JP7614602B2 - LAMINATED FILM STRUCTURE AND METHOD FOR MANUFACTURING SAME - Google Patents

Description

The present invention relates to a laminated film structure and a method for manufacturing the same.

Nitride-based materials exhibit excellent semiconductor properties. For example, gallium nitride (GaN) is implemented as a material for blue light-emitting diodes (LEDs) and blue laser diodes (LDs). In addition, because it has high voltage resistance, it is suitable for applications such as power devices. Therefore, a laminated film structure in which a nitride-based thin film is provided on a substrate is useful in the field of electronic devices. Such nitride-based thin films are generally manufactured by metal-organic chemical vapor deposition (MOCVD). In addition to the MOCVD method, it has also been proposed to manufacture nitride-based thin films by sputtering. Patent documents 1 to 3 disclose technologies related to the manufacture of nitride-based thin films.

Patent Document 1 discloses a method for growing a semiconductor crystal film on a heated substrate surface by injecting a reactive gas onto the substrate surface, characterized in that the reactive gas is injected parallel or at an angle onto the substrate surface, and a pressure diffusion gas is injected toward the substrate (Patent Document 1 claims). In the examples, it is described that GaN is grown on a sapphire substrate using ammonia, hydrogen gas, and TMG (trimethylgallium) gas (Patent Document 1 examples).

Patent Document 2 discloses a metal gallium-infiltrated gallium nitride molded product in which gallium nitride and metal gallium exist as separate phases in the molded product, and the molar ratio of Ga/(Ga+N) in the entire molded product is 55% to 80% (claim 1 of Patent Document 2). In the examples, it is described that the obtained metal gallium-infiltrated gallium nitride molded products are bonded to prepare gallium nitride-based sputtering targets, and that when the obtained target was sputtered, no cracks were found in either RF or DC sputtering, making it possible to form a film ([0102] of Patent Document 2).

Patent Document 3 discloses a method for forming a gallium nitride film, which includes a step of forming an aluminum nitride film on a silicon substrate by sputtering an aluminum target with plasma generated from a mixed gas of a nitrogen-containing gas and a rare gas, and a step of forming a gallium nitride film on the aluminum nitride film, characterized in that the method includes a step of forming an aluminum film on the silicon substrate by sputtering an aluminum target with plasma generated from a rare gas before forming the aluminum nitride film (claim 1 of Patent Document 3).

Japanese Unexamined Patent Publication No. 4-164895 JP 2014-159368 A JP 2013-227198 A

Nitride-based thin films manufactured by conventional methods have problems. To improve device characteristics, it is desirable for the nitride-based thin films that compose the device to have high crystallinity. Here, high crystallinity refers to a state in which the crystal orientation within the thin film is highly aligned. Furthermore, when using nitride-based thin films for applications such as power devices, the most effective substrate is a low-cost Si substrate, which can be made large in diameter.

However, it is difficult to form a highly crystalline nitride thin film (e.g., a gallium nitride thin film) on a Si substrate using the MOCVD method. In other words, to grow a highly crystalline thin film using the MOCVD method, it is necessary to raise the substrate temperature to about 1000°C and form the film at that temperature. This causes a problem that the metal components in the thin film (e.g., gallium) react with the Si substrate during film formation, i.e., melt-back etching occurs. In addition, the thermal expansion coefficient of gallium nitride is significantly different from that of the Si substrate. This causes a problem that the gallium nitride thin film is prone to cracking during the cooling process after film formation. Due to these problems, the MOCVD method cannot use a Si substrate, and requires the use of expensive substrates such as sapphire substrates and gallium nitride single crystal substrates.

On the other hand, when sputtering is used, it is possible to form a film at a low temperature of less than 1000°C. Therefore, it is possible to form a thin film on a Si substrate without causing problems such as meltback etching or cracks. However, there is room for improvement in the crystallinity of conventional nitride-based thin films formed by sputtering. Therefore, in order to fabricate a layered film structure with a highly crystalline nitride-based thin film on a Si substrate, further study of the thin film formation conditions and the interface structure of the layered film structure is required.

In light of these problems, the inventors conducted research and discovered that in a laminated film structure in which a thin film made of a nitride-based material and/or aluminum is provided on a Si substrate, the state near the surface of the Si substrate plays an important role in the crystallinity of the thin film, and that controlling this state is important in obtaining a highly crystalline nitride-based thin film.

The present invention was completed based on these findings, and aims to provide a laminated film structure with high crystallinity and flatness, and a method for manufacturing the same.

The present invention encompasses the following aspects (1) to (15). In this specification, the expression "to" includes both ends of the expression. In other words, "X to Y" is synonymous with "X or more and Y or less." Furthermore, "X and/or Y" is synonymous with "at least one of X and Y (one or both of X and Y)."

(1) a Si(111) substrate;
a first thin film made of a nitride-based material and/or aluminum provided on the Si(111) substrate;
a second thin film made of a nitride-based material provided on the first thin film;
A laminated film structure comprising:
A laminated film structure, comprising an amorphous layer having a thickness of 0 nm or more and less than 1.0 nm on the Si(111) substrate, and a full width at half maximum (FWHM) of a rocking curve of a (0002) plane on the surface of the laminated film structure is 1.50° or less.

(2) The laminated film structure of (1) above, in which the amorphous layer has a thickness of 0 nm and the first thin film is in direct contact with the Si(111) substrate without any other layer therebetween.

(3) The laminated film structure of (2) above, in which the oxygen content within 10 nm from the surface of the Si(111) substrate is 5 at% or less.

(4) The laminated film structure of (2) or (3) above, in which the silicon nitride content within 10 nm from the surface of the Si(111) substrate is 5 at% or less.

(5) The laminated film structure of (1) above, in which the thickness of the amorphous layer is greater than 0 nm and less than 1.0 nm.

(6) The laminated film structure of (5) above, in which the silicon nitride content within 10 nm from the Si(111) substrate surface is 5 at% or less.

(7) A laminated film structure according to any one of (1) to (6) above, in which the arithmetic mean roughness (Ra) of the surface of the laminated film structure is 10.0 nm or less.

(8) A laminated film structure according to any one of (1) to (7) above, in which the first thin film is an aluminum nitride thin film and the second thin film is a gallium nitride thin film.

(9) A laminated film structure according to any one of (1) to (8) above, in which the outermost surface of the structure is composed of a hexagonal gallium nitride layer, and the surface of the gallium nitride layer is gallium (Ga) polar.

(10) A semiconductor device having any one of the laminated film structures (1) to (9) above.

(11) An electronic device including the semiconductor element of (10) above.

(12) A method for producing a laminated film structure according to any one of (1) to (9) above, comprising the following steps:
providing a Si(111) substrate;
immersing the Si(111) substrate in a cleaning solution;
forming a first thin film on the Si(111) substrate by a sputtering method after immersion;
forming a second thin film on the first thin film by a sputtering method;
When forming the first thin film, the sputtering energy (Es) expressed by the formula: Es = [input power (unit: W/ ^cm2 )] / [introduced gas pressure (unit: Pa)] ² is set to 0.1 W/ ^cm2 Pa2 or ^more and 150 W/cm2 ^Pa2 or ^less ;
When forming the second thin film, the sputtering energy (Es) represented by the formula: Es = [input power (unit: W/ ^cm2 )] / [introduced gas pressure (unit: Pa)] ² is set to 0.04 W/ ^{cm2 Pa2} or more and 150 W/cm2 ^Pa2 or ^less .

(13) The method according to (12) above, wherein when forming the first thin film, the degree of vacuum within a film forming apparatus immediately before the film formation is set to 1×10 ⁻⁴ Pa or less.

(14) The method according to (12) or (13) above, in which, when forming the first thin film, only argon gas is introduced into the film formation chamber to form a thin film having a thickness of 1 to 10 nm, and then a gas containing nitrogen is introduced into the film formation chamber to continue film formation.

(15) Any of the methods (12) to (14) above, wherein the thickness of the first thin film is 20 nm or more.

The present invention provides a laminated film structure with high crystallinity and flatness, and a method for manufacturing the same.

1 shows an example of a schematic cross-sectional view of a laminated film structure. 1 shows another example of a schematic cross-sectional view of a laminated film structure.

A specific embodiment of the present invention (hereinafter, referred to as "the present embodiment") will be described. Note that the present invention is not limited to the following embodiment, and various modifications are possible within the scope that does not change the gist of the present invention.

[Laminated Film Structure]
The laminated film structure of this embodiment includes a Si(111) substrate, a first thin film made of a nitride-based material and/or aluminum provided on the Si(111) substrate, and a second thin film made of a nitride-based material provided on the first thin film. An amorphous layer having a thickness of 0 nm or more and less than 1.0 nm is present on the Si(111) substrate. Furthermore, the full width at half maximum (FWHM) of the rocking curve of the (0002) plane on the surface of the laminated film structure is 1.50° or less.

The laminated film structure of this embodiment has a highly flat surface, and the first thin film and the second thin film have high crystallinity. For example, when the crystallinity of the first thin film and the second thin film is evaluated by X-ray diffraction, the rocking curve full width at half maximum (FWHM) of the (0002) plane is 1.50° or less, preferably 1.00° or less, more preferably 0.95° or less, particularly preferably 0.50° or less, and most preferably 0.10° or less. Therefore, the laminated film structure can be suitably used as an underlayer when fabricating light-emitting elements such as LEDs and elements for power devices on a Si substrate. The laminated film structure can also be suitably used as a template substrate for growing a highly crystalline gallium nitride thin film.

To the best of the inventors' knowledge, there have been no reports of a laminated film structure having such a highly flat and highly crystalline nitride-based thin film on a Si substrate. For example, Patent Document 1 discloses growing gallium nitride (GaN) on a sapphire substrate by MOCVD, but the substrate used is not a Si substrate. Patent Document 2 proposes a gallium nitride sintered body for a sputtering target with a low oxygen content, but does not disclose the crystallinity of gallium nitride on a Si substrate. Patent Document 3 discloses a method of inserting gallium nitride as a buffer layer when growing gallium nitride on a Si substrate, but does not disclose in detail the structure between the Si substrate and the aluminum nitride buffer layer.

The Si(111) substrate is a Si substrate whose main surface has a crystal plane orientation of (111). The manufacturing method of the Si(111) substrate is not limited, and it may be manufactured by the Czochralski (CZ) method or the floating zone (FZ) method, or it may be a Si epitaxial substrate in which a Si single crystal layer is epitaxially grown on a Si single crystal substrate manufactured by these methods. In addition, the Si(111) substrate may or may not contain dopant elements such as donors and acceptors on its surface and/or inside.

A first thin film is provided on the Si (111) substrate. The first thin film is made of a nitride-based material and/or aluminum. The nitride-based material is not limited as long as it is a nitride-based compound. The nitride-based material and/or aluminum may or may not contain a dopant element. Examples of the first thin film include a gallium nitride thin film, an aluminum nitride thin film, a titanium nitride thin film, an indium nitride thin film, an aluminum gallium nitride thin film, and an indium gallium nitride thin film. The nitride compound is not limited to those having a stoichiometric composition. For example, the stoichiometric composition of gallium nitride (GaN) is 1:1 in the gallium (Ga) to nitrogen (N) ratio, but deviation from the stoichiometric composition is allowed as long as the crystal structure of gallium nitride is maintained. The first thin film is not limited in its form as long as it is made of a nitride-based material and/or aluminum. It may be made of only a nitride-based material or only aluminum. Alternatively, it may be made of a mixed phase of a nitride-based material and aluminum, or it may be a laminated film of a layer made of a nitride-based material and a layer made of aluminum.

The thickness of the first thin film is not limited as long as it can be considered a thin film. However, if the film thickness is too thin, the crystallinity of the first thin film and the second thin film and the surface flatness of the laminated film structure may be deteriorated. Therefore, the film thickness is preferably 20 nm or more, more preferably 30 nm or more, and even more preferably 40 nm or more. There is no upper limit to the film thickness. The film thickness may be 1000 nm or less, 500 nm or less, or 250 nm or less. The film thickness may be calculated by preparing multiple films sputtered under the same conditions, measuring the film thickness with a contact film thickness measuring device or an optical film thickness measuring device, and using the film formation rate obtained from the film thickness.

A second thin film made of a nitride-based material is provided on the first thin film. The material constituting the second thin film is not limited as long as it is a nitride-based compound. The nitride-based compound may or may not contain a dopant element. Examples of the second thin film include a gallium nitride thin film, an aluminum nitride thin film, a titanium nitride thin film, an indium nitride thin film, an aluminum gallium nitride thin film, and an indium gallium nitride thin film. The thickness of the second thin film is not limited as long as it can be considered a thin film. However, the film thickness is preferably 10 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more. There is no upper limit to the film thickness. The film thickness may be 1000 nm or less, 500 nm or less, or 300 nm or less. The film thickness may be calculated by preparing multiple films sputtered under the same conditions, measuring the film thickness with a contact film thickness measuring device or an optical film thickness measuring device, and using the film formation rate obtained from them.

In the laminated film structure of this embodiment, the surface, for example, the surface of the second thin film, preferably has an arithmetic mean roughness (Ra) of 10.0 nm or less. By reducing the surface roughness in this way, the crystallinity and flatness of the first thin film and the second thin film can be increased. In addition, by reducing the surface roughness of the second thin film, it is possible to epitaxially grow a thin film on the second thin film and fabricate a device such as a semiconductor element having good characteristics. The arithmetic mean roughness (Ra) is preferably 8.0 nm or less, more preferably 5.0 nm or less, and even more preferably 1.0 nm or less. There is no lower limit for the arithmetic mean roughness (Ra). The arithmetic mean roughness (Ra) may be 0.1 nm or more, 0.3 nm or more, or 0.5 nm or more.

In the laminated film structure of this embodiment, the thickness of the amorphous layer on the Si (111) substrate is 0 nm or more and less than 1.0 nm. In other words, the Si (111) substrate may or may not have an amorphous layer. However, if an amorphous layer is provided, its thickness is less than 1.0 nm. The case where an amorphous layer is not provided (first embodiment) and the case where an amorphous layer is provided (second embodiment) are described below.

First, the first embodiment will be described with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view of a laminated film structure in the first embodiment. This laminated film structure (1) comprises a Si (111) substrate (2), a first thin film (3) provided on the Si (111) substrate (2), and a second thin film (4) provided on the first thin film (3). In the first embodiment, there is no amorphous layer. That is, the thickness of the amorphous layer is 0 nm, and the first thin film (3) is in direct contact with the Si (111) substrate (2) without any other layers in between.

The first thin film (3) is in direct contact with the Si (111) substrate (2), which allows the crystallinity of the first thin film (3) and the second thin film (4) to be high. That is, the Si (111) substrate (2) has high crystallinity. The first thin film (3) is in direct contact with the highly crystalline Si (111) substrate (2), which allows the crystallinity to be passed on to the first thin film (3). The crystallinity of the first thin film (3) is then passed on to the second thin film (4). In terms of the manufacturing process, the first thin film (3) and the second thin film (4) are epitaxially grown well. On the other hand, if an excessively thick amorphous layer is present on the Si (111) substrate (2), the epitaxial growth of the first thin film (3) is hindered, and the crystallinity of the first thin film (3) and the second thin film (4) is reduced.

In the first embodiment, other layers may be present between the first thin film (3) and the second thin film, so long as the high crystallinity of the second thin film (4) is maintained. However, from the viewpoint of crystallinity, it is preferable that no other layers are present and that the second thin film (4) is in direct contact with the first thin film (3).

In the first embodiment, the oxygen content within 10 nm from the surface of the Si (111) substrate is preferably 5 at% (atomic %) or less. Here, the oxygen content is the amount of oxygen relative to the total amount of silicon, oxygen, and nitrogen. The oxygen content within 10 nm from the substrate surface is the oxygen content in a region within 10 nm in the height direction from the substrate surface. The height direction is the direction perpendicular to the substrate surface and away from the substrate. The measurement is performed at any position within 10% of the substrate radius from the center of the substrate. This oxygen content is derived from the natural oxide film on the surface of the Si (111) substrate used to manufacture the laminated film structure. That is, when the Si substrate is obtained, the surface is generally covered with a natural oxide film. This natural oxide film is amorphous and has a thickness of about 1 to 3 nm. If the Si substrate with the remaining natural oxide film is used as it is, the amount of oxygen within 10 nm from the substrate surface will increase excessively, and the crystallinity of the first thin film and the second thin film may decrease. In contrast, if a Si substrate from which the native oxide film has been more nearly completely removed is used, the amount of oxygen within 10 nm from the substrate surface is reduced, making it possible to further improve the crystallinity of the first thin film and the second thin film. From the viewpoint of crystallinity, a smaller amount of oxygen is preferable. Therefore, the oxygen content is more preferably 4 at% or less, and even more preferably 3 at% or less. The lower limit of the oxygen content may be 0 at%, but is typically 1 at% or more.

In the first aspect, the silicon nitride content within 10 nm from the Si (111) substrate surface is preferably 5 at% (atomic %) or less. Here, the silicon nitride content is the amount of silicon nitride relative to the total amount of silicon, oxygen, and nitrogen. This silicon nitride is derived from the atmosphere gas (introduced gas) used in the first thin film deposition process during the manufacture of the laminated film structure. That is, when the first thin film is deposited on the Si (111) substrate, if the atmosphere gas contains nitrogen at the initial stage of deposition, a nitriding reaction may occur on the Si substrate surface, resulting in the formation of amorphous silicon nitride. If such silicon nitride is present in large amounts on the Si substrate surface, the crystallinity of the first thin film and the second thin film may be reduced. In contrast, the amount of silicon nitride formed on the Si substrate surface can be suppressed by controlling the atmosphere gas when depositing the first thin film. From the viewpoint of crystallinity, it is preferable that the amount of silicon nitride formed within 10 nm from the substrate surface is small. Therefore, the silicon nitride content is more preferably 4 at% or less, even more preferably 3 at% or less, and particularly preferably 2 at% or less. The silicon nitride content may have a lower limit of 0 at% but is typically 1 at% or more.

Next, the second embodiment will be described with reference to FIG. 2. FIG. 2 is a schematic cross-sectional view of a laminated film structure in the second embodiment. This laminated film structure (1) comprises a Si (111) substrate (2), a first thin film (3) provided on the Si (111) substrate (2), and a second thin film (4) provided on the first thin film (3). In addition, in the second embodiment, an amorphous layer (5) exists between the Si (111) substrate (2) and the first thin film (3). However, the thickness of the amorphous layer (5) is less than 1.0 nm. In other words, the thickness of the amorphous layer (5) is greater than 0 nm and less than 1.0 nm.

By limiting the thickness of the amorphous layer (5) in this way, the crystallinity of the first thin film (3) and the second thin film (4) can be increased even if the amorphous layer (5) is present. On the other hand, if the amorphous layer (5) is excessively thick, the crystal orientation of the first thin film (3) will not be uniform, resulting in a polycrystalline thin film. The material of the amorphous layer is not particularly limited. However, it is typically made of silicon dioxide, silicon nitride and/or magnesium oxide, and more typically made of silicon dioxide. The thickness of the amorphous layer (5) may be 0.5 nm or more and less than 1.0 nm.

In the second embodiment, other layers besides the amorphous layer (5) may be present between the Si(111) substrate (2) and the first thin film (3) as long as the high crystallinity of the first thin film (3) is maintained. However, it is preferable that no other layers exist besides the amorphous layer (5). Also, other layers may exist between the first thin film (3) and the second thin film as long as the high crystallinity of the second thin film (4) is maintained. However, it is preferable that no other layers exist and that the second thin film (4) is in direct contact with the first thin film (3).

In the second embodiment, the oxygen content within 10 nm from the substrate surface is preferably 5 at% (atomic %) or less. Here, the oxygen content is the amount of oxygen relative to the total amount of silicon, oxygen, and nitrogen. The oxygen content within 10 nm from the substrate surface is the oxygen content in the region within 10 nm from the substrate surface, including the amorphous layer. As in the first embodiment, this oxygen content is derived from the natural oxide film on the surface of the Si(111) substrate. If a Si(111) substrate from which the natural oxide film has been more completely removed is used, the amount of oxygen contained within 10 nm from the substrate surface is reduced, and the crystallinity of the first thin film and the second thin film can be further improved. The oxygen content is more preferably 4 at% or less, and even more preferably 3 at% or less. The lower limit of the oxygen content may be 0 at%, but is typically 1 at% or more.

In the second embodiment, the silicon nitride content within 10 nm from the substrate surface is preferably 5 at% (atomic %) or less. This silicon nitride is derived from the atmospheric gas used in the first thin film deposition process, as in the first embodiment. By suppressing the amount of silicon nitride within 10 nm from the substrate surface, it is possible to further improve the crystallinity of the first thin film and the second thin film. From the viewpoint of crystallinity, it is preferable that the amount of silicon nitride is small. Therefore, the silicon nitride content is more preferably 4 at% or less, even more preferably 3 at% or less, and particularly preferably 2 at% or less. The silicon nitride content may have a lower limit of 0 at%, but is typically 1 at% or more.

In both the first and second aspects, the combination of materials constituting the first and second thin films is not limited. The materials constituting the first and second thin films may be the same or different. Furthermore, the first and/or second thin films may be a single layer or may be composed of multiple layers. Examples of combinations of the first thin film/second thin film include aluminum nitride thin film/gallium nitride thin film, titanium nitride thin film/gallium nitride thin film, aluminum nitride thin film/indium gallium nitride thin film, aluminum gallium nitride thin film/aluminum nitride thin film, aluminum gallium nitride thin film/gallium nitride thin film, aluminum thin film/gallium nitride thin film, aluminum thin film/indium gallium nitride thin film, aluminum thin film/aluminum nitride thin film, aluminum thin film/aluminum nitride thin film/gallium nitride thin film, aluminum thin film/titanium nitride thin film/gallium nitride thin film, aluminum thin film/aluminum nitride thin film/indium gallium nitride thin film, aluminum thin film/aluminum gallium nitride thin film/aluminum nitride thin film, and aluminum thin film/aluminum gallium nitride thin film/gallium nitride thin film. Among these, combinations of aluminum nitride thin film/gallium nitride thin film, aluminum thin film/gallium nitride thin film, and aluminum thin film/aluminum nitride thin film/gallium nitride thin film are preferred, and the combination of aluminum nitride thin film/gallium nitride thin film is particularly preferred.

In particular, it is preferable that the first thin film is an aluminum nitride (AlN) thin film and the second thin film is a gallium nitride (GaN) thin film. Gallium nitride (GaN) is useful as a material for light-emitting elements such as blue light-emitting diodes (LEDs) and blue laser diodes (LDs), and semiconductor elements such as power devices. By forming the second thin film from gallium nitride (GaN), the laminated film structure itself can be applied to electronic devices such as light-emitting elements and semiconductor elements. It is also possible to use the laminated film structure as a base substrate and further form gallium nitride (GaN) on it. The nitride (GaN) formed on the laminated film structure is epitaxially grown, so it is possible to make it into a device with good characteristics.

Furthermore, by constructing the first thin film from aluminum nitride (AlN), it is possible to further improve the crystallinity of the gallium nitride (GaN) that constitutes the second thin film. That is, when gallium nitride (GaN) is directly formed on a Si (111) substrate, depending on the film formation conditions, a phenomenon in which silicon (Si) reacts with gallium (Ga), that is, melt-back etching, may occur. In contrast, by providing aluminum nitride (AlN) on a Si (111) substrate, it is possible to suppress melt-back etching even more significantly.

The top surface of the laminated film structure, for example the surface of the second thin film, is preferably composed of a hexagonal gallium nitride layer, and the surface of this gallium nitride layer is preferably gallium (Ga) polar. By making the top surface gallium (Ga) polar, it is possible to suppress the formation of hexagonal facets that make device fabrication difficult when further gallium nitride (GaN) is formed on the laminated film structure.

[Semiconductor elements and electronic devices]
The semiconductor element of this embodiment includes the laminated film structure. The electronic device of this embodiment includes the semiconductor element. Examples of the semiconductor element include light-emitting elements such as blue light-emitting diodes (LEDs) and blue laser diodes (LDs), and power devices such as diodes and transistors. The semiconductor element may include a thin film and/or a thick film made of a nitride-based material such as gallium nitride (GaN) provided on the laminated film structure of this embodiment as a base layer. The semiconductor element and the electronic device may include other functional parts other than the laminated film structure. Due to the high crystallinity of the nitride-based thin film constituting the laminated film structure, the semiconductor element and the electronic device exhibit good characteristics.

[Method of manufacturing laminated film structure]
The laminated film structure of the present embodiment is not limited in its manufacturing method, but can be suitably manufactured according to the following method.

The method for manufacturing the laminated film structure of this embodiment includes the following steps: a step of preparing a Si(111) substrate (substrate preparation step), a step of immersing the Si(111) substrate in a cleaning solution (wet etching step), a step of forming a first thin film on the Si(111) substrate after immersion by a sputtering method (first thin film formation step), and a step of forming a second thin film on the first thin film by a sputtering method (second thin film formation step). When forming the first thin film, the sputtering energy (Es) expressed by the formula: Es = [input power density (unit: W/ ^cm2 )] / [introduced gas pressure (unit: Pa)] ² is set to 0.1 W/ ^cm2 Pa2 or ^more and 150 W/ ^cm2 Pa2 ^or less, and when forming the second thin film, the sputtering energy (Es) expressed by the formula: Es = [input power density (unit: W/ ^cm2 )] / [introduced gas pressure (unit: Pa)] ² is set to 0.04 W/ ^cm2 Pa2 or ^more and 150 W/cm2 ^{Pa2 or} less. Details of each process are described below.

<Substrate preparation process>
In the substrate preparation step, a Si (111) substrate is prepared. The manufacturing method of the Si (111) substrate is not limited, and it may be manufactured by the Czochralski (CZ) method or the floating zone (FZ) method, or it may be a Si epitaxial substrate in which a Si single crystal layer is epitaxially grown on a Si single crystal substrate manufactured by these methods. The Si (111) substrate may or may not contain a dopant element such as a donor or acceptor on its surface and/or inside.

<Wet Etching Process>
In the wet etching process, the prepared Si(111) substrate is immersed in a cleaning solution. Examples of the cleaning solution used for immersion include hydrofluoric acid aqueous solution, sulfuric acid, hydrochloric acid, hydrogen peroxide, ammonium hydroxide, trichloroethylene, acetone, methanol, isopropanol, etc., among which hydrofluoric acid aqueous solution is preferable. An ultrasonic cleaner may also be used when immersing in the cleaning solution. Generally, when a Si(111) substrate is just obtained, its surface is covered with contaminants and a natural oxide film. This natural oxide film is amorphous and has a thickness of about 1 to 3 nm. If a Si(111) substrate with remaining contaminants and natural oxide film is used as it is, the oxygen content within 10 nm from the substrate surface will be excessively increased, and the crystallinity of the first thin film and the second thin film may be reduced. Therefore, a wet etching process is provided to remove (clean) the oxide film on the Si(111) substrate surface. When using a hydrofluoric acid aqueous solution as the cleaning solution, the hydrofluoric acid concentration is preferably 5 to 10 mass %. By setting the hydrofluoric acid concentration to 5 mass % or more, it becomes possible to modify the surface with hydrogen. Furthermore, a high concentration exceeding 10 mass % may increase the surface roughness.

The immersion time of the Si (111) substrate is preferably 5 to 100 seconds. By making the immersion time 5 seconds or more, the oxide film can be sufficiently removed, and the thickness of the amorphous layer in the laminated film structure after manufacture can be reduced. Furthermore, by making the immersion time 100 seconds or less, it is possible to suppress the decrease in surface roughness during etching. The immersion time may be 20 seconds or more and 100 seconds or less. This makes it possible to produce a laminated film structure of the first embodiment with an amorphous layer thickness of 0 nm (no amorphous material exists). The immersion time may be 5 seconds or more and less than 20 seconds. This makes it possible to produce a laminated film structure of the second embodiment with an amorphous layer thickness of more than 0 nm and less than 1.0 nm.

After immersion in the cleaning solution, the remaining droplets on the substrate surface are removed. The remaining droplets can be removed by a method such as surface blowing using nitrogen gas. The Si(111) substrate after wet etching has a flat surface with the oxide film removed to a large extent. The arithmetic mean roughness (Ra) of the processed Si(111) is 0.5 nm or less, preferably 0.3 nm or less. Since the substrate surface is easily contaminated by impurities in the atmosphere after the remaining droplets are removed, it is preferable to proceed to the first thin film deposition process within 24 hours or less. After the wet etching process is completed, the first thin film deposition process may be started within 5 hours or within 1 hour.

<First thin film formation process>
In the first thin film deposition step, the first thin film is deposited on the Si (111) substrate after immersion by a sputtering method. A known method may be used as the sputtering method. Examples of such known methods include DC sputtering, RF sputtering, AC sputtering, DC magnetron sputtering, RF magnetron sputtering, pulse sputtering, and ion beam sputtering. However, DC magnetron sputtering or RF magnetron sputtering is preferred because it allows for uniform and high-speed deposition over a large area.

As the sputtering target, a known target used for forming a nitride thin film or an aluminum thin film can be used. Examples of such targets include metal targets and nitride targets. In addition, from the viewpoint of improving the crystallinity of the entire film, the lower the oxygen content of the sputtering target, the more preferable it is. The oxygen content is preferably 3 at% (atomic%) or less, and more preferably 1 at% or less. Furthermore, the larger the target area, the more it becomes possible to form a film on a large-area substrate, and the more uniform the film thickness and quality are improved. Therefore, the target area is preferably 18 ^cm2 or more, and more preferably 100 ^cm2 or more. The target area refers to the area of one of the main surfaces of the target.

When forming the first thin film, the ultimate vacuum in the film forming apparatus immediately before film formation is preferably 1×10 ⁻⁴ or less, more preferably 7×10 ⁻⁵ Pa or less, more preferably 2×10 ⁻⁵ Pa or less, even more preferably 9×10 ⁻⁶ Pa or less, and particularly preferably 5×10 ⁻⁶ Pa or less. By increasing the vacuum in the apparatus before film formation, the residual gas during film formation is prevented from becoming an impurity and being mixed into the deposited film (nitride-based thin film), and as a result, the crystallinity of the deposited film is further improved. In order to remove the residual gas, a baking process may be performed on the apparatus before film formation. In addition, it is preferable to perform sputtering film formation in a heated state of the substrate. This promotes the migration of particles deposited on the substrate, and a deposited film in a stable crystalline state can be formed. The substrate heating temperature (film formation temperature) is preferably 100 to 800° C., more preferably 200 to 600° C. It is preferable to apply the film formation temperature in stages from a low temperature. The film formation temperature in the initial stage of film formation is preferably 200 to 500°C. This makes it possible to suppress excessive migration and obtain a flat film. Furthermore, by forming the film at 300 to 600°C and then at 500 to 800°C in stages, it becomes possible to achieve both flatness and crystallinity.

As the gas introduced during sputtering, a known gas used in nitride thin film deposition can be used. Such a gas includes a mixed gas of argon (Ar) and nitrogen (N ₂ ). If necessary, other gases such as ammonia may be introduced. However, when forming the first thin film, it is preferable to introduce only argon (Ar) gas into the deposition chamber to deposit a thin film with a thickness of 3 to 10 nm, and then introduce a gas containing nitrogen (N ₂ ) into the deposition chamber to continue deposition. For example, when depositing a film using a metal target (metal aluminum target, etc.), only argon (Ar) gas is introduced at the beginning of deposition to deposit a metal film (aluminum film, etc.) with a thickness of 1 to 10 nm. Thereafter, when a nitrogen (N ₂ )-containing gas (e.g. a mixed gas of nitrogen and argon) is introduced to perform successive deposition, the metal film is nitrided and converted into a nitride film (aluminum nitride film, etc.), and further nitride is deposited on it. This makes it possible to obtain a nitride thin film (aluminum nitride thin film, etc.) with high crystallinity and few nitrogen defects. On the other hand, when nitrogen (N ₂ )-containing gas is introduced at the beginning of film formation, the surface of the Si substrate may be nitrided, and amorphous silicon nitride may be formed. Even when only argon (Ar) gas is introduced, if the thickness of the metal film at the beginning of film formation is less than 1 nm, silicon nitride may be formed on the surface of the Si substrate by the nitrogen (N ₂ ) introduced during the successive film formation. If silicon nitride is formed on the substrate surface, the heteroepitaxial growth of the first thin film may be hindered. On the other hand, if the thickness of the metal film at the beginning of film formation is more than 10 nm, it may be difficult to sufficiently nitride the metal film during the successive film formation. Therefore, the film thickness at the beginning of film formation before the introduction of nitrogen-containing gas is preferably 1 to 10 nm. The film thickness at the beginning of film formation may be 1 to 5 nm.

The sputtering energy (Es) when forming the first thin film is 0.1 W/cm ² Pa ² or more and 150 W/cm ² Pa ² or less. Here, the sputtering energy (Es) is the energy of the sputtered particles during sputtering film formation, and is defined by the formula: Es = [input power density (unit: W/cm ² )] / [introduced gas pressure (unit: Pa)] ^2. The input power density is the input energy per unit area when the actual input power is divided by the area of the sputtering target. This makes it possible to form a first thin film with high crystallinity. Although the detailed reason is not clear, it is presumed that the sputtering energy (Es) changes the characteristics of the sputtered particles, such as the adhesion of the sputtered particles that reach the substrate, the diffusion length when the sputtered particles migrate on the substrate, and/or the penetration depth into the film that has already been deposited, and this affects the crystallinity of the nitride-based thin film. Es may be 0.5 W/cm ² Pa ² or more, 1 W/cm ² Pa ² or more, 2 W/cm ² Pa ² or more, 5 W/cm ² Pa ² or more, 10 W/cm ² Pa ² or more, 15 W/cm ² Pa ² or more, 20 W/cm ² Pa ² or more, or 25 W/cm ² Pa ² or more. Es may be 100 W/cm ² Pa ² or less, 60 W/cm ² Pa ² or less, 30 W/cm ² Pa ² or less, 25 W/cm ² Pa ² or less, 20 W/cm ² Pa ² or less, 15 W/cm ² Pa ² or less, or 10 W/cm ² Pa ² or less.

In addition, when only argon (Ar) gas is introduced at the beginning of film formation and nitrogen ( _N2 )-containing gas is introduced during successive film formation, the sputtering energy (Es) at the beginning of film formation and during successive film formation may be the same or different.

The thickness of the first thin film is preferably 20 nm or more. If the thickness of the first thin film is too thin, the crystallinity of the first thin film and the second thin film and the surface flatness of the laminated film structure may be poor. Therefore, it is desirable that the thickness of the first thin film is relatively thick. The thickness of the first thin film may be 30 nm or more, 40 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, or 80 nm or more. The thickness may be 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, or 50 nm or less.

<Second Thin Film Forming Step>
In the second thin film deposition step, the second thin film is deposited on the first thin film by sputtering. As the sputtering method, a DC magnetron sputtering method, a pulse sputtering method, or an RF magnetron sputtering method, which can deposit a film uniformly and quickly over a large area, is preferable. In addition, as the sputtering target, a known target used for depositing a nitride-based thin film can be used. However, it is preferable to use a nitride-based target (e.g., a gallium nitride target). In addition, the oxygen content of the sputtering target is preferably 3 at% (atomic%) or less, more preferably 1 at% or less. Furthermore, the target area is preferably 18 cm2 or ^more , more preferably 100 ^cm2 or more.

The sputtering deposition is preferably performed in a state where the substrate is heated, as in the deposition of the first thin film. The substrate heating temperature (deposition temperature) is preferably 100 to 800° C., more preferably 300 to 800° C. In addition, as the gas introduced during sputtering, a known gas used in the deposition of a nitride-based thin film can be used. Such a gas can be a mixed gas of argon (Ar) and nitrogen (N ₂ ). If necessary, other gases such as ammonia may be introduced.

When forming the second thin film, the sputtering energy (Es) is set to 0.04 W/cm ² Pa ² or more and 150 W/cm ² Pa ² or less. This makes it possible to form a second thin film with high crystallinity. Es may be 0.1 W/cm ² Pa ² or more, 0.5 W/cm ² Pa ² or more, 1 W/cm ² Pa ² or more, 5 W/cm ² Pa ² or more, 10 W/cm ² Pa ² or more, 20 W/cm ² Pa ² or more, 25 W/cm ² Pa ² or more, or 30 W/cm ² Pa ² or more. Furthermore, Es may be 100 W/cm ² Pa ² or less, 70 W/cm ² Pa ² or less, 35 W/cm ² Pa ² or less, 30 W/cm ² Pa ² or less, or 25 W/cm ² Pa ² or less.

If necessary, a process for further laminating another nitride-based thin film on the second thin film may be provided. For example, a gallium nitride-based thin film may be formed as the second thin film by sputtering, and then another gallium nitride-based thin film may be formed on top of that by MOCVD.

In this manner, the laminated film structure of this embodiment is manufactured.

The present invention will be further described using the following examples and comparative examples. However, the present invention is not limited to the following examples.

[Example 1]
The laminated film structure of Example 1 was produced and evaluated as follows.

(1) Preparation of laminated film structure <Preparation step>
An n-type Si (111) substrate (Matsuzaki Manufacturing Co., Ltd., off-angle: none) was prepared as a Si substrate. This substrate had a diameter of 50±0.5 mmφ, a thickness of 425±25 μm, and a resistivity of 1000 Ω·cm or more.

<Wet Etching Process>
The prepared Si substrate was subjected to a wet etching process (cleaning process). First, hydrofluoric acid (Kanto Chemical Co., Ltd., Ultrapure grade) was diluted with ultrapure water (Kanto Chemical Co., Ltd., Ultrapure grade) to prepare a diluted hydrofluoric acid aqueous solution with a concentration of 5% by mass. Next, the Si substrate was immersed in the prepared diluted hydrofluoric acid aqueous solution for 30 seconds, and the substrate was pulled out of the hydrofluoric acid aqueous solution. Nitrogen gas was then blown to remove the droplets remaining on the substrate surface. This resulted in a Si substrate that had been subjected to a cleaning process (Ra: 0.15 nm). Then, without any time in between, the process proceeded to the deposition process of the first thin film.

<First thin film formation process>
A magnetron sputtering apparatus was used to deposit a first thin film on a wet-etched Si substrate. First, a metal aluminum (Al) target (99.99% by mass purity) was prepared as a sputtering target. The Si substrate was placed in a deposition chamber of the sputtering apparatus together with the target, and the deposition chamber was evacuated. After the degree of vacuum in the deposition chamber (the degree of vacuum achieved before deposition) reached 1.9×10 ⁻⁶ Pa, deposition was started.

The first thin film was formed as follows. First, the gas introduced into the film-forming chamber was argon (flow rate: 20 sccm) alone, and a thin film with a thickness of 3 nm was formed. At this time, the substrate temperature was 300° C., and the sputtering energy (Es) was 20 W/cm ² Pa ^2. Next, the introduced gas was switched to a mixed gas of nitrogen (flow rate: 3 sccm) and argon (flow rate: 17 sccm), and a thin film with a thickness of 47 nm was formed. At this time, the substrate temperature was 750° C., and the sputtering energy (Es) was 5 W/cm ² Pa ^2. As a result, an aluminum nitride thin film with a thickness of 50 nm was formed.

<Step of forming second thin film>
A magnetron sputtering device was used to deposit a second thin film on the deposited first thin film (aluminum nitride thin film). First, a gallium nitride (GaN) target (purity 99.99% by mass) was prepared as a sputtering target. The Si substrate on which the first thin film was deposited was placed in a deposition chamber together with this target. The gas introduced into the deposition chamber was a mixed gas of nitrogen (flow rate: 10 sccm) and argon (flow rate: 10 sccm), and deposition was performed under the conditions of a substrate temperature of 750° C. and a sputtering energy of 20 W/cm ² Pa ^2. As a result, a gallium nitride (GaN) thin film with a thickness of 50 nm was deposited.

In this way, a laminated film structure was produced in which an aluminum nitride thin film (first thin film) and a gallium nitride thin film (second thin film) were provided on a Si substrate. The film formation conditions for the first thin film and the second thin film are also shown in Tables 1 to 3.

(2) Evaluation The obtained laminated film structure was evaluated as follows.

<Structural analysis>
The gap between the Si substrate and the first thin film was analyzed to determine the presence or absence of an amorphous layer and its thickness. The analysis was performed as follows. First, a carbon coat was provided as a protective film on the surface of the laminated film structure, and then a specimen for observation was prepared by performing focused ion beam (FIB) processing. Next, a cross-section of the specimen was observed using a field emission transmission electron microscope (FE-TEM; JEM-2100F manufactured by JEOL Ltd.). The electron beam acceleration voltage was set to 200 kV.

<Oxygen Content and Silicon Nitride Content>
The oxygen content and silicon nitride content within 10 nm from the Si substrate including the amorphous layer were measured by X-ray photoelectron spectroscopy (ESCA; Electron Spectroscopy for Chemical Analysis). In performing the analysis in the depth direction, the film sample was subjected to ion milling with argon (Ar) monomer ions and measured. In the measurement, the content of each element (O, N, Si) was calculated using the peak areas of O1s, N1s, and Si2p, and the amount of oxygen and the amount of silicon nitride were quantified as atomic concentrations relative to the total concentration of silicon (Si), oxygen (O), and nitrogen (N). The details of the measurement conditions were as shown below.

-X-ray source: Monochrome Al-Kα ray (25W, 15kW)
- Radiation X-ray diameter: 100 μm φ
-Pass Energy: 93.9eV (O1s, N1s)
11.75eV (Si2p)
-Step Size: 0.1eV

<Crystalline nature of thin films>
The crystallinity of the first thin film and the second thin film was evaluated using an X-ray diffractometer (D8 DISCOVER, manufactured by Bruker AXS). The analysis was performed in HIGH RESOLUTION mode under conditions of 40 kV and 40 mA. In addition, a monochromator was used to remove CuKα2, and ω-scan was performed. The rocking curve of the (0002) plane was measured to determine the full width at half maximum (FWHM), which was used as an index of the crystallinity of the thin film. The details of the analysis conditions were as follows:

-Radiation source: CuKα radiation (λ=0.15418nm)
- Monochrometer: Ge(220)
-Pathfinder: Crystal3B
- Measurement mode: ω scan - Measurement interval: 0.01°
(0.0005° if half-width is 0.1° or less)
- Measurement time: 0.5 seconds - Measurement range: ω = 0° to 35°

<Polarity and crystallinity of gallium nitride thin films>
The polarity and crystalline phase of the gallium nitride thin film were evaluated using a time-of-flight atom scattering surface analyzer (TOFLAS-3000, Pascal Corporation). The laminated film structure was set in the device so that its film-formed surface was the upper surface, and measurements were performed. The polarity and crystalline phase of the gallium nitride thin film were determined by comparing the pole figures obtained by measurement with the pole figures of each crystalline phase and polarity of the first four outer layers obtained by simulation. The details of the measurement conditions are as shown below.

- Probe: He (atomic scattering)
-Energy: 3 keV
-Beam source-target distance: 805 mm
- Target-detector distance: 395 mm
-Analysis chamber vacuum level: 2× ^10-3 Pa or less

<Surface roughness of laminated film structure>
The arithmetic average roughness (Ra) of the surface of the laminated film structure was measured using a scanning probe microscope (Bruker AXS, NanoScope IIIa) in tapping mode AFM with a visual field of 2 μm×2 μm.

[Examples 2 and 3]
The film formation conditions for the first thin film and the second thin film were as shown in Tables 1 to 3. Except for that, the laminated film structure was produced and evaluated in the same manner as in Example 1.

[Example 4]
In the wet etching process, the Si substrate was immersed for 5 seconds, and the film formation conditions for the first thin film and the second thin film were as shown in Tables 1 to 3. Except for this, the laminated film structure was produced and evaluated in the same manner as in Example 1.

[Example 5]
When the first nitride-based thin film was formed, the initial and subsequent film thicknesses were 3 nm at 500° C. and 44 nm at 750° C., and the film formation conditions for the second nitride-based thin film were as shown in Table 3. Except for this, the laminated film structure was produced and evaluated in the same manner as in Example 1.

[Examples 6 to 17]
The film formation conditions for the first thin film and the second thin film were as shown in Tables 1 to 3. Except for that, the laminated film structure was produced and evaluated in the same manner as in Example 1.

[Example 18 (Comparative)]
In the wet etching process, the immersion time of the Si substrate was set to 2 seconds, and the film formation conditions of the first thin film and the second thin film were set as shown in Tables 1 to 3. Except for that, the laminated film structure was produced and evaluated in the same manner as in Example 1.

[Example 19 (Comparative)]
The film formation conditions for the first thin film and the second thin film were as shown in Tables 1 to 3. Except for that, the laminated film structure was produced and evaluated in the same manner as in Example 1.

[Example 20 (Comparative)]
After the wet etching process, the substrate was stored in the air for one day, and then the first thin film and the second thin film were formed. The film formation conditions for the first thin film and the second thin film were as shown in Tables 1 to 3. Otherwise, the laminated film structure was produced and evaluated in the same manner as in Example 1.

[Examples 21 to 25 (Comparative)]
The film formation conditions for the first thin film and the second thin film were as shown in Tables 1 to 3. Except for that, the laminated film structure was produced and evaluated in the same manner as in Example 1.

(3) Results The evaluation results obtained for Examples 1 to 25 are shown in Table 4. Examples 1 to 17 are working examples, and Examples 18 to 25 are comparative examples.

As shown in Table 4, the samples of Examples 1 to 17, which are working examples, had a small amorphous layer thickness of 0.9 nm or less. In addition, the full width at half maximum (FWHM) was small, at 0.98° or less, and the arithmetic mean roughness (Ra) was small, at 8.1 nm or less. Thus, in Examples 1 to 17, it was possible to successfully fabricate a Ga-polar gallium nitride thin film (nitride-based thin film) that was highly flat and crystalline and had a hexagonal crystal structure.

In contrast, the samples of Examples 18 to 20, which are comparative examples, had a large amorphous layer thickness of 2.0 nm. Therefore, the full width at half maximum (FWHM) and arithmetic mean roughness (Ra) were large, and the crystallinity and surface flatness were poor. For example, in Example 18, in which the Si substrate was immersed for 2 seconds, 2.0 nm of amorphous material thought to be a natural oxide film remained between the Si substrate and the first thin film, and a film with the desired characteristics could not be obtained. In Example 19, in which film formation was performed for 10 seconds using argon and nitrogen, 2.0 nm of amorphous material thought to be an oxide film caused by impurities in the gas remained between the Si substrate and the first thin film, and a film with the desired characteristics could not be obtained. Similarly, in Example 20, which was stored in the air for one day before the formation of the first thin film, 2.0 nm of amorphous material thought to be a natural oxide film caused by impurities in the air remained, and a film with the desired characteristics could not be obtained. In Example 21, in which the sputtering energy (Es) when forming the first thin film and the second thin film was 200 W/cm ² Pa ² , and in Example 22, in which the thickness of the first thin film was 10 nm, a film with the desired characteristics could not be obtained. In Example 23, in which the ultimate vacuum before the formation of the first thin film was 2.3×10 ⁻⁴ Pa, the amount of oxygen was large within 10 nm from the Si surface, and a film with the desired characteristics could not be obtained. In Example 24, in which the sputtering energy (Es) of the first thin film was 0.05 W/cm ² Pa ² , and in Example 25, in which the sputtering energy (Es) of the second thin film was 0.03 W/cm ² Pa ² , a film with the desired characteristics could not be obtained.

REFERENCE SIGNS LIST 1 laminated film structure 2 Si (111) substrate 3 first thin film 4 second thin film 5 amorphous layer

Claims (15)

A Si(111) substrate;
a first thin film made of a nitride-based material and/or aluminum provided on the Si(111) substrate;
a second thin film made of a nitride-based material provided on the first thin film;
A laminated film structure comprising:
A laminated film structure, comprising: an amorphous layer having a thickness of 0 nm or more and less than 1.0 nm on the Si(111) substrate; a full width at half maximum (FWHM) of a rocking curve of a (0002) plane on the surface of the laminated film structure is 1.50° or less; and an arithmetic mean roughness (Ra) of the surface of the laminated film structure is 10.0 nm or less. The laminated film structure of claim 1, wherein the amorphous layer has a thickness of 0 nm, and the first thin film is in direct contact with the Si(111) substrate without any other layer therebetween. The laminated film structure according to claim 2, wherein the oxygen content within 10 nm from the surface of the Si(111) substrate is 5 at% or less. The laminated film structure according to claim 2 or 3, wherein the silicon nitride content within 10 nm from the surface of the Si(111) substrate is 5 at% or less. The laminated film structure of claim 1, wherein the thickness of the amorphous layer is greater than 0 nm and less than 1.0 nm. The laminated film structure according to claim 5, wherein the silicon nitride content within 10 nm from the surface of the Si(111) substrate is 5 at% or less. The laminated film structure according to any one of claims 1 to 6, wherein the full width at half maximum (FWHM) of the rocking curve of the (0002) plane on the surface of the laminated film structure is 0.10° or less. The laminated film structure according to any one of claims 1 to 7, wherein the first thin film is an aluminum nitride thin film and the second thin film is a gallium nitride thin film. 9. The laminated film structure according to claim 1, wherein an outermost surface of the laminated film structure is composed of a hexagonal gallium nitride layer, and the surface of the gallium nitride layer has a gallium (Ga) polarity. A semiconductor device comprising the laminated film structure according to any one of claims 1 to 9. An electronic device including the semiconductor element according to claim 10. A method for producing the laminated film structure according to any one of claims 1 to 9, comprising the following steps:
providing a Si(111) substrate;
immersing the Si(111) substrate in a cleaning solution;
forming a first thin film on the Si(111) substrate by a sputtering method after immersion;
forming a second thin film on the first thin film by a sputtering method;
When forming the first thin film, the sputtering energy (Es) expressed by the formula: Es = [input power density (unit: W/ ^cm2 )] / [introduced gas pressure (unit: Pa)] ² is set to 0.1 W/ ^cm2 Pa2 or ^more and 150 W/cm2 ^{Pa2 or less} ;
When forming the second thin film, the sputtering energy (Es) represented by the formula: Es = [input power density (unit: W/ ^cm2 )] / [introduced gas pressure (unit: Pa)] ² is set to 0.04 W/ ^cm2 Pa2 or ^more and 150 W/cm2 ^{Pa2 or} less. 13. The method according to claim 12, wherein the degree of vacuum in a film forming apparatus immediately before the first thin film is formed is set to 1×10 ⁻⁴ Pa or less. The method according to claim 12 or 13, wherein when forming the first thin film, only argon gas is introduced into the film formation chamber to form a thin film having a thickness of 1 to 10 nm, and then a gas containing nitrogen is introduced into the film formation chamber to continue film formation. The method according to any one of claims 12 to 14, wherein the first thin film has a thickness of 20 nm or more.

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