Method for improving blackening effect of piezoelectric composite film

Abstract

According to the method for improving the blackening effect of the piezoelectric composite film, the film layer surface of the piezoelectric composite film at least comprising the substrate layer and the film layer which are stacked in sequence is subjected to roughening treatment, the effective reaction area of the surface of the piezoelectric composite film is increased, and then the film is placed in the reducing medium to be subjected to blackening reduction heat treatment, so that the blackening effect of the piezoelectric composite film is improved. And the blackened piezoelectric composite film is obtained. The roughened surface can provide more reaction sites, and the interface reaction and mass transfer efficiency between a reducing medium and the film layer is improved, so that the oxygen vacancy concentration is improved within shorter heat treatment time, the piezoelectric composite film which is lower in resistivity and more uniform in blackening can be obtained, and the stability and consistency of the blackening effect of the piezoelectric composite film are improved. The problem that the blackening reaction effect of the piezoelectric composite film is poor is solved.

Description

Technical Field

[0001] This application relates to the field of semiconductor fabrication technology, and in particular to a method for improving the blackening effect of piezoelectric composite films. Background Technology

[0002] Lithium niobate (LiNbO3, LN) and lithium tantalate (LiTaO3, LT) single crystals are key materials for fabricating piezoelectric devices such as surface acoustic waves (SAW) and bulk acoustic waves (BAW), as their high piezoelectric coefficients contribute to achieving low insertion loss in filtering devices. However, the inherently high pyroelectric coefficients and high optical transmittance of these two materials present significant challenges in device manufacturing processes: high pyroelectric coefficients easily lead to the accumulation of static charge on the wafer surface, which may spontaneously release during subsequent processes (such as interdigital electrode fabrication or high-frequency device processing), causing wafer damage, microdomain inversion, or electrode burnout, increasing device defect rates; simultaneously, the optical transmittance of the materials easily affects pattern contrast due to back-side diffuse scattering during photolithography, leading to linewidth distortion. Therefore, before applying LN / LT materials to high-performance, high-reliability piezoelectric devices, it is necessary to effectively reduce their resistivity to suppress pyroelectric effects and reduce their optical transmittance.

[0003] To address the aforementioned issues, chemical reduction treatment (also known as blackening) is typically used to pretreat LN or LT wafers. This process creates oxygen vacancies on the wafer surface through a high-temperature reduction environment, increasing carrier concentration and thus reducing resistivity. Simultaneously, it gives the wafer a brown or black color, reducing light transmittance. Wafers treated with this blackening process can be directly used for subsequent device manufacturing, mitigating to some extent the processing problems caused by pyroelectric effects and light transmittance.

[0004] However, in the process of fabricating piezoelectric composite films using ion implantation and bond-stripping techniques, even when using pre-blackened LN or LT wafers, localized or overall whitening of the film layer still occurs during the high-temperature annealing process after bonding the film layer to the substrate. This indicates that the annealing process causes the film layer to be re-oxidized, resulting in an increase in its resistivity and pyroelectric coefficient, thus negating the original blackening effect. If devices are fabricated directly using this state of the composite film, there is still a risk of damage caused by the accumulation and release of static charge. Therefore, it is necessary to re-blacken the piezoelectric composite film itself after stripping. However, due to the high surface flatness and small specific surface area of ​​the separated film layer, the contact area with the reducing medium is limited in conventional blackening processes, leading to low blackening reaction efficiency, poor effect, and insufficient uniformity, making it difficult to restore and maintain the required low resistivity state of the film layer within a reasonable time. Summary of the Invention

[0005] This application provides a method for improving the blackening effect of piezoelectric composite films, in order to solve the problem of poor blackening reaction effect of piezoelectric composite films.

[0006] This application provides a method for improving the blackening effect of piezoelectric composite films, the method comprising: Prepare a piezoelectric composite film, wherein the structure of the piezoelectric composite film includes at least a substrate layer and a film layer stacked sequentially; The surface of the piezoelectric composite film is roughened. The roughened piezoelectric composite film is placed in a reducing medium for blackening reduction heat treatment to obtain a blackened piezoelectric composite film.

[0007] This application first roughens the surface of the piezoelectric composite film to increase its effective reaction area, and then places the film in a reducing medium for blackening reduction heat treatment. The roughened surface can provide more reaction sites, improve the interfacial reaction and mass transfer efficiency between the reducing medium and the film layer, thereby promoting the increase of oxygen vacancy concentration in a shorter heat treatment time. This helps to obtain a piezoelectric composite film with lower resistivity and more uniform blackening, and improves the stability and consistency of its blackening effect.

[0008] Optionally, the preparation method of the piezoelectric composite film is as follows: A piezoelectric wafer and a substrate are selected; wherein the piezoelectric wafer is a lithium niobate wafer or a lithium tantalate wafer; Preset ions are implanted into the piezoelectric wafer using ion implantation, and the piezoelectric wafer is sequentially divided into a residual mass layer, a separation layer, and a thin film layer. The piezoelectric wafer is bonded to the substrate to obtain a bonded body; The bonded body is subjected to heat treatment to separate the residual layer from the thin film layer, thereby obtaining a piezoelectric composite thin film.

[0009] A separation layer is formed in a piezoelectric wafer by ion implantation of preset ions. The wafer is then bonded to a substrate and the bond is heat-treated. The remaining mass layer is peeled off by using the bubbles generated by the separation layer, thereby obtaining a piezoelectric composite film with a well-defined layered structure. The thickness of the film layer can be controlled by adjusting the ion implantation depth.

[0010] Optionally, the surface of the piezoelectric composite film layer may be roughened by at least one of chemical etching, plasma etching, abrasive grinding, or laser processing.

[0011] Using at least one of the following processes—chemical etching, plasma etching, abrasive grinding, or laser processing—to roughen the surface of the thin film layer can adapt to the needs of different material properties and process conditions. This facilitates the selection of appropriate and efficient roughening methods in actual production, thereby creating a more sufficient reaction interface for subsequent blackening treatment.

[0012] Optionally, the method further includes: If the reducing medium is a solid reducing medium, blackened powder is obtained, wherein the blackened powder is uniformly mixed with reducing powder material and lithium carbonate powder material in a predetermined mass ratio; The piezoelectric composite film is placed in the blackened powder, and the piezoelectric composite film is completely buried by the blackened powder; Adjust the position of the piezoelectric composite film and the distribution of the blackening powder to ensure that the entire outer surface of the piezoelectric composite film layer is in full contact with the blackening powder.

[0013] By configuring the blackening powder as a homogeneous mixture of reducing powder and lithium carbonate powder in a predetermined ratio, and completely burying the piezoelectric composite film within it and ensuring full contact between the outer surface of the film layer and the powder, the uniform generation and release of the reducing atmosphere can be promoted. This helps the film layer obtain more consistent blackening reaction conditions during heat treatment, thereby improving the uniformity of the blackening effect.

[0014] Optionally, in the blackened powder, the reducing powder material accounts for 5 to 10 parts by mass, and the lithium carbonate powder material accounts for 90 to 95 parts by mass. The reducing powder material is one or more of the following: iron powder, aluminum powder, zinc powder, magnesium powder, silicon powder, and carbon powder.

[0015] The reducing powder material in the blackening powder is limited to one or more combinations of iron powder, aluminum powder, zinc powder, magnesium powder, silicon powder and carbon powder, with a mass fraction of 5 to 10 parts, and lithium carbonate powder material is 90 to 95 parts. This ratio helps to control the generation rate and concentration of the reducing atmosphere during the heat treatment process, so that the reduction reaction can be carried out continuously and moderately, thereby improving the blackening effect while reducing gas waste or uneven reaction caused by excessively fast reaction.

[0016] Optionally, the method further includes: If the reducing medium is a gaseous reducing medium, the sealed chamber is filled with gas or the sealed chamber is made to be in a vacuum state. The gas is one or more of hydrogen, carbon monoxide, lithium chloride vapor, nitrogen, and argon; The piezoelectric composite film is placed inside the sealed chamber so that the entire outer surface of the piezoelectric composite film layer is exposed to the gaseous reducing medium inside the sealed chamber.

[0017] By filling a sealed chamber with one or more of hydrogen, carbon monoxide, lithium chloride vapor, nitrogen, and argon, or maintaining a vacuum, and placing the piezoelectric composite film within it so that the outer surface of the film layer is fully exposed to the atmosphere, a controllable and uniform reduction environment can be provided for the blackening reduction heat treatment. This helps the gas medium to fully contact and react with the surface of the film layer, thereby promoting the progress of the blackening process and the consistency of the effect.

[0018] Optionally, the heating temperature of the blackening reduction heat treatment is controlled within the range of 300 degrees Celsius to 550 degrees Celsius; the holding time of the blackening reduction heat treatment is controlled within 24 hours.

[0019] Controlling the heating temperature of the blackening reduction heat treatment within the range of 300°C to 550°C and the holding time within 24 hours helps to ensure that the reduction reaction proceeds fully while reducing the possibility of excessive blackening or material performance degradation caused by excessively high temperature or long time. This improves the effect of reducing the resistivity of the thin film layer while maintaining the stability of its piezoelectric properties.

[0020] Optionally, after obtaining the blackened piezoelectric composite film, the method includes: The outer surface of the piezoelectric composite film that has undergone blackening reduction heat treatment is ground and polished to remove the blackening reaction products and micro-rough structure on the outer surface of the film layer, and to restore the outer surface of the film layer to optical grade smoothness and gloss.

[0021] After obtaining the blackened piezoelectric composite film, grinding and polishing are performed on the outer surface of the film layer to remove the blackening reaction products and micro-rough structure on the surface, so that the outer surface of the film layer can be restored to optical-grade flatness and smoothness, thereby meeting the requirements of subsequent photolithography processes for surface morphology, which helps to improve the accuracy of pattern transfer and the yield of device fabrication.

[0022] Optionally, the preset ions include hydrogen ions, helium ions, nitrogen ions, oxygen ions, or argon ions; The preset ion implantation dose is 2×10 16 ions / cm² to 4×10 16 ions / square centimeter; The implantation energy of the preset ions is between 40 keV and 400 keV.

[0023] Hydrogen ions, helium ions, nitrogen ions, oxygen ions, or argon ions are used as implanted ions, and their dosage is controlled at 2 × 10⁻⁶.16 ions / cm² to 4×10 16 With ions per square centimeter and energy controlled within the range of 40 keV to 400 keV, it is helpful to form a separation layer of suitable depth and concentration in the piezoelectric wafer, thereby achieving effective separation of the thin film layer and the residual layer in subsequent heat treatment, while reducing damage to the lattice structure of the thin film layer.

[0024] Optionally, the substrate is a single-layer structure or a composite structure made of multiple different materials, and the material constituting the substrate is at least one of lithium niobate, lithium tantalate, silicon, quartz, sapphire, silicon carbide or silicon nitride.

[0025] The substrate can be made of at least one of the following materials: lithium niobate, lithium tantalate, silicon, quartz, sapphire, silicon carbide, or silicon nitride, to form a single layer or composite structure. This diversity of material selection and flexibility of structural design helps to adapt to the performance requirements of different application scenarios, while providing a stable support interface for the thin film layer, thereby improving the overall applicability and reliability of the composite thin film.

[0026] As can be seen from the above technical solutions, this application provides a method for improving the blackening effect of piezoelectric composite films. This involves first roughening the surface of the thin film layer of a piezoelectric composite film, which comprises at least a substrate layer and a thin film layer stacked sequentially, to increase its effective reaction area. Then, the film is placed in a reducing medium for blackening reduction heat treatment to obtain a blackened piezoelectric composite film. The roughened surface provides more reaction sites, improving the interfacial reaction and mass transfer efficiency between the reducing medium and the thin film layer. This leads to an increase in oxygen vacancy concentration within a shorter heat treatment time, contributing to obtaining a piezoelectric composite film with lower resistivity and more uniform blackening, and improving the stability and consistency of its blackening effect. This solves the problem of poor blackening reaction effect in piezoelectric composite films. Attached Figure Description

[0027] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the process after roughening treatment in the method for improving the blackening effect of piezoelectric composite films provided in the embodiments of this application.

[0029] Figure 2 A schematic flowchart of the piezoelectric composite film preparation method in the method for improving the blackening effect of piezoelectric composite films provided in the embodiments of this application; Figure 3A schematic diagram of the process of using a solid reducing medium in the method for improving the blackening effect of piezoelectric composite films provided in the embodiments of this application; Figure 4 This is a schematic diagram of the process of using a gaseous reducing medium in the method for improving the blackening effect of piezoelectric composite films provided in the embodiments of this application.

[0030] Illustration: Among them, 100-piezoelectric wafer; 110-residual layer; 120-separation layer; 130-thin film layer; 200-substrate; 300-bonding body; 400-roughened piezoelectric composite film; 500-reduction medium; 510-solid reduction medium; 520-gas reduction medium; 600-blackened piezoelectric composite film. Detailed Implementation

[0031] The embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described below do not represent all embodiments consistent with this application. They are merely examples of systems and methods consistent with some aspects of this application.

[0032] To address the issue of poor blackening reaction in piezoelectric composite films, see [reference needed]. Figure 1 This application provides a method for improving the blackening effect of piezoelectric composite films, the method comprising: S100: Prepare a piezoelectric composite film. The structure of the piezoelectric composite film includes at least a substrate layer and a film layer 130 stacked sequentially.

[0033] S200: Roughen the surface of the film layer 130 of the piezoelectric composite film.

[0034] It should be understood that the blackening process is essentially a chemical reaction between the reducing medium 500 (such as reducing powder or reducing atmosphere) and the surface of the piezoelectric composite film under high-temperature conditions. Through the formation and diffusion of oxygen vacancies, the carrier concentration is increased, thereby reducing its resistivity. In conventional processes, the separated film layer 130 has a relatively small specific surface area due to its high surface flatness, resulting in poor blackening. This application treats the surface of film layer 130 to increase surface roughness, meaning that under the same apparent projected area, its actual physical surface area is significantly increased. This provides more accessible reaction sites for the reducing medium 500, greatly promoting the transfer efficiency of reactants and products at the interface. Due to the significant increase in the reaction interface, the number of particles that can participate in the reaction per unit time increases, resulting in a significant increase in the reduction reaction rate. This allows the composite film material to reach the oxygen vacancy concentration required for the target resistivity in a shorter time, thereby directly shortening the heat treatment time required to achieve the desired blackening effect, improving production efficiency, enhancing the blackening effect, and making the blackening more uniform.

[0035] In some embodiments, the surface of the film layer 130 of the piezoelectric composite film is roughened, including by using at least one of chemical etching, plasma etching, abrasive grinding or laser processing.

[0036] Using at least one of the following processes—chemical etching, plasma etching, abrasive grinding, or laser processing—to roughen the surface of the thin film layer 130 can adapt to the needs of different material properties and process conditions. This facilitates the selection of appropriate and efficient roughening methods in actual production, thereby creating a more sufficient reaction interface for subsequent blackening treatment and ensuring that the thin film layer 130 in the final blackened piezoelectric composite thin film 600 is in a completely blackened state.

[0037] S300: The roughened piezoelectric composite film 400 is placed in a reducing medium 500 for blackening reduction heat treatment to obtain a blackened piezoelectric composite film 600.

[0038] It should be understood that the blackening reduction heat treatment is carried out in a reduction furnace.

[0039] This application first roughens the surface of the thin film layer 130 of the piezoelectric composite film to increase its effective reaction area, and then places the film in a reducing medium 500 for blackening reduction heat treatment. The roughened surface can provide more reaction sites, improve the interfacial reaction and mass transfer efficiency between the reducing medium 500 and the thin film layer 130, thereby promoting the increase of oxygen vacancy concentration in a shorter heat treatment time, which helps to obtain a piezoelectric composite film with lower resistivity and more uniform blackening, and improves the stability and consistency of its blackening effect.

[0040] See Figure 2In some embodiments, the preparation method of the piezoelectric composite film is specifically as follows: S110: Select piezoelectric wafer 100 and substrate 200.

[0041] The piezoelectric wafer 100 is either a lithium niobate wafer or a lithium tantalate wafer. It should be understood that, in this embodiment, the piezoelectric wafer 100 refers to a base material with a certain thickness used to prepare the thin film layer 130. The piezoelectric wafer 100 can be an untreated wafer or a wafer that has undergone blackening treatment. The substrate 200 can be a single-layer substrate or a composite substrate, meaning the substrate 200 includes at least one substrate layer. The material of each substrate layer can be the same or different; this application does not limit this.

[0042] In some embodiments, the substrate 200 is a single-layer structure or a composite structure made of multiple different materials stacked together. The materials constituting the substrate 200 are at least one or more of lithium niobate, lithium tantalate, silicon, quartz, sapphire, silicon carbide or silicon nitride.

[0043] The substrate 200 can be made of at least one or more materials selected from lithium niobate, lithium tantalate, silicon, quartz, sapphire, silicon carbide or silicon nitride to form a single layer or composite structure. This diversity of material selection and flexibility of structural design helps to adapt to the performance requirements of different application scenarios, while providing a stable support interface for the thin film layer 130, thereby improving the overall applicability and reliability of the composite thin film.

[0044] S120: Preset ions are implanted into the piezoelectric wafer 100 by ion implantation, and the piezoelectric wafer 100 is sequentially divided into a residual layer 110, a separation layer 120 and a thin film layer 130.

[0045] It should be understood that the thickness of the thin film layer 130 can be adjusted by adjusting the ion implantation depth. Specifically, the greater the ion implantation depth, the greater the thickness of the prepared thin film layer 130; conversely, the smaller the ion implantation depth, the smaller the thickness of the prepared thin film layer 130.

[0046] In some embodiments, the preset ions include hydrogen ions, helium ions, nitrogen ions, oxygen ions, or argon ions; the injection dose of the preset ions is 2 × 10⁻⁶. 16 ions / cm² to 4×10 16 Ions / cm²; the preset ion implantation energy is 40 keV to 400 keV.

[0047] Hydrogen ions, helium ions, nitrogen ions, oxygen ions, or argon ions are used as implanted ions, and their dosage is controlled at 2 × 10⁻⁶. 16 ions / cm² to 4×10 16The ion density per square centimeter and energy control within the range of 40 keV to 400 keV help to form a separation layer 120 of suitable depth and concentration in the piezoelectric wafer 100, thereby achieving effective separation of the thin film layer 130 and the residual layer 110 in subsequent heat treatment, while reducing damage to the lattice structure of the thin film layer 130.

[0048] S130: Bond the piezoelectric wafer 100 to the substrate 200 to obtain the bond body 300.

[0049] It should be understood that after bonding, the thin film layer 130 of the piezoelectric wafer 100 contacts the substrate 200 and is stacked on the substrate 200. Thus, the bonded body 300 consists of the residual layer 110, the release layer 120, the thin film layer 130, and the substrate 200 stacked sequentially from top to bottom. The bonding method can be surface activation bonding, specifically plasma activation or chemical solution activation.

[0050] In some embodiments, before bonding the piezoelectric wafer 100 to the substrate 200, the method further includes: preparing an isolation layer on the substrate 200.

[0051] Specifically, if the substrate 200 is a single-layer silicon substrate, silicon oxide can be prepared on the single-layer silicon substrate by thermal oxidation, and the generated silicon oxide layer can be used as an isolation layer. Then, the piezoelectric wafer 100 is bonded to the substrate 200 with the isolation layer to obtain a bonded body 300 with the isolation layer, which effectively prevents impurities in the substrate 200 from diffusing into the thin film layer 130, and avoids adverse effects on the electrical performance of subsequent devices.

[0052] It should be noted that the isolation layer fabricated on the substrate 200 can be a single layer or multiple layers. For example, alternating stacked silicon oxide layers and silicon nitride layers can be fabricated on the substrate 200.

[0053] S140: Heat treatment is performed on the bond body 300 to separate the residual layer 110 from the thin film layer 130, so as to obtain a piezoelectric composite film.

[0054] In some embodiments, the step of heat-treating the bond 300 to separate the residual layer 110 from the thin film layer 130 to obtain a piezoelectric composite thin film includes: The bonded body 300 is placed in a heat treatment environment. The temperature of the heat treatment environment is controlled within the range of 100 degrees Celsius to 400 degrees Celsius and maintained for 1 hour to 100 hours. During the heat treatment process, bubbles are formed within the separation layer 120 of the bonded body 300, and these bubbles are then ruptured.

[0055] Specifically, hydrogen ions can form hydrogen bubbles, and helium ions can form helium bubbles. As the heat treatment progresses, the bubbles in the separation layer 120 merge together, and finally the separation layer 120 cracks.

[0056] After the bubble in the separation layer 120 bursts, the residual layer 110 is peeled off from the bond body 300, thereby obtaining a piezoelectric composite film containing a substrate 200 and a thin film layer 130.

[0057] Specifically, the bursting of the bubble separates the residual layer 110 from the thin film layer 130, thereby peeling the residual layer 110 off the bonding body 300 to obtain a piezoelectric composite film, wherein the piezoelectric composite film is composed of a thin film layer 130 and a substrate 200 stacked from top to bottom.

[0058] The bond 300 is placed in a heat treatment environment of 100°C to 400°C for 1 hour to 100 hours, causing bubbles to form and rupture in the separation layer 120, thereby causing the residual layer 110 to peel off from the bond 300, resulting in a piezoelectric composite film containing a substrate 200 and a thin film layer 130. This condition helps to reduce the impact of the separation process on the structural integrity of the thin film layer 130 while achieving interlayer separation, providing a structural basis for subsequent blackening treatment.

[0059] It should be understood that in actual operation, the piezoelectric composite film obtained after step S140, which should be brown film layer 130, is partially or completely whitened. Therefore, after heat treatment of the bond body 300, the originally blackened film layer 130 is partially or completely oxidized, and the following steps need to be performed to change the above phenomenon.

[0060] A separation layer 120 is formed in the piezoelectric wafer 100 by ion implantation of preset ions. The wafer is then bonded to the substrate 200 and the bonded body 300 is heat-treated. The excess layer 110 is peeled off by using the bubbles generated by the separation layer 120, thereby obtaining a piezoelectric composite film with a well-defined layered structure. The thickness of the film layer 130 can be controlled by adjusting the ion implantation depth.

[0061] See Figure 3 In some embodiments, the method further includes: If the reducing medium 500 is a solid reducing medium 510, blackening powder is obtained. The blackening powder is formed by uniformly mixing reducing powder material and lithium carbonate powder material in a predetermined mass ratio. The piezoelectric composite film is placed in blackening powder and completely buried by the blackening powder. Adjust the position of the piezoelectric composite film and the distribution of the blackening powder to ensure that the entire outer surface of the piezoelectric composite film layer 130 is in full contact with the blackening powder.

[0062] It should be understood that the blackening powder reacts in the reduction furnace to produce reducing gas carbon monoxide. This carbon monoxide then performs a blackening reduction heat treatment on the thin film layer 130, thereby repairing the blackening of the thin film layer 130 or inhibiting its whitening. Specifically, the reducing gas carbon monoxide reacts with oxygen in the thin film layer 130, increasing the oxygen vacancy concentration and thus reducing resistivity, thereby repairing the blackening of the thin film layer 130 or inhibiting its whitening.

[0063] By configuring the blackening powder as a uniform mixture of reducing powder and lithium carbonate powder in a predetermined ratio, and completely burying the piezoelectric composite film therein and ensuring that the outer surface of the film layer 130 is in full contact with the powder, the uniform generation and release of the reducing atmosphere can be promoted, which helps the film layer 130 to obtain more consistent blackening reaction conditions during the heat treatment process, thereby improving the uniformity of the blackening effect.

[0064] In some embodiments, the blackening powder contains 5 to 10 parts by mass of reducing powder material and 90 to 95 parts by mass of lithium carbonate powder material; the reducing powder material is one or more combinations of iron powder, aluminum powder, zinc powder, magnesium powder, silicon powder and carbon powder.

[0065] It should be understood that toner can be any powder containing carbon, such as diamond, C. 60 C 70 Graphite powder, activated carbon, carbon black, charcoal, etc.; silicon powder can be elemental silicon powder. For example, the reducing powder can also be any one or more of iron powder, aluminum powder, zinc powder, magnesium powder, silicon powder, and carbon powder mixed with graphene. In this way, the graphene in the mixed powder can greatly enhance the reducing properties of the reducing powder. Before use, the reducing powder in the blackening powder and lithium carbonate powder are weighed according to a preset ratio, mechanically ground, and uniformly mixed. This mixture is then used as a composite reducing agent to carry out the blackening and reduction reaction of the piezoelectric composite film. The lithium carbonate powder also plays a role in improving the uniformity of the reduction.

[0066] Studies have found that the ratio of reducing powder to lithium carbonate powder in the blackening powder has a certain impact on the blackening and reduction effect of the thin film layer 130. Comparative studies revealed that the blackening and reduction effect of the prepared blackened piezoelectric composite thin film 600 is best achieved when the blackening powder is formulated with the following ratio: 5-10 parts by mass of reducing powder and 90-95 parts by mass of lithium carbonate powder. When the amount of reducing powder added is less than 5 parts, it is insufficient to completely blacken the thin film layer 130; when the amount of reducing powder added is greater than 10 parts, the rate of carbon monoxide generation is too fast, and some carbon monoxide cannot be reduced in time, resulting in carbon monoxide waste; when the blackening powder includes 5-10 parts of reducing powder and 90-95 parts of lithium carbonate powder, the thin film layer 130 can be completely blackened without excessive carbon monoxide waste.

[0067] For example, referring to Table 1, a blackened piezoelectric composite film 600 is prepared using the method provided in Example 1 of this application. The piezoelectric wafer 100 is a lithium tantalate wafer with a thickness of 0.25 mm, and the substrate 200 is a silicon wafer with a thickness of 0.25 mm. Blackening powder is buried outside the film layer 130 of the piezoelectric composite film. The blackening powder is iron powder and lithium carbonate powder, wherein the mass ratio of iron powder to lithium carbonate powder is 5:95. In the reduction furnace, the temperature of the blackening reduction heat treatment of the piezoelectric composite film buried in the blackening powder is 530°C, and the holding time is 4 hours.

[0068] Comparative Example 1: The resistivity of the lithium tantalate composite film obtained without blackening treatment is uniform but the values ​​are large.

[0069] Comparative Example 2: The resistivity of the lithium tantalate composite film obtained after blackening treatment with embedded powder was tested. The resistivity values ​​at various locations decreased but were not uniform.

[0070] Comparative Example 3: The resistivity of the lithium tantalate composite film obtained by slight roughening and blackening treatment with powder embedding was tested. The resistivity values ​​at various locations further decreased and the uniformity was improved.

[0071] Comparative Example 4: The resistivity of the lithium tantalate composite film obtained after roughening and blackening treatment with powder embedding was tested. The resistivity at each location continued to decrease and had good uniformity.

[0072] Example 1 of this application: The lithium tantalate composite film obtained by heavy roughening + powder embedding blackening treatment has the best resistivity data and uniformity at each point, and its wafer surface color is the darkest among all examples.

[0073] Table 1:

[0074] Ra (nm) refers to the arithmetic mean deviation of the surface roughness parameter, and its unit is nanometer (nm).

[0075] Furthermore, the study found that the improved blackening effect led to a significant reduction in resistivity. However, in subsequent device performance testing, device performance did not show a clear negative correlation with resistivity. When the resistivity fell below a certain value, the Q value and K of the device... 2 The piezoelectric properties decrease as resistivity decreases. This is because in a high-temperature, oxygen-free environment, oxygen ions escape the LT lattice, forming oxygen vacancies and increasing the carrier concentration within the crystal, thus reducing resistivity. However, simultaneously, due to the small radius of lithium ions, they form strong ionic bonds with oxygen ions. During the escape of oxygen ions, lithium ions escape along with them in the form of Li₂O, resulting in lithium vacancies in the lattice. At this time, some tantalum ions gain electrons and are reduced to form tetravalent tantalum ions, while some tantalum ions also enter lithium vacancies to form anti-tantalum. This leads to the generation of a large number of lattice defects, resulting in a decrease in piezoelectric performance and consequently a decline in device performance. Therefore, as the degree of blackening deepens, oxygen vacancies diffuse and their concentration increases, and the concentration of lattice defects also gradually increases, leading to a decrease in piezoelectric performance. Based on the above comparative examples, further tests and analyses were conducted, testing the piezoelectric performance of the wafers in each example, as detailed in Table 2.

[0076] Table 2:

[0077] Analysis of the above test data reveals that Example 1, due to its higher surface roughness and greater blackening, exhibits a more significant decrease in piezoelectric performance compared to other examples, despite having the lowest resistivity. This results in a decline in the performance of devices fabricated using this wafer. Therefore, higher surface roughness is not always better; there is a certain range. Furthermore, it can be observed that the relationship between surface roughness and wafer piezoelectric performance is not linear but exhibits an inflection point. Before the inflection point, the piezoelectric performance decreases slowly with increasing surface roughness; after the inflection point, a strong correlation emerges between the decrease in piezoelectric performance and the increase in surface roughness. Therefore, a surface roughness of around 25 achieves a balance between low resistivity and good piezoelectric performance, preventing device damage during wafer pyroelectricity fabrication without degrading device performance, representing the optimal range.

[0078] See Figure 4 In some embodiments, the method further includes: If the reducing medium 500 is a gaseous reducing medium 520, the gas is filled into the sealed chamber or the sealed chamber is made into a vacuum state. The gas is one or more of hydrogen, carbon monoxide, lithium chloride vapor, nitrogen, and argon. The piezoelectric composite film is placed inside a sealed chamber so that the entire outer surface of the piezoelectric composite film layer 130 is exposed to the gaseous reducing medium 520 inside the sealed chamber.

[0079] It should be understood that blackening needs to be carried out in a high-temperature, oxygen-free atmosphere. Therefore, lithium chloride vapor, nitrogen, argon, and vacuum are used to obtain a reducing atmosphere by isolating oxygen. Hydrogen and carbon monoxide, in addition to not containing oxygen, have a certain reducing property, so they are more suitable for creating a reducing atmosphere. One or two of the above atmospheres can be selected, for example, argon and nitrogen can be selected to set the atmosphere at a gas flow rate of 5:1.

[0080] By filling a sealed chamber with one or more of hydrogen, carbon monoxide, lithium chloride vapor, nitrogen, and argon, or maintaining a vacuum, and placing the piezoelectric composite film therein so that the outer surface of the film layer 130 is fully exposed to the atmosphere, a controllable and uniform reduction environment can be provided for the blackening reduction heat treatment. This helps the gas medium to fully contact and react with the surface of the film layer 130, thereby promoting the progress of the blackening process and the consistency of the effect.

[0081] In some embodiments, the heating temperature of the blackening reduction heat treatment is controlled within the range of 300 degrees Celsius to 550 degrees Celsius; the holding time of the blackening reduction heat treatment is controlled within 24 hours.

[0082] Controlling the heating temperature of the blackening reduction heat treatment within the range of 300°C to 550°C and the holding time within 24 hours helps to ensure that the reduction reaction proceeds fully while reducing the possibility of excessive blackening or material performance degradation caused by excessively high temperature or long time. This improves the 130 resistivity reduction effect of the thin film layer while maintaining the stability of its piezoelectric properties.

[0083] It should be noted that ion implantation and the stripping of the residual layer 110 will cause some damage to the lattice in the prepared thin film layer 130. Therefore, this application can restore the lattice in the thin film layer 130 during high-temperature annealing, wherein the lattice restoration temperature of the thin film layer 130 is at least 350°C. The annealing temperature of the high-temperature annealing process in this application not only restores the lattice of the thin film layer 130 and maintains the piezoelectric properties of the thin film layer 130, but also re-blackens the whitened thin film layer 130, and the roughened thin film layer 130 can achieve very uniform blackening.

[0084] For example, referring to Table 3, a blackened piezoelectric composite film 600 is prepared using the method provided in Example 2 of this application. The piezoelectric wafer 100 is a lithium tantalate wafer with a thickness of 0.25 mm, and the substrate 200 is a silicon wafer with a thickness of 0.25 mm. The gas reduction medium 520 is hydrogen. In the reduction furnace, the temperature for the blackening reduction heat treatment of the piezoelectric composite film buried in the blackening powder is 530°C, and the holding time is 4 hours.

[0085] Comparative Example 5: The resistivity of the lithium niobate composite film obtained without blackening treatment was tested. The resistivity data at each location were uniform but the values ​​were large.

[0086] Comparative Example 6: The resistivity of the lithium niobate composite film obtained by blackening treatment in a reducing atmosphere was tested. The resistivity values ​​at various locations decreased but were not uniform.

[0087] Comparative Example 7: The resistivity of the lithium niobate composite film obtained by slight roughening and blackening treatment in a reducing atmosphere was tested. The resistivity values ​​at various locations further decreased and the uniformity was improved.

[0088] Comparative Example 8: The resistivity of the lithium niobate composite film obtained after roughening and blackening treatment in a reducing atmosphere was tested. The resistivity at each location continued to decrease and had good uniformity.

[0089] Example 2 of this application: The lithium niobate composite film obtained by heavy roughening and blackening treatment in a reducing atmosphere was tested for resistivity. All points showed the best resistivity data and uniformity, and the surface color of its wafer was the darkest among all examples.

[0090] This is consistent with the results obtained from powder blackening, proving that this method has universality and good reproducibility.

[0091] Table 3:

[0092] Furthermore, the study found that the improved blackening effect led to a significant reduction in resistivity. However, in subsequent device performance testing, device performance did not show a clear negative correlation with resistivity. When the resistivity fell below a certain value, the Q value and K of the device... 2The piezoelectric properties decrease as resistivity decreases. This is because in a high-temperature, oxygen-free environment, oxygen ions escape the LT lattice, forming oxygen vacancies and increasing the carrier concentration within the crystal, thus reducing resistivity. However, simultaneously, due to the small radius of lithium ions, they form strong ionic bonds with oxygen ions. During the escape of oxygen ions, lithium ions escape along with them in the form of Li₂O, resulting in lithium vacancies in the lattice. At this time, some tantalum ions gain electrons and are reduced to form tetravalent tantalum ions, while some tantalum ions also enter lithium vacancies to form anti-tantalum. This leads to the generation of a large number of lattice defects, resulting in a decrease in piezoelectric performance and consequently a decline in device performance. Therefore, as the degree of blackening deepens, oxygen vacancies diffuse and their concentration increases, and the concentration of lattice defects also gradually increases, leading to a decrease in piezoelectric performance. Based on the above comparative examples, the applicant conducted further tests and analyses, testing the piezoelectric performance of the wafers in each example, as detailed in Table 4.

[0093] Table 4:

[0094] Analysis of the test data reveals that Example 2, due to its higher surface roughness and greater blackening, exhibits a more significant decrease in piezoelectric performance compared to other examples, despite having the lowest resistivity. This results in a decline in the performance of devices fabricated using this wafer. Therefore, higher surface roughness is not always better; there is a certain range. Furthermore, the relationship between surface roughness and wafer piezoelectric performance is not linear but exhibits an inflection point. Before the inflection point, the piezoelectric performance decreases slowly with increasing surface roughness; after the inflection point, a strong correlation emerges between the decrease in piezoelectric performance and the increase in surface roughness. Therefore, a surface roughness of around 25 achieves a balance between low resistivity and good piezoelectric performance, preventing device damage due to wafer pyroelectricity during fabrication without degrading device performance—this represents the optimal range. This aligns with the conclusions obtained from the powder-embedded wafer example, demonstrating the universality and good repeatability of this range.

[0095] In some embodiments, after obtaining the blackened piezoelectric composite film 600, the method includes: grinding and polishing the outer surface of the film layer 130 of the piezoelectric composite film that has undergone blackening reduction heat treatment, so as to remove the blackening reaction products and micro-rough structure on the outer surface of the film layer 130, and restore the outer surface of the film layer 130 to optical grade smoothness and gloss.

[0096] It should be understood that after grinding and polishing, the polished blackened piezoelectric composite film 600 can be cleaned to ensure that no impurities adhere to the outer surface of the film.

[0097] After obtaining the blackened piezoelectric composite film 600, the outer surface of its film layer 130 is ground and polished to remove the blackening reaction products and micro-rough structure on the surface, so that the outer surface of the film layer 130 can be restored to optical-grade flatness and smoothness, thereby meeting the requirements of subsequent photolithography processes for surface morphology and helping to improve the accuracy of pattern transfer and the yield of device fabrication.

[0098] As can be seen from the above technical solutions, the embodiments of this application provide a method for improving the blackening effect of piezoelectric composite films. This involves selecting a piezoelectric wafer 100 and a substrate 200; wherein the piezoelectric wafer 100 is a lithium niobate wafer or a lithium tantalate wafer; implanting preset ions into the piezoelectric wafer 100 via ion implantation, sequentially dividing the piezoelectric wafer 100 into a residual layer 110, a separation layer 120, and a thin film layer 130; then bonding the piezoelectric wafer 100 to the substrate 200 to obtain a bonded body 300; then heat-treating the bonded body 300 to separate the residual layer 110 from the thin film layer 130 to obtain a piezoelectric composite film; roughening the surface of the thin film layer 130 of the piezoelectric composite film; and placing the roughened piezoelectric composite film 400 in a reducing medium 500 for blackening reduction heat treatment to obtain a blackened piezoelectric composite film 600, thus solving the problem of poor blackening reaction effect of piezoelectric composite films.

[0099] Similar parts between the embodiments provided in this application can be referred to mutually. The specific implementation methods provided above are only a few examples under the overall concept of this application and do not constitute a limitation on the scope of protection of this application. For those skilled in the art, any other implementation methods extended from the solution of this application without creative effort shall fall within the scope of protection of this application.

Claims

1. A method for improving the blackening effect of piezoelectric composite films, characterized in that, The method includes: Prepare a piezoelectric composite film, wherein the structure of the piezoelectric composite film includes at least a substrate layer and a film layer stacked sequentially; The surface of the piezoelectric composite film is roughened. The roughened piezoelectric composite film is placed in a reducing medium for blackening reduction heat treatment to obtain a blackened piezoelectric composite film.

2. The method according to claim 1, characterized in that, The specific method for preparing the piezoelectric composite film is as follows: A piezoelectric wafer and a substrate are selected; wherein the piezoelectric wafer is a lithium niobate wafer or a lithium tantalate wafer; Preset ions are implanted into the piezoelectric wafer using ion implantation, and the piezoelectric wafer is sequentially divided into a residual mass layer, a separation layer, and a thin film layer. The piezoelectric wafer is bonded to the substrate to obtain a bonded body; The bonded body is subjected to heat treatment to separate the residual layer from the thin film layer, thereby obtaining a piezoelectric composite thin film.

3. The method for improving the blackening effect of piezoelectric composite films according to claim 1, characterized in that, The surface of the piezoelectric composite film is roughened by at least one of chemical etching, plasma etching, abrasive grinding, or laser processing.

4. The method for improving the blackening effect of piezoelectric composite films according to claim 1, characterized in that, The method further includes: If the reducing medium is a solid reducing medium, blackened powder is obtained, wherein the blackened powder is uniformly mixed with reducing powder material and lithium carbonate powder material in a predetermined mass ratio; The piezoelectric composite film is placed in the blackened powder, and the piezoelectric composite film is completely buried by the blackened powder; Adjust the position of the piezoelectric composite film and the distribution of the blackening powder to ensure that the entire outer surface of the piezoelectric composite film layer is in full contact with the blackening powder.

5. The method for improving the blackening effect of piezoelectric composite films according to claim 4, characterized in that, In the blackened powder, the reducing powder material accounts for 5 to 10 parts by mass, and the lithium carbonate powder material accounts for 90 to 95 parts by mass. The reducing powder material is one or more of the following: iron powder, aluminum powder, zinc powder, magnesium powder, silicon powder, and carbon powder.

6. The method for improving the blackening effect of piezoelectric composite films according to claim 1, characterized in that, The method further includes: If the reducing medium is a gaseous reducing medium, the sealed chamber is filled with gas or the sealed chamber is made to be in a vacuum state. The gas is one or more of hydrogen, carbon monoxide, lithium chloride vapor, nitrogen, and argon; The piezoelectric composite film is placed inside the sealed chamber so that the entire outer surface of the piezoelectric composite film layer is exposed to the gaseous reducing medium inside the sealed chamber.

7. The method for improving the blackening effect of piezoelectric composite films according to claim 1, characterized in that, The heating temperature for the blackening reduction heat treatment is controlled within the range of 300 degrees Celsius to 550 degrees Celsius; the holding time for the blackening reduction heat treatment is controlled within 24 hours.

8. The method for improving the blackening effect of piezoelectric composite films according to claim 1, characterized in that, After obtaining the blackened piezoelectric composite film, the method includes: The outer surface of the piezoelectric composite film that has undergone blackening reduction heat treatment is ground and polished to remove the blackening reaction products and micro-rough structure on the outer surface of the film layer, and to restore the outer surface of the film layer to optical grade smoothness and gloss.

9. The method for improving the blackening effect of piezoelectric composite films according to claim 1, characterized in that, The preset ions include hydrogen ions, helium ions, nitrogen ions, oxygen ions, or argon ions; The preset ion implantation dose is 2×10 16 ions / cm² to 4×10 16 ions / square centimeter; The implantation energy of the preset ions is between 40 keV and 400 keV.

10. The method for improving the blackening effect of piezoelectric composite films according to claim 1, characterized in that, The substrate is a single-layer structure or a composite structure made of multiple different materials. The material constituting the substrate is at least one of lithium niobate, lithium tantalate, silicon, quartz, sapphire, silicon carbide or silicon nitride.

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