JP2007217227A - GaN crystal manufacturing method, GaN crystal substrate, and semiconductor device - Google Patents

Abstract

A method for producing a GaN crystal with low dislocation density and good crystallinity, a GaN crystal substrate, and a semiconductor device including the GaN crystal substrate.
A method of manufacturing a GaN crystal is a method of growing a GaN crystal 4 by HVPE using an AlN seed crystal substrate 3 formed of at least a part of an AlN seed crystal grown by a sublimation method. The manufacturing method is characterized in that the curvature radius of curvature of the AlN seed crystal substrate is 5 m or more.
[Selection] Figure 1

Description

  The present invention relates to a method for producing a GaN crystal used for a substrate of a semiconductor device such as a light emitting device, an electronic device, or a semiconductor sensor. More specifically, the present invention relates to a method for manufacturing a GaN crystal having a low dislocation density and good crystallinity, a GaN crystal substrate formed from at least a part of the GaN crystal obtained by the manufacturing method, and a semiconductor device including the GaN crystal substrate.

  Since GaN crystals have a large energy band gap of 3.4 eV and high thermal conductivity, they are attracting attention as materials for semiconductor devices such as short-wavelength light-emitting devices and power electronic devices.

  As a method for growing such a GaN crystal, conventionally, an HVPE (Hydride Vapor Phase Epitaxy) method has been suitably used. In the HVPE method, the substrate for growing the GaN crystal is preferably a GaN crystal substrate formed of GaN, which is the same kind of material as the crystal to be grown, from the viewpoint of the lattice constant consistency of the crystal. A large GaN crystal substrate having a large size is difficult to produce. For this reason, also in the HVPE method, as a substrate for growing a GaN crystal, a heterogeneous substrate such as a large sapphire substrate or a GaAs substrate having a large diameter (hereinafter referred to as a substrate formed of a dissimilar material different from GaN) is used. It is done.

  However, when a GaN substrate is grown on a heterogeneous substrate such as a sapphire substrate or a GaAs substrate by the HVPE method, it is necessary to form a buffer layer by various methods in order to reduce the difference in crystal system and the difference in lattice constant. There is a problem that dislocations frequently occur at the buffer layer and the growth interface.

In order to avoid this problem, a pattern is formed with a mask such as a SiO ₂ film having an opening on the substrate, and the GaN crystal is epitaxially elongated in the lateral direction on the mask to reduce the influence from the growth interface (ELO). There is an Epitaxial Lateral Overgrowth (Epitaxial Lateral Overgrowth) method. However, even in this ELO method, dislocation occurs when the laterally grown portions are joined together.

  Furthermore, there is a method of growing using a GaN crystal substrate itself obtained by processing a GaN crystal grown by this HVPE method as a base substrate, but at present, a high-quality GaN seed crystal substrate as a base substrate is obtained. However, since the fluctuation of the crystal orientation of the GaN seed crystal substrate itself is large, it causes dislocations in the grown GaN crystal.

  The dislocation of the GaN crystal to be grown has a quality that greatly affects the performance of the semiconductor device including the GaN crystal substrate formed from the GaN crystal, and the dislocation is preferably as small as possible. However, in the current situation as described above, it is difficult to obtain a low dislocation density GaN crystal substrate by growing a low dislocation density GaN crystal.

As an attempt to fabricate a GaN crystal substrate with a low dislocation density, an HVPE method is used to form a GaN crystal film on a sapphire substrate using a MOVPE (Metal Organic Vapor Phase Epitaxy) method. A method of growing a GaN crystal to produce a GaN crystal substrate has been proposed (see, for example, Non-Patent Document 1). However, the dislocation density of the GaN crystal substrate obtained by the method of Non-Patent Document 1 is as high as 2 × 10 ⁷ cm ⁻² .

For this reason, a GaN crystal having a low dislocation density and good crystallinity and a GaN crystal substrate, and a semiconductor device including the GaN crystal substrate are desired.
Daniela Gogova and 11 others, “High-Quality 2” Bulk-Like free-standing GaN Grown by Hydride Vapor Phase Epitaxy on a Si-doped Metal Organic Vapor Phase Epitaxial GaN Template with an Ultra Low Dislocation Density ”, Jpn. J. Appl. Phys., Vol. 44 (2005) p.1181-1185

  The present invention provides a method for producing a GaN crystal having a low dislocation density and good crystallinity, a GaN crystal substrate formed from at least a part of the GaN crystal obtained by the production method, and a semiconductor device including the GaN crystal substrate. The purpose is to do.

  The present invention relates to a GaN crystal manufacturing method for growing a GaN crystal by an HVPE method using an AlN seed crystal substrate formed of at least a part of the AlN seed crystal grown by a sublimation method. A method for producing a GaN crystal, wherein a curvature radius of warpage of the substrate is 5 m or more.

In the GaN crystal manufacturing method according to the present invention, the half-value width of the diffraction intensity peak in the rocking curve of the X-ray diffraction with respect to the (0004) plane of the AlN seed crystal substrate can be 50 arcsec or less. Further, the dislocation density of the AlN seed crystal substrate can be set to 1 × 10 ⁶ cm ⁻² or less. Further, the area of the main surface of the AlN seed crystal substrate can be 10 cm ² or more.

In the method for producing a GaN crystal according to the present invention, the total impurity concentration of the GaN crystal can be 1 × 10 ¹⁸ cm ⁻³ or less. In addition, the GaN crystal can be doped with n-type impurities. Furthermore, the n-type impurity can be at least one of silicon and oxygen.

  In the method for producing a GaN crystal according to the present invention, a mask having an opening can be formed on the AlN seed crystal substrate, and the GaN crystal can be epitaxially grown in the lateral direction on the mask.

  The present invention also provides a GaN crystal substrate formed of at least a part of the GaN crystal obtained by the above manufacturing method. Furthermore, the present invention is a semiconductor device including the GaN crystal substrate.

  According to the present invention, a method of manufacturing a GaN crystal having a low dislocation density and good crystallinity, a GaN crystal substrate formed from at least a part of the GaN crystal obtained by the manufacturing method, and a semiconductor device including the GaN crystal substrate Can provide.

(Embodiment 1)
An embodiment of a method for producing a GaN crystal according to the present invention is described with reference to FIGS. 1 and 2 in which an AlN seed crystal substrate 3 formed of at least a part of an AlN seed crystal 2 grown by a sublimation method is used. And a method of manufacturing a GaN crystal, in which the GaN crystal 4 is grown by the HVPE method, wherein the curvature radius of warping of the AlN seed crystal substrate 3 is 5 m or more.

  Since AlN and GaN are the same hexagonal system and have very close lattice constants, a buffer layer is formed on a seed crystal substrate by using an AlN seed crystal substrate as a seed crystal substrate for growing a GaN crystal. It is possible to directly epitaxially grow GaN crystals. Further, since an AlN seed crystal substrate formed of an AlN seed crystal grown by a sublimation method has a low dislocation density and good crystallinity, a GaN crystal grown on this AlN seed crystal substrate also has a low dislocation density. Sexuality improves. Furthermore, since this AlN seed crystal substrate has a very small curvature radius of curvature of 5 m or more, the plane orientation of each crystal lattice plane of the plurality of GaN crystal grains generated during the growth of the GaN crystal is uniform, The dislocations generated when these GaN crystal grains are joined to each other are reduced, and the dislocation density of the GaN crystal is further reduced. In addition, in this application, the curvature radius of the curvature of an AlN seed crystal substrate means the curvature radius of the curvature of the main surface of a substrate, and is computed by measuring the curvature radius in the main surface of a substrate.

  In the GaN crystal manufacturing method of the present embodiment, the half width of the diffraction intensity peak in the rocking curve of the X-ray diffraction for the (0004) plane of the AlN seed crystal substrate 3 shown in FIG. 1 is preferably 50 arcsec or less. AlN seed crystal substrate 3 having good crystallinity with small plane orientation deviation of each crystal lattice plane constituting the AlN seed crystal substrate in which the half width of the diffraction intensity peak in the rocking curve of X-ray diffraction with respect to the (0004) plane is 50 arcsec or less By using this, it is possible to epitaxially grow a GaN crystal with good crystallinity.

In the GaN crystal manufacturing method of this embodiment, the dislocation density of the AlN seed crystal substrate 3 shown in FIG. 1 is preferably 1 × 10 ⁶ cm ⁻² or less. By using the AlN seed crystal substrate 3 with good crystallinity having a dislocation density of 1 × 10 ⁶ cm ⁻² or less, a GaN crystal with good crystallinity can be epitaxially grown. Here, the dislocation density is calculated by measuring the number of etching pits per unit area formed corresponding to the dislocation when the surface of the crystal or the crystal substrate is etched using an acidic or basic etching solution. it can. As an etching solution, for example, a KOH-NaOH mixed melt at 350 ° C. can be used.

In the GaN crystal manufacturing method of the present embodiment, the total impurity concentration of the GaN crystal 4 shown in FIG. 1 is preferably 1 × 10 ¹⁸ cm ⁻³ or less. According to the HVPE method, since the impurities are not mixed into the crystal at the time of crystal growth, the GaN crystal 4 having a high purity such as a total impurity concentration of 1 × 10 ¹⁸ cm ⁻³ or less and a low dislocation density and good crystallinity is grown. be able to. Here, the impurity concentration can be analyzed by a SIMS (secondary ion mass spectrometry) method or the like.

  Further, in the GaN crystal manufacturing method of the present embodiment, the GaN crystal 4 shown in FIG. 1 can be doped with n-type impurities. By doping the GaN crystal 4 with an n-type impurity, conductivity can be imparted to the GaN crystal, which is advantageous in application to a semiconductor device. Here, the n-type impurity is not particularly limited, but is preferably at least one of silicon and oxygen from the viewpoint of easy doping to the GaN crystal in the HVPE method.

In the GaN crystal manufacturing method of the present embodiment, the area of the main surface of the AlN seed crystal substrate 3 shown in FIG. 1 is preferably 10 cm ² or more. By using a large AlN seed crystal substrate having a principal surface area of 10 cm ² or more, a large GaN crystal can be grown.

In the GaN crystal manufacturing method of the present embodiment, as shown in FIG. 3, a mask 30 having an opening 30w is formed on the AlN seed crystal substrate 3, and the GaN crystal 4 is epitaxially grown in the lateral direction on the mask 30. It is preferable to make it. By growing the GaN crystal 4 by the ELO method, the GaN crystal 4 can be epitaxially grown without taking over the dislocation 3d of the AlN seed crystal substrate 3, and the dislocation density of the GaN crystal 4 can be further reduced. Here, the mask 30 is not particularly limited as long as the GaN crystal grows in the lateral direction on the mask 30, but SiO ₂ , Si ₃ N ₄ or the like is preferably used. The opening 30w of the mask 30 is not particularly limited as long as it does not take over the dislocations 3d of the AlN seed crystal substrate 3, but from the viewpoint of ease of mask formation and growth stability, It is better to have a certain size, and it is preferable that one side or diameter of the opening is 5 μm or more. The mask having the opening 30w is formed by stacking mask materials by a CVD method, a sputtering method, or the like, and patterning the mask by a lithography method or the like.

  The manufacturing method of the GaN crystal of this embodiment will be described in detail below. The seed crystal substrate used in the GaN crystal manufacturing method of the present embodiment is an AlN seed crystal substrate formed of at least a part of the AlN seed crystal 2 grown by the sublimation method with reference to FIGS. 3.

The sublimation method in the present embodiment refers to a method of obtaining an AlN crystal (AlN seed crystal 2 in the present embodiment) by sublimating an AlN raw material 1 such as an AlN powder and then solidifying it again with reference to FIG. . In crystal growth by the sublimation method, for example, a high-frequency heating type vertical sublimation furnace 20 as shown in FIG. 2 is used. A crucible 22 having a gas exhaust port 22e is provided at the center of the reaction vessel 21 in the vertical sublimation furnace 20, and a heating body is provided around the crucible 22 to ensure ventilation from the inside of the crucible 22 to the outside. 23 is provided. In addition, a high-frequency heating coil 24 for heating the heating body 23 is provided in the outer central portion of the reaction vessel 21. Further, at the end of the reaction vessel 21, there are a gas introduction port 21 a and a gas exhaust port 21 e for flowing N ₂ gas (nitrogen gas) to the outside of the crucible 22 of the reaction vessel 21, and temperatures of the lower surface and the upper surface of the crucible 22. A radiation thermometer 25 is provided for measuring. Here, the material of the crucible 22 is not particularly limited, but is preferably made of W (tungsten) from the viewpoint of less contamination of impurities into the AlN crystal to be grown (AlN seed crystal 2).

Referring to FIG. 2, AlN seed crystal 2 used in the present invention can be manufactured as follows using vertical vertical sublimation furnace 20 described above. The AlN raw material 1 such as AlN powder is stored in the lower part of the crucible 22, and the temperature in the crucible 22 is increased by heating the heating body 23 using the high-frequency heating coil 24 while flowing N ₂ gas into the reaction vessel 21. By maintaining the temperature on the AlN raw material 1 side of the crucible 22 higher than the temperature of the other portions, the AlN is sublimated from the AlN raw material 1, and the AlN is solidified again on the upper part of the crucible 22. An AlN seed crystal 2 used in the invention is grown.

Here, during the growth of the AlN seed crystal 2, the temperature on the AlN raw material 1 side of the crucible 22 is set to about 2000 ° C. to 2200 ° C., and the temperature of the upper portion of the crucible 22 (the portion where the AlN crystal is grown) is By lowering the temperature by about 1 ° C. to 10 ° C., the AlN seed crystal 2 having good crystallinity can be obtained. In addition, impurities are mixed into the AlN seed crystal 2 by continuously flowing N ₂ gas outside the crucible 22 in the reaction vessel 21 so that the gas partial pressure is about 101.3 hPa to 1013 hPa during crystal growth. Can be reduced.

  During the temperature increase inside the crucible 22, impurities inside the crucible 22 can be removed through the gas exhaust port 21e by raising the temperature of the other portion than the temperature of the crucible 22 on the AlN raw material 1 side. Further, contamination of impurities into the AlN seed crystal 2 can be further reduced.

By the above sublimation method, the AlN seed crystal 2 having good crystallinity having a half width of the diffraction intensity peak in the X-ray rocking curve of the (0004) plane of 50 arcsec or less and a dislocation density of 1 × 10 ⁶ cm ⁻² or less is obtained. can get. By optimizing the conditions of the sublimation method, the half width of the diffraction intensity peak of the AlN seed crystal is about 20 arcsec to 40 arcsec, and the dislocation density is about 1 × 10 ³ cm ⁻² to 1 × 10 ⁵ cm ^−2. It is possible to reduce.

The AlN seed crystal substrate 3 is obtained by cutting out at least a part of the AlN seed crystal 2 thus obtained and polishing the surface thereof. Here, by setting the thickness of the AlN seed crystal substrate 3 to 5 mm or more, the curvature radius of the warp is 5 m or more and the warp is very small, the half width of the diffraction intensity peak is 50 arcsec or less, and the dislocation density is 1 × 10 6. ^An AlN seed crystal substrate 3 having a crystallinity of ⁶ cm ⁻² or less is obtained.

  Next, referring to FIG. 1, GaN crystal 4 is grown by HVPE using AlN seed crystal substrate 3 having a curvature radius of curvature of 5 m or more obtained as described above. Here, the HVPE method in the present embodiment refers to a method of growing a GaN crystal 4 by reacting a gallium chloride gas as a gallium source gas 7 and a nitrogen source gas 8 with reference to FIG.

  In the growth of a GaN crystal by the HVPE method, for example, an HVPE apparatus 10 as shown in FIG. 1 is used. The HVPE apparatus 10 includes a gallium source gas generation chamber 11b for housing a pedestal 13 for placing the AlN seed crystal substrate 3, a gallium boat 12 for containing gallium 6 inside or outside the reaction vessel 11, a gallium source. A halogen-containing gas introduction tube 11a for introducing the halogen-containing gas 5 into the gas generation chamber 11b, and a gallium source gas introduction tube for introducing the gallium source gas 7 generated in the gallium source gas generation chamber 11b into the reaction vessel 11. 11c, a nitrogen source gas introduction pipe 11d for introducing the nitrogen source gas 8 into the reaction vessel 11, a gas exhaust port 11e for exhausting the reacted gas from the reaction vessel 11, and the reaction vessel 11 are heated. A heater 14 is provided.

  With reference to FIG. 1, using the HVPE apparatus 10, for example, a GaN crystal can be produced as follows. First, the AlN seed crystal substrate 3 is placed on the pedestal 13 installed in the reaction vessel 11, and the gallium boat 12 containing gallium 6 is placed in the gallium source gas generation chamber 11b.

Next, while introducing a carrier gas (not shown) into the reaction vessel 11 through the halogen-containing gas introduction tube 11a, the gallium source gas introduction tube 11c, and the nitrogen source gas introduction tube 11d, the inside of the reaction vessel 11 is heated by the heater 14. By heating, the temperature is 800 ° C. or higher and 1100 ° C. or lower, preferably higher than 950 ° C. and lower than 1100 ° C. Here, the carrier gas is not particularly limited as long as it is an inert gas that does not react with gallium and does not interfere with the growth of the GaN crystal. H ₂ gas (hydrogen gas), Ar gas (argon gas), N ₂ Gas etc. are preferably used.

Next, HCl gas (hydrogen chloride gas) as the halogen-containing gas 5 is introduced into the gallium source gas generation chamber 11b through the halogen-containing gas introduction tube 11a together with the carrier gas. In the gallium source gas generation chamber 11b, the gallium 6 in the gallium boat 12 reacts with the HCl gas (halogen-containing gas 5) to generate GaCl gas (gallium chloride gas) as the gallium source gas 7. The GaCl gas (gallium source gas 7) is introduced into the reaction vessel 11 through the gallium source gas introduction pipe 11c. On the other hand, NH ₃ gas (ammonia gas) as nitrogen source gas 8 is introduced into the reaction vessel 11 through the nitrogen source gas introduction pipe 11d together with the carrier gas.

At this time, GaCl gas (gallium source gas 7) and NH ₃ gas (nitrogen source gas 8) react with each other in the reaction vessel 11 to grow a GaN crystal on the AlN seed crystal substrate 3.

Here, the partial pressure of the gallium source gas 7 (approximately the same as the partial pressure of the halogen-containing gas 5) is about 50 Pa to 1 × 10 ⁴ Pa, and the partial pressure of the nitrogen source gas 8 is 5 × 10 ³ Pa to 5 × 10 ^4. Growth of GaN crystal at about Pa, gas ratio (molar ratio) of gallium source gas 7 and nitrogen source gas 8 is about 1:10 to 1: 1000, and the temperature of the AlN seed crystal substrate is about 900 ° C. to 1100 ° C. By adjusting the speed to about 10 μm / hr to 30 μm / hr, a thick group III nitride crystal with good crystallinity can be obtained.

  Here, the carrier gas introduced into the reaction vessel 11 together with the gallium source gas 7 and the nitrogen source gas 8 stabilizes the introduction amount of the gallium source gas or the nitrogen source gas, and the group III element source gas, the nitrogen source gas, It has a function of regulating the reactivity of.

(Embodiment 2)
The GaN crystal substrate according to the present invention is a GaN crystal substrate formed of at least a part of the GaN crystal obtained by the manufacturing method of the first embodiment. Since the GaN crystal substrate of this embodiment has a low dislocation density and good crystallinity, it becomes possible to manufacture a semiconductor device with good characteristics. The GaN crystal substrate of this embodiment is obtained by cutting out at least a part of the GaN crystal obtained by the manufacturing method of Embodiment 1 and treating the surface thereof. The surface treatment method of the crystal is not particularly limited, but a method of polishing the crystal surface to a mirror surface and removing the work-affected layer generated by this polishing by etching is preferably performed.

(Embodiment 3)
A semiconductor device according to the present invention is a semiconductor device including the GaN crystal substrate of the second embodiment. The semiconductor device is not particularly limited as long as it includes the GaN crystal substrate of the second embodiment, and is an optical device (light emitting diode, laser diode, etc.), electronic device (rectifier, bipolar transistor, field effect transistor, HEMT (High Electron Mobility). Transistor; high electron mobility transistor)), semiconductor device such as semiconductor sensor (temperature sensor, pressure sensor, radiation sensor, visible-ultraviolet light detector, etc.) or SAW device (Surface Acoustic Wave Device), A vibrator, a resonator, an oscillator, a micro-electro-mechanical system (MEMS) component, a piezoelectric actuator, or the like can be manufactured. These semiconductor devices can be manufactured by stacking a semiconductor layer, a metal layer, or the like on the surface of the GaN crystal substrate of the second embodiment. Examples of the method for laminating the semiconductor layers include MOVPE method, MBE (Molecular Beam Epitaxy) method and the like. Devices as described above can be manufactured. Examples of the metal layer stacking method include a vacuum deposition method and a sputtering method.

Example 1
(1-1. Growth of AlN seed crystal substrate by sublimation method)
First, referring to FIG. 2, an AlN seed crystal substrate 2 was grown by the sublimation method as follows. AlN powder was stored as the AlN raw material 1 in the lower part of a crucible 22 made of W (tungsten) having an inner diameter of 5.5 cm.

  Next, the temperature in the crucible 22 was raised using the high-frequency heating coil 24 while flowing nitrogen gas into the reaction vessel 21. During the temperature increase in the crucible 22, the temperature of the upper part of the crucible 22 (the side on which the AlN seed crystal 3 is grown) is set higher than the temperature of the lower part of the crucible 22 (the AlN raw material 1 side), Impurities released from inside 22 were removed through gas exhaust port 22e.

  Next, the temperature of the upper part of the crucible 22 is 2100 ° C., the temperature of the lower part is 2150 ° C., AlN is sublimated from the AlN raw material 1, and AlN is solidified again on the upper part of the crucible 22 to grow the AlN seed crystal 2. I let you. During the growth of the AlN seed crystal, nitrogen gas is continuously supplied to the outside of the crucible 22 in the reaction vessel 21 so that the gas partial pressure outside the crucible 22 in the reaction vessel 11 is about 101.3 hPa to 1013 hPa. The introduction amount and the nitrogen gas exhaust amount were controlled. The AlN seed crystal 2 was grown for 50 hours under the above crystal growth conditions, and then cooled to room temperature (25 ° C.) to obtain the AlN seed crystal 2.

The obtained AlN seed crystal 2 was polycrystallized at the outer periphery of the crystal, but within the range of 50.8 mm in diameter from the center of the crystal, diffraction in the rocking curve of the X-ray diffraction for the (0004) plane The half peak width of the intensity peak was 50 arcsec, and the dislocation density was a single crystal with a low dislocation density of 1.0 × 10 ⁻⁶ cm ⁻² and good crystallinity. Here, the dislocation density of the crystal or the crystal substrate is obtained by measuring the number of etching pits per unit area formed corresponding to the dislocation when the surface is etched with a KOH-NaOH mixed melt at 350 ° C. Calculated.

(1-2. Preparation of AlN seed crystal substrate)
The above-mentioned AlN seed crystal 2 is sliced along a plane parallel to the crystal growth surface (C plane) of the AlN seed crystal 2, and the polycrystallized outer peripheral portion is removed, and the surface thereof is polished to a mirror surface to obtain a diameter of 50. An AlN seed crystal substrate 3 of 8 mm × thickness 400 μm was obtained. The curvature radius of the curvature of the main surface of the AlN seed crystal substrate 3 was measured by a stylus surface shape measuring instrument, and found to be 5 m. Further, the square of deviation from the root mean square (MSM) observed by an AFM (Atomic Force Microscope) within the range of 10 μm × 10 μm square of the AlN seed crystal substrate 3 was averaged. The square root of the value) surface roughness was 50 nm (500 Å) or less.

As described above, the curvature radius of the warp is 5 m, the main surface is the C plane, the half width of the diffraction intensity peak in the rocking curve of the X-ray diffraction with respect to the (0004) plane is 50 arcsec, and the dislocation density is 1. An AlN seed crystal substrate 3 of 0 × 10 ⁶ cm ⁻² with small warpage, low dislocation density and good crystallinity was obtained.

  In addition, the AlN seed crystal substrate 3 in the above-described embodiment is prepared by slicing a plane parallel to the C plane of the grown AlN seed crystal 2, but the slice plane of the AlN seed crystal is parallel to the C plane. The plane is not limited to a plane, but can be a plane parallel to the A plane, the R plane, the M plane, or the S plane, or a plane having an arbitrary inclination with respect to these planes.

(1-3. Growth of GaN crystal by HVPE method)
Next, referring to FIG. 1, a GaN crystal was grown by the HVPE method using the AlN seed crystal substrate 3 described above. First, the AlN seed crystal substrate 3 is placed on a pedestal 13 in a quartz reaction vessel 11 (specifically, a quartz reaction tube) of the HVPE apparatus 10 shown in FIG. 1, and a halogen-containing gas introduction tube 11a, While introducing hydrogen gas (not shown) as a carrier gas into the reaction vessel 11 through the gallium source gas introduction tube 11c and the nitrogen source gas introduction tube 11d, the inside of the reaction vessel 11 is heated by the heater 14 and the temperature is adjusted. The temperature was 1050 ° C.

Next, HCl gas as the halogen-containing gas 5 was introduced into the gallium source gas generation chamber 11b through the halogen-containing gas introduction tube 11a together with the carrier gas. In the gallium source gas generation chamber 11b, gallium 6 in the gallium boat 12 reacts with HCl gas (halogen-containing gas 5) to generate GaCl gas as the gallium source gas 7, and this GaCl gas (gallium source gas). 7) was introduced into the reaction vessel 11 through the gallium source gas introduction tube 11c. On the other hand, NH ₃ gas as the nitrogen source gas 8 was introduced into the reaction vessel 11 through the nitrogen source gas introduction pipe 11d together with the carrier gas.

Here, the temperature of the AlN seed crystal substrate is set to 1050 ° C., and the partial pressure of GaCl gas (substantially the same as the partial pressure of HCl gas) and the partial pressure of NH ₃ gas are set so that the growth rate of the GaN crystal is 50 μm / hr. By adjusting, a GaN crystal 4 having a thickness of 2.0 mm was grown without forming a polycrystal. After the temperature of the GaN crystal 4 was lowered to room temperature (25 ° C.), the GaN crystal 4 grown on the AlN seed crystal substrate 3 was taken out from the reaction vessel 11.

(1-4. Preparation of GaN crystal substrate)
The GaN crystal 4 was sliced along a plane parallel to the crystal growth surface (C-plane) of the GaN crystal 4, and the surface was polished into a mirror surface to obtain a GaN crystal substrate having a diameter of 50.8 mm and a thickness of 400 μm. . This GaN crystal substrate had a dislocation density of 5 × 10 ⁴ cm ⁻² , a half-width of a diffraction intensity peak in a rocking curve of X-ray diffraction with respect to the (0004) plane was 50 arcsec, and the dislocation density was low and the crystallinity was good. The RMS surface roughness of this GaN crystal substrate was as good as 50 nm. Further, this GaN crystal substrate is transparent and is considered to have high purity with little contamination of impurities. Here, when the impurity analysis by the SIMS method was performed on the GaN crystal substrate, the concentration of oxygen, which was the most abundant impurity, was 2 × 10 ¹⁷ cm ^−3. Even it was 1 × 10 ¹⁸ cm ⁻³ or less.

(Example 2)
During the growth of the GaN crystal, dichlorosilane gas as a silicon-containing gas is used together with GaCl gas as a gallium source gas 7, ammonia gas (NH ₃ gas) as a nitrogen source gas 8, and hydrogen gas (H ₂ gas) as a carrier gas. (SiH ₂ Cl ₂ gas)) (not shown) was introduced into the reaction vessel 11 in the same manner as in Example 1 to obtain a GaN crystal substrate having a thickness of 400 μm containing silicon as an impurity. This GaN crystal substrate had a dislocation density of 5 × 10 ⁴ cm ⁻² , a half-width of a diffraction intensity peak in a rocking curve of X-ray diffraction with respect to the (0004) plane was 40 arcsec, and the dislocation density was low and the crystallinity was good. Further, the RMS surface roughness of this GaN crystal substrate was as good as 50 nm. Moreover, the impurity mixed most in the GaN crystal substrate was silicon (Si), and its concentration was 1 × 10 ¹⁸ cm ⁻³ .

(Comparative Example 1)
During the growth of the GaN crystal, a GaN crystal substrate (dislocation density is 5 × 10 ⁷ cm ⁻² , the X-ray diffraction rocking curve about the (0004) plane) produced by the HVPE method as a seed crystal substrate. A GaN crystal substrate having a thickness of 400 μm was obtained in the same manner as in Example 1 except that the half width was 120 arcsec. This GaN crystal substrate has a dislocation density of 5 × 10 ⁷ cm ⁻² and a half-width of a diffraction intensity peak in a rocking curve of X-ray diffraction with respect to the (0004) plane of 120 arcsec, resulting in a high dislocation density and poor crystallinity. It was.

  As described above, a GaN crystal is grown by the HVPE method using an AlN seed crystal substrate formed of at least a part of the AlN seed crystal grown by the sublimation method and having a curvature radius of curvature of 5 m or more. A GaN crystal having a low dislocation density and good crystallinity can be obtained.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a schematic cross section showing one embodiment of growth of a GaN crystal in a manufacturing method of a GaN crystal concerning the present invention. It is a schematic cross section which shows one Embodiment of the growth of the AlN seed crystal used for the manufacturing method of the GaN crystal concerning this invention. It is a schematic cross section which shows other embodiment of the growth of the GaN crystal in the manufacturing method of the GaN crystal concerning this invention.

Explanation of symbols

  1 AlN raw material, 2 AlN seed crystal, 3 AlN seed crystal substrate, 3d dislocation, 4 GaN crystal, 5 halogen-containing gas, 6 gallium, 7 gallium raw material gas, 8 nitrogen raw material gas, 10 HVPE apparatus, 11, 21 reaction vessel, 11a Halogen-containing gas introduction pipe, 11b Gallium source gas generation chamber, 11c Gallium source gas introduction pipe, 11d Nitrogen source gas introduction pipe, 11e, 21e, 22e Gas exhaust port, 12 Gallium boat, 13 Pedestal, 14 Heater, 20 Sublimation furnace , 21a Gas introduction port, 22 crucible, 23 heating body, 24 high-frequency heating coil, 25 radiation thermometer, 30 mask, 30w opening.

Claims (10)

A method for producing a GaN crystal, wherein an GaN crystal is grown by an HVPE method using an AlN seed crystal substrate formed of at least a part of an AlN seed crystal grown by a sublimation method,
A method for producing a GaN crystal, wherein the curvature radius of curvature of the AlN seed crystal substrate is 5 m or more.   2. The method for producing a GaN crystal according to claim 1, wherein a half-value width of a diffraction intensity peak in a rocking curve of X-ray diffraction with respect to the (0004) plane of the AlN seed crystal substrate is 50 arcsec or less. 3. The method for producing a GaN crystal according to claim 1, wherein a dislocation density of the AlN seed crystal substrate is 1 × 10 ⁶ cm ⁻² or less. 4. The method for producing a GaN crystal according to claim 1, wherein a total impurity concentration of the GaN seed crystal is 1 × 10 ¹⁸ cm ⁻³ or less. 5.   The method for producing a GaN crystal according to any one of claims 1 to 3, wherein the GaN crystal is doped with an n-type impurity.   6. The method for producing a GaN crystal according to claim 5, wherein the n-type impurity is at least one of silicon and oxygen. The method for producing a GaN crystal according to any one of claims 1 to 6, wherein an area of a main surface of the AlN seed crystal substrate is 10 cm ² or more.   The GaN crystal according to any one of claims 1 to 7, wherein a mask having an opening is formed on the AlN seed crystal substrate, and the GaN crystal is epitaxially grown in the lateral direction on the mask. Manufacturing method.   A GaN crystal substrate formed of at least a part of a GaN crystal obtained by the manufacturing method according to claim 1.   A semiconductor device comprising the GaN crystal substrate of claim 9.

Images