A method and system for preparing a polar controllable aluminum nitride film

Abstract

This invention provides a method and system for preparing aluminum nitride thin films with controllable polarity, relating to the field of aluminum nitride thin film preparation technology. During the growth of the initial layer, inversion layer, and intrinsic layer, this method involves real-time acquisition of the characteristic spectral intensities of target elements such as aluminum, nitrogen, and oxygen in the plasma, determining the proportional relationship between the characteristic spectral intensities of each target element, and then determining the deviation from a preset polarity growth window based on this proportional relationship, thus judging the current deposition environment state according to the deviation. Especially during the growth of the inversion layer, the growth thickness of the inversion layer is controlled within a preset nanometer-scale threshold range by combining the monitoring results of the characteristic spectral intensities. The method of this invention aims to solve the problem of the difficulty in stably and repeatedly preparing polarity-inverted structures in the prior art, and can prepare polarity-inverted aluminum nitride thin films with excellent piezoelectric properties and high reliability.

Description

Technical Field

[0001] This invention relates to the field of aluminum nitride thin film preparation technology, and more specifically, to a method and system for preparing aluminum nitride thin films with controllable polarity. Background Technology

[0002] With the full commercialization of 5G mobile communication technology and the ongoing research and development of 6G communication technology, modern communication systems need to extend beyond the Sub-6GHz band to the millimeter-wave band to meet the demands for greater bandwidth and higher data transmission rates. Simultaneously, emerging application areas such as satellite communication, automotive radar, and the Internet of Things (IoT) are placing higher demands on the performance of filters operating at high frequencies. These applications not only require filters to have higher operating frequencies but also to maintain low insertion loss, sufficient bandwidth, and excellent out-of-band rejection capabilities, while simultaneously meeting stringent requirements for miniaturization, high integration, and reliability. However, the traditional approach of increasing the operating frequency of acoustic filters by thinning the piezoelectric layer has reached its physical limits. When the thickness of the aluminum nitride piezoelectric layer is reduced to the hundreds of nanometers level, it not only faces reliability issues such as weak film mechanical strength, poor adhesion, and low process yield but also causes a significant degradation in piezoelectric performance, manifested as a decrease in electromechanical coupling coefficient and a deterioration in quality factor. This results in narrower filter bandwidth and increased insertion loss, failing to meet the dual performance and reliability requirements of high-frequency applications.

[0003] To achieve breakthroughs in high-frequency filter performance, the industry has proposed an innovative solution based on polarity-reversed aluminum nitride. The core principle of this technology lies in utilizing the opposite piezoelectric response directions of the Al and N polarity crystal orientations of aluminum nitride: when these two polar regions are alternately arranged in a piezoelectric layer to form a periodic structure, the strain directions generated in adjacent regions under the action of an applied electric field are opposite. This effectively suppresses the fundamental vibration modes while enhancing the excitation efficiency of higher-order modes, thereby achieving a significant increase in operating frequency without reducing the thickness of the piezoelectric layer.

[0004] However, the practical application of this technology is severely constrained by the material preparation process. Current polarity control methods are relatively simple, mainly relying on static control of single parameters such as doping concentration or temperature. However, the polar growth condition window for aluminum nitride is extremely narrow, requiring precise and coordinated adjustment of multiple parameters such as power, gas pressure, and gas ratio. Furthermore, in the fabrication of multilayer polarity-reversal structures, the lack of precise control over the growth interface leads to problems such as degraded interlayer crystal quality, high interface defect density, and unclear polarity transition regions, severely affecting the overall piezoelectric properties of the thin film and the operational stability of the device. Existing technologies lack preparation methods capable of real-time monitoring and dynamic adjustment of the deposition environment, making it difficult to precisely control the growth process of polarity-reversal structures and achieve stable and repeatable polarity control effects.

[0005] There is currently no effective technical solution to the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for preparing polarity-controllable aluminum nitride thin films, aiming to solve the problems in the prior art, such as the single polarity control method, inaccurate growth interface control, crystal quality degradation, and lack of real-time monitoring and dynamic adjustment capabilities, which make it difficult to stably and repeatedly prepare polarity-reversed structures. This invention can prepare polarity-reversed aluminum nitride thin films with excellent piezoelectric properties and high reliability.

[0007] In a first aspect, the present invention provides a method for preparing aluminum nitride thin films with controllable polarity, comprising the following steps: S1. After pretreating the substrate, and under aluminum-rich conditions, switch to a combination of process parameters that match the nitrogen polarity, and dynamically adjust the relevant process parameters to grow the initial layer. S2. After the initial layer has grown, and under nitrogen-rich conditions, a polar induction medium containing oxygen is introduced into the deposition environment, and the process parameter combination matching the inversion induction is switched, and the relevant process parameters are dynamically adjusted to grow the inversion layer. S3. After the growth of the inversion layer is completed, stop introducing the polar induction medium and confirm whether the polar induction medium in the deposition environment has been completely removed based on the intensity of the characteristic spectral line of the oxygen element monitored in real time. S4. After confirming that the polar induction medium in the deposition environment has been completely removed, and under nitrogen-rich conditions, switch to a combination of process parameters that match the polarity of aluminum, and dynamically adjust the relevant process parameters to grow the intrinsic layer. S5. By cyclically executing the above steps S1-S4, a multilayer thin film structure with opposite polar orientations is alternately grown on the substrate; wherein, during the growth of the initial layer, the inversion layer and the intrinsic layer, the deposition environment state is judged in real time, and the corresponding relevant process parameters are dynamically adjusted based on the judged deposition environment state. Specifically, the steps for real-time assessment of the sedimentary environment include A1-A2: A1. Real-time acquisition of the characteristic spectral line intensities of multiple target elements in plasma, and determination of the proportional relationship of the characteristic spectral line intensities among the target elements; the multiple target elements include aluminum, nitrogen, and oxygen. A2. Based on the aforementioned proportional relationship, determine the deviation from the corresponding preset polarity growth window, and based on the deviation, determine the current deposition environment state; During the growth of the inversion layer, the growth thickness of the inversion layer is controlled within a preset threshold range by combining the monitoring results of the characteristic spectral line intensity.

[0008] The present invention provides a method for preparing aluminum nitride thin films with controllable polarity. Through step-by-step regulation, real-time monitoring, and dynamic adjustment, it achieves precise control of the polarity of aluminum nitride thin films and stable preparation of multilayer structures. It effectively solves the problems of single polarity control methods, inaccurate control of growth interface, crystal quality degradation, and lack of real-time monitoring and dynamic adjustment capabilities in the prior art. Thus, it is possible to prepare aluminum nitride thin films with excellent piezoelectric properties and high reliability, providing a key material basis for the application of devices such as high-frequency acoustic wave filters.

[0009] Secondly, the present invention provides a polarity-controllable aluminum nitride thin film preparation system, comprising: The first control module is used to switch to a combination of process parameters that match the nitrogen polarity after the substrate has been pretreated and under aluminum-rich conditions, and to dynamically adjust the relevant process parameters to grow the initial layer. The second control module is used to introduce a polar induction medium containing oxygen into the deposition environment after the initial layer has grown and under nitrogen-rich conditions, and to switch to a combination of process parameters that matches the inversion induction, and to dynamically adjust the relevant process parameters to grow the inversion layer. The third control module is used to stop introducing the polar induction medium after the inversion layer growth is completed, and to confirm whether the polar induction medium in the deposition environment has been completely removed based on the characteristic spectral intensity of the oxygen element monitored in real time. The fourth control module is used to switch to a combination of process parameters that match the polarity of aluminum after confirming that the polarity-inducing medium in the deposition environment has been completely removed and under nitrogen-rich conditions, and to dynamically adjust the relevant process parameters to grow the intrinsic layer. The fifth control module is used to alternately grow multilayer thin film structures with opposite polar orientations on the substrate by sequentially running the first control module, the second control module, the third control module and the fourth control module; wherein, during the growth of the initial layer, the inversion layer and the intrinsic layer, the deposition environment state is judged in real time, and the relevant process parameters are dynamically adjusted based on the judged deposition environment state. Specifically, the steps for real-time assessment of the sedimentary environment include A1-A2: A1. Real-time acquisition of the characteristic spectral line intensities of multiple target elements in plasma, and determination of the proportional relationship of the characteristic spectral line intensities among the target elements; the multiple target elements include aluminum, nitrogen, and oxygen. A2. Based on the aforementioned proportional relationship, determine the deviation from the corresponding preset polarity growth window, and based on the deviation, determine the current deposition environment state; During the growth of the inversion layer, the growth thickness of the inversion layer is controlled within a preset threshold range by combining the monitoring results of the characteristic spectral line intensity.

[0010] As can be seen from the above, the method for preparing aluminum nitride thin films with controllable polarity provided by this invention effectively solves the problems of single polarity control methods, inaccurate growth interface control, crystal quality degradation, and lack of real-time monitoring and dynamic adjustment capabilities in the prior art. This method can achieve precise control of the polarity of aluminum nitride thin films and stable preparation of multilayer structures, significantly improving the crystal quality, interface clarity, and repeatability of polarity control of the thin films. Compared with the traditional method of increasing the operating frequency by reducing the thickness of the piezoelectric layer, this application achieves a significant increase in operating frequency without reducing the thickness of the piezoelectric layer through a polarity reversal mechanism. At the same time, it avoids reliability problems such as weak film mechanical strength, poor adhesion, and low process yield, and effectively suppresses the decay of piezoelectric performance. Thus, it is possible to prepare polarity-reversed aluminum nitride thin films with excellent piezoelectric performance and high reliability, providing a key material basis for the application of devices such as high-frequency acoustic wave filters, and has significant progressive and practical value.

[0011] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing embodiments of the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0012] Figure 1 This is a flowchart of a method for preparing a polarity-controllable aluminum nitride thin film according to an embodiment of the present invention.

[0013] Figure 2 This is a schematic diagram of a polarity-controllable aluminum nitride thin film preparation system provided in an embodiment of the present invention.

[0014] Label Explanation: 100, First control module; 200, Second control module; 300, Third control module; 400, Fourth control module; 500, Fifth control module. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0016] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0017] In the fabrication of aluminum nitride thin films for high-frequency communication systems, when multilayer polarity reversal structures are employed to increase operating frequencies, inaccurate control of process parameters in the deposition environment and improper management of the growth interface lead to increased interface defect density and blurred polarity transition regions. This, in turn, degrades the piezoelectric properties of the thin film and reduces device stability. Specifically, interlayer crystal quality degradation and interface defects reduce the electromechanical coupling coefficient and quality factor, resulting in insufficient filter bandwidth and increased insertion loss, failing to meet the dual performance and reliability requirements of high-frequency applications.

[0018] For example, in the manufacturing process of millimeter-wave filters for satellite communication terminals, when technicians grow multilayer aluminum nitride films with alternating nitrogen and aluminum polar orientations, the lack of dynamic adjustment of sputtering power, operating gas pressure, and gas flow rate parameters, as well as incomplete purification after introducing oxygen as a polarity-inducing medium, leads to residual oxygen at the interface between the inversion layer and the intrinsic layer. This causes blurring of the polarity transition region and accumulation of crystal defects, thereby weakening the filter's out-of-band rejection capability at high frequencies. This prevents the filter from effectively filtering out interference signals, directly affecting the signal integrity and data transmission efficiency of the communication system.

[0019] If the above issues are not addressed, the overall piezoelectric properties of the thin film will fail to meet design requirements, and the device may experience performance drift or failure under long-term operating conditions, severely impacting the reliability of communication systems and data transmission quality. Furthermore, a high defect rate during fabrication will reduce product yield, increase manufacturing costs, and hinder the practical application of this technology in fields such as 5G / 6G communications and the Internet of Things.

[0020] For reference, see the appendix. Figure 1 This invention provides a method for preparing aluminum nitride thin films with controllable polarity, comprising the following steps: S1. After pretreating the substrate, and under aluminum-rich conditions, switch to a combination of process parameters that match the nitrogen polarity, and dynamically adjust the relevant process parameters to grow the initial layer; the relevant process parameters include sputtering energy parameters and process gas flow rate parameters; the sputtering energy parameters include sputtering power and working gas pressure; S2. After the initial layer growth is completed, and under nitrogen-rich conditions, a polar induction medium containing oxygen is introduced into the deposition environment, and the process parameter combination matching the inversion induction is switched, and the relevant process parameters are dynamically adjusted to grow the inversion layer; the polar induction medium is oxygen. S3. After the inversion layer growth is completed, stop introducing the polar induction medium and perform purification treatment on the polar induction medium. Confirm whether the polar induction medium in the deposition environment has been completely removed based on the characteristic spectral intensity of oxygen element monitored in real time. S4. After confirming that the polar induction medium in the deposition environment has been completely removed, and under nitrogen-rich conditions, switch to a combination of process parameters that match the polarity of aluminum, and dynamically adjust the relevant process parameters to grow the intrinsic layer. S5. By cyclically executing the above steps S1-S4, a multilayer thin film structure with opposite polar orientations is alternately grown on the substrate; wherein, during the growth of the initial layer, the inversion layer and the intrinsic layer, the deposition environment state is judged in real time, and the corresponding relevant process parameters are dynamically adjusted based on the judged deposition environment state. Specifically, the steps for real-time assessment of the sedimentary environment include A1-A2: A1. Real-time acquisition of characteristic spectral line intensities of multiple target elements in plasma, and determination of the proportional relationship between characteristic spectral line intensities of each target element; multiple target elements include aluminum (film-forming element), nitrogen (reacting element), and oxygen (corresponding element to polar induction medium); A2. Based on the proportional relationship, determine the deviation from the corresponding preset polarity growth window, and determine the current depositional environment state based on the deviation; During the growth of the inversion layer, the growth thickness of the inversion layer is controlled within a preset nanometer threshold range (≤10nm) by combining the monitoring results of the characteristic spectral line intensity.

[0021] For ease of understanding, the following explains some key terms in this embodiment: Aluminum nitride (AlN) thin film polarity: Aluminum nitride (AlN) thin films have two main crystal orientations: aluminum polarity (Al-polar) and nitrogen polarity (N-polar). These two polarities correspond to different atomic arrangements in the crystal structure, resulting in opposite directions of piezoelectric response. In piezoelectric devices, by precisely controlling the polarity of the thin film, the propagation mode of sound waves can be modulated, thereby optimizing device performance.

[0022] Aluminum-rich conditions vs. nitrogen-rich conditions: In the preparation of aluminum nitride thin films, aluminum-rich conditions refer to a deposition environment where the relative content of aluminum is higher than that of nitrogen, which is conducive to the formation of aluminum polar films. Conversely, nitrogen-rich conditions indicate a relatively high nitrogen content, which is conducive to the formation of nitrogen polar films. Aluminum-rich or nitrogen-rich conditions can be controlled by precisely regulating the gas flow rate ratio in the deposition environment.

[0023] Sputtering energy parameters: Sputtering energy parameters mainly include sputtering power and working pressure. Sputtering power determines the energy and density of ions in the plasma, thus affecting the sputtering rate and thin film growth kinetics. Working pressure affects the degree of scattering and energy loss of sputtered particles before reaching the substrate, significantly influencing the compactness and crystal quality of the thin film.

[0024] Polar induction medium: A polar induction medium refers to a medium that, during the growth of aluminum nitride thin films, induces a reversal of the film's polarity by introducing specific elements or compounds. For example, oxygen can act as a polar induction medium under certain conditions, promoting the formation of a polarity-reversed layer by altering lattice defects or surface energy.

[0025] Characteristic spectral line intensities: In plasma emission spectroscopy (OES) monitoring, different elements emit light of specific wavelengths when excited by plasma; the intensities of these lights are called characteristic spectral line intensities. By acquiring and analyzing these characteristic spectral line intensities in real time, the relative abundance of each element in the plasma can be quantitatively determined, thereby enabling real-time monitoring of the deposition environment.

[0026] Polar growth window: The polar growth window refers to the range of process parameters that allow for the stable growth of films with specific polarities during the preparation of aluminum nitride films. This window is usually very narrow, requiring precise and coordinated adjustments to multiple parameters such as sputtering power, working pressure, gas ratio, and growth temperature.

[0027] Traditional aluminum nitride thin films suffer from interface defects, unclear polarity transitions, and imprecise control of growth conditions when fabricating multilayer polarity-reversed structures. Failure to address these issues will severely impact the overall piezoelectric properties of the film and the stability of the device. To address this, this application proposes a polarity-controllable aluminum nitride thin film fabrication method. By dynamically adjusting process parameters stepwise and monitoring the deposition environment in real time, the polarity of the aluminum nitride thin film can be controlled, effectively solving the interface defects and polarity transition problems in multilayer structures.

[0028] This method includes the following steps: In step S1, after pretreatment of the substrate and under aluminum-rich conditions, the process parameter combination matching the nitrogen polarity is switched, and the relevant process parameters are dynamically adjusted to grow the initial layer. The relevant process parameters include sputtering energy parameters and process gas flow rate parameters; the sputtering energy parameters include sputtering power and operating pressure. This step aims to ensure that the initial layer has a stable nitrogen polar orientation, avoiding crystal defects caused by unstable conditions. For example, the substrate can be silicon or polycrystalline molybdenum substrates to accommodate BAW device integration. The pretreatment process may include standard RCA cleaning and hydrofluoric acid treatment of the silicon substrate to remove the native oxide layer, or ultrasonic cleaning of the molybdenum substrate with acetone and ethanol and surface activation with dilute hydrochloric acid. During the initial layer growth, nitrogen-polar aluminum nitride can be directly grown under aluminum-rich conditions (e.g., a nitrogen to argon flow rate ratio of 1:2). The process parameters can be set as follows: sputtering power in the range of 550W-650W, operating pressure in the range of 0.3Pa-0.5Pa, and growth temperature of 450°C. During the growth process, the ratio of characteristic spectral line intensities between aluminum and nitrogen can be monitored in real time and maintained within the range of 1.5-2.0. In this way, a nitrogen polar initial layer with a thickness of 150-200 nm can be grown.

[0029] In step S2, after the initial layer growth is completed and under nitrogen-rich conditions, a polar induction medium containing oxygen is introduced into the deposition environment. The process parameter combination is then switched to match the inversion induction, and the relevant process parameters are dynamically adjusted to grow the inversion layer. The polar induction medium is oxygen. This step utilizes oxygen to induce polarity reversal, while dynamic adjustment ensures the uniformity of the inversion layer growth and the accuracy of the polarity conversion, preventing interface blurring. For example, after the initial layer growth is completed, the deposition environment can be adjusted to nitrogen-rich conditions (e.g., a nitrogen to argon flow rate ratio of 2:1). Simultaneously, the sputtering power is appropriately reduced to 400W-500W, and the working pressure is increased to 0.7Pa-0.9Pa. Based on this, oxygen is introduced as a dopant gas, and its concentration can be controlled within the range of 1%-2%. During the inversion layer growth process, the ratio of the characteristic spectral line intensities between aluminum and nitrogen can be monitored in real time and controlled within the range of 1.0-1.3. By strictly controlling the growth time, it can be ensured that the thickness of the inversion layer does not exceed 10nm.

[0030] In step S3, after the inversion layer growth is complete, the introduction of the polar induction medium is stopped, and the polar induction medium is purified. The complete removal of the polar induction medium from the deposition environment is confirmed by real-time monitoring of the characteristic spectral intensity of oxygen. This step ensures environmental purity, preventing residual oxygen from interfering with subsequent layer growth and thus maintaining the integrity of the interlayer interface. For example, after the inversion layer growth is complete, the oxygen doping gas can be turned off, and the growth conditions can be maintained for 60 seconds. During this period, the characteristic spectral intensity of oxygen can be monitored in real time to confirm whether the doping gas has been completely removed.

[0031] In step S4, after confirming that the polar inducing medium in the deposition environment has been completely removed, and under nitrogen-rich conditions, the process parameter combination matching the aluminum polarity is switched, and the relevant process parameters are dynamically adjusted to grow the intrinsic layer. This step ensures that the intrinsic layer grows under contamination-free conditions, maintaining the stability of the aluminum polar orientation. For example, after confirming that there are no doped gas residues in the deposition environment, aluminum polar intrinsic layer growth can be performed. The process parameters can be set as follows: sputtering power in the range of 400W-500W, working gas pressure in the range of 0.7Pa-0.9Pa, nitrogen to argon flow ratio of 2:1, and growth temperature of 500℃. By real-time monitoring of the ratio of characteristic spectral line intensities between aluminum and nitrogen (e.g., controlled in the range of 1.0-1.3), process stability can be ensured. In this way, high-quality aluminum polar aluminum nitride with a thickness of 200-300nm can be grown.

[0032] In step S5, by cyclically executing steps S1-S4, multilayer thin film structures with opposite polar orientations are alternately grown on the substrate. During the growth of the initial layer, the inversion layer, and the intrinsic layer, the deposition environment state is monitored in real time, and the corresponding process parameters are dynamically adjusted based on the monitored deposition environment state. This step achieves precise alternating growth of the multilayer structure, ensuring clear polarity of each layer and overall structural coherence. Specifically, the steps for real-time monitoring of the deposition environment state include A1-A2: In step A1, the intensity of characteristic spectral lines of multiple target elements in the plasma is acquired in real time, and the proportional relationship between the intensity of characteristic spectral lines of each target element is determined. The multiple target elements include aluminum (film-forming element), nitrogen (reacting element), and oxygen (corresponding element to the polar induction medium). This step provides a real-time data foundation for the environmental state. For example, the intensity of characteristic spectral lines of aluminum (e.g., 394.4 nm, 396.1 nm), nitrogen (e.g., 746.8 nm), and oxygen (e.g., 777 nm) in the plasma can be monitored simultaneously using an optical emission spectrometer (OES), and a real-time monitoring system for the proportional relationship of multiple elements can be established.

[0033] In step A2, based on the proportional relationship, the deviation from the corresponding preset polar growth window is determined, and the current deposition environment state is judged according to the deviation. This step allows for dynamic adjustment of parameters to maintain optimal growth conditions and prevent performance degradation caused by deviation from the window. For example, the ratio of the characteristic spectral line intensities between aluminum and nitrogen elements acquired in real time is compared with the threshold range in the preset polar growth window, the amount exceeding the threshold range is calculated as the deviation, and the current deposition environment state is judged according to the direction of the deviation.

[0034] During the growth of the inversion layer, the growth thickness was controlled within a preset nanometer-scale threshold range (≤10nm) by combining the monitoring results of characteristic spectral line intensity. This control precisely controlled the thickness of the inversion layer and optimized the interface quality and the sharpness of the polarity transition.

[0035] The following example will provide a more detailed explanation of the above technical solution: Suppose we need to fabricate an aluminum nitride thin film with a multilayer polarity reversal structure for use in a high-frequency acoustic wave filter. First, a silicon substrate, cleaned with standard RCA and treated with hydrofluoric acid, is placed in a magnetron sputtering system. In step S1, the system first initiates sputtering under aluminum-rich conditions (e.g., an N2 / Ar flow ratio of 1:2) and switches to a combination of process parameters matched to nitrogen polarity: sputtering power set to 600 W, working pressure set to 0.4 Pa, and growth temperature set to 450 °C. During this process, an optical emission spectrometer monitors the intensity of characteristic spectral lines of aluminum and nitrogen in the plasma in real time and calculates their ratio. When the ratio of the characteristic spectral line intensities between aluminum and nitrogen stabilizes in the range of 1.5-2.0, the system determines that the current deposition environment is favorable for nitrogen polarity growth and continues to grow an initial nitrogen polarity layer of approximately 180 nm.

[0036] After the initial layer growth is complete, the process proceeds to step S2. The system switches the deposition environment to nitrogen-rich conditions (e.g., N2 / Ar flow ratio of 2:1) and adjusts the sputtering power to 450 W and the working pressure to 0.8 Pa. Simultaneously, oxygen is introduced into the deposition environment as a polar induction medium, with its concentration controlled at 1.5%. During this stage, the system continuously monitors the ratio of characteristic spectral line intensities between aluminum and nitrogen, maintaining it within the range of 1.0–1.3. By precisely controlling the growth time, the thickness of the inversion layer is ensured to be kept below 8 nm.

[0037] After the inversion layer growth is complete, proceed to step S3. The system stops introducing oxygen and maintains the growth conditions for 60 seconds for purification. During this period, the optical emission spectrometer continuously monitors the intensity of the characteristic spectral lines of oxygen. When the intensity of the characteristic spectral lines of oxygen stabilizes within a preset error range for a preset observation time, the system determines that the oxygen in the deposition environment has been completely removed and outputs a trigger signal allowing switching to the aluminum polarity matching process parameter combination.

[0038] Subsequently, step S4 is performed. After confirming that the deposition environment has been purified, the system switches to a combination of process parameters matching the aluminum polarity under nitrogen-rich conditions (N2 / Ar flow ratio of 2:1): sputtering power is set to 450W, working pressure is set to 0.8Pa, and growth temperature is set to 500℃. During this process, the system continuously monitors the ratio of characteristic spectral line intensities between aluminum and nitrogen and controls it within the range of 1.0-1.3 to grow an intrinsic aluminum polar layer of approximately 250nm.

[0039] Finally, in step S5, by cyclically executing steps S1-S4, multilayer thin film structures with opposite polar orientations can be alternately grown on the substrate. During each growth of the initial layer, inversion layer, and intrinsic layer, the system maintains real-time monitoring of the deposition environment. For example, in step A1, the characteristic spectral intensities of aluminum, nitrogen, and oxygen elements in the plasma are acquired in real time, and their proportional relationships are determined. In step A2, based on these proportional relationships, the deviation from the corresponding preset polar growth window is determined, and the current deposition environment state is judged according to the deviation, thereby dynamically adjusting the corresponding process parameters to ensure the polar orientation and crystal quality of each layer.

[0040] Through the above embodiments, the polarity-controllable aluminum nitride thin film preparation method of this application can effectively solve the problems of interface defects, unclear polarity transition, and imprecise control of growth conditions existing in traditional methods. Compared with traditional methods that rely on static control of a single parameter, this application achieves precise control of the polarity growth of aluminum nitride thin films by introducing a multi-parameter synergistic regulation mechanism and closed-loop feedback control. For example, during the growth of the inversion layer, by real-time monitoring of the characteristic spectral line intensity of oxygen and controlling its thickness within the nanometer-scale threshold range, the sharpness and crystal quality of the polarity inversion interface are significantly improved, avoiding performance degradation caused by the ambiguity of the polarity transition region in traditional methods. In addition, the deposition environment is purified and confirmed before each layer growth, effectively avoiding interference from residual polarity-inducing media on the growth of subsequent layers, ensuring the purity and stability of the polarity of each layer in the multilayer structure. This dynamic and refined control strategy enables the prepared multilayer polarity-inverted aluminum nitride thin films to have higher piezoelectric performance and device stability, providing a reliable material basis for applications such as high-frequency acoustic wave filters.

[0041] Specifically, the combination of process parameters that matches the nitrogen polarity includes: The sputtering power range is 550W-650W; The working air pressure range is 0.3Pa-0.5Pa; The growth temperature is 450℃; The ratio of the characteristic spectral line intensities between aluminum and nitrogen ranges from 1.5 to 2.0.

[0042] Specifically, the process parameter combinations matched with reversal induction include: The sputtering power range is 400W-500W; The working air pressure range is 0.7Pa-0.9Pa; The concentration range of the polar induction medium is 1%-2%; The ratio of the characteristic spectral line intensities between aluminum and nitrogen ranges from 1.0 to 1.3.

[0043] Specifically, the combination of process parameters that matches the aluminum polarity includes: The sputtering power range is 400W-500W; The working air pressure range is 0.7Pa-0.9Pa; The growth temperature is 500℃; The ratio of the characteristic spectral line intensities between aluminum and nitrogen ranges from 1.0 to 1.3.

[0044] In some embodiments, the specific steps in step A2 include: A21. Compare the proportional relationship with the threshold range in the polar growth window, calculate the amount exceeding the threshold range as the deviation, and determine the current depositional environment state based on the direction of the deviation.

[0045] The proportional relationship refers to the ratio of the characteristic spectral line intensities among multiple target elements (including aluminum, nitrogen, and oxygen) determined after real-time acquisition of their characteristic spectral line intensities in the plasma. For example, it could be the ratio of the characteristic spectral line intensities of aluminum to nitrogen (Al / N ratio) or the ratio of the characteristic spectral line intensities of oxygen to nitrogen (O / N ratio) acquired in real-time by optical emission spectroscopy (OES). These proportional relationships are key indicators reflecting the relative concentrations of each element in the deposition environment and are directly related to the growth polarity of the thin film. The threshold range within the polar growth window refers to one or more pre-set parameter ranges that define the deposition environment state under specific process conditions, enabling the stable growth of thin films with a specific polarity (such as nitrogen polarity or aluminum polarity). These threshold ranges are determined based on extensive experimental data and theoretical analysis, and are used to guide and determine whether the deposition process is in the desired polar growth state. The deviation refers to the difference between the real-time monitored proportional relationship and the pre-set threshold range within the polar growth window. This difference can be an absolute or relative value, and its purpose is to quantify the degree to which the current deposition environment deviates from the ideal state. The direction of deviation refers to the specific direction in which the real-time monitored ratio deviates from the preset threshold range. For example, if the Al / N ratio is higher than the upper limit of the ideal range, the deviation direction is "higher than the upper limit"; if it is lower than the lower limit, the deviation direction is "lower than the lower limit." This directional judgment is crucial for subsequent process parameter adjustments because it indicates which element needs to be added or removed, or how to adjust other process parameters to correct the deviation. Determining the current deposition environment state refers to a qualitative or quantitative assessment of the current film growth environment based on the calculated deviation and its direction of deviation. For example, if the Al / N ratio is higher than the upper limit of the nitrogen polar growth window, the current environment may be determined to be "aluminum-rich"; if it is lower than the lower limit, it may be determined to be "nitrogen-rich." This determination provides a decision-making basis for subsequent dynamic process parameter adjustments.

[0046] This application's scheme acquires the intensity of characteristic spectral lines of target elements in plasma in real time and determines their proportional relationship. This proportional relationship is then precisely compared with a preset threshold range within a polar growth window. By calculating the amount exceeding the threshold range as the deviation, this application can obtain a quantitative value indicating that the deposition environment deviates from ideal conditions. Furthermore, based on the specific direction of the deviation, the system can clearly determine whether the current deposition environment is aluminum-rich, nitrogen-rich, or has excessive or insufficient oxygen. This quantitative and directional judgment mechanism significantly improves the accuracy and reliability of real-time judgment of the deposition environment. During the growth of the initial layer, inversion layer, and intrinsic layer, this precise judgment mechanism is closely integrated with the steps of dynamically adjusting relevant process parameters, enabling more accurate and timely adjustments to sputtering energy parameters (such as sputtering power and working gas pressure) and process gas flow parameters. For example, when the deposition environment deviates from ideal conditions, the system can accurately identify the degree and direction of the deviation, thereby adjusting process parameters in a targeted manner, avoiding over-adjustment or under-adjustment caused by ambiguous judgments in traditional methods. This precise control capability is crucial for ensuring the clarity of the polarity transition region. Especially when controlling the thickness of the inversion layer within a preset nanometer threshold range (≤10nm), even minute deviations in environmental conditions need to be accurately identified and corrected, thereby effectively improving the overall crystal quality and piezoelectric performance of the multilayer thin film structure.

[0047] The following is a concrete example. When preparing a nitrogen-polar initial layer, the preset polar growth window may require the ratio of characteristic spectral line intensities between aluminum and nitrogen to be within the range of 1.5-2.0. During film growth, the system continuously collects the characteristic spectral line intensities of aluminum and nitrogen in the plasma and calculates the current Al / N ratio. For example, if the real-time monitored Al / N ratio is 2.1, the system compares it to the preset threshold range of 1.5-2.0. At this point, the system calculates the amount exceeding the threshold range as 0.1 (i.e., 2.1 minus 2.0), as the current deviation. Simultaneously, since 2.1 is higher than 2.0, the system determines that the deviation is "above the upper limit," and thus determines the current deposition environment state as "aluminum-rich." Based on this clear quantitative deviation and directional judgment, the control system can immediately issue instructions, such as appropriately increasing the nitrogen flow rate or slightly reducing the sputtering power, to readjust the Al / N ratio back to the ideal range of 1.5-2.0, thereby ensuring that the initial layer can stably grow a high-quality nitrogen-polar structure.

[0048] Through the above technical solution, this application provides a method for quantitatively assessing the state of the deposition environment, avoiding errors caused by subjective judgment. Furthermore, based on the direction of deviation, the judgment of the environment state not only has a quantitative degree but also a clear directionality. This precise quantification and directional judgment allows for more accurate and timely dynamic adjustment of relevant process parameters during the growth of the initial layer, inversion layer, and intrinsic layer. This significantly improves the clarity of the polarity transition region, reduces interface defects, ensures precise control of the inversion layer thickness within a preset nanometer-scale threshold range (≤10nm), and ultimately enhances the overall crystal quality and piezoelectric properties of the multilayer thin film structure, effectively solving the problem of insufficient polarity control precision leading to decreased thin film performance in traditional methods.

[0049] In some embodiments, the step of: [further steps are included before confirming that the polarity-inducing medium in the deposition environment has been completely removed] B1. Acquire residual spectral data of each element in the plasma under the premise of stopping the introduction of polar induction medium; B2. Based on residual spectral data, the preset background noise threshold is corrected to eliminate the impact of sedimentation chamber wall accumulation effect and observation window contamination on monitoring accuracy, and the corrected background noise threshold is obtained. The following steps confirm that the polar-inducing medium in the deposition environment has been completely removed: C1. Calculate the relative deviation between the characteristic spectral line intensities of the corresponding elements in the polar induced medium and the corrected background noise threshold; C2. When the relative deviation stabilizes within the preset error range within the preset observation time, it is determined that the deposition environment has been purified, and a trigger signal is output that allows switching to a process parameter combination that matches the aluminum polarity.

[0050] Specifically, under the premise of ceasing the introduction of polar induction medium, residual spectral data of each element in the plasma are collected to obtain the true background noise information of the current deposition environment, providing a benchmark for subsequent corrections. This step can be achieved in several ways. For example, an optical emission spectrometer (OES) can be used to continuously monitor the plasma and record the characteristic spectral intensity data of all detectable target elements (such as aluminum, nitrogen, oxygen, etc.) for a period of time after the introduction of polar induction medium is stopped; or, a mass spectrometer can be used to analyze the residual gas composition in the deposition chamber in real time, obtain the concentration information of each residual gas component, and convert it into corresponding equivalent spectral intensity data.

[0051] Based on this, the preset background noise threshold is corrected using residual spectral data to eliminate the impact of sediment accumulation on the chamber walls and contamination of the observation window on monitoring accuracy, resulting in a corrected background noise threshold. The preset background noise threshold may become inaccurate due to factors such as chamber usage time, sediment accumulation, and observation window contamination. Correcting this threshold using collected residual spectral data aims to establish a more accurate noise benchmark that better reflects the current environment, thereby improving the accuracy of subsequent polar-induced medium removal assessments. For example, the collected residual spectral data can be compared with historical data, and a dynamic background noise baseline can be calculated using statistical methods (such as moving average or Kalman filtering), which can then be used as the corrected background noise threshold. Alternatively, after stopping the introduction of polar-induced medium, a period of time can be allowed for the plasma to stabilize, and the characteristic spectral line intensity of the element corresponding to the polar-induced medium (such as oxygen) in the plasma at this point can be used as the corrected background noise threshold.

[0052] Subsequently, the relative deviation between the characteristic spectral line intensities of the corresponding elements in the polar-induced medium and the corrected background noise threshold is calculated. This step aims to quantify the residual level of the polar-induced medium in the current depositional environment. By calculating the relative deviation between the real-time monitored spectral line intensities of the corresponding elements in the polar-induced medium and the corrected background noise threshold, it is possible to more accurately assess whether the polar-induced medium has decreased to an acceptable level, avoiding misjudgments caused by background noise interference. For example, a percentage deviation can be used, i.e., (real-time spectral line intensity - corrected threshold) / corrected threshold * 100%; or, the ratio of the absolute deviation to the corrected threshold can be used, i.e., (real-time spectral line intensity - corrected threshold) / corrected threshold.

[0053] Finally, when the relative deviation stabilizes within a preset error range over a preset observation period, the deposition environment is deemed cleaned, and a trigger signal is output allowing switching to a process parameter combination that matches the aluminum polarity. This step is the final judgment and control stage of the cleanup process. Requiring the relative deviation to remain stable within a preset error range for a certain period ensures thorough and stable removal of the polarity-inducing medium, preventing premature process switching due to instantaneous fluctuations or incomplete removal, thus guaranteeing the quality and accuracy of the subsequent aluminum polarity intrinsic layer growth. The output trigger signal automates and precisely controls the process flow. For example, a time window (e.g., 30 seconds) can be set; if the continuously monitored relative deviation values ​​within this window all fall within a preset error range (e.g., ±5%), the cleanup is deemed complete. Alternatively, a statistical process control (SPC) method can be used to calculate the mean and standard deviation of the relative deviation; when the mean stabilizes within the preset error range and the standard deviation is less than a certain threshold, the cleanup is deemed complete.

[0054] This application's solution addresses the issue of insufficient monitoring accuracy by introducing residual spectral data acquisition and a background noise threshold correction mechanism, ensuring accurate judgment of the removal status of the polar-induced medium and thus improving the reliability of interlayer interface control. Specifically, after stopping the introduction of the polar-induced medium, the system first acquires residual spectral data of each element in the plasma, providing true background information of the current deposition environment and laying the foundation for subsequent corrections. Next, based on this residual spectral data, a preset background noise threshold is corrected, directly eliminating noise interference introduced by the cumulative effect of the deposition chamber walls and contamination of the observation window, thereby improving the accuracy of the monitoring benchmark. Subsequently, the system calculates the relative deviation between the characteristic spectral line intensity of the corresponding element in the polar-induced medium and the corrected background noise threshold, using the corrected benchmark for deviation evaluation, enhancing detection accuracy. To ensure thoroughness and stability of the removal, the system requires that this relative deviation remain stable within a preset error range for a preset observation period before determining that the deposition environment has been purified and outputting a trigger signal allowing switching to a process parameter combination matching aluminum polarity. The synergistic effect of this dynamic correction and stability verification effectively solves the monitoring error problem caused by environmental factors, ensuring that the deposition environment can be reliably purified after the growth of the inversion layer is completed, providing a pure and stable environment for the subsequent growth of the aluminum polar intrinsic layer, thereby ensuring the high quality of the interface between layers in the multilayer thin film structure and the precise control of polar orientation.

[0055] The following is a specific example. After the inversion layer is grown, the introduction of oxygen into the deposition environment as a polarity-inducing medium is stopped. At this time, an optical emission spectrometer integrated into the side window of the sputtering chamber continuously collects characteristic spectral line intensity data of aluminum, nitrogen, and oxygen in the plasma, for example, once per second for 60 seconds. The average value of the oxygen characteristic spectral line intensity collected over these 60 seconds is used as the corrected background noise threshold for the current deposition environment. Subsequently, the system calculates in real time the percentage deviation between the currently monitored oxygen characteristic spectral line intensity and the aforementioned corrected background noise threshold. For example, if the correction threshold is X and the real-time intensity is Y, the relative deviation is (YX) / X*100%. The system is set to a preset observation duration of 30 seconds and a preset error range of ±5%. When the relative deviation between the calculated oxygen element characteristic spectral line intensity and the corrected background noise threshold is stable between -5% and +5% for 30 consecutive seconds, the system determines that the deposition environment has been purified and automatically sends a signal to the main controller, indicating that it can switch to the process parameter combination that matches the aluminum polarity and start growing the intrinsic layer.

[0056] Through the above technical solution, this application can effectively eliminate the impact of the accumulation effect of the deposition chamber wall and the contamination of the observation window on the monitoring accuracy of polar-induced medium removal. This ensures accurate judgment of the removal status of polar-induced medium in the deposition environment, avoiding premature or delayed switching of process parameters due to misjudgment, thereby guaranteeing the purity and precise control of the polar orientation of the subsequent growth layer (aluminum polar intrinsic layer). In the above-mentioned multilayer thin film structure preparation method, this precise interface control significantly improves the quality of the interlayer interface and crystal integrity, thereby optimizing the piezoelectric performance and device stability of the entire multilayer thin film structure, providing a reliable material basis for achieving breakthroughs in high-frequency filter performance.

[0057] In some embodiments, during the growth of the inversion layer, the step of dynamically adjusting the relevant process parameters based on the determined deposition environment state includes: D1. Real-time monitoring of the rate of change of the characteristic spectral line intensity of aluminum relative to sputtering power to identify the reaction state switching point on the target surface; D2. When the rate of change exceeds the preset mutation threshold, it is determined that the target surface has entered the hysteresis zone where it transitions from the metal mode to the reaction mode. Within the hysteresis zone, the sputtering rate drop caused by the introduction of the polar induction medium is compensated by adjusting the pulse duty cycle or pulse frequency of the sputtering power supply, so as to maintain the compositional uniformity of the inversion layer during the growth process.

[0058] To achieve real-time monitoring of the intensity of characteristic spectral lines of aluminum, an optical emission spectrometer can be used to continuously acquire the plasma spectrum within the sputtering chamber, and a photomultiplier tube or CCD detector can be used to convert the spectral line intensity at a specific wavelength (e.g., 394.4 nm or 396.1 nm for aluminum) into an electrical signal. Alternatively, a multi-channel spectrometer can be used to simultaneously monitor the characteristic spectral lines of multiple target elements, with one channel dedicated to monitoring the intensity of the characteristic spectral lines of aluminum, and real-time data analysis performed by a data processing unit. To obtain the rate of change of the characteristic spectral line intensity of aluminum relative to sputtering power, the sputtering power can be periodically fine-tuned by the control system while simultaneously recording the changes in the intensity of the characteristic spectral lines of aluminum, and then the ratio or derivative value between the two can be calculated. Furthermore, under the premise of relatively stable sputtering power, when external factors such as polar inducing media are introduced to change the surface state of the target material, the change in the intensity of the characteristic spectral lines of aluminum over time can be observed, and the rate of change can be evaluated in conjunction with the power setpoint. Identifying the switching points of the reaction states on the target surface can be achieved by setting a preset threshold. When the rate of change of the characteristic spectral line intensity of aluminum relative to the sputtering power exceeds this threshold, it is determined to be a switching point. Alternatively, a model can be built by training historical sputtering data using machine learning algorithms to predict and identify switching points of the reaction states on the target surface, for example, by analyzing the inflection points of the spectral line intensity change trend.

[0059] When the aforementioned rate of change exceeds a preset abrupt change threshold, the system determines that the target surface has entered a hysteresis region, transitioning from the metallic mode to the reactive mode. This preset abrupt change threshold can be calibrated experimentally by observing typical values ​​of the rate of change in the intensity of aluminum characteristic spectral lines under different sputtering conditions, and empirically setting a value that can effectively distinguish between stable and transitional modes. Alternatively, based on theoretical models or simulation results, the theoretical critical value of the rate of change in the intensity of aluminum characteristic spectral lines during the transition from the metallic mode to the reactive mode on the target surface when a polar-induced medium is introduced can be calculated. Within the hysteresis region, to compensate for the drop in sputtering rate caused by the introduction of the polar-induced medium, the pulse duty cycle or pulse frequency of the sputtering power supply can be adjusted. For example, by sending a command to the pulse sputtering power supply through the control system to adjust its pulse duty cycle, appropriately increasing the duty cycle within the hysteresis region to increase the instantaneous sputtering power and compensate for the decrease in sputtering rate. Alternatively, by changing the pulse frequency, for example, appropriately increasing the pulse frequency within the hysteresis region, the number of bombardments to the target per unit time can be increased, thereby maintaining the sputtering rate. This compensation mechanism aims to maintain the compositional uniformity of the inversion layer during growth, ensuring that aluminum and nitrogen atoms (as well as oxygen atoms) are deposited on the substrate in a constant ratio, thereby forming a stoichiometrically stable film.

[0060] This application addresses the challenges posed by the introduction of polar-induced media by dynamically adjusting the deposition environment during the growth of the inversion layer. Specifically, when a polar-induced medium (e.g., oxygen) is introduced to induce polarity reversal, the target surface gradually transitions from a metallic mode to a reactive mode. This transition is not linear but involves a hysteresis region where the sputtering rate significantly decreases, leading to film composition inhomogeneity if left uncontrolled. To accurately capture and address this change, this approach monitors the rate of change of the characteristic spectral line intensity of aluminum in the plasma relative to the sputtering power in real time. The characteristic spectral line intensity of aluminum directly reflects the concentration of aluminum atoms in the plasma, while the sputtering power is a key parameter affecting the sputtering process. By monitoring the rate of change between these two parameters, the switching point of the reactive state on the target surface can be sensitively identified. When this rate of change exceeds a preset abrupt change threshold, the system determines that the target surface has entered the hysteresis region transitioning from a metallic mode to a reactive mode. Once in the hysteresis region, to compensate for the drop in sputtering rate caused by the introduction of the polar-induced medium, this approach dynamically adjusts the pulse duty cycle or pulse frequency of the sputtering power supply. Adjusting the pulse duty cycle or pulse frequency can alter the energy input and ion bombardment efficiency to the target material per unit time, thereby offsetting to some extent the decrease in sputtering yield caused by the formation of a reactive layer on the target surface. This precise, real-time pulse parameter adjustment effectively maintains the relative stability of the sputtering rate, ensuring the compositional uniformity of the film during the inversion layer growth process. This approach, combined with the aforementioned technique of real-time determination of the deposition environment state (by real-time acquisition of the characteristic spectral line intensities of multiple target elements in the plasma, determining the proportional relationship between the characteristic spectral line intensities of each target element, determining the deviation from the corresponding preset polarity growth window based on the proportional relationship, and judging the current deposition environment state based on the deviation), forms a more complete closed-loop control system. In the overall polarity-controllable aluminum nitride thin film preparation method, the deposition environment state is first determined, and relevant process parameters are dynamically adjusted accordingly. Based on this, this approach further refines the control over the sputtering rate drop caused by the introduction of the polarity-inducing medium during the inversion layer growth process, providing more precise control. This layered and synergistic control strategy not only ensures that the inversion layer grows within a preset nanoscale threshold range (≤10nm), but also effectively solves the problem of compositional inhomogeneity caused by the introduction of polar-induced media, thereby guaranteeing the crystal quality and piezoelectric properties of the inversion layer and laying the foundation for the subsequent growth of high-quality intrinsic layers.

[0061] In one specific implementation, an optical emission spectrometer can be used to continuously monitor the plasma within the sputtering chamber during the growth of the inversion layer. This spectrometer is configured to acquire the characteristic spectral line intensities of aluminum (e.g., at wavelengths of 394.4 nm or 396.1 nm) in real time. Simultaneously, the control system records the current sputtering power. The system calculates the instantaneous rate of change of the aluminum characteristic spectral line intensity with sputtering power, for example, by performing differential or regression analysis on continuously acquired data points. For instance, when oxygen is introduced as a polar induction medium, the control system closely monitors the rate of change of the aluminum characteristic spectral line intensity relative to the sputtering power. Once this rate of change suddenly drops and exceeds a pre-set abrupt change threshold (which can be calibrated through prior experiments, e.g., when the rate of change drops by more than a certain percentage), the system determines that the target surface has transitioned from a predominantly metallic sputtering mode to a hysteresis region of oxide-covered reaction mode. Within this hysteresis region, to compensate for the decrease in the aluminum target sputtering rate caused by the introduction of oxygen, the control system immediately sends a command to the pulsed sputtering power supply. For example, the system can dynamically increase the duty cycle of the pulse power supply, making the power output time longer within each pulse cycle, thereby increasing the average energy input to the target per unit time. Alternatively, the system can increase the frequency of the pulse power supply, increasing the number of bombardments to the target per unit time. In this way, even if the target surface is oxidized, the sputtering yield of aluminum atoms can be maintained to a certain extent, thereby ensuring a relatively stable number of aluminum atoms deposited on the substrate, and thus maintaining the compositional uniformity of the inversion layer throughout the growth process.

[0062] Through the above technical solution, this application effectively solves the technical problem of sputtering rate drop caused by the introduction of polar inducing medium during the preparation of polar controllable aluminum nitride thin films, which in turn affects the compositional uniformity of the inversion layer. Specifically, by real-time monitoring of the rate of change of the intensity of the characteristic spectral lines of aluminum relative to the sputtering power, the hysteresis region of the target surface transitioning from the metallic mode to the reactive mode can be accurately identified. This accurate identification allows the system to intervene at critical moments, dynamically adjusting the pulse duty cycle or pulse frequency of the sputtering power supply to provide timely and targeted compensation for the drop in sputtering rate. This compensation mechanism ensures that the compositional uniformity of the inversion layer is maintained during the critical stage of introducing the polar inducing medium and inducing polarity reversal. In the above method, the growth thickness of the inversion layer is strictly controlled within a preset nanometer-scale threshold range (≤10 nm), and maintaining compositional uniformity is crucial to ensuring that such a thin inversion layer has a stable crystal structure and the expected piezoelectric properties. Therefore, this approach not only ensures the growth quality of the inversion layer and avoids crystal defects and performance degradation caused by uneven composition, but also provides a stable interface for the subsequent growth of high-quality intrinsic aluminum polarity layers, thereby improving the overall performance of the entire multilayer polarity inversion aluminum nitride thin film structure and the reliability of the device.

[0063] Reference Appendix Figure 2 This invention provides a polarity-controllable aluminum nitride thin film preparation system (this polarity-controllable aluminum nitride thin film preparation system adopts the polarity-controllable aluminum nitride thin film preparation method of the above embodiments, and the specific process is referred to the corresponding steps above), including: The first control module 100 is used to switch to a combination of process parameters that match the nitrogen polarity after pretreatment of the substrate and under aluminum-rich conditions, and to dynamically adjust the relevant process parameters to grow the initial layer. The second control module 200 is used to introduce a polar induction medium containing oxygen into the deposition environment after the initial layer growth is completed and under nitrogen-rich conditions, and to switch to a process parameter combination that matches the inversion induction, and to dynamically adjust the relevant process parameters to grow the inversion layer. The third control module 300 is used to stop the introduction of polar induction medium after the growth of the inversion layer is completed, and to confirm whether the polar induction medium in the deposition environment has been completely removed based on the intensity of the characteristic spectral line of oxygen element monitored in real time. The fourth control module 400 is used to switch to a combination of process parameters that match the polarity of aluminum after confirming that the polarity-inducing medium in the deposition environment has been completely removed and under nitrogen-rich conditions, and to dynamically adjust the relevant process parameters to grow the intrinsic layer. The fifth control module 500 is used to alternately grow multilayer thin film structures with opposite polar orientations on the substrate by sequentially running the first control module 100, the second control module 200, the third control module 300 and the fourth control module 400; wherein, during the growth of the initial layer, the inversion layer and the intrinsic layer, the deposition environment state is judged in real time, and the relevant process parameters are dynamically adjusted based on the judged deposition environment state. Specifically, the steps for real-time assessment of the sedimentary environment include A1-A2: A1. Real-time acquisition of the characteristic spectral line intensities of multiple target elements in plasma, and determination of the proportional relationship between the characteristic spectral line intensities of each target element; the multiple target elements include aluminum, nitrogen, and oxygen. A2. Based on the proportional relationship, determine the deviation from the corresponding preset polarity growth window, and determine the current depositional environment state based on the deviation; During the growth of the inversion layer, the growth thickness of the inversion layer is controlled within a preset threshold range by combining the monitoring results of the characteristic spectral line intensity.

[0064] In this document, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, without necessarily requiring or implying any such actual relationship or order between these entities or operations.

[0065] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing aluminum nitride thin films with controllable polarity, characterized in that, Includes the following steps: S1. After pretreating the substrate, and under aluminum-rich conditions, switch to a combination of process parameters that match the nitrogen polarity, and dynamically adjust the relevant process parameters to grow the initial layer. S2. After the initial layer has grown, and under nitrogen-rich conditions, a polar induction medium containing oxygen is introduced into the deposition environment, and the process parameter combination matching the inversion induction is switched, and the relevant process parameters are dynamically adjusted to grow the inversion layer. S3. After the growth of the inversion layer is completed, stop introducing the polar induction medium and confirm whether the polar induction medium in the deposition environment has been completely removed based on the intensity of the characteristic spectral line of the oxygen element monitored in real time. S4. After confirming that the polar induction medium in the deposition environment has been completely removed, and under nitrogen-rich conditions, switch to a combination of process parameters that match the polarity of aluminum, and dynamically adjust the relevant process parameters to grow the intrinsic layer. S5. By cyclically executing the above steps S1-S4, a multilayer thin film structure with opposite polar orientations is alternately grown on the substrate; wherein, during the growth of the initial layer, the inversion layer and the intrinsic layer, the deposition environment state is judged in real time, and the corresponding relevant process parameters are dynamically adjusted based on the judged deposition environment state. Specifically, the steps for real-time assessment of the sedimentary environment include A1-A2: A1. Real-time acquisition of the characteristic spectral line intensities of multiple target elements in plasma, and determination of the proportional relationship of the characteristic spectral line intensities among the target elements; the multiple target elements include aluminum, nitrogen, and oxygen. A2. Based on the aforementioned proportional relationship, determine the deviation from the corresponding preset polarity growth window, and based on the deviation, determine the current deposition environment state; During the growth of the inversion layer, the growth thickness of the inversion layer is controlled within a preset threshold range by combining the monitoring results of the characteristic spectral line intensity.

2. The method for preparing aluminum nitride thin films with controllable polarity according to claim 1, characterized in that, The relevant process parameters include sputtering power and working gas pressure.

3. The method for preparing aluminum nitride thin films with controllable polarity according to claim 1, characterized in that, The polar induction medium is oxygen.

4. The method for preparing aluminum nitride thin films with controllable polarity according to claim 1, characterized in that, The process parameter combination that matches nitrogen polarity includes: The sputtering power range is 550W-650W; The working air pressure range is 0.3Pa-0.5Pa; The growth temperature is 450℃; The ratio of the characteristic spectral line intensities between the aluminum and nitrogen elements ranges from 1.5 to 2.

0.

5. The method for preparing aluminum nitride thin films with controllable polarity according to claim 1, characterized in that, The process parameter combination matched with the reversal-induced induction includes: The sputtering power range is 400W-500W; The working air pressure range is 0.7Pa-0.9Pa; The concentration range of the polar induction medium is 1%-2%; The ratio of the characteristic spectral line intensities between the aluminum and nitrogen elements ranges from 1.0 to 1.

3.

6. The method for preparing aluminum nitride thin films with controllable polarity according to claim 1, characterized in that, The combination of process parameters matching the aluminum polarity includes: The sputtering power range is 400W-500W; The working air pressure range is 0.7Pa-0.9Pa; The growth temperature is 500℃; The ratio of the characteristic spectral line intensities between the aluminum and nitrogen elements ranges from 1.0 to 1.

3.

7. The method for preparing aluminum nitride thin films with controllable polarity according to claim 1, characterized in that, The specific steps in step A2 include: A21. Compare the proportional relationship with the threshold range in the polar growth window, calculate the amount exceeding the threshold range as the deviation, and determine the current deposition environment state based on the direction of the deviation.

8. The method for preparing aluminum nitride thin films with controllable polarity according to claim 1, characterized in that, Before confirming that the polar-induced medium in the deposition environment has been completely removed, the following steps are also included: B1. Under the premise of stopping the introduction of the polar induction medium, collect the residual spectral data of each element in the plasma; B2. Based on the residual spectral data, the preset background noise threshold is corrected to eliminate the impact of the accumulation effect of the deposition chamber wall and the contamination of the observation window on the monitoring accuracy, and the corrected background noise threshold is obtained. The following steps confirm that the polar-inducing medium in the deposition environment has been completely removed: C1. Calculate the relative deviation between the characteristic spectral line intensity of the corresponding element in the polar induced medium and the corrected background noise threshold; C2. When the relative deviation stabilizes within a preset error range within a preset observation period, it is determined that the deposition environment has been purified.

9. The method for preparing aluminum nitride thin films with controllable polarity according to claim 1, characterized in that, The steps for dynamically adjusting relevant process parameters based on the determined deposition environment state during the growth of the inversion layer include: D1. Real-time monitoring of the rate of change of the characteristic spectral line intensity of the aluminum element relative to the sputtering power to identify the reaction state switching point on the target surface; D2. When the rate of change exceeds a preset mutation threshold, it is determined that the target surface has entered a hysteresis zone transitioning from the metal mode to the reaction mode. Within the hysteresis zone, the sputtering rate drop caused by the introduction of the polar induction medium is compensated by adjusting the pulse duty cycle or pulse frequency of the sputtering power supply, so as to maintain the compositional uniformity of the inversion layer during the growth process.

10. A polarity-controllable aluminum nitride thin film preparation system, characterized in that, include: The first control module is used to switch to a combination of process parameters that match the nitrogen polarity after the substrate has been pretreated and under aluminum-rich conditions, and to dynamically adjust the relevant process parameters to grow the initial layer. The second control module is used to introduce a polar induction medium containing oxygen into the deposition environment after the initial layer has grown and under nitrogen-rich conditions, and to switch to a combination of process parameters that matches the inversion induction, and to dynamically adjust the relevant process parameters to grow the inversion layer. The third control module is used to stop introducing the polar induction medium after the inversion layer growth is completed, and to confirm whether the polar induction medium in the deposition environment has been completely removed based on the characteristic spectral intensity of the oxygen element monitored in real time. The fourth control module is used to switch to a combination of process parameters that match the polarity of aluminum after confirming that the polarity-inducing medium in the deposition environment has been completely removed and under nitrogen-rich conditions, and to dynamically adjust the relevant process parameters to grow the intrinsic layer. The fifth control module is used to alternately grow multilayer thin film structures with opposite polar orientations on the substrate by sequentially running the first control module, the second control module, the third control module and the fourth control module; wherein, during the growth of the initial layer, the inversion layer and the intrinsic layer, the deposition environment state is judged in real time, and the relevant process parameters are dynamically adjusted based on the judged deposition environment state. Specifically, the steps for real-time assessment of the sedimentary environment include A1-A2: A1. Real-time acquisition of the characteristic spectral line intensities of multiple target elements in plasma, and determination of the proportional relationship of the characteristic spectral line intensities among the target elements; the multiple target elements include aluminum, nitrogen, and oxygen. A2. Based on the aforementioned proportional relationship, determine the deviation from the corresponding preset polarity growth window, and based on the deviation, determine the current deposition environment state; During the growth of the inversion layer, the growth thickness of the inversion layer is controlled within a preset threshold range by combining the monitoring results of the characteristic spectral line intensity.

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