A preparation process of a lithium niobate single crystal thin film

Abstract

The application relates to the technical field of crystal synthesis, and discloses a preparation process of a lithium niobate monocrystal thin film, which comprises the following steps: S1, a containing groove is formed on the surface of a cutting mold; S2, lithium niobate monocrystal is cut into a thin piece, then the lithium niobate thin piece is placed in the containing groove of the cutting mold, a buffer material is filled, the lithium niobate thin piece is mechanically ground and thinned; S3, a SiO2 layer is deposited on the surface of a substrate and polished, the lithium niobate thin piece is bonded with the substrate, and heat treatment is carried out to form a covalent connection; S4, after the buffer material is dissolved by a solvent, the cutting mold is removed, then the lithium niobate thin piece is further thinned in a chemical polishing mode, and the lithium niobate monocrystal thin film is obtained. The lithium niobate monocrystal thin piece is fixed by the cutting mold with the containing groove, and the buffer material is filled at the gap, so that the risk of the lithium niobate monocrystal being cracked during mechanical grinding is reduced; meanwhile, the lithium niobate monocrystal thin piece is not permanently fixed with the cutting mold, and is convenient to remove.

Description

Technical Field

[0001] This invention belongs to the field of crystal synthesis technology, specifically relating to a process for preparing lithium niobate single crystal thin films. Background Technology

[0002] Lithium niobate crystal (LiNbO3, LN) possesses excellent electro-optic, ferroelectric, piezoelectric, and nonlinear properties. It is also heat-resistant, corrosion-resistant, and physically and chemically stable, making it widely recognized as a candidate material for "optical silicon." Lithium niobate crystals cannot form naturally and can only be obtained through artificial synthesis. LN crystals have a Mohs hardness of 5, unlike single-crystal silicon, microcrystalline glass, ceramics, and cadmium zinc telluride, which are either hard or soft-brittle. It is a material intermediate between soft-brittle and hard-brittle, thus its material removal mechanism and processing methods are fundamentally different from those of hard-brittle materials. With the development of optoelectronic technology, there is a demand for LN crystals to have a damage-free surface after processing, a high degree of global planarization, a wafer roughness Ra of less than 1 nm, no defects or altered layers, no scratches, and no abrasive grain embedding.

[0003] Traditional methods for processing lithium niobate (LN) crystals, such as grinding and mechanical polishing, are inefficient, produce large surface roughness, and are prone to defects such as cracks, chipping, and embedded abrasive particles, making it difficult to obtain high-quality, damage-free surfaces. Currently, LN crystal processing often employs chemical mechanical polishing (CMP), where LN crystal wafers are first bonded to a silicon substrate, and then the wafers are thinned to a certain thickness through mechanical grinding and chemical polishing. This method addresses the issues of processing efficiency and precision to some extent, but the risk of wafer cracking still exists during mechanical grinding, resulting in a product yield of less than 80%. Therefore, a new process for preparing lithium niobate thin films is urgently needed to improve the product qualification rate. Summary of the Invention

[0004] To address the shortcomings mentioned in the background art, the present invention aims to provide a process for preparing lithium niobate single crystal thin films. The lithium niobate single crystal thin films are fixed by a cutting mold with a receiving groove, and buffer material is filled in the gaps, thereby reducing the risk of cracking of lithium niobate single crystals during mechanical grinding. At the same time, the lithium niobate single crystal thin films and the cutting mold are not permanently fixed, making them easy to remove.

[0005] The objective of this invention can be achieved through the following technical solutions: A process for preparing a lithium niobate single-crystal thin film includes the following steps: S1. A receiving groove is made on the surface of the cutting mold by grinding and etching, and the edge of the receiving groove is sloping. S2. Cut the lithium niobate single crystal into thin slices with a thickness of 200~400μm, then place the lithium niobate slices in the receiving groove of the cutting mold, then fill the gap between the lithium niobate slices and the receiving groove with buffer material, then reduce the thickness of the lithium niobate slices to less than 100μm by mechanical grinding, and finally polish them to a surface roughness ≤0.5nm. S3. Polish the substrate surface to a roughness of ≤0.5nm, then deposit a SiO2 layer on the substrate surface, polish the SiO2 layer surface to a roughness of ≤0.5nm, and finally bond the thinned lithium niobate sheet to the substrate and use heat treatment to make the lithium niobate and SiO2 layer form a covalent bond. S4. Dissolve the buffer material with a solvent, remove the cutting mold, and then use chemical polishing to further thin the lithium niobate sheet to a thickness of 80~200nm to obtain the lithium niobate single crystal film.

[0006] More preferably, the cutting mold is made of glass, ceramic, or graphite.

[0007] More preferably, the number of receiving tanks is one or more, and the bottom diameter of the receiving tank is greater than or equal to the diameter of the lithium niobate sheet.

[0008] More preferably, the edge of the receiving groove is one or a combination of straight slopes, convex slopes, concave slopes, and stepped slopes.

[0009] More preferably, the buffer material is a polyimide material, and the solvent is one of dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylacetamide.

[0010] More preferably, the substrate is one of a silicon substrate, a quartz substrate, a sapphire substrate, a silicon nitride substrate, and a silicon carbide substrate.

[0011] More preferably, the heat treatment temperature in step S3 is 420~450℃, and the time is 10~15min.

[0012] The beneficial effects of this invention are: This invention achieves dual confinement of the lithium niobate single crystal wafer in the receiving groove by creating a receiving groove on the surface of the cutting mold to support and fix the wafer, while simultaneously filling and sealing it with a buffer material. This fixation of the lithium niobate single crystal wafer without bonding effectively prevents the wafer from moving or falling during processing. At the same time, the buffer material at the edge of the lithium niobate single crystal wafer can effectively buffer stress and avoid breakage during mechanical grinding and thinning. The substrate is bonded after mechanical thinning is completed. The buffer material can withstand high-temperature heat treatment. After bonding is completed, the buffer material can be dissolved by an organic solvent to remove the cutting mold, facilitating subsequent chemical polishing. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic diagram of the substrate structure for preparing lithium niobate single crystal thin films according to the present invention; Figure 2 This is a schematic diagram of the process flow of step S1 in the preparation process of the lithium niobate single crystal thin film of the present invention. Figure 3 This is a schematic diagram of the process flow of step S2 in the preparation process of the lithium niobate single crystal thin film of the present invention. Figure 4 This is a schematic diagram of the process flow of step S3 in the preparation process of lithium niobate single crystal thin film of the present invention. Figure 5 This is a schematic diagram of the process flow of step S4 in the preparation process of the lithium niobate single crystal thin film of the present invention.

[0015] In the picture: 1-Cutting mold, 101-Receiving groove, 2-Lithium niobate, 3-Polyimide, 4-Substrate, 5-SiO2 layer. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1 A substrate for preparing lithium niobate single-crystal thin films includes receiving grooves formed on the surface of a cutting die. The cutting die can be made of high-temperature resistant materials such as glass, ceramic, or graphite, capable of withstanding heat treatment temperatures while maintaining low material cost. The edges of the receiving grooves are sloped, and there can be one or more receiving grooves. The bottom diameter of the receiving groove is greater than or equal to the diameter of the lithium niobate thin film to be processed. Figure 1 As shown, the edge of the receiving tank is a straight slope ( Figure 1 a) Convex slope ( Figure 1 b) Concave slope ( Figure 1 c) and stepped slopes ( Figure 1 d) One or more combinations.

[0018] Example 2 like Figures 2-5As shown, a process for preparing a lithium niobate single-crystal thin film includes the following steps: S1. A receiving groove 101 is formed on the surface of the cutting mold 1 by grinding and etching, and the edge of the receiving groove 101 is sloping. S2. Cut the lithium niobate single crystal into thin slices with a thickness of 200~400μm, then place the lithium niobate 2 thin slices in the receiving groove 101 of the cutting mold, then fill the gap between the lithium niobate 2 thin slices and the receiving groove 101 with polyimide 3 material, then reduce the thickness of the lithium niobate 2 thin slices to less than 100μm by mechanical grinding, and finally polish it to a surface roughness ≤0.5nm; S3. Polish the substrate surface to a roughness ≤0.5nm, then deposit SiO2 layer 5 on the substrate 4, polish the surface of SiO2 layer 5 to a roughness ≤0.5nm, and finally bond the thinned lithium niobate 2 sheet to the substrate 4. Heat to 420~450℃ for 10~15min to form a covalent bond between lithium niobate 2 and SiO2 layer. S4. Dissolve the polyimide 3 material in a solvent (dimethyl sulfoxide, N-methylpyrrolidone or N,N-dimethylacetamide), remove the cutting mold 1, and then further thin the lithium niobate 2 sheet to a thickness of 80~200nm by chemical polishing to obtain the lithium niobate single crystal film.

[0019] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0020] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A process for preparing a lithium niobate single-crystal thin film, characterized in that, Includes the following steps: S1. A receiving groove is made on the surface of the cutting mold by grinding and etching, and the edge of the receiving groove is sloping. S2. Cut the lithium niobate single crystal into thin slices with a thickness of 200~400μm, then place the lithium niobate slices in the receiving groove of the cutting mold, then fill the gap between the lithium niobate slices and the receiving groove with buffer material, then reduce the thickness of the lithium niobate slices to less than 100μm by mechanical grinding, and finally polish them to a surface roughness ≤0.5nm. S3. Polish the substrate surface to a roughness of ≤0.5nm, then deposit a SiO2 layer on the substrate surface, polish the SiO2 layer surface to a roughness of ≤0.5nm, and finally bond the thinned lithium niobate sheet to the substrate and use heat treatment to make the lithium niobate and SiO2 layer form a covalent bond. S4. Dissolve the buffer material with a solvent, remove the cutting mold, and then use chemical polishing to further thin the lithium niobate sheet to a thickness of 80~200nm to obtain the lithium niobate single crystal film.

2. The preparation process of lithium niobate single crystal thin film according to claim 1, characterized in that, The cutting mold is made of glass, ceramic, or graphite.

3. The preparation process of lithium niobate single crystal thin film according to claim 1, characterized in that, The number of the receiving tanks is one or more, and the bottom diameter of the receiving tank is greater than or equal to the diameter of the lithium niobate sheet.

4. The preparation process of lithium niobate single crystal thin film according to claim 1, characterized in that, The edge of the receiving groove is one or a combination of straight slopes, convex slopes, concave slopes, and stepped slopes.

5. The preparation process of lithium niobate single crystal thin film according to claim 1, characterized in that, The buffer material is a polyimide material, and the solvent is one of dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylacetamide.

6. The preparation process of lithium niobate single crystal thin film according to claim 1, characterized in that, The substrate is one of silicon substrate, quartz substrate, sapphire substrate, silicon nitride substrate and silicon carbide substrate.

7. The preparation process of lithium niobate single crystal thin film according to claim 1, characterized in that, In step S3, the heat treatment temperature is 420~450℃ and the time is 10~15min.

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