JP6875708B2 - Crystallized structure and method for manufacturing it - Google Patents

Description

The present invention relates to a crystal laminated structure and a method for producing the same.

Conventionally, the MBE (Molecular Beam Epitaxy) method and the PLD (Pulsed Laser Deposition) method are known as methods for growing a β-Ga ₂ O _{3 single crystal film (see, for example, Patent Documents 1 and 2).} Further, a growth method by a sol-gel method, a MOCVD (Metal Organic Chemical Vapor Deposition) method, or a mist CVD method is also known.

Japanese Unexamined Patent Publication No. 2013-56803 Japanese Patent No. 4565062

However, in the MBE method, since the crystal grows in the high vacuum chamber, it is difficult to increase the diameter of _{the β-Ga 2} O _{3 single crystal film.} Further, in general, when the growth temperature is raised, a high-quality film can be obtained, but since the re-evaporation of the raw material gas increases, a sufficient film forming rate cannot be obtained, which is not suitable for mass production.

Further, regarding the PLD method, the source (source of raw material to the substrate) is the point source, and the growth rate differs between the place directly above the source and other places, so that the in-plane distribution of the film thickness tends to be uneven. Not suitable for the growth of large-area membranes. Moreover, since the film formation rate is low and it takes a long time to grow a thick film, it is not suitable for mass production.

Regarding the sol-gel method, MOCVD method, and mist CVD method, it is relatively easy to increase the diameter, but impurities contained in the raw materials used are incorporated into the _{β-Ga 2} O _{3 single crystal film during epitaxial growth.} , It is difficult to obtain a high-purity single crystal film.

Therefore, one object of the present invention, the method of growing β-Ga ₂ O ₃ single crystal film which can be grown β-Ga ₂ O ₃ single crystal film of a high quality and large diameter efficiently It is an object of the present invention to provide a crystal laminated structure having a grown β-Ga ₂ O _{3 system single crystal film, and a method for producing the same.}

One aspect of the present invention provides the following crystal laminated structures [1] and [2] in order to achieve the above object.

[1] and _Ga 2 _{O 3} based substrate, anda _β-Ga 2 _{O 3} single crystal film provided on a main surface of the _Ga 2 _{O 3} based substrate, the _β-Ga 2 _{O 3} system single The crystal film is a crystal laminated structure having a residual carrier concentration of 1 × 10 ¹³ / cm ^{3 or less.}

According to the present invention, according to a _{method for growing a β-Ga 2} O ₃ system single crystal film capable of efficiently growing a high quality and large diameter β-Ga 2 O 3 system single crystal film, and a method for growing the _{β-Ga 2} O _{3 system single crystal film.} A grown crystal laminated structure and a method for producing the same can be provided.

FIG. 1 is a vertical cross-sectional view of the crystal laminated structure according to the embodiment. FIG. 2 is a vertical cross-sectional view of the vapor phase growth apparatus according to the embodiment. FIG. 3 shows the growth driving force and the growth temperature _{of the Ga 2} O ₃ crystal in each of the cases where the gallium chloride-based gas is composed of only GaCl gas and the case where it is composed of only GaCl _{3 gas, which is obtained by the thermal equilibrium calculation.} It is a graph showing a relationship. Figure 4 represents obtained by heat balance calculation, GaCl gas obtained from the reaction of Ga and Cl _2, GaCl ₂ gas, GaCl ₃ gas, and (GaCl ₃₎ the relationship between the equilibrium partial pressure and the ambient temperature of ₂ gas It is a graph. FIG. 5 is a graph showing the relationship between _{the equilibrium partial pressure of GaCl and the O 2 / GaCl supply partial pressure ratio when the atmospheric temperature of Ga 2} O ₃ crystal growth is 1000 ° C., which is obtained by the thermal equilibrium calculation. FIG. 6 was obtained by a 2θ-ω scan of a crystal laminated structure in which a _{Ga 2} O ₃ single crystal film was epitaxially grown on the main surface _{of a Ga 2} O ₃ substrate having a plane orientation of (010). It is a graph which shows the X-ray diffraction spectrum. FIG. 7 shows a 2θ-ω scan of a crystal laminated structure in which a _{Ga 2} O ₃ single crystal film was epitaxially grown at 1000 ° C. on the main surface _{of a Ga 2} O ₃ substrate having a plane orientation of (−201). It is a graph which shows the X-ray diffraction spectrum obtained by. FIG. 8 is obtained by a 2θ-ω scan of a crystal laminated structure in which a _{Ga 2} O ₃ single crystal film is epitaxially grown on the main surface _{of a β-Ga 2} O ₃ substrate having a plane orientation of (001). It is a graph which shows the X-ray diffraction spectrum. FIG. 9 is obtained by a 2θ-ω scan of a crystal laminated structure in which a _{Ga 2} O ₃ single crystal film is epitaxially grown on the main surface _{of a β-Ga 2} O ₃ substrate having a plane orientation of (101). It is a graph which shows the X-ray diffraction spectrum. 10 (a) and 10 (b) are graphs showing the concentration of impurities in the crystal laminated structure measured by secondary ion mass spectrometry (SIMS). FIG. 11A shows carriers in the depth direction in a crystal laminated structure in which a β-Ga ₂ O _{3 crystal film is epitaxially grown on a β-Ga 2} O ₃ substrate whose main surface orientation is (001). It is a graph which shows the profile of density. FIG. 11B is a graph showing the withstand voltage characteristics of the above-mentioned laminated structure. FIG. 12 shows a profile of carrier concentration in the depth direction in a crystal laminated structure in which a β-Ga ₂ O _{3 crystal film is epitaxially grown on a β-Ga 2} O ₃ substrate whose main surface orientation is (010). It is a graph showing.

[Embodiment]
(Structure of crystal laminated structure)
FIG. 1 is a vertical cross-sectional view of the crystal laminated structure 1 according to the embodiment. The crystal laminated structure 1 has a Ga ₂ O ₃ system substrate 10 and _{a β-Ga 2} O ₃ system single crystal film 12 formed by epitaxial crystal growth on the main surface 11 of _{the Ga 2} O _{3 system substrate 10.}

The Ga ₂ O ₃ system substrate 10 is a substrate made of a Ga ₂ O ₃ system single crystal having a β-type crystal structure. Here, the Ga ₂ O ₃ system single crystal refers to a Ga ₂ O _{3 single crystal or a Ga 2} O ₃ single crystal to which an element such as Al or In is added. For example, it is a Ga ₂ O ₃ single crystal _{to which Al and In are added (Ga x} Al _y In _(1-xy) ) ₂ O ₃ (0 <x ≦ 1, 0 ≦ y ≦ 1, 0 <x + y). ≦ 1) It may be a single crystal. When Al is added, the bandgap widens, and when In is added, the bandgap narrows. Further, the Ga ₂ O ₃ system substrate 10 may contain conductive impurities such as Si.

The plane orientation of main surface 11 of Ga ₂ O ₃ based substrate 10, for example, (010), (- 201) and (001), or (101).

The Ga ₂ O ₃ system substrate 10 is obtained by slicing a bulk crystal of _{a Ga 2} O ₃ system single crystal grown by a melt growth method such as an FZ (Floating Zone) method or an EFG (Edge Defined Film Fed Growth) method. It is formed by polishing the surface.

The β-Ga ₂ O ₃ system single crystal film 12 is _{composed of a Ga 2} O ₃ system single crystal having a β type crystal structure, similarly to the _{Ga 2} O _{3 system substrate 10.} Further, the β-Ga ₂ O ₃ system single crystal film 12 may contain conductive impurities such as Si.

(Structure of vapor deposition apparatus)
Hereinafter, an example of a structure of a vapor phase growth apparatus used for growing the β-Ga ₂ O ₃ single crystal film 12 of the present embodiment.

FIG. 2 is a vertical cross-sectional view of the vapor phase growth apparatus 2 according to the embodiment. The gas phase growth device 2 is a gas phase growth device for the HVPE (Halide Vapor Phase Epitaxy) method, and is a first gas introduction port 21, a second gas introduction port 22, a third gas introduction port 23, and an exhaust gas. It has a reaction chamber 20 having a port 24, and a first heating means 26 and a second heating means 27 that are installed around the reaction chamber 20 and heat a predetermined area in the reaction chamber 20.

The HVPE method has a higher film formation rate than the PLD method and the like. In addition, the in-plane distribution of the film thickness is highly uniform, and a large-diameter film can be grown. Therefore, it is suitable for mass production of crystals.

In the reaction chamber 20, a reaction vessel 25 containing a Ga raw material is arranged, a raw material reaction region R1 in which a gallium raw material gas is generated, and a Ga ₂ O ₃ system substrate 10 are arranged, and a β-Ga ₂ O ₃ system is arranged. It has a crystal growth region R2 in which the single crystal film 12 is grown. The reaction chamber 20 is made of, for example, quartz glass.

Here, the reaction vessel 25 is, for example, quartz glass, and the Ga raw material contained in the reaction vessel 25 is metallic gallium.

The first heating means 26 and the second heating means 27 can heat the raw material reaction region R1 and the crystal growth region R2 of the reaction chamber 20, respectively. The first heating means 26 and the second heating means 27 are, for example, resistance heating type or radiant heating type heating devices.

The first gas introduction port 21 uses _{a Cl-containing gas which is Cl 2} gas or an HCl gas as a carrier gas (N ₂ gas, Ar gas or He gas) which is an inert gas, and is used as a raw material reaction region R1 of the reaction chamber 20. It is a port for introducing inside. The second gas introduction port 22 is for adding a dopant such as Si to an oxygen-containing gas such as _{O 2} gas or H _{2 O gas which is a raw material gas of oxygen and a β-Ga 2} O _{3 system single crystal film 12.} chloride-based gas (e.g., silicon tetrachloride, etc.) is the port for introducing the crystal growth region R2 of the reaction chamber 20 using a carrier gas is an inert gas (N ₂ gas, Ar gas or He gas) .. The third gas introducing port 23 is a port for introducing the carrier gas is an inert gas (N ₂ gas, Ar gas or He gas) into the crystal growth region R2 of the reaction chamber 20.

(Growth of β-Ga ₂ O ₃ system single crystal film)
Hereinafter, an example of a process of growing β-Ga ₂ O ₃ single crystal film 12 of the present embodiment.

First, the raw material reaction region R1 of the reaction chamber 20 is heated by using the first heating means 26, and the ambient temperature of the raw material reaction region R1 is kept at a predetermined temperature.

Next, a Cl-containing gas is introduced from the first gas introduction port 21 using a carrier gas, and the metallic gallium in the reaction vessel 25 and the Cl-containing gas are reacted in the raw material reaction region R1 under the above-mentioned atmospheric temperature. Produces gallium chloride-based gas.

At this time, the atmospheric temperature in the raw material reaction region R1 is such that the partial pressure of the GaCl gas is the highest among the gallium chloride-based gases generated by the reaction of the metallic gallium and the Cl-containing gas in the reaction vessel 25. The temperature is preferred. Here, the gallium chloride-based gas includes GaCl gas, GaCl ₂ gas, GaCl ₃ gas, (GaCl ₃ ) ₂ gas and the like.

The GaCl gas is a gas contained in the gallium chloride-based gas that can maintain the growth driving force of the _{Ga 2} O _{3 crystal up to the highest temperature.} Since growth at a high growth temperature is effective for obtaining high-purity, high-quality Ga ₂ O ₃ crystals, gallium chloride-based gas having a high partial pressure of GaCl gas having a high growth driving force at a high temperature is generated. This is preferable for the growth of the β-Ga ₂ O ₃ system single crystal film 12.

FIG. 3 shows the growth driving force and the growth temperature _{of the Ga 2} O ₃ crystal in each of the cases where the gallium chloride-based gas is composed of only GaCl gas and the case where it is composed of only GaCl _{3 gas, which is obtained by the thermal equilibrium calculation.} It is a graph showing a relationship. The calculation conditions are that _{an inert gas such as N 2} is used as the carrier gas, the pressure inside the furnace is 1 atm, the supply partial pressure of _{GaCl gas and GaCl 3} ^{gas is 1 × 10 -3} atm, and the O ₂ / GaCl partial pressure ratio is 10. And said.

The horizontal axis of FIG. 3 _{represents the growth temperature (° C.) of the Ga 2} O ₃ crystal, and the vertical axis represents the crystal growth driving force (atm). The larger the value of the crystal growth driving force, the more efficiently the Ga ₂ O ₃ crystal grows.

FIG. 3 shows that the upper limit of the temperature at which the growth driving force is maintained is higher when GaCl gas is used as the raw material gas for Ga _{than when GaCl 3 gas is used.}

If hydrogen is contained in the atmosphere when the β-Ga ₂ O ₃ system single crystal film 12 is grown, the surface flatness and crystal growth driving force of the _{β-Ga 2} O _{3 system single crystal film 12 will increase. It is preferable to use a Cl 2} gas containing no hydrogen as the Cl-containing gas because the amount is lowered.

Figure 4 was obtained by heat balance calculation, GaCl gas obtained from the reaction of Ga and Cl _2, GaCl ₂ gas, GaCl ₃ gas, and (GaCl _{3) 2} gas equilibrium partial pressure and reaction time of the ambient temperature of the It is a graph showing a relationship. Other calculation conditions, using an inert gas, e.g. _{N 2} or the like as a carrier gas, and the reactor pressure 1 atm, the supply partial pressure of Cl ₂ gas and 3 × ¹⁰ -3 atm.

The horizontal axis of FIG. 4 represents the atmospheric temperature (° C.), and the vertical axis represents the equilibrium partial pressure (atm). The higher the equilibrium partial pressure, the more gas is produced.

FIG. 4 shows that the equilibrium partial pressure of GaCl gas, which can particularly enhance the growth driving force of _{Ga 2} O ₃ crystals, is increased by reacting metallic gallium with Cl-containing gas at an atmospheric temperature of about 300 ° C. or higher. That is, it shows that the partial pressure ratio of GaCl gas among gallium chloride-based gases is high. From this, it can be said that it is preferable to react the metallic gallium in the reaction vessel 25 with the Cl-containing gas in a state where the atmospheric temperature of the raw material reaction region R1 is maintained at 300 ° C. or higher by the first heating means 26.

Further, for example, under an atmospheric temperature of 850 ° C., the partial pressure ratio of GaCl gas is overwhelmingly high (the equilibrium partial pressure of GaCl gas is 4 orders of magnitude larger than _{that of GaCl 2} gas and 8 orders of magnitude larger than _{that of GaCl 3 gas).} Gases other than gas contribute little to the growth of _{Ga 2} O _{3 crystals.}

In consideration of the life of the first heating means 26 and the heat resistance of the reaction chamber 20 made of quartz glass or the like, the metal in the reaction vessel 25 is kept at an atmospheric temperature of the raw material reaction region R1 of 1000 ° C. or lower. It is preferable to react gallium with a Cl-containing gas.

Next, in the crystal growth region R2, the gallium chloride-based gas generated in the raw material reaction region R1 and the oxygen-containing gas introduced from the second gas introduction port 22 are mixed, and the mixed gas is Ga ₂ O ₃ The system substrate 10 is exposed, and the β-Ga ₂ O ₃ system single crystal film 12 is epitaxially grown on _{the Ga 2} O _{3 system substrate 10.} At this time, the pressure in the crystal growth region R2 in the furnace accommodating the reaction chamber 20 is maintained at, for example, 1 atm.

Here, Si, in the case of forming a _β-Ga 2 _{O 3} single crystal film 12 containing an additive element such as Al is the gas inlet port 22, a raw material gas of the additive element (e.g., silicon tetrachloride (SiCl ₄ ) Etc.) are also introduced into the crystal growth region R2 together with the gallium chloride gas and the oxygen-containing gas.

If hydrogen is contained in the atmosphere when the β-Ga ₂ O ₃ system single crystal film 12 is grown, the surface flatness and crystal growth driving force of the _{β-Ga 2} O _{3 system single crystal film 12 will increase.} Therefore, it is preferable to use an _{O 2} gas containing no hydrogen as the oxygen-containing gas.

FIG. 5 is a graph showing the relationship between _{the equilibrium partial pressure of GaCl and the O 2 / GaCl supply partial pressure ratio when the atmospheric temperature of Ga 2} O ₃ crystal growth is 1000 ° C., which is obtained by the thermal equilibrium calculation. Here, the _{ratio of the supply partial pressure of the O 2} gas to the supply partial pressure of the GaCl gas _{is referred to as the O 2} / GaCl supply partial pressure ratio. In this calculation, the value of the supply partial pressure of GaCl gas ^{is fixed at 1 × 10 -3} _{atm, an inert gas such as N 2} is used as the carrier gas, the pressure inside the furnace is set to 1 atm, and the O ₂ gas is supplied. The value of the partial pressure was changed.

The horizontal axis of FIG. 5 represents the O ₂ / GaCl supply partial pressure ratio, and the vertical axis represents the equilibrium partial pressure (atm) of the GaCl gas. The smaller the supply partial pressure of GaCl gas, the more _{GaCl gas is consumed for the growth of Ga 2} O ₃ crystals, that is, the more efficiently the Ga ₂ O ₃ crystals are growing.

FIG. 5 shows that the equilibrium partial pressure of the GaCl gas drops sharply when _{the O 2 / GaCl supply partial pressure ratio becomes 0.5 or more.}

Therefore, in order _{to efficiently grow the β-Ga 2} O ₃ system single crystal film 12, the ratio of the O ₂ gas supply partial pressure in the crystal growth region R2 to the GaCl gas supply partial pressure is 0.5 or more. It is preferable to grow the β-Ga ₂ O ₃ system single crystal film 12 in this state.

FIG. 6 is obtained by a 2θ-ω scan of a crystal laminated structure in which a _{Ga 2} O ₃ single crystal film is epitaxially grown on the main surface _{of a β-Ga 2} O ₃ substrate having a plane orientation of (010). It is a graph which shows the X-ray diffraction spectrum. Growth conditions were the furnace pressure 1 atm, the carrier gas _{N 2} gas, GaCl supply partial pressure 5 × ¹⁰ -4 _atm, and O 2 / GaCl supply partial pressure ratio 5.

The horizontal axis of FIG. 6 represents the angle 2θ (degree) formed by the incident direction and the reflected direction of X-rays, and the vertical axis represents the diffraction intensity (arbitrary unit) of X-rays.

6, _β-Ga 2 _{O 3} spectrum of the substrate _(β-Ga 2 _{O 3} No crystal film), and 800 ℃, 850 ℃, 900 ℃ , 950 ℃, 1000 ℃, and respectively at 1050 ℃ β-Ga ₂ O ₃ shows the spectrum of a crystal film was epitaxially grown crystal multilayer structure. The thickness of the β-Ga ₂ O ₃ crystal film of these crystal laminated structures is about 300 to 1000 nm.

According to FIG. 6, the (-313) plane, which is seen in the spectrum of the crystal laminated structure in _{which the β-Ga 2} O ₃ crystal film is grown at a growth temperature of 800, 850 ° C., is due to the presence of unoriented grains. The diffraction peaks of the (-204) plane and the (-712) plane or the (512) plane disappear in the spectrum of the crystal laminated structure in which the _{β-Ga 2} O _{3 crystal film is grown at a growth temperature of 900 ° C. or higher.} .. This indicates that a β-Ga ₂ O ₃ single crystal film can be obtained by _{growing the Ga 2} O ₃ single crystal film at a growth temperature of 900 ° C. or higher.

Even when the plane orientation of the main surface of the β-Ga ₂ O ₃ substrate is (-201), (001), or (101), the β-Ga ₂ O ₃ crystal film is formed at a growth temperature of 900 ° C. or higher. By growing β-Ga ₂ O ₃ , a β-Ga 2 O 3 single crystal film is obtained. Further, even in the case of using the other _Ga 2 _{O 3} system board in place of _Ga 2 _{O 3} substrate, in the case of forming the other _Ga 2 _{O 3} based crystal film in place of _Ga 2 _{O 3} crystal film Even if there is, the same evaluation result as the above evaluation result can be obtained. That is, when _{the plane orientation of the main surface of the Ga 2} O ₃ system substrate 10 is (010), (-201), (001), or (101), β-Ga ₂ O _{3 is formed at a growth temperature of 900 ° C. or higher.} By growing the system single crystal film 12, the β-Ga ₂ O ₃ system single crystal film 12 can be obtained.

FIG. 7 shows 2θ-ω of a crystal laminated structure in which a _{β-Ga 2} O ₃ single crystal film is epitaxially grown on the main surface _{of a β-Ga 2} O ₃ substrate having a plane orientation of (-201). It is a graph which shows the X-ray diffraction spectrum obtained by scanning. The growth conditions of this β-Ga ₂ O ₃ single crystal film are as follows: the pressure in the furnace is 1 atm, the carrier gas is N ₂ gas, the partial pressure of GaCl supply is 5 × 10 ^-4 atm, and the ratio of partial pressure of _{O 2 / GaCl supply is 5.} , The growth temperature was 1000 ° C.

_{FIG. 7 shows the spectrum of a β-Ga 2} O ₃ substrate (without β-Ga ₂ O ₃ crystal film) in which the plane orientation of the main surface is (-201), and 1000 ° C. on the β-Ga ₂ O _{3 substrate.} The spectrum of the crystal laminated structure obtained by epitaxially growing the β-Ga ₂ O _{3 crystal film is shown in.} The thickness of the β-Ga ₂ O ₃ crystal film of this crystal laminated structure is about 300 nm.

FIG. 8 is obtained by a 2θ-ω scan of a crystal laminated structure in which a _{Ga 2} O ₃ single crystal film is epitaxially grown on the main surface _{of a β-Ga 2} O ₃ substrate having a plane orientation of (001). It is a graph which shows the X-ray diffraction spectrum. The growth conditions of this β-Ga ₂ O ₃ single crystal film are as follows: the pressure in the furnace is 1 atm, the carrier gas is N ₂ gas, the partial pressure of GaCl supply is 5 × 10 ^-4 atm, and the ratio of partial pressure of _{O 2 / GaCl supply is 5.} , The growth temperature was 1000 ° C.

_{FIG. 8 shows the spectrum of a β-Ga 2} O ₃ substrate (without β-Ga ₂ O ₃ crystal film) in which the plane orientation of the main surface is (001), and on the β-Ga ₂ O ₃ substrate at 1000 ° C. The spectrum of the crystal laminated structure obtained by epitaxially growing the β-Ga ₂ O _{3 crystal film is shown.} The thickness of the β-Ga ₂ O ₃ crystal film of this crystal laminated structure is about 6 μm.

FIG. 9 is obtained by a 2θ-ω scan of a crystal laminated structure in which a _{Ga 2} O ₃ single crystal film is epitaxially grown on the main surface _{of a β-Ga 2} O ₃ substrate having a plane orientation of (101). It is a graph which shows the X-ray diffraction spectrum. The growth conditions of this β-Ga ₂ O ₃ single crystal film are as follows: the pressure in the furnace is 1 atm, the carrier gas is N ₂ gas, the partial pressure of GaCl supply is 5 × 10 ^-4 atm, and the ratio of partial pressure of _{O 2 / GaCl supply is 5.} , The growth temperature was 1000 ° C.

_{FIG. 9 shows the spectrum of a β-Ga 2} O ₃ substrate (without β-Ga ₂ O ₃ crystal film) in which the plane orientation of the main surface is (101), and on the β-Ga ₂ O ₃ substrate at 1000 ° C. The spectrum of the crystal laminated structure obtained by epitaxially growing the β-Ga ₂ O _{3 crystal film is shown.} The thickness of the β-Ga ₂ O ₃ crystal film of this crystal laminated structure is about 4 μm.

The horizontal axes of FIGS. 7, 8 and 9 represent the angle 2θ (degree) formed by the incident direction and the reflected direction of the X-ray, and the vertical axis represents the diffraction intensity (arbitrary unit) of the X-ray.

According to FIGS. 7, 8 and 9, the diffraction peak of the spectrum of the crystal laminated structure in _{which the β-Ga 2} O _{3 crystal film is grown at the growth temperature of 1000 ° C. is the diffraction of the spectrum of the β-Ga 2} O ₃ substrate. Consistent with the peak. _{The result is that β-Ga 2} O ₃ crystals _{on the main surface of the β-Ga 2} O ₃ substrate whose main surface orientation is (-201), (001), or (101) at a growth temperature of 1000 ° C. It is shown that a β-Ga ₂ O ₃ single crystal film can be obtained by growing the film.

10 (a) and 10 (b) are graphs showing the concentration of impurities in the crystal laminated structure measured by secondary ion mass spectrometry (SIMS).

The horizontal axis of FIGS. 10A and 10B _{represents the depth (μm) of the β-Ga 2} O ₃ single crystal film of the crystal laminated structure from the main surface 13, and the vertical axis represents the concentration of each impurity (atoms). / Cm ³ ) is represented. Here, the depth of the interface between the β-Ga ₂ O ₃ substrate and the β-Ga ₂ O _{3 single crystal film of the crystal laminated structure is about 0.3 μm.} The horizontal arrows on the right side of FIGS. 10 (a) and 10 (b) represent the measurable lower limit of the concentration of each impurity element.

_{The β-Ga 2} O ₃ single crystal film of the crystal laminated structure used in this measurement has a main surface orientation of (010) _{on the main surface of the β-Ga 2} O ₃ substrate at a growth temperature of 1000 ° C. It is a grown film.

FIG. 10A shows the concentration of C, Sn, and Si in the crystal laminated structure, and FIG. 10B shows the concentration of H and Cl in the crystal laminated structure. According to FIGS. 10A and 10B, the concentration of each impurity element in the β-Ga ₂ O ₃ single crystal film is close to the measurable lower limit value, which is almost the same as the concentration in the _{Ga 2} O _{3 substrate.} does not change. This indicates that the β-Ga ₂ O ₃ single crystal film is a highly pure film.

The same evaluation result can be obtained when the plane orientation of the main surface of the β-Ga ₂ O _{3 substrate is (-201), (101), or (001).} Further, even when another Ga ₂ O ₃ system substrate is used instead of the β-Ga ₂ O _{3 system substrate, another Ga 2} O ₃ system single crystal _{is used instead of the β-Ga 2} O _{3 system} single crystal film. Even when a film is formed, an evaluation result similar to the above evaluation result can be obtained.

According to FIG. 10 (b), the β-Ga ₂ O ₃ single crystal film contains Cl of about 5 × 10 ¹⁶ (atoms / cm ³ ) or less. This is because the Ga ₂ O ₃ single crystal film is formed by the HVPE method using a Cl-containing gas. _{Normally, when a Ga 2} O ₃ single crystal film is formed by a method other than the HVPE method, Cl is not contained in the Ga ₂ O ₃ single crystal film because Cl-containing gas is not used, and at least 1 It does not contain Cl of × 10 ¹⁶ (atoms / cm ^{3) or more.}

FIG. 11A shows carriers in the depth direction in a crystal laminated structure in which a β-Ga ₂ O _{3 crystal film is epitaxially grown on a β-Ga 2} O ₃ substrate whose main surface orientation is (001). It is a graph which shows the profile of density.

The horizontal axis of FIG. 11A _{represents the depth (μm) from the surface of the β-Ga 2} O ₃ crystal film, and the vertical axis represents the carrier concentration, that is, the donor concentration N _d and the acceptor concentration N, which are the net donor concentrations. represents the difference _a ^{(cm -3).} Also, drawn curve in terms of in the figure, when the built-in potential when the relative dielectric constant of the _β-Ga 2 _{O 3} 10, contacting the Pt to _β-Ga 2 _{O 3} and 1.5V It is a theoretical curve showing the relationship between the donor concentration and the depletion layer thickness.

The procedure used to measure the data shown in FIG. 11 (a) is shown below. First, the plane orientation of the main surface is (001), and an undoped β-Ga ₂ O ₃ crystal film having a thickness of about 15 μm is formed _{on an n-type β-Ga 2} O _{3 substrate doped with Sn by the HVPE method.} It was epitaxially grown. Here, undoping means that the intended doping has not been performed, and does not deny the inclusion of unintended impurities.

The β-Ga ₂ O ₃ substrate was a 10 mm square substrate with a thickness of 600 μm, and the carrier concentration was approximately 6 × 10 ¹⁸ cm ^-3 . The growth conditions of the β-Ga ₂ O ₃ single crystal film are as follows: the pressure in the furnace is 1 atm, the carrier gas is N ₂ gas, the partial pressure of GaCl supply is 5 × 10 ^-4 atm, and the ratio of partial pressure of _{O 2 / GaCl supply is 5.} The growth temperature was 1000 ° C.

Next, for surface flattening, the surface of the undoped β-Ga ₂ O ₃ crystal film was polished by CMP for 3 μm.

Next, a Schottky electrode is formed on the β-Ga ₂ O ₃ crystal film, and an _{ohmic electrode is formed on the β-Ga 2} O ₃ substrate, and the bias voltage is changed in the range of + 0 to -10 V to perform CV measurement. went. Then, the profile of the carrier concentration in the depth direction was calculated from the result of the CV measurement.

Here, the Schottky electrode is a circular electrode having a diameter of 800 μm, which has a laminated structure in which a Pt film having a thickness of 15 nm, a Ti film having a thickness of 5 nm, and an Au film having a thickness of 250 nm are laminated in this order. The ohmic electrode is a square electrode having a side of 10 mm and having a laminated structure in which a Ti film having a thickness of 50 nm and an Au film having a thickness of 300 nm are laminated in this order.

In FIG. 11A, there are no measurement points in a region shallower than 12 μm, which is equal to the thickness _{of the β-Ga 2} O _{3 crystal film, and the horizontal axis coordinates of all the measurement points are 12 μm.} ing. _{This indicates that the entire region of the β-Ga 2} O ₃ crystal film is depleted in the range of the bias voltage of + 0 to -10 V.

Therefore, as a matter of course, even when the bias voltage is 0, the entire region of the _{β-Ga 2} O _{3 crystal film is depleted.} According to the theoretical curve, the donor concentration when the depletion layer thickness is 12 μm is about 1 × 10 ¹³ cm ^-3 , so that the residual carrier concentration of the β-Ga ₂ O ₃ crystal film is 1 × 10 ¹³ cm ^-3. The following is estimated to be a very low value.

Since the residual carrier concentration of the β-Ga ₂ O ₃ ^{crystal film is 1 × 10 13} cm ^-3 or less, for example, by doping with a Group IV element, _{the carrier concentration of the β-Ga 2} O ₃ crystal film can be reduced to 1 ×. It can be controlled in the range of 10 ¹³ to 1 × 10 ²⁰ cm ^-3.

FIG. 11B is a graph showing the withstand voltage characteristics of the crystal laminated structure.

The horizontal axis of FIG. 11B represents the applied voltage (V), and the vertical axis represents the current density (A / cm ² ).
The straight line drawn by the points in the figure represents the lower limit of measurement.

The procedure used to measure the data shown in FIG. 11B is shown below. First, a crystal laminated structure composed of the above-mentioned β-Ga ₂ O ₃ substrate and β-Ga ₂ O _{3 crystal film was prepared.}

Next, a Schottky electrode was formed on the β-Ga ₂ O ₃ crystal film, _{and an ohmic electrode was formed on the β-Ga 2} O ₃ substrate, and a voltage of 1000 V was applied to measure the current density.

Here, the Schottky electrode is a circular electrode having a diameter of 200 μm, which has a laminated structure in which a Pt film having a thickness of 15 nm, a Ti film having a thickness of 5 nm, and an Au film having a thickness of 250 nm are laminated in this order. The ohmic electrode is a square electrode having a side of 10 mm and having a laminated structure in which a Ti film having a thickness of 50 nm and an Au film having a thickness of 300 nm are laminated in this order.

FIG. 11B shows that even when a voltage of 1000 V is applied, the leakage current in the crystal laminated structure ^{is very small, about 1 × 10-5} A / cm ² , and dielectric breakdown does not occur. There is. This result is considered to be due to the fact that the β-Ga ₂ O ₃ crystal film is a high-quality crystal film with few crystal defects and the donor concentration is low.

FIG. 12 shows a profile of carrier concentration in the depth direction in a crystal laminated structure in which a β-Ga ₂ O _{3 crystal film is epitaxially grown on a β-Ga 2} O ₃ substrate whose main surface orientation is (010). It is a graph showing.

The horizontal axis of FIG. 12 _{represents the depth (μm) from the surface of the β-Ga 2} O ₃ crystal film, and the vertical axis represents the carrier concentration, that is, the difference between the _{donor concentration N d} and the acceptor concentration N _{a, which is the net donor concentration.} Represents (cm ^-3 ). Also, drawn curve in terms of in the figure, when the built-in potential when the relative dielectric constant of the _β-Ga 2 _{O 3} 10, contacting the Pt to _β-Ga 2 _{O 3} and 1.5V It is a theoretical curve showing the relationship between the donor concentration and the depletion layer thickness.

The procedure used to measure the data shown in FIG. 12 is shown below. First, the plane orientation of the main surface is (010), and _{an undoped β-Ga 2} O ₃ crystal film is formed _{on an n-type β-Ga 2} O ₃ substrate doped with Sn by the HVPE method in an amount of about 0.9 μm. It was epitaxially grown to the thickness of.

The β-Ga ₂ O ₃ substrate was a square substrate having a thickness of 600 μm and a side of 10 mm, and the carrier concentration was about 6 × 10 ¹⁸ cm ^-3 . The growth conditions of the β-Ga ₂ O ₃ single crystal film are as follows: the pressure in the furnace is 1 atm, the carrier gas is N ₂ gas, the partial pressure of GaCl supply is 5 × 10 ^-4 atm, and the ratio of partial pressure of _{O 2 / GaCl supply is 5.} The growth temperature was 1000 ° C.

Next, a Schottky electrode is formed on the undoped β-Ga ₂ O ₃ crystal film, _{and an ohmic electrode is formed on the β-Ga 2} O ₃ substrate, and the bias voltage is changed in the range of + 0 to -10 V to CV. Measurements were made. Then, the profile of the carrier concentration in the depth direction was calculated from the result of the CV measurement.

Here, the Schottky electrode is a circular electrode having a diameter of 400 μm, which has a laminated structure in which a Pt film having a thickness of 15 nm, a Ti film having a thickness of 5 nm, and an Au film having a thickness of 250 nm are laminated in this order. The ohmic electrode is a square electrode having a side of 10 mm and having a laminated structure in which a Ti film having a thickness of 50 nm and an Au film having a thickness of 300 nm are laminated in this order.

In FIG. 12, the horizontal axis coordinates of the measurement points when the bias voltage is 0 are 0.85 μm (the measurement points in the region deeper than 0.85 μm are the measurement points when the bias voltage is close to −10 V). According to the theoretical curve, the donor concentration when the depletion layer thickness is 0.85 μm is about 2.3 × 10 ¹⁵ cm ^-3 , so that the residual carrier concentration of the β-Ga ₂ O ₃ crystal film is 3 × 10 It is estimated to be a very low value of ¹⁵ cm ^{-3 or less.}

(Effect of embodiment)
According to the above embodiment, by using the HVPE method, and generation condition of a gallium raw material gas, by controlling the growth conditions of the β-Ga ₂ O ₃ single crystal film, high-quality, large diameter β- The Ga ₂ O ₃ system single crystal film can be efficiently grown. Further, since the β-Ga ₂ O ₃ system single crystal film is excellent in crystal quality, a high quality crystal film can be grown on _{the β-Ga 2} O _{3 system single crystal film.} Therefore, it is possible to use a crystalline layered structure comprising a β-Ga ₂ O ₃ single crystal film according to the present embodiment for the production of high-quality semiconductor device.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be carried out within a range that does not deviate from the gist of the invention.

Moreover, the embodiment described above does not limit the invention according to the claims. It should also be noted that not all combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

1 ... Crystal laminated structure, 10 ... Ga ₂ O ₃ system substrate, 11 ... Main surface, 12 ... β-Ga ₂ O ₃ system single crystal film

Claims (1)

Ga ₂ O ₃ system board and
_{A β-Ga 2} O ₃ system single crystal film provided on the main surface of the Ga ₂ O _{3 system substrate and}
Including
The β-Ga ₂ O ₃ system single crystal film is a crystal laminated structure having a residual carrier concentration of 1 × 10 ¹³ / cm ^{3 or less.}

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