KOH etching. It is a scanning electron microscope (SEM) photograph at the time of growing a GaN crystal layer by HVPE method on a sapphire substrate (left figure) and a GaN template (right figure). The upper and lower photographs are SEM photographs before and after etching the crystal surface with a KOH solution, respectively.
- SEM scanning electron microscope
- the Ga polar face is resistant to KOH etching.
- the N-polar surface is easily etched by the KOH solution, and when etched, the surface is uneven. Therefore, if the surface after GaN crystal growth is KOH etched, the Ga polarity and N polarity can be easily determined.
- FIG. 15 shows a comparative example of band diagrams when LEDs are created on the + C plane and the ⁇ C plane, calculated by numerical simulation.
- FIG. 15 shows band diagrams when crystal layers are grown on the + C plane (upper figure) and the ⁇ C plane (lower figure).
- the vertical axis represents energy [eV]
- the horizontal axis represents distance [nm] from the crystal surface.
- n-GaN, InGaN, and p-GaN are grown sequentially from the initial substrate side.
- InGaN has a larger lattice constant and a smaller band gap than GaN.
- the InGaN layer formed on n-GaN is subjected to compressive stress, and piezoelectric polarization occurs in the crystal. Therefore, a strong piezoelectric polarization electric field is generated from the surface side of the InGaN layer toward the substrate side. Therefore, at both ends of InGaN, the energy level of n-GaN is relatively increased, and the energy level of p-GaN is decreased. Therefore, when growing in the + C axis direction, the barrier is lowered, and electrons flowing from the n-GaN side overflow and flow without contributing to light emission.
- InGaN formed on n-GaN is subjected to compressive stress, and piezoelectric polarization occurs in the crystal. Therefore, a strong piezoelectric polarization electric field is generated from the substrate side to the surface side of the InGaN layer. Therefore, at both ends of InGaN, the energy level of n-GaN is relatively lowered and the energy level of p-GaN is raised. Therefore, when grown in the ⁇ C-axis direction, the barriers at both ends of InGaN are increased.
- the LED using the ⁇ C plane emits light more efficiently than the GaN crystal layer using the + C plane.
- the InGaN crystal layer increases the wavelength of the LED by increasing the In composition.
- In x Ga 1-x N having a high In composition ratio X In is required.
- FIG. 16 shows a comparative example of the magnitude of In incorporation on the ⁇ C plane and the + C plane.
- the relationship between the flow rate f TMIn [ ⁇ mol / min] (horizontal axis) of trimethylindium (TMIn) and the In composition ratio X In (vertical axis) on the GaN surface is shown.
- the black circles and white circles in the graph show the experimental results when InGaN is grown on the N polar face and the Ga polar face, respectively.
- the In composition ratio X In did not differ between the N polar face and the Ga polar face.
- the In composition ratio X In becomes higher when In is taken into the N polar face than when In is taken into the Ga polar face. Therefore, a GaN crystal layer grown on the -C plane can realize a long wavelength LED.
- Example 1 a nitride semiconductor crystal manufacturing apparatus 200 is used to grow a GaN crystal layer with a GaCl 3 gas partial pressure of 1.0 ⁇ 10 ⁇ 2 atm, a growth temperature of 1200 ° C., and a growth time of 12 minutes. It was.
- As the metal gallium 212 in the first reaction chamber 210 7N grade (purity 99.99999%) metal gallium was used.
- the nitride semiconductor substrate 101 of this example is a -C-plane GaN (000-1) substrate.
- Nitrogen (N 2 ) carrier gas and high-purity Cl 2 gas are supplied to the first zone Z1.
- the supply pressure of the N 2 carrier gas and the Cl 2 gas is adjusted, and the partial pressure of the Cl 2 gas is 5 ⁇ 10 ⁇ 3 atm with respect to the total flow rate in the reaction tube 200 system.
- the total flow rate in the reaction tube 200 system refers to the total flow rate of the gas flowing through the crystal growth part G1.
- the reaction tube temperature in the first zone Z1 is adjusted to 800 ° C.
- the reaction tube temperature in the first zone Z1 is equal to the temperature at which the source gas reacts in the first zone Z1.
- the flow rate of the Cl 2 gas, the total flow rate of the gas flowing in the crystal growth section G1 can be calculated by the product of the partial pressure of Cl 2 gas.
- N 2 carrier gas and high-purity Cl 2 gas are supplied to the second zone Z2. Partial pressure of Cl 2 gas, to adjust the supply amount of N 2 carrier gas and a Cl 2 gas, the total flow reaction tube 200 system, a 1 ⁇ 10 -2 atm.
- the reaction tube temperature in the second zone Z2 is adjusted to 800 ° C.
- the reaction tube temperature in the second zone Z2 is equal to the temperature at which the source gas reacts in the second zone Z2.
- the growth chamber 230 is supplied with N 2 carrier gas and NH 3 gas. In the growth chamber 230, the exhaust speed and the supply amount of the N 2 carrier gas and NH 3 gas are adjusted. In the growth chamber 230, the partial pressure of NH 3 gas is 8 ⁇ 10 ⁇ 2 atm, and the partial pressure of GaCl 3 gas is 1.0 ⁇ 10 ⁇ 2 atm.
- the growth chamber 230 is a mixed gas atmosphere of N 2 carrier gas and NH 3 gas.
- the supply partial pressure of NH 3 gas is 8 ⁇ 10 ⁇ 2 atm with respect to the total flow rate of the gas flowing into the growth chamber 230.
- the GaCl 3 gas generated in the first reaction chamber 210 is supplied to the growth chamber 230, and the growth of the GaN crystal layer is started.
- the supply of GaCl 3 gas is stopped and the temperature is lowered to room temperature in a mixed gas atmosphere of N 2 carrier gas and NH 3 gas.
- the supply partial pressure of NH 3 gas at the time of cooling is 8 ⁇ 10 ⁇ 2 atm with respect to the total flow rate of the gas flowing into the growth chamber 230.
- FIG. 17 shows the relationship between the partial pressure of GaCl 3 gas and the growth rate of the GaN crystal layer.
- FIG. 17 shows the relationship between the growth temperature (Growth Temperature [° C.]) and the growth rate (Growth rate [ ⁇ m / h]) when crystal growth of GaN is performed.
- the nitride semiconductor crystal manufacturing apparatus 250 was used, the partial pressure of the GaCl 3 gas could not be made higher than 8.0 ⁇ 10 ⁇ 3 atm. However, the nitride semiconductor crystal manufacturing apparatus 200 can increase the partial pressure of the GaCl 3 gas to 9.0 ⁇ 10 ⁇ 3 atm or more.
- the partial pressure of GaCl 3 gas is 1 ⁇ 10 ⁇ 2 atm
- the growth temperature is 1200 ° C. or higher
- the partial pressure of GaCl 3 gas is about twice that when the partial pressure of GaCl 3 gas is 5 ⁇ 10 ⁇ 3 atm. Growth rate is obtained.
- Region A refers to a region where the growth rate decreases linearly as the growth temperature increases. In general, it is believed that increasing the growth rate reduces the quality of the crystal. However, if a region having a high growth rate is used in the region A, high quality and high-speed growth can be realized.
- FIG. 18 shows a cross-sectional photograph and a bird's-eye photograph of an SEM of the GaN crystal layer according to Example 1.
- the surface appearance of the GaN crystal layer of this example was mirror-like, and no pits and protrusions were observed. That is, by increasing the partial pressure of GaCl 3 gas to 1.0 ⁇ 10 ⁇ 2 atm, the GaN crystal layer is made uniform by increasing the growth temperature to 1200 ° C. even though the growth rate is increased. Growing to.
- the GaN crystal of this example has high surface flatness.
- the X-ray diffraction half width (Tilt) of the GaN (0002) plane was 570 arcsec. The smaller the X-ray diffraction half width value, the better the crystallinity of the GaN crystal layer.
- Example 2 In Example 2, the GaN crystal layer was grown at a growth temperature of 1300 ° C. Conditions other than the growth temperature are the same as in the first embodiment. The growth rate of Example 2 is slower than the growth rate of Example 1. However, the crystallinity of the GaN crystal layer of Example 2 is such that the FWHM of the GaN (0002) plane is 374 arcsec. That is, in Example 2, the crystallinity of the GaN crystal layer can be further improved by setting the growth temperature higher than in the case of Example 1.
- Example 3 the GaN crystal layer was grown by setting the partial pressure of GaCl 3 gas to 9.0 ⁇ 10 ⁇ 3 atm.
- the conditions other than the partial pressure of the GaCl 3 gas are basically the same as those in the first embodiment except for a part. Differences between the third embodiment and the first embodiment will be described below.
- Example 3 in the first step, the partial pressure of the Cl 2 gas supplied to the first zone Z1 is set to 4.5 ⁇ 10 ⁇ 3 atm with respect to the total flow rate in the reaction tube 200 system. In the second step, the partial pressure of the Cl 2 gas supplied to the second zone Z2 is set to 9 ⁇ 10 ⁇ 3 atm with respect to the total flow rate in the reaction tube 200 system. As shown in FIG. 17, in Example 3, high-speed growth of about 250 ⁇ m / h was successful. The crystallinity of Example 3 was comparable to that of Example 1.
- Example 4 In Example 4, a GaN crystal layer was grown on a sapphire (0001) substrate at a growth temperature of 1250 ° C. and a growth time of 15 minutes.
- the conditions other than the growth temperature and the initial substrate are basically the same as those in the first embodiment except for a part. Differences between the fourth embodiment and the first embodiment will be described below.
- the atmosphere in the growth chamber 230 was only N 2 carrier gas.
- the total flow rate of the N 2 carrier gas when raising the substrate temperature is 3500 sccm.
- NH 3 gas and the generated GaCl 3 gas are supplied to the growth chamber 230 to perform crystal growth of GaN.
- the supply of GaCl 3 gas is stopped, and the temperature is lowered to room temperature in a mixed gas atmosphere of N 2 carrier gas and NH 3 gas.
- the supply partial pressure of NH 3 gas at this time is adjusted to 8 ⁇ 10 ⁇ 2 atm with respect to the total flow rate of the gas flowing into the growth chamber 230.
- FIG. 19 shows an optical micrograph of the GaN crystal layer according to Example 4.
- FIG. 19 shows cross-sectional views of a GaN crystal layer and a sapphire substrate taken at 500 and 1000 times.
- a (10-11) facet plane having an angle of about 60 degrees with the growth surface was observed. That is, the crystal diameter of the GaN crystal layer increases with the GaN crystal layer.
- FIG. 20 shows the photoluminescence (PL) spectrum of the GaN crystal layer according to Example 4.
- the PL spectrum of this example was measured at room temperature using a He—Cd laser with a wavelength of 325 nm. Clear near-band edge emission is observed at a wavelength of 365 nm. On the other hand, no light emission due to defects or impurities is observed in the long wavelength band (400 to 800 nm). That is, the GaN crystal layer according to Example 4 contains very little impurities.
- Example 5 In Example 5, the GaN crystal layer was grown with a growth time of 30 minutes. Conditions other than the growth time are the same as in the third embodiment.
- FIG. 21 shows a cross-sectional SEM photograph of the GaN crystal layer according to Example 5.
- the thickness of the GaN crystal layer in this example is 128 ⁇ m. Even if the thickness of the GaN crystal layer is 100 ⁇ m or more, the uniformity of the GaN surface is maintained and the surface flatness is high. As described above, by using the GaN crystal layer growth method of this example, a thick GaN crystal layer can be grown.
- Comparative Example 1 In Comparative Example 1, the GaN crystal layer was grown at a growth temperature of 1050 ° C. Conditions other than the growth temperature are the same as in the first embodiment.
- FIG. 22 shows a bird's-eye SEM photograph of the GaN crystal layer according to Comparative Example 1.
- the GaN crystal layer of this example has poor migration of raw materials on the surface of the GaN crystal and has a rough surface form.
- the X-ray diffraction half width of the GaN (0002) plane was 3214 arcsec.
- Comparative Example 2 In Comparative Example 2, the GaN crystal layer was grown at a growth temperature of 1100 ° C. Conditions other than the growth temperature are the same as in the first embodiment.
- FIG. 23 shows an SEM bird's-eye view of the GaN crystal layer according to Comparative Example 2.
- the flatness of the GaN crystal layer of this example is improved as compared with the case of Comparative Example 1, the surface morphology is rough as compared with the case of Example 1.
- the X-ray diffraction half width of the GaN (0002) plane was 1854 arcsec.
- Comparative Example 3 In Comparative Example 3, a GaN crystal layer was grown using the nitride semiconductor crystal manufacturing apparatus 200 with a GaCl 3 gas partial pressure of 5 ⁇ 10 ⁇ 3 atm, a growth temperature of 1100 ° C., and a growth time of 20 minutes. As the metal gallium 212 in the first reaction chamber 210, 7N grade (purity 99.99999%) metal gallium was used.
- the nitride semiconductor substrate 101 of this example is a -C-plane GaN (000-1) substrate.
- the first zone Z1 is supplied with N 2 carrier gas and high purity Cl 2 gas.
- the partial pressure of the Cl 2 gas is 2.5 ⁇ 10 ⁇ 3 atm with respect to the total flow rate in the reaction tube 200 system.
- the reaction tube temperature in the first zone Z1 is adjusted to 800 ° C.
- N 2 carrier gas and high-purity Cl 2 gas are supplied to the second zone Z2. Partial pressure of Cl 2 gas, to adjust the supply amount of N 2 carrier gas and a Cl 2 gas, the total flow reaction tube 200 system, a 5 ⁇ 10 -3 atm.
- the reaction tube temperature in the second zone Z2 is adjusted to 800 ° C.
- the growth chamber 230 is supplied with N 2 carrier gas and NH 3 gas. In the growth chamber 230, the exhaust speed and the supply amount of the N 2 carrier gas and NH 3 gas are adjusted. In the growth chamber 230, the partial pressure of NH 3 gas is 8 ⁇ 10 ⁇ 2 atm, and the partial pressure of GaCl 3 gas is 5 ⁇ 10 ⁇ 3 atm.
- the inside of the growth chamber 230 during the temperature rise of the substrate temperature is a mixed gas atmosphere of N 2 carrier gas and NH 3 gas.
- the supply partial pressure of NH 3 gas is set to 1 ⁇ 10 ⁇ 1 atm with respect to the total flow rate of the gas flowing into the growth chamber 230.
- the GaCl 3 gas generated in the first reaction chamber 210 is supplied to the growth chamber 230, and the growth of the GaN crystal layer is started.
- the supply of GaCl 3 gas is stopped and the temperature is lowered to room temperature in a mixed gas atmosphere of N 2 carrier gas and NH 3 gas.
- the supply partial pressure of NH 3 gas when the temperature is lowered is 8 ⁇ 10 ⁇ 1 atm with respect to the total flow rate of the gas flowing into the growth chamber 230.
- FIG. 24 shows an SEM bird's-eye view of the GaN crystal layer according to Comparative Example 3.
- the surface of the GaN crystal layer of this example is rough and has poor flatness.
- the FWHM of the GaN (0002) plane was 852 arcsec.
- Comparative Example 3 has a lower surface flatness of the GaN crystal layer and a slower growth rate than Example 1.
- Comparative Example 4 In Comparative Example 4, the GaN crystal layer was grown at a growth temperature of 1200 ° C. Conditions other than the growth temperature are the same as in Comparative Example 3. The growth rate of Comparative Example 4 is about 100 ⁇ m / h, which is slower than the growth rate of Comparative Example 3.
- FIG. 25 shows an SEM bird's-eye view of the GaN crystal layer according to Comparative Example 4.
- the surface of the GaN crystal layer of this example is rough, the flatness is increased as compared with the case of Comparative Example 3 shown in FIG.
- Comparative Example 4 the surface flatness of the GaN crystal layer is poor and the growth rate is slow as compared with Examples 1 and 2.
- FIG. 26 is a diagram for explaining a method of setting conditions for growing a nitride semiconductor crystal.
- the horizontal axis represents the growth temperature [° C.]
- the vertical axis represents the growth rate [ ⁇ m / h].
- the solid line shows the relationship between the growth temperature and the growth rate when the type of gas supplied to the substrate and the partial pressure are changed.
- nitride semiconductor crystal having good crystallinity at a high speed it is necessary to optimally set the growth temperature and the growth rate.
- a sufficient growth rate has not been obtained, and a further increase in the growth rate is required.
- the growth rate decreases when the growth temperature of the substrate is increased. Therefore, in the conventional technical idea, it has been usual to grow a nitride semiconductor crystal in a low temperature region (zone Z1) having a higher growth rate than the high temperature region (zone Z2) where the growth rate starts to decrease.
- the growth rate of the crystal itself is not sufficient, and it has not been conceivable to use the zone Z2 in which the growth rate decreases.
- the growth rate of the nitride semiconductor crystal is simply increased, there is a problem that the crystallinity is deteriorated.
- the conventional THVPE method the growth rate decreases when the growth temperature is increased, while there is a trade-off problem that the growth cannot be stably performed in the ⁇ C-axis direction and the impurity concentration increases when the growth temperature is decreased. It was.
- the applicant succeeded in growing a nitride semiconductor crystal using the zone Z2, which has not been used so far, by controlling the partial pressure of the gallium trihalide gas. That is, a nitride semiconductor crystal having high crystallinity was grown at high speed by setting the partial pressure of the gallium trihalide gas to 9.0 ⁇ 10 ⁇ 3 atm or more and using the zone Z2.
- the growth temperature is higher than in the case of using the zone Z1, so that the source gas is activated and can be easily transported to a stable position on the crystal growth surface.
- the growth temperature is low, the raw material gas is crystallized before it is sufficiently transported on the crystal growth surface, resulting in poor crystallinity.
- the growth can be stably performed in the ⁇ C axis direction. Therefore, the growth surface is stabilized, so that the crystallinity of the nitride semiconductor crystal is improved.
- the THVPE method of this example succeeded in solving the trade-off problem that the conventional THVPE method had.
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Abstract
Description
特許文献1 国際公開第2011/142402号パンフレット
第1工程では、金属ガリウム212とハロゲンガスとを反応させて一ハロゲン化ガリウムガスを生成する。例えばハロゲンガスとは、Cl2ガス、臭素(Br2)ガス、ヨウ素(I2)ガスである。
Ga(l) + 1/2Cl2(g) → GaCl(g) ・・・(1)
ここで(l)および(g)はそれぞれ物質が液体およびガス状態であることを示す。
第2工程では、生成した一ハロゲン化ガリウムガスとハロゲンガスとを反応させて三ハロゲン化ガリウムガスを生成する。具体的には、第2工程では、第1工程で生成した一塩化ガリウムとCl2ガスとを反応させる。第2工程において三塩化ガリウムガスを生成する反応は、反応式(2)で表わされる。
GaCl(g) + Cl2(g) →GaCl3(g) ・・・(2)
成長工程では、成長室230の結晶成長部G1において、第2工程で生成されたGaCl3ガスとNH3ガスを反応させて、GaN結晶層を成長する。
実施例1では、窒化物半導体結晶製造装置200を用いて、GaCl3ガスの分圧を1.0×10-2atm、成長温度を1200℃、成長時間を12分間としてGaN結晶層を成長させた。第1反応室210における金属ガリウム212は、7Nグレード(純度99.99999%)の金属ガリウムを用いた。本例の窒化物半導体基板101は、-C面GaN(000-1)基板を用いた。
実施例2では、成長温度を1300℃としてGaN結晶層を成長させた。成長温度以外の条件は、実施例1の場合と同一である。実施例2の成長速度は、実施例1の成長速度よりも遅い。しかしながら、実施例2のGaN結晶層の結晶性は、GaN(0002)面のX線回折半値幅が374arcsecである。即ち、実施例2では、実施例1の場合よりも、成長温度を高温にすることにより、GaN結晶層の結晶性をさらに向上することができる。
実施例3では、GaCl3ガスの分圧を9.0×10-3atmとしてGaN結晶層を成長させた。GaCl3ガスの分圧以外の条件は、一部を除き、基本的に実施例1の場合と同一である。実施例3と実施例1との相違点について、以下に説明する。
実施例4では、成長温度を1250℃、成長時間を15分として、サファイア(0001)基板上にGaN結晶層を成長させた。成長温度および初期基板以外の条件は、一部を除き、基本的に実施例1の場合と同様である。実施例4と実施例1との相違点について、以下に説明する。
実施例5では、成長時間を30分としてGaN結晶層を成長した。成長時間以外の条件は、実施例3の場合と同様である。
比較例1では、成長温度を1050℃としてGaN結晶層を成長させた。成長温度以外の条件は、実施例1の場合と同一である。
比較例2では、成長温度を1100℃としてGaN結晶層を成長させた。成長温度以外の条件は、実施例1の場合と同一である。
比較例3では、窒化物半導体結晶製造装置200を用い、GaCl3ガスの分圧を5×10-3atm、成長温度を1100℃、成長時間を20分間としてGaN結晶層を成長させた。第1反応室210における金属ガリウム212は、7Nグレード(純度99.99999%)の金属ガリウムを用いた。本例の窒化物半導体基板101は、-C面GaN(000-1)基板を用いた。
比較例4では、成長温度を1200℃としてGaN結晶層を成長させた。成長温度以外の条件は、比較例3の場合と同一である。比較例4の成長速度は、100μm/h程度であり、比較例3の成長速度よりも遅い。
Claims (24)
- 基板を用意する工程と、
分圧が9.0×10-3atm以上である三ハロゲン化ガリウムガスを前記基板上に供給する工程と、
前記基板上に、GaN結晶を-C軸方向に成長させる工程と
を備え、
前記GaN結晶の成長温度が1200℃以上である窒化物半導体結晶の製造方法。 - 金属ガリウムとハロゲンガスとを反応させて一ハロゲン化ガリウムガスを生成する第1工程と、
生成した前記一ハロゲン化ガリウムガスとハロゲンガスとを反応させて前記三ハロゲン化ガリウムガスを生成する第2工程と
をさらに備える請求項1に記載の窒化物半導体結晶の製造方法。 - 基板を用意する工程と、
分圧が9.0×10-3atm以上である三ハロゲン化アルミニウムガスを前記基板上に供給する工程と、
前記基板上に、AlN結晶を-C軸方向に成長させる工程と
を備え、
前記AlN結晶の成長温度が1400℃以上である窒化物半導体結晶の製造方法。 - 金属アルミニウムとハロゲンガスとを反応させて前記三ハロゲン化アルミニウムガスを生成する第1工程と
をさらに備える請求項3に記載の窒化物半導体結晶の製造方法。 - 前記第1工程が行われる第1反応室と前記第2工程が行われる第2反応室の間の抑制構造において、前記第1工程で生成された前記一ハロゲン化ガリウムガスの濃度が低下することを抑制する請求項2に記載の窒化物半導体結晶の製造方法。
- 前記抑制構造は、前記第1反応室および前記第2反応室の間の経路であり、
前記経路の断面積は、前記第1反応室および前記第2反応室の断面積よりも小さい請求項5に記載の窒化物半導体結晶の製造方法。 - 前記第2反応室は、前記三ハロゲン化ガリウムガスの流速を減速させる複数の仕切り板を備える請求項5または6に記載の窒化物半導体結晶の製造方法。
- 前記基板は、前記窒化物半導体結晶と異なる材料である請求項1から7のいずれか一項に記載の窒化物半導体結晶の製造方法。
- 前記第1工程が行われる第1反応室に供給される前記ハロゲンガスの分圧は、9.0×10-3atm以上である請求項2または4に記載の窒化物半導体結晶の製造方法。
- 前記GaN結晶、もしくは、前記AlN結晶を-C軸方向に成長させる工程の後に、前記窒化物半導体結晶の上面を切り出す工程と、切り出された前記窒化物半導体結晶の上面にさらに結晶を成長させる工程と、を繰り返す工程
をさらに備える請求項1から9のいずれか一項に記載の窒化物半導体結晶の製造方法。 - 前記三ハロゲン化ガリウムガス、または、前記三ハロゲン化アルミニウムガスは、それぞれ三塩化ガリウムガス、または、三塩化アルミニウムガスである請求項1から10のいずれか一項に記載の窒化物半導体結晶の製造方法。
- 前記GaN結晶、もしくは、前記AlN結晶を-C軸方向に成長させる工程は、THVPE法(トリハライド気相成長法)で成長させる請求項1から11のいずれか一項に記載の窒化物半導体結晶の製造方法。
- 分圧が9.0×10-3atm以上である三ハロゲン化ガリウムガスを生成して、基板上に供給するガス供給部と、
前記基板が設置され、前記基板上に、GaN結晶を-C軸方向に成長させる成長室と、
前記GaN結晶の成長温度を1200℃以上に制御する温度制御部と
を備える窒化物半導体結晶の製造装置。 - 前記ガス供給部は、
金属ガリウムとハロゲンガスとを反応させて一ハロゲン化ガリウムガスを生成する第1反応室と、
生成した前記一ハロゲン化ガリウムガスとハロゲンガスとを反応させて前記三ハロゲン化ガリウムガスを生成する第2反応室と
を備える請求項13に記載の窒化物半導体結晶の製造装置。 - 分圧が9.0×10-3atm以上である三ハロゲン化アルミニウムガスを生成して、基板上に供給するガス供給部と、
前記基板が設置され、前記基板上に、AlN結晶を-C軸方向に成長させる成長室と、
前記AlN結晶の成長温度を1400℃以上に制御する温度制御部と
を備える窒化物半導体結晶の製造装置。 - 前記ガス供給部は、
金属アルミニウムとハロゲンガスとを反応させて前記三ハロゲン化アルミニウムガスを生成する第1反応室と
を備える請求項15に記載の窒化物半導体結晶の製造装置。 - 前記第1反応室において生成された前記一ハロゲン化ガリウムガスの濃度が低下することを抑制する抑制構造を、前記第1反応室と前記第2反応室との間に備える請求項14に記載の窒化物半導体結晶の製造装置。
- 前記抑制構造は、前記第1反応室および前記第2反応室の間の経路であり、
前記経路の断面積は、前記第1反応室および前記第2反応室の断面積よりも小さい請求項17に記載の窒化物半導体結晶の製造装置。 - 前記第2反応室は、前記三ハロゲン化ガリウムガスの流速を減速させる複数の仕切り板を備える請求項14に記載の窒化物半導体結晶の製造装置。
- 前記第1反応室に供給される前記ハロゲンガスの分圧は、9.0×10-3atm以上である請求項14または16に記載の窒化物半導体結晶の製造装置。
- 結晶の直径が4インチ以上、かつ、反りの曲率半径が100m以上であり、
前記結晶の不純物濃度が1×1017/cm3以下であり、
前記結晶は、GaN結晶、もしくは、AlN結晶である窒化物半導体結晶。 - -C面の結晶面積が、+C面の結晶面積よりも大きい請求項21に記載の窒化物半導体結晶。
- 100μm以上の厚みを有する請求項21または22に記載の窒化物半導体結晶。
- -C面の転位密度が1×105cm-2以下である請求項21から23のいずれか一項に記載の窒化物半導体結晶。
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Also Published As
Publication number | Publication date |
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EP3059336A4 (en) | 2017-07-12 |
JP6510413B2 (ja) | 2019-05-08 |
JPWO2015037232A1 (ja) | 2017-03-02 |
EP3059336A1 (en) | 2016-08-24 |
US20160186361A1 (en) | 2016-06-30 |
US10125433B2 (en) | 2018-11-13 |
JP2019073439A (ja) | 2019-05-16 |
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