A biaxially textured aluminum nitride-like epitaxial thin film, a method for preparing the same and applications thereof

Abstract

The application belongs to the technical field of thin film material preparation, and particularly relates to a biaxial texture aluminum nitride epitaxial film and a preparation method and application thereof. The preparation method provided by the application is based on ion-assisted deposition of a transition layer to prepare the biaxial texture aluminum nitride epitaxial film. Firstly, the application prepares a transition layer on the surface of a substrate wafer, and realizes regular arrangement and preferred growth of the transition layer grains in a certain direction in the plane by an ion-assisted deposition method; and the aluminum nitride film on the transition layer realizes biaxial texture epitaxial (single crystal-like) growth by taking the regularly arranged transition layer as a template. Therefore, the preparation method provided by the application can obtain the single crystal-like aluminum nitride film, and the aluminum nitride film has high piezoelectric response coefficients and electromechanical coupling coefficients, can reduce the propagation loss of sound waves in the film, and can be applied to surface acoustic wave devices or bulk acoustic wave devices as a piezoelectric material. Moreover, the method provided by the application is simple to operate and is compatible with large-scale integrated circuit process equipment.

Description

Technical Field

[0001] This invention belongs to the field of thin film material preparation technology, specifically relating to a biaxial textured aluminum nitride epitaxial thin film, its preparation method, and its application. Background Technology

[0002] Surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices can be used in various radio frequency devices, resonators, sensors, and micro-actuators. Piezoelectric thin films, as the substrate for acoustic wave excitation and transmission, are the core chip materials for these devices. The piezoelectric response coefficient and acoustic wave transmission loss of the material determine the overall performance of the device and are constrained by the type and crystallographic orientation of the material. For polycrystalline thin films, preparing thin film materials with a biaxial textured preferred orientation, where all grains are arranged in a specific crystal direction perpendicular to the substrate surface and along a specific in-plane alignment, can maximize the piezoelectric response coefficient and minimize the acoustic wave transmission loss.

[0003] Aluminum nitride is an excellent piezoelectric material due to its high acoustic wave propagation speed, good chemical stability, and low dispersion. For aluminum nitride, the c-axis (002) direction has the largest piezoelectric response coefficient. The crystal structure of aluminum nitride is as follows: Figure 1 As shown. Because the formation of nitrogen-aluminum bonds along the c-axis requires high particle energy, it is difficult to prepare c-axis preferred-oriented aluminum nitride films, which readily form other preferred orientations or no preferred orientation at all. Furthermore, in addition to c-axis preferred orientation, controlling the in-plane grain orientation along a specific a-axis or b-axis is even more challenging.

[0004] Magnetron sputtering is a commonly used thin film deposition technique in semiconductor manufacturing, and it can be used to prepare aluminum nitride thin films. Traditional aluminum nitride thin film magnetron sputtering deposition processes include... Figure 2 As shown: The substrate and sputtering target are placed opposite each other in a vacuum chamber (the substrate and sputtering target are placed horizontally). The substrate is heated to a certain temperature by the base. A certain proportion of reactive gases (nitrogen and argon) are introduced into the vacuum chamber. A high voltage is applied to the sputtering target to ionize the gas and form plasma. The plasma bombards the sputtering target, and the sputtered particles leave the target surface with a certain direction and energy, reach the substrate surface, and reach the equilibrium position through horizontal diffusion, continuously growing to form a thin film.

[0005] Although traditional magnetron sputtering can prepare aluminum nitride thin films, it can only produce c-axis oriented aluminum nitride thin films and cannot control the in-plane orientation of the grains. Summary of the Invention

[0006] The purpose of this invention is to provide a biaxially textured aluminum nitride-like epitaxial thin film, its preparation method, and its applications. The preparation method provided by this invention utilizes magnetron sputtering technology to grow biaxially textured aluminum nitride-like epitaxial thin films, ensuring that the c-axis crystal direction of all grains is perpendicular to the substrate surface, while their a-axis or b-axis is also aligned in the same direction within the plane. Therefore, the preparation method provided by this invention can obtain near-single-crystal aluminum nitride thin films with high piezoelectric response coefficients and electromechanical coupling coefficients, reducing acoustic wave propagation losses in the thin film. It can be used as a piezoelectric material in surface acoustic wave (SAW) devices or bulk acoustic wave (BAW) devices.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing biaxially textured aluminum nitride epitaxial thin films, comprising the following steps:

[0009] (1) The substrate wafer is placed horizontally in a vacuum chamber; a metal target and an ion source are set above the surface of the substrate wafer. The metal target is a ring-shaped single target or a planar single target, and the ion source is a Kaufman ion source or an anode layer ion source. The first angle formed by the normal of the surface of the metal target and the normal of the surface of the substrate wafer is >0° and <90°, and the second angle formed by the normal of the surface of the ion source and the normal of the surface of the substrate wafer is >0° and <90°. A first voltage is applied to the metal target for magnetron sputtering, and the ion source is turned on at the same time to achieve ion-assisted deposition of a transition layer on the surface of the substrate wafer. The grain orientation inside the transition layer obtained on the surface of the substrate wafer is in the same direction in the direction perpendicular to the surface of the substrate wafer and also in the same direction in the direction parallel to the surface of the substrate wafer.

[0010] (2) An aluminum target is placed above a substrate wafer on which a transition layer is deposited. The third angle formed by the normal of the surface of the aluminum target and the normal of the surface of the substrate wafer is greater than 0° and less than 90°. Nitrogen and argon are introduced into the vacuum chamber. A second voltage is applied to the aluminum target for magnetron sputtering to deposit the biaxial textured aluminum nitride epitaxial film on the surface of the transition layer.

[0011] Preferably, the substrate wafer comprises a silicon substrate, a silicon carbide substrate, a diamond substrate, or an aluminum oxide substrate; the surface roughness of the substrate wafer is <2nm; and the thickness of the substrate wafer is 0.1-1mm.

[0012] Preferably, the metal target includes a molybdenum target, a tungsten target, a titanium target, a silver target, or an aluminum target.

[0013] Preferably, the first included angle, the second included angle, and the third included angle are independently 30 to 60°.

[0014] Preferably, the straight-line distance between the center of the metal target surface and the center of the substrate wafer surface is 50-150 mm; the straight-line distance between the center of the ion source surface and the center of the substrate wafer surface is 50-150 mm.

[0015] The straight-line distance between the center of the aluminum target surface and the center of the substrate wafer surface is 30–60 mm.

[0016] Preferably, in step (1), before applying the first voltage to the metal target for magnetron sputtering, the method further includes: evacuating the vacuum chamber to a vacuum level ≤10. -5 Pa, and then argon gas is introduced into the vacuum chamber, and the gas pressure is maintained <1 Pa; the conditions for magnetron sputtering include: the first voltage is 300-500V, the current of the ion source is 0.3-1A, and the heating temperature of the substrate wafer is >100℃.

[0017] Preferably, in step (1), the deposition thickness of the transition layer is ≥5nm.

[0018] Preferably, in step (2): the flow ratio of nitrogen to argon is >3:1; the conditions for magnetron sputtering include: gas pressure <0.3Pa, second voltage of 500-600V, and heating temperature of the substrate wafer >300℃.

[0019] The present invention provides a biaxial textured aluminum nitride epitaxial thin film prepared by the preparation method described above. The c-axis crystal direction of the grains inside the biaxial textured aluminum nitride epitaxial thin film is perpendicular to the surface of the substrate wafer, while the a-axis or b-axis crystal direction is arranged in the same direction inside the aluminum nitride epitaxial thin film.

[0020] This invention provides the application of the biaxial textured aluminum nitride epitaxial thin film described above as a chip material in surface acoustic wave devices or bulk acoustic wave devices.

[0021] This invention provides a method for preparing biaxial textured aluminum nitride epitaxial thin films, comprising the following steps: (1) placing a substrate wafer horizontally in a vacuum chamber; setting a metal target and an ion source above the surface of the substrate wafer, wherein the metal target is a ring-shaped single target or a planar single target, and the ion source is a Kaufman ion source or an anode layer ion source; the first angle formed by the normal of the surface of the metal target and the normal of the surface of the substrate wafer is >0° and <90°, and the second angle formed by the normal of the surface of the ion source and the normal of the surface of the substrate wafer is >0° and <90°; applying a first voltage to the metal target for magnetron sputtering, and simultaneously turning on... An ion source is used to deposit an ion-assisted transition layer on the surface of the substrate wafer. The grain orientation of the transition layer obtained on the surface of the substrate wafer is in the same direction in the direction perpendicular to the surface of the substrate wafer and in the same direction in the direction parallel to the surface of the substrate wafer. (2) An aluminum target is set above the substrate wafer on which the transition layer is deposited. The third angle formed by the normal of the surface of the aluminum target and the normal of the surface of the substrate wafer is >0° and <90°. Nitrogen and argon are introduced into the vacuum chamber. A second voltage is applied to the aluminum target for magnetron sputtering. The biaxial textured aluminum nitride epitaxial film is deposited on the surface of the transition layer. The present invention prepares a biaxial textured aluminum nitride epitaxial film based on an ion-assisted deposition transition layer: First, the present invention prepares a transition layer on the surface of the substrate wafer. The transition layer grains are preferentially grown in a certain direction in the plane by ion-assisted deposition. The aluminum nitride film on it is grown in a biaxial textured epitaxial (single crystal) manner using the regularly arranged transition layer as a template. Therefore, the preparation method provided by this invention can obtain near-single-crystal aluminum nitride thin films with high piezoelectric response coefficients and electromechanical coupling coefficients, which can reduce the propagation loss of sound waves in the thin film. It can be used as a piezoelectric material in surface acoustic wave (SAW) devices or bulk acoustic wave (BAW) devices. Furthermore, the method provided by this invention is simple to operate and easily compatible with large-scale integrated circuit process equipment.

[0022] This invention provides a biaxially textured aluminum nitride epitaxial thin film prepared by the method described above. The c-axis crystal direction of the grains within the biaxially textured aluminum nitride epitaxial thin film is perpendicular to the substrate wafer surface, while the a-axis or b-axis crystal directions are aligned in the same direction within the aluminum nitride epitaxial thin film. The aluminum nitride polycrystalline thin film prepared by the method provided by this invention has a preferred orientation of biaxial texture and can be used as a chip material in surface acoustic wave (SAW) devices or bulk acoustic wave (BAW) devices. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the aluminum nitride crystal structure;

[0024] Figure 2 A schematic diagram of a traditional aluminum nitride thin film magnetron sputtering deposition process;

[0025] Figure 3 This is a schematic diagram of the method for preparing biaxial textured aluminum nitride epitaxial thin films based on ion-assisted deposition of a transition layer provided by the present invention;

[0026] Figure 4 This is a schematic diagram of the ion-assisted deposition transition layer;

[0027] Figure 5 This is a schematic diagram of the deposition of aluminum nitride-based epitaxial thin films;

[0028] Figure 6 This is an out-of-plane orientation diagram of the aluminum nitride epitaxial thin film crystal structure prepared in Example 1 of the present invention;

[0029] Figure 7 This is an in-plane orientation diagram of the aluminum nitride epitaxial thin film crystal structure prepared in Example 1 of the present invention;

[0030] Figure 8 The image shows the surface morphology of the aluminum nitride epitaxial thin film prepared in Example 1 of this invention.

[0031] Figure 9 This is an out-of-plane orientation diagram of the aluminum nitride epitaxial thin film crystal structure prepared in Example 2 of the present invention;

[0032] Figure 10 The image shows the surface morphology of the aluminum nitride epitaxial thin film prepared in Example 2 of this invention.

[0033] Figure 11 This is an out-of-plane orientation diagram of the aluminum nitride thin film crystal structure prepared in Comparative Example 1 of this invention;

[0034] in, Figure 4 and Figure 5 In the diagram: 1 is the substrate wafer, 2 is the transition layer, and 3 is the biaxial textured aluminum nitride epitaxial film. Detailed Implementation

[0035] This invention provides a method for preparing biaxially textured aluminum nitride epitaxial thin films, comprising the following steps:

[0036] (1) The substrate wafer is placed horizontally in a vacuum chamber; a metal target and an ion source are set above the surface of the substrate wafer. The metal target is a ring-shaped single target or a planar single target, and the ion source is a Kaufman ion source or an anode layer ion source. The first angle formed by the normal of the surface of the metal target and the normal of the surface of the substrate wafer is >0° and <90°, and the second angle formed by the normal of the surface of the ion source and the normal of the surface of the substrate wafer is >0° and <90°. A first voltage is applied to the metal target for magnetron sputtering, and the ion source is turned on at the same time to achieve ion-assisted deposition of a transition layer on the surface of the substrate wafer. The grain orientation inside the transition layer obtained on the surface of the substrate wafer is in the same direction in the direction perpendicular to the surface of the substrate wafer and also in the same direction in the direction parallel to the surface of the substrate wafer.

[0037] (2) An aluminum target is placed above a substrate wafer on which a transition layer is deposited. The third angle formed by the normal of the surface of the aluminum target and the normal of the surface of the substrate wafer is greater than 0° and less than 90°. Nitrogen and argon are introduced into the vacuum chamber. A second voltage is applied to the aluminum target for magnetron sputtering to deposit the biaxial textured aluminum nitride epitaxial film on the surface of the transition layer.

[0038] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0039] This invention places a substrate wafer horizontally within a vacuum chamber; a metal target and an ion source are positioned above the surface of the substrate wafer. The metal target is either a ring-shaped single target or a planar single target, and the ion source is either a Kaufman ion source or an anode layer ion source. The first angle formed by the normal to the surface of the metal target and the normal to the surface of the substrate wafer is greater than 0° and less than 90°, and the second angle formed by the normal to the surface of the ion source and the normal to the surface of the substrate wafer is greater than 0° and less than 90°. A first voltage is applied to the metal target for magnetron sputtering, while the ion source is simultaneously activated, resulting in an ion-assisted deposition transition layer on the surface of the substrate wafer. The grain orientation within the transition layer obtained on the surface of the substrate wafer is the same in both directions perpendicular to and parallel to the surface of the substrate wafer.

[0040] In this invention, the substrate wafer preferably comprises a silicon substrate, a silicon carbide substrate, a diamond substrate, or an aluminum oxide substrate. The surface roughness of the substrate wafer is preferably <2 nm; the thickness of the substrate wafer is preferably 0.1–1 mm.

[0041] In this invention, the metal target preferably includes a molybdenum target, a tungsten target, a titanium target, a silver target, or an aluminum target. In this invention, the transition layer obtained by magnetron sputtering of the metal target can also serve as the bottom electrode layer.

[0042] In this invention, the first included angle is preferably 30–60°. The second included angle is preferably 30–60°.

[0043] In this invention, the linear distance between the center of the metal target surface and the center of the substrate wafer surface is preferably 50–150 mm. The linear distance between the center of the ion source surface and the center of the substrate wafer surface is also preferably 50–150 mm.

[0044] In this invention, before applying a first voltage to the metal target for magnetron sputtering, the invention preferably further includes: evacuating the vacuum chamber to a vacuum level ≤10. -5 Pa, then argon gas is introduced into the vacuum chamber, and the gas pressure is maintained <1 Pa. The preferred conditions for magnetron sputtering include: the first voltage is preferably 300–500 V; the current of the ion source is preferably 0.3–1 A; and the heating temperature of the substrate wafer is preferably >100 °C.

[0045] In this invention, the thickness of the transition layer is preferably ≥5nm.

[0046] After obtaining the transition layer, the present invention places an aluminum target above the substrate wafer on which the transition layer is deposited, wherein the third angle formed by the normal of the surface of the aluminum target and the normal of the surface of the substrate wafer is greater than 0° and less than 90°; nitrogen and argon are introduced into the vacuum chamber, and a second voltage is applied to the aluminum target for magnetron sputtering to deposit the biaxial textured aluminum nitride epitaxial film on the surface of the transition layer.

[0047] In this invention, the third included angle is preferably 30–60°. The linear distance between the center of the aluminum target surface and the center of the substrate wafer surface is preferably 30–60 mm. The flow rate ratio of the nitrogen gas to the argon gas is preferably >3:1. The magnetron sputtering conditions preferably include: a gas pressure preferably <0.3 Pa. The second voltage is preferably 500–600 V. The heating temperature of the substrate wafer is preferably >300 °C.

[0048] The present invention provides a biaxial textured aluminum nitride epitaxial thin film prepared by the preparation method described above. The c-axis crystal direction of the grains inside the biaxial textured aluminum nitride epitaxial thin film is perpendicular to the surface of the substrate wafer, while the a-axis or b-axis crystal direction is arranged in the same direction inside the aluminum nitride epitaxial thin film.

[0049] This invention provides the application of the biaxial textured aluminum nitride epitaxial thin film described above as a chip material in surface acoustic wave devices or bulk acoustic wave devices.

[0050] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0051] Example 1

[0052] This embodiment uses magnetron sputtering to prepare biaxial textured aluminum nitride epitaxial thin films, and the steps are as follows:

[0053] The substrate wafer is a 2-inch silicon substrate, with P-type doping, a thickness of 0.5 mm, and a surface roughness of less than 2 nm. The substrate is placed horizontally on the sample stage in the vacuum chamber. The sample stage can rotate around the center, and the sample stage controls the substrate temperature at 400℃.

[0054] A high-purity sputtered molybdenum target is positioned on one tilted side of the substrate wafer, with a distance of 140 mm between the target and the wafer surface. A Kaufman ion source is positioned on the other tilted side of the substrate wafer (opposite to the molybdenum target), also with a distance of 140 mm between the source and the wafer surface. A high-purity sputtered aluminum target is positioned at another tilted position on the substrate wafer, with a distance of 60 mm between this target and the wafer surface. The angles between the normals of the high-purity sputtered molybdenum target, aluminum target, and ion source and the normal of the substrate wafer surface are all 50°. The positional relationships between the high-purity sputtered molybdenum target, aluminum target, and ion source and the substrate are as follows: Figure 3 As shown;

[0055] The vacuum chamber was evacuated to a vacuum level of 10. -5 Below Pa, argon gas at 3 sccm is introduced, with a pressure of approximately 0.1 Pa. A magnetron sputtering process is performed on a high-purity molybdenum target at 480 V, while simultaneously turning on the ion source with a current of 0.5 A and a substrate heating temperature of 400 degrees Celsius to achieve ion-assisted deposition of the transition layer, such as... Figure 4 This is a schematic diagram of an ion-assisted deposition transition layer; the grain orientation inside the transition layer is the same in the direction perpendicular to the substrate wafer surface and also in the direction parallel to the substrate wafer surface.

[0056] After 5 minutes of deposition, the molybdenum target sputtering and ion source were turned off, and 80 sccm of nitrogen and 2 sccm of argon gas were introduced at a pressure of approximately 0.23 Pa. Magnetron sputtering was performed on a high-purity aluminum target at 580 V, with the substrate heated to 400 degrees Celsius. This resulted in a polycrystalline aluminum nitride film with the c-axis perpendicular to the substrate wafer surface and the a-axis along the same direction within the plane, achieving biaxial textured epitaxial growth. Figure 5 This is a schematic diagram of an aluminum nitride-based epitaxial thin film.

[0057] After two hours of continuous growth, the process was stopped, and the substrate with the grown aluminum nitride film was removed.

[0058] Figure 6 This is an out-of-plane orientation pattern (X-ray diffraction pattern) of the aluminum nitride epitaxial thin film crystal structure prepared in Example 1 of this invention. Figure 7 This is an X-ray Phi scan of the aluminum nitride thin film grown on the substrate in Embodiment 1 of the present invention. Figure 6It can be seen that only the (002) peak appears, indicating that the aluminum nitride film has a c-axis preferred orientation out of plane. Figure 7 It can be seen that the aluminum nitride thin film is preferentially oriented in the same direction within the plane, thus achieving a near-single crystal growth.

[0059] Figure 8 This is a scanning electron microscope image of an aluminum nitride thin film grown on a substrate. The aluminum nitride thin film has a smooth surface and a grain diameter of about 50 nm. The roughness measured by atomic force microscopy is 3.37 nm.

[0060] Example 2

[0061] This embodiment uses magnetron sputtering to prepare biaxial textured epitaxial polycrystalline aluminum nitride thin films, and the steps are as follows:

[0062] The substrate wafer is a 2-inch silicon substrate, with P-type doping, a thickness of 0.5 mm, and a surface roughness of less than 2 nm. The substrate is placed horizontally on the sample stage in the vacuum chamber. The sample stage can rotate around the center, and the sample stage controls the substrate temperature at 400℃.

[0063] A high-purity sputtered titanium target is positioned on one tilted side of the substrate wafer, with a distance of 140 mm between the target and the wafer surface. A Kaufman ion source is positioned on the other tilted side of the substrate wafer (opposite to the titanium target), also with a distance of 140 mm between the source and the wafer surface. A high-purity sputtered aluminum target is positioned at another tilted position on the substrate wafer, with a distance of 60 mm between this target and the wafer surface. The angles between the normal phases on the surfaces of the high-purity sputtered titanium target, aluminum target, and ion source and the normal to the substrate wafer surface are all 50°. The positional relationships between the high-purity sputtered titanium target, aluminum target, and ion source and the substrate are as follows: Figure 3 As shown;

[0064] The vacuum chamber was evacuated to a vacuum level of 10. -5 Below Pa, 3 sccm of argon gas is introduced at a pressure of about 0.1 Pa. A voltage of 480 V is applied to a high-purity titanium target for magnetron sputtering. At the same time, the ion source is turned on with an ion source current of 0.5 A and the substrate heating temperature is 400 degrees Celsius to achieve ion-assisted deposition of the transition layer. The grain orientation inside the transition layer is the same in the direction perpendicular to the substrate wafer surface and also in the same direction parallel to the substrate wafer surface.

[0065] After 5 minutes of deposition, the titanium target sputtering and ion source were turned off, and 80 sccm of nitrogen and 2 sccm of argon were introduced at a pressure of about 0.23 Pa. A voltage of 580 V was applied to the high-purity aluminum target for magnetron sputtering, and the substrate was heated to 400 degrees Celsius. This resulted in a polycrystalline aluminum nitride film with the c-axis perpendicular to the substrate wafer surface and the a-axis along the same direction in the plane, thus achieving biaxial textured epitaxial growth.

[0066] After two hours of continuous growth, the process was stopped, and the substrate with the grown aluminum nitride film was removed.

[0067] Figure 9 The image shows the out-of-plane orientation pattern (X-ray diffraction pattern) of the aluminum nitride epitaxial thin film crystal structure prepared in Example 2 of this invention. Figure 9 It can be seen that only the (002) peak appears, indicating that the aluminum nitride film has a c-axis preferred orientation out of the plane.

[0068] Figure 10 The image shows a scanning electron microscope (SEM) image of an aluminum nitride thin film grown on a substrate in Example 2. The aluminum nitride thin film has a smooth surface, a grain diameter of approximately 40 nm, and an atomic force microscope (AFM) analysis shows a roughness of 3.15 nm.

[0069] Comparative Example 1

[0070] This comparative example uses a traditional magnetron sputtering process to prepare aluminum nitride thin films. The steps are as follows: the substrate wafer is a 2-inch silicon substrate, the silicon substrate is P-type doped, the thickness is 0.5 mm, and the surface roughness is less than 2 nm; the substrate is placed horizontally on the sample stage in the vacuum chamber, the sample stage can rotate around the center, and the sample stage controls the substrate temperature at 400℃.

[0071] A high-purity sputtering aluminum target is positioned directly opposite the substrate wafer (the angle between the normal to the aluminum target surface and the normal to the substrate wafer surface is 0°), with a distance of 60 mm between the aluminum target and the substrate wafer surface. The positional relationship between the high-purity sputtering aluminum target and the substrate is as follows: Figure 2 As shown;

[0072] The vacuum chamber was evacuated to a vacuum level of 10. -5 Below Pa, 80 sccm of nitrogen and 2 sccm of argon are introduced, with a gas pressure of about 0.23 Pa. A voltage of 580 V is applied to a high-purity aluminum target for magnetron sputtering, and the substrate is heated to 400 degrees Celsius to deposit a polycrystalline aluminum nitride film.

[0073] After two hours of continuous growth, the process was stopped, and the substrate with the grown aluminum nitride film was removed.

[0074] Figure 11 This is the out-of-plane orientation pattern (X-ray diffraction pattern) of the aluminum nitride thin film crystal structure prepared in Comparative Example 1 of this invention. Figure 11 It can be seen that the out-of-plane c-axis preferred orientation of the aluminum nitride thin film was not achieved.

[0075] As can be seen from the above embodiments, the preparation method provided by the present invention first prepares a transition layer on the surface of a substrate wafer, and then achieves preferential growth of the transition layer grains in a plane with a regular arrangement in a certain direction through ion-assisted deposition; the aluminum nitride thin film on it uses this regularly arranged transition layer as a template to achieve biaxial textured epitaxial (single crystal-like) growth. Therefore, the method provided by the present invention can obtain a single crystal-like aluminum nitride thin film with a high piezoelectric response coefficient and electromechanical coupling coefficient, which can reduce the propagation loss of sound waves in the thin film, and can be used as a piezoelectric material in surface acoustic wave devices or bulk acoustic wave devices.

[0076] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a biaxially textured aluminum nitride epitaxial thin film, characterized in that, Includes the following steps: (1) Place the substrate wafer horizontally in a vacuum chamber; set a metal target and an ion source above the surface of the substrate wafer, wherein the metal target is a ring-shaped single target or a planar single target, and the ion source is a Kaufman ion source or an anode layer ion source; the metal target includes a molybdenum target, a tungsten target, a titanium target, a silver target or an aluminum target; the first angle formed by the normal of the surface of the metal target and the normal of the surface of the substrate wafer is 30~60°, and the second angle formed by the normal of the surface of the ion source and the normal of the surface of the substrate wafer is 30~60°; the straight-line distance between the center of the surface of the metal target and the center of the surface of the substrate wafer is 50~150mm; the straight-line distance between the center of the surface of the ion source and the center of the surface of the substrate wafer is 50~150mm; apply a first voltage to the metal target for magnetron sputtering, and simultaneously turn on the ion source to achieve ion-assisted deposition of a transition layer on the surface of the substrate wafer, wherein the grain orientation of the transition layer obtained on the surface of the substrate wafer is in the same direction in the direction perpendicular to the surface of the substrate wafer, and also in the same direction in the direction parallel to the surface of the substrate wafer; (2) An aluminum target is placed above a substrate wafer on which a transition layer is deposited. The third angle formed by the normal of the aluminum target surface and the normal of the substrate wafer surface is 30~60°. The straight-line distance between the center of the aluminum target surface and the center of the substrate wafer surface is 30~60mm. Nitrogen and argon are introduced into the vacuum chamber. A second voltage is applied to the aluminum target for magnetron sputtering to deposit the biaxial textured aluminum nitride epitaxial film on the surface of the transition layer.

2. The preparation method according to claim 1, characterized in that, The substrate wafer includes a silicon substrate, a silicon carbide substrate, a diamond substrate, or an aluminum oxide substrate; the surface roughness of the substrate wafer is <2nm; and the thickness of the substrate wafer is 0.1~1mm.

3. The preparation method according to claim 1, characterized in that, In step (1), before applying the first voltage to the metal target for magnetron sputtering, the process further includes: evacuating the vacuum chamber to a vacuum level ≤10. -5 Pa, and then argon gas is introduced into the vacuum chamber, and the gas pressure is maintained <1 Pa; the conditions for magnetron sputtering include: the first voltage is 300~500V, the current of the ion source is 0.3~1A, and the heating temperature of the substrate wafer is >100℃.

4. The preparation method according to claim 1 or 3, characterized in that, In step (1), the thickness of the transition layer is ≥5nm.

5. According to the preparation method of claim 1, in step (2): the flow ratio of nitrogen gas and argon gas is >3:1; the conditions for magnetron sputtering include: The air pressure is <0.3Pa, the second voltage is 500~600V, and the heating temperature of the substrate wafer is >300℃.

6. The biaxially textured aluminum nitride epitaxial thin film prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The c-axis crystal direction of the grains inside the biaxial textured aluminum nitride epitaxial film is perpendicular to the surface of the substrate wafer, while the a-axis or b-axis crystal directions are arranged in the same direction within the aluminum nitride epitaxial film.

7. The application of the biaxial textured aluminum nitride epitaxial thin film as described in claim 6 as a chip material in surface acoustic wave devices or bulk acoustic wave devices.

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