A method for preparing a scandium aluminum nitride film

Abstract

The application relates to a preparation method of a scandium aluminum nitride film, and belongs to the field of semiconductor materials. The preparation method of the scandium aluminum nitride film comprises the following steps: step 1, obtaining a basic substrate and a functional composite layer obtained by epitaxial growth on the basic substrate, wherein the functional composite layer comprises an aluminum nitride base layer and a gallium nitride sacrificial layer; step 2, stripping the gallium nitride sacrificial layer from the surface of the aluminum nitride base layer to obtain a template containing the basic substrate and the aluminum nitride base layer; and step 3, growing a scandium aluminum nitride film layer on the aluminum nitride base layer of the template. According to the application, the gallium nitride sacrificial layer is epitaxially grown on the aluminum nitride base layer, the aluminum nitride base layer is prevented from being oxidized during the transfer process between different process equipment, the crystal quality of the aluminum nitride base layer is guaranteed, conditions for epitaxially growing a scandium aluminum nitride film layer with high crystal quality are provided, and the crystal quality and the piezoelectric constant of the scandium aluminum nitride film are improved.

Description

Technical Field

[0001] This application belongs to the field of semiconductor materials, specifically relating to a method for preparing scandium aluminum nitrogen thin films. Background Technology

[0002] Aluminum nitride (AlN) materials possess advantages such as high acoustic wave transmission speed, good temperature stability, and low dielectric loss, making them one of the ideal materials for next-generation filters. Growing high-quality aluminum nitride films using epitaxial technology is fundamental to the fabrication of high-quality BAW filters, especially high-quality FBAR filters. Furthermore, adding scandium (Sc) to AlN can effectively improve the electromechanical coupling coefficient of the material. Currently, single-crystal ScAlN thin films represent one of the development directions for preparing high-performance filter materials.

[0003] AlN single-crystal thin films can be chemically synthesized using metal-organic chemical vapor deposition (MOCVD), but stress issues arise during heteroepitaxial growth, especially when fabricating large-size and / or thick films, leading to warping or cracking. While other processes, such as physical vapor deposition (PVD), can address the stress problem when preparing aluminum nitride films, growing ScAlN films using a different Sc / Al alloy target often results in polycrystalline films, reducing subsequent device performance. Existing techniques propose growing a high-quality MO~AlN (aluminum nitride monolayer) seed layer using a combination of MOCVD and PVD, followed by PVD growth of ScAlN on the seed layer, inheriting the crystal quality and surface finish of the underlying seed layer. This method significantly improves the overall performance of AlN while maintaining low in-plane stress. However, this growth method involves two or more devices, requiring inter-device transfer during the epitaxial process, which easily leads to contamination and surface oxidation. Summary of the Invention

[0004] In view of this, this application provides a method for preparing scandium aluminum nitride (ScAlN) thin films, wherein an aluminum nitride (AlN) substrate layer and a gallium nitride (GaN) sacrificial layer are epitaxially grown sequentially on a substrate, and then the gallium nitride sacrificial layer is peeled off, so as to avoid oxidation of the aluminum nitride substrate layer during the transfer between different devices. Thus, scandium aluminum nitride films can be grown on the aluminum nitride substrate layer through different epitaxial deposition processes, which is beneficial to improving the crystal quality of scandium aluminum nitride films.

[0005] In a first aspect, this application provides a method for preparing a scandium aluminum nitride thin film, the method comprising the following steps: Step 1, obtaining a base substrate and a functional composite layer obtained by epitaxial growth on the base substrate, the functional composite layer comprising an aluminum nitride substrate layer and a gallium nitride sacrificial layer; the aluminum nitride substrate layer being in contact with the base substrate, the gallium nitride sacrificial layer being disposed on the side surface of the aluminum nitride substrate layer facing away from the base substrate; Step 2, peeling the gallium nitride sacrificial layer from the surface of the aluminum nitride substrate layer to obtain a template containing the base substrate and the aluminum nitride substrate layer; Step 3, growing a scandium aluminum nitride film layer on the aluminum nitride substrate layer of the template. This application epitaxially grows an aluminum nitride substrate on a base substrate, using a high-quality aluminum nitride substrate as a seed crystal to lay the foundation for the subsequent epitaxial growth of a high-crystal-quality scandium aluminum nitride film. Furthermore, this application grows a gallium nitride (GaN) sacrificial layer on the side of the aluminum nitride substrate facing away from the base substrate, serving as a protective layer for the aluminum nitride substrate. This prevents the aluminum nitride substrate from being exposed to the atmosphere during transfer between different process equipment, thus avoiding oxidation caused by reactions with free oxygen molecules. The removal of the gallium nitride sacrificial layer does not affect the subsequent growth and quality of the scandium aluminum nitride film. This application allows for the use of multiple epitaxial growth processes in combination, avoiding the stress problems associated with using only MOCVD heteroepitaxial technology. By adjusting the epitaxial process conditions, it is beneficial to improve the crystal quality and piezoelectric constant of the scandium aluminum nitride film, resulting in advantages such as low acoustic transmission loss and high efficiency when applied in filters.

[0006] Preferably, the growth conditions for the aluminum nitride substrate include: a temperature of 1100~1300℃, a pressure of 30~200 Torr, a gas volumetric flow rate of 10~30 sccm for the aluminum source, and a gas volumetric flow rate of 10~20 slm for ammonia. This application uses metal-organic chemical vapor deposition (MOCVD) to prepare the aluminum nitride substrate. By controlling the process conditions, a single-crystal aluminum nitride substrate can be obtained, providing conditions for the subsequent growth of a high-quality scandium aluminum nitride film.

[0007] Preferably, the root mean square roughness (RMS) of the aluminum nitride substrate layer is in the range of 0.5 ≤ Rq ≤ 0.8 nm. This application controls the aluminum nitride substrate layer to have a low roughness, which is beneficial for improving the growth quality of the subsequent scandium aluminum nitride film layer. Furthermore, using a thinner gallium nitride sacrificial layer on the aluminum nitride substrate layer with low roughness can ensure complete coverage of the aluminum nitride substrate layer, thereby avoiding oxidation and contamination problems during the transfer of the aluminum nitride substrate layer between devices.

[0008] Preferably, the full width at half maximum (FWHM) of the (002) peak in the aluminum nitride substrate is in the range of 0.2° ≤ FWHM ≤ 0.6°. By controlling the FWHM of the (002) peak in the aluminum nitride substrate, the c-axis lattice order of the aluminum nitride substrate is ensured, forming a single-crystal aluminum nitride substrate, which helps to reduce crystal defects and improve the growth quality of the subsequent scandium aluminum nitride film.

[0009] Preferably, the thickness of the aluminum nitride substrate layer is 50~100 nm.

[0010] Preferably, the growth conditions of the gallium nitride sacrificial layer include: a temperature of 800~900℃, a pressure of 50~70 Torr, a gas volumetric flow rate of 300~380 sccm for the gallium source, and a gas volumetric flow rate of 40~60 slm for the nitrogen source. The gallium nitride sacrificial layer is disposed on the aluminum nitride substrate. By fully covering the aluminum nitride substrate, the aluminum nitride substrate is completely isolated from the atmospheric environment, avoiding oxidation and contamination problems caused by the transfer of epitaxial wafers between devices.

[0011] Preferably, the gallium nitride sacrificial layer comprises 1 to 10 gallium nitride monolayers. In this application, the gallium nitride sacrificial layer is composed of gallium nitride monolayers. By limiting the thickness of the gallium nitride layer to 1 to 10 monolayers, it is possible to ensure that the GaN sacrificial layer can completely cover the aluminum nitride substrate, avoiding oxidation caused by uncovered areas, while also avoiding the problem of incomplete desorption of the GaN sacrificial layer during subsequent baking due to excessive thickness.

[0012] Preferably, the gallium nitride layer comprises 3 to 5 gallium nitride monolayers, and more preferably comprises 4 gallium nitride monolayers.

[0013] Preferably, step 2, which involves peeling the gallium nitride sacrificial layer from the aluminum nitride substrate, includes: baking the functional composite layer to peel the gallium nitride sacrificial layer from the aluminum nitride substrate; introducing argon gas during the baking process at a flow rate of 20-50 sccm; baking at a temperature of 500-900°C for 2-30 minutes; and baking at a pressure of 2-4 mTorr. Baking removes the gallium nitride sacrificial layer from the aluminum nitride substrate, exposing the complete aluminum nitride surface, achieving complete peeling of the sacrificial layer within the vacuum chamber. Simultaneously, baking helps remove impurities such as water and oxygen accumulated on the epitaxial wafer surface, ensuring a clean surface and facilitating the subsequent preparation of a high-quality scandium aluminum nitride film. It also preheats the aluminum nitride substrate, improving the efficiency of subsequent scandium aluminum nitride film preparation. Argon gas (Ar) is introduced during the baking process, and the argon gas flow rate is controlled. This allows the argon gas to act as a protective gas, ensuring stable pressure within the cavity and suppressing the reaction between aluminum nitride and residual water and oxygen in the cavity after high-temperature gallium nitride desorption. In this application, the combination of sacrificial layer coverage and in-cavity desorption technology effectively isolates the epitaxial wafer completely from the atmosphere. Furthermore, the growth and desorption of the sacrificial layer are performed directly in situ using MOCVD and PVD systems, resulting in a simple and efficient process.

[0014] Preferably, the flow rate of the argon gas is 25~35 sccm; the temperature of the baking treatment is 600~800℃; and the baking time is 10~15 min, for example, baking at 650℃ for 10 min.

[0015] Preferably, the baking process further includes a baking pressure of 2-4 mTorr. Controlling the baking process at a lower pressure facilitates the escape and removal of the gallium nitride sacrificial layer.

[0016] Preferably, the growth conditions of the scandium aluminum nitride film include: a scandium aluminum alloy sputtering target, a sputtering power of 1500~3000 W, a substrate temperature of 500~800℃, a nitrogen source gas volumetric flow rate of 100~200 sccm, an argon source gas volumetric flow rate of 20~50 sccm, and a working pressure of 2~6 mTorr. This application employs physical vapor deposition (PVD) for the epitaxial growth of the scandium aluminum nitride film. By controlling the growth process of the scandium aluminum nitride film, it is beneficial to modulate the stress problems caused by lattice mismatch and thermal mismatch in the scandium aluminum nitride heteroepitaxial growth, thereby obtaining a scandium aluminum nitride film with a relatively high thickness. Simultaneously, it ensures that the scandium aluminum nitride film has low residual stress, avoiding cracks and also preventing the impact of excessive warpage on subsequent chip processes.

[0017] Preferably, the thickness of the scandium aluminum nitrogen film layer is 200~1000 nm.

[0018] Based on the scandium aluminum nitride (SAN) thin film preparation method of this application, an aluminum nitride substrate is used as the growth basis for the SNA film, providing conditions for growing a high-quality SNA film. Subsequent SNA films can be grown using different processes than those used with the aluminum nitride substrate, such as physical vapor deposition (PVD). This avoids the stress problems caused by lattice mismatch and thermal mismatch during single-crystal aluminum nitride heteroepitaxial growth using only MOCVD. By setting a gallium nitride (GaN) sacrificial layer, the aluminum nitride substrate is isolated from air contact during transfer between different process equipment, thus preventing oxidation of the aluminum nitride substrate. Furthermore, the GaN sacrificial layer can be removed by baking in the SNA film preparation equipment without affecting the crystal quality of the aluminum nitride substrate, thereby improving the crystal quality of the subsequent SNA film grown on the aluminum nitride substrate. The scandium aluminum nitride thin film prepared by the method of this application includes an aluminum nitride substrate and a scandium aluminum nitride film layer. The scandium aluminum nitride film layer is nucleated and crystallized on a high-quality aluminum nitride substrate to obtain a near-single-crystal scandium aluminum nitride thin film, which ensures high crystal quality and piezoelectric constant, reduces acoustic transmission loss, improves transmission efficiency, and is beneficial for application in high-performance filters. Attached Figure Description

[0019] Figure 1 A flowchart illustrating a specific embodiment of the preparation method of scandium aluminum nitrogen thin film in this application; Figure 2 The XRD diffraction analysis results are for the scandium aluminum nitrogen thin films prepared in Examples 1, 4 and Comparative Examples 1-2 of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0021] In existing technologies, metal-organic chemical vapor deposition (MOCVD) can be used to prepare AlN single-crystal thin films with high crystal quality (hereinafter referred to as MO-AlN), but it is difficult to overcome the stress problem caused by heteroepitaxial growth. Existing technologies have proposed a process combining MOCVD and physical vapor deposition (PVD) to achieve the preparation of near-single-crystal scandium aluminum nitride films, improving crystal quality to some extent. However, this still cannot meet the performance requirements of high-frequency broadband filters, and the overall process needs further optimization.

[0022] The inventors of this application discovered during the preparation of scandium aluminum nitride thin films that scandium aluminum nitride thin films are prone to oxidation upon contact with air during extracavity transfer between different processes. After the aluminum nitride thin film used as the growth template is oxidized, an Al-NO mixed bond region is formed at the interface, making the interface blurred and indistinct. The scandium aluminum nitride layer has difficulty effectively inheriting the (002) lattice orientation of the underlying MO-AlN, resulting in a decrease in the overall (002) peak full width at half maximum (FWHM) of the scandium aluminum nitride thin film prepared by physical vapor deposition (hereinafter referred to as PVD-ScAlN). This indicates a reduction in the crystal quality and C-axis order of PVD-ScAlN, which will seriously hinder the acoustic transmission of thick FBAR filter devices, reduce the Q factor of the device, increase the insertion loss of the device, and thus seriously affect the working performance of the device. At the same time, the O replacing the N bond at the interface can affect the lattice structure of PVD-ScAlN, causing polarity reversal of PVD-ScAlN in local areas, reducing the electromechanical coupling coefficient of PVD-ScAlN. K t 2 This severely impacts the bandwidth of subsequent devices.

[0023] In view of this, this application provides a method for preparing a scandium aluminum nitride thin film, the method comprising the following steps: Step 1, obtaining a base substrate and a functional composite layer obtained by epitaxial growth on the base substrate, the functional composite layer comprising an aluminum nitride substrate layer and a gallium nitride sacrificial layer; the aluminum nitride substrate layer is in contact with the base substrate, and the gallium nitride sacrificial layer is disposed on the side surface of the aluminum nitride substrate layer opposite to the base substrate; Step 2, peeling the gallium nitride sacrificial layer from the surface of the aluminum nitride substrate layer to obtain a template containing the base substrate and the aluminum nitride substrate layer; Step 3, growing a scandium aluminum nitride film layer on the aluminum nitride substrate layer of the template.

[0024] In some embodiments, this application can use a single-crystal AlN thin film material prepared by MOCVD process as a seed crystal, and perform nucleation and crystallization growth on the seed crystal template using processes such as PVD to obtain a near-single-crystal scandium aluminum nitride thin film. The gallium nitride sacrificial layer prevents oxidation of the seed crystal template during transfer between different process equipment, ensuring the quality of the seed crystal template. This facilitates the control of single-crystal growth of the scandium aluminum nitride film during the nucleation and crystallization process, resulting in high crystal quality.

[0025] Figure 1 Flowcharts illustrating methods for preparing scandium aluminum nitride thin films according to some specific embodiments of this application are shown, such as... Figure 1As shown, this application first uses MOCVD technology to epitaxially grow an aluminum nitride (ANT) substrate on a substrate (base substrate), and then grows a gallium nitride (GaN) sacrificial layer in situ on the ANT substrate. The GaN sacrificial layer serves as an anti-oxidation protective layer for the ANT substrate. The substrate with both the GaN sacrificial layer and the ANT substrate is then transferred between the MOCVD and PVD equipment. Next, the substrate with both the GaN sacrificial layer and the ANT substrate is baked in the PVD equipment. Under high temperature and low pressure conditions, the GaN sacrificial layer is peeled off from the surface of the ANT substrate, resulting in a template containing only the base substrate and the ANT substrate. Finally, a scandium aluminum nitride (SAM) functional layer is grown in situ on the ANT substrate using PVD technology.

[0026] Optionally, the base substrate can be a conventional semiconductor single crystal material in the art, such as silicon, sapphire, or silicon carbide.

[0027] In some embodiments, the aluminum nitride substrate layer can be grown using a metal-organic chemical vapor deposition (MOCVD) process; the scandium aluminum nitride film layer can be grown using a physical vapor deposition (PVD) process.

[0028] In some embodiments, the gallium nitride sacrificial layer comprises 1 to 10 gallium nitride monolayers. In this application, a gallium nitride monolayer refers to a monolayer formed by the orderly arrangement of gallium nitride molecules on a deposition surface, which can be prepared by MOCVD growth.

[0029] Optionally, to avoid oxidation of the aluminum nitride substrate, after growing the aluminum nitride substrate, a gallium nitride sacrificial layer is grown in situ on the aluminum nitride substrate using MOCVD technology. After growing the gallium nitride sacrificial layer, the functional composite layer is transferred to a PVD device, where it is baked to remove the gallium nitride sacrificial layer, and then the scandium aluminum nitride film layer is grown in situ. In this application, the in-situ growth of the gallium nitride sacrificial layer means that after growing the aluminum nitride, it is not necessary to change the growth equipment; only the input source is changed, and growth continues in the same equipment. The in-situ growth of the scandium aluminum nitride film layer means that growth is performed in the original equipment without moving the base substrate and the position of the aluminum nitride substrate.

[0030] Example The technical solution of this application will be described below with reference to specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all from ordinary commercially available products, and the devices or equipment used are all purchased from conventional market sales channels.

[0031] Example 1 The method for preparing scandium aluminum nitrogen thin films in this embodiment includes the following steps: Step 1: Using a silicon wafer as the base substrate, a functional composite layer is epitaxially grown on the base substrate. The functional composite layer includes an aluminum nitride substrate layer and a gallium nitride sacrificial layer epitaxially grown sequentially on the silicon wafer. The aluminum nitride substrate layer is grown on the surface of the base substrate using MOCVD technology. The growth conditions include: a temperature of 1100℃, a pressure of 100 Torr, a gas volumetric flow rate of 10 sccm for the aluminum source, and a gas volumetric flow rate of 10 slm for the nitrogen source. The prepared aluminum nitride substrate layer has a root mean square roughness Rq of 0.8 nm and a full width at half maximum (FWHM) of 0.4° for the (002) peak.

[0032] The gallium nitride sacrificial layer was grown in situ on the surface of the aluminum nitride substrate away from the base substrate using MOCVD. The growth conditions included a temperature of 850°C, a pressure of 70 Torr, a gas volumetric flow rate of 300 sccm for the gallium source, and a gas volumetric flow rate of 40 slm for the nitrogen source. The resulting gallium nitride sacrificial layer consisted of four gallium nitride monolayers.

[0033] Step 2: Remove the functional composite layer from the MOCVD equipment and place it in the PVD equipment. Then, bake the functional composite layer to peel the gallium nitride sacrificial layer from the aluminum nitride substrate surface, obtaining a template containing the base substrate and the aluminum nitride substrate. The baking conditions include: argon gas is introduced during the baking process at a flow rate of 20 sccm, a temperature of 650℃, a time of 10 min, and a pressure of 2 mTorr.

[0034] Step 3: Grow a scandium aluminum nitrogen film on the aluminum nitride substrate of the template. The growth conditions of the scandium aluminum nitrogen film include: the sputtering target is a scandium aluminum alloy target, the sputtering power is 2000 W, the substrate temperature is 500℃, the gas volume flow rate of the nitrogen source is 100 sccm, the gas volume flow rate of the argon source is 20 sccm, the working pressure is 2 mTorr, and the thickness of the resulting scandium aluminum nitrogen film is 200 nm.

[0035] Example 2 The method for preparing scandium aluminum nitrogen thin films in this embodiment includes the following steps: Step 1: Using a silicon wafer as the base substrate, a functional composite layer is epitaxially grown on the base substrate. The functional composite layer includes an aluminum nitride substrate layer and a gallium nitride sacrificial layer epitaxially grown sequentially on the silicon wafer. The aluminum nitride substrate layer is grown on the surface of the base substrate using MOCVD technology. The growth conditions include: a temperature of 1200℃, a pressure of 30 Torr, a gas volumetric flow rate of 20 sccm for the aluminum source, and a gas volumetric flow rate of 15 slm for the nitrogen source. The prepared aluminum nitride substrate layer has a root mean square roughness Rq of 0.5 nm and a (002) peak full width at half maximum (FWHM) of 0.2°.

[0036] The gallium nitride sacrificial layer was grown in situ on the surface of the aluminum nitride substrate away from the base substrate using MOCVD. The growth conditions included a temperature of 850°C, a pressure of 50 Torr, a gas volumetric flow rate of 380 sccm for the gallium source, and a gas volumetric flow rate of 50 slm for the nitrogen source. The resulting gallium nitride sacrificial layer consisted of 10 gallium nitride monolayers.

[0037] Step 2: Remove the functional composite layer from the MOCVD equipment and place it in the PVD equipment. Then, bake the functional composite layer to peel the gallium nitride sacrificial layer from the aluminum nitride substrate surface, obtaining a template containing the base substrate and the aluminum nitride substrate. The baking conditions include: argon gas is introduced during the baking process at a flow rate of 20 sccm, a temperature of 1200℃, a time of 2 min, and a pressure of 3 mTorr.

[0038] Step 3: Grow a scandium aluminum nitrogen film on the aluminum nitride substrate of the template. The growth conditions of the scandium aluminum nitrogen film include: the sputtering target is a scandium aluminum alloy target, the sputtering power is 2500 W, the substrate temperature is 650℃, the gas volume flow rate of the nitrogen source is 150 sccm, the gas volume flow rate of the argon source is 40 sccm, the working pressure is 4 mTorr, and the thickness of the obtained scandium aluminum nitrogen film is 600 nm.

[0039] Example 3 The method for preparing scandium aluminum nitrogen thin films in this embodiment includes the following steps: Step 1: Using a silicon wafer as the base substrate, a functional composite layer is epitaxially grown on the base substrate. The functional composite layer includes an aluminum nitride substrate layer and a gallium nitride sacrificial layer epitaxially grown sequentially on the silicon wafer. The aluminum nitride substrate layer is grown on the surface of the base substrate using MOCVD technology. The growth conditions include: a temperature of 1300℃, a pressure of 200 Torr, a gas volumetric flow rate of 30 sccm for the aluminum source, and a gas volumetric flow rate of 20 slm for the nitrogen source. The prepared aluminum nitride substrate layer has a root mean square roughness Rq of 0.8 nm and a full width at half maximum (FWHM) of 0.4° for the (002) peak.

[0040] The gallium nitride sacrificial layer was grown in situ on the surface of the aluminum nitride substrate away from the base substrate using MOCVD. The growth conditions included a temperature of 900℃, a pressure of 60 Torr, a gas volumetric flow rate of 340 sccm for the gallium source, and a gas volumetric flow rate of 60 slm for the nitrogen source. The resulting gallium nitride sacrificial layer consisted of five gallium nitride monolayers.

[0041] Step 2: Remove the functional composite layer from the MOCVD equipment and place it in the PVD equipment. Then, bake the functional composite layer to peel the gallium nitride sacrificial layer from the aluminum nitride substrate surface, obtaining a template containing the base substrate and the aluminum nitride substrate. The baking conditions include: argon gas is introduced during the baking process at a flow rate of 20 sccm, a temperature of 500℃, a time of 30 min, and a pressure of 4 mTorr.

[0042] Step 3: Grow a scandium aluminum nitrogen film on the aluminum nitride substrate of the template. The growth conditions of the scandium aluminum nitrogen film include: the sputtering target is a scandium aluminum alloy target, the sputtering power is 3000 W, the substrate temperature is 800℃, the gas volume flow rate of the nitrogen source is 200 sccm, the gas volume flow rate of the argon source is 50 sccm, the working pressure is 6 mTorr, and the thickness of the obtained scandium aluminum nitrogen film is 1000 nm.

[0043] Example 4 The method for preparing the scandium aluminum nitride thin film in this embodiment differs from that in Example 1 only in that the gallium nitride sacrificial layer prepared in step 1 comprises 20 gallium nitride monolayers.

[0044] Example 5 The preparation method of the scandium aluminum nitride thin film in this embodiment differs from that in Example 1 only in that the root mean square roughness Rq of the aluminum nitride substrate is 1.5 nm.

[0045] Comparative Example 1 The preparation method of the scandium aluminum nitride thin film in this comparative example differs from that in Example 1 only in that the gallium nitride sacrificial layer and baking process are omitted. After the aluminum nitride substrate layer is prepared in step 1, it is directly transferred to the PVD equipment for the subsequent preparation of the scandium aluminum nitride film layer in step 3.

[0046] Comparative Example 2 The method for preparing the scandium aluminum nitride thin film in this embodiment differs from that in Example 1 only in that the baking process is omitted, and in step 2, after the functional composite layer is placed in the PVD equipment, the scandium aluminum nitride film layer is directly grown on the gallium nitride sacrificial layer.

[0047] Experimental Example 1 X-ray diffraction (XRD) analysis was performed on the scandium aluminum nitride films obtained by the preparation methods of Examples 1-5 and Comparative Examples 1-2. The full width at half maximum (FWHM) of the (002) peak of each scandium aluminum nitride film was measured. The XRD diffraction analysis results of the scandium aluminum nitride films prepared in Examples 1, 4, and Comparative Examples 1-2 are as follows: Figure 2 As shown in Table 1, the piezoelectric constants (D33 values) of the scandium aluminum nitrogen films prepared by the methods of Example 1 and Comparative Example 1 were tested using a quasi-static D33 tester.

[0048] Table 1

[0049] As shown in Table 1, the half-width at half-maximum (WHM) of the (002) peak of the scandium aluminum nitride thin film prepared in Example 1 is 553" (WHM is in arcseconds, 1" = 1 / 3600°). In contrast, the half-width at half-maximum (WHM) of the (002) peak of the scandium aluminum nitride thin film prepared in Comparative Example 1, after omitting the gallium nitride sacrificial layer and baking process, is 1127". This demonstrates that the gallium nitride sacrificial layer and baking process in this application can significantly reduce the WHM of the (002) peak of the scandium aluminum nitride thin film and improve the crystal quality of the scandium aluminum nitride thin film. Simultaneously, the D33 test results also show that the piezoelectric constant of Example 1 is significantly greater than that of Comparative Example 1 and is close to that of single-crystal scandium aluminum nitride, indicating that the scandium aluminum nitride thin film of Example 1 has better c-axis ordering. Compared to Comparative Example 1, it greatly suppresses the generation of polarity reversal, thereby avoiding piezoelectric polarization cancellation caused by polarity reversal. This demonstrates that the gallium nitride sacrificial layer and baking process of this application have the advantage of improving the crystal quality of scandium aluminum nitride thin films, thereby improving the dielectric properties of scandium aluminum nitride thin films and promoting their application in high-frequency broadband filters.

[0050] Compared with Example 1 and Comparative Example 2, if gallium nitride baking is not performed, the entire gallium nitride layer will remain on the aluminum nitride substrate, becoming an insertion layer between the aluminum nitride substrate and the scandium aluminum nitride film. Due to the strong coupling between the insertion layer and the aluminum nitride substrate and film, a more complex stress situation will be brought about. Moreover, the insertion of gallium nitride will cause lattice mismatch at the interface, which will seriously affect the crystal quality of aluminum nitride.

[0051] Comparing Examples 1 and 4, the scandium aluminum nitride film prepared in Example 4 using an excessively thick gallium nitride sacrificial layer has a half-width at half-maximum (FWHM) of 760" for the (002) peak, indicating a decrease in crystal quality. This is because an excessively thick gallium nitride sacrificial layer leads to incomplete removal of the sacrificial layer during subsequent baking, resulting in some gallium nitride remaining on the aluminum nitride substrate. This creates a mixed structure of gallium nitride and aluminum nitride in localized areas, thereby reducing the crystal quality of the scandium aluminum nitride film to some extent. This application, by controlling the thickness of the gallium nitride sacrificial layer to 1-10 gallium nitride monolayers, can protect the aluminum nitride substrate from oxidation while ensuring the removal effect of subsequent baking, thus improving the crystal quality of the subsequent scandium aluminum nitride film.

[0052] In Example 5, based on Example 1, the root-mean-square roughness of the aluminum nitride substrate was increased to 1.5 nm, and the full width at half maximum (FWHM) of the (002) peak of the prepared scandium aluminum nitride film was 858". However, the crystal quality also decreased to some extent. This may be because the higher surface roughness prevents the gallium nitride sacrificial layer from completely covering the aluminum nitride substrate, thus posing a risk of oxidation to the aluminum nitride substrate during inter-device transfer. Oxidation affects the crystal quality of the subsequently grown scandium aluminum nitride film. This application, by controlling the root-mean-square roughness of the aluminum nitride substrate between 0.5 and 0.8 nm, helps to reduce or avoid the oxidation risk of the aluminum nitride substrate, thereby ensuring the crystal quality of the scandium aluminum nitride film.

[0053] Examples 2 and 3 have similar crystal quality and surface roughness. Combining Examples 1-3, it can be seen that under the process conditions of this application, the gallium nitride sacrificial layer + baking process can very effectively optimize the crystal quality and piezoelectric coefficient of scandium aluminum nitride. Furthermore, the process steps can be directly designed and operated in-situ within the equipment, without the need for external equipment. The process steps are simple and convenient to operate, greatly optimizing the crystal quality and piezoelectric performance of scandium aluminum nitride while ensuring the overall high efficiency of the process.

[0054] Experimental Example 2 Auger electron spectroscopy (AES) was used to determine the oxygen content of the scandium aluminum nitride films prepared in Example 1 and Comparative Example 1, thus identifying the degree of oxidation of each film sample. AES results showed that no oxygen content was detected at the interface in Example 1, while the detected oxygen content at the interface in Comparative Example 1 was 1 × 10⁻⁶. -16 It is evident that by setting a gallium nitride sacrificial layer and baking treatment, this application helps to protect the aluminum nitride substrate and reduce the risk of oxidation of the gallium nitride substrate during transfer between devices, thereby avoiding oxidation problems of the aluminum nitride substrate and improving the crystal quality of scandium aluminum nitride thin film.

[0055] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a scandium aluminum nitrogen thin film, characterized in that, The preparation method includes the following steps: Step 1: Obtain a base substrate and a functional composite layer grown on the base substrate by epitaxial growth, wherein the functional composite layer includes an aluminum nitride substrate layer and a gallium nitride sacrificial layer. The aluminum nitride substrate layer is in contact with the base substrate, and the gallium nitride sacrificial layer is disposed on the side surface of the aluminum nitride substrate layer opposite to the base substrate; The process involves growing an aluminum nitride substrate using MOCVD, and then growing a gallium nitride sacrificial layer in situ on the aluminum nitride substrate. After growing the gallium nitride sacrificial layer, the functional composite layer is transferred to a PVD device. The gallium nitride sacrificial layer is provided to isolate the aluminum nitride substrate from contact with air during the transfer between different process devices. Step 2: Peel the gallium nitride sacrificial layer from the surface of the aluminum nitride substrate to obtain a template containing a base substrate and an aluminum nitride substrate; peeling the gallium nitride sacrificial layer from the surface of the aluminum nitride substrate includes: baking the functional composite layer to peel the gallium nitride sacrificial layer from the surface of the aluminum nitride substrate. Step 3: Grow a scandium aluminum nitrogen film layer on the aluminum nitride substrate layer of the template.

2. The preparation method according to claim 1, characterized in that, The growth conditions for the aluminum nitride substrate include: a temperature of 1100~1300℃, a pressure of 30~200 Torr, a gas volume flow rate of 10~30 sccm for the aluminum source, and a gas volume flow rate of 10~20 slm for ammonia.

3. The preparation method according to claim 1, characterized in that, The root mean square roughness Rq of the aluminum nitride substrate layer ranges from 0.5 ≤ Rq ≤ 0.8 nm; and / or, The full width at half maximum (FWHM) of the (002) peak in the aluminum nitride substrate ranges from 0.2° to 0.6°; and / or, The thickness of the aluminum nitride substrate is 50~100 nm.

4. The preparation method according to claim 1, characterized in that, The growth conditions for the gallium nitride sacrificial layer include: a temperature of 800~900℃, a pressure of 50~70 Torr, a gas volumetric flow rate of 300~380 sccm for the gallium source, and a gas volumetric flow rate of 40~60 slm for the nitrogen source.

5. The preparation method according to claim 1, characterized in that, The gallium nitride sacrificial layer comprises 1 to 10 gallium nitride monolayers.

6. The preparation method according to claim 5, characterized in that, The gallium nitride sacrificial layer comprises 3 to 5 gallium nitride monolayers.

7. The preparation method according to claim 1, characterized in that, Argon gas is introduced during the baking process, and the flow rate of the argon gas is 20~50 sccm; the baking temperature is 500~900℃, and the baking time is 2~30 min.

8. The preparation method according to claim 7, characterized in that, The argon gas flow rate is 25-35 sccm; the baking temperature is 600-800℃; and the baking time is 10-15 min; and / or, The baking process also includes a baking pressure of 2-4 mTorr.

9. The preparation method according to claim 1, characterized in that, The growth conditions for the scandium-aluminum-nitrogen film include: the sputtering target is a scandium-aluminum alloy target, the sputtering power is 1500~3000 W, the substrate temperature is 500~800℃, the gas volume flow rate of the nitrogen source is 100~200 sccm, the gas volume flow rate of the argon source is 20~50 sccm, and the working pressure is 2~6 mTorr.

10. The preparation method according to claim 9, characterized in that, The thickness of the scandium aluminum nitrogen film is 200~1000nm.

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