AlScN film with lattice matching buffer layer and preparation method of AlScN film

Abstract

The invention discloses an AlScN thin film with a lattice matching buffer layer, the AlScN thin film is of a stacked structure formed by a substrate, an intermediate lattice matching buffer layer and a piezoelectric thin film surface layer, an intrinsic AlN thin film is grown on the substrate in situ to serve as the intermediate lattice matching buffer layer, and AlScN is deposited on the intermediate lattice matching buffer layer to serve as the piezoelectric thin film surface layer; an intrinsic AlN thin film is grown on a substrate in situ to serve as a lattice matching intermediate layer, then an AlScN thin film is prepared through magnetron sputtering double-target co-sputtering, the AlScN thin film of a laminated structure is formed, the crystal quality and lattice matching performance of the AlScN thin film can be remarkably improved, the matching performance is beneficial to reduction of crystal defects and reduction of the phase separation phenomenon in the thin film, and the performance of the AlScN thin film is improved. According to the preparation method, the structural integrity and stability of the material are enhanced, the prepared AlScN film is more compact, more uniform and high in quality, the physical and electrical properties of the material are remarkably improved, and meanwhile, the economic cost is saved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly to an AlScN thin film with a lattice-matched buffer layer and a preparation method thereof. Background Art

[0002] AlScN (aluminum scandium nitride) is an important wide-bandgap semiconductor material with broad application potential. Its wide-bandgap property makes it suitable for high-power and high-frequency electronic devices, as well as ultraviolet LEDs and lasers. By adjusting the ratio of aluminum and scandium elements, its optical and electronic properties can be optimized. In addition, AlScN can be combined with other nitride materials to improve the performance of integrated circuits. Its preparation process is relatively environmentally friendly, meeting the requirements of sustainable development and promoting the development of materials science and engineering. However, in the preparation of Al 1-x Sc x N alloys, due to the different crystal structures of the binary compounds (AlN and ScN), they are not easily soluble in each other. Therefore, most efforts in magnetron sputtering deposition epitaxial Al 1-x Sc x N alloys are based on non-equilibrium processes, and it is somewhat difficult to prepare c-axis oriented Al 1-x Sc x N with high crystal quality. Using relatively inexpensive c-sapphire as a substrate, Al 1-x Sc x N thin films of general quality can be prepared, showing a wurtzite structure and growing in the c-axis direction. However, there is a large lattice mismatch coefficient and thermal expansion coefficient between the c-sapphire substrate and wurtzite-structured Al 1-x Sc x N, which will cause large stress in Al 1-x Sc x N on the substrate, thereby triggering the generation of dislocations and cracks. These defects not only affect the crystallinity of Al 1- x Sc x N, but may also significantly reduce its performance and reliability in electronic devices. Although some studies have shown that intrinsic AlN, SiC, and GaN with a lattice more matched to Al 1-x Sc x N can be used as substrates for growing Al 1-x Sc x N, the high cost of these three substrates makes them unreasonable in practical applications.

[0003] It is particularly necessary to select a substrate material with lattice parameters and thermal expansion coefficients similar to those of the AlScN thin film and with good economic benefits, which not only helps to improve Al 1-x Sc xThe quality and performance of the N film can also promote its wide adoption in practical applications. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an AlScN film with a lattice-matched buffer layer and a preparation method thereof, to solve the problems of dislocation and crack caused by the dissimilar lattice parameters and thermal expansion coefficients of the AlScN film, and at the same time solve the problem of high material cost.

[0005] The AlScN film with a lattice-matched buffer layer of the present invention has a stacked structure formed by a substrate, an intermediate lattice-matched buffer layer, and a piezoelectric thin film surface layer. An intrinsic AlN film is in-situ grown on the substrate as the intermediate lattice-matched buffer layer, and AlScN is deposited on the intermediate lattice-matched buffer layer as the piezoelectric thin film surface layer;

[0006] Further, the intermediate lattice-matched buffer layer is a wurtzite columnar lattice;

[0007] Further, the thickness of the intermediate lattice-matched buffer layer is 70 - 90 nm;

[0008] Further, the intermediate lattice-matched buffer layer is formed on the substrate by magnetron sputtering;

[0009] Further, the substrate is c-sapphire;

[0010] Further, the piezoelectric thin film surface layer is prepared by dual-target magnetron co-sputtering, and the Sc doping concentration of the piezoelectric thin film surface layer is 8 - 31%.

[0011] The present invention also discloses a preparation method of an AlScN film with a lattice-matched buffer layer, including the following steps:

[0012] S1, cleaning and treating the substrate;

[0013] S2, preparing the intermediate lattice-matched buffer layer: using an aluminum target as the aluminum source, in an ultra-pure working gas environment, adopting DC pulsed sputtering technology, the power of the DC pulsed sputtering is 300 - 450 W, and the substrate temperature is room temperature - 550 °C;

[0014] S3, preparing the piezoelectric thin film surface layer: using magnetron co-sputtering technology for simultaneous sputtering of the Al target and the Sc target to prepare an AlScN film as the piezoelectric thin film surface layer;

[0015] Further, in step S1, the substrate is ultrasonically cleaned multiple times in an alternating bath of acetone, alcohol, and deionized water to remove contaminants on the surface of the substrate; then it is placed in a vacuum chamber, the substrate is heated to a temperature of 550 °C, and then ultra-pure gas is intermittently introduced into the chamber to clean fine particulate contaminants on the surface of the substrate;

[0016] Furthermore, in step S3, a DC pulsed power supply is used to sputter an Al target, and an RF power supply is used to sputter a Sc target simultaneously to deposit an Sc-doped AlScN thin film;

[0017] Furthermore, in step S3, before co-sputtering, the Sc target is pre-sputtered with a power of 250 - 350 W. During the co-sputtering process, the power of the DC pulsed power supply for sputtering the Al target is 400 - 500 W, the power of the RF power supply for sputtering the Sc target is 200 - 500 W, and the co-sputtering time is 60 - 80 minutes.

[0018] The beneficial effects of the present invention are as follows: The AlScN thin film with a lattice-matched buffer layer and its preparation method of the present invention grow an intrinsic AlN thin film in situ on a substrate as a lattice-matched intermediate layer, and then use magnetron sputtering double-target co-sputtering to prepare an AlScN thin film, forming a stacked AlScN thin film structure. By using the lattice-matched intermediate layer, the lattice parameters and thermal expansion coefficients of the thin film are similar, which can significantly improve the crystal quality and lattice matching of the AlScN thin film. This matching helps to reduce crystal defects, reduce the phase separation phenomenon inside the thin film, enhance the structural integrity and stability of the material. The prepared AlScN thin film is denser, more uniform and of higher quality, significantly improving the physical and electrical properties of the material, and at the same time, saving economic costs. Description of the Drawings

[0019] The present invention will be further described below with reference to the drawings and embodiments:

[0020] Figure 1 It is a bilayer stacked structure where the AlScN thin film does not have an intermediate lattice-matched buffer layer;

[0021] Figure 2 It is a triple-layer stacked structure where the AlScN thin film has an intermediate lattice-matched buffer layer;

[0022] Figure 3 It is the 2θ-XRD phase scanning results of Examples 1, 2, and 3;

[0023] Figure 4 It is the 2θ-XRD phase scanning results of Examples 4, 5, and 6;

[0024] Figure 5 It is the comparison of XRC FWHM between the case with an AlN lattice-matched intermediate layer (Example 4) and the case without an intermediate layer (Example 1);

[0025] Figure 6 It is the comparison of XRC FWHM between the case with an AlN lattice-matched intermediate layer (Example 5) and the case without an intermediate layer (Example 2);

[0026] Figure 7 XRC FWHM comparison for the case with an AlN lattice-matched interlayer (Example 6) and without an interlayer (Example 3). Detailed implementation manners

[0027] For the AlScN thin film with a lattice-matched buffer layer in this embodiment, the AlScN thin film forms a stacked structure composed of a substrate, an intermediate lattice-matched buffer layer, and a piezoelectric thin film surface layer. An intrinsic AlN thin film is in-situ grown on the substrate as the intermediate lattice-matched buffer layer, and AlScN is deposited on the intermediate lattice-matched buffer layer as the piezoelectric thin film surface layer; the substrate, the intermediate lattice-matched buffer layer, and the piezoelectric thin film surface layer form a three-layer stacked structure, with the substrate at the bottom layer, the intermediate lattice-matched buffer layer in the middle, and the piezoelectric thin film surface layer at the upper layer.

[0028] By improving the lattice matching, making the lattice parameters and thermal expansion coefficients of the thin film similar, it can significantly improve the crystal quality and lattice matching of the AlScN thin film. This kind of matching helps to reduce crystal defects, reduce the phase separation phenomenon inside the thin film, and enhance the structural integrity and stability of the material.

[0029] In this embodiment, the intermediate lattice-matched buffer layer is a wurtzite columnar lattice; to improve the lattice matching, the thickness of the intermediate lattice-matched buffer layer is 70 - 90 nm; the intermediate lattice-matched buffer layer is formed on the substrate by magnetron sputtering; in the stacked structure, the intermediate lattice-matched layer is made of AlN, preferably with a thickness of 80 nm. It is prepared by DC pulsed magnetron sputtering. In the experiment, an aluminum target with a purity of 99.995% is used as the aluminum source, and a scandium target with a purity of 99.995% is used as the scandium source. During the magnetron sputtering process, 20 sccm and 35 sccm of argon and nitrogen are mixed and introduced into the cavity, and the purity of both gases is 99.995%. The DC pulsed sputtering power of the aluminum target is 300 W - 450 W, and the substrate temperature is room temperature - 550 °C.

[0030] In this embodiment, the substrate is c-sapphire; the bottom layer structure uses c-sapphire, and its price is lower than that of aluminum nitride (AlN), gallium nitride (GaN), and silicon carbide (SiC). In addition, compared with the traditional silicon (Si) substrate, c-sapphire has the same close-packed hexagonal structure as the intrinsic wurtzite-type aluminum nitride. Specifically, the lattice constant of c-sapphire is about 4.76 angstroms, while the lattice constant of aluminum nitride is about 3.11 angstroms. Therefore, the lattice mismatch coefficient between the two is relatively small, about 34%. Further analyzing the thermal expansion coefficient, the thermal expansion coefficient of silicon is 2.6×10 -6 K -1 while the thermal expansion coefficient of c-sapphire is about 6.5×10 -6 K -1, the thermal expansion coefficient of aluminum nitride is about 4.5×10 -6 K -1 . Therefore, the difference in thermal expansion coefficient between c-sapphire and aluminum nitride is small, and the interfacial stress generated during temperature change is also low, which is beneficial to improving the adhesion and stability of the film.

[0031] Therefore, the preferred structure is:

[0032] The bottom layer structure is a c-sapphire substrate of 2×2 cm 2 .

[0033] The middle layer structure is a wurtzite columnar crystal AlN lattice-matching buffer layer of 2×2 cm 2 , with a thickness of 80 nm.

[0034] The top layer structure is an AlScN piezoelectric thin film layer of 2×2 cm 2 with Sc concentrations of 8, 15, and 31%.

[0035] In this embodiment, the piezoelectric thin film surface layer is prepared by dual-target magnetron sputtering co-sputtering, and the Sc doping concentration of the piezoelectric thin film surface layer is 8-31%. The top layer of the laminated structure is AlScN, preferably with a thickness of 800 nm; flexible doping concentration adjustment, by adjusting the power of the radio frequency power supply and the DC pulsed power supply to precisely control the Sc doping concentration (such as 8%, 15%, and 31%), so as to optimize the performance of the AlScN thin film. "Dual-target magnetron sputtering co-sputtering" means using a Sc target and an aluminum target and performing magnetron sputtering simultaneously. This embodiment also discloses a method for preparing an AlScN thin film with a lattice-matching buffer layer, including the following steps:

[0036] S1, substrate cleaning treatment; perform multiple ultrasonic cleanings on the c-sapphire substrate in an alternating bath of acetone, alcohol, and deionized water to remove contaminants on the substrate surface. Then put it into a vacuum chamber and evacuate it to 3.2×E-3 Pa, and then heat the substrate to 550 °C. After that, intermittently introduce argon and nitrogen with a purity of 99.995% into the cavity, with a duration of 5 minutes and an interval of 5 minutes, and use ultra-pure gas to clean fine particle contaminants on the substrate surface;

[0037] S2. Prepare an intermediate lattice-matching buffer layer: Using an aluminum target as the aluminum source, in an ultra-pure working gas environment, adopt DC pulsed sputtering technology. The power of the DC pulsed sputtering is 300 - 450 W, and the substrate temperature is room temperature - 550 °C. During the preparation of the AlN intermediate lattice-matching layer, the sputtering power has a significant impact on the deposition rate and film quality of the AlN layer. A higher sputtering power usually increases the deposition rate but may lead to an increase in film stress and the generation of crystal defects. Therefore, selecting an appropriate power range is the key to ensuring film quality. In this application, when the DC pulsed power of the Al target reaches 450 W, the quality of the AlN intermediate layer is optimal. When the power exceeds 450 W and reaches 500 W, the quality of the AlN intermediate layer deteriorates, and cracking occurs. The substrate temperature also plays an important role in the crystal structure and properties of the AlN layer. At a lower substrate temperature, there may be more amorphous phases and defects in the film, while at a higher temperature, the crystal growth is more orderly, which can improve the crystallization quality and densification of the film. By optimizing the sputtering power and substrate temperature, the lattice matching of the AlN layer can be effectively improved, thereby enhancing the overall performance of the stacked structure. When the substrate temperature reaches 550 °C, the quality of the AlN intermediate layer is the best;

[0038] S3. Prepare the piezoelectric thin film surface layer: Magnetron co-sputtering of Al target and Sc target is carried out to prepare AlScN thin film as the piezoelectric thin film surface layer; The co-sputtering technology of sputtering Al target with DC pulsed power supply and Sc target with RF power supply at the same time is adopted to deposit Sc-doped AlScN thin film; Before co-sputtering, the Sc target is pre-sputtered with a power of 250-350W. During the co-sputtering process, the power of sputtering Al target with DC pulsed power supply is 400-500W, the power of sputtering Sc target with RF power supply is 200-500W, and the co-sputtering time is 60-80 minutes. The Sc-doped AlScN thin film is prepared by using double targets. During the sputtering process, the Al target is sputtered with DC pulsed power supply, and the power is preferably 450W; The Sc target is sputtered with RF power supply, and the RF sputtering power is 200W-500W. During the co-sputtering of AlScN, the argon flow rate is 20sccm and the nitrogen flow rate is 35sccm. RF power supply is used as the power supply for co-sputtering to prepare the AlScN top thin film. Because previous studies have shown that when using RF (radio frequency) power supply, due to the fact that the RF power supply can generate a stronger electric field at a higher frequency, it can effectively excite gas molecules, increasing the degree of ionization and activation ability of the gas. Therefore, the activation ratio of nitrogen in the magnetron sputtering chamber atmosphere usually increases, which is beneficial to the combination of nitrogen atoms with aluminum atoms and Sc atoms to form high-quality AlScN thin films with wurtzite structure. Specifically, the RF power supply can generate more high-energy electrons in the atmosphere. When these high-energy electrons collide with nitrogen molecules, they can effectively excite and ionize nitrogen molecules to form nitrogen ions (N+) and reactive nitrogen species. These activated nitrogen species can react with aluminum during the deposition process to form compounds such as aluminum nitride (AlN), thereby improving the quality and performance of the thin film. In addition, in the experiment, the DC pulsed power of the Al target is fixed (preferably 450W), and by changing the RF power of the Sc target, the Sc doping content of AlScN is adjusted. The RF power of Sc is preferably 200, 300, 500W, corresponding to the top piezoelectric thin films of AlScN with Sc doping concentrations of 8, 15, and 31% respectively.

[0039] In the following embodiments, the stacked structures of Embodiments 1, 2, and 3 are as Figure 1 shown. This stacked structure is to directly deposit AlScN thin film on the c-sapphire substrate by using magnetron sputtering technology, and there is no AlN lattice matching intermediate layer. The stacked structures of Embodiments 4, 5, and 6 are as Figure 1 shown. This stacked structure is to first deposit an AlN lattice matching intermediate layer on the c-sapphire substrate by using magnetron sputtering technology, and then deposit AlScN top thin films with Sc doping concentrations of 8, 15, and 31%.

[0040] Embodiment 1

[0041] Directly on a c-sapphire substrate, using a co-sputtering technique that combines a radio frequency power supply for a Sc target and a DC pulse for an Al target, deposit an AlScN top piezoelectric thin film with a Sc doping concentration of 8%.

[0042] Steps: First, treat the c-sapphire substrate to remove surface contaminants. Then, use a radio frequency power supply with a power of 300 W to pre-sputter a Sc target with a purity of 99.995% for ten minutes. Subsequently, use a DC pulse power supply with a power of 450 W to sputter the Al target, and at the same time use a radio frequency power supply with a power of 200 W to co-sputter the scandium target. The sputtering time is 80 minutes, and finally an AlScN thin film with a thickness of 800 nm and a scandium doping content of 8% is prepared.

[0043] Example 2

[0044] Directly on a c-sapphire substrate, using a co-sputtering technique that combines a radio frequency power supply for a Sc target and a DC pulse for an Al target, deposit an AlScN top piezoelectric thin film with a Sc doping concentration of 8%.

[0045] Steps: First, treat the c-sapphire substrate to remove surface contaminants. Then, use a radio frequency power supply with a power of 300 W to pre-sputter a Sc target with a purity of 99.995% for ten minutes. Subsequently, use a DC pulse power supply with a power of 450 W to sputter the Al target, and at the same time use a radio frequency power supply with a power of 300 W to co-sputter the Sc target. The sputtering time is 70 minutes, and finally an AlScN thin film with a thickness of 800 nm and a scandium doping content of 15% is prepared.

[0046] Example 3

[0047] Directly on a c-sapphire substrate, using a co-sputtering technique that combines a radio frequency power supply for a Sc target and a DC pulse for an Al target, deposit an AlScN top piezoelectric thin film with a Sc doping concentration of 8%.

[0048] Steps: First, treat the c-sapphire substrate to remove surface contaminants. Then, use a radio frequency power supply with a power of 300 W to pre-sputter a Sc target with a purity of 99.995% for ten minutes. Subsequently, use a DC pulse power supply with a power of 450 W to sputter the Al target, and at the same time use a radio frequency power supply with a power of 500 W to co-sputter the Sc target. The sputtering time is 60 minutes, and finally an AlScN thin film with a thickness of 800 nm and a scandium doping content of 31% is prepared.

[0049] Example 4

[0050] First, an 80-nm AlN lattice-matched intermediate layer is deposited on a c-sapphire substrate by DC pulsed magnetron sputtering. Finally, a top-layer piezoelectric AlScN film with a Sc doping concentration of 8% is deposited by a co-sputtering technique combining an RF power supply for the Sc target and a DC pulsed power supply for the Al target.

[0051] Steps: First, the c-sapphire substrate is treated to remove surface contaminants. Then, an AlN lattice-matched intermediate layer with a thickness of 80 nm is grown on the c-sapphire substrate. Subsequently, an RF power supply with a power of 300 W is used to pre-sputter a Sc target with a purity of 99.995% for ten minutes. Subsequently, a DC pulsed power supply with a power of 450 W is used to sputter the Al target, and at the same time, an RF power supply with a power of 200 W is used to co-sputter the Sc target. The sputtering time is 80 minutes, and finally, an AlScN film with a thickness of 800 nm and a Sc doping content of 8% is prepared.

[0052] Example Five

[0053] First, an 80-nm AlN lattice-matched intermediate layer is deposited on a c-sapphire substrate by DC pulsed magnetron sputtering. Finally, a top-layer piezoelectric AlScN film with a Sc doping concentration of 15% is deposited by a co-sputtering technique combining an RF power supply for the Sc target and a DC pulsed power supply for the Al target.

[0054] Steps: First, the c-sapphire substrate is treated to remove surface contaminants. Then, an AlN lattice-matched intermediate layer with a thickness of 80 nm is grown on the c-sapphire substrate. Subsequently, an RF power supply with a power of 300 W is used to pre-sputter a Sc target with a purity of 99.995% for ten minutes. Subsequently, a DC pulsed power supply with a power of 450 W is used to sputter the Al target, and at the same time, an RF power supply with a power of 300 W is used to co-sputter the Sc target. The sputtering time is 70 minutes, and finally, an AlScN film with a thickness of 800 nm and a Sc doping content of 15% is prepared.

[0055] Example Six

[0056] First, an 80-nm AlN lattice-matched intermediate layer is deposited on a c-sapphire substrate by DC pulsed magnetron sputtering. Finally, a top-layer piezoelectric AlScN film with a Sc doping concentration of 8% is deposited by a co-sputtering technique combining an RF power supply for the Sc target and a DC pulsed power supply for the Al target.

[0057] Steps: First, the c-sapphire substrate is processed to remove surface contaminants. Then, a lattice-matched AlN intermediate layer with a thickness of 80 nm is grown on the c-sapphire substrate. Subsequently, a Sc target with a purity of 99.995% is pre-sputtered for ten minutes using a radio frequency power supply with a power of 300 W. Subsequently, the Al target is sputtered using a DC pulsed power supply with a power of 450 W, and the Sc target is co-sputtered using a radio frequency power supply with a power of 500 W. The sputtering time is 60 minutes, and finally, an AlScN thin film with a thickness of 800 nm and a Sc doping content of 31% is prepared.

[0058] XRD (X-ray Diffraction) phase analysis of the laminated structure:

[0059] Figure 3 The 2θ-XRD phase scanning results for Examples 1, 2, and 3 show that when the Sc doping concentrations are 8%, 15%, and 31%, relatively tall wurtzite AlScN 002 characteristic peaks are shown. However, when the doping concentration is too high at 31%, the 002 characteristic peak is low, indicating poor crystallinity at this time with a high Sc concentration. There are the following reasons to explain. When the Sc doping concentration reaches 31%, it will cause partial phase separation in the sample structure. The reason is that a higher doping concentration may cause the Sc element to be no longer evenly distributed in the lattice, forming a Sc-rich phase and a Sc-poor phase, resulting in the degradation of the overall crystal structure. High-concentration Sc doping may cause lattice matching problems and corresponding stress changes. And there are also large internal stresses (such as residual stresses) inside the thin film, which also cause the 002 diffraction peak to have a large width. Because when there are large internal stresses in the thin film, the distortion of the crystal structure will lead to wider diffraction peaks.

[0060] Figure 4 The 2θ-XRD phase scanning results for Examples 4, 5, and 6 show that when the Sc doping concentrations are 8%, 15%, and 31%, wurtzite AlScN 002 characteristic peaks that are taller compared to Examples 1 and 2 are shown. When the doping concentration is as high as 31%, the characteristic peak belonging to wurtzite AlScN 002 is enhanced, and the peak width becomes narrower. This shows that at the three Sc doping concentrations, the crystallinity is improved after inserting an AlN intermediate lattice-matched layer between the sapphire and AlScN, and the phase separation phenomenon inside the thin film is also alleviated.

[0061] Analysis of the crystallization quality results of the laminated structure by XRC (X-ray Reflection Curve):

[0062] Through the detailed analysis of the XRC (X-ray diffraction) data results, it can be clearly seen that in Examples 4, 5, and 6 with an AlN lattice-matched intermediate layer, compared to Examples 1, 2, and 3 without an intermediate layer, the XRC full width at half maximum (FWHM) is significantly reduced. The XRC FWHM of Examples 1, 2, and 3 decreases from 4.3°, 4.2°, and 6.8° to 1.8°, 2.1°, and 2.4°

[0063] This is because the introduction of the AlN intermediate layer can effectively improve the crystallization quality of the crystal, reduce defects and dislocations in the crystal, thereby making the lattice arrangement of the crystal more orderly, resulting in a reduction in the XRC FWHM.

[0064] In addition, in the examples with an AlN intermediate layer, the angle of the 002 characteristic peak is closer to the fully relaxed angle without residual stress. This is because the AlN intermediate layer plays a good role in lattice matching and buffering, and can relieve the stress caused by the lattice mismatch and the difference in thermal expansion coefficient between the c-sapphire substrate and the AlScN thin film. The presence of the AlN intermediate layer enables the AlScN thin film to be deposited more uniformly during growth, reducing the accumulation of stress, so that the angle of the 002 characteristic peak is closer to the state without residual stress. The reason for this phenomenon can be explained from the perspective of crystallography. When the AlScN thin film is directly deposited on the c-sapphire substrate, due to the lattice mismatch and the mismatch of thermal expansion coefficients, large stresses will be generated in the thin film. These stresses will affect the growth and arrangement of the crystal, resulting in more defects and dislocations in the crystal, thus increasing the XRC FWHM and deviating the angle of the 002 characteristic peak from the fully relaxed angle. The lattice constant of the AlN intermediate layer is closer to that of the AlScN thin film, which can better match the lattice structures of the two, thereby reducing the generation of stress and improving the quality and stability of the crystal.

[0065] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. An AlScN film with a lattice matching buffer layer, characterized in that: The AlScN film is stacked by a substrate, an intermediate lattice matching buffer layer and a piezoelectric film surface layer. An intrinsic AlN film is in-situ grown on the substrate as the intermediate lattice matching buffer layer, and AlScN is deposited on the intermediate lattice matching buffer layer as the piezoelectric film surface layer.

2. The AlScN thin film with a lattice matching buffer layer according to claim 1, characterized in that: The intermediate lattice matching buffer layer is a wurtzite columnar lattice.

3. The AlScN film with a lattice matching buffer layer according to claim 2, characterized in that: The thickness of the intermediate lattice matching buffer layer is 70-90 nm.

4. The AlScN film with a lattice matching buffer layer according to claim 3, characterized in that: The intermediate lattice matching buffer layer is generated on the substrate by magnetron sputtering.

5. The AlScN film with a lattice matching buffer layer according to claim 1, characterized in that: The substrate is c-sapphire.

6. The AlScN film with a lattice matching buffer layer according to claim 1, characterized in that: The piezoelectric film surface layer is prepared by dual-target magnetron co-sputtering, and the Sc doping concentration of the piezoelectric film surface layer is 8-31%.

7. The method for preparing an AlScN thin film with a lattice matching buffer layer according to claim 1, characterized in that: The following steps are involved: S1, substrate cleaning process; S2, preparing an intermediate lattice matching buffer layer: using an aluminum target as an aluminum source, in an ultra-pure working gas environment, using a DC pulse sputtering technique, the power of the DC pulse sputtering is 300-450W, and the substrate temperature is room temperature to 550°C; S3, preparing a piezoelectric film surface layer: using a magnetron co-sputtering technique in which an Al target material and a Sc target material are sputtered simultaneously to prepare an AlScN film as a piezoelectric film surface layer.

8. The method for preparing an AlScN thin film with a lattice matching buffer layer according to claim 7, characterized in that: In step S1, the substrate is ultrasonically cleaned multiple times in an alternating bath of acetone, alcohol and deionized water to remove contaminants on the surface of the substrate; then it is placed in a vacuum chamber, the substrate is heated to a temperature of 550°C, and then ultrapure gas is intermittently introduced into the chamber to clean fine particle contaminants on the surface of the substrate.

9. The method for preparing an AlScN thin film with a lattice matching buffer layer according to claim 7, characterized in that: In step S3, a DC pulse power source is used to sputter an Al target material, and a radio frequency power source is used to sputter a Sc target material, so as to deposit a Sc-doped AlScN film.

10. The method for preparing an AlScN thin film with a lattice matching buffer layer according to claim 9, characterized in that: In step S3, the Sc target is pre-sputtered before co-sputtering, with a power of 250-350W. During the co-sputtering process, the power of the DC pulse power supply for sputtering the Al target is 400-500W, and the power of the RF power supply for sputtering the Sc target is 200-500W. The co-sputtering time is 60-80 minutes.

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