JP2010042950A - METHOD FOR PRODUCING AlN CRYSTAL, METHOD FOR PRODUCING AlN SUBSTRATE AND METHOD FOR PRODUCING PIEZOELECTRIC VIBRATOR - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an AlN crystal by which crystallinity is enhanced, a method for producing an AlN substrate and a method for producing a piezoelectric vibrator. <P>SOLUTION: The method for producing the AlN crystal 10 comprises a step of preparing an AlN base substrate 11, a step of growing the AlN crystal 10 on the AlN base substrate 11 and a step of separating the AlN base substrate 11 from the AlN crystal 10. One of the AlN base substrate 11 and the AlN crystal 10 has an absorption coefficient to light having a wavelength of 280 nm or less of 100 cm<SP>-1</SP>or more, and the other of the AlN base substrate 11 and AlN crystal 10 has an absorption coefficient to light having at least a partial wavelength range of 220 nm or more and 280 nm or less of less than 100 cm<SP>-1</SP>. In the separating step, the light is irradiated from the side having a lower absorption coefficient in the AlN base substrate 11 and the AlN crystal 10. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an AlN (aluminum nitride) crystal manufacturing method, an AlN substrate manufacturing method, and a piezoelectric vibrator manufacturing method.

The AlN crystal is attracting attention as a substrate material for optical devices and electronic devices because it has an energy band gap of 6.2 eV, a thermal conductivity of about 3.3 WK ⁻¹ cm ⁻¹ and a high electrical resistance. .

A method for producing a group III nitride semiconductor crystal containing such an AlN crystal is disclosed, for example, in Japanese translations of PCT publication No. 2007-536732 (Patent Document 1). Specifically, a lift-off layer made of InGaN (indium gallium nitride) or the like is formed on a silicon carbide (SiC) substrate, and an epitaxial layer as a group III nitride semiconductor crystal is formed on the lift-off layer. Thereafter, the lift-off layer is irradiated with light that is not absorbed by the SiC substrate or the group III nitride semiconductor crystal and is absorbed by the lift-off layer. Light is absorbed by the lift-off layer, and the lift-off layer is heated and disappeared to separate the SiC substrate and the group III nitride semiconductor crystal. Thus, a group III nitride semiconductor crystal is manufactured by growing a group III nitride semiconductor crystal on the base substrate and removing the base substrate.
Special Table 2007-537732

  Patent Document 1 discloses that since the crystal lattice matching between SiC and group III nitride is close, generally a high-quality group III nitride semiconductor crystal can be manufactured by using a SiC substrate. However, since SiC and AlN are different materials, the crystal lattice matching between SiC and AlN does not match. For this reason, when an AlN crystal is grown on a SiC substrate, there is a problem that the crystallinity of the AlN crystal is not sufficient.

  Therefore, a technique for growing an AlN crystal on an AlN substrate can be considered. However, if the technique of irradiating light disclosed in Patent Document 1 is applied to this technique, light is similarly absorbed by the AlN substrate and the AlN crystal, so it is difficult to absorb light only by the AlN substrate. is there. For this reason, there is a problem that the base substrate cannot be removed.

  As another technique, a method of removing an underlying substrate by a mechanical method such as slicing or polishing after growing an AlN crystal on an AlN substrate can be considered. However, when the base substrate is removed by a mechanical method, stress is applied to the AlN crystal. For this reason, there is a problem that the crystallinity of the AlN crystal is lowered such that the AlN crystal is easily broken and cracks are generated in the AlN crystal.

  The present invention has been made in view of the above problems, and an object thereof is to provide an AlN crystal manufacturing method, an AlN substrate manufacturing method, and a piezoelectric vibrator manufacturing method that improve crystallinity.

In order to improve the crystallinity of the AlN crystal, the present inventor has intensively studied the conditions for separating the AlN base substrate and the AlN crystal by irradiating light when an AlN substrate is used as the base substrate. As a result, it has been found that when the absorption coefficient of AlN is 100 cm ⁻¹ or more, when AlN is irradiated with light, A (aluminum) atoms and N (nitrogen) atoms in AlN are easily decomposed effectively.

Therefore, the method for producing an AlN crystal of the present invention includes a step of preparing an AlN base substrate, a step of growing an AlN crystal on the AlN base substrate, and a step of separating the AlN base substrate from the AlN crystal. One of the AlN base substrate and the AlN crystal has an absorption coefficient of 100 cm ⁻¹ or more for light having a wavelength of 280 nm or less. The other of the AlN base substrate and the AlN crystal has an absorption coefficient of less than 100 cm ⁻¹ in at least a part of the wavelength region of light having a wavelength of 220 nm or more and 280 nm or less. In the separating step, light is irradiated from the other side of the AlN base substrate and the AlN crystal having a low absorption coefficient.

  According to the AlN crystal manufacturing method of the present invention, an AlN crystal is grown on an AlN base substrate. Since the base substrate and the crystal to be grown have the same composition, it is possible to suppress a decrease in crystallinity of the AlN crystal due to a difference in crystal lattice matching.

Further, one of the AlN base substrate and the AlN crystal has an absorption coefficient of 100 cm ⁻¹ or more for light having a wavelength of 280 nm or less. When one of the AlN base substrate and the AlN crystal having an absorption coefficient of 100 cm ⁻¹ or more is irradiated with light, the light is absorbed by this one. Thereby, this one temperature rises, the bond between the Al atom and the N atom is released, and the N atom is dissociated from the AlN. Further, the absorption coefficient in at least a partial region of light having a wavelength of 220 nm or more and 280 nm or less of the other of the AlN base substrate and the AlN crystal is less than 100 cm ⁻¹ . Thereby, even if light is irradiated to the other whose absorption coefficient is less than 100 cm ⁻¹ , light absorption is suppressed, and an increase in temperature is suppressed. For this reason, on the other hand, the release of the bond between the Al atom and the N atom is suppressed, so that deterioration of crystallinity can be suppressed. Therefore, one of the AlN base substrate and the AlN crystal that has a low absorption coefficient (the other one of the AlN base substrate and the AlN crystal that has an absorption coefficient for light having a wavelength of 220 nm or more and 280 nm or less is less than 100 cm ⁻¹ ). By irradiating light toward the other side (the other of the AlN base substrate and the AlN crystal having an absorption coefficient of 100 cm ⁻¹ or more for light having a wavelength of 280 nm or less), the dissociation of N is promoted near the interface with one of the other can do. As a result, they can be separated from each other in the vicinity of the interface between the AlN base substrate and the AlN crystal. Therefore, since the AlN base substrate can be separated from the AlN crystal without applying stress, it is possible to suppress a decrease in crystallinity of the manufactured AlN crystal.

  As described above, the AlN base substrate can be separated from the AlN crystal with improved crystallinity without applying stress. Therefore, an AlN crystal with improved crystallinity can be produced.

  Preferably, in the AlN crystal manufacturing method, light having a wavelength of 300 nm or less is irradiated in the separation step.

This makes it easier to effectively decompose one Al atom and N atom having an absorption coefficient of 100 cm ⁻¹ or more for light having a wavelength of 280 nm or less in the AlN base substrate or the AlN crystal. For this reason, since the AlN base substrate and the AlN crystal can be more easily separated, an AlN crystal with improved crystallinity can be manufactured more easily.

Preferably, in the AlN crystal manufacturing method, in the growing step, an AlN crystal having a dislocation density of 1 × 10 ⁷ cm ⁻² or less is grown.

  In the present invention, since the AlN crystal is grown on the AlN base substrate, lattice mismatch can be suppressed. For this reason, an AlN crystal with a low dislocation density can be grown as described above.

  In the AlN crystal manufacturing method, preferably, one of the AlN base substrate and the AlN crystal contains 2 ppm or more of a group 14 element.

Thereby, an AlN base substrate or AlN crystal having an absorption coefficient of 100 cm ⁻¹ or more for light having a wavelength of 280 nm or less can be realized.

  In this specification, “Group 14” means the Group IVA of the former IUPAC (The International Union of Pure and Applied Chemistry) system. That is, the group 14 element includes at least one element of carbon (C), silicon (Si), germanium (Ge), tin (Zn), lead (Pb), and ununquadium (Uuq).

  Preferably, in the AlN crystal manufacturing method, in the preparing step, a base substrate having a thickness of 200 μm or more is prepared.

  Thereby, the crystallinity of the base substrate can be improved. For this reason, the crystallinity of the AlN crystal grown on the underlying substrate can be further improved.

  The method for producing an AlN substrate of the present invention includes a step of producing an AlN crystal by any one of the methods for producing an AlN crystal described above and a step of forming the AlN crystal on a different substrate.

  According to the method for manufacturing an AlN substrate of the present invention, an AlN crystal having improved crystallinity is formed on a heterogeneous substrate. For this reason, when an inexpensive substrate is used as the heterogeneous substrate, an AlN substrate having an AlN crystal with reduced cost and improved crystallinity can be manufactured.

  The method for manufacturing a piezoelectric vibrator of the present invention includes a step of manufacturing an AlN crystal by the method of manufacturing an AlN crystal and a step of forming an electrode layer on the AlN crystal.

According to the method for manufacturing a piezoelectric vibrator of the present invention, an AlN crystal with improved crystallinity is used. Thereby, a piezoelectric vibrator having an excellent electromechanical coupling coefficient kt ² and an acoustic quality factor (Q value) can be manufactured.

According to the AlN crystal manufacturing method, the AlN substrate manufacturing method, and the piezoelectric vibrator manufacturing method of the present invention, since the base substrate having the same composition as the AlN crystal is used, an AlN crystal that suppresses a decrease in crystallinity is grown. can do. Further, since the absorption coefficient is irradiated from the other side of the AlN underlying substrate and AlN crystal is less than 10 cm ^-1, the light to one of the AlN underlying substrate and AlN crystal absorption coefficient is 10 cm ^-1 or more, crystalline It is possible to separate the AlN base substrate and the AlN crystal while suppressing deterioration of the substrate. Therefore, an AlN crystal, an AlN substrate, and a piezoelectric vibrator having improved crystallinity can be manufactured.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Embodiment 1)
FIG. 1 is a cross-sectional view schematically showing an AlN crystal in the present embodiment. With reference to FIG. 1, the AlN crystal 10 in this Embodiment is demonstrated.

As shown in FIG. 1, the AlN crystal 10 in the present embodiment has an absorption coefficient of less than 10 cm ⁻¹ for light having a wavelength of 300 nm or less, and preferably 7 cm ⁻¹ or less.

  The absorption coefficient is a value calculated from the thickness of the AlN crystal by measuring the transmittance with, for example, an ultraviolet-visible spectrophotometer.

The AlN crystal 10 preferably has a dislocation density of 1 × 10 ⁷ cm ⁻² or less, more preferably 1 × 10 ⁶ cm ⁻² or less. In this case, the characteristics can be improved when a device is produced using the AlN crystal 10.

  The dislocation density can be measured by, for example, counting the number of pits formed by etching in molten KOH (potassium hydroxide) and dividing by the unit area.

  The shape of the AlN crystal 10 is not particularly limited. For example, it is a thin film having a thickness of 200 μm or less, and can be more preferably used in the case of a bulk crystal of 200 μm or more.

  FIG. 2 is a flowchart showing a method for producing an AlN crystal in the present embodiment. Next, with reference to FIG. 2, a method for manufacturing the AlN crystal 10 in the present embodiment will be described.

FIG. 3 is a cross-sectional view schematically showing the base substrate in the present embodiment. As shown in FIGS. 2 and 3, first, an AlN base substrate 11 is prepared (step S1). In this embodiment, the absorption coefficient for light of a wavelength 280nm is 100 cm ^-1 or more, preferably 1000 cm ^-1 or more, more preferably prepares the AlN underlying substrate 11 is 10000 cm ^-1 or higher. An AlN base substrate 11 having a dislocation density of preferably 1 × 10 ⁷ cm ⁻² or less, more preferably 1 × 10 ⁶ cm ⁻² or less is prepared. In this case, an AlN crystal 10 having a low dislocation density can be grown on the AlN base substrate 11.

  Specifically, a base substrate for growing the AlN base substrate 11 is prepared. The base substrate may be AlN or a different substrate made of a material other than AlN. An AlN base substrate 11 is grown on the base substrate. The growth method is not particularly limited. Sublimation method, HVPE (Hydride Vapor Phase Epitaxy) method, MBE (Molecular Beam Epitaxy) method, MOCVD (Metal Organic Chemical Vapor Deposition) It is possible to employ a vapor phase growth method such as a deposition method, a liquid phase method such as a flux method, a high nitrogen pressure solution method, or the like. The base substrate is removed from the AlN base substrate 11 as necessary.

In order to prepare the AlN base substrate 11 having an absorption coefficient of 100 cm ⁻¹ or more, the AlN base substrate 11 is preferably grown so as to contain 2 ppm or more group 14 element. For example, when the AlN base substrate 11 is grown, a raw material in which a group 14 element of 2 ppm or more is added to AlN in the raw material is prepared. The upper limit of the group 14 element contained in the raw material is, for example, 0.1%. As a supply source of the group 14 element, at least one of Si and C is preferably used, and SiC is preferably mixed with the raw material AlN.

Further, when the AlN base substrate 11 is grown, it is grown to have a thickness H11 of preferably 200 μm or more, more preferably 1 mm or more. When the AlN base substrate 11 is grown to have a thickness H11 of 200 μm or more, the crystallinity of the AlN base substrate 11 can be improved, preferably 1 × 10 ⁷ cm ⁻² or less, more preferably 1 × 10 ^6. An AlN crystal having a dislocation density of cm ⁻² or less can be obtained. An AlN crystal having a thickness of 200 μm or more may be grown to cut out the AlN base substrate 11 having a predetermined thickness H11.

  The main surface 11a of the AlN base substrate 11 has a size of, for example, 2 inches or more. Thereby, the large-diameter AlN crystal 10 can be grown.

  In addition, the method of preparing the AlN base substrate 11 is not particularly limited to this, and is prepared by an arbitrary method.

FIG. 4 is a cross-sectional view schematically showing a state in which an AlN crystal is grown in the present embodiment. Next, as shown in FIGS. 2 and 4, an AlN crystal 10 is grown on the main surface 11a of the AlN base substrate 11 (step S2). In this step S2, an AlN crystal 10 having an absorption coefficient for light having a wavelength of 280 nm or less is less than 100 cm ⁻¹ , preferably 7 cm ⁻¹ or less.

The growth method of the AlN crystal 10 is not particularly limited, and a vapor phase growth method such as a sublimation method, HVPE method, MBE method, or MOCVD method, a liquid phase method such as a flux method, a high nitrogen pressure solution method, or the like can be employed. . In order to grow the AlN crystal 10 having an absorption coefficient of less than 100 cm ^−1, it is preferable to prepare a raw material having a high purity, for example.

In the growing step S2, the AlN crystal 10 is grown so as to have a dislocation density of preferably 1 × 10 ⁷ cm ⁻² or less, more preferably 1 × 10 ⁶ cm ⁻² or less. In the present embodiment, it is possible to suppress an increase in the dislocation density due to the difference in the lattice mismatch ratio between the growing AlN crystal 10 and the AlN base substrate 11, and thus, the AlN crystal 10 having a low dislocation density is thus obtained. Can grow. The lower the dislocation density, the better. However, from the viewpoint of easy production, the lower limit of the dislocation density is, for example, about 1 × 10 ² cm ⁻² .

  In the growing step S2, the AlN crystal 10 is grown so that the light transmittance is preferably 50% or more, and particularly the light transmittance of a wavelength of 280 nm or less is 50% or more. In order to have such a transmittance, for example, it is preferable to adjust the film thickness of the growing AlN crystal 10.

  In the present embodiment, in the growing step S2, the thin-film AlN crystal 10 is grown from the viewpoint of reducing the cost and increasing the transmittance.

  FIG. 5 is a cross-sectional view schematically showing a state in which light is irradiated from the AlN crystal side in the present embodiment. FIG. 6 is a cross-sectional view schematically showing a state where the AlN crystal and the AlN base substrate are separated in the present embodiment. Next, as shown in FIGS. 2, 5, and 6, the AlN crystal 10 is separated from the AlN base substrate 11 (step S3). In this step S3, light is irradiated from the AlN crystal substrate 10 which is the other side of the AlN base substrate 11 and the AlN crystal 10 which has a low absorption coefficient toward the AlN base substrate 11 which is one side which has a high absorption coefficient. . In the present embodiment, light is irradiated from above the growth surface of the AlN crystal 10 toward all interfaces between the AlN crystal 10 and the AlN base substrate 11.

  The light to be irradiated preferably has a wavelength of 300 nm or less, more preferably 266 nm or less. As a light source for irradiating such light, for example, a laser is used.

When light is irradiated from the side of the AlN crystal 10 having a low absorption coefficient in this way, the AlN crystal 10 has a light absorption coefficient of less than 100 cm ⁻¹ for light having a wavelength of 280 nm or less, and thus the AlN crystal 10 hardly absorbs light. Transparent. For this reason, even if light is irradiated to the AlN crystal 10, the influence on the good crystallinity of the AlN crystal 10 can be reduced. On the other hand, since the absorption coefficient of light with a wavelength of 280 nm or less of the AlN base substrate 11 is 100 cm ⁻¹ or more, the light transmitted through the AlN crystal 10 is absorbed by the AlN base substrate 11 located at the interface with the AlN crystal 10. The As a result, the temperature of the region near the interface with the AlN crystal 10 in the AlN base substrate 11 rises, the bond between Al atoms and N atoms in the AlN base substrate 11 is released, and the N atoms are dissociated. As a result, the AlN base substrate 11 and the AlN crystal 10 are separated. That is, the AlN base substrate 11 can be removed from the AlN crystal 10 without applying mechanical stress.

  By performing the above steps S1 to S3, the AlN crystal 10 shown in FIG. 1 can be manufactured. The AlN base substrate 11 separated from the AlN crystal 10 is reused as a base substrate for growing another AlN crystal 10, and the above-described steps S2 and S3 are carried out, so that one AlN base substrate is obtained. A plurality of AlN crystals 10 can be manufactured from 11.

  Since the AlN crystal 10 manufactured in this manner is grown on the AlN base substrate 11, the crystallinity can be improved. Furthermore, since the AlN crystal 10 is manufactured without applying mechanical stress, it is possible to suppress the deterioration of the crystallinity of the AlN crystal 10 due to the removal of the AlN base substrate 11. Therefore, according to the present embodiment, the AlN crystal 10 with improved crystallinity can be realized.

  In the present embodiment, it is not necessary to grow the AlN crystal by adding the thickness to be removed as in the case of mechanical processing such as polishing and slicing. For this reason, the material cost of the AlN crystal to be removed can be reduced. Therefore, the method for manufacturing the AlN crystal 10 in the present embodiment is advantageous in terms of cost.

  The AlN crystal 10 thus manufactured with improved crystallinity and reduced cost is produced by, for example, light emitting elements such as light emitting diodes and laser diodes, rectifiers, bipolar transistors, field effect transistors, HEMTs (High Electron Mobility Transistors). Electronic devices such as high electron mobility transistors), temperature sensors, pressure sensors, radiation sensors, semiconductor sensors such as visible-ultraviolet light detectors, SAW devices (surface acoustic wave devices), vibrators, resonances It can be suitably used for a substrate for a device such as a child, an oscillator, a micro electro mechanical system (MEMS) component, or a piezoelectric actuator.

(Embodiment 2)
FIG. 7 is a cross-sectional view schematically showing an AlN crystal in the present embodiment. With reference to FIG. 7, the AlN crystal 15 in the present embodiment will be described.

As shown in FIG. 1, the AlN crystal 15 in the present embodiment has an absorption coefficient for light having a wavelength of 280 nm or less of 100 cm ⁻¹ or more and preferably 1000 cm ⁻¹ or more.

The dislocation density of the AlN crystal 15 is the same as that of Embodiment 1, and is preferably 1 × 10 ⁷ cm ⁻² or less, more preferably 1 × 10 ⁶ cm ⁻² or less. The shape of the AlN crystal 10 is not particularly limited, but is a thin film as in the first embodiment, for example.

Next, a method for manufacturing the AlN crystal 15 in the present embodiment will be described with reference to FIG. The manufacturing method of the AlN crystal 15 in the present embodiment is basically the same as the manufacturing method of the AlN crystal 10 in the first embodiment, but the AlN crystal 15 has an absorption coefficient of 100 cm for light having a wavelength of 280 nm or less. ^-1 or more (one), and the AlN base substrate 16 is different from the first embodiment in that the absorption coefficient for light having a wavelength of 280 nm or less is less than 100 cm ^-1 (the other). That is, the present embodiment is different in that the absorption coefficient of the AlN crystal 15 is lower than that of the AlN base substrate 16 and light is irradiated from the AlN base substrate 16 (the other side).

Specifically, first, an AlN base substrate 16 is prepared (step S1). In the present embodiment, an AlN base substrate 16 having an absorption coefficient for light having a wavelength of 280 nm or less is less than 100 cm ⁻¹ , preferably 7 cm ⁻¹ or less. The method of preparing the AlN base substrate 16 is different from that of the first embodiment in that the AlN base substrate 16 is manufactured using, for example, a raw material having a low impurity concentration, that is, a high raw material purity.

  Further, in the preparing step S1, it is preferable to prepare the AlN base substrate 11 so that the light transmittance is preferably 50% or more, and particularly the light transmittance of a wavelength of 280 nm or less is 50% or more.

Next, an AlN crystal 15 is grown on the AlN base substrate 16 (step S2). In this step S2, an AlN crystal 15 having an absorption coefficient for light having a wavelength of 280 nm or less of 100 cm ⁻¹ or more, preferably 1000 cm ⁻¹ or more is grown.

As a method for growing such an AlN crystal 15, it is preferable to grow the AlN crystal 15 so as to contain a 14-group element of 2 ppm or more. For example, when the AlN crystal 15 is grown, a raw material for the AlN crystal 15 is prepared so that the AlN crystal 15 contains a group 14 element of 2 ppm or more. The upper limit of the group 14 element contained in the raw material is, for example, 0.1%. As a supply source of the group 14 element, at least one of Si and C is preferably used, and SiC is preferably mixed with the raw material AlN. In the case of this impurity, the AlN crystal 15 having an absorption coefficient of 100 cm ⁻¹ or more can be grown, and the dislocation density of the grown AlN crystal 15 can be kept low.

In the growing step S2, as in the first embodiment, the AlN crystal 10 is grown so as to have a dislocation density of preferably 1 × 10 ⁷ cm ⁻² or less, more preferably 1 × 10 ⁶ cm ⁻² or less. In step S2, the thin AlN crystal 10 is grown from the viewpoint of cost reduction, as in the first embodiment.

  FIG. 8 is a cross-sectional view schematically showing a state in which light is irradiated from the AlN crystal side in the present embodiment. FIG. 8 is a cross-sectional view schematically showing a state where the AlN crystal and the AlN base substrate are separated in the present embodiment. Next, as shown in FIGS. 2 and 8, the AlN crystal 15 is separated from the AlN base substrate 16 (step S3). In this step S3, light is irradiated from the AlN base substrate 16 side, which is the other side of the AlN base substrate 16 and the AlN crystal 15, which has the low absorption coefficient, to the AlN crystal 15 which is the one side, which has a high absorption coefficient. The light to be irradiated has a wavelength of preferably 300 nm or less, more preferably 266 nm or less, as in the first embodiment.

Thus, when light is irradiated from the AlN base substrate 16 side, the AlN base substrate 16 has an absorption coefficient of less than 100 cm ⁻¹ for light with a wavelength of 280 nm or less. Is done. Since the absorption coefficient of light with a wavelength of 280 nm or less of the AlN crystal 15 is 100 cm ⁻¹ or more, the light transmitted through the AlN base substrate 16 is absorbed by the AlN crystal 15 located at the interface with the AlN base substrate 16. Thereby, the temperature of the AlN crystal 15 in the vicinity of the interface with the AlN base substrate 16 rises, the bond between the Al atom and the N atom is released, and the N atom is dissociated. As a result, the AlN base substrate 16 and the AlN crystal 15 are separated. That is, the AlN base substrate 16 can be removed from the AlN crystal 15 without applying mechanical stress.

  By performing the above steps S1 to S3, the AlN crystal 15 shown in FIG. 7 can be manufactured.

(Embodiment 3)
FIG. 9 is a cross-sectional view schematically showing an AlN substrate in the present embodiment. With reference to FIG. 9, the AlN substrate 20 in the present embodiment will be described.

  As shown in FIG. 9, the AlN substrate 20 includes a heterogeneous substrate 21, a connection layer 22 formed on the heterogeneous substrate 21, and an AlN crystal 10 formed on the connection layer 22.

  The AlN crystal 10 is the same as the AlN crystal 10 of the first embodiment. Instead of the AlN crystal 10, the AlN crystal 15 of the second embodiment may be used. The heterogeneous substrate 21 is a material different from AlN, and is preferably a material having a lower cost than AlN. For example, a Si substrate, a sapphire substrate, or the like is preferably used.

Then, the manufacturing method of the AlN substrate 20 in this Embodiment is demonstrated.
First, the AlN crystal 10 is manufactured according to the method for manufacturing the AlN crystal 10 of the first embodiment. The AlN crystal 15 may be manufactured according to the method of manufacturing the AlN crystal 15 of the second embodiment.

  Next, a heterogeneous substrate 21 made of the above-described material is prepared. Then, the heterogeneous substrate 21 and the AlN crystal 10 are connected by the connection layer 22 made of the above-described material. This connection layer 22 is, for example, solder, and solder-connects the dissimilar substrate 21 and the AlN crystal 10. As a result, the AlN crystal 10 can be wafer-bonded on the heterogeneous substrate 21.

  By performing the above steps, the AlN substrate 20 shown in FIG. 9 can be manufactured. Even if the thickness of the AlN crystal 10 is thin, it can be used as a substrate for the above-described applications. For this reason, the AlN substrate 20 with improved crystallinity and reduced cost can be manufactured.

(Embodiment 4)
FIG. 10 is a cross-sectional view schematically showing the piezoelectric vibrator in the present embodiment. With reference to FIG. 10, the piezoelectric vibrator 30 according to the present embodiment will be described.

  As shown in FIG. 10, the piezoelectric vibrator 30 includes an AlN crystal 10, an electrode layer 31 formed on the lower surface of the AlN crystal 10, and an electrode layer 32 formed on the upper surface of the AlN crystal 10.

  The AlN crystal 10 is the same as the AlN crystal 10 of the first embodiment. The AlN crystal 10 has a plate shape. Instead of the AlN crystal 10, the AlN crystal 15 of the second embodiment may be used. The pair of electrode layers 31 and 32 sandwich both surfaces of the AlN crystal 10. The electrode layers 31 and 32 can be made of an anisotropic conductive material, metal, or the like having a small conductive resistance in the thickness direction.

Next, a method for manufacturing the piezoelectric vibrator 30 in the present embodiment will be described.
First, the AlN crystal 10 is manufactured according to the method for manufacturing the AlN crystal 10 of the first embodiment. If necessary, a step of processing the AlN crystal 10 into a predetermined shape as a piezoelectric vibration member is further performed. The AlN crystal 15 may be manufactured according to the method of manufacturing the AlN crystal 15 of the second embodiment.

  Next, the electrode layer 31 is formed on the lower surface of the AlN crystal 10, and the electrode layer 32 is formed on the upper surface. The formation method of the electrode layers 31 and 32 is not specifically limited, For example, it can form by a vapor deposition method etc.

By performing the above steps, the piezoelectric vibrator shown in FIG. 10 can be manufactured. Since the piezoelectric vibrator manufactured in this manner uses an AlN crystal with improved crystallinity as a piezoelectric vibration member, a piezoelectric vibrator having an excellent electromechanical coupling coefficient kt ² and an acoustic quality factor (Q value) is manufactured. be able to.

  In this example, the effect of irradiating light from the other side having a low absorption coefficient to the one side having a high absorption coefficient among the AlN base substrate and the AlN crystal was examined.

  Specifically, an AlN crystal was grown by a sublimation method using the crystal growth apparatus 100 shown in FIG. FIG. 11 is a schematic diagram showing the crystal growth apparatus used in this example.

  As shown in FIG. 11, the crystal growth apparatus 100 mainly includes a crucible 115, a heating body 119, a reaction vessel 122, and a high-frequency heating coil 123. A heating body 119 is provided around the crucible 115 so as to ensure ventilation between the inside and outside of the crucible 115. A reaction vessel 122 is provided around the heating body 119. A high-frequency heating coil 123 for heating the heating body 119 is provided at the outer central portion of the reaction vessel 122. In addition, radiation thermometers 121 a and 121 b for measuring temperatures above and below the crucible 115 are provided at the upper and lower portions of the reaction vessel 122.

  The crystal growth apparatus 100 may include various elements other than those described above, but illustration and description of these elements are omitted for convenience of description.

  First, in step S1 for preparing the AlN base substrate 11, the following procedure was performed. Specifically, a SiC substrate was prepared as a base substrate for growing the AlN base substrate 11. This base substrate was placed on top of the crucible 115 in the reaction vessel 122. As a raw material 17 for the AlN base substrate 11, a raw material comprising AlN powder and 3% by mass of SiC powder with respect to the AlN powder was prepared. This raw material 17 was accommodated in the lower part of the crucible 115. Thereafter, while flowing nitrogen gas into the reaction vessel 122, the temperature in the crucible 115 is increased using the high-frequency heating coil 123, the temperature of the SiC base substrate is 1900 ° C., the temperature of the raw material 17 is 2000 ° C., and the raw material 17 is Sublimation and recrystallization were performed on the SiC base substrate to grow an AlN crystal having a thickness of 5 mm on the SiC base substrate with a growth time of 30 hours.

  During the growth of the AlN crystal constituting the AlN base substrate 11, the nitrogen gas is continuously supplied to the reaction vessel 122, and the nitrogen gas is exhausted so that the gas partial pressure in the reaction vessel 122 is about 10 kPa to 100 kPa. The amount was controlled.

Both surfaces of the obtained AlN crystal were mirror-polished to prepare an AlN base substrate 11. As a result of measuring the absorption coefficient at 300 K and a wavelength of 280 nm for this AlN base substrate 11 with an ultraviolet-visible spectrophotometer, it was 200 cm ⁻¹ or more. When the dislocation density was evaluated, it was measured to be 8 × 10 ⁵ cm ⁻² .

  Next, in step S2 for growing the AlN crystal 10 on the AlN base substrate 11, the following procedure was performed. Specifically, the AlN base substrate 11 was placed on the crucible 115 in the reaction vessel 122. A high-purity AlN powder was prepared as a raw material 17 for the AlN crystal 10. This raw material 17 was accommodated in the lower part of the crucible 115. Thereafter, while flowing nitrogen gas into the reaction vessel 122, the temperature in the crucible 115 is increased using the high-frequency heating coil 123, the temperature of the AlN base substrate 11 is 1800 ° C., the temperature of the raw material 17 is 2000 ° C., and the raw material 17 The AlN crystal 10 having a thickness of 300 μm was grown on the AlN base substrate 11 with a growth time of 3 hours.

  During the growth of the AlN crystal 10, the nitrogen gas was continuously flowed into the reaction vessel 122, and the exhaust amount of the nitrogen gas was controlled so that the gas partial pressure in the reaction vessel 122 became about 10 kPa to 100 kPa.

When the dislocation density of the obtained AlN crystal 10 was evaluated, it was measured to be 1 × 10 ⁶ cm ⁻² . Moreover, as a result of measuring the absorption coefficient in 300K and wavelength 280nm with the ultraviolet visible spectrophotometer, it was 25 cm <^-1> or less.

  Next, in step S3 for separating the AlN base substrate 11 from the AlN crystal 10, the following procedure was performed. Specifically, as shown in FIG. 5, Nd (neodymium) − from the growth surface side of the AlN crystal 10 toward the AlN base substrate 11 in a state where the AlN base substrate 11 and the AlN crystal 10 are laminated. YAG laser harmonics (wavelength 266 nm) were irradiated.

  As a result, the AlN crystal 10 and the AlN base substrate 11 were peeled off at the interface between the AlN crystal 10 and the AlN base substrate 11. As a result, the AlN base substrate 11 could be removed from the AlN crystal 10.

As described above, according to the present example, even when the AlN base substrate 11 is used to grow the AlN crystal 10 having good crystallinity, the absorption coefficient for the light of the wavelength of the AlN crystal 10 is 10 cm ^−. If the absorption coefficient for light of the wavelength of the AlN base substrate 11 is less than ^{1 and} is 10 cm ⁻¹ or more, no mechanical stress is applied by irradiating light from the other side (AlN crystal 10 side) having a low absorption coefficient. Further, it was confirmed that the AlN base substrate 11 can be removed from the AlN crystal 10.

  Although the embodiments and examples of the present invention have been described above, it is also planned from the beginning to appropriately combine the features of the embodiments and examples. The embodiments and examples disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims for patent, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims for patent.

It is sectional drawing which shows schematically the AlN crystal in Embodiment 1 of this invention. It is a flowchart which shows the manufacturing method of the AlN crystal in Embodiment 1 of this invention. It is sectional drawing which shows schematically the base substrate in Embodiment 1 of this invention. It is sectional drawing which shows roughly the state as which the AlN crystal was grown in Embodiment 1 of this invention. It is sectional drawing which shows roughly the state which has irradiated the light from the AlN crystal | crystallization side in Embodiment 1 of this invention. It is sectional drawing which shows schematically the state which the AlN crystal | crystallization and the AlN base substrate isolate | separated in Embodiment 1 of this invention. It is sectional drawing which shows roughly the AlN crystal in Embodiment 2 of this invention. It is sectional drawing which shows schematically the state which has irradiated the light from the AlN crystal side in Embodiment 3 of this invention. It is sectional drawing which shows schematically the AlN board | substrate in Embodiment 3 of this invention. It is sectional drawing which shows schematically the piezoelectric vibrator in Embodiment 4 of this invention. It is the schematic which shows the crystal growth apparatus used for the Example.

Explanation of symbols

  10, 15 AlN crystal, 11, 16 AlN base substrate, 11a main surface, 17 raw material, 20 AlN substrate, 21 heterogeneous substrate, 22 connection layer, 30 piezoelectric vibrator, 31, 32 electrode layer, 100 crystal growth apparatus, 115 crucible 119 heating body, 121a, 121b radiation thermometer, 122 reaction vessel, 123 high frequency heating coil.

Claims (7)

Preparing an AlN base substrate;
Growing an AlN crystal on the AlN base substrate;
Separating the AlN base substrate from the AlN crystal,
One of the AlN base substrate and the AlN crystal has an absorption coefficient of 100 cm ⁻¹ or more for light having a wavelength of 280 nm or less, and the other of the AlN base substrate and the AlN crystal has a wavelength of 220 nm or more and 280 nm or less. An absorption coefficient of less than 100 cm ⁻¹ for light in at least some wavelength regions,
The method of manufacturing an AlN crystal, wherein in the separating step, light is irradiated from the other side having a low absorption coefficient among the AlN base substrate and the AlN crystal.   The method for producing an AlN crystal according to claim 1, wherein in the separating step, the light having a wavelength of 300 nm or less is irradiated. 3. The method for producing an AlN crystal according to claim 1, wherein in the growing step, the AlN crystal having a dislocation density of 1 × 10 ⁷ cm ⁻² or less is grown.   One of the said AlN base substrate and the said AlN crystal | crystallization is a manufacturing method of the AlN crystal | crystallization in any one of Claims 1-3 containing 2 ppm or more of 14 group elements.   5. The method for producing an AlN crystal according to claim 1, wherein, in the preparing step, the base substrate having a thickness of 200 μm or more is prepared. A step of producing an AlN crystal by the method of producing an AlN crystal according to claim 1;
Forming the AlN crystal on a heterogeneous substrate. A step of producing an AlN crystal by the method of producing an AlN crystal according to claim 1;
And a step of forming an electrode layer on the AlN crystal.

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