CN117597008A - A method for improving warpage of injected wafer and piezoelectric single crystal film and preparation method thereof - Google Patents

Abstract

The invention provides a method for improving warpage of an implanted wafer, a piezoelectric monocrystalline film and a preparation method thereof. By adopting the technical scheme of the invention, the piezoelectric wafer is bonded with the supporting substrate in advance to obtain the rigid bonding structure, so that the non-uniform thermal expansion of the piezoelectric wafer can be effectively restrained, the wafer warping problem caused in the ion implantation process is greatly improved, and the yield of the piezoelectric monocrystalline film is improved.

Description

A method for improving warpage of injected wafer and piezoelectric single crystal film and preparation method thereof

Technical field

The invention relates to the technical field of electronic information materials, and specifically relates to a method for improving the warpage of an injected wafer and a piezoelectric single crystal film and a preparation method thereof.

Background technique

With the rapid development of mobile communication technology and the comprehensive deployment of 5G wireless communication networks, higher performance requirements have been put forward for RF front-end modules. As the core module of the RF front-end, filters are also developing towards high frequency, large bandwidth, low loss and good temperature stability. There are two main types of RF filters: surface acoustic wave filters and bulk acoustic wave filters. However, traditional acoustic filters based on lithium niobate and lithium tantalate single crystal materials cannot have both the above performance characteristics and are difficult to meet the needs of new 5G communication technologies. . In recent years, high-performance RF filters based on piezoelectric single crystal films have received widespread attention in the industry. The underlying support substrate usually has a higher sound speed and can achieve a waveguide effect, thus limiting the dissipation of sound wave energy and improving the quality factor. At the same time, the unique properties of each layer of material can optimize device service performance.

Ion beam lift-off is currently one of the commonly used methods to obtain high-quality piezoelectric single crystal films. This preparation technology mainly includes steps such as ion implantation, bonding and thermal lift-off. For example, Chinese invention patent CN111883648A discloses a method for preparing a piezoelectric film, a piezoelectric film and a bandpass filter, including obtaining multiple piezoelectric wafers and multiple preset substrate wafers; Perform ion implantation to obtain multiple ion-implanted piezoelectric wafers; the multiple ion-implanted piezoelectric wafers have an ion implantation damage layer; combine the multiple ion-implanted piezoelectric wafers with multiple preset linings The bottom wafer is bonded to obtain multiple bonded wafers; the multiple bonded wafers are annealed. During the annealing process, the in-plane stress of the multiple bonded wafers is controlled to adjust the multiple bonded wafers. The peeling thickness of the wafer at the corresponding ion implantation damaged layer results in multiple piezoelectric films. This method can reduce the deviation between different wafer glass thicknesses. However, during the operation, due to the anisotropy of the piezoelectric material and thermal stress generated during the ion implantation process, the piezoelectric wafer will warp after implantation. , causing adverse effects on subsequent processes and reducing production yield.

In view of this, it is necessary to improve the existing technology to solve the technical problem of wafer warpage caused by ion implantation existing in the existing technology.

Contents of the invention

In view of this, in order to solve the above problems, the present invention provides a method for improving the warpage of the injected wafer and a piezoelectric single crystal film and a preparation method thereof. The piezoelectric wafer is bonded to the supporting substrate in advance to obtain rigidity. The bonding structure can effectively suppress the uneven thermal expansion deformation of the piezoelectric wafer during the ion implantation process, greatly improve the wafer warpage problem faced in the process of preparing piezoelectric single crystal films, and improve the performance of piezoelectric single crystals. Film yield.

In order to achieve the above object, the present invention provides a method for improving the warpage of an implanted wafer. Specifically, the technical solution includes: sequentially crystallizing the piezoelectric wafer twice with a first support substrate and a second support substrate. Through circular bonding, a rigid composite bonding structure is obtained, which suppresses the thermal stress generated by the piezoelectric wafer during the ion implantation process.

Preferably, the first support substrate is made of at least one of sapphire, silicon, silicon carbide, quartz, diamond, gallium nitride, and gallium arsenide.

Preferably, the thermal conductivity of the first support substrate is greater than the thermal conductivity of the piezoelectric wafer.

Preferably, during the ion implantation process, the first support substrate uses its thermal conductivity to conduct away the heat generated on the surface of the piezoelectric wafer and weaken the thermal effect, and the first support substrate has rigid properties, Its stiffness properties can be used to suppress thermal deformation during temperature rise.

Further, in order to achieve another object, the present invention also provides a method for preparing a piezoelectric wafer based on the above technical solution. Specifically, it includes sequentially including the piezoelectric wafer and the first support liner. Bottom bonding-ion implantation to form a damaged layer-piezoelectric wafer bonded to the second supporting substrate-applying lateral mechanical external force to the first supporting substrate to cause the damaged layer to split and peel to obtain the Piezoelectric single crystal film.

Through the above technical solution, the impact of the wafer's internal stress on the piezoelectric wafer during the ion implantation and annealing processes is improved, and uneven thermal expansion deformation inside the wafer is avoided. The specific steps include

providing a piezoelectric wafer, the piezoelectric wafer including opposing first polished surfaces and second polished surfaces;

Provide a first support substrate, perform first wafer bonding on the first support substrate and the first polished surface to form a first bonding structure;

Perform ion implantation on the first bonding structure in a direction from the second polishing surface to the first polishing surface to form a damaged layer inside the piezoelectric wafer;

Provide a second support substrate, and perform a second wafer bonding of the first bonding structure and the second support substrate to form a second bonding structure;

The second bonding structure is annealed, and mechanical external force peeling is performed by applying a transverse mechanical external force to the first support substrate, causing it to split along the injected damaged layer, and then peeled off to obtain The piezoelectric single crystal film.

Preferably, the piezoelectric wafer and the first support substrate undergo a first wafer bonding, and the bonding method includes a polymer bonding method or a direct bonding method to obtain the rigid third piezoelectric wafer. One bond structure.

Preferably, the first bonding structure and the second support substrate undergo a second wafer bonding, and the bonding method adopts a direct bonding method.

Preferably, the polymer bonding method adhesively bonds the piezoelectric wafer to the first support substrate by introducing a polymer layer, and the polymer includes phenylpropylcyclobutene or polyimide. any kind.

Preferably, the direct bonding method includes directly bonding the piezoelectric wafer to the first support substrate or the first bonding structure to the second support substrate, and the bonding conditions include: The temperature range is 25~400℃, and the bonding pressure is 0~4000 mbar.

Preferably, the piezoelectric wafer is made of one or a combination of lithium niobate, lithium tantalate, quartz, lithium tetraborate, and lanthanum gallium silicate.

Preferably, the thickness of the piezoelectric wafer is 100~1000 µm.

Preferably, the material of the second support substrate is at least one of sapphire, silicon, silicon carbide, quartz, diamond, gallium nitride, and gallium arsenide.

Preferably, the thickness of the first support substrate is 100~1000 μm.

Preferably, the thickness of the second supporting substrate is 100~1000 μm.

Preferably, the ion species used in the ion implantation are one or more of hydrogen ions and helium ions.

Preferably, the energy range of the ion implantation is 15~500 keV, the dose of ion implantation is 1×10 ¹⁶ ~5×10 ¹⁷ ions/cm ² , and the injection time is determined according to the energy and dose of the injected ions.

Preferably, in the step of annealing the second bonding structure, the annealing temperature ranges from 80 to 500°C, the annealing time ranges from 1 to 8 hours, and the annealing atmosphere is vacuum, nitrogen or inert gas.

Preferably, the thickness of the piezoelectric single crystal film obtained by peeling is 0.1~5µm.

Preferably, the stripped remaining material is ground and polished, and then thinned to obtain a piezoelectric single crystal film with a thickness of 20 to 200 µm.

Piezoelectric materials, taking lithium niobate as an example, have a thermal expansion coefficient of c-axis of 2.7×10 ^-6 /K, and a and b-axis thermal expansion coefficients of 19.2×10 ^-6 /K. They are anisotropic, so When the ion beam lift-off process is used to prepare piezoelectric single crystal films, uncontrollable factors during the ion implantation process, such as implant uniformity, cooling methods and other factors, generate thermal stress, which causes warping and deformation of the piezoelectric wafer after ion implantation. problem arises. Adopting the above technical solution can greatly improve the problem of wafer warpage during the preparation process, thereby improving the yield of piezoelectric single crystal thin films.

Beneficial technical effects obtained by the present invention:

1. Adopting the technical solution of the present invention, by pre-bonding the piezoelectric wafer with the supporting substrate, a rigid bonding structure is obtained, which effectively suppresses the uneven thermal expansion and deformation of the piezoelectric wafer during the ion implantation process, and greatly improves the stability of the piezoelectric wafer. Improve the wafer warping problem faced in the process of preparing piezoelectric single crystal films and improve the yield of piezoelectric single crystal films.

2. Adopting the technical solution of the present invention, by using materials with high thermal conductivity such as silicon carbide as the supporting substrate, and utilizing its excellent thermal conductivity and large stiffness characteristics, the heat generated during the ion implantation process is conducted away in time, and It can effectively suppress the thermal deformation of the piezoelectric wafer during the temperature rise process, thereby reducing the voids and bubbles generated at the bonding interface during the bonding process, enhancing the bonding strength, and avoiding mechanical external force peeling at the bonding interface. Peeling occurs instead of peeling at the damaged layer, greatly improving the success rate of device structure preparation.

3. Adopting the technical solution of the present invention, on the basis of the existing technology, by introducing another supporting substrate and applying mechanical external force to the piezoelectric wafer, the method is different from the method of applying mechanical external force to the piezoelectric wafer in the prior art. Peeling off or direct peeling off without applying external force can easily lead to poor uniformity of single crystal film thickness and film fragmentation. Instead, by applying lateral mechanical external force to the first support substrate in the second bonding substrate, This can achieve better peeling while ensuring the uniformity of the single crystal film. In particular, it can effectively suppress the uneven thermal expansion deformation of the piezoelectric wafer during the ion implantation process, greatly improving the process of preparing piezoelectric single crystals. The problem of wafer warpage faced in the thin film process is improved to improve the yield of piezoelectric single crystal thin films.

4. Using the technical solution of the present invention, on the basis that the ion implantation energy and dose of the existing technology remain unchanged, the structure of the conventional implanted wafer is improved, and another supporting wafer is introduced for bonding to form a composite. The structure is then subjected to subsequent processes. Under the same thermal effect from the outside world, the thermal deformation is reduced, which improves the rigidity of the bonded structure and improves the success rate of subsequent device preparation.

5. By adopting the technical solution of the present invention, the peeled residual material can be recycled after relevant treatment, and can also be thinned to obtain a thicker piezoelectric single crystal film, which improves production efficiency.

Description of drawings

Figure 1 is a process flow chart of the piezoelectric single crystal thin film in the prior art of the present invention.

Figure 2 is a schematic structural flow diagram of preparing a piezoelectric single crystal film in the prior art of the present invention.

Figure 3 is a process flow chart for preparing a piezoelectric single crystal film according to the present invention.

Figure 4 is a schematic structural flow diagram of preparing a piezoelectric single crystal film according to the present invention.

Figure 5 is a schematic structural diagram of the supporting substrate material and piezoelectric wafer provided by the present invention.

Figure 6 is a schematic structural diagram of the first bonding structure of the present invention.

Figure 7 is a schematic diagram of the bonding structure in the ion implantation process of the present invention.

Figure 8 is a schematic structural diagram of the second bonding structure of the present invention.

Figure 9 is a schematic structural diagram of the piezoelectric single crystal film prepared by the present invention.

Figure 10a is a schematic diagram of the action of mechanical external force in the prior art.

Figure 10b is a schematic diagram of the action of mechanical external force in the present invention.

Figure 11a is a schematic flow chart of peeling off under the action of mechanical external force in the prior art.

Figure 11b is a schematic flow chart of peeling off under the action of mechanical external force in the present invention.

Figure 12 is a comparison chart of the deformation amount of simulated ion implantation at different temperatures in Example 1 and Comparative Example 1.

Figure 13 is a comparison chart of the deformation amount of simulated ion implantation at different temperatures in Example 1 and Example 3-4.

Figure 14 is a comparison chart of the deformation amount of simulated ion implantation at different temperatures in Example 2 and Comparative Example 4.

In the drawings, the corresponding numbers are: 1-piezoelectric wafer, 101-first polished surface, 102-second polished surface, 2-first support substrate, 3-second support substrate, 4-damage layer , 5-piezoelectric single crystal film.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments These are part of the embodiments of this application, but not all of them.

Referring to Figures 1 and 2, there is a process flow chart and a schematic structural diagram of a conventional method for preparing a piezoelectric single crystal film in the prior art, which specifically includes:

S1. Provide a piezoelectric wafer, including opposite first polished surfaces and second polished surfaces;

S2. Perform ion implantation on the first polished surface of the piezoelectric wafer to obtain the damaged layer;

S3. Provide a supporting substrate, and perform wafer bonding between the supporting substrate and the first polished surface or the second polished surface of the piezoelectric wafer to obtain a bonding structure;

S4. Anneal the bonded structure, split along the damaged layer, and peel off to obtain a piezoelectric single crystal film of a certain thickness, which is then peeled off.

Obviously, the existing technology usually uses a single-sided bonding method, which cannot avoid the wafer warpage generated during the ion implantation process, which affects the quality of the wafer film, as well as the bubbles and bubbles at the bonding interface caused by the wafer warpage. The voids make the strength of the bonding interface weak. During the peeling process, it is easy to peel along the bonding interface rather than along the damaged layer, which reduces the success rate of device structure preparation.

Based on this, the present invention provides a method for preparing a piezoelectric single crystal film, which reduces the generation of ion implantation by performing wafer bonding on two polished surfaces of the piezoelectric wafer and two support substrates respectively. Thermal stress weakens the thermal effect, improves the bonding strength, and obtains a stronger composite bonding structure. Through the peeling method of mechanical external force, a piezoelectric single crystal film is obtained.

Specifically, the above preparation method includes performing wafer bonding twice on the oppositely arranged first polished surface and the second polished surface of the piezoelectric wafer with the first support substrate and the second support substrate, respectively, to obtain a rigid The composite bonding structure suppresses the thermal stress generated by the piezoelectric wafer during the ion implantation process; wherein, the material of the first supporting substrate is sapphire, silicon, silicon carbide, quartz, diamond, gallium nitride, arsenide At least one of gallium makes the thermal conductivity of the first support substrate greater than the thermal conductivity of the piezoelectric wafer.

During the ion implantation process, the first support substrate uses its thermal conductivity to conduct away the heat generated on the surface of the piezoelectric wafer and weaken the thermal effect. At the same time, the large stiffness characteristics of the first support substrate are used to suppress the temperature rise process. Thermal deformation.

Refer to Figures 3 and 4, which are flow charts and structural schematic diagrams of the preparation method of the piezoelectric wafer film of the present invention. Specifically,

S1. Provide a piezoelectric wafer, which includes a first polished surface and a second polished surface arranged oppositely;

S2. Provide a first support substrate, and perform first wafer bonding on the first support substrate and the first polished surface to form a first bonding structure;

S3. Perform ion implantation into the first bonding structure, the injection direction is along the direction from the second polishing surface to the first polishing surface, and a damage layer with a preset depth is formed inside the piezoelectric wafer;

S4. Provide a second support substrate, and perform a second wafer bonding on the second polished surface and the second support substrate to form a second bonding structure;

S5. Perform annealing treatment on the second bonding structure, and perform external force peeling by applying lateral mechanical external force to the first support substrate, causing it to split along the injected damage layer, and then peeling off to obtain the piezoelectric unit. crystal film.

As one of the preferred embodiments, the first polishing surface can also be thinned in S1. Thinning methods include but are not limited to chemical mechanical polishing or etching of the piezoelectric wafer surface.

Specifically, the maximum depth of thinning is 10~500µm; after thinning the first polished surface, the piezoelectric wafer and the first support substrate are bonded for the first time. The thickness of the first bonding structure is 100~1500µm.

By thinning the first polished surface, not only the bonding strength can be ensured, but also bonding can be achieved with a thinner bonding structure thickness, which is more conducive to peeling in the S4 step; moreover, after the thinning process, Compared with the existing technology, a piezoelectric wafer with a thinner thickness can shorten the heat conduction path, which is more conducive to the first support substrate to conduct heat away from the surface of the piezoelectric wafer, better suppressing thermal effects, and avoiding The problem of wafer warpage caused by ion implantation.

Refer to Figures 5-9, which are structural diagrams of the S1-S5 process flow.

Referring to FIG. 5 , a piezoelectric wafer 1 , a first supporting substrate 2 and a second supporting substrate 3 are first provided, wherein the piezoelectric wafer 1 has a first polishing surface 101 and a second polishing surface 102 arranged oppositely.

Referring to FIG. 6 , the first supporting substrate 2 is bonded to the first polished surface 101 of the piezoelectric wafer 1 to form a first bonding structure.

Referring to FIG. 7 , ion implantation is performed on the second polished surface 102 of the piezoelectric wafer 1 to form a damaged layer 4 inside the piezoelectric wafer at a predetermined depth.

Referring to FIG. 8 , the second supporting substrate 3 is bonded to the surface of the second polished surface 102 to form a second bonding structure, thereby forming an overall composite bonding structure.

Referring to Figure 9, after the second bonding structure is annealed, a mechanical external force is applied to the first bonding structure (or the first bonding structure + the piezoelectric wafer) to cause splitting of the damaged layer 4 to obtain a structure with Piezoelectric single crystal film 5, the piezoelectric single crystal film has a piezoelectric wafer - a second supporting substrate.

After ion implantation is performed on the second polished surface of the first bonding structure, the second wafer bonding is continued to form a composite bonding structure. After peeling along the damaged layer, a piezoelectric single crystal film is obtained. After thinning the film after peeling, another piezoelectric single crystal film with different thicknesses can be obtained. That is, using the technical solution of the present invention, two piezoelectric single crystal films can be obtained. Piezoelectric single crystal films of different thicknesses greatly improve production efficiency.

The material of the first supporting substrate is preferably silicon carbide, which has excellent thermal conductivity and can promptly conduct away the heat generated by ion implantation during the ion implantation process in S3, thereby weakening the thermal effect of the piezoelectric wafer, and using silicon carbide to The large stiffness characteristics suppress thermal deformation during temperature rise, suppress wafer warpage to the greatest extent, and provide a flatter surface for the second wafer bonding of S4, which reduces the bonding cost during the second wafer bonding. Bubbles and cavities on the bonding interface during the bonding process can be avoided to avoid peeling off from the bonding interface rather than the damage layer during the S5 peeling process, and improve the success rate of piezoelectric wafer thin film preparation. Existing technologies usually use higher annealing temperatures to enhance the rigidity of the bonding interface structure. However, due to the large difference in thermal expansion coefficients between different materials, it becomes more difficult to peel off the damaged layer at higher temperatures. Therefore, by using The technical solution of the present invention, by selecting silicon carbide with excellent thermal conductivity as the supporting substrate, not only improves the problem of wafer warping caused during the ion implantation process, but also improves the strength of the bonding interface and avoids the problem of wafer warping during the peeling process. The problem of peeling from the bonding interface also increases the area of action of mechanical external force during the peeling process.

Further, refer to Figures 10a, 10b, 11a and 11b respectively, which are schematic diagrams of peeling off using mechanical external force in the prior art and the present invention respectively.

In the prior art, refer to Figure 10a, step 3 uses mechanical external force for mechanical peeling, which requires the application of mechanical external force along the lateral direction of the piezoelectric wafer, and its thickness depends on the thickness of the piezoelectric wafer; while in the present invention, refer to Figure 10b, Step 5 (⑥ in the figure) uses mechanical external force to mechanically peel off, which is to apply mechanical external force along the lateral direction of the first support substrate and the piezoelectric wafer, and its thickness depends on the thickness of the piezoelectric wafer.

Further, refer to Figure 11a, which shows the thickness acted upon by mechanical external force in the prior art, and is calculated as h ₁ ; refer to Figure 11b, which shows the thickness acted upon by mechanical external force in the present invention, calculated as h ₂ , where h ₂ is equal to h ₁ + The thickness of the first support substrate is obviously h ₂ >h ₁ . Using the technical solution of the present invention, the action area of the lateral mechanical external force is significantly larger than that of the prior art, so it is more conducive to mechanical peeling. Uniformity and accuracy of force. Obviously, by improving the bonding strength, the present invention is different from the prior art method of using mechanical external force to peel along the piezoelectric single crystal. It applies lateral mechanical external force to the support substrate and increases the area of action of the mechanical force, thus ensuring that Under the premise of uniformity of single crystal film, better peeling can be achieved.

The technical solution of the present invention will be described in detail below through specific examples.

Example 1

This embodiment provides a method for preparing a piezoelectric single crystal film. This method mainly solves the problem in the prior art that thermal stress is generated during the ion implantation process, causing the piezoelectric wafer to warp after implantation.

This embodiment provides a method for preparing a piezoelectric single crystal film. By introducing a first support substrate, stress constraints are applied to the piezoelectric single crystal wafer in the first bonding structure, thereby suppressing unevenness during the ion implantation process. Thermal expansion occurs.

Referring to flow chart 1, the preparation method in this embodiment includes the following steps:

Step 1: Provide a piezoelectric wafer 1, polish both sides of the piezoelectric wafer 1, and obtain a first polished surface and a second polished surface opposite to each other. As shown in Figure 2, in this embodiment, the piezoelectric wafer 1 has a first polished surface and a second polished surface. The material of circle 1 is lithium niobate (LN) as an example. Specifically, it is 128°Y-cut lithium niobate with a thickness of 300µm.

Step 2: Provide the first supporting substrate 2 and the second supporting substrate 3 respectively, as shown in Figure 3; in this embodiment, the material of the first supporting substrate 2 and the second supporting substrate 3 is silicon carbide, with a thickness of is 500µm.

The first polished surface 101 of the piezoelectric wafer 1 and the first support substrate 2 are wafer bonded using the direct bonding method to obtain the first bonding structure. The bonding temperature is 75°C and the bonding pressure is 1000 mbar. In this embodiment, the bonding structure is a combination of 128° Y-cut lithium niobate (piezoelectric wafer 1) and silicon carbide (first support substrate 2). The total thickness of the bonding structure is 800µm, and the upper layer is a piezoelectric wafer. .

Step 3: Perform ion implantation on the first bonding structure. The implantation direction is from the second polished surface to the first polished surface of the piezoelectric wafer 1 to form a damage layer 4 at a preset depth range inside the piezoelectric wafer 1, such as As shown in Figure 7; helium ions are selected for ion implantation, the injection energy is 300 keV, the dose of implanted ions is 1.5×10 ¹⁷ ions/cm ² , and the injection time is 6 hours.

Step 4: Provide the second supporting substrate 3 and perform wafer bonding with one side of the damaged layer 4 in the first bonding structure to obtain the second bonding structure, as shown in Figure 8. The bonding temperature is 75°C. , the bonding pressure is 1000 mbar, which can also be selected according to actual needs.

Step 5: perform annealing treatment on the second bonding structure to cause cleavage along the implanted damage layer 4, thereby peeling off the piezoelectric single crystal film 5 of a certain thickness, as shown in Figure 9. The annealing temperature is 250°C, the annealing time is 3 hours, and the annealing is performed in a nitrogen atmosphere. After the annealing is completed, the piezoelectric wafer is split along the damaged layer 4, thereby peeling off a certain thickness of the piezoelectric single crystal film. On the other hand, the stripped residue can be recycled after grinding, polishing, post-annealing and other treatments, or it can be thinned by chemical mechanical polishing to obtain a thicker piezoelectric single crystal film.

After polishing, thinning and other processes, the stripped remaining material can be recycled as the first bonding structure; it can also be thinned through chemical mechanical polishing to obtain a thicker piezoelectric single crystal film. Using the technical solution of the present invention, multiple piezoelectric single crystal films with different thicknesses can be obtained.

Example 2

The difference between this embodiment and Embodiment 1 is that in S2, the first bonding structure is obtained by using a polymer bonding method, and everything else is the same as Embodiment 1.

Step 2: Provide the first supporting substrate 2, which is made of silicon carbide and has a thickness of 500µm.

The first polished surface of the piezoelectric wafer 1 and the first supporting substrate 2 are wafer bonded using a polymer bonding method to obtain a first bonding structure. Specifically include,

In this embodiment, phenylpropylcyclobutene is selected as the polymer, the polymer is introduced between the first polished surface of the piezoelectric wafer and the first support substrate 2 , and the polymer is spin-coated on the first support substrate 2 The surface, as the intermediate layer, is pre-dried at 60°C after spin coating, and the drying time is 30 minutes; it is heated again to 250°C for bonding and solidification, and the curing time is 10 minutes; it is kept warm for 10 minutes, and then quickly cooled to room temperature, with a cooling speed of 20 ℃/min.

Example 3

The difference between this embodiment and Embodiment 1 is that sapphire (SAP) is used as the first supporting substrate, and other processes are the same to obtain a piezoelectric single crystal film with an LN/SiC structure (second bonding structure).

Example 4

The difference between this embodiment and Embodiment 1 is that silicon (Si) is selected as the first supporting substrate, and other processes are the same to obtain a piezoelectric single crystal film with an LN/SiC structure (second bonding structure).

Comparative example 1

The only difference between this comparative example and Embodiment 1 is that it does not include the first supporting substrate. That is, common methods in the prior art are used, as shown in Figure 2, to directly bond the supporting substrate to the surface of the piezoelectric wafer after ion implantation. bottom, and use mechanical external force to peel off. The process of bonding the supporting substrate is the same as that of the second bonding structure in Embodiment 1, and the process of ion implantation and mechanical external force peeling is also the same as that of Embodiment 1.

Comparative example 2

The difference between this comparative example and Comparative Example 1 is that no external mechanical force is applied, and the damaged layer formed by ion implantation is directly annealed and peeled off.

Comparative example 3

The difference between this comparative example and Example 2 is that the polymer bonding method adopts the existing process. After the polymer is spin-coated on the second polished surface of the piezoelectric wafer, it is heated to 60°C, pre-dried for 30 minutes, and then Raise the temperature to 200℃ for curing, the curing time is 60 minutes, and then cool down naturally to room temperature.

Comparative example 4

The difference between this comparative example and Embodiment 2 is that the first supporting substrate is not included, and other steps are the same as those in Embodiment 2.

Table 1 Thermal expansion coefficient and thermal conductivity of common piezoelectric wafers

Lithium tantalate (LiTaO ₃ ) Lithium niobate (LiNbO ₃ ) Thermal expansion coefficient (ppm/℃) {16.1,16.1,4.1} {15.4,15.9,7.6} Thermal conductivity (W/(m·K)) 4.4 4.2

Refer to Table 1 for the thermal expansion coefficient and thermal conductivity of commonly used piezoelectric wafers. Refer to Table 2 for the stiffness coefficient, thermal expansion coefficient and thermal conductivity of commonly used support substrates. As can be seen from Table 1 and Table 2, the thermal expansion coefficients of the piezoelectric wafer and the supporting substrate are quite different. Due to the anisotropy of different materials, the thermal effect during the ion implantation process can easily cause the piezoelectric wafer to warp. Generally, the dose and energy of ions determine the thickness and quality of the piezoelectric single crystal film. Therefore, optimized ion implantation conditions are generally selected during actual operations. Therefore, the present invention does not limit these conditions. Use state-of-the-art ion implant metering and energy.

Therefore, to improve the warpage of the piezoelectric wafer, it is necessary to conduct heat away in time while maintaining the same ion implantation conditions. In view of this, the present invention selects a heat transfer medium with better thermal conductivity to solve this problem. By using a material with high thermal conductivity as a supporting substrate, the present invention conducts heat away in time through its excellent thermal conductivity, weakens the thermal effect on the surface of the piezoelectric wafer, suppresses thermal deformation, and improves the structure of the piezoelectric wafer. , introducing a support substrate with a smaller thermal expansion coefficient and greater stiffness, and bonding to form a composite bonding structure to improve the overall rigidity and thermal deformation resistance.

Table 2 Stiffness constants, thermal expansion coefficients and thermal conductivities of commonly used support substrates

Sapphire (SAP) Silicon (Si) 4H type silicon carbide (4H-SiC) Stiffness coefficient (GPa) C ₁₁ =490.2C ₃₃ =490.2C ₄₄ =145.4C ₁₂ =165.4C ₁₃ =113C ₁₄ =-23.2 C ₁₁ =166C ₄₄ =79.6C ₁₂ =63.9 C ₁₁ =501C ₃₃ =553C ₄₄ =163C ₁₂ =111C ₁₃ =52 Thermal expansion coefficient (ppm/℃) {5.0,6.6} 2.7 {3.1,2.2} Thermal conductivity (W/(m·K)) 32.5 142 370

Referring again to Table 2, the thermal conductivities of the supporting substrate materials SiC, sapphire and silicon are listed in the table. They are much greater than the thermal conductivities of lithium niobate piezoelectric wafers (LN). From high to low thermal conductivity respectively SiC>Silicon>Sapphire, the thermal conductivity of SiC is higher than that of sapphire or silicon, and the thermal conductivity of sapphire is higher than that of piezoelectric wafers, while other substrate materials, such as quartz, diamond, gallium nitride, and gallium arsenide , its thermal conductivity is also significantly better than that of the piezoelectric wafer. In this embodiment, it is also possible to dissipate heat, improve overall rigidity and thermal deformation resistance, and suppress wafer warpage. Therefore, any substrate material with a thermal conductivity greater than that of the piezoelectric wafer can produce the above effects. As the most preferred embodiment, SiC is the best supporting substrate material.

Rigidity performance characterization of bonded structures:

Compare the deformation amount of the piezoelectric wafer simulated with ion implantation at different temperatures for the bonding structures of the comparative example and the embodiment. The specific method includes: using the thermal effect during simulated ion implantation (at different temperatures) to compare the bonding structure with the piezoelectric wafer. The deformation of the piezoelectric wafer is compared, and the rigidity of the bonding structure is characterized by the deformation of the piezoelectric wafer at different heating temperatures.

Referring to Figure 12, a comparison chart of the deformation amount of the piezoelectric wafer in the piezoelectric wafer film obtained in Example 1 and Comparative Example 1 respectively; Figure 13 shows the bonding structures of Example 1 and Examples 3-4 at different temperatures. The relative deformation comparison chart below. Among them, the bonding structure refers to the second bonding structure, that is, the bonding structure between the piezoelectric single crystal and the second supporting substrate. The final results obtained in Example 1, Examples 3-4 and Comparative Example 1 have the same bonding structure. Structured piezoelectric wafer films.

It can be seen from Figure 12 that when heated to the same temperature, the deformation amount of the bonding structure between silicon carbide and the piezoelectric wafer in Example 1 is significantly less than the deformation amount in Comparative Example 1; it can be seen from Figure 13 that the deformation amount of the bonding structure between silicon carbide and the piezoelectric wafer in Example 1 The deformation amount of the bonding structure between silicon carbide and the piezoelectric wafer of Example 1 is also significantly lower than that of the bonding structure obtained with other support substrate materials, indicating that the rigidity of the bonding structure of Example 1 is greater than that of the piezoelectric wafer. and other supporting substrate materials. Obviously, the higher the bonding strength, the better the stability of the composite bonding structure. When external thermal effects are input, the entire composite bonding structure can act as a more stable rigid whole to suppress thermal deformation; in other words, when external thermal effects are input, the entire composite bonding structure can suppress thermal deformation. During the ion implantation process, the bonding structure should have sufficient rigidity or a small thermal expansion coefficient to suppress the deformation during the implantation process.

Furthermore, the above results are consistent with the thermal conductivity results in Table 2, which shows that the use of supporting substrate materials with higher thermal conductivity and greater stiffness in the present invention can achieve lower deformation and better It effectively suppresses the occurrence of wafer warpage during the ion implantation process and obtains a flatter and higher-quality piezoelectric film.

Further, comparing Example 1 and Comparative Example 2, it is easy to cause unevenness in the thickness of the single crystal film without applying external force, and the probability of the film breaking during the peeling process is high. Obviously, this method The technical solution of adding a first support substrate in the invention can play an important role in the uniformity of the thickness of the prepared piezoelectric single crystal film and the yield rate of the product during the peeling process.

Refer to Figure 14, which is a comparison chart of the deformation amount of the bonding structures of Example 2 and Comparative Example 4. It can be seen from the figure that the results obtained by the polymer bonding method are the same as those obtained by the direct bonding method. When heated to the same temperature, the deformation amount of the bonded structure is much smaller than that of a single piezoelectric wafer.

Comparing Example 2 and Comparative Example 3, the bonding process adopted in this example significantly shortens the solidification time and cooling time compared with the bonding method in the prior art (Comparative Example 3), thus also shortening the piezoelectric The thermal effect time of the wafer and the heating time of the piezoelectric wafer are shortened, which can further suppress the deformation during the injection process and improve the product success rate and product quality.

Under the same external thermal effect (the same energy and metering of ion implantation), the composite bonding structure has greater rigidity, which reduces the thermal deformation compared to before improvement, thereby improving the success rate of subsequent processes; due to the overall rigidity and bonding The bonding strength is improved, and by preferentially bonding the first support substrate on the surface of the piezoelectric wafer, the area of action of mechanical external force is increased, which can greatly improve the yield of piezoelectric single crystal thin films.

Obviously, through the above analysis, the bonding method of the present invention has a more significant inhibitory effect on the deformation of the piezoelectric single crystal during the ion implantation process after adding the first supporting substrate.

In summary, based on the above analysis, the piezoelectric wafer will produce thermal effects during the ion implantation process. Due to the anisotropy of thermal expansion of the piezoelectric wafer, the piezoelectric wafer will undergo warping deformation. On the one hand, this warping deformation Affects the quality of the piezoelectric single crystal film; on the other hand, it also has a great impact on the strength of the bonding structure, which will make it difficult to peel off. This impact mainly includes: excessive warping deformation, which will cause the bonding structure to There are voids and bubbles in the bonding interface. Excessive number of voids and bubbles reduces the bonding strength of the bonding structure. As a result, during the peeling process, the bonding structure will first separate from the bonding interface with weaker bonding strength instead of damaging it. The layer structure is peeled off, thereby reducing the success rate of preparing the device structure. On the other hand, the traditional process usually selects a single-sided support substrate. When peeling off by mechanical external force peeling, the lateral mechanical external force needs to act on the piezoelectric wafer. Due to the limitation of the thickness of the piezoelectric wafer, The peeling process will cause a certain degree of damage to the in-plane thickness uniformity of the piezoelectric single crystal film, thereby affecting the quality of the piezoelectric single crystal film. Therefore, the present invention uses two support substrates, preferably silicon carbide as the substrate material, and utilizes the good thermal conductivity of silicon carbide to conduct away the heat generated during the ion implantation process in time, weaken the thermal effect, reduce the amount of thermal deformation, thereby avoiding The problem of wafer warpage caused by the ion implantation process.

Generally, the main cause of wafer warpage is the thermal stress generated during the ion implantation process, and the thermal stress is mainly related to the ion implantation energy and dose. However, in practical applications, in order to maintain the thickness of the piezoelectric single crystal film , the ion implantation energy and dose generally remain unchanged. Therefore, in order to improve the problem of wafer warpage caused by the ion implantation process, the present invention uses increased rigidity of the bonding structure or a smaller thermal expansion coefficient to suppress the deformation during the ion implantation process, by adding a first supporting substrate, and The ion implantation energy and dose are not changed, thereby ensuring the quality and thickness of the piezoelectric single crystal film. The structure of the conventional implanted wafer is improved, and another support wafer is introduced for bonding to form a composite structure for subsequent processes. Under the same thermal effect from the outside world, the composite structure has greater rigidity so that the thermal deformation is reduced compared with before improvement, thereby improving the success rate of subsequent processes.

The above are only preferred embodiments of the present invention, which do not limit the scope of the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any changes, modifications, substitutions, integrations, and parameter changes to these embodiments that are within the spirit and spirit of the present invention through conventional substitutions or can achieve the same functions without departing from the principles and spirit of the present invention shall fall within the scope of the present invention. into the protection scope of the present invention.

Claims (10)

1. A method for improving the warpage of an implanted wafer, which includes sequentially bonding the piezoelectric wafer twice with a first support substrate and a second support substrate to obtain a rigid structure and thermal deformation resistance. The composite bonding structure suppresses the thermal stress and thermal deformation generated by the piezoelectric wafer during the ion implantation process; The material of the first supporting substrate is at least one of sapphire, silicon, silicon carbide, quartz, diamond, gallium nitride, and gallium arsenide; the thermal conductivity of the first supporting substrate is greater than that of the piezoelectric Thermal conductivity of the wafer; During the ion implantation process, the first support substrate uses its thermal conductivity to conduct away the heat generated on the surface of the piezoelectric wafer, weakening the thermal effect, and the first support substrate has rigid properties and can utilize its Stiffness properties suppress thermal deformation during temperature increases. 2. A method for preparing a piezoelectric single crystal film, characterized in that the method for improving the warpage of the injected wafer as claimed in claim 1 is applied to the preparation of the piezoelectric single crystal film; the preparation steps include: The electric wafer is bonded to the first supporting substrate - the damaged layer is formed by ion implantation - the piezoelectric wafer is bonded to the second supporting substrate - a transverse mechanical external force is applied to the first supporting substrate to cause the damaged layer Cleavage occurs and the piezoelectric single crystal film is peeled off. 3. The preparation method of piezoelectric single crystal thin film according to claim 2, characterized in that the specific steps include: providing a piezoelectric wafer, the piezoelectric wafer including opposing first polished surfaces and second polished surfaces; Provide a first support substrate, perform first wafer bonding on the first support substrate and the first polished surface to form a first bonding structure; Perform ion implantation on the first bonding structure in a direction from the second polishing surface to the first polishing surface to form a damaged layer inside the piezoelectric wafer; Provide a second support substrate, and perform a second wafer bonding on the second polished surface and the second support substrate to form a second bonding structure; The second bonding structure is annealed, and the external force is peeled off by applying a transverse mechanical external force to the first support substrate, causing it to split along the damaged layer, and the piezoelectric layer is peeled off to obtain the piezoelectric layer. Single crystal film. 4. The method for preparing a piezoelectric single crystal film according to claim 3, characterized in that the piezoelectric wafer and the first support substrate are bonded for the first time, and the first time Wafer bonding adopts polymer bonding method and/or direct bonding method to obtain the first bonding structure with rigidity; the first bonding structure and the second support substrate perform a second wafer bonding The second wafer bonding adopts direct bonding method. 5. The method for preparing a piezoelectric single crystal film according to claim 4, wherein the polymer bonding method bonds the piezoelectric wafer to the first support substrate by introducing a polymer layer. Bonding, the polymer includes any one of phenylpropylcyclobutene or polyimide; And/or, the polymer bonding method includes first preheating the polymer layer and then raising the temperature to a temperature higher than the curing temperature of the polymer, then bonding and solidifying, and then rapidly cooling to room temperature through heat preservation; And/or, the polymer includes phenylpropylcyclobutene; the bonding and curing temperature is 250~300°C, the curing time is 10~20min; the heat preservation time is 5~15min; the rapid cooling rate is 15 ~30℃/min; And/or, the direct bonding method includes directly bonding the piezoelectric wafer to the first support substrate or the first bonding structure to the second support substrate, and the bonding conditions include temperature The range is 25~400℃, and the bonding pressure is 0~4000mbar. 6. The method for preparing a piezoelectric single crystal film according to claim 3, wherein the material of the piezoelectric wafer is lithium niobate, lithium tantalate, quartz, lithium tetraborate, or gallium lanthanum silicate. one or a combination of more; And/or, the thickness of the piezoelectric wafer is 100~1000 μm; And/or, the material of the second support substrate is one of sapphire, silicon, silicon carbide, quartz, diamond, gallium nitride, and gallium arsenide; And/or, the thickness of the first supporting substrate is 100~1000 μm; And/or, the thickness of the second supporting substrate is 100~1000 μm. 7. The method for preparing a piezoelectric single crystal film according to claim 3, wherein the ion type used in the ion implantation is hydrogen ions or helium ions; And/or, the energy range of the ion implantation is 15~500 keV, and the dose of ion implantation is 1×10 ¹⁶ ~5×10 ¹⁷ ions/cm ² . 8. The method for preparing a piezoelectric single crystal film according to claim 7, wherein in the step of annealing the second bonding structure, the annealing temperature range is 80~500°C, and the annealing time is 1 Between ~8 hours, the annealing atmosphere is vacuum, nitrogen or inert gas. 9. The method for preparing a piezoelectric single crystal film according to any one of claims 2 to 8, characterized in that the thickness of the piezoelectric single crystal film obtained by peeling is 0.1~5 μm; And/or, the remaining material after stripping is ground and polished, and then thinned to obtain a piezoelectric single crystal film with a thickness of 20 to 200 μm. 10. A piezoelectric single crystal film prepared by the preparation method according to any one of claims 2 to 9.