Preparation method for loading strip-shaped optical waveguide on silicon nitride on thin-film lithium niobate

Abstract

The invention discloses a preparation method for loading a strip-shaped optical waveguide on silicon nitride on thin-film lithium niobate, and belongs to the technical field of optical waveguides, and the preparation method comprises the steps: S1, preparing a thin-film lithium niobate substrate; s2, depositing a silicon nitride film with the thickness of Xnm on the surface of the film lithium niobate substrate by utilizing PECVD (Plasma Enhanced Chemical Vapor Deposition); s3, the surface of the silicon nitride film is smoothed through CMP; s4, reducing the content of hydrogen in the silicon nitride thin film by adopting RTA under the condition of 500 DEG C; s5, depositing silicon nitride with the thickness of Ynm on the surface of the silicon nitride thin film by using PECVD (plasma enhanced chemical vapor deposition); s6, smoothing the surface of the silicon nitride film by using a CMP process; s7, under the condition of 500 DEG C, reducing the hydrogen content in the silicon nitride film by adopting RTA; s8, spin-coating photoresist on the surface of the silicon nitride thin film; s9, photoetching and developing the photoresist; s10, etching the silicon nitride thin film by adopting a dry method; and S11, removing the photoresist.

Description

Technical Field

[0001] The invention belongs to the technical field of optical waveguides, and in particular relates to a method for preparing a silicon nitride loaded strip type optical waveguide on a lithium niobate thin film. Background Art

[0002] As we all know, silicon nitride is considered to be an ideal choice to replace traditional lithium niobate materials because of its similar refractive index to lithium niobate (specifically, the refractive index of lithium niobate is 2.14, while the refractive index of silicon nitride is about 2.0), as well as its excellent high-power handling capability, excellent insulation performance and wide optical transparency window. In particular, silicon nitride has shown great potential in the application of loading strip-type optical waveguides on thin-film lithium niobate. It can not only avoid the complex lithium niobate etching process, but also provide more stable and reliable performance.

[0003] In the process of preparing silicon nitride films, LPCVD (high temperature and low pressure chemical vapor deposition) and PECVD (plasma enhanced chemical vapor deposition) are the two most common deposition methods. However, since lithium niobate materials cannot withstand the high temperature environment in the LPCVD process, this greatly limits its application scope in certain application scenarios.

[0004] In contrast, the use of PECVD to deposit silicon nitride films on thin-film lithium niobate has obvious advantages. The PECVD method can be deposited at a lower temperature, thus avoiding the damage of high temperature to the lithium niobate material. However, the silicon nitride film deposited by this method usually contains a high hydrogen content, about 20% hydrogen bonds. This high hydrogen content will lead to a decrease in the crystallinity of the film, resulting in more amorphous areas in the film. The presence of this amorphous structure will increase the roughness of the film surface, which in turn will increase the loss of the silicon nitride film waveguide, making it difficult to further reduce the loss. Summary of the invention

[0005] The present invention provides a method for preparing a silicon nitride loaded strip optical waveguide on a thin-film lithium niobate. By combining a step-by-step deposition technique with a chemical mechanical planarization and a rapid annealing process, the goal of preparing a low-loss silicon nitride loaded strip optical waveguide on a thin-film lithium niobate is achieved.

[0006] The object of the present invention is to provide a method for preparing a silicon nitride loaded strip-type optical waveguide on a thin-film lithium niobate, comprising:

[0007] S1, preparing a thin film lithium niobate substrate;

[0008] S2, using PECVD to deposit a silicon nitride film with a thickness of X nm on the surface of the thin film lithium niobate substrate;

[0009] S3, smoothing the surface of the silicon nitride film by CMP;

[0010] S4, using RTA to reduce the hydrogen content in the silicon nitride film at 500°C;

[0011] S5, depositing silicon nitride with a thickness of Y nm on the surface of the silicon nitride film by PECVD;

[0012] S6, smoothing the surface of the silicon nitride film by using a CMP process;

[0013] S7, using RTA at 500°C to reduce the hydrogen content in the silicon nitride film;

[0014] S8, spin coating photoresist on the surface of the silicon nitride film;

[0015] S9, photolithography and developing photoresist;

[0016] S10, etching the silicon nitride film by dry method;

[0017] S11. Remove the photoresist.

[0018] Preferably, the range of X is 100-200.

[0019] Preferably, X is 100, or 150 or 200.

[0020] Preferably, Y is in the range of 100-200.

[0021] Preferably, Y is 100, or 150 or 200.

[0022] Preferably, S9 specifically includes: exposing the waveguide pattern with an electron beam, and developing and removing the photoresist at unexposed positions.

[0023] Preferably, S11 specifically includes: removing the photoresist by using a butanone solution.

[0024] The advantages and positive effects of the present invention are:

[0025] In the present invention, the deposition process of the loading strip silicon nitride film layer is carried out in two or more steps by plasma enhanced chemical vapor deposition (PECVD) technology. In each step of the deposition process, the thickness of the film is controlled between 100 and 200 nanometers. Such thickness control is to ensure the stability of the deposition process and the quality of the film. If the thickness of the deposition is less than 100 nanometers, then the control of the process parameters needs to be more precise, which will undoubtedly increase the difficulty and uncertainty of the process operation. On the contrary, if the thickness of the deposition exceeds 200 nanometers, the stress inside the film will increase significantly, which may cause the film to crack or peel off, thereby affecting the overall performance and reliability of the film.

[0026] In order to ensure the flatness of the silicon nitride film surface, chemical mechanical planarization (CMP) technology is used to process the film surface after each deposition step. CMP technology can effectively reduce the roughness of the film surface, thereby providing a smoother surface for subsequent processes. After the treatment is completed, the silicon nitride film is treated by a 500°C rapid annealing (RTA) process. The main purpose of the RTA process is to reduce the hydrogen content in the film, thereby increasing the crystallinity of the film and further optimizing the performance of the film.

[0027] Through the above-mentioned deposition, planarization and annealing processes, a high-quality silicon nitride film can be finally deposited on the thin film lithium niobate. In order to realize the preparation of silicon nitride loaded strip-type optical waveguide on low-loss thin film lithium niobate, the present invention also adopts electron beam exposure and dry etching processes. Electron beam exposure technology can provide high-precision pattern transfer, while the dry etching process can accurately remove excess silicon nitride film, thereby forming the required loaded strip-type optical waveguide structure. Through these fine process steps, the present invention successfully prepared a silicon nitride loaded strip-type optical waveguide with excellent performance, providing important technical support for applications in related fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Flowchart of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to further understand the content, features and effects of the present invention, the following embodiments are given as examples and described in detail with reference to the accompanying drawings:

[0030] The technical solution of the present invention is:

[0031] See also Figure 1 , a method for preparing a silicon nitride loaded strip-type optical waveguide on a thin-film lithium niobate, comprising:

[0032] Step 1: First, you need to prepare a thin-film lithium niobate substrate, which is the basis of the entire process.

[0033] Step 2: Next, a layer of silicon nitride film with a thickness of 100 to 200 nanometers is deposited on the surface of the thin-film lithium niobate substrate using plasma enhanced chemical vapor deposition (PECVD) technology. This step is to form a protective layer on the surface of the substrate for subsequent processing.

[0034] Step 3: In order to ensure the flatness of the silicon nitride film surface, chemical mechanical planarization (CMP) technology is used to smooth the film surface, thereby reducing the surface roughness and laying a good foundation for subsequent process steps.

[0035] Step 4: To further improve the quality of the silicon nitride film, the film is treated at a high temperature of 500 degrees Celsius using rapid thermal annealing (RTA) technology to reduce the hydrogen content in it. This step helps improve the stability and reliability of the film.

[0036] Step 5: After completing the above steps, PECVD technology is used again to deposit a layer of silicon nitride film with a thickness of 100 to 200 nanometers on the surface of the already deposited silicon nitride film with a thickness of 100 to 200 nanometers. In this way, a silicon nitride film with a total thickness of 200 to 400 nanometers is obtained on the surface of the thin-film lithium niobate substrate.

[0037] Step 6: In order to ensure that the surface of the newly deposited silicon nitride film is also flat, the CMP process is used again to smooth the surface of the film to further reduce the surface roughness and ensure the smooth progress of subsequent processes.

[0038] Step 7: To further optimize the quality of the silicon nitride film, the film is treated again at 500 degrees Celsius using rapid thermal annealing (RTA) technology to reduce the hydrogen content in the film. This step helps improve the overall performance of the film.

[0039] Step 8: Spin-coat a layer of photoresist on the surface of the silicon nitride film. The photoresist may be HSQ photoresist. This step is to form the desired pattern in the subsequent photolithography process.

[0040] Step 9: Next, the photolithography development process is carried out. The waveguide pattern is accurately transferred to the HSQ photoresist through electron beam exposure technology, and then the HSQ photoresist in the unexposed position is removed through the development process to form the desired pattern.

[0041] Step 10: In order to accurately etch the silicon nitride film, dry etching technology is used. During the etching process, key parameters such as gas ratio, bias power, and reaction chamber pressure are finely controlled to ensure that the sidewall morphology of the silicon nitride film is steep and avoid side etching, thereby ensuring the accuracy and reliability of the waveguide structure.

[0042] Step 11: Finally, the photoresist needs to be removed. Using butanone solution as a remover, the HSQ photoresist is completely removed by chemical dissolution, thus completing the entire process.

[0043] In the present invention, the deposition process of the loading strip silicon nitride film layer is carried out in two or more steps by plasma enhanced chemical vapor deposition (PECVD) technology. In each step of the deposition process, the thickness of the silicon nitride film is controlled between 100 and 200 nanometers. Such thickness control is to ensure the stability of the deposition process and the reliability of the film quality. If the thickness of the deposition is less than 100 nanometers, then the control of the process parameters needs to be more precise, which will undoubtedly increase the difficulty and uncertainty of the process operation. On the contrary, if the thickness of the deposition exceeds 200 nanometers, the stress inside the film will increase significantly, which may cause the film to crack or peel off, thereby affecting its performance and reliability.

[0044] In order to ensure the surface quality of silicon nitride film, chemical mechanical planarization (CMP) treatment is performed after each deposition step. CMP is an effective surface treatment technology that can significantly reduce the roughness of the film surface, thereby providing a smoother surface for subsequent processes. After the treatment is completed, the silicon nitride film is treated by a 500°C rapid annealing (RTA) process. The RTA process can perform high-temperature treatment on the film in a short time, thereby effectively reducing the hydrogen content in the film, improving the crystallinity of the film, and further optimizing its performance.

[0045] Through the above-mentioned deposition, CMP treatment and RTA process, a high-quality silicon nitride film is finally deposited on the thin-film lithium niobate. In order to realize the preparation of silicon nitride loaded strip-type optical waveguide on low-loss thin-film lithium niobate, the present invention also adopts electron beam exposure and dry etching process. Electron beam exposure technology can provide high-precision pattern transfer, while dry etching process can accurately remove excess material, thereby forming the required silicon nitride loaded strip-type optical waveguide structure on the thin-film lithium niobate. Through these fine process steps, the present invention successfully prepares silicon nitride loaded strip-type optical waveguides with excellent performance, providing important technical support for applications in related fields.

[0046] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a silicon nitride loaded strip-type optical waveguide on a thin-film lithium niobate, characterized in that: include: S1, preparing a thin film lithium niobate substrate; S2, using PECVD to deposit a silicon nitride film with a thickness of X nm on the surface of the thin film lithium niobate substrate; S3, using CMP to smooth the surface of the silicon nitride film; S4, using RTA to reduce the hydrogen content in the silicon nitride film at 500°C; S5, depositing silicon nitride with a thickness of Y nm on the surface of the silicon nitride film by PECVD; S6, smoothing the surface of the silicon nitride film by using a CMP process; S7, using RTA to reduce the hydrogen content in the silicon nitride film at 500°C; S8, spin coating photoresist on the surface of the silicon nitride film; S9, photolithography and developing photoresist; S10, etching the silicon nitride film by dry method; S11. Remove the photoresist.

2. The method for preparing the silicon nitride loaded strip type optical waveguide on thin film lithium niobate according to claim 1, characterized in that: The range of X is 100~200.

3. The method for preparing the silicon nitride loaded strip type optical waveguide on thin film lithium niobate according to claim 2, characterized in that: X is 100, or 150 or 200.

4. The method for preparing the silicon nitride loaded strip type optical waveguide on thin film lithium niobate according to claim 1, characterized in that: The range of Y is 100~200.

5. The method for preparing the silicon nitride loaded strip type optical waveguide on thin film lithium niobate according to claim 4, characterized in that: Y is 100, 150 or 200.

6. The method for preparing the silicon nitride loaded strip type optical waveguide on thin film lithium niobate according to claim 1, characterized in that: S9 specifically includes: exposing the waveguide pattern with an electron beam, and developing and removing the photoresist at unexposed positions.

7. The method for preparing the silicon nitride loaded strip type optical waveguide on thin film lithium niobate according to claim 1, characterized in that: S11 specifically includes: removing the photoresist by using a butanone solution.

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