JP4565062B2 - Thin film single crystal growth method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for growing a thin film single crystal, and more particularly to a method for growing a thin film single crystal capable of forming a high-quality thin film single crystal.
[0002]
[Prior art]
Light-emitting elements in the ultraviolet region are particularly expected for the realization of mercury-free fluorescent lamps, photocatalysts that provide a clean environment, and new-generation DVDs that realize higher-density recording. Against this background, GaN-based blue light-emitting elements have been realized, but further light sources with shorter wavelengths have been demanded. In recent years, as a conventional thin film growth method for growing a ZnO thin film on a substrate, PLD ( A Pulsed Laser Deposition method has been proposed (see, for example, Patent Document 1).
[0003]
According to the PLD method described in Patent Document 1, a ZnO target, which is a composition material of a target thin film, is pulsedly irradiated with a laser in a very low pressure oxygen atmosphere, and components constituting the target are converted into a plasma or a molecular state. A thin film of ZnO is grown on the substrate by flying to the substrate. Thereby, a thin film can be easily produced with a simple apparatus.
[0004]
[Patent Document 1]
JP 2002-68889 A (FIG. 3)
[0005]
[Problems to be solved by the invention]
However, in the conventional thin film growth method, ZnO is liberated as a cluster from the target made of the composition material of the target thin film, and it may be deposited on the substrate as it is, so that the ZnO molecules are uneven on the substrate. Therefore, a thin film with poor surface flatness may be formed. Further, since the target may be deteriorated or deteriorated by laser irradiation, it has been a factor that hinders the growth of the thin film single crystal.
[0006]
Accordingly, an object of the present invention is to provide a method for growing a thin film single crystal capable of forming a high quality thin film single crystal.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention prepares a substrate made of β-Ga ₂ O ₃ single crystal , and irradiates a metal target made of a pure metal or alloy with an excitation beam from the metal target to the pure metal or the metal. In an atmosphere of a gas that liberates atoms, molecules, or ions of the alloy and binds to the released atoms, molecules, or ions, the atoms, molecules, or ions and the gas are present on the substrate. Provided is a method for growing a thin film single crystal characterized by growing a single crystal thin film formed by bonding .
[0008]
According to this configuration, when a metal target is irradiated with an excitation beam, the metal atoms constituting the metal target are excited, and chemical species such as metal atoms, molecules, ions, etc. are generated from the metal target by thermal and photochemical action. The liberated chemical species bind to radicals in the atmosphere, which grows on the substrate and forms a thin film on the substrate.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a schematic configuration of a film forming apparatus according to a first embodiment of the present invention. This film forming apparatus 1 forms a film by the PLD method, and includes a chamber 2 having a space 20 that can be evacuated, a target base 5 that holds a target 3 disposed in the chamber 2, and an outside of the chamber 2. , A rotation mechanism 11 that rotates the target base 5, a substrate holding unit 7 that is disposed in the chamber 2, holds the substrate 6, and includes a heater that can heat the substrate 6 to 1500 ° C., and the chamber 2. A radical injection part 8 for injecting radicals from the pipe 2a, an exhaust part 9 having a vacuum pump (not shown) for exhausting the space part 20 and evacuating the space part 20 through the pipe 2b; And a laser unit 4 that irradiates the target 3 with laser light as an excitation beam.
[0010]
The target 3 is made of a pure metal or an alloy, for example, high-purity Ga or an alloy containing Ga.
[0011]
The laser unit 4 includes a laser oscillating unit 41 that irradiates a laser beam 42 in a pulse form using an Nd: YAG laser, a KrF excimer laser, an ArF excimer laser, or the like as a laser source, and a laser beam 42 emitted from the laser oscillating unit 41 as a target. 3 and lenses 43 and 44 for condensing light.
[0012]
The substrate 6 faces the target 3 so that chemical species such as metal atoms 33 dissociated from the target 3 can contribute to film formation when the target 3 is irradiated with the laser beam 42.
[0013]
The radical injection section 8, NH ₃ containing oxygen gas containing oxygen gas, ozone, pure ozone gas, N ₂ O gas, NO ₂ gas, oxygen gas containing oxygen radicals, oxygen radicals, nitrogen radicals, NH ₃ gas, nitrogen radicals One or two or more gases among the gases, that is, a gas bonded to atoms liberated from the target 3 during film formation is injected into the space portion 20.
[0014]
Next, a method for growing a thin film single crystal according to the first embodiment will be described. This growth method includes a step of preparing a substrate 6 for growing a thin film and a step of growing a thin film on the substrate 6. Here, the case of forming a thin film made of β-Ga ₂ O ₃ on a substrate 6 made of β-Ga ₂ O _3.
[0015]
(1) Preparation of Substrate 6 First, a β-Ga ₂ O ₃ single crystal is formed by FZ (Floating Zone) method. That is, both are melted in the contact portion between the β-Ga ₂ O ₃ seed crystal and the β-Ga ₂ O ₃ polycrystalline material in the quartz tube. When dissolved β-Ga ₂ O ₃ polycrystalline raw material is lowered together with the β-Ga ₂ O ₃ seed crystal, β-Ga ₂ O ₃ or β-Ga ₂ O ₃ single crystal on the crystal is generated. Next, the substrate 6 is produced from this β-Ga ₂ O ₃ single crystal. Note that when the crystal is grown in the b-axis <010> orientation, the cleavage of the (100) plane becomes strong, and thus the substrate 6 is manufactured by cutting along a plane perpendicular to the (100) plane. . When the crystal is grown in the a-axis <100> orientation and the c-axis <001> orientation, the cleaving properties of the (100) plane and (001) are weakened, so that the workability of all the faces is improved, as described above. There is no limit on the cut surface.
[0016]
(2) Growth of Thin Film A thin film is grown on the substrate 6 by using the film forming apparatus 1 described above. That is, for example, the target 3 made of Ga is fixed to the target base 5 as the target 3. A substrate 6 made of a β-Ga ₂ O ₃ single crystal is held on the substrate holder 7. The air in the space part 20 is exhausted by the vacuum pump of the exhaust part 9, and the degree of vacuum in the space part 20 is set to about 1 × 10 ⁻⁹ torr, for example, and then oxygen gas is injected into the space part 20 for example. The heater (not shown) is energized by the substrate holding unit 7 at about 10 ⁻⁷ torr, and the temperature of the substrate 6 is heated to 300 ° C. to 1500 ° C., for example. Next, oxygen radicals are injected into the space 20 by the radical injection part 8 to obtain 1 × 10 ⁻⁴ to 1 × 10 ⁻⁶ torr. When the laser beam 42 having a laser output of 100 mW, a repetition frequency of 10 Hz, and a wavelength of 266 nm is irradiated from the laser unit 4 to the rotating target 3, the Ga atoms constituting the target 3 are excited and are thermally and photochemically. By the action, chemical species such as Ga atoms, Ga ions, excited Ga atoms, and excited Ga ions emitted from the target 3 are combined with oxygen radicals in the atmosphere on the substrate 6 to form a β-Ga ₂ O ₃ single crystal. Is done. The formed β-Ga ₂ O ₃ single crystal grows on the substrate 6, and a β-Ga ₂ O ₃ thin film single crystal is formed on the substrate 6. The grown β-Ga ₂ O ₃ thin film single crystal exhibited n-type conductivity. This conductivity is thought to be due to oxygen defects.
[0017]
According to the first embodiment, the following effects can be obtained.
(B) Since chemical species such as metal atoms, metal ions, excited metal atoms, and excited metal ions released from the target 3 are combined with atoms in the atmosphere, β-Ga ₂ O having high surface flatness and high quality is obtained. _A thin film made of _three single crystals can be grown on a substrate.
[0018]
FIG. 2 shows a cross section of a MIS type light emitting device according to the second embodiment of the present invention. The MIS type light emitting device 60 includes a substrate 6 made of β-Ga ₂ O ₃ single crystal, a β-Ga ₂ O ₃ thin film single crystal 61 having n-type conductivity formed on the upper surface of the substrate 6, Insulating layer 62 made of β-Ga ₂ O ₃ thin film crystal formed on the upper surface of n-type β-Ga ₂ O ₃ thin film single crystal 61, gold electrode 63 formed on the upper surface of insulating layer 62, and gold electrode And a bonding 67 attached to the lower surface of the substrate 6 and connected to the lead 66.
[0019]
The insulating layer 62 is free from oxygen defects of 10 to 1000 nm on the surface formed by annealing at 900 ° C. in an oxygen atmosphere.
[0020]
According to the light emitting device 60 according to the second embodiment, a light emitting device having an emission wavelength near 260 nm is obtained.
[0021]
Next, a third embodiment of the present invention will be described. In the third embodiment, the film forming apparatus 1 according to the first embodiment is used. However, the target 3 uses Zn or a metal made of an alloy containing Zn, and grows a ZnO-based thin film single crystal on the substrate.
[0022]
According to the third embodiment, when a metal target made of Zn or an alloy containing Zn is irradiated with an excitation beam, the metal target is constituted, but Zn atoms or other atoms are excited, and thermal / photochemistry is performed. By chemical action, chemical species such as Zn atoms, Zn ions, excited Zn atoms, and excited Zn ions emitted from the metal target are combined with radicals in the atmosphere, which grow on the substrate and form a ZnO-based thin film on the substrate. A single crystal is formed.
[0023]
A buffer layer made of a ZnO-based thin film crystal may be grown on a substrate made of a β-Ga ₂ O ₃ -based single crystal, and a ZnO-based thin film single crystal may be grown on the buffer layer. According to this configuration, since a ZnO-based thin film single crystal of the same kind as the buffer layer is grown on the buffer layer, a lattice mismatch is reduced, and a ZnO-based thin film single crystal having good crystallinity can be formed. it can.
[0024]
A fourth embodiment of the present invention will be described. In the fourth embodiment, the film forming apparatus 1 according to the first embodiment is used. However, the atmosphere is composed of one or more of nitrogen radicals, NH ₃ gas, and NH ₃ gas containing nitrogen radicals, and a GaN-based thin film single crystal is grown on the substrate.
[0025]
According to the fourth embodiment, when an excitation beam is irradiated onto a metal target made of Ga or an alloy containing Ga, the metal target is constituted, but Ga atoms or other atoms are excited, and thermal / photochemistry is performed. By chemical action, chemical species such as Ga atoms, Ga ions, excited Ga atoms, and excited Ga ions emitted from the metal target are combined with radicals in the atmosphere, which grow on the substrate and grow on the substrate. A single crystal is formed.
[0026]
A buffer layer made of a GaN-based thin film crystal may be grown on a substrate made of a β-Ga ₂ O ₃ -based single crystal, and the GaN-based thin film single crystal may be grown on the buffer layer. According to this configuration, in order to grow the same kind of GaN-based thin film single crystal of the same kind as the buffer layer on the buffer layer, lattice mismatch is reduced, and a GaN-based thin film single crystal having good crystallinity is formed. be able to.
[0027]
【Example】
Next, examples of the present invention will be described. In this example, a thin film single crystal is grown on the substrate 6 by embodying the conditions shown in the first embodiment.
[0028]
In Example 1 of the present invention, Ga is used as the material of the target 3, and β-Ga ₂ O ₃ is used as the substrate 6. While oxygen radicals are injected, the substrate temperature is 400 ° C., the laser output is 100 mW, The target 3 is irradiated with laser light 42 having a repetition frequency of 10 Hz and a degree of vacuum of 1 × 10 ⁻⁵ torr and a wavelength of 266 nm.
This laser oscillation unit 41 has a fundamental wave of 1.064 μm, which is the oscillation wavelength of a Qsw Nd: YAG laser, and uses a non-illustrated nonlinear optical crystal to pulsate 355 nm, which is a third harmonic, and 266 nm, which is a fourth harmonic. Is possible. After irradiation with the laser beam 42, a colorless and transparent β-Ga ₂ O ₃ thin film was grown on the β-Ga ₂ O ₃ substrate 6. FIG. 3 shows an atomic force microscope (AFM) photograph of the β-Ga ₂ O ₃ thin film of Example 1.
[0029]
In Example 2 of the present invention, the substrate temperature in Example 1 was set to 1000 ° C., and the other conditions were the same as those in Example 1. 4 shows an atomic force microscope (AFM) photograph of the β-Ga ₂ O ₃ thin film of Example 2, and FIG. 9A shows a pattern by reflection high-energy electron diffraction (RHEED). As is clear from FIG. 9A, it can be seen that a high-quality β-Ga ₂ O ₃ thin film single crystal has grown.
[0030]
In Example 3 of the present invention, Ga is used as the material of the target 3 and the substrate 6 is made of β-Ga ₂ O ₃ , and the substrate temperature is 400 ° C. while irradiating N ₂ O radicals, and the laser output. The target 3 is irradiated with laser light 42 having a wavelength of 266 nm at 100 mW, a repetition frequency of 10 Hz, and a degree of vacuum of 1 × 10 ⁻⁵ torr.
FIG. 5 shows an atomic force microscope (AFM) photograph of the β-Ga ₂ O ₃ thin film of Example 3.
[0031]
In Example 4 of the present invention, the substrate temperature in Example 3 was set to 1000 ° C., and the other conditions were the same as those in Example 3. 6 shows an atomic force microscope (AFM) photograph of the β-Ga ₂ O ₃ thin film of Example 4, and FIG. 9B shows a pattern by reflection high-energy electron diffraction (RHEED). As is apparent from FIG. 9B, it can be seen that a high-quality β-Ga ₂ O ₃ thin film single crystal has grown.
[0032]
FIG. 7 shows an atomic force microscope (AFM) photograph of a β-Ga ₂ O ₃ thin film according to Example 5 of the present invention. In Example 5, Ga is used as the material of the target 3 and the substrate 6 is made of β-Ga ₂ O _3. While irradiating oxygen radicals, the substrate temperature is 1000 ° C., the laser output is 100 mW, and the repetition frequency. The target 3 is irradiated with laser light having a wavelength of 355 nm at 10 Hz and a degree of vacuum of 1 × 10 ⁻⁵ torr.
[0033]
FIG. 8 shows a scanning electron microscope (SEM) photograph of the β-Ga ₂ O ₃ thin film according to Comparative Example 1. In this comparative example 1, Ga ₂ O ₃ is used as the material of the target 3 and the substrate 6 is made of β-Ga ₂ O ₃ , the substrate temperature is 1000 ° C., the laser output is 200 mW, the repetition frequency in an oxygen atmosphere. The target 3 is irradiated with laser light 42 having a wavelength of 355 nm at 10 Hz and a degree of vacuum of 1 × 10 ⁻⁵ torr. After irradiation with the laser beam 42, a white thin film grew on the β-Ga ₂ O ₃ substrate 6. This indicates that the cluster-like material is attached to the substrate 6, and the β-Ga ₂ O ₃ film hardly grows.
[0034]
In Comparative Example 2, Ga ₂ O ₃ is used as the material of the target 3, and the substrate 6 is made of β-Ga ₂ O _3. Under a NO ₂ radical atmosphere, the substrate temperature is 1000 ° C., the laser output is 100 mW, and repeated. The target 3 is irradiated with laser light 42 having a frequency of 10 Hz and a degree of vacuum of 1 × 10 ⁻⁵ torr and a wavelength of 266 nm. After irradiation with the laser beam 42, a transparent thin film was grown on the β-Ga ₂ O ₃ substrate 6. FIG. 9C shows a pattern of the grown β-Ga ₂ O ₃ thin film by reflection high-energy electron diffraction (RHEED). As is clear from FIG. 9C, a high-quality β-Ga ₂ O ₃ thin film single crystal has not grown.
[0035]
In Comparative Example 3, Ga ₂ O ₃ is used as the material of the target 3 and the substrate 6 is made of β-Ga ₂ O _3. Under an oxygen radical atmosphere, the substrate temperature is 1000 ° C., the laser output is 100 mW, the repetition frequency. The target 3 is irradiated with laser light 42 having a wavelength of 266 nm at 10 Hz and a degree of vacuum of 1 × 10 ⁻⁵ torr. After irradiation with the laser beam 42, a transparent thin film was grown on the β-Ga ₂ O ₃ substrate 6. FIG. 9D shows a pattern by reflection high-energy electron diffraction (RHEED) of the grown β-Ga ₂ O ₃ thin film. As is apparent from FIG. 9D, a high-quality β-Ga ₂ O ₃ thin film single crystal has not grown.
[0036]
According to each of the above embodiments, a good quality colorless and transparent β-Ga ₂ O is formed on a substrate 6 made of β-Ga ₂ O _{3 in} a N ₂ O radical or oxygen radical atmosphere using a Ga target. ₃ Thin film single crystals could be grown (see FIGS. 3 to 7).
[0037]
On the other hand, according to each comparative example, when a target made of Ga ₂ O ₃ was used, a good thin film single crystal was not generated. This shows that the target made of Ga is suitable for the growth of a thin film single crystal. As can be seen from FIG. 9, a β-Ga ₂ O ₃ thin film single crystal is grown on a substrate 6 in which the presence of N ₂ O radicals or oxygen radicals is made of β-Ga ₂ O ₃ in addition to the Ga target. It is effective in making it.
[0038]
As a method of growing a β-Ga ₂ O ₃ single crystal thin film on a substrate made of β-Ga ₂ O ₃ single crystal, it has been described PLD method, without being limited to the PLD method, MBE method, A physical vapor deposition method such as MOCVD method or a chemical vapor deposition method such as thermal CVD or plasma CVD may be used.
[0039]
The target has been described as a metal plate in terms of its properties, but is not limited to metal, and may be made of a solid other than metal or liquid. Further, the target is not limited to the one made of Ga, but may be an alloy containing Ga, a metal made of Zn or an alloy containing Zn. This increases the degree of freedom in selecting the type of film to be formed.
[0040]
In addition to the laser beam, the excitation beam may be an electron beam, an ion beam, or the like as long as it can irradiate a metal target and release metal atoms and the like.
[0041]
Further, the wavelength of the laser is not limited to 266 nm, and may be other wavelengths such as 355 nm and 193 nm. The laser output may be 10 mW to 400 mW.
[0042]
Furthermore, the substrate temperature may be 300 ° C to 1500 ° C. This temperature range is a temperature range for flattening and densely growing a film to be grown, that is, a temperature range for improving crystallization.
[0043]
The degree of vacuum in the chamber 2 may be 1 to 1 × 10 ⁻¹⁰ torr. Even in this vacuum range, a β-Ga ₂ O ₃ -based thin film single crystal can be grown.
[0044]
【The invention's effect】
As described above, according to the present invention, when a metal target is irradiated with an excitation beam, metal atoms constituting the metal target are excited, and a chemical species such as a metal atom is generated from the metal target by a thermal / photochemical action. Is liberated, and the liberated chemical species are combined with radicals in the atmosphere, which grow on the substrate and form a thin film on the substrate, so that a high-quality thin film single crystal can be formed.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a film forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of a laminate formed by the thin film device according to the first embodiment of the invention.
_{3 is} an atomic force microscope (AFM) photograph of a β-Ga ₂ O ₃ thin film in Example 1 of the present invention. FIG.
FIG. 4 is an atomic force microscope (AFM) photograph of a β-Ga ₂ O ₃ thin film in Example 2 of the present invention.
5 is an atomic force microscope (AFM) photograph of a β-Ga ₂ O ₃ thin film in Example 3 of the present invention. FIG.
FIG. 6 is an atomic force microscope (AFM) photograph of a β-Ga ₂ O ₃ thin film in Example 4 of the present invention.
7 is an atomic force microscope (AFM) photograph of a β-Ga ₂ O ₃ thin film in Example 5 of the present invention. FIG.
8 is a scanning electron microscope (SEM) photograph of a grown β-Ga ₂ O ₃ thin film in Comparative Example 1 of the present invention. FIG.
FIGS. 9A to 9D are photographs of RHEED patterns of each thin film in the presence of each radical.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Film-forming apparatus 2 Chamber 2a Pipe 2b Pipe 3 Target 4 Laser apparatus 5 Target base 6 Substrate 7 Substrate holding part 8 Radical injection part 9 Exhaust part 11 Rotating mechanism 20 Space part 33 Dissociated metal atom 41 Laser oscillation part 42 Laser light 43 44 Lens 60 MIS type light emitting element 61 Thin film single crystal 62 Insulating layer 63, 64 Electrode 65, 67 Bonding 66, 68 Lead

Claims (8)

preparing a substrate made of β-Ga ₂ O ₃ single crystal ,
A metal target made of a pure metal or alloy is irradiated with an excitation beam to release atoms, molecules or ions of the pure metal or alloy from the metal target and bind to the released atoms, molecules or ions. A method for growing a thin film single crystal, comprising growing a single crystal thin film formed by bonding the atoms, molecules, or ions and the gas on the substrate in a gas atmosphere . Atmosphere in the gas, the growth method of the thin-film single crystal according to claim 1, characterized in that it comprises a radical. 2. The method for growing a thin film single crystal according to claim 1, wherein the gas atmosphere has a degree of vacuum of 1-1.times.10.sup.- ¹⁰ torr. 2. The method for growing a thin film single crystal according to claim 1, wherein the gas atmosphere has a degree of vacuum of 1 * 10 < ^-4 > to 1 * 10 < ^-6 > torr.   2. The thin film single crystal growth method according to claim 1, wherein the excitation beam is a laser beam.   The method of growing a thin film single crystal according to claim 1, wherein the substrate is heated to 300 ° C to 1500 ° C. Atmosphere in the gas, oxygen gas containing oxygen gas, ozone, Ri Do pure ozone gas, N 2 _O gas, NO ₂ gas, oxygen gas containing oxygen radicals, and one or more gases of oxygen radicals,
The metal target is made of Ga or an alloy containing Ga,
The thin film of single crystal growth method of the thin-film single crystal according to claim 1, comprising the β-Ga ₂ O ₃ system. The single-crystal thin film made of beta -Ga ₂ O ₃ system, β-Ga ₂ O ₃ system buffer layer is formed of a thin film crystal according to claim 1, wherein the growing the buffer layer Growth method of thin film single crystal.

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