Preparation method of piezoelectric single crystal composite film material

Abstract

The application belongs to the technical field of semiconductor material manufacturing, and particularly relates to a preparation method of a piezoelectric single crystal composite film material, which comprises the following steps: ion implantation of a piezoelectric functional material, wet oxidation treatment of a surface of a supporting substrate, subsequent cleaning and blow-drying, activation treatment of the surface of the supporting substrate and the piezoelectric functional material using oxygen and nitrogen mixed plasma, pre-bonding and standing in a low vacuum environment, nitrogen annealing, thinning and peeling. The preparation method has the advantages of simple process and low cost. The composite film prepared by the method has high bonding strength, no damage at a peeling interface, and effectively avoids collapse and fragments, effectively improves yield, and is beneficial to industrialized production.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor material manufacturing, and in particular relates to a method for preparing a piezoelectric single crystal composite thin film material. Background Art

[0002] RF acoustic filters are an indispensable component of the RF front-end for mobile communications. With the rapid development of 5G communication technology and the Internet of Things, the requirements for core performance indicators such as operating frequency, rectangularity, out-of-band suppression, bandwidth, size, power, and temperature stability are constantly increasing. Microacoustic devices based on bulk single-crystal piezoelectric functional materials suffer from low energy conversion efficiency, low operating frequency, poor temperature stability, and large size. These issues make them unable to meet the demands of complex environments and the future development of miniaturized and integrated devices. Therefore, breakthrough research in high-performance piezoelectric functional materials is urgently needed.

[0003] The research, development and preparation of piezoelectric single crystal thin film composite materials, through the liberalized composite film layer structure design, can not only ensure that the piezoelectric functional materials have good single crystal properties, but also have the characteristics of low acoustic wave energy loss, good temperature characteristics, and good thermal conductivity based on the size effect of thickness and the boundary effect and performance composite effect of the composite film. The key performance indicators of micro-acoustic devices prepared based on piezoelectric single crystal thin film composite materials in terms of Q value, operating frequency, rectangularity, temperature stability, integration, miniaturization, and heat dissipation are significantly improved.

[0004] Conventional methods for preparing piezoelectric single crystal thin film composite materials include the smart peeling method, which combines ion implantation and wafer bonding processes. Although this method can produce piezoelectric single crystal thin films, it has the following defects: low bonding strength, large damage to the peeling interface, warping, and problems such as cracking and fragmentation, which reduce the yield. At the same time, the process conditions such as activation and pre-bonding are harsh and cumbersome, which increases costs and is not conducive to industrial production. Summary of the Invention

[0005] In response to the current technical problems, the present invention provides a method for preparing a piezoelectric single crystal composite thin film material. The method has a simple process and low cost. The composite film prepared by this method has high bonding strength, no damage to the peeling interface, and low warping. At the same time, it effectively avoids cracking and fragmentation, effectively improves the yield, and is conducive to industrial production.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for preparing a piezoelectric single crystal composite thin film material comprises the following steps:

[0008] (1) Ion implantation of piezoelectric functional materials;

[0009] (2) the surface of the supporting substrate is subjected to a wet oxidation treatment, and then cleaned with deionized water and dried with nitrogen gas;

[0010] (3) Activating the surface of the supporting substrate and the piezoelectric functional material using a mixed plasma of oxygen and nitrogen;

[0011] (4) Pre-bonding and standing under low vacuum environment;

[0012] (5) Nitrogen annealing, thinning, and stripping.

[0013] The present invention first implants ions into the piezoelectric functional material to form a defect layer in the middle of the piezoelectric single crystal, and performs a wet oxidation treatment on the surface of the supporting substrate; in a vacuum environment, the surface of the piezoelectric functional material and the surface of the oxidized supporting material are activated by mixed plasma, and then the piezoelectric functional material and the supporting material wafers are pre-bonded and allowed to stand in a low vacuum environment, and then nitrogen annealed, thinned, and peeled to prepare a piezoelectric single crystal composite thin film material with good quality and high yield.

[0014] Preferably, before use, the supporting substrate and the piezoelectric functional material are polished on one side, with a thickness of 50-1000 μm and a size of 3-12 inches; the piezoelectric functional material is polished on both sides, with a thickness of 50-1000 μm and a size of 3-12 inches, so that they can be reused after peeling to save costs. The root mean square roughness of the polished surfaces of the supporting substrate and the piezoelectric functional material are both less than 0.5 nm to ensure that the bonding surfaces between the wafers can fully contact.

[0015] Preferably, the piezoelectric functional material and supporting substrate are cleaned with acetone, RCA-1 standard solution, and deionized water, followed by nitrogen blow-drying, before use. This effectively removes organic matter, oxides, and other surface contaminants and attached particles from the wafer surface. Furthermore, preferably, the piezoelectric functional material and supporting substrate are placed on a cleaning table with a rotation speed of 2500-3000 rpm, a deionized water rinse time of 1-50 seconds, and a nitrogen blow-dry time of 1-30 seconds.

[0016] Further preferably, the concentration of the acetone solution is 10-60%, and the cleaning time is 1-50 min; the cleaning time of the RCA-1 standard solution is 1-50 min; the cleaning time of deionized water is 1-50 s; and the nitrogen drying time is 1-30 s.

[0017] Preferably, the ion species is a mixture of one or more of H ions, He ions, and O ions; the ion implantation energy is 1-300 keV, and the implantation dose is 1×10 15 -1×10 18 / cm 2The reasonable selection of ion implantation energy and implantation dose is the premise for achieving complete peeling. Too large or too small values ​​are not conducive to peeling, which will cause peeling failure, chipping, fragmentation or greater damage to the peeling interface.

[0018] Preferably, the process conditions of wet oxidation treatment are: the mixing ratio of concentrated oxidizing ammonia solution is NH4OH:H2O2:H2O=3-6:1-3:3, the oxidation time is 1-120min, the process temperature is ≤65°C, NH4OH first corrodes the natural oxide layer on the surface of the silicon wafer, and H2O2 forms a new thicker oxide film on the surface of the silicon wafer, which is beneficial to increasing the number of hydroxyl groups on the surface of the wafer and improving the bonding strength. At the same time, a layer of porous silicon oxide amorphous layer is generated on the surface of the oxidized wafer. The presence of this oxide layer strengthens the atomic diffusion and structural reorganization ability of the bonding layer during the annealing process, thereby further improving the bonding strength, reducing film shedding (reducing the phenomenon of piezoelectric film shedding), and improving the yield; compared with conventional methods for preparing oxide layers such as chemical vapor deposition, magnetron sputtering, etc., the process of the present invention is more streamlined, easy to operate, and reduces process costs.

[0019] Preferably, the process conditions for the activation treatment are: the vacuum degree of the plasma activation chamber is 1×10 -5 -1Pa, to prevent particle contamination, the oxygen plasma gas flow rate used is 100-500sccm, the nitrogen plasma gas flow rate is 100-500sccm, the plasma emitter upper frequency power is 40-80W, the lower frequency power is 10-50W, and the process time is 15-90s to ensure the uniformity and efficiency of activation; the use of mixed oxygen and nitrogen plasma activation treatment, compared with single plasma activation, increases the number of hydrophilic groups and other nitrogen-containing functional groups that are beneficial to pre-bonding on the surface of the silicon substrate, thereby increasing the number of covalent bonds, which is beneficial to improving the bonding strength.

[0020] Preferably, the pre-bonding process conditions are: vacuum degree is 1×10 -5 -1Pa, to prevent particle contamination, the process temperature is 10-50℃, the process time is 1-120s, the pre-bonding pressure is 0-20kN, and it is left to stand for 8-10h; the residual moisture on the bonding interface is gradually completely discharged with the growth of time, and the spontaneous bonding of the sample is gradually carried out fully. Spontaneous bonding is of great significance to increasing the wafer bonding area and reducing bonding defects. It is the guarantee for achieving high-quality wafer bonding. The application of appropriate pressure is conducive to high-quality bonding. Excessive pressure leads to high cost and reduced efficiency.

[0021] Preferably, the process conditions for nitrogen annealing are: nitrogen flow rate of 1-2 L / min, annealing temperature of 100-150°C, and holding temperature for 1-50 hours after reaching the preset annealing temperature; the thermal expansion coefficient of Si wafer is quite different from that of LiNbO3 wafer. If the annealing temperature is too high, it will cause problems such as chipping, fragmentation, warping, and debonding, which will affect the bonding strength, structural integrity, and peeling interface damage.

[0022] Preferably, the supporting substrate is one or more composite substrates of Si and SiC, and the piezoelectric functional material is one of crystal materials of LiNbO3 and LiTaO3.

[0023] Preferably, the nitrogen flow rate is 1-2 L / min, the stripping temperature is 100-300° C., and the insulation time is 10-50 h.

[0024] Preferably, after nitrogen annealing, the piezoelectric functional material is thinned to 200-350 μm. The thinned piezoelectric functional material can reduce stress release during the stripping process, improve the stripping success rate, reduce stripping interface damage, and improve the yield rate.

[0025] The technical solution of the present invention is based on the characteristics of silicon wafers and piezoelectric single crystal materials. It adopts two processes, wet oxidation treatment and mixed plasma activation, to increase the number of hydrophilic groups and other nitrogen-containing functional groups on the surface of the silicon substrate that are beneficial to pre-bonding, thereby increasing the number of covalent bonds and improving the bonding strength. With the increase in bonding strength, the film shedding is reduced, and the yield rate is effectively improved. A layer of porous silicon oxide amorphous layer is generated on the surface of the wafer after oxidation. The existence of this oxide layer strengthens the atomic diffusion and structural reorganization ability of the bonding layer during the annealing process, so that the bonding strength is further improved. After the two wafers are pre-bonded, they are annealed, thinned, and peeled. The annealing process is based on the characteristics of silicon wafers and piezoelectric single crystal materials. The difference in thermal expansion coefficients between the two is relatively large. At the same time, combined with the ion implantation process, The process conditions and pre-bonding are finally determined to determine the annealing and stripping method of the present invention. The appropriate annealing, stripping temperature and holding time are adopted, so that the problem of stress release concentration in the annealing process caused by the mismatch of thermal expansion coefficients between different materials is improved, and the probability of wafer warping and fragmentation and stripping damage is greatly reduced; the annealing and stripping method is adopted to significantly improve the bonding strength, ensure the integrity of the bonding structure, reduce the damage of the stripping interface, avoid the problem of chipping and fragmentation, and improve the yield; in conjunction with the thinning process, the stress release during stripping is reduced, which is conducive to complete and damage-free stripping, and the warping is reduced, thereby improving the yield; the method of the present invention finally obtains a composite film with low warping, high yield and high bonding strength, and the damage to the stripping interface is relatively small.

[0026] The present invention provides a novel method for bonding and stripping heterogeneous wafers, which uses a two-step process of wet oxidation and mixed plasma activation to perform surface activation treatment on a supporting substrate and a piezoelectric functional layer material after ion implantation, then pre-bonds the two wafers under a vacuum environment, and finally nitrogen anneals, thins, and strips the pre-bonded wafer to complete the preparation of the material. The method is suitable for bonding between supporting substrates such as silicon and silicon carbide with large differences in thermal expansion coefficients and low bonding energy and single-crystal piezoelectric functional materials such as lithium tantalate and lithium niobate, and can obtain a composite film with high bonding strength, low warpage, and high yield.

[0027] The present invention provides a preparation method for a piezoelectric single crystal composite thin film material, which utilizes an intelligent stripping method to combine ion implantation and wafer bonding processes, optimizes the ion implantation process, cooperates with wet oxidation and mixed plasma activation processes, and adopts appropriate annealing methods, thinning processes, and stripping methods, so that problems such as low bonding strength and low yield between different materials are improved, and the probability of wafer warping and fragmentation and damage to the stripping interface are greatly reduced, which not only improves the bonding strength, but also enables continuous and complete stripping of the film, reduces damage to the stripping interface, film shedding, etc., and effectively avoids chipping, fragmentation, etc., improves the yield, and effectively reduces the process cost, which is beneficial to the production and application of the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the structure of piezoelectric functional material and supporting substrate;

[0029] Figure 2 Schematic diagram of the structure of the piezoelectric functional material after ion implantation;

[0030] Figure 3 Schematic diagram of the structure of the supporting substrate after wet oxidation treatment;

[0031] Figure 4 Schematic diagram of the structure of the composite material after bonding;

[0032] Figure 5 Schematic diagram of the structure of the composite material after thinning;

[0033] Figure 6 Schematic diagram of the structure of the product after stripping;

[0034] Figure 7 This is the peeling interface diagram in Example 1;

[0035] Figure 8 This is a peeling interface diagram of the unqualified product in Comparative Example 1;

[0036] Figure 9 This is a schematic diagram of the material structure after nitrogen annealing in Example 1;

[0037] Figure 10 This is a schematic diagram of the structure of the material after nitrogen annealing in Comparative Example 4;

[0038] Figure 11 is a process flow chart of the preparation method of the present invention;

[0039] In the figure, 1 is a piezoelectric functional material, 1-1 is a residual layer, 1-2 is an injection layer, 1-3 is a thin film layer, 2 is a supporting substrate, and 2-1 is an oxide layer. DETAILED DESCRIPTION

[0040] In order to more clearly illustrate the overall concept of the present invention, the following is a detailed description by way of example. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited by the specific embodiments disclosed below.

[0041] The specific technical solutions of the present invention are as follows:

[0042] A method for preparing a piezoelectric single crystal composite thin film material, the process flow is as follows Figure 11 As shown, the following steps are included:

[0043] (1) Ion implantation of piezoelectric functional materials;

[0044] (2) the surface of the supporting substrate is subjected to a wet oxidation treatment, and then cleaned with deionized water and dried with nitrogen gas;

[0045] (3) Activating the surface of the supporting substrate and the piezoelectric functional material using a mixed plasma of oxygen and nitrogen;

[0046] (4) Pre-bonding and standing under low vacuum environment;

[0047] (5) Nitrogen annealing, thinning, and stripping.

[0048] Among them, the piezoelectric functional material and the supporting substrate are cleaned with acetone, RCA-1 standard solution, and deionized water in sequence before use and blown dry with nitrogen, which can effectively remove organic matter, oxides, and other surface pollutants and attached particles on the chip surface; the concentration of the acetone solution is 10-60%, specifically 10%, 20%, 30%, 40%, 50%, and 60% can be selected, and the cleaning time is 1-50 minutes, specifically 1 minute, 5 minutes, 10 minutes, and 20 minutes can be selected. , 35min, 50min; the cleaning time of RCA-1 standard solution is 1-50min; the cleaning time of deionized water is 1-50s; the nitrogen drying time is 1-30s; placed on the cleaning table, the cleaning table speed is 2500-3000rpm, the deionized water rinsing time is 1-50s, specifically 10s, 20s, 35s, 45s, 50s, etc. can be selected, the nitrogen drying time is 1-30s, specifically 5s, 10s, 25s, 30s, etc. can be selected.

[0049] The ion type is a mixture of one or more elements selected from H ions, He ions, and O ions. H ions and O ions, H ions and He ions, He ions and O ions, etc. can be selected. The ion implantation energy is 1-300keV, specifically 30keV, 50keV, 80keV, 100keV, 150keV, 200keV, etc. can be selected. The implantation dose is 1×10 15 -1×10 18 / cm 2 , you can choose 1×10 15 / cm 2 , 1×10 17 / cm 2 , 1×10 18 / cm 2 The reasonable selection of ion implantation energy and implantation dose is the premise for achieving complete peeling. Too large or too small values ​​are not conducive to peeling, which will cause peeling failure, chipping, fragmentation or greater damage to the peeling interface.

[0050] The mixing ratio of concentrated oxidizing ammonia solution in the wet oxidation process is NH4OH:H2O2:H2O=3-6:1-3:3, specifically NH4OH:H2O2:H2O=3:1:3, NH4OH:H2O2:H2O=2:1:1, NH4OH:H2O2:H2O=4:2:3, NH4OH:H2O2:H2O=6:1:3, NH4OH:H2O2:H2O=4:3:3, etc. The oxidation time is 1-120min, the process temperature is ≤65°C, and the process temperatures can be selected as 65°C, 50°C, 40°C, 30°C, 23°C, 20°C, etc. First, NH4OH corrodes the natural oxide layer on the surface of the silicon wafer, and H2O2 forms a new thicker oxide film on the surface of the silicon wafer, which is beneficial to increasing the number of hydroxyl groups on the wafer surface and improving the bonding strength. At the same time, a porous silicon oxide amorphous layer is generated on the surface of the oxidized wafer. The presence of this oxide layer strengthens the atomic diffusion and structural reorganization capabilities of the bonding layer during the annealing process, thereby further improving the bonding strength, reducing film shedding, and improving the yield. Compared with conventional methods for preparing oxide layers such as chemical vapor deposition and magnetron sputtering, the process used in the present invention is more streamlined and reduces process costs.

[0051] Activation treatment process conditions: The vacuum degree of the plasma activation chamber is 1×10 -5 -1Pa, to prevent particle contamination, the oxygen plasma gas flow rate used is 100-500sccm, specifically 100sccm, 300sccm, 400sccm, 500sccm, etc., the nitrogen plasma gas flow rate is 100-500sccm, specifically 100sccm, 300sccm, 400sccm, 500sccm, etc., the plasma emitter upper frequency power is 40-80W, specifically 40W, 50W , 55W, 60W, 65W, 80W, etc., the lower frequency power is 10-50W, specifically 10W, 20W, 35W, 40W, 45W, 50W, etc., the process time is 15-90s, to ensure the uniformity and efficiency of activation; the use of oxygen and nitrogen mixed plasma activation treatment, compared with single plasma activation, increases the number of hydrophilic groups on the surface of the silicon substrate and other nitrogen-containing functional groups that are beneficial to pre-bonding, thereby increasing the number of covalent bonds, which is beneficial to improving the bonding strength.

[0052] Pre-bonding process conditions: vacuum degree is 1×10 -5-1Pa, to prevent particle contamination, the process temperature is 10-50℃, specifically 10℃, 20℃, 23℃, 25℃, 30℃, 40℃, 50℃, etc. can be selected, the process time is 1-120s, the pre-bonding pressure is 0-20kN, specifically 0kN, 5kN, 10kN, 15kN, 20kN, etc. can be selected, and it is left to stand for 8-10h, specifically 8h, 9h, 10h, etc.; the residual moisture at the bonding interface is gradually completely discharged with the growth of time, and the spontaneous bonding of the sample is gradually carried out fully. Spontaneous bonding is of great significance to increasing the wafer bonding area and reducing bonding defects. It is the guarantee for achieving high-quality wafer bonding. The application of appropriate pressure is conducive to high-quality bonding. Excessive pressure leads to high cost, reduced efficiency, and smaller impact.

[0053] The process conditions of nitrogen annealing are: nitrogen flow rate of 1-2L / min, annealing temperature of 100-150℃, and holding temperature for 1-50h after reaching the preset annealing temperature; the thermal expansion coefficient of Si wafer is quite different from that of LiNbO3 wafer. If the annealing temperature is too high, it will cause problems such as chipping, fragmentation, warping, and debonding, which will affect the bonding strength, structural integrity, and peeling interface damage.

[0054] Before use, the supporting substrate and piezoelectric functional material are polished on one side, with a thickness of 50-1000μm and a size of 3-12 inches. The piezoelectric functional material is polished on both sides, with a thickness of 50-1000μm and a size of 3-12 inches. This allows for reuse after peeling to save costs. The root mean square roughness of the polished surfaces of the supporting substrate and the piezoelectric functional material are both less than 0.5nm, ensuring that the bonding surfaces between the wafers are in full contact.

[0055] The supporting substrate is one or more composite substrates of Si and SiC; the piezoelectric functional material is one crystal material of LiNbO3 and LiTaO3.

[0056] The process conditions for stripping are: nitrogen flow rate of 1-2 L / min, stripping temperature of 100-300°C, and insulation time of 10-50h.

[0057] After nitrogen annealing, the piezoelectric functional material is thinned to 200-350 μm, specifically 200 μm, 250 μm, 300 μm, 330 μm, and 350 μm.

[0058] The specific embodiments of the present invention are as follows:

[0059] The following formula for calculating the yield rate is: number of qualified products / total number × 100%;

[0060] The standards for qualified products are: no warping (Warp < 65μm, bow < 55μm), no fragments, no scratches, no cracks (i.e., large interface damage), no film shedding, etc. The film layer thickness of the piezoelectric functional material is within the range of 300-700nm.

[0061] The bonding energy is tested and recorded using the plunger method to obtain the bonding energy (bonding strength).

[0062] Example 1

[0063] A method for preparing a piezoelectric single crystal composite thin film material, comprising the following steps: Figure 11 As shown:

[0064] Provide a 6-inch single crystal silicon as a supporting substrate 2, a 6-inch lithium niobate wafer as a piezoelectric functional material 1, such as Figure 1 As shown; the thickness of the single crystal silicon substrate is 625 μm, and the thickness of the lithium niobate wafer is 500 μm; the root mean square roughness of the polished surfaces of the single crystal silicon substrate and the lithium niobate wafer is less than 0.5 nm, the single crystal silicon substrate is single-sided polished, and the lithium niobate wafer is double-sided polished;

[0065] The two wafers to be bonded were placed in a Petri dish containing acetone and ultrasonically cleaned for 30 minutes using a 30% acetone solution to remove contaminants and attached particles. The wafers were then immersed in a water bath with RCA-1 standard solution for 50 minutes to dissolve organic matter and oxides on the wafer surfaces. Finally, the single crystal silicon substrate and lithium niobate wafer were placed on a cleaning table with a speed set to 3000 rpm. The surfaces were cleaned with deionized water and dried with nitrogen. The deionized water cleaning time was 25 seconds, and the nitrogen drying time was 5 seconds.

[0066] The cleaned lithium niobate wafer was placed in an ion implanter and hydrogen ions were implanted. The hydrogen ion implantation energy was 50 keV and the implantation dose was 1×10 17 / cm 2 , forming a thin film layer 1-3, an injection layer 1-2 and a residual layer 1-1 on a lithium niobate wafer, such as Figure 2 As shown;

[0067] Next, the single crystal silicon substrate was placed in a concentrated oxidizing ammonia solution for wet oxidation treatment. The temperature was room temperature (23°C). The ratio (volume ratio) of the concentrated oxidizing ammonia solution was NH4OH:H2O2:H20=6:1:3. The oxidation time was 45 minutes. The surface was formed as shown in the following figure. Figure 3 The oxide layer 2-1 film shown is then sent to a cleaning station to be cleaned with deionized water and blown dry with nitrogen. The cleaning station speed is 3000 rpm, the deionized water rinse time is 25 seconds, and the nitrogen blow-drying time is 5 seconds.

[0068] The wafer to be bonded is placed in the activation chamber, sealed and evacuated, and the surface of the single crystal silicon substrate and lithium niobate wafer is activated using a mixed plasma of oxygen and nitrogen. The vacuum degree of the plasma activation chamber is 1×10 -2 Pa, the oxygen plasma gas flow rate used is 100 sccm, the nitrogen plasma gas flow rate is 100 sccm, the plasma emitter upper frequency power is 65 W, the lower frequency power is 45 W, and the process time is 60 s;

[0069] At room temperature (23°C), the activated silicon substrate and lithium niobate wafer are aligned on the alignment stage and then sent into the bonding chamber. After vacuuming, the two wafers are bonded together and a pressure of 10kN is applied. The process time is 60s to complete the pre-bonding. Figure 4 This is the state after the two wafers are pre-bonded. After standing for 8 hours, the residual moisture on the bonding interface is gradually completely discharged over time, and the spontaneous bonding of the sample is gradually completed.

[0070] After standing, annealing treatment was performed at a temperature of 130°C, a heating rate of 0.5°C / min, and a nitrogen flow rate of 2L / min to eliminate interfacial stress, remove water molecules, and improve bonding strength. The material was kept at the preset annealing temperature for 20 hours, and then cooled at a cooling rate of 0.5°C until it reached room temperature. The material state after annealing was free of warping, as shown in Figure 9.

[0071] Thinning process: Piezoelectric functional materials are thinned to 300μm, such as Figure 5 As shown, stress release is reduced to improve the success rate of peeling;

[0072] Stripping process: After thinning, the nitrogen flow rate is 2L / min, and the temperature is increased at a rate of 0.5℃ / min to 200℃ and kept at this temperature for 20h. The temperature is then lowered at a rate of 0.5℃ / min until it reaches room temperature.

[0073] Stripping is completed, such as Figure 6 As shown in Figure 2, the interface after peeling is not damaged (no cracks). Figure 7 As shown (view under a microscope), the lithium niobate piezoelectric functional material can be reused after peeling.

[0074] The bonding energy obtained from the test is 1.81 J / m 2 , the yield rate is 90.3%.

[0075] Example 2

[0076] A method for preparing a piezoelectric single crystal composite thin film material:

[0077] A 4-inch single-crystalline silicon substrate is provided as a supporting substrate 2, and a 4-inch lithium tantalate wafer is provided as a piezoelectric functional material 1; the thickness of the single-crystalline silicon substrate is 625 μm, and the thickness of the lithium tantalate wafer is 500 μm; the root mean square roughness of the polished surfaces of the single-crystalline silicon substrate and the lithium tantalate wafer is less than 0.5 nm, the single-crystalline silicon substrate is polished on one side, and the lithium niobate wafer is polished on both sides;

[0078] The two wafers to be bonded were placed in a Petri dish containing acetone and ultrasonically cleaned for 30 minutes using a 10% acetone solution to remove surface contaminants and attached particles. The two wafers were then immersed in a water bath with RCA-1 standard solution for 50 minutes to dissolve organic matter and oxides on the wafer surfaces. Finally, the single crystal silicon substrate and lithium tantalate wafer were placed on a cleaning table with a speed set to 3000 rpm. The surfaces were cleaned with deionized water and dried with nitrogen. The deionized water cleaning time was 25 seconds, and the nitrogen drying time was 5 seconds.

[0079] The cleaned lithium tantalate wafer was placed in an ion implanter and hydrogen ions were implanted. The hydrogen ion implantation energy was 40 keV and the implantation dose was 5×10 17 / cm 2 , forming a thin film layer 1-3, an injection layer 1-2 and a residual layer 1-1 on a lithium tantalate wafer;

[0080] Next, the single crystal silicon substrate was placed in a concentrated oxidizing ammonia solution for oxidation treatment at room temperature. The ratio of the concentrated oxidizing ammonia solution was NH4OH:H2O2:H20 = 4:3:3. The oxidation time was 45 minutes, and a 2-1 oxide layer thin film was formed on the surface. The substrate was then sent to a cleaning station for cleaning with deionized water and dried with nitrogen. The cleaning station speed was 3000 rpm, the deionized water rinsing time was 25 seconds, and the nitrogen drying time was 5 seconds.

[0081] The wafer to be bonded is placed in the activation chamber, sealed and evacuated, and the surface of the single crystal silicon substrate and lithium niobate wafer is activated using a mixed plasma of oxygen and nitrogen. The vacuum degree of the plasma activation chamber is 1×10 -2 Pa, the oxygen plasma gas flow rate used is 100 sccm, the nitrogen plasma gas flow rate is 100 sccm, the plasma emitter upper frequency power is 65 W, the lower frequency power is 45 W, and the process time is 60 s;

[0082] At room temperature (23°C), the activated silicon substrate and lithium tantalate wafer were aligned on the alignment stage and then placed into the bonding chamber. After evacuation, the two wafers were bonded together and a pressure of 0 kN was applied. The process took 60 seconds to complete the pre-bonding. The two wafers were in the state after pre-bonding and were left to stand for 8 hours.

[0083] After standing, annealing treatment was performed at 128°C, a heating rate of 0.5°C / min, and a nitrogen flow rate of 2L / min to eliminate interfacial stress, remove water molecules, and improve bonding strength. The preset annealing temperature was maintained for 20 hours, and the cooling rate was 0.5°C until the temperature reached room temperature.

[0084] Thinning process: Piezoelectric functional materials are thinned to 300μm to reduce stress release and improve the success rate of peeling;

[0085] Stripping process: After thinning, the nitrogen flow rate is 2L / min, and the temperature is increased at a rate of 0.5℃ / min to 200℃ and kept at this temperature for 20h. The temperature is then lowered at a rate of 0.5℃ / min until it reaches room temperature.

[0086] Peeling complete.

[0087] The bonding energy obtained from the test is 1.78J / m 2 , the yield rate is 90%.

[0088] Example 3

[0089] A method for preparing a piezoelectric single crystal composite thin film material:

[0090] The differences from Example 1 are as follows, and the rest are the same as Example 1;

[0091] After standing, annealing treatment was performed at a temperature of 125°C, a heating rate of 0.5°C / min, and a nitrogen flow rate of 2L / min to eliminate interfacial stress, remove water molecules, and improve bonding strength. The preset annealing temperature was maintained for 20 hours, and the cooling rate was 0.5°C until the temperature reached room temperature.

[0092] Thinning process: Piezoelectric functional materials are thinned to 330μm to reduce stress release and improve the success rate of peeling;

[0093] Stripping process: After thinning, the nitrogen flow rate is 2L / min, and the temperature is increased at a rate of 0.5℃ / min to 210℃ and kept at this temperature for 20h. The temperature is then lowered at a rate of 0.5℃ / min until it reaches room temperature.

[0094] Peeling complete.

[0095] The bonding energy obtained from the test is 1.74 J / m 2 ;The yield rate is 88.5%.

[0096] Comparative Example 1

[0097] A method for preparing a piezoelectric single crystal composite thin film material:

[0098] The differences from Example 1 are as follows, and the rest are the same as Example 1;

[0099] Use single N2 plasma activation: Place the product to be bonded into the activation chamber, seal and evacuate, and use single nitrogen plasma to activate the surface of the single crystal silicon substrate and lithium niobate wafer. The vacuum degree of the plasma activation chamber is 1×10 -2 Pa, the nitrogen plasma gas flow rate used is 200 sccm, the upper frequency power of the plasma emitter is 65 W, the lower frequency power is 45 W, and the process time is 60 s.

[0100] The bonding energy obtained from the test is 1.46 J / m 2 ; The yield rate is 78.8%; the unqualified products in the final product have cracks on the peeling interface (large damage), such as Figure 8 Shown (view under microscope).

[0101] Comparative Example 2

[0102] A method for preparing a piezoelectric single crystal composite thin film material:

[0103] The differences from Example 1 are as follows, and the rest are the same as Example 1;

[0104] The specific activation process is as follows: the wafer to be bonded is placed in the activation chamber, sealed and evacuated, and the surface of the single crystal silicon substrate and lithium niobate wafer is activated using a mixed plasma of oxygen and carbon tetrafluoride. The vacuum degree of the plasma activation chamber is 1×10 -2 Pa, the oxygen plasma gas flow rate is 100 sccm, the carbon tetrafluoride plasma gas flow rate is 100 sccm, the plasma emitter upper frequency power is 65 W, the lower frequency power is 45 W, and the process time is 60 s.

[0105] The bonding energy obtained from the test is 1.69 J / m 2 , the yield rate is 85.1%.

[0106] Comparative Example 3

[0107] A method for preparing a piezoelectric single crystal composite thin film material:

[0108] The difference from Example 1 is that the wet oxidation process is omitted, and the rest is the same as Example 1;

[0109] The test bonding energy is 1.57 J / m 2 , the yield rate is 83.5%.

[0110] Comparative Example 4

[0111] A method for preparing a piezoelectric single crystal composite thin film material:

[0112] The differences from Example 1 are as follows, and the rest are the same as Example 1;

[0113] After standing, annealing treatment was carried out at an annealing temperature of 160°C, a heating rate of 0.5°C / min, a nitrogen flow rate of 2L / min, and the preset annealing temperature was maintained for 20 hours. The cooling rate was 0.5°C until the temperature reached room temperature.

[0114] After annealing, the bonded substrates undergo varying degrees of warping and debonding, some of which are as follows: Figure 10 As shown, lithium niobate undergoes premature exfoliation.

[0115] By comparing the above embodiments and comparative examples, comparative examples 1 and 2 use plasmas different from those of the embodiments, and their bonding energy and yield are significantly lower than those of the embodiments. It can be seen that a single plasma and a mixed plasma different from the present invention are difficult to improve the bonding energy and yield; comparative example 3 omits the wet oxidation process relative to embodiment 1, and the final preparation quality is poor and the yield is poor. The implementation of the wet oxidation process also plays an important role in the present invention. The low yield of comparative examples 1-3 is mainly due to the low bonding energy, which easily causes cracks and piezoelectric film shedding during annealing and peeling; comparative example 4 uses a nitrogen annealing process different from that of the embodiment, and the bonded substrate warps and debonds, and the lithium niobate peels prematurely, making it impossible to effectively bond and peel off the product. The nitrogen annealing process conditions of the embodiment provide favorable guarantees for the preparation of qualified composite films. In summary, the products prepared in the present invention have very significant improvements in bonding energy and yield compared to the comparative examples, proving that the processes of the present invention cooperate with each other to produce high-quality products with high yields, which are suitable for industrial production, which is not achievable in the comparative examples.

[0116] The present invention provides a method for preparing a piezoelectric single crystal composite thin film material, which utilizes an intelligent stripping method to combine ion implantation and wafer bonding processes, optimizes the ion implantation process, cooperates with wet oxidation and mixed plasma activation processes, and adopts appropriate annealing methods, thinning processes and stripping processes, so that problems such as low bonding strength and low yield between heterogeneous materials are improved, and the probability of wafer warping and fragmentation and damage to the stripping interface are greatly reduced, which not only improves the bonding strength, but also enables continuous and complete stripping of the film, reduces damage to the stripping interface, film shedding, etc., and effectively avoids chipping, fragmentation, etc., improves the yield, and effectively reduces the process cost, which is beneficial to the production and application of the process.

[0117] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a piezoelectric single crystal composite thin film material, characterized in that: The steps include: (1) Ion implantation of piezoelectric functional materials; (2) wet oxidation treatment of the support substrate surface, followed by cleaning and drying; (3) Activating the surface of the supporting substrate and the piezoelectric functional material using a mixed plasma of oxygen and nitrogen; (4) Pre-bonding and standing under low vacuum environment; (5) Nitrogen annealing, thinning, and stripping; Before use, the support substrate and the piezoelectric functional material are polished on one side and polished on both sides, and the root mean square roughness of the polished surfaces of the support substrate and the piezoelectric functional material are both less than 0.5 nm; The ion species of the ion implantation are one or more ion mixtures of H ions, He ions, and O ions; the ion implantation energy is 1-300 keV, and the implantation dose is 1×10 15 -1×10 18 / cm 2 ; The process conditions of the wet oxidation treatment are as follows: the mixing ratio of concentrated oxidizing ammonia solution is NH4OH:H2O2:H2O=3-6:1-3:3, the oxidation time is 1-120min, and the process temperature is ≤65°C; The process conditions of the activation treatment are as follows: the vacuum degree of the plasma activation chamber is 1×10 -5 -1Pa, the oxygen plasma gas flow rate is 100-500sccm, the nitrogen plasma gas flow rate is 100-500sccm, the plasma emitter upper frequency power is 40-80W, the lower frequency power is 10-50W, and the process time is 15-90s; The supporting substrate is one or more composite substrates of Si and SiC; the piezoelectric functional material is one of crystal materials of LiNbO3 and LiTaO3.

2. The method for preparing a piezoelectric single crystal composite thin film material according to claim 1, characterized in that: Before use, the support substrate and the piezoelectric functional material are polished on one side, with a thickness of 50-1000 μm and a size of 3-12 inches, and the piezoelectric functional material is polished on both sides, with a thickness of 50-1000 μm and a size of 3-12 inches.

3. The method for preparing a piezoelectric single crystal composite thin film material according to claim 1, characterized in that: The piezoelectric functional material and the supporting substrate were cleaned with acetone, RCA-1 standard solution, and deionized water in sequence before use and then dried with nitrogen.

4. The method for preparing a piezoelectric single crystal composite thin film material according to claim 1, characterized in that: The process conditions of the pre-bonding are: vacuum degree is 1×10 -5 -1Pa, process temperature is 10-50℃, process time is 1-120s, pre-bonding pressure is 0-20kN, and it is left to stand for 8-10h.

5. The method for preparing a piezoelectric single crystal composite thin film material according to claim 1, characterized in that: The process conditions of the nitrogen annealing are as follows: a nitrogen flow rate of 1-2 L / min, an annealing temperature of 100-150° C., and the temperature is maintained for 1-50 hours after reaching the preset annealing temperature.

6. The method for preparing a piezoelectric single crystal composite thin film material according to claim 1, characterized in that: The process conditions for the stripping are as follows: a nitrogen flow rate of 1-2 L / min, a stripping temperature of 100-300° C., and the temperature is maintained at a preset annealing temperature for 10-50 hours.

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