JP2005343722A - METHOD FOR GROWING AlN CRYSTAL, AlN CRYSTAL SUBSTRATE AND SEMICONDUCTOR DEVICE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for growing an AlN crystal whereby a large AlN crystal can be obtained, an AlN crystal substrate and a semiconductor device containing the AlN crystal substrate. <P>SOLUTION: In the method for growing the AlN crystal 2, the AlN crystal is grown through a sublimation method by using a first AlN seed crystal 1 grown through an HVPE method. In an alternative method for growing the AlN crystal, the AlN crystal 2 is grown through the sublimation method by using a second AlN seed crystal 1 as a seed crystal, wherein the second AlN seed crystal 1 is at least a portion of the AlN crystal 2 obtained through the method for growing the AlN crystal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an AlN crystal growth method used for a substrate of a semiconductor device such as a light emitting element, an electronic element, or a semiconductor sensor. More particularly, the present invention relates to a method for growing a large AlN crystal, an AlN crystal substrate, and a semiconductor device including the AlN crystal substrate.

  Group III nitride crystals such as AlN crystals are very useful as materials for forming semiconductor devices such as light-emitting elements, electronic elements, and semiconductor sensors.

  Methods for producing such AlN crystals include sublimation method, HVPE (Hydride Vapor Phase Epitaxy) method, MBE (Molecular Beam Epitaxy) method, MOCVD (Metal Organic Chemical Vapor Deposition; organic). Vapor deposition methods such as metal chemical vapor deposition have been proposed.

  Here, in the sublimation method, a crystal having good crystallinity with a small half-value width of X-ray diffraction can be obtained without using a seed crystal, but it is difficult to grow a large crystal (for example, see Non-Patent Document 1) .

  However, in the sublimation method, when a large SiC seed crystal is used as a seed crystal and an AlN crystal is grown on the SiC seed crystal, the lattice constant and the linear expansion coefficient are greatly different between the SiC seed crystal and the AlN crystal. In addition, there is a problem that a large tensile stress is applied to the AlN crystal during cooling after the growth of the AlN crystal and the AlN crystal is cracked (for example, see Non-Patent Document 2).

  On the other hand, in the HVPE method, which is one of the vapor phase growth methods, a large (large diameter) AlN crystal is obtained by growing an AlN crystal on a substrate such as a Si substrate or a SiC substrate. (For example, refer nonpatent literature 3).

  However, even in the HVPE, since the lattice constant and the linear expansion coefficient are greatly different between the Si substrate or SiC substrate and the group III nitride crystal, it is difficult to obtain a crystal with good crystallinity. For example, an AlN crystal grown on a Si substrate or a SiC substrate has a large half width of X-ray diffraction.

The MBE method and the MOCVD method are disadvantageous for producing a large AlN crystal because the crystal growth rate is low.
M. Tanaka and four others, “Morphology and X-Ray Diffraction Peak Widths of Aluminum Nitride Single Crystals Prepared by the Sublimation Method”, Jpn. J. Appl. Phys., Vol36, (1997), Pt.2, No. 8B, p.L1062-L1064 L. Liu and three others, “Raman characterization and stress analysis of AlN grown on SiC by sublimation”, J. Appl. Phys., Vol. 92, Nov. (2002), No. 1, p.5183-5188 Yu. Melnik and 11 others, “AlN substrate: fabrication via vapor phase growth and characterization”, Phys. Stat. Sol., (A) 200, (2002), No. 1, p.22-25

  An object of the present invention is to solve the above problems and provide an AlN crystal growth method capable of obtaining a large AlN crystal, an AlN crystal substrate, and a semiconductor device including the AlN crystal substrate.

  The present invention is an AlN crystal growth method in which an AlN crystal is grown by a sublimation method using a first AlN seed crystal grown by an HVPE method.

  In the AlN crystal growth method according to the present invention, the crystal growth plane of the first AlN seed crystal can be a (0001) plane or a (000-1) plane. Alternatively, a first AlN seed crystal having a diameter of 5 cm or more can be used.

  In the AlN crystal growth method according to the present invention, a second AlN seed crystal that is at least a part of the AlN crystal obtained by the AlN crystal growth method is prepared as a seed crystal, and the second AlN crystal is prepared. An AlN crystal can be grown by a sublimation method using a seed crystal.

  Further, the present invention uses an AlN seed crystal in which a seed crystal protective material having a sublimation rate at the crystal growth temperature equal to or lower than that of an AlN seed crystal is adhered to the flatly processed back surface of the AlN seed crystal by a sublimation method. This is a method for growing an AlN crystal to grow a crystal.

  The present invention also provides an AlN crystal substrate obtained by cutting at least a part of the AlN crystal obtained by the above-described AlN crystal growth method and polishing the surface thereof.

  Furthermore, this invention is a semiconductor device containing said AlN crystal substrate.

  As described above, according to the present invention, an AlN crystal growth method capable of obtaining a large AlN crystal, an AlN crystal substrate, and a semiconductor device including the AlN crystal substrate can be provided.

  One AlN crystal growth method according to the present invention is a method of growing an AlN crystal 2 by a sublimation method using a first AlN seed crystal 1 grown by an HVPE method with reference to FIG.

  The first AlN seed crystal grown by the HVPE method has a large crystal growth rate and provides a large seed crystal. Here, when an AlN crystal is grown on the first AlN seed crystal by the sublimation method, since the lattice constant and the linear expansion coefficient of the seed crystal and the crystal to be grown coincide with each other, a large AlN crystal can be formed without causing cracks. Can be obtained.

  Here, the HVPE method in the present invention refers to an AlN crystal (first AlN seed crystal in the present invention) by reacting a halogenated Al gas as the Al source gas 7 with a nitrogen source gas 8 with reference to FIG. 1) refers to the method of growing.

  In crystal growth by the HVPE method, for example, an HVPE apparatus 20 as shown in FIG. 2 is used. The HVPE apparatus 20 includes a pedestal 22 for placing the base substrate 9 on the reaction vessel 21, an Al source gas inlet 21 a for introducing the Al source gas 7 onto the base substrate 9, and a nitrogen source gas 8 on the base substrate 9. Is provided with a nitrogen source gas inlet 21b for exhausting, an exhaust outlet 21c for exhausting the reacted gas, and a heater 25 for heating the reaction vessel 21.

With reference to FIG. 2, using the HVPE apparatus 20, for example, an AlN crystal can be produced as follows. On the pedestal 22 installed in the reaction vessel 21, an SiC substrate is disposed as the base substrate 9, an Al halide gas as the Al source gas 7, and NH ₃ gas as the nitrogen source gas 8 are introduced into the reaction vessel 21. Then, the Al source gas 7 and the nitrogen source gas 8 are reacted to grow the first AlN seed crystal 1 on the base substrate 9. The partial pressure of the Al source gas 7 is about 50 Pa to 1 × 10 ⁴ Pa, the partial pressure of the nitrogen source gas 8 is about 5 × 10 ³ Pa to 5 × 10 ⁴ Pa, the gas of the Al source gas 7 and the nitrogen source gas 8 The ratio (molar ratio) is about 1:10 to 1: 1000, the temperature of the base substrate 9 is about 900 ° C. to 1100 ° C., and the growth rate of the AlN seed crystal 1 is adjusted to about 10 μm / hr to 30 μm / hr. Thus, a large first AlN seed crystal 1 with good crystallinity is obtained.

Here, when introducing the Al source gas and the nitrogen source gas, a carrier gas such as H ₂ gas, N ₂ gas or Ar gas can be used. By adding the carrier gas to the Al source gas or nitrogen source gas, the amount of introduction of the Al source gas or nitrogen source gas can be stabilized, and the reactivity between the Al source gas and the nitrogen source gas can be adjusted, A large AlN seed crystal with good crystallinity can be obtained efficiently.

Although not shown, it is also possible to laterally grow the AlN seed crystal by the HVPE method using the surface of the base substrate as an uneven surface. It is also possible to form an intermediate layer on the base substrate and grow an AlN seed crystal on the intermediate layer. By these methods, the crystallinity of the AlN seed crystal can be improved and the dislocation density can be reduced. Here, the intermediate layer is not particularly limited, but it is preferable to form an AlN amorphous layer from the viewpoint of improving crystallinity by reducing the dislocation density of the AlN seed crystal. The AlN amorphous layer can be formed on the base substrate by causing the base substrate temperature to be about 500 ° C. to 600 ° C., for example, by HVPE, and reacting the halogenated Al gas and NH ₃ gas on the base substrate. it can.

Next, an AlN crystal is grown by a sublimation method using the large first AlN seed crystal obtained by the HVPE method. Here, the sublimation method in the present invention refers to FIG. 1, after sublimating an AlN raw material 5 such as an AlN powder, the AlN seed crystal 1 is solidified again, and the AlN seed crystal 1 is formed with the AlN crystal 2. A method of growing. In crystal growth by the sublimation method, for example, a high-frequency heating type vertical sublimation furnace 10 as shown in FIG. 1 is used. A BN-made crucible 12 having an exhaust port 12c is provided as a crystal growth container in the center of the reaction vessel 11 in the vertical sublimation furnace 10 to ensure ventilation around the crucible 12 from the inside of the crucible to the outside. The heating body 14 is provided to do this. In addition, a high-frequency heating coil 24 for heating the crucible 12 is provided at the outer central portion of the reaction vessel 11. Further, at the end of the reaction vessel 21, the N ₂ gas introduction port 11 a and the N ₂ gas exhaust port 11 c for flowing N ₂ gas to the outside of the crucible 12 of the reaction vessel 11, and the temperatures of the lower surface and the upper surface of the crucible 12 are provided. A radiation thermometer 16 is provided for measuring.

With reference to FIG. 1, for example, AlN crystal 2 can be manufactured as follows using vertical sublimation furnace 10. The AlN seed crystal 1 is housed in the upper part of the crucible 12, the AlN raw material 5 such as AlN powder is housed in the lower part of the crucible 12, and the high-frequency heating coil 24 is used to flow the N ₂ gas into the reaction vessel 11. By raising the temperature and maintaining the temperature on the AlN raw material 5 side of the crucible 12 higher than the temperature on the AlN seed crystal 1 side, AlN was sublimated from the AlN raw material 5 and placed on top of the crucible 12. On the AlN seed crystal 1, AlN is solidified again to grow an AlN crystal 2.

Here, during the growth of the AlN crystal 2, the temperature on the AlN raw material 5 side of the crucible 12 is about 2000 ° C. to 2200 ° C., and the temperature on the AlN seed crystal 1 side in the upper part of the crucible (crystal growth vessel 12) is set to the AlN raw material 5. By making the temperature about 10 ° C. to 100 ° C. lower than the temperature on the side, the AlN crystal 2 having good crystallinity can be obtained efficiently. Further, during the crystal growth, N ₂ gas is continuously supplied to the outside of the crucible 12 in the reaction vessel 11 so that the gas partial pressure is about 101.3 hPa to 1013 hPa, thereby reducing the contamination of impurities into the AlN crystal 2. can do.

  During the temperature rise inside the crucible 12, the surface of the AlN seed crystal 1 is cleaned by etching during the temperature rise by making the temperature on the AlN seed crystal 1 side of the crucible 12 higher than the temperature on the AlN raw material 5 side. At the same time, impurities released from the inside of the AlN seed crystal 1 and the crucible 12 during the temperature rise can be removed through the exhaust port 12c, and contamination of the impurities into the AlN crystal 2 can be further reduced.

  FIG. 1 shows a case where the AlN crystal 2 is grown directly on the AlN seed crystal 1. Although not shown, after an intermediate layer is formed on the AlN seed crystal 1, an AlN crystal can be grown on the intermediate layer by a sublimation method. Here, the chemical composition and manufacturing method of the intermediate layer are not particularly limited.

  In the AlN crystal growth method according to the present invention, it is preferable that the crystal growth surface of the first AlN seed crystal is a (0001) plane or a (000-1) plane. In the growth of the AlN seed crystal by the HVPE method, since the crystal growth of the (0001) plane or the (000-1) plane is easy, the first growth of the AlN crystal by the sublimation method using the AlN seed crystal is also performed. By making the crystal growth surface of the AlN seed crystal a (0001) plane or a (000-1) plane, growth of a large crystal is facilitated.

  In the AlN seed crystal growth method according to the present invention, the diameter of the first AlN seed crystal is preferably 5 cm or more. According to the HVPE method, a large-diameter AlN seed crystal having a diameter of 5 cm or more can be easily produced. By using a large-diameter AlN seed crystal having a diameter of 5 cm, a large-sized AlN seed crystal can be obtained even in the sublimation method. An AlN crystal can be produced.

  Another AlN crystal growth method according to the present invention is a method of growing an AlN crystal by a sublimation method using at least a part of the AlN crystal obtained by the AlN crystal growth method as a second AlN seed crystal. It is. By using the AlN crystal obtained by the sublimation method as a seed crystal and further growing the AlN crystal by the sublimation method, a large AlN crystal with high crystallinity can be easily produced.

  Still another AlN crystal growth method according to the present invention is described with reference to FIG. 1, on a flatly processed back surface of an AlN seed crystal 1, a seed crystal having a sublimation rate at the crystal growth temperature of AlN seed crystal 1 or less. In this method, an AlN crystal 2 is grown by a sublimation method using an AlN seed crystal 1 to which a protective material 13 is adhered. Here, in this growth method, the growth method of the AlN seed crystal is not particularly limited, and an AlN seed crystal (first or second AlN seed crystal) grown by the sublimation method or the HVPE method is used. .

By sticking the seed crystal protective material 13 to the back surface of the AlN seed crystal 1 to prevent sublimation of AlN from the back surface of the AlN seed crystal, it is possible to prevent generation of voids in the grown AlN crystal. it can. Here, the seed crystal protective material is not particularly limited as long as the sublimation rate at the growth temperature of the AlN crystal is equal to or lower than that of the AlN seed crystal. For example, nitrides such as BN and AlN, carbides such as TiC, Y ₂ An oxide such as O ₃ or ZrO ₂ , C (carbon), or the like can be used.

  One AlN crystal substrate according to the present invention is shown in FIG. 3 to FIG. 5, and as shown in FIG. 3, at least a part of the AlN crystal 2 grown on the AlN seed crystal 1 by the AlN crystal growth method described above. Is cut out as shown in FIG. 4 and the surface thereof is polished as shown in FIG.

  Here, as shown in FIGS. 4 and 5, the AlN crystal 2 is cut out together with the AlN seed crystal 1 (FIG. 4A), and the surface is polished (FIG. 5A), and only the AlN crystal 2 is removed. Any one of the cut (FIG. 4B) and the polished surface (FIG. 5B) can be used as the AlN crystal substrate.

  A semiconductor device according to the present invention includes the AlN crystal substrate described above. By using the large AlN crystal substrate in the present invention, a semiconductor device including the AlN crystal substrate can be obtained efficiently. Examples of the semiconductor device including the AlN crystal substrate in the present invention include light emitting elements such as light emitting diodes and laser diodes, electronic elements such as rectifiers, bipolar transistors, field effect transistors, and HEMTs (High Electron Mobility Transistors). Examples include a temperature sensor, a pressure sensor, a radiation sensor, a semiconductor sensor such as a visible-ultraviolet light detector, and a SAW device (Surface Acoustic Wave Device).

(Example 1)
On the AlN seed crystal (diameter 50 mm × thickness 1.5 mm, after polishing the surface to a mirror surface and then etching and removing the polishing damage layer) by sublimation method on the AlN crystal grown by HVPE method An AlN crystal was grown as follows.

  Referring to FIG. 1, AlN raw material 5 such as AlN powder was housed in the lower part of a BN crucible 12, and the first AlN seed crystal 1 was placed on the upper part of the crucible 12 having an inner diameter of 48 mm. The first AlN seed crystal is processed flat, and is arranged so that the BN material as the seed crystal protective material 13 is in close contact with the back surface of the AlN seed crystal 1. AlN sublimation from the back side was prevented.

Next, the temperature in the crucible 12 was raised using the high-frequency heating coil 15 while flowing N ₂ gas into the reaction vessel 11. During the temperature rise in the crucible 12, the temperature on the AlN seed crystal 1 side of the crucible 12 is set higher than the temperature on the AlN raw material 5 side, and the surface of the AlN seed crystal 1 is cleaned by etching during the temperature rise. Impurities released from the inside of the AlN seed crystal 1 and the crucible 12 during the warming were removed through the exhaust port 12c.

Next, the temperature of the AlN seed crystal 1 side of the crucible 12 is 2100 ° C., the temperature of the AlN raw material 5 side is 2150 ° C., AlN is sublimated from the AlN raw material 5, and the AlN seed crystal disposed at the top of the crucible 12 1, AlN was solidified again to grow an AlN crystal 2. During AlN crystal growth, it continued to flow N ₂ gas on the outside of the crucible 12 in the reaction vessel 11, as the outer gas partial pressure of the crucible 12 in the reaction vessel 11 is about 101.3HPa～1013hPa, N ₂ The amount of gas introduced and the amount of N ₂ gas exhaust were controlled. An AlN crystal was grown for 50 hours under the above crystal growth conditions, and then cooled to room temperature (25 ° C.) to obtain an AlN crystal.

  The obtained AlN crystal was polycrystallized in the outer peripheral portion of the crystal, but the half-value width of X-ray diffraction was 200 ars within the range of 42 mm in diameter from the center of the crystal, which can be used as a substrate for a semiconductor device. It was an AlN single crystal. The thickness of the AlN crystal was 7.5 mm at the thick part and 4.5 mm at the thin part.

  Next, the obtained AlN crystal was sliced on a plane parallel to the crystal growth surface (C plane) of the AlN crystal 2 as shown in FIG. 4, and the polycrystallized outer peripheral portion was removed, and FIG. As shown, the surface was polished to a mirror surface and etched to obtain an AlN crystal substrate having a diameter of 4.2 mm and a thickness of 1.5 mm. RMS (Root Mean Square) surface roughness measured by an AFM (Atomic Force Microscope) within a 10 μm square range of this AlN crystal substrate. The thickness was 50 nm (500 mm) or less.

  In addition, the AlN crystal substrate in the above-mentioned example is produced by slicing a plane parallel to the C plane of the grown AlN crystal, but the slice plane of the AlN crystal is limited to a plane parallel to the C plane. The surface can be a plane parallel to the A plane, R plane, M plane or S plane, or a plane having an arbitrary inclination with respect to these planes.

  As described above, a large AlN crystal can be obtained by growing an AlN crystal by a sublimation method using an AlN seed crystal grown by an HVPE method.

  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.

  As described above, the present invention can be widely used for AlN crystal growth methods that can obtain large AlN crystals, AlN crystal substrates, and semiconductor devices including AlN crystal substrates.

In this invention, it is a schematic diagram which shows the sublimation furnace which makes an AlN crystal grow by a sublimation method using an AlN seed crystal. In this invention, it is a schematic diagram which shows the HVPE apparatus which grows an AlN seed crystal by HVPE method. It is a schematic diagram which shows the process of growing an AlN crystal | crystallization on an AlN seed crystal in this invention. It is a schematic diagram which shows the process of cutting off an AlN crystal in this invention. Here, (a) shows the portion where the AlN crystal is cut out together with the AlN seed crystal, and (b) and (c) show the portion where only the AlN crystal is cut off. It is a schematic diagram which shows the process of grind | polishing the group III nitride crystal cut out in this invention. Here, (a) shows a state where the group III nitride crystal cut together with the seed crystal is polished, and (b) shows a state where the cut group III nitride crystal is polished.

Explanation of symbols

1 AlN seed crystal, 2 AlN crystal, 5 AlN raw material, 7 Al source gas, 8 nitrogen source gas 9 underlying substrate 10 sublimation furnace, 11 and 21 the reaction vessel, 11a N ₂ gas inlet, 11c N ₂ gas exhaust port , 12 crucible, 13 seed crystal protective material, 14 heating element, 15 high-frequency heating coil, 16 radiation thermometer, 20 HVPE device, 21a Al source gas inlet, 21b nitrogen source gas inlet, 22 pedestal, 25 heater.

Claims (7)

  An AlN crystal growth method in which an AlN crystal is grown by a sublimation method using a first AlN seed crystal grown by an HVPE method.   The method for growing an AlN crystal according to claim 1, wherein a crystal growth surface of the first AlN seed crystal is a (0001) plane or a (000-1) plane.   The method for growing an AlN crystal according to claim 1, wherein the diameter of the first AlN seed crystal is 5 cm or more.   A second AlN seed crystal that is at least part of the AlN crystal obtained by the AlN crystal growth method according to any one of claims 1 to 3 is prepared as a seed crystal, and the second AlN seed is prepared. A method for growing an AlN crystal, in which an AlN crystal is grown by sublimation using the crystal.   An AlN crystal is grown by a sublimation method using the AlN seed crystal in which a seed crystal protective material having a sublimation rate at a crystal growth temperature equal to or lower than the AlN seed crystal is adhered to the flatly processed back surface of the AlN seed crystal. AlN crystal growth method.   An AlN crystal substrate obtained by cutting at least a part of an AlN crystal obtained by the AlN crystal growth method according to any one of claims 1 to 5 and polishing the surface thereof.   A semiconductor device comprising the AlN crystal substrate according to claim 6.

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