TWI875852B - Multilayer film structure, semiconductor element, electronic device, and method for manufacturing multilayer film structure - Google Patents

Abstract

The present invention provides a multilayer film structure with high crystallinity and flatness and a manufacturing method thereof. The multilayer film structure comprises: a Si(111) substrate; a first thin film disposed on the Si(111) substrate, comprising a nitride-based material and/or aluminum; and a second thin film disposed on the first thin film, comprising a nitride-based material, and in the multilayer film structure, there is an amorphous layer with a thickness of 0 nm or more and less than 1.0 nm on the Si(111) substrate, and the half-value width (FWHM) of the wobble curve of the (0002) plane on the surface of the multilayer film structure is less than 1.50°.

Description

Multilayer film structure, semiconductor element, electronic device, and method for manufacturing multilayer film structure

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

Nitride materials show excellent semiconductor properties. For example, gallium nitride (GaN) is installed as a material for blue light emitting diodes (LED) or blue laser diodes (LD). In addition, due to its high voltage resistance, it is suitable for use in power devices and the like. Therefore, a multilayer film structure having a nitride thin film disposed on a substrate is effectively used in the field of electronic devices. Such nitride thin films are usually manufactured by metal organic chemical vapor deposition (MOCVD). In addition, in addition to the MOCVD method, the sputtering method for manufacturing nitride thin films has also been proposed. As documents that disclose the technology related to the manufacture of nitride thin films, patent documents 1 to 3 can be cited.

Patent document 1 discloses a method for growing a semiconductor crystal film, which is a method for growing a semiconductor crystal film on a heated substrate surface by spraying a reaction gas on the substrate surface. The method is characterized in that the reaction gas is sprayed parallel to or obliquely on the substrate surface, and a pressure diffusion gas is sprayed toward the substrate at the same time (the scope of application of patent document 1). Moreover, in the embodiment, the following contents are recorded: GaN is grown on a sapphire substrate using ammonia, hydrogen and trimethyl gallium (TMG) gas (the embodiment of patent document 1).

Patent document 2 discloses a metallic gallium-infiltrated gallium nitride molded product, which is characterized in that gallium nitride and metallic gallium exist as different phases in the molded product, and the molar ratio of Ga/(Ga+N) in the entire molded product is 55% or more and 80% or less (claim 1 of patent document 2). In addition, the following contents are described in the embodiment: the obtained metallic gallium-infiltrated gallium nitride molded product is joined to produce a gallium nitride-based sputtering target; and after sputtering the obtained target, a film can be formed without cracks in both radio frequency (RF) sputtering and direct current (DC) sputtering (patent document 2 [0102]).

Patent document 3 discloses a method for forming a gallium nitride film, which includes: forming an aluminum nitride film on a silicon substrate by sputtering an aluminum target using plasma generated by a mixed gas of a nitrogen-containing gas and a rare gas; and forming a gallium nitride film on the aluminum nitride film. The method for forming a gallium nitride film is characterized in that it includes the following steps: before forming the aluminum nitride film, forming an aluminum film on the silicon substrate by sputtering an aluminum target using plasma generated by a rare gas (claim 1 of patent document 3).

[Prior art literature]

[Patent Literature]

[Patent document 1] Japanese Patent Publication No. 4-164895

[Patent Document 2] Japanese Patent Publication No. 2014-159368

[Patent Document 3] Japanese Patent Publication No. 2013-227198

There are problems with nitride-based thin films made using previous methods. In order to improve device characteristics, it is ideal that the nitride-based thin films constituting the device have high crystallinity. Here, high crystallinity refers to a state in which the crystal orientation within the thin film is highly uniform. In addition, when nitride-based thin films are used for power devices and other purposes, Si substrates that can be enlarged in diameter and are low-cost are the most effective substrates.

However, it is difficult to form a highly crystalline nitride-based thin film (such as a gallium nitride thin film) on a Si substrate using the MOCVD method. That is, in order to grow a highly crystalline thin film using the MOCVD method, the substrate temperature needs to be raised to about 1000°C and the film needs to be formed at this temperature. Therefore, there is a phenomenon that the metal component (such as gallium) in the thin film reacts with the Si substrate during film formation, that is, meltback etching occurs. In addition, the thermal expansion coefficient of gallium nitride is very different from that of the Si substrate. Therefore, during the cooling process after film formation, there is a problem that cracks are easily formed in the gallium nitride thin film. Due to this problem, Si substrates cannot be used in the MOCVD method, and expensive substrates such as sapphire substrates or gallium nitride single crystal substrates need to be used.

On the other hand, when the sputtering method is used, the film can be formed at a low temperature below 1000°C. Therefore, a thin film can be formed on a Si substrate without causing problems such as melt-back etching or cracks. However, there is room for improvement in the crystallinity of the previous nitride-based thin films formed by the sputtering method. Therefore, in order to produce a multilayer film structure including a highly crystalline nitride-based thin film on a Si substrate, it is expected to further study the film formation conditions of the thin film or the interface structure of the multilayer film structure.

In view of this problem, the inventors and others conducted research and obtained the following insights: In a multilayer film structure having a thin film containing a nitride-based material and/or aluminum disposed 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 controlling it is important in obtaining a highly crystalline nitride-based thin film.

The present invention is completed based on this insight, and its purpose is to provide a multilayer film structure with high crystallinity and flatness and a method for manufacturing the same.

The present invention includes the following forms (1) to (15). Furthermore, in this specification, the expression "~" includes the numerical values at both ends. That is, "X~Y" is synonymous with "X or more and Y or less". In addition, "X and/or Y" is synonymous with "at least one of X and Y (one or both of X and Y)".

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

(2) A multilayer film structure as described in (1), wherein the thickness of the amorphous layer is 0 nm, and the first film is in direct contact with the Si (111) substrate without passing through other layers.

(3) A multilayer film structure as described in (2), wherein the oxygen content within 10 nm from the surface of the Si (111) substrate is less than 5 at%.

(4) A multilayer film structure as described in (2) or (3), wherein the silicon nitride content within 10 nm from the surface of the Si (111) substrate is less than 5 at%.

(5) A multilayer film structure as described in (1), wherein the thickness of the amorphous layer is greater than 0 nm and less than 1.0 nm.

(6) A multilayer film structure as described in (5), wherein the silicon nitride content within 10 nm from the surface of the Si (111) substrate is less than 5 at%.

(7) A multilayer film structure as described in any one of (1) to (6), wherein the arithmetic mean roughness (Ra) of the surface of the multilayer film structure is less than 10.0 nm.

(8) A multilayer film structure as described in any one of (1) to (7), wherein the first film is an aluminum nitride film and the second film is a gallium nitride film.

(9) A multilayer film structure as described in any one of (1) to (8), wherein 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 comprising a multilayer film structure as described in any one of (1) to (9).

(11) An electronic device comprising the semiconductor element as described in (10).

(12) A method for manufacturing a multilayer film structure as described in any one of (1) to (9), comprising the following steps: a step of preparing a Si (111) substrate; a step of immersing the Si (111) substrate in a cleaning solution; a step of forming a first thin film on the immersed Si (111) substrate by a sputtering method; and a step of forming a second thin film on the first thin film by a sputtering method, and when forming the first 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 0.1 W/ ^{cm2Pa2 or more} and 150 W/ ^cm2Pa2 or less. ² or less, when forming the second thin film, the sputtering energy (Es) represented by the formula: Es=[input power density (unit: W/cm ² )]/[introduced gas pressure (unit: Pa)] ² is set to 0.04 W/cm ² Pa ² or more and 150 W/cm ² Pa ² or less.

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

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

(15) A method as described in any one of (12) to (14), wherein the thickness of the first thin film is greater than 20 nm.

According to the present invention, a multilayer film structure having high crystallinity and flatness and a method for manufacturing the same are provided.

1: Laminated film structure

2:Si(111) substrate

3: First film

4: Second film

5: Amorphous layer

Figure 1 shows an example of a cross-sectional schematic diagram of a multilayer film structure.

FIG2 shows another example of a cross-sectional schematic diagram of a multilayer film structure.

The specific implementation method of the present invention (hereinafter referred to as "this implementation method") is described. Furthermore, the present invention is not limited to the following implementation method, and various changes can be made within the scope of not changing the main purpose of the present invention. In addition, in the following implementation method, it should not be limited to the specific combination of each element for interpretation, and any combination is allowed.

[Laminar film structure]

The multilayer film structure of this embodiment includes: a Si(111) substrate; a first thin film, disposed on the Si(111) substrate, comprising a nitride-based material and/or aluminum; and a second thin film, disposed on the first thin film, comprising a nitride-based material. An amorphous layer having a thickness of 0 nm or more and less than 1.0 nm exists on the Si(111) substrate. The half-value width (FWHM) of the swing curve of the (0002) plane on the surface of the multilayer film structure is less than 1.50°.

The multilayer film structure of this embodiment has a highly flat surface, and the first film and the second film have high crystallinity. For example, when the crystallinity of the first film and the second film is evaluated by X-ray diffraction, the half-value width (FWHM) of the wobble curve of the (0002) plane is less than 1.50°, preferably less than 1.00°, further preferably less than 0.95°, particularly preferably less than 0.50°, and most preferably less than 0.10°. Therefore, the multilayer film structure can be preferably used as a base layer when making light-emitting elements such as LEDs or power devices on Si substrates. In addition, the multilayer film structure can be preferably used as a template substrate for growing highly crystalline gallium nitride thin films.

As far as the inventors know, there is no report of a multilayer film structure including a highly flat and highly crystalline nitride-based thin film on a Si substrate. For example, Patent Document 1 discloses the growth of 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 there is no description of the crystallinity of gallium nitride on a Si substrate. Patent Document 3 discloses a method of loading gallium nitride as a buffer layer when growing gallium nitride on a Si substrate, but there is no detailed description of the structure between the Si substrate and the aluminum nitride buffer layer.

Si(111) substrate is a Si substrate whose main surface has a crystal plane orientation of (111) plane. The method of manufacturing Si(111) substrate is not limited, and it can be manufactured by Czochraski (CZ) method or floating zone (FZ) method, or it can 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, Si(111) substrate may contain doping elements such as donors or acceptors on its surface and/or inside, or it may not contain them.

A first thin film is provided on a Si (111) substrate. The first thin film includes a nitride material and/or aluminum. The nitride material is not limited as long as it is a nitride compound. The nitride material and/or aluminum may contain a dopant element or may not contain it. 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. Furthermore, the nitride compound is not limited to a compound of a stoichiometric composition. For example, the ratio of gallium (Ga) to nitrogen (N) in the stoichiometric composition of gallium nitride (GaN) is 1:1, but as long as the crystal structure of gallium nitride is maintained, a deviation from the stoichiometric composition is allowed. In addition, as long as the first film contains nitride-based materials and/or aluminum, its morphology is not limited. It may contain only nitride-based materials or only aluminum. Alternatively, it may contain a mixed phase of nitride-based materials and aluminum, or it may be a laminated film of a layer containing a nitride-based material and a layer containing aluminum.

As long as the first film can be regarded as a thin film, its thickness is not limited. However, when the film thickness is too thin, the crystallinity of the first film and the second film or the surface flatness of the laminated film structure may be poor. Therefore, the film thickness is preferably greater than 20nm, more preferably greater than 30nm, and further preferably greater than 40nm. The upper limit of the film thickness is not limited. The film thickness may be less than 1000nm, less than 500nm, or less than 250nm. The film thickness may be any one of 20nm~1000nm, 20nm~500nm, 20nm~250nm, 30nm~1000nm, 30nm~500nm, 30nm~250nm, 40nm~1000nm, 40nm~500nm and 40nm~250nm. Regarding the film thickness, you can prepare multiple films sputtered under the same conditions, find the film thickness using a contact-type film thickness meter or an optical film thickness meter, and use the film formation rate found to calculate.

A second thin film including a nitride 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 compound. The nitride compound may contain a dopant element, 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. In addition, as long as the second thin film can be regarded as a thin film, its thickness is not limited. However, the film thickness is preferably greater than 10 nm, further preferably greater than 20 nm, and more preferably greater than 30 nm. The upper limit of the film thickness is not limited. The film thickness may be less than 1000 nm, less than 500 nm, or less than 300 nm. The film thickness can be any one of 10nm~1000nm, 10nm~500nm, 10nm~300nm, 20nm~1000nm, 20nm~500nm, 20nm~300nm, 30nm~1000nm, 30nm~500nm, and 30nm~300nm. Regarding the film thickness, multiple films sputtered under the same conditions can be prepared, and the film thickness can be obtained using a contact film thickness meter or an optical film thickness meter, and the film formation rate obtained from these can be used for calculation.

Regarding the multilayer film structure of the present embodiment, it is preferred that the arithmetic mean roughness (Ra) of its surface, for example, the surface of the second film, is less than 10.0 nm. By reducing the surface roughness in this way, the crystallinity and flatness of the first film and the second film can be improved. In addition, by reducing the surface roughness of the second film, it is possible to further epitaxially grow a thin film thereon, thereby manufacturing devices such as semiconductor elements with good characteristics. The arithmetic mean roughness (Ra) is preferably less than 8.0 nm, more preferably less than 5.0 nm, and further preferably less than 1.0 nm. The lower limit of the arithmetic mean roughness (Ra) is not limited. The arithmetic mean roughness (Ra) can be greater than 0.1 nm, greater than 0.3 nm, or greater than 0.5 nm. The arithmetic mean roughness (Ra) can be any one of 0.1nm~8.0nm, 0.1nm~5.0nm, 0.1nm~1.0nm, 0.3nm~8.0nm, 0.3nm~5.0nm, 0.3nm~1.0nm, 0.5nm~8.0nm, 0.5nm~5.0nm and 0.5nm~1.0nm.

The thickness of the amorphous layer on the Si(111) substrate of the multilayer film structure of this embodiment is greater than 0 nm and less than 1.0 nm. That is, the amorphous layer may be included on the Si(111) substrate, or it may not be included. In the case where the amorphous layer is included, its thickness is less than 1.0 nm. The following describes the case where the amorphous layer is not included (first form) and the case where the amorphous layer is included (second form).

First, the first form is described using FIG1. FIG1 is a schematic cross-sectional view of a multilayer film structure of the first form. The multilayer film structure (1) includes: a Si (111) substrate (2), a first thin film (3) disposed on the Si (111) substrate (2), and a second thin film (4) disposed on the first thin film (3). In the first form, 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 passing through other layers.

By directly contacting the first film (3) with the Si (111) substrate (2), the crystallinity of the first film (3) and the second film (4) can be improved. That is, the crystallinity of the Si (111) substrate (2) is high. By directly contacting the first film (3) with the highly crystalline Si (111) substrate (2), its crystallinity is continued by the first film (3). Then, the crystallinity of the first film (3) is continued by the second film (4). According to the performance derived from the manufacturing method, the first film (3) and the second film (4) are well epitaxially grown. In contrast, if there is an excessively thick amorphous layer on the Si (111) substrate (2), the epitaxial growth of the first film (3) is hindered, and the crystallinity of the first film (3) and the second film (4) becomes low.

In the first form, as long as the high crystallinity of the second film (4) is maintained, other layers may exist between the first film (3) and the second film. However, from the perspective of crystallinity, it is preferred that no other layers exist and the second film (4) is in direct contact with the first film (3).

In the first form, it is preferred that the oxygen content within 10 nm from the surface of the Si (111) substrate is less than 5 at% (atomic %). Here, the oxygen content is the amount of oxygen relative to the total amount of silicon, oxygen and nitrogen. In addition, the oxygen content within 10 nm from the substrate surface is the oxygen content in the region within 10 nm from the substrate surface in the height direction. In addition, the height direction refers to the direction perpendicular to the substrate surface and away from the substrate. In addition, the measurement is performed at any position within a range of 10% of the substrate radius starting from the center of the substrate. The oxygen-containing source is a natural oxide film on the surface of the Si (111) substrate used for manufacturing a multilayer film structure. That is, the Si substrate is generally covered with a natural oxide film when it is just obtained. The natural oxide film is amorphous and has a thickness of about 1 nm to 3 nm. If a Si substrate with a residual natural oxide film is used directly, the amount of oxygen within 10nm from the substrate surface will increase excessively, and the crystallinity of the first and second films may decrease. In contrast, if a Si substrate with a natural oxide film removed in a more nearly complete state is used, the amount of oxygen within 10nm from the substrate surface will be suppressed, thereby further improving the crystallinity of the first and second films. From the perspective of crystallinity, the less oxygen, the better. Therefore, the oxygen content is preferably less than 4at%, and further preferably less than 3at%. The lower limit of the oxygen content can be 0at%, but typically it is more than 1at%. The oxygen content can also be any one of 0at%~4at%, 0at%~3at%, 1at%~4at% and 1at%~3at%.

In the first form, it is preferred that the silicon nitride content within 10 nm from the surface of the Si (111) substrate is 5 at% (atomic %) or less. The silicon nitride content here refers to the amount of silicon nitride relative to the total amount of silicon, oxygen and nitrogen. The silicon nitride originates from the ambient gas (introduced gas) used in the first thin film film formation step when manufacturing the multilayer film structure. That is, when the first thin film is formed on the Si (111) substrate, if the ambient gas contains nitrogen at the initial stage of film formation, a nitridation reaction occurs on the surface of the Si substrate to form amorphous silicon nitride. If such silicon nitride exists in large amounts on the surface of the Si substrate, the crystallinity of the first and second thin films may decrease. In contrast, by controlling the ambient gas when forming the first thin film, the amount of silicon nitride formed on the surface of the Si substrate can be suppressed. From the perspective of crystallinity, it is preferred that the amount of silicon nitride within 10 nm from the substrate surface is small. Therefore, the silicon nitride content is preferably less than 4 at%, further preferably less than 3 at%, and particularly preferably less than 2 at%. The lower limit of the silicon nitride content may be 0 at%, but typically it is greater than 1 at%. The silicon nitride content may be any of 0 at% to 4 at%, 0 at% to 3 at%, 0 at% to 2 at%, 1 at% to 4 at%, 1 at% to 3 at%, and 1 at% to 2 at%.

Next, the second form is described using FIG. 2. FIG. 2 is a schematic cross-sectional view of a multilayer film structure of the second form. The multilayer film structure (1) includes: a Si (111) substrate (2), a first thin film (3) disposed on the Si (111) substrate (2), and a second thin film (4) disposed on the first thin film (3). In addition, in the second form, an amorphous layer (5) exists between the Si (111) substrate (2) and the first thin film (3). However, its thickness is less than 1.0 nm. That is, 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, even if the amorphous layer (5) exists, the crystallinity of the first film (3) and the second film (4) can be improved. In contrast, if the amorphous layer (5) is too thick, the crystal orientation of the first film (3) is inconsistent, and it becomes a polycrystalline film. Furthermore, the material of the amorphous layer is not particularly limited. However, it typically includes silicon dioxide, silicon nitride and/or magnesium oxide, and more typically includes silicon dioxide. In addition, the thickness of the amorphous layer (5) can also be greater than 0.5nm and less than 1.0nm.

In the second form, as long as the high crystallinity of the first film (3) is maintained, other layers other than the amorphous layer (5) may exist between the Si (111) substrate (2) and the first film (3). However, it is preferred that no other layers other than the amorphous layer (5) exist. In addition, as long as the high crystallinity of the second film (4) is maintained, other layers may also exist between the first film (3) and the second film. However, it is preferred that no other layers exist and the second film (4) is in direct contact with the first film (3).

In the second form, it is preferred that the oxygen content within 10 nm from the substrate surface is 5 at% (atomic %) or less. Here, the oxygen content is the amount of oxygen relative to the total amount of silicon, oxygen and nitrogen. In addition, the so-called oxygen content within 10 nm from the substrate surface is the oxygen content of the region within 10 nm from the substrate surface, that is, the part including the amorphous layer. The oxygen contained is the same as in the first form, and is derived from the natural oxide film on the surface of the Si (111) substrate. If a Si (111) substrate is used in which the natural oxide film has been removed in a more nearly complete state, the amount of oxygen contained within 10 nm from the substrate surface is suppressed, thereby further improving the crystallinity of the first film and the second film. The oxygen content is more preferably less than 4 at%, and further preferably less than 3 at%. The lower limit of the oxygen content can be 0 at%, but is typically greater than 1 at%. The oxygen content can be any one of 0at%~4at%, 0at%~3at%, 1at%~4at% and 1at%~3at%.

In the second form, the silicon nitride content within 10 nm from the substrate surface is preferably 5 at% (atomic %) or less. The silicon nitride is derived from the ambient gas used in the first thin film forming step, as in the first form. By suppressing the amount of silicon nitride within 10 nm from the substrate surface, the crystallinity of the first thin film and the second thin film can be further improved. From the perspective of crystallinity, the amount of silicon nitride is preferably small. Therefore, the silicon nitride content is more preferably 4 at% or less, further preferably 3 at% or less, and particularly preferably 2 at% or less. The lower limit of the silicon nitride content may be 0 at%, but is typically 1 at% or more. The silicon nitride content may be any one of 0 at% to 4 at%, 0 at% to 3 at%, 0 at% to 2 at%, 1 at% to 4 at%, 1 at% to 3 at%, and 1 at% to 2 at%.

Neither the first form nor the second form limits the combination of materials constituting the first film and the second film. The materials constituting the first film and the second film may be the same or different. In addition, the first film and/or the second film may be a single layer or may include multiple layers. As a combination of the first film/the second film, there are listed: aluminum nitride film/gallium nitride film, titanium nitride film/gallium nitride film, aluminum nitride film/indium gallium nitride film, aluminum gallium nitride film/aluminum nitride film, aluminum gallium nitride film/gallium nitride film, aluminum film/gallium nitride film, aluminum film/indium gallium nitride film, aluminum film/aluminum nitride film, aluminum film/aluminum nitride film/gallium nitride film, aluminum film Film/titanium nitride film/gallium nitride film, aluminum film/aluminum nitride film/indium gallium nitride film, aluminum film/aluminum gallium nitride film/aluminum nitride film, aluminum film/aluminum gallium nitride film/gallium nitride film, preferably a combination of aluminum nitride film/gallium nitride film, aluminum film/gallium nitride film, aluminum film/aluminum nitride film/gallium nitride film, and particularly preferably a combination of aluminum nitride film/gallium nitride film.

It is particularly preferred 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), or semiconductor elements such as power devices. By forming the second thin film with gallium nitride (GaN), the multilayer film structure itself can be applied to electronic devices such as light-emitting elements or semiconductor elements. In addition, the multilayer film structure can be used as a base substrate, and gallium nitride (GaN) can be further formed thereon. Since the gallium nitride (GaN) formed on the multilayer film structure is epitaxially grown, a device with good characteristics can be produced.

Furthermore, by forming the first thin film with aluminum nitride (AlN), the crystallinity of gallium nitride (GaN) forming the second thin film can be further improved. That is, if gallium nitride (GaN) is directly formed on a Si (111) substrate, depending on the film forming conditions, a reaction between silicon (Si) and gallium (Ga) may occur, i.e., melt-back etching. In contrast, by setting aluminum nitride (AlN) on a Si (111) substrate, melt-back etching can be further significantly suppressed.

The laminated film structure preferably has its outermost surface, such as the surface of the second thin film, composed of a hexagonal gallium nitride layer, and the surface of the gallium nitride layer is gallium (Ga) polar. By making the outermost surface gallium (Ga) polar, when further forming gallium nitride (GaN) on the laminated film structure, the formation of hexagonal facets that make device manufacturing difficult can be suppressed.

[Semiconductor components and electronic equipment]

The semiconductor element of the present embodiment includes the multilayer film structure. In addition, the electronic device of the present embodiment includes the semiconductor element. As the semiconductor element, for example, light-emitting elements such as blue light-emitting diodes (LEDs) or blue laser diodes (LDs), power devices such as diodes or transistors, etc. can be exemplified. The semiconductor element uses the multilayer film structure of the present embodiment as a base layer, and may include a thin film and/or thick film containing a nitride material such as gallium nitride (GaN) disposed thereon. In addition, the semiconductor element or the electronic device may also include other functional parts other than the multilayer film structure. Due to the high crystallinity of the nitride thin film constituting the multilayer film structure, the semiconductor element or the electronic device exhibits good characteristics.

[Manufacturing method of multilayer film structure]

The manufacturing method of the multilayer film structure of this embodiment is not limited. However, it can be preferably manufactured according to the following method.

The manufacturing method of the multilayer 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 immersed Si (111) substrate by sputtering (first thin film forming step); and a step of forming a second thin film on the first thin film by sputtering (second thin film forming step). In addition, when forming the first thin film, the sputtering energy (Es) expressed by the formula: Es = [input power density (unit: W/cm ² )] / [introduced gas pressure (unit: Pa)] ² is set to 0.1 W/cm ² Pa ² or more and 150 W/cm ² Pa ² or less, and when forming the second thin film, the sputtering energy (Es) expressed by the formula: Es = [input power density (unit: W/cm ² )] / [introduced gas pressure (unit: Pa)] ² is set to 0.04 W/cm ² Pa ² or more and 150 W/cm ² Pa ² or less. The details of each step are described below.

<Substrate preparation steps>

In the substrate preparation step, a Si (111) substrate is prepared. The manufacturing method of the Si (111) substrate is not limited, and it can be manufactured by the Czochraski (CZ) method or the floating zone (FZ) method, or it can 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 contain a dopant element such as a donor or an acceptor on its surface and/or inside, or it may not contain it.

<Wet etching steps>

In the wet etching step, the prepared Si (111) substrate is immersed in a cleaning solution. Examples of the cleaning solution used during immersion include aqueous hydrofluoric acid solution, sulfuric acid, hydrochloric acid, hydrogen peroxide, ammonium hydroxide, trichloroethylene, acetone, methanol, isopropyl alcohol, etc., among which aqueous hydrofluoric acid solution is preferred. In addition, an ultrasonic cleaner can be used in conjunction with immersion in the cleaning solution. The Si (111) substrate is generally covered with contaminants or a natural oxide film on its surface when it is just obtained. The natural oxide film is amorphous and has a thickness of about 1 nm to 3 nm. If a Si (111) substrate with residual contaminants or a natural oxide film is used directly, the oxygen content within 10 nm from the substrate surface will increase excessively, and the crystallinity of the first film and the second film may decrease. Therefore, a wet etching step is provided to remove the oxide film on the surface of the Si (111) substrate (cleaning treatment). When a hydrofluoric acid aqueous solution is used as the cleaning solution, the hydrofluoric acid concentration is preferably 5 mass% to 10 mass%. By making the hydrofluoric acid concentration above 5 mass%, hydrogen can be modified on the surface. In addition, at a high concentration exceeding 10 mass%, the surface roughness may increase.

The immersion time of the Si (111) substrate is preferably 5 seconds to 100 seconds. By setting the immersion time to more than 5 seconds, the oxide film is sufficiently removed, and the thickness of the amorphous layer can be reduced in the laminated film structure after manufacturing. In addition, by setting the immersion time to less than 100 seconds, the reduction of the surface roughness during etching can be suppressed. The immersion time can also be more than 20 seconds and less than 100 seconds. In this way, a laminated film structure of the first form with an amorphous layer thickness of 0nm (no amorphous) can be manufactured. The immersion time can also be more than 5 seconds and less than 20 seconds. In this way, a laminated film structure of the second form with an amorphous layer thickness greater than 0nm and less than 1.0nm can be manufactured.

After being immersed in the cleaning solution, the residual droplets on the surface of the substrate are removed. The residual droplets can be removed by methods such as surface sweeping using nitrogen gas. Regarding the Si(111) substrate after wet etching, the oxide film is removed to a considerable extent and its surface is flat. The arithmetic mean roughness (Ra) of the Si(111) substrate after treatment is less than 0.5nm, preferably less than 0.3nm. After removing the residual droplets, the substrate surface is easily contaminated by impurities in the environment, so it is better to enter the first thin film forming step without leaving more than 24 hours. After the wet etching step is completed, it can be transferred to the first thin film forming step within 5 hours, or it can be transferred within 1 hour.

<First thin film forming step>

In the first thin film forming step, a first thin film is formed on the Si (111) substrate after immersion by sputtering. As the sputtering method, a known method can be used. As such known methods, there are: DC sputtering method, RF sputtering method, AC sputtering method, DC magnetron sputtering method, RF magnetron sputtering method, pulse sputtering method and ion beam sputtering method. However, DC magnetron sputtering method or RF magnetron sputtering method, which can form a film uniformly over a large area and at a high speed, is preferred.

As a sputtering target, a known target used in the formation of a nitride-based thin film or an aluminum thin film can be used. As such a target, a metal target or a nitride-based target can be listed. In addition, from the viewpoint of improving the crystallinity of the entire film, the lower the oxygen content of the sputtering target, the better. The oxygen content is preferably less than 3 at% (atomic %), and further preferably less than 1 at%. Moreover, the larger the target area, the more films can be formed on a large-area substrate, and at the same time, the uniformity of the film thickness or film quality is improved. Therefore, the target area is preferably greater than 18 ^cm2 , and more preferably greater than 100 ^cm2 . Furthermore, the target area is the area of one side of the main surface of the target.

When forming the first thin film, it is preferred to set the vacuum degree in the film forming device immediately before film formation to 1×10 ^-4 Pa or less, more preferably to 7×10 ^-5 Pa or less, more preferably to 2×10 ^-5 Pa or less, further preferably to 9×10 ^-6 Pa or less, and particularly preferably to 5×10 ^-6 Pa or less. By increasing the vacuum degree in the device before film formation, residual gas during film formation is prevented from becoming impurities 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 residual gas, the device before film formation may also be subjected to a baking treatment. In addition, sputtering film formation is preferably performed in a state where the substrate is heated. Thereby, the migration of particles deposited on the substrate can be promoted, and a deposited film in a stable crystalline state can be formed. The substrate heating temperature (film forming temperature) is preferably 100°C to 800°C, more preferably 200°C to 600°C. The film forming temperature is preferably increased stepwise from a low temperature. In addition, the film forming temperature at the initial stage of film forming is preferably 200°C to 500°C. This can suppress excessive migration and obtain a flat film. Furthermore, by forming the film stepwise at 300°C to 600°C and then at 500°C to 800°C, both flatness and crystallinity can be taken into consideration.

As the gas introduced during sputtering, a known gas used in the formation of nitride-based thin films can be used. As such a gas, a mixed gas of argon (Ar) and nitrogen ( _N2 ) can be listed. In addition, other gases such as ammonia can also be introduced as needed. However, it is preferred that when forming the first thin film, only argon (Ar) gas is introduced into the film forming chamber to form a thin film with a film thickness of 3nm~10nm, and then a gas containing nitrogen ( _N2 ) is introduced into the film forming chamber to continue film formation. For example, when a metal target (metal aluminum target, etc.) is used for film formation, only argon (Ar) gas is introduced at the initial stage of film formation to form a metal film (aluminum film, etc.) with a thickness of 1nm~10nm. Then, when a nitrogen ( _N2 )-containing gas (e.g., a mixed gas of nitrogen and argon) is introduced for successive film formation, the metal film is nitrided and converted into a nitride film (aluminum nitride film, etc.), and nitride is further deposited thereon. This allows a nitride-based thin film (aluminum nitride film, etc.) with high crystallinity and few nitrogen defects to be obtained. In contrast, if a nitrogen ( _N2 )-containing gas is introduced at the beginning of film formation, the surface of the Si substrate is nitrided, and amorphous silicon nitride is sometimes formed. In addition, 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 is sometimes formed on the surface of the Si substrate due to the nitrogen ( _N2 ) 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 initial stage of film formation exceeds 10nm, it may be difficult to fully nitride the metal film during the successive film formation. Therefore, the film thickness at the initial stage of film formation before the introduction of the nitrogen-containing gas is preferably 1nm to 10nm. The film thickness at the initial stage of film formation may be 1nm to 5nm.

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 sputtering particles when the sputtering film is formed, and is defined by the formula: Es = [input power density (unit: W/cm ² )] / [introduction gas pressure (unit: Pa)] ^2. The input power density refers to the input energy per unit area when the actual input power is divided by the sputtering target area. Thereby, a first thin film with high crystallinity can be formed. The detailed reason is uncertain, but the properties of the sputtered particles, such as the adhesion of the sputtered particles reaching the substrate, the diffusion length of the sputtered particles when migrating on the substrate, and/or the penetration depth into the deposited film, change according to the magnitude of the sputtering energy (Es), and it is inferred that the crystallinity of the nitride-based thin film is affected. 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. Furthermore, 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. Es can be 0.5W/cm ² Pa ² ~100W/cm ² Pa ² , 0.5W/cm ² Pa ² ~60W/cm ² Pa ² , 0.5W/cm ² Pa ² ~30W/cm ² Pa ² , 0.5W/cm ² Pa ² ~25W/cm ² Pa ² , 0.5W/cm ² Pa ² ~20W/cm ² Pa ² , 0.5W/cm ² Pa ² ~15W/cm ² Pa ² , 0.5W/cm ² Pa ² ~10W/cm ² Pa ² , 1W/cm ² Pa ² ~100W/cm ² Pa ² , 1W/cm ² Pa ² ~60W/cm ² Pa ² , 1W/cm ² Pa ² ~30W/cm ² Pa ^2. 1W/cm ² Pa ² ~25W/cm ² Pa ² , 1W/cm ² Pa ² ~20W/cm ² Pa ² , 1W/cm ² Pa ² ~15W/cm ² Pa ² , 1W/cm ² Pa ² ~10W/cm ² Pa ² , 2W/cm ² Pa ² ~100W/cm ² Pa ² , 2W/cm ² Pa ² ~60W/cm ² Pa ² 、2W/cm ² Pa ² ~30W/cm ² Pa ² 、2W/cm ² Pa ² ~25W/cm ² Pa ² 、2W/cm ² Pa ² ~20W/cm ² Pa ² 、2W/cm ² Pa ² ~15W/cm ² Pa ² 、2W/cm ² Pa ² ~10W/cm ² Pa ² , 5W/cm ² Pa ² ~100W/cm ² Pa ² , 5W/cm ² Pa ² ~60W/cm ² Pa ² , 5W/cm ² Pa ² ~30W/cm ² Pa ² , 5W/cm ² Pa ² ~25W/cm ² Pa ² , 5W/cm ² Pa ² ~20W/cm ² Pa ² , 5W/cm ² Pa ² ~15W/cm ² Pa ² , 5W/cm ² Pa ² ~10W/cm ² Pa ² , 10W/cm ² Pa ² ~100W/cm ² Pa ² , 10W/cm ² Pa ² ~60W/cm ² Pa ² , 10W/Cm ² Pa ² ~30W/Cm ² Pa ² , 10W/cm ² Pa ² ~25W/cm ² Pa ² 、10W/cm ² Pa ² ~20W/cm ² Pa ² , 10W/cm ² Pa ² ~15W/cm ² Pa ² , 15W/cm ² Pa ² ~100 W/cm ² Pa ² , 15W/cm ² Pa ² ~60W/cm ² Pa ² , 15W/cm ² Pa ² ~30W/cm ² Pa ² , 15W/cm ² Pa ² ~25W/cm ² Pa ² , 15W/cm ² Pa ² ~20W/cm ² Pa ² , 20W/cm ² Pa ² ~100W/cm ² Pa ² , 20W/cm ² Pa ² ~60W/cm ² Pa ² , 20W/cm ² Pa ² ~30W/cm ² Pa ² , 20W/cm ² Pa ² ~25W/cm ² Pa ² , any one of 25 W/cm ² Pa ² to 100 W/cm ² Pa ² , 25 W/cm ² Pa ² to 60 W/cm ² Pa ² , and 25 W/cm ² Pa ² to 30 W/cm ² Pa ² .

Furthermore, when only argon (Ar) gas is introduced at the initial stage of film formation and nitrogen (N ₂ ) gas is introduced during successive film formation, the sputtering energy (Es) at the initial stage of film formation and during successive film formation may be the same or different.

The thickness of the first film is preferably 20 nm or more. When the thickness of the first film is too thin, the crystallinity of the first film and the second film or the surface flatness of the laminated film structure may be poor. Therefore, the thickness of the first film is preferably thick to a certain extent. The thickness of the first 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. The film thickness can be any one of 30nm~90nm, 30nm~80nm, 30nm~70nm, 30nm~60nm, 30nm~50nm, 40nm~90nm, 40nm~80nm, 40nm~70nm, 40nm~60nm, 40nm~50nm, 50nm~90nm, 50nm~80nm, 50nm~70nm, 50nm~60nm, 60nm~90nm, 60nm~80nm, 60nm~70nm, 70nm~90nm, 70nm~80nm and 80nm~90nm.

<Second thin film forming step>

In the second thin film forming step, a second thin film is formed on the first thin film by sputtering. As a sputtering method, a DC magnetron sputtering method, a pulse sputtering method, or an RF magnetron sputtering method that can form a film uniformly over a large area and at a high speed is preferred. In addition, as a sputtering target, a well-known target used in the formation of a nitride-based thin film can be used. However, it is preferred to use a nitride-based target (e.g., a gallium nitride target). In addition, the oxygen content of the sputtering target is preferably less than 3 at% (atomic %), and more preferably less than 1 at%. Furthermore, the target area is preferably greater than 18 ^cm2 , and more preferably greater than 100 ^cm2 .

Sputtering film formation is similar to the film formation of the first thin film, and is preferably performed under a heated substrate. The substrate heating temperature (film formation temperature) is preferably 100°C to 800°C, and more preferably 300°C to 800°C. In addition, as the introduced gas during sputtering, a known gas used in the film formation of a nitride-based thin film can be used. As such a gas, a mixed gas of argon (Ar) and nitrogen ( _N2 ) can be listed. In addition, other gases such as ammonia can also be introduced as needed.

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. Thereby, a second thin film with high crystallinity can be formed. 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. Es can be 0.1W/cm ² Pa ² ~100W/cm ² Pa ² , 0.1W/cm ² Pa ² ~70W/cm ² Pa ² , 0.1W/cm ² Pa ² ~35W/cm ² Pa ² , 0.1W/cm ² Pa ² ~30 W/cm ² Pa ² , 0.1W/cm ² Pa ² ~25W/cm ² Pa ² , 0.5W/cm ² Pa ² ~100W/cm ² Pa ² , 0.5W/cm ² Pa ² ~70W/cm ² Pa ² , 0.5W/cm ² Pa ² ~35W/cm ² Pa ² , 0.5W/cm ² Pa ² ~30W/cm ² Pa ² , 0.5W/cm ² Pa ² ~25W/cm ² Pa ² , 1W/cm ² Pa ² ~100W/cm ² Pa ² , 1W/cm ² Pa ² ~70W/cm ² Pa ² , 1W/cm ² Pa ² ~35W/cm ² Pa ² , 1W/cm ² Pa ² ~30W/cm ² Pa ² , 1W/cm ² Pa ² ~25W/cm ² Pa ² , 5W/cm ² Pa ² ~100W/cm ² Pa ² , 5W/cm ² Pa ² ~70W/cm ² Pa ² , 5W/cm ² Pa ² ~35W/cm ² Pa ² , 5W/cm ² Pa ² ~30W/cm ² Pa ² , 5W/cm ² Pa ² ~25W/cm ² Pa ² , 10W/cm ² Pa ² ~100W/cm ² Pa ² , 10W/cm ² Pa ² ~70W/cm ² Pa ² , 10W/cm ² Pa ² ~35W/cm ² Pa ² , 10W/cm ² Pa ² ~30W/cm ² Pa ² , 10W/cm ² Pa ² ~25W/cm ² Pa ² , 20W/cm ² Pa ² ~100W/cm ² Pa ² , 20W/cm ² Pa ² ~70W/cm ² Pa ² , 20W/cm ² Pa ² ~35W/cm ² Pa ² , 20W/cm ² Pa ² ~30W/cm ² Pa ² , 20W/cm ² Pa ² ~25W/cm ² Pa ² , 25W/cm ² Pa ² ~100W/cm ² Pa ² ,25W/cm ² Pa ² Any one of 25W/ ^cm2Pa2 ~70W/ ^cm2Pa2 , 25W/ ^cm2Pa2 ~ ^35W / ^cm2Pa2 , ^25W / ^cm2Pa2 ~ ^30W / ^cm2Pa2 , ^30W / ^cm2Pa2 ~ ^{100W/cm2Pa2 , 30W} / ^{cm2Pa2 ~70W/cm2Pa2 ,} and 30W ^{/ cm2Pa2} ~ ^{35W / cm2Pa2} .

If necessary, a step of further laminating other nitride-based films on the second film can be provided. For example, after a gallium nitride-based film is formed as the second film by sputtering, a gallium nitride-based film can be further formed thereon by MOCVD.

In this way, the multilayer film structure of this embodiment is manufactured.

[Implementation example]

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

[Example 1]

The multilayer film structure of Example 1 was prepared and evaluated as follows.

(1) Fabrication of multilayer film structures

<Preparation steps>

As the Si substrate, an n-type Si (111) substrate (Matsuzaki Manufacturing Co., Ltd., off-angle: none) was prepared. The diameter of the substrate was 50±0.5 mmΦ, the thickness was 425±25 μm, and the resistivity was more than 1000 Ω. cm.

<Wet etching steps>

The prepared Si substrate was subjected to wet etching treatment (cleaning treatment). 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 mass%. Then, 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. Then, nitrogen gas was blown to remove the droplets remaining on the surface of the substrate. In this way, a Si substrate (Ra: 0.15nm) that had been subjected to the cleaning treatment was obtained. After that, the first film formation step was entered without leaving any time.

<First film forming step>

Using a magnetron sputtering device, the first thin film was formed on a Si substrate that had been subjected to a wet etching process. First, a metal aluminum (Al) target (purity 99.99 mass%) was prepared as a sputtering target. The Si substrate and the target were placed in the film forming chamber of the sputtering device, and the film forming chamber was evacuated. After the vacuum level in the film forming chamber (the vacuum level reached before film formation) reached 1.9×10 ^-6 Pa, film formation began.

The first thin film was formed as follows. First, the gas introduced into the film forming chamber was set to only argon (flow rate: 20 sccm), and a thin film with a thickness of 3 nm was formed. At this time, the substrate temperature was set to 300°C, and the sputtering energy (Es) was set to 20 W/cm ² Pa ² . Then, 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 set to 750°C, and the sputtering energy (Es) was set to 5 W/cm ² Pa ² . In this way, an aluminum nitride thin film with a thickness of 50 nm was formed.

<Second film forming step>

Using a magnetron sputtering device, a second thin film is formed on the first thin film (aluminum nitride thin film). First, a gallium nitride (GaN) target (purity 99.99 mass%) is prepared as a sputtering target. The Si substrate on which the first thin film is formed is placed in a film forming chamber together with the target. The gas introduced into the film forming chamber is set to a mixed gas of nitrogen (flow rate: 10sccm) and argon (flow rate: 10sccm), and the film is formed under the conditions of a substrate temperature of 750°C and a sputtering energy ^of 20W/ ^cm2Pa2 . A gallium nitride (GaN) thin film with a thickness of 50nm is formed.

In this way, a multilayer film structure having an aluminum nitride film (first film) and a gallium nitride film (second film) disposed on a Si substrate was produced. Furthermore, the film forming conditions of the first film and the second film are also shown in Tables 1 to 3, respectively.

(2) Evaluation

The obtained multilayer film structure was evaluated as follows.

<Structural analysis>

The presence and thickness of the amorphous layer were checked by analyzing the Si substrate and the first thin film. The analysis was performed as follows. First, a carbon coating was set on the surface of the multilayer structure as a protective film, and then a focused ion beam (FIB) was processed to produce an observation sample. Then, a field emission-transmission electron microscope (FE-TEM: JEM-2100F manufactured by JEOL Ltd.) was used to observe the cross section of the sample. At this time, the electron beam acceleration voltage was set to 200 kV.

<Amount of oxygen and silicon nitride>

The oxygen content and silicon nitride content within 10nm of the Si substrate containing the amorphous layer were measured by X-ray photoelectron spectroscopy (Electron Spectroscopy for Chemical Analysis, ESCA). When performing the analysis in the depth direction, the film sample was ion-milled by argon (Ar) monomer ions for measurement. In the measurement, the content of each element (O, N, Si) was calculated using the peak area of O1s, N1s and Si2p, and the amount of oxygen and silicon nitride was quantified using an atomic density meter relative to the total concentration of silicon (Si), oxygen (O) and nitrogen (N). In addition, the details of the measurement conditions are shown below.

-X-ray source: monochromatic Al-Kα ray (25W, 15kW)

-X-ray irradiation diameter: 100μmΦ

-Pass Energy: 93.9eV (O1s, N1s) 11.75eV (Si2p)

-Step Size: 0.1eV

<Crystallinity of thin film>

The crystallinity of the first and second films was evaluated using an X-ray diffraction device (Bruker AXS, D8 DISCOVER). The analysis was performed in high resolution mode at 40 kV and 40 mA. In addition, a monochromator was used to perform ω scanning in order to remove CuKα2. The swing curve of the (0002) plane was measured, and the half-value width (FWHM) was calculated as an indicator of the crystallinity of the film. The details of the analysis conditions are shown below.

-Radiation source: CuKα radiation (λ=0.15418nm)

-Monochromator: Ge(220)

-Pathfinder: Crystal3B

-Measurement mode: ω scan

-Measurement interval: 0.01° (0.0005° when the half-height width is less than 0.1°)

-Measurement time: 0.5 seconds

-Measurement range: ω=0°~35°

<Polarity and crystallinity of gallium nitride thin films>

The polarity and crystal phase of the gallium nitride thin film were evaluated using a time-of-flight atomic scattering surface analysis device (PASCAL Co., Ltd., TOFLAS-3000). The multilayer film structure was set on the device in such a way that its film-forming surface became the upper surface, and the measurement was performed. The polarity and crystal phase of the gallium nitride thin film were determined by comparing the polar diagram obtained by the measurement with the polar diagram of each crystal phase and polarity up to the surface 4 layers obtained by analogy. The details of the measurement conditions are shown below.

-Probe: He (atomic scattering)

-Energy: 3keV

- Beam source-target distance: 805mm

-Target-detector distance: 395mm

-Analysis chamber vacuum degree: below 2×10 ^-3 Pa

<Surface roughness of multilayer film structures>

The arithmetic mean roughness (Ra) of the surface of the multilayer structure was measured. The measurement was performed using a scanning probe microscope (Bruker AXS, NanoScopeIIIa) in Tapping Mode AFM with a field of view of 2μm×2μm.

[Example 2 and Example 3]

The film forming conditions of the first film and the second film are shown in Tables 1 to 3. In addition, the preparation and evaluation of the multilayer film structure were carried out in the same manner as in Example 1.

[Example 4]

During the wet etching process, the immersion time of the Si substrate was set to 5 seconds, and the film formation conditions of the first and second films are shown in Tables 1 to 3. In addition, the preparation and evaluation of the multilayer film structure were carried out in the same manner as in Example 1.

[Example 5]

When the first nitride-based thin film was formed, the film thickness was set to 3nm at 500℃ and 44nm at 750℃ for the film formation after the initial stage. The film formation conditions of the second nitride-based thin film are shown in Table 3. Other than that, the multilayer film structure was prepared and evaluated in the same manner as in Example 1.

[Example 6~Example 17]

The film forming conditions of the first film and the second film are shown in Tables 1 to 3. In addition, the preparation and evaluation of the multilayer film structure were carried out in the same manner as in Example 1.

[Example 18 (Comparison)]

During the wet etching process, the immersion time of the Si substrate was set to 2 seconds, and the film formation conditions of the first and second films are shown in Tables 1 to 3. In addition, the preparation and evaluation of the multilayer film structure were carried out in the same manner as in Example 1.

[Example 19 (Comparison)]

The film forming conditions of the first film and the second film are shown in Tables 1 to 3. In addition, the preparation and evaluation of the multilayer film structure were carried out in the same manner as in Example 1.

[Example 20 (Comparison)]

After the wet etching treatment, the first and second thin films were formed after being stored in an atmospheric environment for 1 day. The film forming conditions of the first and second thin films are shown in Tables 1 to 3. In addition, the multilayer film structure was prepared and evaluated in the same manner as in Example 1.

[Example 21~Example 25 (Comparison)]

The film forming conditions of the first film and the second film are shown in Tables 1 to 3. In addition, the preparation and evaluation of the multilayer film structure were carried out in the same manner as in Example 1.

(3) Results

The evaluation results obtained for Examples 1 to 25 are shown in Table 4. In addition, Examples 1 to 17 are implementation examples, and Examples 18 to 25 are comparative examples.

As shown in Table 4, the thickness of the amorphous layer of the samples of Examples 1 to 17 as the embodiments is as small as 0.9nm or less. In addition, the full width at half maximum (FWHM) is as small as 0.98° or less, and the arithmetic mean roughness (Ra) is as small as 8.1nm or less. Thus, in Examples 1 to 17, highly flat, highly crystalline, and hexagonal Ga-polar gallium nitride thin films (nitride-based thin films) were successfully produced.

In contrast, the thickness of the amorphous layer of the samples of Examples 18 to 20 as comparative examples was as large as 2.0 nm. Therefore, the full width at half maximum (FWHM) and the arithmetic mean roughness (Ra) were large, and the crystallinity and surface flatness were poor. For example, in Example 18, where the immersion time of the Si substrate was 2 seconds, 2.0 nm of amorphous material was considered to be a natural oxide film between the Si substrate and the first film, and a film with the required characteristics could not be obtained. In Example 19, where the film was formed for 10 seconds under argon and nitrogen, 2.0 nm of amorphous material was considered to be a natural oxide film caused by impurities in the gas, and a film with the required characteristics could not be obtained. In Example 20, which was stored in an atmospheric environment for one day before forming the first thin film, the 2.0 nm residue was considered to be amorphous natural oxide film caused by impurities in the atmosphere, and a film with the required characteristics could not be obtained. In Example 21, in which the sputtering energy (Es) was set to 200 W/cm ² Pa ² when forming the first and second thin films, or in Example 22, in which the film thickness of the first thin film was set to 10 nm, a film with the required characteristics could not be obtained. In Example 23, in which the vacuum degree before forming the first thin film was set to 2.3×10 ^-4 Pa, the amount of oxygen within 10 nm from the Si substrate surface was large, and a film with the required characteristics could not be obtained. In Example 24 in which the sputtering energy (Es) of the first thin film was set to 0.05 W/cm ² Pa ² or in Example 25 in which the sputtering energy (Es) of the second thin film was set to 0.03 W/cm ² Pa ² , a film having the required characteristics could not be obtained.

[Table 1]

1: Laminated film structure

2:Si(111) substrate

3: First film

4: Second film

Claims (15)

A multilayer film structure comprises: a Si(111) substrate; a first thin film disposed on the Si(111) substrate, comprising a nitride-based material and/or aluminum; and a second thin film disposed on the first thin film, comprising a nitride-based material, wherein an amorphous layer having a thickness of 0 nm or more and less than 1.0 nm exists on the Si(111) substrate, the half-value width (FWHM) of the wobble curve of the (0002) plane on the surface of the multilayer film structure is less than 0.10°, and the arithmetic mean roughness (Ra) of the surface of the multilayer film structure is less than 10.0 nm. A multilayer film structure as described in claim 1, wherein the thickness of the amorphous layer is 0 nm, and the first film is in direct contact with the Si (111) substrate without passing through other layers. The multilayer film structure as described in claim 2, wherein the oxygen content within 10 nm from the surface of the Si (111) substrate is less than 5 at%. The multilayer film structure as described in claim 2, wherein the silicon nitride content within 10 nm from the surface of the Si (111) substrate is less than 5 at%. A multilayer film structure as described in claim 1, wherein the thickness of the amorphous layer is greater than 0 nm and less than 1.0 nm. The multilayer film structure as described in claim 5, wherein the silicon nitride content within 10 nm from the surface of the Si (111) substrate is less than 5 at%. A multilayer film structure as described in claim 1, wherein the thickness of the second film is greater than 10 nm and less than 1000 nm. A multilayer film structure as described in claim 1, wherein the first film is an aluminum nitride film and the second film is a gallium nitride film. A multilayer film structure as described in any one of claim 1 to claim 8, wherein the outermost surface of the multilayer film structure is composed of a hexagonal gallium nitride layer, and the surface of the gallium nitride layer is gallium (Ga) polarity. A semiconductor device comprising a multilayer film structure as described in any one of claims 1 to 9. An electronic device comprising a semiconductor element as described in claim 10. A method for manufacturing a multilayer film structure, the multilayer film structure comprising: a Si (111) substrate; a first thin film disposed on the Si (111) substrate, comprising a nitride-based material and/or aluminum; and a second thin film disposed on the first thin film, comprising a nitride-based material, wherein a non-nitride-based material having a thickness of not less than 0 nm and less than 1.0 nm exists on the Si (111) substrate. The present invention relates to a multilayer structure having a crystalline layer, a half-value width (FWHM) of a wobble curve of a (0002) plane on the surface of the multilayer structure is less than 1.50°, and an arithmetic average roughness (Ra) of the surface of the multilayer structure is less than 10.0 nm. The manufacturing method of the multilayer structure comprises the following steps: preparing a Si (111) substrate; immersing the Si (111) substrate in a cleaning solution; A step of forming a first thin film by sputtering on the Si (111) substrate after immersion; and a step of forming a second thin film by sputtering on the first thin film, and when forming the first thin film, the sputtering energy (Es) represented by the formula: Es = [input power density (unit: W/cm ² )] / [introduced gas pressure (unit: Pa)] ² is set to 0.1 W/cm ² Pa ² or more and 150 W/cm ² Pa ² or less, and when forming the second thin film, the sputtering energy (Es) represented by the formula: Es = [input power density (unit: W/cm ² )] / [introduced gas pressure (unit: Pa)] ² is set to 0.04 W/cm ² Pa ² or more and 150 W/cm ² Pa ² or less. The method for manufacturing a multilayer film structure as claimed in claim 12, wherein when forming the first thin film, the vacuum degree in the film forming apparatus immediately before film formation is set to 1×10 ^-4 Pa or less. A method for manufacturing a multilayer film structure as described in claim 12, wherein when forming the first film, only argon gas is introduced into the film forming chamber to form a film with a thickness of 1nm to 10nm, and then nitrogen-containing gas is introduced into the film forming chamber to continue film formation. A method for manufacturing a multilayer film structure as described in any one of claim 12 to claim 14, wherein the thickness of the first film is greater than 20 nm.

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