Non-uniformly polarized piezoelectric single crystal film and preparation method thereof

Abstract

The invention provides a non-uniformly polarized piezoelectric single crystal film and a preparation method thereof, and relates to the technical field of functional semiconductor materials. The method comprises the following steps: preparing a plurality of piezoelectric single crystal wafers, formal substrates and a plurality of temporary substrates, performing ion implantation on bonding surfaces of the piezoelectric single crystal wafers to obtain the piezoelectric single crystal wafers subjected to ion implantation, bonding the piezoelectric single crystal wafers with the formal substrates and the temporary substrates to obtain a first formal bonding wafer and a first temporary bonding wafer, and then performing annealing stripping to obtain a second formal bonding wafer and a second temporary bonding wafer; and the first formal stripping sheet and the first temporary stripping sheet are bonded and de-bonded in sequence to obtain the non-uniformly polarized piezoelectric single crystal film. According to the method, each layer of piezoelectric single crystal film only needs to be subjected to one-time annealing stripping temperature, serious warping of the wafer is avoided, and the preparation stability and the film quality of the non-uniformly polarized piezoelectric single crystal film are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of functional semiconductor materials, and more specifically, to a non-uniformly polarized piezoelectric single crystal thin film and a preparation method thereof. Background Art

[0002] Piezoelectric single crystal thin film materials such as lithium niobate have extensive applications in acoustics and optics due to their excellent properties. In a piezoelectric single crystal, the centers of positive and negative charges do not coincide, and the direction from the positive charge to the negative charge is the polarization direction of the piezoelectric single crystal. During the preparation of a piezoelectric single crystal thin film, the polarization direction inside the thin film is usually uniform. However, if there are non-uniformly distributed different polarization directions in the thin film, the thin film will also have unique properties, namely a non-uniformly polarized piezoelectric single crystal thin film, which can be applied to fields such as acoustic filters and optical communication.

[0003] Currently, the main methods for preparing piezoelectric single crystal thin films are divided into two types: external electric field polarization and ion implantation bonding. External electric field polarization means preparing periodic metal electrodes on one side of the piezoelectric single crystal and uniform electrodes on the other side, and applying a periodic electric field to induce polarization reversal of the piezoelectric single crystal. However, this method has problems such as difficult electrode lithography, uneven edges between regions with opposite polarization directions, and the high electric field may breakdown the piezoelectric crystal. Moreover, this method can only prepare thin films with a 180° polarization reversal and the same domain width.

[0004] The Chinese invention patent with the patent publication number CN110534474A discloses a method for preparing a thin film on a substrate, including the following steps: providing a thin film transfer substrate including a first surface and a second surface; performing ion implantation on the first surface to form an implantation damage layer; providing a support substrate including a third surface and a fourth surface; bonding the thin film transfer substrate and the support substrate to form a bonded substrate; annealing the bonded substrate in a water bath, an oil bath or a salt bath, and simultaneously processing the bonded substrate with ultrasonic or megasonic power to peel the bonded substrate along the implantation damage layer to obtain a thin film on the support substrate. By using a water bath, an oil bath or a salt bath as the annealing medium to anneal the bonded substrate and processing the bonded substrate with ultrasonic or megasonic power during annealing, the bonded substrate is peeled under conditions lower than the expected peeling temperature, reducing the ion implantation dose, optimizing the thermal stress distribution during hetero-material bonding, reducing the production cost, and improving the thin film quality and yield. The polarization direction inside the thin film prepared by this patent is uniform, and the preparation process of a non-uniformly polarized piezoelectric single crystal thin film is not involved.

[0005] The Chinese invention patent with the patent publication number CN111883648B discloses a preparation method of a piezoelectric thin film, a piezoelectric thin film and a band-pass filter. The method includes: obtaining a plurality of piezoelectric wafers and a plurality of preset substrate wafers; performing ion implantation on the plurality of piezoelectric wafers to obtain a plurality of ion-implanted piezoelectric wafers; an ion implantation damage layer is present in the plurality of ion-implanted piezoelectric wafers; bonding the plurality of ion-implanted piezoelectric wafers with the plurality of preset substrate wafers to obtain a plurality of bonded wafers; performing annealing treatment on the plurality of bonded wafers, and during the annealing treatment, regulating the in-plane stress of the plurality of bonded wafers to adjust the peeling thickness at which the plurality of bonded wafers peel at the corresponding ion implantation damage layer to obtain a plurality of piezoelectric thin films; wherein, the deviation of the peeling thickness between the plurality of piezoelectric thin films is less than a first preset thickness threshold. The polarization direction inside the thin film prepared by this patent is uniform, and the preparation process of non-uniformly polarized piezoelectric single crystal thin films is not involved. Summary of the Invention

[0006] The inventors' research found that: ion implantation bonding, that is, injecting hydrogen or helium ions into a piezoelectric single crystal wafer, bonding with a substrate and then performing annealing and peeling, so as to transfer the piezoelectric single crystal wafer to the substrate. Repeating this step and changing the orientation of the piezoelectric single crystal wafer each time bonding is performed can obtain a non-uniformly polarized piezoelectric single crystal thin film. However, due to the different thermal expansion coefficients of the piezoelectric single crystal wafer and the substrate, the piezoelectric single crystal wafer composite substrate (also known as the first formal bonding sheet, the first temporary bonding sheet, the first functional bonding sheet) will warp during annealing and peeling. For example, the thermal expansion coefficients of lithium tantalate and silicon are 16.1 ppm / °C and 3 ppm / °C respectively. If the piezoelectric single crystal wafer is bonded multiple times and annealed and peeled multiple times, the previously transferred wafer will withstand cyclic thermal stress multiple times, resulting in severe warping. When the warp value of the wafer is greater than 20 μm, the bonding process cannot continue. If the warping accumulates continuously, it is extremely easy to cause damage or even breakage of the thin film. If each layer of piezoelectric single crystal thin film only needs to go through the annealing and peeling temperature once, the severe warping of the wafer can be avoided, and the preparation stability and thin film quality of the non-uniformly polarized piezoelectric single crystal thin film can be improved.

[0007] To solve the above problems, on the one hand, the present invention provides a preparation method of a non-uniformly polarized piezoelectric single crystal thin film, and the preparation method includes the following steps:

[0008] S1: Prepare a plurality of piezoelectric single crystal wafers, a formal substrate and a plurality of temporary substrates, and perform ion implantation on the bonding surface of the piezoelectric single crystal wafers to obtain ion-implanted piezoelectric single crystal wafers;

[0009] Optionally, there are at least 2 piezoelectric single crystal wafers and at least 1 temporary substrate.

[0010] Optionally, the material of the piezoelectric single crystal wafer is any one of single crystal lithium niobate, magnesium-doped single crystal lithium niobate or single crystal lithium tantalate.

[0011] Optionally, the materials of the formal substrate and several temporary substrates are any one of silicon, quartz, sapphire, silicon carbide or diamond. During the preparation process, the materials of the formal substrate and the temporary substrate can be the same or different.

[0012] Optionally, the surface roughness of the piezoelectric single crystal wafer is less than 0.5 nm. Optionally, the surface roughness of the piezoelectric single crystal wafer is less than 0.2 nm.

[0013] Optionally, the surface roughnesses of the formal substrate and the temporary substrate are both less than 0.5 nm. Optionally, the surface roughnesses of the formal substrate and the temporary substrate are both less than 0.2 nm.

[0014] Optionally, the warp of the piezoelectric single crystal wafer is less than 5 μm.

[0015] Optionally, the warps of the formal substrate and the temporary substrate are both less than 5 μm. In this application, limiting the warps of the formal substrate and the temporary substrate within a certain range can ensure the normal progress of bonding. If the warp is too large, bonding may not be possible.

[0016] S2: Bond the bonding surface of the ion-implanted piezoelectric single crystal wafer to the formal substrate to obtain the first formal bonding sheet, and bond the bonding surface of the ion-implanted piezoelectric single crystal wafer to the temporary substrate to obtain the first temporary bonding sheet.

[0017] Optionally, the implanted ions can be hydrogen ions or helium ions. The implantation dose can be 1×10^14 - 1×10^18 ions / cm 2 , and the implantation energy can be 50 - 500 keV to form a damaged layer at a depth of 100 nm - 2 μm from the bonding surface. Optionally, the implantation dose is 2×10 16 ions / cm 2 , and the implantation energy is 150 keV.

[0018] Optionally, the warps of the first formal bonding sheet and the first temporary bonding sheet are both less than 5 μm.

[0019] S3: Anneal and peel the first formal bonding sheet and the first temporary bonding sheet respectively to obtain the first formal peeled sheet and the first temporary peeled sheet;

[0020] Optionally, the implanted ions form defects at high temperatures. During the annealing and peeling process, the piezoelectric single-crystal wafer fractures along the damaged layer, separating the piezoelectric single-crystal wafer to obtain a piezoelectric single-crystal wafer on the formal substrate (abbreviated as the first formal peeling sheet) and a piezoelectric single-crystal wafer on the temporary substrate (abbreviated as the first temporary peeling sheet). The surface roughness of the piezoelectric single-crystal wafer of the fractured first formal peeling sheet is reduced to less than 0.5 nm using a chemical mechanical polishing process, and the surface roughness of the piezoelectric single-crystal wafer of the fractured first temporary peeling sheet is reduced to less than 0.5 nm using a chemical mechanical polishing process.

[0021] S4: Bond the first formal peeling sheet and the first temporary peeling sheet to obtain a first composite sheet.

[0022] Optionally, the first formal peeling sheet and the first temporary peeling sheet can be bonded using a plasma room-temperature bonding process.

[0023] S5: Debond the temporary substrate in the first composite sheet to obtain two non-uniformly polarized piezoelectric single-crystal thin films with different polarization directions.

[0024] Optionally, debonding can be performed by soaking in a chemical solvent. For example, debonding can be performed using the chemical solvent N-methylpyrrolidone (NMP), heated to 60 °C to improve the dissolution efficiency. After debonding, two non-uniformly polarized piezoelectric single-crystal thin films with different polarization directions are obtained, and the surface roughness of the upper piezoelectric single-crystal sub-layer is reduced to less than 0.5 nm using a chemical mechanical polishing process.

[0025] S6: Repeat steps S4 - S5, and then continue bonding to obtain a non-uniformly polarized piezoelectric single-crystal thin film. The non-uniformly polarized piezoelectric single-crystal thin film includes a formal substrate layer and n piezoelectric single-crystal sub-layers with different polarization directions disposed on the formal substrate layer from bottom to top;

[0026] where n is not less than 2.

[0027] Specifically, the different polarization directions can be such that the polarization directions of adjacent piezoelectric single-crystal sub-layers are opposite along the vertical direction, or opposite along the horizontal direction, or the polarization directions are the same but adjacent sub-layers are rotated 180° around the polarization direction. In other words, the polarization directions of adjacent piezoelectric single-crystal sub-layers do not necessarily have to be opposite and can be rotated by any angle.

[0028] Furthermore, the preparation method of a non-uniformly polarized piezoelectric single-crystal thin film with three different polarization directions includes the following steps: Bond two non-uniformly polarized piezoelectric single-crystal thin films with different polarization directions and the first temporary peeling sheet to obtain a first composite sheet; Debond the temporary substrate in the first composite sheet to obtain a non-uniformly polarized piezoelectric single-crystal thin film with three different polarization directions.

[0029] Furthermore, the preparation method of the non-uniformly polarized piezoelectric single-crystal thin film with 4 different polarization directions includes the following steps: Bond a non-uniformly polarized piezoelectric single-crystal thin film with 3 different polarization directions and a first temporary release sheet to obtain a first composite sheet; Debond the temporary substrate in the first composite sheet to obtain a non-uniformly polarized piezoelectric single-crystal thin film with 4 different polarization directions.

[0030] In the present invention, by using a number of temporary substrates, each layer of the piezoelectric single-crystal thin film only needs to undergo the annealing and peeling temperature once, which can avoid serious warping of the wafer and improve the preparation stability and film quality of the non-uniformly polarized piezoelectric single-crystal thin film. In addition, the preparation method of the non-uniformly polarized piezoelectric single-crystal thin film prepared in this application is simple and easy to implement, and maximally avoids the damage of the cyclic thermal stress to the film. The obtained non-uniformly polarized piezoelectric single-crystal thin film has high crystal quality, and the polarization direction and thickness can be simply adjusted, and acoustic or optical devices with excellent performance can be prepared.

[0031] Optionally, the preparation method further includes the following steps:

[0032] S20: Prepare a functional layer on the formal substrate to obtain a functional substrate;

[0033] Optionally, the material of the functional layer is any one of silicon oxide, aluminum oxide, aluminum nitride, silicon nitride, hafnium oxide, zirconium oxide or titanium oxide.

[0034] Optionally, the functional layer can be prepared on the formal substrate by methods such as thermal oxidation, bonding or deposition.

[0035] S21: Bond the bonding surface of the ion-implanted piezoelectric single-crystal wafer to the functional layer of the functional substrate to obtain a first functional bonded sheet, and bond the bonding surface of the ion-implanted piezoelectric single-crystal wafer to the temporary substrate to obtain a first temporary bonded sheet;

[0036] S30: Anneal and peel the first functional bonded sheet and the first temporary bonded sheet respectively to obtain a first functional release sheet and a first temporary release sheet;

[0037] S40: Bond the first functional release sheet and the first temporary release sheet to obtain a first functional composite sheet;

[0038] S50: Debond the temporary substrate in the first functional composite sheet to obtain a non-uniformly polarized piezoelectric single-crystal thin film with 2 different polarization directions;

[0039] S60: Repeat steps S40 - S50 to obtain an n-layer non-uniformly polarized piezoelectric single-crystal thin film with different polarization directions. The n-layer non-uniformly polarized piezoelectric single-crystal thin film includes a formal substrate layer, a functional layer, and n piezoelectric single-crystal sub-layers with different polarization directions arranged on the functional layer from bottom to top.

[0040] Optionally, the formal substrate or the functional substrate is bonded to the bonding surface of the ion-implanted piezoelectric single-crystal wafer by means of plasma room-temperature bonding;

[0041] Among them, the plasma room-temperature bonding temperature is 20-30 °C, the pressure is 200-500 kPa, and the plasma activation time is 2-5 min.

[0042] Optionally, the bonding surface of the ion-implanted piezoelectric single-crystal wafer is bonded to the temporary substrate with a temporary bonding adhesive; further, the temporary bonding adhesive is one of polyimide or benzocyclobutene, and this temporary bonding adhesive can withstand the annealing temperature and can be debonded by chemical solvent immersion subsequently.

[0043] Optionally, the annealing and peeling temperature is 100-300 °C. Optionally, the annealing and peeling temperature is 160-200 °C.

[0044] Optionally, the thickness of the formal substrate layer is 200 μm - 1000 μm;

[0045] and / or the thickness of the piezoelectric single-crystal sublayer is 10 nm - 2000 nm.

[0046] Optionally, the thickness of the functional layer is 0.1 μm - 10 μm.

[0047] Optionally, the thickness of the formal substrate layer is 500 μm - 800 μm;

[0048] and / or the thickness of the piezoelectric single-crystal sublayer is 200 nm - 1000 nm.

[0049] Optionally, the thickness of the functional layer is 3 μm - 7 μm.

[0050] On the other hand, the present invention provides a non-uniformly polarized piezoelectric single-crystal thin film, which is prepared by the above preparation method, and the warp of the non-uniformly polarized piezoelectric single-crystal thin film is less than 20 μm.

[0051] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0052] (1) The preparation method proposed by the present invention enables each layer of piezoelectric single-crystal wafer to only withstand the annealing and peeling temperature once, avoiding warping failure or even fragmentation of the piezoelectric single-crystal wafer under cyclic thermal stress, thereby improving the preparation success rate and film quality of the non-uniformly polarized piezoelectric single-crystal thin film. Further, the polarization direction and thickness of each layer of piezoelectric single-crystal sublayer can be flexibly controlled, and both the piezoelectric single-crystal wafer and the temporary substrate can be reused.

[0053] (2) The preparation method proposed by the present invention has a flatter domain wall compared with the external electric field polarization method, and the single crystal property will not be damaged due to the electric field-induced polarization reversal. Description of the Drawings

[0054] The drawings described herein are used to provide a further understanding of the present invention, and constitute a part of the present invention. The schematic embodiments and descriptions thereof are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0055] Figure 1 An exemplary embodiment showing a schematic diagram of the non-uniformly polarized piezoelectric single crystal thin film structure of the present invention in Example 1, wherein 1 - formal substrate, 2 - functional layer, 3 - non-uniformly polarized piezoelectric single crystal thin film, 31 - piezoelectric single crystal sub-layer.

[0056] Figure 2 Shows the preparation flow chart of the non-uniformly polarized piezoelectric single crystal thin film in Example 1.

[0057] Figure 3 Shows the warpage test diagrams of the formal substrate (a), the first functional release sheet (b), and two non-uniform single crystal lithium niobate thin films with opposite polarization directions (c) in Example 1. Detailed Embodiments

[0058] In order to more clearly explain the overall concept of the present invention, the following will be described in detail by way of examples in conjunction with the drawings of the specification.

[0059] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention may 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.

[0060] Example 1

[0061] The preparation method of the non-uniformly polarized piezoelectric single crystal thin film includes the following steps:

[0062] (1) Prepare several single crystal lithium niobate wafers, 1 formal substrate and several temporary substrates. First, ion implantation is carried out on the -Z plane of the Z-cut single crystal lithium niobate wafer. The diameter of the single crystal lithium niobate wafer is 6 inches, the thickness is 0.5 mm, the surface roughness is 0.4 nm, and the warp value of the piezoelectric single crystal wafer is 4 μm. The implanted ion is a helium ion, the implantation dose is 2×10 16 ions / cm 2 , the implantation energy is 150 keV, and a damaged layer is formed at a depth of 400 nm on the -Z plane. Multiple single crystal lithium niobate wafers can be ion implanted, or the remaining single crystal lithium niobate wafers can be ion implanted multiple times after peeling off the single crystal lithium niobate thin film for recycling.

[0063] (2) Bond the post-injection single-crystalline lithium niobate wafer - Z plane to the formal substrate and the temporary substrate respectively. The formal substrate is a silicon wafer with a thickness of 0.5 mm, a warp value of less than 5 μm, and a silicon oxide functional layer is prepared on the formal substrate through a thermal oxidation process to obtain a functional substrate. The thickness of the silicon oxide functional layer is 300 nm, and the surface roughness is 0.4 nm. The temporary substrate is a silicon wafer without a functional layer, with a wafer thickness of 0.5 mm, a surface roughness of 0.4 nm, and a warp value of 4 μm. Bond the single-crystalline lithium niobate wafer - Z plane to the functional layer surface of the functional substrate using a plasma room-temperature bonding process to obtain the first functional bonded wafer, and bond the single-crystalline lithium niobate wafer - Z plane to the temporary substrate using a polyimide temporary bonding adhesive to obtain several first temporary bonded wafers. The plasma room-temperature bonding temperature is 25 °C, the pressure is 300 kPa, and the plasma activation time is 3 min.

[0064] (3) Place the first functional bonded wafer and the first temporary bonded wafers into an annealing furnace for annealing and peeling. The annealing furnace temperature is 100 °C. The implanted helium ions form defects at high temperatures, the damaged layer breaks, and the single-crystalline lithium niobate wafer is separated along the damaged layer to obtain the single-crystalline lithium niobate thin film (the first functional peeled wafer) on the formal substrate and the single-crystalline lithium niobate thin films (several first temporary peeled wafers) on the temporary substrate. Use a chemical mechanical polishing process to reduce the surface roughness of the single-crystalline lithium niobate thin films on the peeled first functional peeled wafer and the first temporary peeled wafers to 0.4 nm, polish the thickness of the single-crystalline lithium niobate thin film on the first functional peeled wafer to 200 nm, and polish the thickness of the single-crystalline lithium niobate thin film on the first temporary peeled wafers to 300 nm. Measure the warp values of the first functional peeled wafer and the first temporary peeled wafers.

[0065] (4) Bond the polished first functional peeled wafer and the first temporary peeled wafers relatively. Use a plasma room-temperature bonding process with a plasma room-temperature bonding temperature of 20 °C, a pressure of 200 kPa, and a plasma activation time of 2 min. At this time, the polarization directions of the two bonded single-crystalline lithium niobate thin films are opposite.

[0066] (5) Dissolve the temporary bonding adhesive by soaking in a chemical solvent, thereby debonding the temporary substrate. The chemical solvent used for debonding is N-methylpyrrolidone (NMP), and heating to 60 °C improves the dissolution efficiency. After debonding, two non-uniform single-crystalline lithium niobate thin films with opposite polarization directions are obtained. Use a chemical mechanical polishing process to reduce the roughness of the upper single-crystalline lithium niobate thin film to 0.4 nm and the thickness to 200 nm.

[0067] (6) Repeat steps (4)-(5) to bond two more single-crystalline lithium niobate thin films with opposite polarization directions to obtain a 4-layer non-uniformly polarized lithium niobate thin film with different polarization directions. Specifically, for the flowchart of preparing the non-uniformly polarized piezoelectric single-crystalline thin film, refer to Figure 2As shown. The schematic diagram of the non-uniformly polarized piezoelectric single-crystal thin film structure obtained is referred to Figure 1 as shown.

[0068] X-ray diffraction analysis can be used to characterize the polarization direction of the non-uniformly polarized single-crystal lithium niobate thin film. In this embodiment, the direction relationship between adjacent two single-crystal lithium niobate sub-layers is a 180° rotation around the X-axis. By using XRD to measure the (122) pole figure of the non-uniformly polarized lithium niobate thin film, six points with an interval of 60° can be observed on the pole figure, while only three points with an interval of 120° can be observed for the uniformly polarized Z-cut lithium niobate thin film, thus proving that the adjacent lithium niobate thin films in this thin film have achieved non-uniform polarization with a 180° flip along the X-axis.

[0069] Scanning electron microscopy can be used to characterize the thickness of each single-crystal sub-layer of the non-uniformly polarized single-crystal lithium niobate thin film. The prepared non-uniformly polarized single-crystal lithium niobate thin film is cut along the thickness direction, and the cross-section is observed with a scanning electron microscope. Since the chemical mechanical polishing (abbreviation: CMP) process is used during the preparation process to ensure the flatness of the surface of each lithium niobate single-crystal sub-layer, a straight interface can be observed between each single-crystal lithium niobate sub-layer. Measuring the distance between each interface can obtain the thickness of each single-crystal lithium niobate sub-layer.

[0070] Example 2

[0071] The preparation method of the non-uniformly polarized piezoelectric single-crystal thin film includes the following steps:

[0072] (1) Prepare 2 single-crystal lithium tantalate wafers, 1 formal substrate and 1 temporary substrate. First, ion implantation is carried out on the X surface of the X-cut single-crystal lithium tantalate wafer. The diameter of the single-crystal lithium tantalate wafer is 6 inches, the thickness is 0.5 mm, the surface roughness is 0.3 nm, and the warp value of the piezoelectric single-crystal wafer is 2 μm. The implanted ion is hydrogen ion, the implantation dose is 5×10 16 ions / cm 2 , the implantation energy is 150 keV, and a damaged layer is formed at a depth of 600 nm on the X surface. Ion implantation is carried out on the Y surface of another Y-cut single-crystal lithium tantalate wafer with the same parameters.

[0073] (2) Bond the X-cut single-crystal lithium tantalate wafer and the Y-cut single-crystal lithium tantalate wafer after ion implantation to the formal substrate and the temporary substrate respectively. The formal substrate is a silicon carbide wafer without a functional layer, with a thickness of 0.5 mm, a surface roughness of 0.3 nm, and a warp value of less than 5 μm. The temporary substrate is a silicon wafer without a functional layer, with a thickness of 0.5 mm, a surface roughness of 0.4 nm, and a warp value of 2 μm. Bond the X surface of the X-cut single-crystal lithium tantalate wafer to the formal substrate using a plasma room-temperature bonding process to obtain the first formal bonded wafer, and bond the Y surface of the Y-cut single-crystal lithium tantalate wafer to the temporary substrate using benzocyclobutene temporary bonding glue to obtain the first temporary bonded wafer. The plasma room-temperature bonding temperature is 30 °C, the pressure is 300 kPa, and the plasma activation time is 3 min.

[0074] (3) Place the first formal bonded wafer and the first temporary bonded wafer in an annealing furnace for annealing and peeling. The temperature of the annealing furnace is 180 °C. The implanted hydrogen ions form defects at high temperatures, the damaged layer breaks, and the single-crystal lithium tantalate film is separated along the damaged layer to obtain the X-cut single-crystal lithium tantalate film on the formal substrate and the Y-cut single-crystal lithium tantalate film on the temporary substrate. Use a chemical mechanical polishing process to reduce the roughness of the X-cut single-crystal lithium tantalate film on the formal substrate and the Y-cut single-crystal lithium tantalate film on the temporary substrate to 0.3 nm, polish the thickness of the single-crystal lithium tantalate film on the first formal peeled wafer to 400 nm, and polish the thickness of the single-crystal lithium tantalate on the first temporary peeled wafer to 500 nm, and measure the warp values of the first formal peeled wafer and the first temporary peeled wafer.

[0075] (4) Bond the X-cut single-crystal lithium tantalate film on the formal substrate and the Y-cut single-crystal lithium tantalate film on the temporary substrate relatively. Use a plasma room-temperature bonding process, with a plasma room-temperature bonding temperature of 20 °C, a pressure of 400 kPa, and a plasma activation time of 4 min. At this time, the polarization directions and tangential directions of the two single-crystal lithium tantalate films are different.

[0076] (5) Dissolve the temporary bonding glue by soaking with a chemical solvent, so that the temporary substrate is debonded. The chemical solvent used for debonding is N-methylpyrrolidone (NMP), and heating to 60 °C improves the dissolution efficiency. After debonding, two non-uniformly polarized single-crystal lithium tantalate films with different polarization directions are obtained. Use a chemical mechanical polishing process to reduce the roughness of the upper single-crystal lithium tantalate film to 0.3 nm and the thickness to 400 nm.

[0077] The polarization direction and the single-crystal sub-layer thickness of the non-uniformly polarized single-crystal lithium tantalate film can be characterized by X-ray diffraction analysis and scanning electron microscopy. The method refers to Example 1.

[0078] Example 3

[0079] The preparation method of the non-uniformly polarized piezoelectric single-crystal film includes the following steps:

[0080] (1) Prepare one single-crystal lithium tantalate wafer, one single-crystal lithium niobate wafer, one formal substrate and one temporary substrate. First, perform ion implantation on the X surface of the X-cut single-crystal lithium tantalate wafer. The diameter of the single-crystal lithium tantalate wafer is 6 inches, the thickness is 0.5 mm, the surface roughness is 0.3 nm, and the warp value of the piezoelectric single-crystal wafer is 3 μm. The implanted ion is hydrogen ion, the implantation dose is 5×10 16 ions / cm 2 , the implantation energy is 150 keV, and a damaged layer is formed at a depth of 600 nm from the X surface. Perform ion implantation on the X surface of another X-cut single-crystal lithium niobate wafer. The diameter of the single-crystal lithium niobate wafer is 6 inches, the thickness is 0.5 mm, the surface roughness is 0.4 nm, and the warp value of the wafer is 3 μm. The implanted ion is helium ion, the implantation dose is 2×10 16 ions / cm 2 , the implantation energy is 150 keV, and a damaged layer is formed at a depth of 400 nm from the X surface.

[0081] (2) Bond the implanted X-cut single-crystal lithium tantalate wafer and X-cut single-crystal lithium niobate wafer to the formal substrate and the temporary substrate respectively. The formal substrate is a sapphire wafer without a functional layer. The thickness of the sapphire wafer is 0.5 mm, the surface roughness is 0.3 nm, and the warp of the formal substrate is less than 5 μm. The temporary substrate is a silicon wafer without a functional layer. The thickness of the wafer is 0.5 mm, the surface roughness is 0.4 nm, and the warp value of the temporary substrate is 3 μm. Bond the X surface of the X-cut single-crystal lithium tantalate wafer to the formal substrate using the plasma room-temperature bonding process to obtain the first formal bonded wafer, and bond the X surface of the X-cut single-crystal lithium niobate wafer to the temporary substrate using benzocyclobutene temporary bonding glue to obtain the first temporary bonded wafer. The plasma room-temperature bonding temperature is 30 °C, the pressure is 300 kPa, and the plasma activation time is 3 min.

[0082] (3) Place the first formal bonded wafer and the first temporary bonded wafer in an annealing furnace for annealing and peeling. The temperature of the annealing furnace is 200 °C. The implanted hydrogen ions and helium ions form defects at high temperature, the damaged layer breaks, and the single-crystal lithium tantalate and lithium niobate thin films are separated along the damaged layer to obtain the X-cut single-crystal lithium tantalate thin film on the formal substrate and the X-cut single-crystal lithium niobate thin film on the temporary substrate. Use the chemical mechanical polishing process to reduce the roughness of the X-cut single-crystal lithium tantalate thin film on the formal substrate and the X-cut single-crystal lithium niobate thin film on the temporary substrate to 0.3 nm. Polish the thickness of the single-crystal lithium tantalate thin film on the first formal peeled wafer to 400 nm, and polish the thickness of the single-crystal lithium niobate on the first temporary peeled wafer to 500 nm, and measure the warp of the first formal peeled wafer and the first temporary peeled wafer.

[0083] (4) Bond the X-cut single-crystal lithium tantalate film on the polished formal substrate and the X-cut single-crystal lithium niobate film on the temporary substrate relatively. The plasma room-temperature bonding process is adopted, the plasma room-temperature bonding temperature is 20 °C, the pressure is 400 kPa, and the plasma activation time is 4 min.

[0084] (5) Dissolve the temporary bonding glue by soaking with a chemical solvent, so as to debond the temporary substrate. The chemical solvent used for debonding is N-methylpyrrolidone (NMP), and it is heated to 60 °C to improve the dissolution efficiency. After debonding, a non-uniformly polarized piezoelectric single-crystal film with different polarization directions of the two layers of materials is obtained. The surface roughness of the upper single-crystal lithium niobate film is reduced to 0.3 nm and the thickness is reduced to 400 nm by chemical mechanical polishing process.

[0085] Example 4

[0086] The preparation method of the non-uniformly polarized piezoelectric single-crystal film comprises the following steps:

[0087] (1) Prepare 2 pieces of 42° Y-cut single-crystal lithium tantalate wafers, 1 piece of formal substrate and 1 piece of temporary substrate. First, ion implantation is carried out on the 42° Y-plane of the 42° Y-cut single-crystal lithium tantalate wafer. The diameter of the single-crystal lithium tantalate wafer is 4 inches, the thickness is 0.25 mm, the surface roughness is 0.2 nm, and the warp value of the piezoelectric single-crystal wafer is 2 μm. The implanted ion is hydrogen ion, and the implantation dose is 3×10 16 ions / cm 2 , the implantation energy is 150 keV, and a damaged layer is formed at a depth of 600 nm from the 42° Y-plane.

[0088] (2) Bond the implanted 42° Y-cut single-crystal lithium tantalate wafers to the formal substrate and the temporary substrate respectively. The formal substrate is a 4-inch silicon wafer grown with silicon nitride. The thickness of the silicon wafer is 0.5 mm, the surface roughness is 0.3 nm, and the warp value of the formal substrate is less than 5 μm. The temporary substrate is a silicon wafer without a functional layer. The thickness of the wafer is 0.5 mm, the surface roughness is 0.4 nm, and the warp value of the temporary substrate is 2 μm. Bond the 42° Y-plane of the 42° Y-cut single-crystal lithium tantalate wafer to the formal substrate by the plasma room-temperature bonding process to obtain the first formal bonded sheet, and bond the 42° Y-plane of the 42° Y-cut single-crystal lithium niobate wafer to the temporary substrate with benzocyclobutene temporary bonding glue to obtain the first temporary bonded sheet. The plasma room-temperature bonding temperature is 30 °C, the pressure is 300 kPa, and the plasma activation time is 3 min.

[0089] (3) Place the first formal bonding sheet and the first temporary bonding sheet into an annealing furnace for annealing and peeling. The temperature of the annealing furnace is 160 °C. The implanted hydrogen ions form defects at high temperatures, the damaged layer breaks, and the single-crystal tantalum lithium niobate and lithium niobate thin films are separated along the damaged layer to obtain a 42° Y-cut single-crystal tantalum lithium niobate thin film on the formal substrate and a 42° Y-cut single-crystal lithium niobate thin film on the temporary substrate. Use chemical mechanical polishing process to reduce the roughness of the 42° Y-cut single-crystal tantalum lithium niobate thin film on the formal substrate after peeling to 0.3 nm, polish the thickness of the single-crystal tantalum lithium niobate thin film on the first formal peeling sheet to 400 nm, polish the thickness of the single-crystal lithium niobate on the first temporary peeling sheet to 500 nm, and measure the warpage of the first formal peeling sheet and the first temporary peeling sheet.

[0090] (4) Bond the 42° Y-cut single-crystal tantalum lithium niobate thin film on the formal substrate and the 42° Y-cut single-crystal lithium niobate thin film on the temporary substrate relatively, and rotate the X-axis 90° clockwise around the wafer normal. Adopt plasma room temperature bonding process, the plasma room temperature bonding temperature is 20 °C, the pressure is 400 kPa, and the plasma activation time is 4 min.

[0091] (5) Dissolve the temporary bonding glue by soaking with chemical solvent, so that the temporary substrate is debonded. The chemical solvent used for debonding is N-methylpyrrolidone (NMP), and heating to 60 °C can improve the dissolution efficiency. After debonding, two piezoelectric single-crystal thin films with different materials are obtained. Use chemical mechanical polishing process to reduce the roughness of the upper single-crystal lithium niobate thin film to 0.3 nm and reduce the thickness to 400 nm.

[0092] (6) Repeat steps (4)-(5), each time rotate the X-axis 90° clockwise around the wafer normal when bonding the temporary bonding sheet and the formal bonding sheet, and bond 4 single-crystal tantalum lithium niobates with different polarization directions.

[0093] Comparative Example 1

[0094] (1) Prepare 2 pieces of 42° Y-cut single-crystal tantalum lithium niobate wafers, 1 piece of formal substrate and 1 piece of temporary substrate. First, perform ion implantation on the 42° Y plane of the 42° Y-cut single-crystal tantalum lithium niobate wafer. The diameter of the single-crystal tantalum lithium niobate wafer is 4 inches, the thickness is 0.25 mm, the surface roughness is 0.2 nm, and the wafer warpage value warp is 2 μm. The implanted ion is hydrogen ion, the implantation dose is 3×10 16 ions / cm 2 , the implantation energy is 150 keV, and a damaged layer is formed at a depth of 600 nm from the 42° Y plane.

[0095] (2) Bond the 42°Y-cut single-crystal lithium tantalate wafers after injection to the formal substrate and the temporary substrate respectively. The formal substrate is a 4-inch silicon wafer with silicon nitride grown on it. The thickness of the silicon wafer is 0.5 mm, the surface roughness is 0.3 nm, and the warp value of the formal substrate is less than 5 μm. The temporary substrate is a silicon wafer without a functional layer. The thickness of the wafer is 0.5 mm, the surface roughness is 0.4 nm, and the warp value of the temporary substrate is 2 μm. Bond the 42°Y face of the 42°Y-cut single-crystal lithium tantalate wafer to the formal substrate using the plasma room-temperature bonding process to obtain the first formal bonded wafer, and bond the 42°Y face of the 42°Y-cut lithium niobate wafer to the temporary substrate using benzocyclobutene temporary bonding glue to obtain the first temporary bonded wafer. The plasma room-temperature bonding temperature is 30 °C, the pressure is 300 kPa, and the plasma activation time is 3 min.

[0096] (3) Put the first formal bonded wafer and the first temporary bonded wafer into an annealing furnace for annealing and peeling. The temperature of the annealing furnace is 400 °C. After peeling, the warp value of the wafer is 40.537 μm, and subsequent bonding cannot be carried out.

[0097] Comparative Example 2

[0098] (1) Prepare several X-cut single-crystal lithium tantalate wafers and 1 silicon wafer. First, perform ion implantation on the X face of the X-cut single-crystal lithium tantalate wafer. The diameter of the single-crystal lithium tantalate wafer is 6 inches, the thickness is 0.5 mm, the surface roughness is 0.3 nm, and the warp value of the wafer is 3 μm. The implanted ion is hydrogen ion, the implantation dose is 5×10 16 ions / cm 2 , and the implantation energy is 150 keV to form a damaged layer at a depth of 600 nm on the X face.

[0099] (2) Bond the implanted X-cut single-crystal lithium tantalate wafer to the silicon wafer. The size of the silicon wafer is 6 inches, the thickness is 0.5 mm, the surface roughness is 0.3 nm, and the warp value of the silicon wafer is less than 5 μm. The plasma room-temperature bonding temperature is 30 °C, the pressure is 300 kPa, and the plasma activation time is 3 min.

[0100] (3) Put the bonded wafer into an annealing furnace for annealing and peeling. The temperature of the annealing furnace is 180 °C. The implanted hydrogen ions form defects at high temperature, and the damaged layer breaks. Separate the single-crystal lithium tantalate thin film along the damaged layer to obtain the X-cut single-crystal lithium tantalate thin film (the first peeled film) on the substrate. Use the chemical mechanical polishing process to reduce the roughness of the X-cut single-crystal lithium tantalate thin film on the peeled silicon wafer to 0.3 nm, polish the thickness of the single-crystal lithium tantalate thin film on the first peeled film to 400 nm, and measure the warp value of the first peeled film to be 13.547 μm.

[0101] (4) Bond the second ion-implanted X-cut single-crystal lithium tantalate wafer to the polished first release sheet again, with the bonding parameters the same as before. When bonding, the second implanted sheet rotates 180° around the normal of the wafer surface in the Y-axis direction.

[0102] (5) Place the bonded sheet after the second bonding into an annealing furnace for annealing and peeling. The peeling parameters are the same as above to obtain two layers of non-uniformly polarized piezoelectric single-crystal thin films with opposite polarization directions. Measure the warpage of the non-uniformly polarized piezoelectric single-crystal thin film. Due to the annealing thermal stress again, the warpage of the non-uniformly polarized piezoelectric single-crystal thin film reaches 32.356 μm. If the third layer of lithium tantalate wafer is bonded continuously, there will be unbonded areas at the bonding interface due to the high warpage, resulting in a decrease in the bonding force and easy debonding.

[0103] Perform warpage tests on the non-uniformly polarized piezoelectric single-crystal thin films prepared in Examples 1-4 and Comparative Examples 1-2. The results are shown in Table 1 for reference.

[0104] Table 1

[0105]

[0106] Figure 3 Shows the warpage test diagrams of the formal substrate (a), the first functional release sheet (b), and two layers of non-uniform single-crystal lithium niobate thin films with opposite polarization directions (c) in Example 1.

[0107] Referring to Table 1, the non-uniformly polarized piezoelectric single-crystal thin film prepared by the preparation method of the present invention can enable each layer of piezoelectric single-crystal thin film to only undergo the annealing and peeling temperature once, avoiding serious warpage of the wafer, making the warpage warp of the non-uniformly polarized piezoelectric single-crystal thin film less than 20 μm, which can ensure continuous bonding and further improve the preparation stability and film quality of the non-uniformly polarized piezoelectric single-crystal thin film.

[0108] The above are only the embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A method for preparing a non-uniformly polarized piezoelectric single crystal thin film, characterized in that: The preparation method comprises the following steps: S1: preparing a plurality of piezoelectric single crystal wafers, a formal substrate and a plurality of temporary substrates, and performing ion implantation on the bonding surface of the piezoelectric single crystal wafer to obtain an ion-implanted piezoelectric single crystal wafer; S2: bonding the bonding surface of the ion-implanted piezoelectric single crystal wafer to a formal substrate to obtain a first formal bonding sheet, and bonding the bonding surface of the ion-implanted piezoelectric single crystal wafer to a temporary substrate to obtain a first temporary bonding sheet; S3: annealing and peeling the first formal bonding sheet and the first temporary bonding sheet respectively to obtain a first formal peeling sheet and a first temporary peeling sheet; S4: bonding the first formal release sheet and the first temporary release sheet to obtain a first composite sheet; S5: debonding the temporary substrate in the first composite sheet to obtain two layers of non-uniformly polarized piezoelectric single crystal thin films with different polarization directions; S6: repeating steps S4-S5 to obtain a non-uniformly polarized piezoelectric single crystal film, wherein the non-uniformly polarized piezoelectric single crystal film includes, from bottom to top, a formal substrate layer and n piezoelectric single crystal sub-layers with different polarization directions disposed on the formal substrate layer; Wherein, n is not less than 2.

2. The method for preparing the non-uniformly polarized piezoelectric single crystal thin film according to claim 1, characterized in that: The preparation method also includes the following steps: S20: preparing a functional layer on the formal substrate to obtain a functional substrate; S21: bonding the bonding surface of the ion-implanted piezoelectric single crystal wafer to the functional layer of the functional substrate to obtain a first functional bonding sheet, and bonding the bonding surface of the ion-implanted piezoelectric single crystal wafer to the temporary substrate to obtain a first temporary bonding sheet; S30: annealing and peeling the first functional bonding sheet and the first temporary bonding sheet respectively to obtain a first functional peeling sheet and a first temporary peeling sheet; S40: bonding the first functional release sheet and the first temporary release sheet to obtain a first functional composite sheet; S50: debonding the temporary substrate in the first functional composite sheet to obtain two layers of non-uniformly polarized piezoelectric single crystal thin films with different polarization directions; S60: Repeat steps S40-S50 to obtain n layers of non-uniformly polarized piezoelectric single crystal films with different polarization directions, wherein the n layers of non-uniformly polarized piezoelectric single crystal films with different polarization directions include, from bottom to top, a formal substrate layer, a functional layer, and n layers of piezoelectric single crystal sublayers with different polarization directions arranged on the functional layer.

3. The method for preparing the non-uniformly polarized piezoelectric single crystal thin film according to claim 1 or 2, characterized in that: The formal substrate or the functional substrate is bonded to the bonding surface of the ion-implanted piezoelectric single crystal wafer by plasma room temperature bonding; Among them, the plasma room temperature bonding temperature is 20-30°C, the pressure is 200-500kPa, and the plasma activation time is 2-5min.

4. The method for preparing the non-uniformly polarized piezoelectric single crystal thin film according to claim 1 or 2, characterized in that: Bonding the bonding surface of the ion-implanted piezoelectric single crystal wafer to a temporary substrate using a temporary bonding adhesive; Furthermore, the temporary bonding adhesive is one of polyimide or benzocyclobutene.

5. The method for preparing the non-uniformly polarized piezoelectric single crystal thin film according to claim 1 or 2, characterized in that: The temperature of annealing and stripping is 100-300°C.

6. The method for preparing the non-uniformly polarized piezoelectric single crystal thin film according to claim 1 or 2, characterized in that: The thickness of the formal substrate layer is 200μm-1000μm; And / or the piezoelectric single crystal sublayer has a thickness of 10nm-2000nm.

7. The method for preparing the non-uniformly polarized piezoelectric single crystal thin film according to claim 2, characterized in that: The thickness of the functional layer is 0.1 μm-10 μm.

8. The method for preparing the non-uniformly polarized piezoelectric single crystal thin film according to claim 1, characterized in that: The material of the piezoelectric single crystal sublayer is any one of single crystal lithium niobate, magnesium-doped single crystal lithium niobate or single crystal lithium tantalate; And / or the material of the formal substrate layer is any one of silicon, quartz, sapphire, silicon carbide or diamond.

9. The method for preparing the non-uniformly polarized piezoelectric single crystal thin film according to claim 2, characterized in that: The material of the functional layer is any one of silicon oxide, aluminum oxide, aluminum nitride, silicon nitride, hafnium oxide, zirconium oxide or titanium oxide.

10. A non-uniformly polarized piezoelectric single crystal film, characterized in that: The non-uniformly polarized piezoelectric single crystal film is prepared by any one of the preparation methods of claims 1-9, and the warp of the non-uniformly polarized piezoelectric single crystal film is less than 20 μm.

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