CN116338857A - Preparation method of low-loss thin film lithium niobate optical waveguide based on electron beam photoresist - Google Patents
Preparation method of low-loss thin film lithium niobate optical waveguide based on electron beam photoresist Download PDFInfo
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- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 title claims abstract description 146
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- 239000008367 deionised water Substances 0.000 claims description 25
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- 235000012239 silicon dioxide Nutrition 0.000 claims description 9
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 8
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 7
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 7
- 238000011010 flushing procedure Methods 0.000 claims description 7
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- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 5
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- PQXKHYXIUOZZFA-UHFFFAOYSA-M lithium fluoride Chemical compound [Li+].[F-] PQXKHYXIUOZZFA-UHFFFAOYSA-M 0.000 abstract description 8
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/13—Integrated optical circuits characterised by the manufacturing method
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/13—Integrated optical circuits characterised by the manufacturing method
- G02B6/136—Integrated optical circuits characterised by the manufacturing method by etching
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12035—Materials
- G02B2006/1204—Lithium niobate (LiNbO3)
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12166—Manufacturing methods
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12166—Manufacturing methods
- G02B2006/12176—Etching
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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Abstract
The invention provides a preparation method of a low-loss thin film lithium niobate optical waveguide based on electron beam photoresist, which comprises the following steps: s1, providing a pre-prepared thin film lithium niobate wafer as a substrate; s2, spin-coating electron beam photoresist on the surface of the thin film lithium niobate layer, and pre-baking the photoresist; s3, transferring a mask pattern to the photoresist on the surface of the baked photoresist by using an electron beam exposure process, and post-baking a sample; s4, developing and fixing the baked photoresist in sequence to form a photoresist mask layer, then etching the thin film lithium niobate layer by using an inductive coupling plasma etching process, transferring the pattern on the photoresist to the thin film lithium niobate layer, and taking argon as etching gas; and S5, removing the residual photoresist on the thin film lithium niobate layer to obtain the low-loss thin film lithium niobate optical waveguide. The invention does not need to additionally grow a hard mask, has high processing precision, does not generate lithium fluoride byproduct deposition, and effectively reduces the edge roughness of the waveguide and the waveguide transmission loss.
Description
Technical Field
The invention relates to the field of thin film lithium niobate optical waveguides, in particular to a preparation method of a low-loss thin film lithium niobate optical waveguide based on electron beam photoresist.
Background
Lithium niobate is a multifunctional material with the characteristics of electro-optic effect, nonlinear optics, piezoelectricity, ferroelectric and the like, and is widely applied in the fields of optical communication, integrated optoelectronic devices and the like. Compared with bulk material lithium niobate, the thin film lithium niobate has excellent electro-optical characteristics, on-chip integration and other characteristics, and becomes a potential solution for next generation photon integrated devices. The research and development of devices such as modulators, optical microcavities, mode converters and the like based on a thin film lithium niobate platform provides possibility for solving the current optical communication and signal processing requirements. In order to realize optoelectronic devices based on thin film lithium niobate, various integrated optical waveguide structures need to be designed. The optical waveguide structure with high processing precision and low loss is prepared by the process, and has very important significance for processing large-scale thin film lithium niobate optoelectronic devices and effectively improving the device performance.
However, the process of preparing low-loss thin film lithium niobate waveguides remains an international challenge. The use of photolithographic and etching processes to fabricate waveguides on thin film lithium niobate wafers is a recent research focus. The traditional preparation method of the thin film lithium niobate waveguide is to etch the thin film lithium niobate by adopting a hard mask such as metal or silicon dioxide, for example, the patent numbers of the invention of CN114755761A and CN110764185A are that the thin film lithium niobate is etched by adopting a metal hard mask, and the method is to use fluorine-based gas, so that byproducts such as lithium fluoride and the like are necessarily generated to be attached to the surface of the waveguide in the etching process, thereby increasing the roughness of the side wall of the waveguide and further improving the transmission loss of the waveguide. On the other hand, hard masks can reduce the dimensional accuracy of waveguide fabrication, which is detrimental to fine processing. In addition, growing the hard mask also increases the process steps of waveguide preparation, and increases the complexity of the process flow.
The processing precision and transmission loss of the waveguide have great influence on the performance of an optoelectronic device based on a thin film lithium niobate platform, so a new process preparation scheme needs to be explored to realize the preparation of the thin film lithium niobate optical waveguide with high processing precision and low loss.
Disclosure of Invention
In view of the above, the invention provides a preparation method of a low-loss thin film lithium niobate optical waveguide based on electron beam photoresist, which has the advantage of high processing precision, simultaneously avoids the growth of a hard mask, simplifies the processing process flow, avoids the generation of lithium fluoride byproducts, and effectively reduces waveguide loss.
The technical scheme of the invention is realized as follows: the invention provides a preparation method of a low-loss thin film lithium niobate optical waveguide based on electron beam photoresist, which comprises the following steps:
s1, providing a pre-prepared thin film lithium niobate wafer as a substrate, wherein the thin film lithium niobate wafer sequentially comprises a silicon substrate layer, a silicon dioxide layer and a thin film lithium niobate layer from bottom to top;
s2, spin-coating electron beam photoresist on the surface of the thin film lithium niobate layer, and pre-baking the photoresist;
s3, transferring a mask pattern to the photoresist on the surface of the baked photoresist by using an electron beam exposure process, and post-baking a sample;
s4, developing and fixing the baked photoresist in sequence to form a photoresist mask layer, then etching the thin film lithium niobate layer by using an inductive coupling plasma etching process, transferring the pattern on the photoresist to the thin film lithium niobate layer, wherein etching gas is argon;
and S5, removing the residual photoresist on the thin film lithium niobate layer to obtain the low-loss thin film lithium niobate optical waveguide.
In the step S2, AR-P6200.13 is adopted for the electron beam photoresist, the spin speed of the photoresist is 2000-3000r/min, and the photoresist homogenizing time is 1-2min.
Based on the above technical solution, preferably, in step S2, before spin-coating the electron beam photoresist, the thin film lithium niobate wafer needs to be cleaned, and the cleaning method includes: putting a film lithium niobate sample into acetone for ultrasonic treatment for 5-10min, putting into isopropanol solution for ultrasonic treatment for 5-10min, and then flushing for 10-15s under deionized water.
Based on the above technical solution, preferably, the methods of pre-baking and post-baking in steps S2 and S3 are: placing the sample on a heating plate, and baking at 130-150deg.C for 1-2min.
Based on the technical proposal, preferably, in the etching process of the step S4, the flow rate of argon is 30-50sccm, the radio frequency power is 100-150W, the ICP power is 600-800W, the etching selection ratio of lithium niobate to photoresist is (1-1.3) to 1, and the etching rate of lithium niobate is about 30-50nm/min; and transferring the pattern of the photoresist mask layer to the lithium niobate layer after etching for 8-12min to form the ridge-shaped thin film lithium niobate optical waveguide with the etching depth of 350-370 nm.
Based on the above technical solution, preferably, the method for removing the residual photoresist in step S5 includes: soaking the sample in the photoresist removing solution for 1-3h, dissolving the residual photoresist, and then taking out the sample and flushing the sample for 10-30s under deionized water; the degumming liquid is N-methyl pyrrolidone or acetone.
On the basis of the above technical solution, preferably, after removing the residual photoresist in step S5, the organic byproduct residue needs to be removed, and the method comprises the following steps: placing the sample in a cleaning solution, heating in a water area of 60-80 ℃ for 30-60min, dissolving residual organic matters on a lithium niobate layer, taking out the sample, and washing for 10-30s under deionized water to finally obtain the thin film lithium niobate optical waveguide; the cleaning solution is prepared from ammonia water, hydrogen peroxide and deionized water according to the volume ratio of (1-2) to (1-3) to 5.
Based on the above technical solution, preferably, the thickness of the lithium niobate layer in the step S1 is 600nm, the thickness of the silicon dioxide layer is 4.7 μm, and the thickness of the silicon substrate layer is 0.525mm.
On the basis of the technical scheme, preferably, the width of the low-loss thin film lithium niobate optical waveguide wire is larger than 1 mu m, the etching depth of the waveguide is smaller than 400nm, and the inclination angle of the side wall of the waveguide is 60-65 degrees.
Compared with the prior art, the preparation method of the low-loss thin film lithium niobate optical waveguide based on the electron beam photoresist has the following beneficial effects:
(1) Compared with the traditional scheme, the invention adopts the electron beam photoresist as the mask, does not need to additionally grow a hard mask, and has more concise process steps.
(2) The electron beam photoresist used in the invention enables the processing precision of the thin film lithium niobate optical waveguide to reach 10 nanometers, and compared with the traditional hard mask scheme, the processing precision is higher, the side wall roughness is low, and the invention can construct a lithium niobate device easy to integrate based on the processing precision and provides a process foundation for the development of large-scale lithium niobate integration.
(3) According to the invention, pure argon is selected as etching gas, and compared with the mixed etching of argon and fluorine-based gas in the traditional scheme, the method does not generate lithium fluoride byproduct deposition, and effectively reduces the edge roughness of the waveguide and the waveguide transmission loss.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method for preparing a thin film lithium niobate optical waveguide based on an electron beam photoresist mask according to the present invention;
FIGS. 2 a-2 e are diagrams of variations of the process preparation of a thin film lithium niobate optical waveguide according to the method of FIG. 1; in the figure, a 1-lithium niobate layer, a 2-silicon dioxide layer, a 3-silicon substrate layer and a 4-photoresist mask layer;
FIG. 3 is a scanning electron microscope image of a waveguide cross-section obtained using the thin film lithium niobate optical waveguide fabrication method of FIG. 1;
FIGS. 4a and 4b are graphs comparing an etched waveguide using an electron beam resist mask with a etched waveguide using a metal mask, FIG. 4a being an etched waveguide using an electron beam resist mask, and FIG. 4b being an etched waveguide using a metal mask;
fig. 5a and 5b are graphs comparing the processing precision of the electron beam photoresist mask etched waveguide and the metal mask etched waveguide when the design width is 1.5 μm, fig. 4a is the electron beam photoresist mask etched waveguide, and fig. 4b is the metal mask etched waveguide.
Detailed Description
The following description of the embodiments of the present invention will clearly and fully describe the technical aspects of the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, are intended to fall within the scope of the present invention.
The developing solution MIBK is prepared from MIBK (methyl isobutyl ketone) and IPA (isopropyl alcohol) according to the volume ratio of 1:3.
Example 1
The preparation method of the low-loss thin film lithium niobate optical waveguide based on the electron beam photoresist of the embodiment comprises the following steps:
s1, obtaining a thin film lithium niobate wafer sample to be processed, wherein the thin film lithium niobate comprises a 600nm thick lithium niobate layer, a 4.7 mu m thick silicon dioxide layer and a 0.525mm thick silicon substrate layer as shown in FIG. 2 a. Cleaning a sample: and (3) putting the film lithium niobate wafer sample into acetone for ultrasonic treatment for 8min, putting into isopropanol solution for ultrasonic treatment for 10min, taking out, and washing for 15s under deionized water.
S2, spin-coating electron beam photoresist, as shown in FIG. 2b, placing a thin film lithium niobate sample wafer in a photoresist homogenizing machine, spin-coating an AR-P6200.13 photoresist layer, and rotating for 1min at 2000r/min to obtain a photoresist layer with the thickness of 600 nm; and (3) carrying out pre-baking after glue homogenizing, and placing the sample on a heating plate and baking for 1min at 150 ℃.
S3, transferring the designed mask pattern onto the photoresist layer by adopting an electron beam lithography process, and after lithography, post-baking the sample wafer and baking for 1min at 150 ℃.
S4, as shown in FIG. 2c, developing and fixing the sample subjected to electron beam lithography. The sample is soaked in MIBK developer for 70s to develop, and then the sample wafer is taken out and soaked in isopropanol fixing solution for 30s to fix, so that a photoresist mask layer is formed.
And S5, as shown in FIG. 2d, etching the thin film lithium niobate layer in the sample wafer by using an inductive coupling plasma etching process. Argon is used as etching gas, the gas flow rate is 30sccm during etching, the radio frequency power is 100W, the ICP power is 600W, the etching selection ratio of lithium niobate to photoresist is 1.2:1, the etching rate of lithium niobate is about 30nm/min, and the pattern of a photoresist mask layer is transferred onto the lithium niobate layer after etching for 12min, so that the ridge-shaped film lithium niobate optical waveguide with the etching depth of 360nm is formed.
S6, as shown in FIG. 2e, the photoresist layer remained on the lithium niobate layer 3 is cleaned by adopting a photoresist removing solution. The sample was immersed in N-methylpyrrolidone for 2 hours, the remaining photoresist was dissolved, and then the sample was taken out and rinsed under deionized water for 10 seconds.
S7, as shown in FIG. 2e, placing the sample in an RCA solution formed by ammonia water, hydrogen peroxide and deionized water in a ratio of 1:1:5, heating the solution in a water area at 60 ℃ for 30min, dissolving residual organic matters on a lithium niobate layer, taking out the sample, and washing the sample under deionized water for 10S to finally obtain the thin film lithium niobate optical waveguide.
The low-loss thin film lithium niobate optical waveguide prepared in this example has linewidths of 1 μm, 1.5 μm, and 2 μm, ridge waveguide etching depth of 360nm, and waveguide sidewall inclination angle of 64.2 ° (see fig. 3).
Example 2
The preparation method of the low-loss thin film lithium niobate optical waveguide based on the electron beam photoresist of the embodiment comprises the following steps:
s1, obtaining a thin film lithium niobate wafer sample to be processed, wherein the thin film lithium niobate comprises a 600nm thick lithium niobate layer, a 4.7 mu m thick silicon dioxide layer and a 0.525mm thick silicon substrate layer as shown in FIG. 2 a. Cleaning a sample, putting the sample of the film lithium niobate wafer into acetone for ultrasonic treatment for 5min, putting into isopropanol solution for ultrasonic treatment for 5min, taking out, and washing for 10s under deionized water.
S2, spin-coating electron beam photoresist, as shown in FIG. 2b, placing a film lithium niobate sample wafer in a photoresist homogenizing machine, spin-coating an AR-P6200.13 photoresist layer, and rotating for 2min at 2000r/min to obtain the photoresist layer with the thickness of 600 nm. And (3) carrying out pre-baking after glue homogenizing, placing the sample on a heating plate, and baking for 2min at 130 ℃.
S3, transferring the designed mask pattern onto the photoresist layer by adopting an electron beam lithography process, and after lithography, post-baking the sample wafer and baking for 2min at 130 ℃.
S4, as shown in FIG. 2c, developing and fixing the sample subjected to electron beam lithography. The sample is soaked in MIBK developer for 70s to develop, and then the sample wafer is taken out and soaked in isopropanol fixing solution for 30s to fix, so that a photoresist mask layer is formed.
And S5, as shown in FIG. 2d, etching the thin film lithium niobate layer in the sample wafer by using an inductive coupling plasma etching process. Argon is used as etching gas, the gas flow rate in the etching process is 40sccm, the radio frequency power is 100W, the ICP power is 600W, the etching selection ratio of lithium niobate to photoresist is 1:1, the etching rate of lithium niobate is about 30nm/min, and the pattern of the photoresist mask layer is transferred to the lithium niobate layer after etching for 10min, so that the ridge-shaped film lithium niobate optical waveguide with the etching depth of 350nm is formed.
S6, as shown in FIG. 2e, the photoresist layer remained on the lithium niobate layer is cleaned by adopting a photoresist removing solution. The sample was immersed in N-methylpyrrolidone for 1h, the remaining photoresist was dissolved, and then the sample was taken out and rinsed under deionized water for 10s.
S7, as shown in FIG. 2e, placing the sample in an RCA solution formed by ammonia water, hydrogen peroxide and deionized water in a ratio of 2:3:5, heating the solution for 30min at 60 ℃ in a water area, dissolving residual organic matters on a lithium niobate layer, taking out the sample, and flushing the sample for 10S under deionized water to finally obtain the thin film lithium niobate optical waveguide.
The low-loss thin film lithium niobate optical waveguide prepared by the embodiment has line widths of 1 μm, 1.5 μm and 2 μm, ridge waveguide etching depth of 350nm and waveguide side wall inclination angle of 60 degrees.
Example 3
The preparation method of the low-loss thin film lithium niobate optical waveguide based on the electron beam photoresist of the embodiment comprises the following steps:
s1, obtaining a thin film lithium niobate wafer sample to be processed, wherein the thin film lithium niobate comprises a 600nm thick lithium niobate layer, a 4.7 mu m thick silicon dioxide layer and a 0.525mm thick silicon substrate layer as shown in FIG. 2 a. Cleaning a sample, putting the sample of the film lithium niobate wafer into acetone for ultrasonic treatment for 10min, putting into isopropanol solution for ultrasonic treatment for 10min, taking out, and washing for 15s under deionized water.
S2, spin-coating electron beam photoresist, as shown in FIG. 2b, placing a film lithium niobate sample wafer in a spin-coating machine to spin-coat an AR-P6200.13 photoresist layer, and rotating for 1min at 3000r/min to obtain the photoresist layer with the thickness of 500 nm. And (3) carrying out pre-baking after glue homogenizing, placing the sample on a heating plate, and baking for 1min at 150 ℃.
S3, transferring the designed mask pattern onto the photoresist layer by adopting an electron beam lithography process, and after lithography, post-baking the sample wafer and baking for 1min at 150 ℃.
S4, as shown in FIG. 2c, developing and fixing the sample subjected to electron beam lithography. The sample is soaked in MIBK developer for 70s to develop, and then the sample wafer is taken out and soaked in isopropanol fixing solution for 30s to fix, so that a photoresist mask layer is formed.
And S5, as shown in FIG. 2d, etching the thin film lithium niobate layer in the sample wafer by using an inductive coupling plasma etching process. Argon is used as etching gas, the gas flow rate in the etching process is 50sccm, the radio frequency power is 150W, the ICP power is 800W, the etching selection ratio of lithium niobate to photoresist is 1.3:1, the etching rate of lithium niobate is about 50nm/min, and the pattern of the photoresist mask layer is transferred onto the lithium niobate layer after etching for 8min, so that the ridge-shaped film lithium niobate optical waveguide with the etching depth of 370nm is formed.
S6, as shown in FIG. 2e, the photoresist layer remained on the lithium niobate layer is cleaned by adopting a photoresist removing solution. The sample was immersed in acetone for 3 hours, the remaining photoresist was dissolved, and then the sample was taken out and rinsed in deionized water for 30 seconds.
S7, as shown in FIG. 2e, placing the sample in an RCA solution formed by ammonia water, hydrogen peroxide and deionized water in a ratio of 1:1:5, heating the solution in a water area at 80 ℃ for 60min, dissolving residual organic matters on a lithium niobate layer, taking out the sample, and flushing the sample for 30S under deionized water to finally obtain the thin film lithium niobate optical waveguide.
The low-loss thin film lithium niobate optical waveguide prepared by the embodiment has line widths of 1 μm, 1.5 μm and 2 μm, ridge waveguide etching depth of 370nm and waveguide side wall inclination angle of 63 degrees.
Example 4
The preparation method of the low-loss thin film lithium niobate optical waveguide based on the electron beam photoresist of the embodiment comprises the following steps:
s1, obtaining a thin film lithium niobate wafer sample to be processed, wherein the thin film lithium niobate comprises a 600nm thick lithium niobate layer, a 4.7 mu m thick silicon dioxide layer and a 0.525mm thick silicon substrate layer as shown in FIG. 2 a. Cleaning a sample, putting the film lithium niobate wafer sample into acetone for ultrasonic treatment for 8min, putting into isopropanol solution for ultrasonic treatment for 6min, taking out, and flushing for 12s under deionized water.
S2, spin-coating electron beam photoresist, as shown in FIG. 2b, placing a thin film lithium niobate sample wafer in a photoresist homogenizing machine, spin-coating an AR-P6200.13 photoresist layer, and rotating 2800r/min for 1.5min to obtain the photoresist layer with the thickness of 500 nm. And (3) carrying out pre-baking after glue homogenizing, placing the sample on a heating plate, and baking for 1.5min at 140 ℃.
S3, transferring the designed mask pattern onto the photoresist layer by adopting an electron beam lithography process, and after the lithography is finished, post-drying the sample wafer and drying for 1.5min at 140 ℃.
S4, as shown in FIG. 2c, developing and fixing the sample subjected to electron beam lithography. The sample is soaked in MIBK developer for 70s to develop, and then the sample wafer is taken out and soaked in isopropanol fixing solution for 30s to fix, so that a photoresist mask layer is formed.
And S5, as shown in FIG. 2d, etching the thin film lithium niobate layer in the sample wafer by using an inductive coupling plasma etching process. Argon is used as etching gas, the gas flow rate in the etching process is 40sccm, the radio frequency power is 130W, the ICP power is 750W, the etching selection ratio of lithium niobate to photoresist is 1.1:1, the etching rate of lithium niobate is about 45nm/min, and the pattern of the photoresist mask layer is transferred onto the lithium niobate layer after etching for 8min, so that the ridge-shaped film lithium niobate optical waveguide with the etching depth of 360nm is formed.
S6, as shown in FIG. 2e, the photoresist layer remained on the lithium niobate layer 3 is cleaned by adopting a photoresist removing solution. The sample was immersed in N-methylpyrrolidone or acetone for 2 hours, the remaining photoresist was dissolved, and then the sample was taken out and rinsed in deionized water for 20 seconds.
S7, as shown in FIG. 2e, placing the sample in an RCA solution formed by ammonia water, hydrogen peroxide and deionized water in a ratio of 2:1:5, heating the solution in a water area at 75 ℃ for 50min, dissolving residual organic matters on a lithium niobate layer, taking out the sample, and washing the sample under deionized water for 25S to finally obtain the thin film lithium niobate optical waveguide.
The low-loss thin film lithium niobate optical waveguide prepared by the embodiment has line widths of 1 μm, 1.5 μm and 2 μm, ridge waveguide etching depth of 360nm and waveguide side wall inclination angle of 65 degrees.
Example 5
Example 5 differs from example 1 in that: the etching selectivity ratio of the lithium niobate to the photoresist is 1:1, and the etching rate of the lithium niobate is about 50nm/min. The low-loss thin film lithium niobate optical waveguide prepared by the embodiment has line widths of 1 μm, 1.5 μm and 2 μm, ridge waveguide etching depth of 350nm and waveguide sidewall inclination angle of 64.7 degrees.
Example 6
Example 6 differs from example 1 in that: the ratio of ammonia water, hydrogen peroxide and deionized water in the RCA solution is 2:1:5. The low-loss thin film lithium niobate optical waveguide prepared by the embodiment has line widths of 1 μm, 1.5 μm and 2 μm, ridge waveguide etching depth of 360nm and waveguide side wall inclination angle of 63.8 degrees.
Comparative example 1
Comparative example 1a conventional thin film lithium niobate waveguide fabrication process was used, and a Cr mask was used to etch the thin film lithium niobate, with a gas of argon and fluorine based gas 1:1 mixed etching.
Comparative example 2
Comparative example 2a conventional thin film lithium niobate waveguide fabrication process was used, and a Cr mask was used to etch the thin film lithium niobate, with a gas of argon and fluorine based 1:2 mixed etching.
The waveguides prepared in comparative examples 1-2 had large edge roughness, significant deposition, and small physical and design dimensions. Fig. 4a and 5a show the waveguides prepared in example 1, fig. 4b and 5b show the waveguides prepared in comparative example 1, and fig. 4 shows the etched waveguide edge roughness of the metal mask is greater than that of the etched waveguide of the electron beam photoresist mask, which has more obvious deposition and increases waveguide transmission loss. As shown in FIG. 5, the actual size of the electron beam photoresist mask etched waveguide is within 20nm of the design size, and the actual size of the metal mask etched waveguide is more than 270nm of the design size.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.
Claims (9)
1. A preparation method of a low-loss thin film lithium niobate optical waveguide based on electron beam photoresist is characterized by comprising the following steps: the method comprises the following steps:
s1, providing a pre-prepared thin film lithium niobate wafer as a substrate, wherein the thin film lithium niobate wafer sequentially comprises a silicon substrate layer, a silicon dioxide layer and a thin film lithium niobate layer from bottom to top;
s2, spin-coating electron beam photoresist on the surface of the thin film lithium niobate layer, and pre-baking the photoresist;
s3, transferring a mask pattern to the photoresist on the surface of the baked photoresist by using an electron beam exposure process, and post-baking a sample;
s4, developing and fixing the baked photoresist in sequence to form a photoresist mask layer, then etching the thin film lithium niobate layer by using an inductive coupling plasma etching process, transferring the pattern on the photoresist to the thin film lithium niobate layer, wherein etching gas is argon;
and S5, removing the residual photoresist on the thin film lithium niobate layer to obtain the low-loss thin film lithium niobate optical waveguide.
2. The method for preparing the low-loss thin film lithium niobate optical waveguide based on the electron beam photoresist, as claimed in claim 1, is characterized in that: in the step S2, AR-P6200.13 is adopted for the electron beam photoresist, the spin speed of the photoresist is 2000-3000r/min, and the photoresist homogenizing time is 1-2min.
3. The method for preparing the low-loss thin film lithium niobate optical waveguide based on the electron beam photoresist as claimed in claim 2, wherein the method comprises the following steps: in step S2, the thin film lithium niobate wafer needs to be cleaned before spin-coating the electron beam photoresist, and the cleaning method comprises the following steps: putting a film lithium niobate sample into acetone for ultrasonic treatment for 5-10min, putting into isopropanol solution for ultrasonic treatment for 5-10min, and then flushing for 10-15s under deionized water.
4. The method for preparing the low-loss thin film lithium niobate optical waveguide based on the electron beam photoresist, as claimed in claim 1, is characterized in that: the methods of pre-drying and post-drying in the steps S2 and S3 are as follows: placing the sample on a heating plate, and baking at 130-150deg.C for 1-2min.
5. The method for preparing the low-loss thin film lithium niobate optical waveguide based on the electron beam photoresist, as claimed in claim 1, is characterized in that: in the etching process of the step S4, the flow rate of argon is 30-50sccm, the radio frequency power is 100-150W, the ICP power is 600-800W, the etching selection ratio of lithium niobate to photoresist is (1-1.3) to 1, and the etching rate of lithium niobate is about 30-50nm/min; and transferring the pattern of the photoresist mask layer to the lithium niobate layer after etching for 8-12min to form the ridge-shaped thin film lithium niobate optical waveguide with the etching depth of 350-370 nm.
6. The method for preparing the low-loss thin film lithium niobate optical waveguide based on the electron beam photoresist, as claimed in claim 1, is characterized in that: the method for removing the residual photoresist in the step S5 comprises the following steps: soaking the sample in the photoresist removing solution for 1-3h, dissolving the residual photoresist, and then taking out the sample and flushing the sample for 10-30s under deionized water; the degumming liquid is N-methyl pyrrolidone or acetone.
7. The method for preparing the low-loss thin film lithium niobate optical waveguide based on the electron beam photoresist, as claimed in claim 6, is characterized in that: after removing the residual photoresist in step S5, the organic byproduct residues are also required to be removed, and the method comprises the following steps: placing the sample in a cleaning solution, heating in a water area of 60-80 ℃ for 30-60min, dissolving residual organic matters on a lithium niobate layer, taking out the sample, and washing for 10-30s under deionized water to finally obtain the thin film lithium niobate optical waveguide; the cleaning solution is prepared from ammonia water, hydrogen peroxide and deionized water according to the volume ratio of (1-2) to (1-3) to 5.
8. The method for preparing the low-loss thin film lithium niobate optical waveguide based on the electron beam photoresist, as claimed in claim 1, is characterized in that: the thickness of the lithium niobate layer in the step S1 is 600nm, the thickness of the silicon dioxide layer is 4.7 mu m, and the thickness of the silicon substrate layer is 0.525mm.
9. The method for preparing the low-loss thin film lithium niobate optical waveguide based on the electron beam photoresist, as claimed in claim 1, is characterized in that: the width of the low-loss thin film lithium niobate optical waveguide wire is larger than 1 mu m, the etching depth of the waveguide is smaller than 400nm, and the inclination angle of the side wall of the waveguide is 60-65 degrees.
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| CN116953850A (en) * | 2023-09-19 | 2023-10-27 | 济南量子技术研究院 | Lithium niobate thin film waveguide device and preparation method thereof |
| CN116953850B (en) * | 2023-09-19 | 2024-01-19 | 济南量子技术研究院 | Lithium niobate thin film waveguide device and preparation method thereof |
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