Preparation method of piezoelectric single crystal composite film material

Abstract

The invention 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 of: carrying out ion implantation on a piezoelectric functional material, carrying out wet oxidation treatment on the surface of a support substrate, and then cleaning and blow-drying to obtain the piezoelectric single crystal composite film material. Oxygen and nitrogen mixed plasma is used for activating the surfaces of a supporting substrate and a piezoelectric functional material, pre-bonding, standing, nitrogen annealing, thinning and stripping are carried out in a low-vacuum environment, the preparation method is simple in process and low in cost, and the composite film prepared through the method is high in bonding strength, free of damage to a stripping interface and good in bonding performance. And meanwhile, cracking and fragmentation are effectively avoided, the yield is effectively improved, and industrial production is facilitated.

Description

Technical Field

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

[0002] As an indispensable part of the mobile communication radio frequency front end, with the rapid development of 5G communication technology and the Internet of Things, the requirements for core indicators of radio frequency acoustic filters such as operating frequency, rectangularity, out-of-band rejection, bandwidth, volume, power, and temperature stability are constantly increasing. Microacoustic devices based on bulk single crystal piezoelectric functional materials have problems such as low energy conversion efficiency, low operating frequency, poor temperature stability, and large volume, and cannot meet the application requirements of complex environments and the future development of device miniaturization and integration. There is an urgent need to achieve breakthrough research on high-performance piezoelectric functional materials.

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

[0004] The conventional method for preparing piezoelectric single crystal thin film composites is the smart peeling method. The smart peeling method combines ion implantation and wafer bonding processes. Although this method can prepare 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 will also occur, resulting in a reduction in the yield. At the same time, the process conditions for processes such as activation and pre-bonding are demanding and cumbersome, increasing costs and being unfavorable for industrial production. Summary of the Invention

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

[0006] The technical solution of the present invention is as follows:

[0007] A preparation method of a piezoelectric single crystal composite thin film material, comprising the following steps:

[0008] (1) Ion implantation is performed on a piezoelectric functional material;

[0009] (2) The surface of the support substrate is subjected to wet oxidation treatment, then washed with deionized water and dried with nitrogen gas.

[0010] (3) The surfaces of the support substrate and the piezoelectric functional material are activated using a mixed plasma of oxygen and nitrogen.

[0011] (4) Pre-bonding and standing are carried out in a low-vacuum environment.

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

[0013] In the present invention, ions are first implanted into the piezoelectric functional material to form a defect layer in the middle of the piezoelectric single crystal wafer, and wet oxidation treatment is performed on the surface of the support substrate; in a vacuum environment, the surfaces of the piezoelectric functional material and the oxidized support material are activated using a mixed plasma, and then the two wafers of the piezoelectric functional material and the support material are pre-bonded and allowed to stand in a low-vacuum environment, and then nitrogen annealing, thinning, and peeling are carried out to prepare a piezoelectric single crystal composite thin film material with good quality and a high yield.

[0014] Preferably, before use, the support substrate is single-sided polished, with a thickness of 50 - 1000 μm and a size of 3 - 12 inches, and the piezoelectric functional material is double-sided polished, with a thickness of 50 - 1000 μm and a size of 3 - 12 inches, so as to be reused after peeling, saving costs. The root mean square roughness of the polished surfaces of the support substrate and the piezoelectric functional material is less than 0.5 nm, ensuring sufficient contact between the bonding surfaces of the wafers.

[0015] Preferably, before use, the piezoelectric functional material and the support substrate are successively cleaned with acetone, RCA-1 standard solution, and deionized water and dried with nitrogen gas, which can effectively remove organic substances, oxides, and other surface contaminants and attached particles on the wafer surface. Further preferably, the piezoelectric functional material and the support substrate are placed on a cleaning table, the cleaning table rotates at a speed of 2500 - 3000 rpm, the deionized water rinsing time is 1 - 50 s, and the nitrogen gas drying time is 1 - 30 s.

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

[0017] Preferably, the ion species is one or a mixture of ions of any of the elements 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 reasonable selection of ion implantation energy and implantation dose is the prerequisite for achieving complete peeling. If the values are too large or too small, it is not conducive to peeling, and it will cause problems such as inability to peel, chip breakage, fragmentation, or significant damage to the peeling interface.

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

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

[0020] Preferably, the process conditions for pre-bonding are as follows: the vacuum degree is 1×10 -5 -1 Pa to prevent particle contamination, the process temperature is 10 - 50 °C, the process time is 1 - 120 s, the pre-bonding pressure is 0 - 20 kN, and it is left standing for 8 - 10 h. The moisture remaining at the bonding interface gradually drains completely over time, and the spontaneous bonding of the sample wafers gradually proceeds sufficiently. Spontaneous bonding is of great significance for increasing the bonding area of the wafers and reducing bonding defects, and it is the guarantee for achieving high-quality wafer bonding. Applying an appropriate pressure is beneficial for high-quality bonding. Excessive pressure will increase the cost and reduce the efficiency.

[0021] Preferably, the process conditions for nitrogen annealing are as follows: the nitrogen flow rate is 1-2 L / min, the annealing temperature is 100-150 °C, and after reaching the preset annealing temperature, it is held for 1-50 h. The thermal expansion coefficient of the Si wafer is quite different from that of the LiNbO3 wafer. If the annealing temperature is too high, problems such as chipping, fragmentation, warping, and debonding will occur, which will have a great impact on the bonding strength, the integrity of the structure, and the damage to the peeling interface.

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

[0023] Preferably, the nitrogen flow rate is 1-2 L / min, the peeling temperature is 100-300 °C, and it is held for 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 the stress release during the peeling process, improve the peeling success rate, reduce the damage to the peeling interface, and improve the yield.

[0025] The technical solution of the present invention is based on the characteristics of silicon wafers and piezoelectric single-crystal materials. By using the two processes of wet oxidation treatment and mixed plasma activation, the number of hydrophilic groups and other nitrogen-containing functional groups beneficial for pre-bonding on the surface of the silicon substrate is increased, thereby increasing the number of covalent bonds and improving the bonding strength. With the increase in bonding strength, film peeling is reduced, and the yield is effectively improved; after oxidation, a porous silicon oxide amorphous layer is formed on the surface of the wafer. The existence of this oxide layer enhances the atomic diffusion and structural reorganization ability of the bonding layer during the annealing process, further improving the bonding strength; after the two wafers are pre-bonded, annealing, thinning, and peeling are carried out. Based on the characteristics of silicon wafers and piezoelectric single-crystal materials, the thermal expansion coefficients of the two are quite different. Combining the process conditions of ion implantation and pre-bonding, the annealing and peeling methods of the present invention are finally determined. By using appropriate annealing and peeling temperatures and holding times, the problem of stress release concentration during annealing caused by the mismatch of thermal expansion coefficients between different materials is improved, and the occurrence probability of wafer warping and fragmentation and peeling damage is greatly reduced; by using this annealing and peeling method, the bonding strength is significantly improved, the integrity of the bonding structure is ensured, the damage to the peeling interface is reduced, the problems of chipping and fragmentation are avoided, and the yield is improved; combined with the thinning process, the stress release during peeling is reduced, which is beneficial for complete and damage-free peeling, and reduces warping, improving the yield; through the method of the present invention, a composite film with low warping, high yield, and high bonding force is finally obtained, and the damage to the peeling interface is small.

[0026] The present invention provides a novel method for heterogeneous wafer bonding and peeling. The surface activation treatment of the support substrate and the piezoelectric functional layer material after ion implantation is carried out by two-step processes of wet oxidation and mixed plasma activation. Then, the above two wafers are pre-bonded in a vacuum environment. Finally, the pre-bonded wafer is subjected to nitrogen annealing, thinning, and peeling to complete the preparation of the material. This method is applicable to the bonding between support substrates such as silicon and silicon carbide with large differences in thermal expansion coefficients and low bonding energies, 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 of a piezoelectric single-crystal composite film material, which combines the ion implantation and wafer bonding processes by using the intelligent peeling method, optimizes the ion implantation process, cooperates with the wet oxidation and mixed plasma activation processes, and adopts appropriate annealing methods, thinning processes, and peeling methods, so as to improve the problems such as low bonding strength and low yield between different materials, greatly reduce the occurrence probability of wafer warpage and fragmentation, and the damage of the peeling interface, not only improve the bonding strength, but also enable the continuous and complete peeling of the film, reduce the damage of the peeling interface, film shedding, etc., and effectively avoid chipping, fragmentation, etc., improve the yield, and effectively reduce the process cost, which is beneficial to the production and application of the process. Brief Description of the Drawings

[0028] Figure 1 It is a schematic structural diagram of a piezoelectric functional material and a support substrate;

[0029] Figure 2 It is a schematic structural diagram of the piezoelectric functional material after ion implantation;

[0030] Figure 3 It is a schematic structural diagram of the support substrate after wet oxidation treatment;

[0031] Figure 4 It is a schematic structural diagram of the bonded composite material;

[0032] Figure 5 It is a schematic structural diagram of the thinned composite material;

[0033] Figure 6 It is a schematic structural diagram of the peeled product;

[0034] Figure 7 It is a peeling interface diagram in Example 1;

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

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

[0037] Figure 10 Schematic diagram of the structure of the material after nitrogen annealing in Comparative Example 4;

[0038] Figure 11 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 implantation layer, 1-3 is a thin film layer, 2 is a support substrate, and 2-1 is an oxide layer. Specific embodiments

[0040] In order to more clearly illustrate the overall concept of the present invention, the following will be described in detail by way of examples. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0041] The specific technical solution of the present invention is as follows:

[0042] A preparation method of a piezoelectric single crystal composite thin film material, the process flow is as Figure 11 shown, including the following steps:

[0043] (1) Ion implantation is performed on the piezoelectric functional material;

[0044] (2) The surface of the support substrate is subjected to wet oxidation treatment, then washed with deionized water and dried with nitrogen;

[0045] (3) The surfaces of the support substrate and the piezoelectric functional material are activated using a mixed plasma of oxygen and nitrogen;

[0046] (4) Pre-bonding and standing are performed in a low vacuum environment;

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

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

[0049] The ion species is an ion mixture of one or more of H ions, He ions, and O ions, and H ions and O ions, H ions and He ions, He ions and O ions, etc. can be selected; the ion implantation energy is 1-300 keV, specifically 30 keV, 50 keV, 80 keV, 100 keV, 150 keV, 200 keV, etc. can be selected, and the implantation dose is 1×10 15 -1×10 18 / cm 2 , specifically 1×10 15 / cm 2 、 1×10 17 / cm 2 、 1×10 18 / cm 2 etc. A reasonable selection of the ion implantation energy and the implantation dose is a prerequisite for achieving complete peeling. If the value is too large or too small, it is not conducive to peeling, and it will cause effects such as inability to peel, chip breakage, fragmentation, or large damage to the peeling interface.

[0050] In the process of wet oxidation treatment, the mixing ratio of the strong oxidizing ammonia solution is NH4OH:H2O2:H2O = 3 - 6:1 - 3:3. Specifically, it can be selected as 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:H20 = 4:3:3, etc. The oxidation time is 1 - 120 min, and the process temperature ≤ 65°C. The process temperature 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 silicon wafer surface, and H2O2 forms a new and thicker oxide film on the silicon wafer surface, which is beneficial to increasing the number of hydroxyl groups on the wafer surface and improving the bonding force. At the same time, a porous silicon oxide amorphous layer is formed on the surface of the oxidized wafer. The existence of this oxide layer strengthens the atomic diffusion and structural recombination ability of the bonding layer during the annealing process, further improving the bonding strength, reducing film peeling, and increasing the yield. Compared with the conventional methods for preparing oxide layers such as chemical vapor deposition and magnetron sputtering, the process used in the present invention is more concise, reducing the process cost.

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

[0052] Process conditions for pre-bonding: The vacuum degree is 1×10 -5-1 Pa to prevent particle contamination, process temperature is 10 - 50 °C, specifically, 10 °C, 20 °C, 23 °C, 25 °C, 30 °C, 40 °C, 50 °C, etc. can be selected; process time is 1 - 120 s, pre-bonding pressure is 0 - 20 kN, specifically, 0 kN, 5 kN, 10 kN, 15 kN, 20 kN, etc. can be selected; leave it standing for 8 - 10 h, specifically, 8 h, 9 h, 10 h, etc. can be selected; the residual moisture at the bonding interface is gradually and completely discharged with the increase of time, and the spontaneous bonding of the sample wafer gradually proceeds sufficiently. Spontaneous bonding is of great significance for increasing the wafer bonding area and reducing bonding defects, and is the guarantee for achieving high-quality wafer bonding. Applying appropriate pressure is beneficial to high-quality bonding. Excessive pressure will increase the cost and reduce the efficiency, and the impact is also relatively small.

[0053] Process conditions for nitrogen annealing: nitrogen gas flow rate is 1 - 2 L / min, annealing temperature is 100 - 150 °C, and keep the temperature for 1 - 50 h after reaching the preset annealing temperature; the thermal expansion coefficient of the Si wafer is quite different from that of the LiNbO3 wafer. Excessive annealing temperature will cause problems such as wafer breakage, fragmentation, warping, and debonding, which will have a greater impact on the bonding strength, structural integrity, and damage to the peeling interface.

[0054] Before using the support substrate and the piezoelectric functional material, the support substrate is single-sided polished, with a thickness of 50 - 1000 μm and a size of 3 - 12 inches; the piezoelectric functional material is double-sided polished, with a thickness of 50 - 1000 μm and a size of 3 - 12 inches, so as to be reused after peeling and save costs. The root mean square roughness of the polished surfaces of both the support substrate and the piezoelectric functional material is less than 0.5 nm, ensuring that the bonding surfaces between the wafers can be in full contact.

[0055] The support substrate is one or more composite substrates of Si, SiC, etc.; the piezoelectric functional material is one of the crystal materials of LiNbO3, LiTaO3.

[0056] Process conditions for peeling: nitrogen gas flow rate is 1 - 2 L / min, peeling temperature is 100 - 300 °C, and keep the temperature for 10 - 50 h.

[0057] After nitrogen annealing, thin the piezoelectric functional material to 200 - 350 μm, specifically, 200 μm, 250 μm, 300 μm, 330 μm, 350 μm can be selected.

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

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

[0060] The qualified product standards are as follows: the product has no warpage (Warp < 65μm, bow < 55μm), no fragments, no scratches, no cracks (i.e., large interfacial damage), no film peeling, etc., and the film thickness range of the thin film layer of the piezoelectric functional material is within 300 - 700nm.

[0061] Use the insertion method to test and record the bonding energy, and obtain the bonding energy (bonding strength) through testing.

[0062] Example 1

[0063] A preparation method of a piezoelectric single crystal composite thin film material, the specific steps are as Figure 11 shown:

[0064] Provide a 6-inch single crystal silicon as the support substrate 2, and a 6-inch lithium niobate wafer as the piezoelectric functional material 1, as Figure 1 shown; the thickness of the single crystal silicon substrate is 625μm, and the thickness of the lithium niobate wafer is 500μm; the root mean square roughness of the polished surfaces of the single crystal silicon substrate and the lithium niobate wafer is less than 0.5nm, the single crystal silicon substrate is polished on one side, and the lithium niobate wafer is polished on both sides;

[0065] Put the two wafers to be bonded into a petri dish filled with acetone respectively, use a 30% acetone solution for ultrasonic cleaning for 30 minutes to remove wafer contaminants and attached particles, etc., then soak the two wafers in an RCA-1 standard solution in a water bath for 50 minutes to dissolve the organic matter and oxides on the wafer surface, and finally place the single crystal silicon substrate and the lithium niobate wafer on the cleaning table respectively. The cleaning table rotation speed is set to 3000rpm, use deionized water to clean the surface and dry it with nitrogen. The cleaning time of deionized water is 25s, and the nitrogen drying time is 5s;

[0066] Put the cleaned lithium niobate wafer into an ion implanter, inject hydrogen ions, the hydrogen ion implantation energy is 50keV, and the implantation dose is 1×10 17 / cm 2 , to form a thin film layer 1-3, an implanted layer 1-2 and a residual layer 1-1 on the lithium niobate wafer, as Figure 2 shown;

[0067] Next, put the single crystal silicon substrate into a strong oxidizing ammonia solution for wet oxidation treatment. The temperature is room temperature (23°C), and the ratio (volume ratio) of the strong oxidizing ammonia solution is NH4OH:H2O2:H20 = 6:1:3. The oxidation time is 45 minutes, and an oxide layer 2-1 thin film as Figure 3 shown is generated on the surface. Then send it to the cleaning table, use deionized water to clean and dry it with nitrogen. The cleaning table rotation speed is 3000rpm, the deionized water rinsing time is 25s, and the nitrogen drying time is 5s;

[0068] Place the wafer to be bonded into the activation chamber. After sealing and evacuating, use a mixed plasma of oxygen and nitrogen to activate the surface of the single-crystalline silicon substrate and the lithium niobate wafer. The vacuum degree of the plasma activation chamber is 1×10 -2 Pa. The gas flow rate of the oxygen plasma used is 100 sccm, the gas flow rate of the nitrogen plasma is 100 sccm, the upper-frequency power on the plasma emitter is 65 W, the lower-frequency power is 45 W, and the process time is 60 s;

[0069] Under the condition of room temperature (23 °C), after the activated silicon substrate and lithium niobate wafer are aligned on the alignment stage, they are sent into the bonding chamber. After evacuating, the two wafers are bonded together and a pressure of 10 kN is applied. The process time is 60 s to complete pre-bonding. As Figure 4 shown in is the state after pre-bonding of the two wafers. Let it stand for 8 h. The moisture remaining at the bonding interface gradually drains out completely over time, and the spontaneous bonding of the sample gradually proceeds sufficiently;

[0070] After standing, perform annealing treatment. The annealing temperature is 130 °C, the heating rate is 0.5 °C / min, the nitrogen gas flow rate is 2 L / min, eliminate the interface stress, remove water molecules, improve the bonding strength, hold at the preset annealing temperature for 20 h, and the cooling rate is 0.5 °C, cool down until room temperature. The state of the annealed material has no warping, as shown in 9;

[0071] Thinning process: The piezoelectric functional material is thinned to 300 μm, as Figure 5 shown, reduce stress release to improve the peeling success rate;

[0072] Peeling process: After thinning, the nitrogen gas flow rate is 2 L / min, heat up, the heating rate is 0.5 °C / min, reach 200 °C and hold for 20 h, and the cooling rate is 0.5 °C / min, cool down until room temperature;

[0073] Peeling is completed, as Figure 6 shown. The interface after peeling has no damage (no cracks), as Figure 7 shown (view under the microscope). The lithium niobate piezoelectric functional material after peeling can be reused.

[0074] The bonding energy measured is 1.81 J / m 2 , and the yield is 90.3%.

[0075] Example 2

[0076] A preparation method of a piezoelectric single-crystal composite thin film material:

[0077] Provide a 4-inch single-crystalline silicon as the support substrate 2 and a 4-inch lithium tantalate wafer as the 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 both 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] Put the two wafers to be bonded into a petri dish filled with acetone respectively, and use a 10% acetone solution for ultrasonic cleaning for 30 min to remove the contaminants and attached particles on the wafer surface. Subsequently, soak the two wafers in an RCA-1 standard solution in a water bath for 50 min to dissolve the organic substances and oxides on the wafer surface. Finally, place the single-crystalline silicon substrate and the lithium tantalate wafer on the cleaning table respectively. Set the rotation speed of the cleaning table to 3000 rpm, clean the surface with deionized water and dry it with nitrogen. The cleaning time of the deionized water is 25 s, and the nitrogen drying time is 5 s;

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

[0080] Next, put the single-crystalline silicon substrate into a strong oxidizing ammonia solution for oxidation treatment at room temperature. The ratio of the strong oxidizing ammonia solution is NH4OH:H2O2:H20 = 4:3:3, and the oxidation time is 45 min. An oxide layer 2-1 thin film is formed on the surface. Then, send it to the cleaning table, clean it with deionized water and dry it with nitrogen. The rotation speed of the cleaning table is 3000 rpm, the deionized water rinsing time is 25 s, and the nitrogen drying time is 5 s;

[0081] Put the wafers to be bonded into the activation chamber. After sealing and evacuating, use a mixed plasma of oxygen and nitrogen to activate the surfaces of the single-crystalline silicon substrate and the lithium niobate wafer. The vacuum degree of the plasma activation chamber is 1×10 -2 Pa, the gas flow rate of the oxygen plasma used is 100 sccm, the gas flow rate of the nitrogen plasma is 100 sccm, the upper frequency power on the plasma emitter is 65 W, the lower frequency power is 45 W, and the process time is 60 s;

[0082] Under the condition of room temperature (23 °C), after the activated silicon substrate and the lithium tantalate wafer are aligned on the alignment table, they are sent into the bonding chamber. After evacuating, the two wafers are bonded together and a pressure of 0 kN is applied. The process time is 60 s to complete the pre-bonding. For the state after the pre-bonding of the two wafers, let it stand for 8 h;

[0083] After standing still, annealing treatment is carried out. The annealing temperature is 128 °C, the heating rate is 0.5 °C / min, the nitrogen gas flow rate is 2 L / min, the interfacial stress is eliminated, water molecules are removed, the bonding strength is improved, and it is kept at the preset annealing temperature for 20 h. The cooling rate is 0.5 °C until it cools down to room temperature;

[0084] Thinning process: The piezoelectric functional material is thinned to 300 μm to reduce stress release and improve the peeling success rate;

[0085] Peeling process: After thinning, the nitrogen gas flow rate is 2 L / min, heating is carried out, the heating rate is 0.5 °C / min, it is kept at 200 °C for 20 h, and the cooling rate is 0.5 °C / min until it cools down to room temperature;

[0086] The peeling is completed.

[0087] The bonding energy measured by testing is 1.78 J / m 2 , and the yield is 90%.

[0088] Example 3

[0089] A preparation method of 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 still, annealing treatment is carried out. The annealing temperature is 125 °C, the heating rate is 0.5 °C / min, the nitrogen gas flow rate is 2 L / min, the interfacial stress is eliminated, water molecules are removed, the bonding strength is improved, and it is kept at the preset annealing temperature for 20 h. The cooling rate is 0.5 °C until it cools down to room temperature;

[0092] Thinning process: The piezoelectric functional material is thinned to 330 μm to reduce stress release and improve the peeling success rate;

[0093] Peeling process: After thinning, the nitrogen gas flow rate is 2 L / min, heating is carried out, the heating rate is 0.5 °C / min, it is kept at 210 °C for 20 h, and the cooling rate is 0.5 °C / min until it cools down to room temperature;

[0094] The peeling is completed.

[0095] The bonding energy measured by testing is 1.74 J / m 2 ; the yield is 88.5%.

[0096] Comparative Example 1

[0097] A preparation method of 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] Single N2 plasma activation: Place the product to be bonded into the activation chamber. After sealing and evacuating, use a single nitrogen plasma to perform surface activation on the single-crystalline silicon substrate and the lithium niobate wafer. The vacuum degree of the plasma activation chamber is 1×10 -2 Pa. The gas flow rate of the nitrogen plasma used is 200 sccm. The upper frequency power on the plasma emitter is 65 W, the lower frequency power is 45 W, and the process time is 60 s.

[0100] The measured bonding energy is 1.46 J / m 2 ; The yield is 78.8%; There are cracks (relatively large damage) at the peeling interface of the unqualified products in the finally obtained products, as Figure 8 shown (view under the microscope).

[0101] Comparative Example 2

[0102] A preparation method of a piezoelectric single crystal composite thin film material:

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

[0104] The specific activation process is as follows: Place the wafer to be bonded into the activation chamber. After sealing and evacuating, use a mixed plasma of oxygen and carbon tetrafluoride to perform surface activation on the single-crystalline silicon substrate and the lithium niobate wafer. The vacuum degree of the plasma activation chamber is 1×10 -2 Pa. The gas flow rate of the oxygen plasma used is 100 sccm, the gas flow rate of the carbon tetrafluoride plasma is 100 sccm. The upper frequency power on the plasma emitter is 65 W, the lower frequency power is 45 W, and the process time is 60 s.

[0105] The measured bonding energy is 1.69 J / m 2 , and the yield is 85.1%.

[0106] Comparative Example 3

[0107] A preparation method of 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 are the same as those in Example 1;

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

[0110] Comparative Example 4

[0111] A preparation method of a piezoelectric single crystal composite thin film material:

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

[0113] After standing still, annealing treatment is carried out. The annealing temperature is 160 °C, the heating rate is 0.5 °C / min, the nitrogen gas flow rate is 2 L / min. When the preset annealing temperature is reached, keep warm for 20 h, and the cooling rate is 0.5 °C until the temperature drops to room temperature.

[0114] After annealing, the bonded substrates show different degrees of warping and debonding. Some of the warping is as Figure 10 shown, and the phenomenon of premature peeling of lithium niobate occurs.

[0115] By comparing the above-mentioned examples and comparative examples, in Comparative Examples 1 and 2, plasmas different from those in the examples are used, and their bonding energies and yields are significantly lower than those in the examples. It can be seen that a single plasma and a hybrid plasma different from the present invention are difficult to improve the bonding energy and yield; in Comparative Example 3, the wet oxidation process is omitted compared with Example 1, and the final prepared quality is poor and the yield is not good. The implementation of the wet oxidation process also plays an important role in the present invention. The low yields of Comparative Examples 1-3 are mainly due to the low bonding energy, and cracks and peeling of the piezoelectric thin film are likely to occur during annealing and peeling; in Comparative Example 4, a nitrogen annealing process different from that in the example is used, and the bonded substrate shows warping and debonding, and the phenomenon of premature peeling of lithium niobate occurs, and the product cannot be effectively peeled off after bonding. The nitrogen annealing process conditions in the example provide a favorable guarantee for preparing a qualified composite thin film. In summary, compared with the products prepared in the comparative examples, the present invention has very obvious improvements in bonding energy and yield, which proves that the processes of the present invention cooperate with each other, and can prepare products with higher quality and higher yield, which is suitable for industrial production and cannot be achieved by the comparative examples.

[0116] A preparation method of a piezoelectric single crystal composite thin film material provided by the present invention combines ion implantation and wafer bonding processes by using an intelligent peeling method, optimizes the ion implantation process, cooperates with wet oxidation and hybrid plasma activation processes, and adopts appropriate annealing methods, thinning processes and peeling processes, so as to improve the problems of low bonding strength and low yield between heterogeneous materials, greatly reduce the occurrence probability of wafer warping and fragmentation and the damage of the peeling interface, not only improve the bonding strength, but also enable the film to be continuously and completely peeled off, reduce the damage of the peeling interface and film peeling, etc., and at the same time effectively avoid chip breakage, fragmentation, etc., improve the yield, and effectively reduce the process cost, which is beneficial to the production and application of the process.

[0117] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and retouches can be made, and these improvements and retouches should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a piezoelectric single crystal composite thin film material, characterized in that, It includes the following steps: (1) Ion implantation is carried out on the piezoelectric functional material; (2) The surface of the support substrate is subjected to wet oxidation treatment, and then cleaned and dried; (3) The surfaces of the support substrate and the piezoelectric functional material are activated using a mixed plasma of oxygen and nitrogen; (4) Pre-bonding and standing are carried out in a low-vacuum environment; (5) Nitrogen annealing, thinning, and peeling.

2. The preparation method of a piezoelectric single crystal composite thin film material according to claim 1, wherein, Before use, the support substrate is single-sided polished, with a thickness of 50 - 1000 μm and a size of 3 - 12 inches, and the piezoelectric functional material is double-sided polished, with a thickness of 50 - 1000 μm and a size of 3 - 12 inches. The root mean square roughness of the polished surfaces of both the support substrate and the piezoelectric functional material is less than 0.5 nm.

3. The preparation method of a piezoelectric single crystal composite thin film material according to claim 1, characterized in that, Before use, the piezoelectric functional material and the support substrate are successively cleaned with acetone, RCA-1 standard solution, and deionized water and dried with nitrogen.

4. The preparation method of a piezoelectric single crystal composite thin film material according to claim 1, wherein, The ion species for the ion implantation are ions 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 2 .

5. The preparation method of a piezoelectric single crystal composite thin film material according to claim 1, characterized in that, The process conditions for the wet oxidation treatment: the mixing ratio of the strong oxidizing ammonia solution is NH4OH:H2O2:H2O = 3 - 6:1 - 3:3, the oxidation time is 1 - 120 min, and the process temperature ≤ 65 °C.

6. The preparation method of a piezoelectric single crystal composite thin film material according to claim 1, wherein, The process conditions for the activation treatment: the vacuum degree of the plasma activation chamber is 1×10 -5 -1 Pa, the flow rate of the oxygen plasma gas used is 100 - 500 sccm, the flow rate of the nitrogen plasma gas is 100 - 500 sccm, the upper frequency power on the plasma emitter is 40 - 80 W, the lower frequency power is 10 - 50 W, and the process time is 15 - 90 s.

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

8. The preparation method of a piezoelectric single crystal composite thin film material according to claim 1, characterized in that, The process conditions for the nitrogen annealing: the nitrogen gas flow rate is 1 - 2 L / min, the annealing temperature is 100 - 150 °C, and it is kept at the preset annealing temperature for 1 - 50 h.

9. The preparation method of a piezoelectric single crystal composite thin film material according to claim 1, characterized in that, The process conditions for the peeling: the nitrogen gas flow rate is 1 - 2 L / min, the peeling temperature is 100 - 300 °C, and it is kept at the preset annealing temperature for 10 - 50 h.

10. The preparation method of a piezoelectric single crystal composite thin film material according to claim 1, wherein, The support substrate is one or more composite substrates of Si, SiC; the piezoelectric functional material is one of the crystal materials of LiNbO3, LiTaO3.

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