JP6946999B2 - Method for forming gallium oxynitride crystal film - Google Patents

Description

The present invention relates to a method for forming a gallium oxynitride crystal film.

Gallium nitride (hereinafter referred to as GaN) has been in the limelight mainly as a material constituting a blue light emitting diode. GaN is also industrially useful as a wide bandgap semiconductor, and recently, a power device using GaN has been developed by utilizing the high withstand voltage characteristic of the wide bandgap semiconductor. In addition, gallium oxide (III) (hereinafter referred to as Ga ₂ O ₃ ) is a material having a larger bandgap than GaN, and its use as a deep ultraviolet light emitting material has been studied. Transistors for high withstand voltage have been developed using this. Attempts have been made to grow single crystals for both GaN and Ga ₂ O _{3, and some results have been obtained.} However, there are problems with the quality of the grown single crystals and the high prices are hindering their widespread use in the industrial field.

C. Tang, Y. Bando, Y. Huang, C. Zhi, D. Golberg, X. Xu, J. Zhao, and Y. Li, Nanotechnology 21 (2010) 115705. Y. Zhang, J. Yan, Q. Li, C. Qu, L. Zhang, and T. Li, Physica B 406 (2011) 3079. C.-C. Hu, Y.-L. Lee, and H. Teng, J. Phys. Chem. C 115 (2011) 2805.

By the way, since gallium oxynitride (hereinafter referred to as GaON), which is a compound composed of gallium, oxygen and nitrogen _{, has an intermediate composition between GaN and Ga 2} O ₃ , its band gap is GaN and Ga ₂ O. It is a material that is expected to be a value between _{3 and 3.} Utilizing this, it is expected to be applied to materials that control the band structure and maximize the device characteristics and photocatalytic functions.

However, there are very few studies on GaON. Therefore, the crystal phase that determines the band structure has not yet been determined (Non-Patent Documents 1 to 3). In addition, it is not clear whether the image that the crystal structure of GaON is a structure in which the nitrogen atom of GaN is replaced with an oxygen atom or a structure in which the oxygen atom of Ga ₂ O ₃ is replaced with a nitrogen atom is appropriate. rice field.

In general, catalytic function is strongly influenced by the atomic arrangement on the surface of the material. Therefore, when GaON is applied to a material having a catalytic function, a forming method capable of predeterminedly controlling the crystal structure contained in the crystal phase is required. For example, the photocatalytic action of titanium oxide (IV) (hereinafter referred to as TiO ₂ ) is well known, and it mainly absorbs light in the ultraviolet region to exert its effect, but it is doped with nitrogen against _{TiO 2.} Titanium oxynitride (hereinafter referred to as TiON) is known to have higher photocatalytic efficiency than _{TIO 2 because it absorbs light on the more visible region side.} Ga ₂ O ₃ is also known as a material having a photocatalytic activity as well as TiO _2, but a metal oxynitride each other, since the crystal structure is completely different in the TiON and GaON, Metallurgical knowledge of TiON is It cannot be applied as it is.

Reflecting the above background, there has been a demand for a process technique for producing different GaON crystal phases.

The present invention has been made to solve the above problems, and is a method for forming a film of GaON, which is a gallium oxynitride, in which Ga ₂ O ₃ is used as a sputtering target and oxygen gas is used as a reaction gas. And nitrogen gas is introduced into the film forming chamber, and a film forming step of obtaining a GaON precursor film by sputtering film formation, and after the film forming step, the GaON precursor film is heated in a vacuum to obtain a GaON film. The post-annealing treatment step is provided , and when the flow rate ratio of the nitrogen gas to the oxygen gas is 1/2 or less, the crystal structure of the GaON film is a β-gallia structure, and when it is 1 or more and 2 or less, the above. Provided is a method for forming a gallium oxynitride crystal film, wherein the crystal structure of the GaON film is a spinel type structure, and when the number is 4 or more, the crystal structure of the GaON film is a wurtzite type structure .

As described above, the GaON film having various crystal structures can be formed by the present invention. For example, since material properties such as photocatalytic properties largely depend on the crystal structure thereof, the present invention makes it possible to obtain a GaON film having a desired crystal structure and obtain good material properties.

It is a figure which shows the structure of the film forming apparatus for carrying out the method of forming the gallium oxynitride crystal film of this invention. The XRD pattern (a) and the GIXRD pattern (b) of the GaON film obtained by forming a film with an oxygen gas flow rate of 1 sccm and a nitrogen gas flow rate of 1 sccm and performing post-annealing treatment. These are the XRD pattern (a) and the GIXRD pattern (b) of the GaON film obtained by forming a film with an oxygen gas flow rate of 1 sccm and a nitrogen gas flow rate of 2 sccm and performing post-annealing treatment. These are the XRD pattern (a) and the GIXRD pattern (b) of the GaON film obtained by forming a film with an oxygen gas flow rate of 1 sccm and a nitrogen gas flow rate of 4 sccm and performing post-annealing treatment. These are the XRD pattern (a) and the GIXRD pattern (b) of the GaON film obtained by forming a film with only the nitrogen gas flow rate of 4 sccm without introducing oxygen gas and performing post-annealing treatment. The XRD pattern (a) and the GIXRD pattern (b) of the GaON film obtained by forming a film with an oxygen gas flow rate of 1 sccm and a nitrogen gas flow rate of 0.5 sccm and performing post-annealing treatment.

In general, the crystal phase in which the metal oxynitride exists is affected by the ease of crystallization. The present inventor changes the formation phase of GaON when the crystallization rate is adjusted by changing the flow rate ratio of the oxygen gas and the nitrogen gas introduced into the film forming chamber during the sputtering film formation. I got the finding. That is, the present inventor can control the crystal structure of the GaON film by setting the ratio of the flow rate of the nitrogen gas to the flow rate of the oxygen gas during the sputtering film formation to a predetermined value based on the above findings. Inspired by this, the present invention was completed.

First, when the flow rate of nitrogen gas is made smaller than the flow rate of oxygen gas, that is, when oxygen gas is mainly introduced as a reaction gas and a film is formed, β-Ga, which is the most stable crystal structure for _{Ga 2} O _{3, is formed.} The structural structure of ₂ O _{3 is maintained, and β-Ga 2} O (N) ₃ , which is a compound in which a part of the oxygen atom of _{β-Ga 2} O ₃ is replaced with a nitrogen atom, is produced. _{The crystallization of β-Ga 2} O ₃ on the silicon substrate is promoted by heating at 600 ° C. or higher and proceeds at a sufficient rate.

Second, when the flow rate of oxygen gas and the flow rate of nitrogen gas are equivalent, the structure of the produced GaON film is _{an intermediate structure between Ga 2} O ₃ and GaN, and the structure is Ga ₂ O ₃ and Both GaN are less likely to crystallize than when they are simple substances. This is because if Ga ₂ O ₃ is used as the basic skeleton, the crystal structure is disturbed by substituting the oxygen atom with a nitrogen atom. Similarly, when GaN is used as the basic skeleton, a divalent anion invades by substituting a part of the nitrogen atom with an oxygen atom, so that the crystal lattice is also disturbed. _{In Ga 2} O ₃ , which is a polymorph of _{crystals, γ-Ga 2} O ₃ is the coldest phase and has the lowest crystallinity. That is, if the flow rate of oxygen gas and the flow rate of nitrogen gas are equal, _{a crystal structure similar to the above-mentioned γ-Ga 2} O ₃ , that is, a spinel-type structure is formed.

Thirdly, when only nitrogen gas is introduced without introducing oxygen gas to perform sputtering film formation, most of the nitrogen atoms are incorporated into the generated GaON film, but oxygen is also contained in a certain proportion. It is contained. At this time, a wurtzite-type crystal, that is, a crystal having a structure similar to the crystal structure of GaN is generated. It is considered that a structure in which a part of the nitrogen atom position in the crystal structure of GaN is replaced with an oxygen atom is generated.

Hereinafter, embodiments of the present invention will be described in detail. Moreover, the embodiment of the present invention is not limited to the following examples as long as it does not deviate from the scope of the gist of the present invention.

First, the configuration of the apparatus for carrying out the film forming process in the present invention will be described.

FIG. 1 is a sputtering apparatus used in the film forming process in the present invention, which is a film forming apparatus for sputtering a substance derived from the sputtering target onto a substrate. The inside of the film forming chamber 2 of the sputtering apparatus of FIG. 1 is exhausted to a vacuum, and the inside of the film forming chamber 2 is provided with a sputtering target 3, a holding mechanism 4, a substrate 5, a heater 6, and a gas introduction port 7.

The substrate 5 is arranged at a position facing the sputtering target 3, and the substrate 5 is placed on the heater 6. The film can be formed while heating the substrate 5 with the heater 6, or the inside of the film forming chamber 2 can be evacuated and the post-annealing process can be performed after the film formation. The sputtering apparatus 1 is provided with a gas introduction port 7 connected to the film forming chamber 2 from the outside, and argon as a sputtering gas is used as a reaction gas into the film forming chamber 2 through the gas introduction port 7. Introduce nitrogen gas and oxygen gas. The flow rate of each gas was set in sccm units (standardized under the conditions of standard cc / min., Pressure 1 atm (atmospheric pressure 1013 hPa), and temperature 25 ° C.).

The sputtering target 3 is held by the holding mechanism 4 so as to make the distance from the substrate 5 appropriate. The sputtering apparatus 1 further includes a mechanism (not shown) for generating a high-frequency electric field or magnetic field between the target 3 and the substrate 5 or around the substrate 5 in order to realize a predetermined condition for sputtering film formation.

Further, in the case of producing a thin film, it is desirable to rotate the substrate with respect to an axis penetrating the center of the substrate 5 in order to equalize the composition distribution of the film deposited on the substrate.

[Implementation conditions]
Using the above configuration of the sputtering apparatus 1, an RF magnetron sputtering apparatus was adopted as the sputtering apparatus 1, and Ga ₂ O ₃ was used as the sputtering target 3. The inside of the film forming chamber 2 of the sputtering apparatus 1 is exhausted by a turbo molecular pump (not shown), and the flow rate when introducing oxygen gas and nitrogen gas into the film forming chamber 2 by a mass flow controller (not shown) is measured. Controlled. A 4-inch size Si (100) single crystal substrate was used as the substrate. Here, the silicon substrate is used because the surface is covered with an oxide film so that the crystal arrangement does not affect the epitaxial growth as an amorphous substrate. The input power to the RF magnetron sputtering gun was set to 60 W, and the temperature of the substrate 5 was set to room temperature to form a film. After the film formation, the substrate 5 on which the GaON precursor film was formed was taken out and cut into a size of 12 mm × 12 mm to prepare a sample for measurement. The measurement sample was post-annealed in vacuum at a temperature of 300 ° C. or higher and 800 ° C. or lower for 1 hour. Since the temperature of the Ga ₂ O ₃ is a sputtering target 3 is Ga ₂ O ₃ film exceeds 1000 ° C. to evaporate, post-annealing temperature is required to be 1000 ° C. or less.

Next, the GaON film produced by the post-annealing treatment is subjected to an X-ray diffraction (X-Ray Diffraction, hereinafter referred to as XRD) pattern by the θ-2θ method using an X-ray diffractometer, and the crystal structure is obtained from the XRD pattern. Was analyzed. Further, the measurement was performed by the oblique incident X-ray diffraction (Grazing Incident X-Ray Diffraction, hereinafter referred to as GIXRD) method. At this time, the incident angle of the X-ray with respect to the measurement surface was set to 1.5 °. Here, the GIXRD method has an advantage that it is difficult to detect diffraction from a silicon substrate, and it is possible to detect crystals that are not oriented inside the GaON film with high sensitivity. Hereinafter, the XRD pattern and the GIXRD pattern are collectively referred to as a diffraction pattern.

FIG. 2A is an XRD pattern of a sample in which a GaON precursor film formed with an oxygen gas flow rate of 1 sccm and a nitrogen gas flow rate of 1 sccm is post-annealed at each temperature. FIG. 2B is a GIXRD pattern for the sample. It can be seen that the diffraction patterns for all the samples treated at the respective temperatures in the post-annealing treatment step tend to be broad with no actual diffraction peaks and hardly crystallized. In the post-annealing treatment at 800 ° C., according to the diffraction pattern obtained, a diffraction peak corresponding to the crystal plane of the spinel-type Ga ₂ O ₃ structure, i.e. _{γ-Ga 2 O 3 γ (} 311), γ (422 ) And γ (440) can be identified. According to this diffraction pattern, the intensity ratio between the diffraction peaks is also different from that of _{γ-Ga 2} O ₃ which contains only oxygen without containing nitrogen. Such an amorphous state in which the diffraction peak is not actualized and shows a broad diffraction pattern is generated because a part of oxygen atoms in the crystal is replaced with nitrogen atoms.

The oxygen atoms supplied to the surface of the substrate and contained in the GaON precursor film _{are both derived from Ga 2} O ₃ of the sputtering target and those derived from oxygen gas ionized and dissociated in plasma. Is. On the other hand, the nitrogen atoms supplied to the substrate surface and contained in the GaON precursor membrane are limited to those in which nitrogen gas is ionized and dissociated in plasma.

_{For comparison, when Ga 2} O ₃ is sputtered on a silicon substrate without introducing nitrogen gas, the deposited film does not contain nitrogen. When the deposited film is crystallized by post-annealing treatment, randomly oriented β-Ga ₂ O ₃ is produced. The diffraction peak appearing in the diffraction pattern for this β-Ga ₂ O ₃ is sharper than the diffraction peak in the diffraction pattern obtained for GaON generated in this example. This clearly indicates that the crystal structure is affected by the presence of nitrogen in the GaON film. In general, γ-Ga ₂ O ₃ is the lowest temperature phase in _{Ga 2} O ₃ which is a polymorph of crystals. The GaON film contains a large amount of nitrogen atoms _{, which makes it difficult to crystallize into either Ga 2} O ₃ or GaN, raises the crystallization temperature, and produces spinel-type crystals in the low-temperature phase. it is conceivable that.

FIG. 3A is an XRD pattern after post-annealing a GaON precursor film formed with an oxygen gas flow rate of 1 sccm and a nitrogen gas flow rate of 2 sccm. FIG. 3B is a GIXRD pattern for the sample. The apparatus and implementation conditions used in this embodiment are the same as those in the first embodiment except for the flow rate ratio of the gas introduced into the film forming chamber 2. In this example, the flow rate of nitrogen gas is double that of Example 1. According to the obtained XRD pattern and GIXRD pattern, as in the case of Example 1, the crystal phase of the produced GaON film is a spinel in which a nitrogen atom is contained in a crystal having a structure similar to _{γ-Ga 2} O _3. It is a type crystal. Although the diffraction pattern obtained in this example shows a shape as a diffraction peak as compared with the diffraction pattern obtained in Example 1, the diffraction peak is broad and is the same as in the case of Example 1. It reflects the low crystallinity of GaON. The diffraction intensity seen in the XRD pattern of FIG. 3A is small. On the other hand, in the GIXRD pattern of FIG. 3B, the GIXRD method can detect weak diffraction from small crystals, so that a clearer diffraction peak is observed. In particular, the diffraction peak appearing at 2θ = 30 to 38 ° is separated into γ (220) and γ (311).

FIG. 4A is an XRD pattern after post-annealing a GaON precursor film formed with an oxygen gas flow rate of 1 sccm and a nitrogen gas flow rate of 4 sccm. FIG. 4B is a GIXRD pattern for the sample. The apparatus and implementation conditions used in this embodiment are the same as those in the first embodiment except for the flow rate ratio of the gas introduced into the film forming chamber 2. In this example, when the temperature of the post-annealing treatment is 700 ° C. or lower, the diffraction peak appearing in the diffraction pattern is broad, indicating the presence of microcrystals, as in the case of Examples 1 and 2. However, when the temperature of the post-annealing treatment is 800 ° C., the diffraction peak appearing at 2θ = 32 ° becomes larger than the diffraction peak appearing at 2θ = 36 °, and the crystals produced in Examples 1 and 2 are formed. It can be clearly seen that different crystals are formed. The positions of these diffraction peaks are similar to those in the diffraction pattern obtained from GaN of wurtzite crystals. In particular, the characteristics of the diffraction pattern in which the three diffraction peaks (100), (002) and (101) appear at 2θ = 30 to 38 ° are consistent with the standard GaN diffraction pattern obtained from the powder sample. ing. Here, in the GaN polycrystal, the diffraction from the (101) plane is the largest observed among these three diffraction peaks, whereas the diffraction pattern obtained in this example ((a) in FIG. 4). In (b) and (b), the diffraction from the (100) plane is the largest. This also reflects that the morphology of the crystal is affected by the inclusion of nitrogen atoms in the GaN crystal.

Incidentally, wurtzite type crystal of Ga ₂ O ₃ is α-Ga ₂ O _3. Since the diffraction peak position obtained from α-Ga ₂ O ₃ is completely different from the position in the diffraction pattern ((a) and (b) of FIG. 4) obtained in this example, it was obtained in this example. It is considered that the GaON crystal has a structure in which some of the nitrogen atoms in the GaN crystal are replaced with oxygen atoms instead of _{Ga 2} O _3.

FIG. 5A is an XRD pattern after post-annealing a GaON precursor film formed by introducing only nitrogen gas without introducing oxygen gas and setting the flow rate of nitrogen gas to 4 sccm. FIG. 5B is a GIXRD pattern for the sample. The apparatus and implementation conditions used in this embodiment are the same as those in the first embodiment except for the flow rate ratio of the gas introduced into the film forming chamber 2. Similar to the diffraction pattern obtained for the GaON film generated in Example 3 ((a) and (b) in FIG. 4), the diffraction angle is similar to the diffraction peak position in the diffraction pattern obtained for the wurtzite type GaN crystal. A peak appears in. Here, as compared with the diffraction patterns obtained for the GaON film produced in Example 3 ((a) and (b) in FIG. 4), the crystal planes of (100), (002) and (101) are respectively. It can be seen that the derived diffraction peaks are completely separated from each other, and the GaON film produced in this example has improved crystal facetability as compared with the GaON film produced under the conditions of Example 4. In this embodiment, oxygen gas is not supplied to the film forming chamber 2. Therefore, the oxygen source contained in the generated GaON film is only the oxygen previously contained in the sputtering target. That is, it is considered that most of the oxygen atoms in the GaON film derived from oxygen previously contained in the sputtering target are replaced by nitrogen atoms to form a GaON film containing a small amount of oxygen atoms.

FIG. 6A is an XRD pattern after post-annealing a GaON precursor film formed with an oxygen gas flow rate of 1 sccm and a nitrogen gas flow rate of 0.5 sccm. FIG. 6B is a GIXRD pattern for the sample. The apparatus and implementation conditions used in this embodiment are the same as those in the first embodiment except for the flow rate ratio of the gas introduced into the film forming chamber 2. In this example, the presence of _{β-Ga 2} O ₃ is characterized, which is significantly different from the GaON film formed in Examples 1 to 4, that is, when the nitrogen gas flow rate is larger than the oxygen gas flow rate. A diffraction pattern has been obtained. Further, in Examples 1 to 4, that is, when the nitrogen gas flow rate is larger than the oxygen gas flow rate, the temperature at which crystallization proceeds during the post-annealing treatment is 700 ° C. or higher and 800 ° C. or lower. On the other hand, when the temperature of the post-annealing treatment is 500 ° C. or higher, a diffraction peak derived from _{β-Ga 2} O _{3 appears.} This indicates that the crystallization temperature of the GaON film produced in Examples 1 to 4 is significantly lower than that of the GaON film. The GaON film produced in this example is _{β-Ga 2} O (N) _{3 in} which a part of the oxygen atom of _{β-Ga 2} O _{3 is replaced with a nitrogen atom.} When the flow rate of oxygen gas is increased more than the flow rate of nitrogen gas, that is, when the flow rate of nitrogen gas relative to the flow rate of oxygen gas is decreased, the crystal structure of GaON becomes closer to β-Ga ₂ O ₃ and β-, which is a sputtering target. The basic crystal structure of Ga ₂ O ₃ is maintained, but gallium atoms are formed in the generated GaON film unless the flow rate of nitrogen gas introduced into the film forming chamber 2 during sputtering deposition is set to zero. _{Β-Ga 2} O (N) ₃ is produced by ensuring that at least a part of the anions bonded to is replaced with a nitrogen atom.

It is expected to be used as a material for high withstand voltage power devices, light emitting devices, photocatalysts, etc.

1 Sputtering device 2 Deposition chamber 3 Sputtering target 4 Holding mechanism 5 Substrate 6 Heater

Claims (4)

It is a method of forming a film of GaON, which is a gallium oxynitride.
_{A film forming step of using Ga 2} O ₃ as a sputtering target, introducing oxygen gas and nitrogen gas as reaction gases into the film forming chamber, and performing sputtering film formation to obtain a GaON precursor film.
After the film forming step, a post-annealing treatment step of heating the GaON precursor film in a vacuum to obtain a GaON film is provided .
The flow rate ratio of the nitrogen gas to the oxygen gas is
When it is 1/2 or less, the crystal structure of the GaON film is a β-gaul structure.
When it is 1 or more and 2 or less, the crystal structure of the GaON film is a spinel type structure.
A method for forming a gallium oxynitride crystal film, wherein the crystal structure of the GaON film is a wurtzite-type structure when the number is 4 or more. The flow rate ratio of the nitrogen gas to the oxygen gas, when it is 1/2 or less, the GaON film is a _{β-Ga 2 O (N)} 3, the gallium oxynitride crystal film according to claim 1 Forming method. The post-annealing process is
The flow rate ratio of the nitrogen gas to the oxygen gas is
When it is 1/2 or less, it is heated at a temperature of 500 ° C. or higher and 1000 ° C. or lower.
When it is 1 or more and 2 or less or 4 or more, it is a step of heating at a temperature of 800 ° C. or more and 1000 ° C. or less.
The method for forming a gallium nitride crystal film according to claim 1 or 2. It is a method of forming a film of GaON, which is a gallium oxynitride.
Ga as a sputtering target ₂ O ₃ Introducing oxygen gas and nitrogen gas as reaction gases into the film formation chamber and sputtering film formation to obtain a GaON precursor film.
After the film forming step, the GaON precursor film is heated in a vacuum to obtain a GaON film, and the flow rate ratio of the nitrogen gas to the oxygen gas is determined.
When it is 1/2 or less, it is heated at a temperature of 500 ° C. or higher and 1000 ° C. or lower.
When it is 1 or more and 2 or less or 4 or more, the step of heating at a temperature of 800 ° C. or more and 1000 ° C. or less and
A method for forming a gallium oxynitride crystal film.

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