阅读说明：本技术 基于氧化硅掩膜的铌酸锂光子芯片制备方法 (Preparation method of lithium niobate photonic chip based on silicon oxide mask ) 是由 金贤敏 王楚涵 李轩坤 于 2020-04-28 设计创作，主要内容包括：一种基于氧化硅掩膜的铌酸锂光子芯片制备方法,利用等离子体增强气相沉积法沉积得到用于保护铌酸锂图案的二氧化硅掩膜层,然后依次涂设导电胶和光刻胶并通过电子束光刻得到所需图案,实现亚微米级的脊状波导的制备,再通过反应离子刻蚀以及采用氩离子刻蚀铌酸锂,形成带有二氧化硅掩膜的铌酸锂图案层和脊状波导。本发明能够实现宽度在亚微米量级的传输损耗低的片上脊状波导且具有较高的加工效率、加工精度高和加工可控性,可用于制备的侧壁光滑度高、光学传输损耗低的光学波导及其他相关的片上微纳光学元件。(A method for preparing a lithium niobate photonic chip based on a silicon oxide mask comprises the steps of utilizing a plasma enhanced vapor deposition method to deposit and obtain a silicon dioxide mask layer for protecting a lithium niobate pattern, then sequentially coating a conductive adhesive and a photoresist, obtaining a required pattern through electron beam lithography, realizing the preparation of a submicron ridge waveguide, and then forming a lithium niobate pattern layer with the silicon dioxide mask and the ridge waveguide through reactive ion etching and argon ion etching of lithium niobate. The invention can realize the on-chip ridge waveguide with low transmission loss and the width of submicron order, has higher processing efficiency, high processing precision and processing controllability, and can be used for preparing the optical waveguide with high side wall smoothness and low optical transmission loss and other related on-chip micro-nano optical elements.)

1. A preparation method of a lithium niobate waveguide based on a silicon oxide film is characterized in that a silicon dioxide mask layer for protecting a lithium niobate pattern is obtained by deposition through a plasma enhanced vapor deposition method, then conductive glue and photoresist are sequentially coated, a required pattern is obtained through electron beam lithography, the submicron ridge waveguide is prepared, and then a lithium niobate pattern layer with the silicon dioxide mask and the ridge waveguide are formed through reactive ion etching and argon ion etching of lithium niobate.

2. The method of claim 1, wherein the silicon dioxide mask layer is deposited by plasma enhanced chemical deposition and has a thickness of 500 nm to 1 μm.

3. The method of claim 1, wherein the conductive paste is applied at a temperature of 90 ℃ for 90 seconds.

4. The method of claim 1, wherein the photoresist is applied at a temperature of 180 ℃ for 4 minutes.

5. The method for preparing a lithium niobate waveguide based on a silicon oxide film as claimed in claim 1, wherein the reactive ion etching is performed by performing reactive etching on lithium niobate with argon ions, the etching protective gas is argon gas of 80sccm, sulfur hexafluoride gas of 8sccm, the argon ion power is 600W, the etching time is 5 minutes, and the etching temperature is 10 ℃.

6. The method for preparing a lithium niobate waveguide based on a silicon oxide film according to claim 1, wherein the lithium niobate is etched by using argon ions, the ridge waveguides with different depths are obtained by adjusting the thickness of the silicon dioxide mask layer, and the etching temperature, pressure, radio frequency, etching time and/or ion power, and the higher the ion power is, the deeper the etching depth is, the larger the height of the obtained ridge waveguides is.

7. The method of claim 6, wherein the adjusting comprises: the etching rate of the silicon dioxide mask layer is 116 nanometers per minute, the etching rate of the lithium niobate thin film is 44 nanometers per minute, and the selectivity ratio is 1: 2.63.

8. The method for preparing a lithium niobate waveguide based on a silicon oxide thin film according to claim 6 or 7, wherein the adjustment is: the silicon dioxide film of 500 nm corresponds to the etched lithium niobate ridge waveguide with a height of 200 nm.

9. A lithium niobate waveguide produced by the method according to any one of claims 1 to 8.

Technical Field

The invention relates to a technology in the field of photonic chips, in particular to a method for preparing a lithium niobate photonic chip based on a silicon oxide mask, which can be used for preparing an optical waveguide with high side wall smoothness and low optical transmission loss and other related on-chip micro-nano optical elements.

Background

The lithium niobate is used as an important material in the aspects of optical modulator design, cavity quantum electrodynamics experiments, microwave photonics and the like, and is mainly used for preparing optical structures. However, because of their very low refractive index difference, small mode confinement, high bending loss, and general polarization independence, it is difficult to fabricate compact optical structures in materials with existing processes.

The existing etching technology related to lithium niobate is mainly based on ion grinding etching, ion beam enhanced etching and focused ion beam etching, and the existing etching technology is low in technical efficiency and low in precision, cannot obtain a submicron-grade structure, and has great difficulty when being applied to optical integration of larger scale and size. How to find a suitable solution to realize high-efficiency and high-precision submicron waveguide structure to realize large-scale optical integration is an important issue facing the field of photonics.

Disclosure of Invention

The invention provides a preparation method of a lithium niobate photonic chip based on a silicon oxide mask, aiming at the defect that the existing on-chip micro-nano processing technology is difficult to construct a submicron-level optical structure on a lithium niobate thin film, and the preparation method can realize an on-chip ridge waveguide with low transmission loss and width in the submicron level, has higher processing efficiency, high processing precision and processing controllability, and can be used for preparing an optical waveguide with high side wall smoothness and low optical transmission loss and other related on-chip micro-nano optical elements.

The invention is realized by the following technical scheme:

the invention relates to a preparation method of a lithium niobate waveguide based on a silicon oxide film, which comprises the steps of utilizing a plasma enhanced vapor deposition method to deposit and obtain a silicon dioxide mask layer for protecting a lithium niobate pattern, then sequentially coating a conductive adhesive and a photoresist, obtaining a required pattern through electron beam lithography, realizing the preparation of a submicron ridge waveguide, and then forming a lithium niobate pattern layer with the silicon dioxide mask and the ridge waveguide through reactive ion etching and adopting argon ion etching lithium niobate.

The silicon dioxide mask layer is obtained by deposition through a plasma enhanced chemical deposition method, and the thickness of the silicon dioxide mask layer is 500 nanometers to 1 micrometer.

The conductive adhesive is SX AR-PC 5000/90.2, preferably the gluing temperature is 90 ℃, and the gluing time is 90 seconds.

The photoresist adopts high-resolution electron beam positive photoresist AR-P6200, the temperature for gluing is preferably 180 ℃, and the time is 4 minutes.

The reactive ion etching is obtained by performing reactive etching on lithium niobate by using argon ions, preferably, the etching protective gas is argon gas of 80sccm, sulfur hexafluoride gas of 8sccm, the argon ion power is 600W, the etching time is 5 minutes, and the etching temperature is 10 ℃.

The method is characterized in that lithium niobate is etched by adopting argon ions, the thickness of the silicon dioxide mask layer, the etching temperature, the pressure, the radio frequency, the etching time and/or the ion power are/is adjusted to obtain the ridge waveguides with different depths, and the higher the ion power is, the deeper the etching depth is, and the larger the height of the obtained ridge waveguides is.

The adjustment specifically comprises the following steps: the etching rate of the silicon dioxide mask layer is 116 nanometers per minute, the etching rate of the lithium niobate film is 44 nanometers per minute, and the selection ratio is 1: 2.63; the height of the silicon dioxide film with the preference of 500 nanometers corresponding to the etched lithium niobate ridge waveguide is 200 nanometers.

Technical effects

The invention integrally solves the technical problems of the on-chip ridge waveguide with low transmission loss and submicron-order width, and higher processing efficiency, processing precision and processing controllability.

Compared with the prior art, the invention further has the following technical effects:

1. the limit of ion grinding etching, ion beam enhanced etching, focused ion beam etching and the like on the width of the ridge waveguide to be processed is broken through. The width of the ridge waveguide is reduced from micron level to submicron level by using an electron beam lithography method, so that the size of the on-chip micro-optical device and the integration efficiency of the on-chip micro-optical device are greatly improved, and large-scale optical preparation and integration are possible.

2. Breaks through the limitation of smoothness of the lithium niobate waveguide by using metal (such as chromium and aluminum) as a conducting layer. The conducting resin is used as a conducting layer, so that the roughness of the waveguide can be reduced, a better etching effect is achieved, and the efficiency is higher.

3. The silicon dioxide is deposited by utilizing a plasma enhanced vapor deposition method to generate a silicon dioxide mask layer, so that a lithium niobate pattern in the process of etching the lithium niobate is protected, the controllability of the etching process is improved, and deeper etching depth can be obtained.

4. By adjusting the thickness of the mask layer of the silicon dioxide and the related parameters (such as temperature, pressure, radio frequency, etching time, ion power and the like) of the instrument, the ridge waveguides with different depths can be obtained, and then integrated optical elements with different functions can be prepared.

Drawings

FIG. 1 is a schematic flow diagram of the present invention;

in the figure: silicon dioxide film 6, silicon dioxide mask layer 7, photoresist 8, conductive adhesive 9 and lithium niobate film 10.

Detailed Description

As shown in fig. 1, this embodiment relates to a process for preparing a lithium niobate waveguide based on a silicon oxide mask by using plasma enhanced chemical vapor deposition, electron beam lithography and reactive ion etching, and specifically includes the following steps:

step 1) plasma enhanced chemical deposition of silicon dioxide, namely taking a lithium niobate film sample with the size of 1cm × 1cm, and depositing a silicon dioxide mask layer 7 on the surface of a lithium niobate film 10 by using a plasma enhanced chemical deposition method, wherein the operation breaks through the limitation of ion grinding etching, ion beam enhanced etching, focused ion beam etching and the like on the width of a ridge waveguide to be processed.

The lithium niobate thin film sample in this example includes: a 0.5mm silicon substrate (not shown in FIG. 1), a 4.7 μm silicon dioxide thin film 6, and SiO₂A 600nm lithium niobate thin film 10 on the film.

Step 2) electron beam lithography: a 400nm thick photoresist 8 is spin-coated on the silicon dioxide mask layer 7 for increasing the etching depth, and a conductive paste 9 for conducting electron beams is further coated on the photoresist 8. After normal exposure, the conductive paste is dissolved in water. Subsequently, the resultant was developed with methyl isobutyl (methyl) ketone for 75 seconds and fixed with isopropyl alcohol for 60 seconds.

The photoresist 8 in this embodiment is a high resolution electron beam positive resist AR-P6200.

The conductive adhesive 9 in this embodiment is SX AR-PC 5000/90.2 conductive adhesive.

The silicon dioxide mask layer 7 can increase the etching depth, enable the height of the waveguide to be more controllable, increase the smoothness of the side wall, reduce the roughness of the waveguide structure, achieve a better etching effect and enable the waveguide transmission efficiency to be higher; by adjusting the thickness of the mask layer of the silicon dioxide and the related parameters (such as temperature, pressure, radio frequency, etching time, ion power and the like) of the instrument, the ridge waveguides with different depths can be obtained, and then integrated optical elements with different functions can be prepared.

Step 3) reactive ion etching of silicon dioxide: the use of a reactive ion etcher to etch silicon dioxide until the silicon oxide mask exposed to the photoresist is completely removed breaks through the smoothness limitation of lithium niobate waveguides using metals (e.g., chromium, aluminum) as the conductive layer.

Step 4) Ar⁺Etching lithium niobate: the method comprises the steps of etching lithium niobate by using argon ion reaction, controlling etching time to obtain the designed etching depth, depositing silicon dioxide by using a plasma enhanced vapor deposition method to generate a silicon dioxide mask layer, and adjusting the thickness of the mask layer of the silicon dioxide, the temperature, the pressure, the radio frequency, the etching time, the ion power and the like of an instrument to obtain the ridge waveguides with different depths so as to prepare the integrated optical elements with different functions.

Step 5) cleaning the residual layer: after removing the residual photoresist 8 using an organic deglued solution, the sample was placed in 5% hydrofluoric acid until the silicon dioxide mask layer 7 was completely removed.

Through specific practical experiments, under the specific environment that a silicon dioxide mask layer (500 nanometers to 1 micrometer) is deposited by using a plasma enhanced chemical deposition method, the ridge waveguide on the chip with low transmission loss and the width and the height in the submicron order can be obtained by adopting a method of etching lithium niobate (the etching parameters are 80sccm of argon, 8sccm of sulfur hexafluoride gas, the ion power is 600W, the etching time is 5 minutes and the etching temperature is 10 ℃) by adopting conductive adhesive SX AR-PC 5000/90.2 (the temperature of gluing is 90 ℃ and the time is 90 seconds), high-resolution electron beam positive adhesive AR-P6200 (the temperature of gluing is 180 ℃ and the time is 4 minutes) and argon ion reaction.

Compared with the prior art, the method can realize the on-chip ridge waveguide with low transmission loss and the width in the submicron order, has higher processing efficiency, high processing precision and processing controllability, and can be used for preparing the optical waveguide with high side wall smoothness and low optical transmission loss and other related on-chip micro-nano optical elements.

The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.