阅读说明：本技术 一种铌酸锂薄膜表面制作光学微纳图形的方法 (Method for manufacturing optical micro-nano graph on surface of lithium niobate thin film ) 是由 曾嵘 庄池杰 马昕雨 沈瞿欢 王华磊 吴长春 于 2019-11-28 设计创作，主要内容包括：本发明涉及一种铌酸锂薄膜表面制作光学微纳图形的方法,属于微纳加工技术领域,包括：制作电子束曝光所需版图；对铌酸锂衬底进行清洗、烘干；在铌酸锂衬底上溅射金属导电层；在铌酸锂衬底上旋涂电子束胶；将铌酸锂衬底进行第一次电子束曝光制作标记；显影和定影；在铌酸锂衬底上磁控溅射金属制作金属标记；去胶剥离金属掩蔽的图形,制成带有金属突起标记的铌酸锂片；在铌酸锂片上旋涂电子束胶；将铌酸锂片进行第二次电子束曝光制作图形；显影和定影；进行图形转移,形成微纳结构。通过本发明所述方法,可在不导电的铌酸锂材料上制作侧壁陡直的图形,且可制作尺寸900nm以下的微纳图形,所制作的光波导折射率对比度大,可减小光器件尺寸,提高光器件性能。(The invention relates to a method for manufacturing an optical micro-nano graph on the surface of a lithium niobate film, belonging to the technical field of micro-nano processing and comprising the following steps: making a layout required by electron beam exposure; cleaning and drying the lithium niobate substrate; sputtering a metal conducting layer on a lithium niobate substrate; spin-coating electron beam glue on a lithium niobate substrate; carrying out first electron beam exposure on the lithium niobate substrate to manufacture a mark; developing and fixing; making a metal mark on a lithium niobate substrate by magnetron sputtering metal; removing the photoresist and stripping the metal masking pattern to prepare a lithium niobate sheet with a metal protrusion mark; spin-coating electron beam glue on a lithium niobate sheet; carrying out secondary electron beam exposure on the lithium niobate sheet to manufacture a pattern; developing and fixing; and carrying out pattern transfer to form a micro-nano structure. By the method, the graph with steep side wall can be manufactured on the non-conductive lithium niobate material, the micro-nano graph with the size of less than 900nm can be manufactured, the refractive index contrast of the manufactured optical waveguide is high, the size of an optical device can be reduced, and the performance of the optical device can be improved.)

1. A method for manufacturing an optical micro-nano graph on the surface of a lithium niobate thin film is characterized by comprising the following steps:

step 1, making a layout required by electron beam exposure;

step 2, cleaning and drying the lithium niobate substrate;

step 3, sputtering a metal conducting layer on the lithium niobate substrate;

step 4, spin-coating electron beam glue on the lithium niobate substrate;

step 5, carrying out first electron beam exposure on the lithium niobate substrate to manufacture a mark;

step 6, developing and fixing;

step 7, making a metal mark on the lithium niobate substrate by magnetron sputtering metal;

step 8, removing the photoresist and stripping the metal masking pattern to prepare a lithium niobate sheet with a metal protrusion mark;

step 9, spin-coating electron beam glue on the lithium niobate sheet;

step 10, carrying out secondary electron beam exposure on the lithium niobate sheet to manufacture a pattern;

step 11, developing and fixing;

and 12, carrying out pattern transfer to form a micro-nano structure.

2. The method for manufacturing the optical micro-nano graph on the surface of the lithium niobate thin film according to claim 1, wherein in the step 1, the layout comprises a first layer of marks and a second layer of graphs; the first layer is marked as a square with a side length of more than 4 μm or a cross with a width of more than 4 μm.

3. The method for manufacturing an optical micro-nano pattern on the surface of the lithium niobate thin film according to claim 1, wherein in the step 3, a metal conducting layer with the thickness of 10-50 nm is manufactured on the lithium niobate substrate by adopting magnetron sputtering, and the metal conducting layer is a metal which does not react with an alkaline developing solution.

4. The method for manufacturing the optical micro-nano graph on the surface of the lithium niobate thin film according to claim 1, wherein in the step 4, an electron beam glue PMMA is spin-coated on a lithium niobate substrate at a rotation speed of 2000r/min, and the lithium niobate substrate is placed on a hot plate at 170 ℃ for drying for 15 minutes, wherein the thickness of the electron beam glue film is 700-800 nm.

5. The method for manufacturing the optical micro-nano graph on the surface of the lithium niobate thin film according to claim 1, wherein in the step 5, the lithium niobate substrate is sent to an electron beam exposure machine to manufacture a first layer of mark, the electron beam exposure machine has 80kV voltage and 0.6-6.8 nA beam current, and the exposure dose is 4-8C/m²。

6. The method for manufacturing the optical micro-nano pattern on the surface of the lithium niobate thin film according to claim 1, wherein in the step 6, the developing solution is an electronic grade and is a mixed solution of MIBK and IPA, the volume ratio of MIBK to IPA is 1:3, and the developing time is 60-180 s;

the fixer is electronic grade, and the fixer is rinsed for 30s by using ethanol and then the sample is dried by using nitrogen.

7. The method for manufacturing the optical micro-nano graph on the surface of the lithium niobate thin film according to claim 1, wherein in the step 7, the thickness of the magnetron sputtering metal is 60-200 nm.

8. The method for manufacturing the optical micro-nano graph on the surface of the lithium niobate thin film according to claim 1, wherein in the step 8, the electron beam glue is removed by ultrasound in acetone, and the graph masked by the metal is peeled off, wherein the ultrasound power is 2-10W, and the ultrasound time is 5-10 minutes; and cleaning the lithium niobate substrate by using ethanol and deionized water, and drying by using nitrogen to prepare the lithium niobate sheet with the metal protrusion marks.

9. The method for manufacturing an optical micro-nano pattern on the surface of the lithium niobate thin film according to claim 1, wherein in the step 9, a high temperature adhesive tape is coated on the lithium niobate sheet with the metal protrusion marks at two diagonally opposite corners, electron beam glue HSQ is spin-coated at a rotating speed of 2000r/min, wherein the thickness of the electron glue film is 300-500 nm, and the electron glue film is baked for 2 minutes on a hot plate at 150 ℃ after the spin-coating.

10. The method for manufacturing the optical micro-nano graph on the surface of the lithium niobate thin film according to claim 9, wherein in the step 10, the high-temperature adhesive tape of the lithium niobate sheet obliquely opposite to two corners is replaced by a conductive adhesive tape and then is placed into an electron beam exposure machine again, the electron beam exposure machine has 80kV voltage and 0.6-6.5 nA beam current, and the exposure dose is 0.7-4C/m²And measuring the resistance between the lithium niobate sheet and the metal tray by a multimeter to be below 100k omega.

Technical Field

The invention relates to a method for manufacturing an optical micro-nano graph on the surface of a lithium niobate thin film, belonging to the technical field of micro-nano processing.

Background

Lithium niobate material (LiNbO)₃) The crystal is a non-conductive uniaxial crystal, and has wide application prospect in the fields of optical signal processing, quantum electrodynamics and optomechanics due to the wide light-transmitting window (340-4600 nm) and excellent electro-optic, acousto-optic, nonlinear optics and piezoelectric properties. The single crystal lithium niobate thin film can be prepared by ion implantation and bonding technology, and due to the appearance of the lithium niobate thin film, the lithium niobate material is more emphasized in the field of integrated optics.

At present, the manufacturing method of the lithium niobate optical waveguide mainly comprises titanium diffusion and proton exchange after photoetching. In the photoetching process, patterns on a mask are transferred to photosensitive photoresist by ultraviolet light exposure, and the exposed positive photoresist or the unexposed negative photoresist is removed by development. The titanium diffusion method is to oxidize titanium metal under high temperature, then titanium diffuses from the crystal surface into the crystal in the form of ions, and shows an increase in refractive index in optical properties, thereby forming a waveguide. The proton exchange method is to replace hydrogen ions in a proton source with lithium ions in lithium niobate at a certain temperature to change the refractive index of the lithium niobate and form a waveguide. However, the two processes of titanium diffusion and proton exchange have the following defects:

(1) both titanium diffusion and proton exchange methods can only produce optical waveguides with small refractive index difference (<0.02), resulting in weak limitation on optical signals, large optical mode field size, reduced optical device performance, and increased device size.

(2) Li is easy to diffuse outwards from the surface of the substrate in the titanium diffusion process, and the surface lacking Li can generate z-polarized planar waveguide, thereby seriously affecting the performance of an optical device. The proton exchange process can only be applied to x-cut and z-cut lithium niobate wafers because the acid solution can cause chemical corrosion to the y-cut wafers. In addition, proton exchange can only increase the refractive index of the extraordinary light, and high-temperature annealing treatment is also needed to solve the problems of unstable refractive index and attenuation of the electro-optic effect.

(3) The size of the pattern produced by photoetching can only be made to be more than 1 mu m, and the fine pattern can not be processed.

(4) The actual size of the optical waveguide manufactured by titanium diffusion and proton exchange is 7-10 mu m.

The PMMA electron beam glue has the characteristics of high resolution, high contrast and low sensitivity, but the etching resistance is poor, and when a nano structure is manufactured, the etching resistance of PMMA is weakened due to the fact that the pattern is fine and thin PMMA glue needs to be coated evenly, and the masking effect cannot be achieved in dry etching. Hsq (hydrogen silsesquioxane) e-beam resist is a negative resist with very high resolution and is widely used in e-beam exposure, but its sensitivity to electrons is very low, which increases the dose and time of the e-beam required for e-beam exposure, and limits its larger scale application.

In addition, most of the transparent materials applied in the optical field have low conductivity, which leads to charge accumulation during the electron beam exposure process, and affects the deflection of the electron beam, thereby causing defects and drift of the pattern. Therefore, this problem is usually solved by forming a very thin (10-15nm) conductive layer of metal on the top surface of the substrate with low conductivity, which makes the electrons more susceptible to lateral drift and affects the steepness of the sidewall of the pattern.

Disclosure of Invention

In order to solve the problems, the invention aims to provide a method for manufacturing an optical micro-nano graph on the surface of a lithium niobate film through electron beam exposure, in particular to a method for manufacturing the optical micro-nano graph on the surface of the lithium niobate film by using negative electron beam glue, which can manufacture a lithium niobate film micro-nano structure with the size less than 900nm in a short process time, and the manufactured lithium niobate film micro-nano structure has smooth and steep side wall, accurate size and strong repeatability.

The purpose of the invention is realized by the following technical scheme:

a method for manufacturing an optical micro-nano graph on the surface of a lithium niobate film comprises the following steps:

step 1, making a layout required by electron beam exposure;

step 2, cleaning and drying the lithium niobate substrate;

step 3, sputtering a metal conducting layer on the lithium niobate substrate;

step 4, spin-coating electron beam glue on the lithium niobate substrate;

step 5, carrying out first electron beam exposure on the lithium niobate substrate to manufacture a mark;

step 6, developing and fixing;

step 7, making a metal mark on the lithium niobate substrate by magnetron sputtering metal;

step 8, removing the photoresist and stripping the metal masking pattern to prepare a lithium niobate sheet with a metal protrusion mark;

step 9, spin-coating electron beam glue on the lithium niobate sheet;

step 10, carrying out secondary electron beam exposure on the lithium niobate sheet to manufacture a pattern;

step 11, developing and fixing;

and 12, carrying out pattern transfer to form a micro-nano structure.

Further, in step 1, the layout comprises a first layer of marks and a second layer of graphs; the first layer is marked as a square with a side length of more than 4 μm or a cross with a width of more than 4 μm.

Further, in step 2, the cleaning and drying the lithium niobate substrate includes: and repeatedly cleaning the lithium niobate substrate with ethanol, acetone and deionized water, and drying in an oven for 15-20 min.

Further, in the step 3, a metal conducting layer of 10-50 nm is manufactured on the lithium niobate substrate by adopting magnetron sputtering, wherein the metal conducting layer is made of metal which does not react with an alkaline developing solution.

Further, in the step 4, spin-coating electron beam glue PMMA on the lithium niobate substrate at the rotating speed of 2000r/min, and placing the lithium niobate substrate on a hot plate at the temperature of 170 ℃ for drying for 15 minutes after spin-coating, wherein the thickness of the electron beam glue PMMA is 700-800 nm.

Further, in the above-mentioned case,in step 5, the lithium niobate substrate is sent to an electron beam exposure machine to manufacture a first layer of mark, the electron beam exposure machine has 80kV voltage and 0.6-6.8 nA beam current, and the exposure dose is 4-8C/m²。

Further, in the step 6, the developing solution is an electronic grade and is a mixed solution of MIBK and IPA, the volume ratio of the MIBK to the IPA is 1:3, and the developing time is 60-180 s;

the fixer is electronic grade, and the fixer is rinsed for 30s by using ethanol and then the sample is dried by using nitrogen.

Further, in step 7, the thickness of the magnetron sputtering metal is 60-200 nm.

Further, in the step 8, removing electron beam glue and stripping the metal-masked pattern in acetone by ultrasound, wherein the ultrasound power is 2-10W, and the ultrasound time is 5-10 minutes; and cleaning the lithium niobate substrate by using ethanol and deionized water, and drying by using nitrogen to prepare the lithium niobate sheet with the metal protrusion marks.

Further, in step 9, a lithium niobate sheet with a metal protrusion mark is covered with a high temperature adhesive tape at two diagonally opposite corners, electron beam glue HSQ is spin-coated at a rotating speed of 2000r/min, wherein the thickness of the electron glue film is 300-500 nm, and the electron glue film is placed on a hot plate at 150 ℃ after spin-coating and baked for 2 minutes.

Further, in step 10, the high-temperature adhesive tape with the lithium niobate sheet obliquely opposite to two corners is replaced by a conductive adhesive tape and then is placed into an electron beam exposure machine again, the electron beam exposure machine has 80kV voltage and 0.6-6.5 nA beam current, and the exposure dose is 0.7-4C/m²And measuring the resistance between the lithium niobate sheet and the metal tray by a multimeter to be below 100k omega.

Further, in step 11, the developing solution is MF319, and the developing time is 2 minutes; the fixation is soaking for 2 minutes by using deionized water and washing for 30 seconds.

The invention has the beneficial effects that:

(1) by the method, the graph with steep side wall can be manufactured on the non-conductive lithium niobate material, and the manufactured graph has smooth side wall. The smoothness of the sidewalls of the lithium niobate pattern is limited by the smoothness of the sidewalls of the etch mask. The sidewall smoothness of the glue is better than with a hard mask such as metal or silicon dioxide. Therefore, the etching-resistant electron beam resist HSQ is used as a mask to directly etch the lithium niobate, and a graph with smooth side wall can be manufactured. In addition, because the electron beam exposure precision is high, and the technical scheme of electron beam exposure HSQ is reliable, the size of the manufactured graph is accurate and controllable, and the experimental repeatability is high.

(2) And (3) adopting electron beam exposure to manufacture micro-nano patterns with the size of less than 900 nm. According to the rayleigh criterion, the lithography accuracy is limited by the wavelength of light, the accuracy is higher the shorter the wavelength, and the electron is a matter wave with extremely short wavelength, which means that the accuracy of electron beam exposure is higher than lithography, and thus can reach the nanometer level.

(3) By adopting an etching processing technology, the coating material around the manufactured optical waveguide is air (the refractive index is 1), the refractive index of the lithium niobate is about 2.2, and the difference between the refractive indexes of the lithium niobate and the lithium niobate is large, so that light can be better limited; while the traditional process of manufacturing optical waveguide on lithium niobate is titanium diffusion or proton exchange process, the refractive index difference between the waveguide and the surrounding medium material is only 0.02 or less. The optical waveguide manufactured based on the method has high refractive index contrast, and can reduce the size of an optical device and improve the performance of the optical device.

(4) The electron beam glue HSQ has large exposure current and small exposure dosage when being used for carrying out electron beam exposure, and saves time and cost.

(5) The first electron beam exposure provides a focusing mark for the second electron beam exposure, and splicing errors easily generated during exposure of HSQ electron beam negative photoresist can be avoided.

Drawings

FIG. 1 is a flow chart of a method for manufacturing a micro-nano graph on the surface of lithium niobate.

FIG. 2 is a sectional electron microscope image of the HSQ electron beam paste produced on the surface of lithium niobate according to the present invention, wherein the HSQ electron beam paste is 1-HSQ electron beam paste, and the lithium niobate is 2-substrate.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The electron beam exposure machine used in this example was manufactured by Nanobeam, Inc. of the United kingdom under the model No. NB 5.

A method for manufacturing an optical micro-nano graph on the surface of a lithium niobate thin film is shown in figure 1 and comprises the following steps:

step 1, a layout required by electron beam exposure is manufactured in drawing software (such as AutoCAD or Ledit), and the layout comprises a first layer of marks and a second layer of graphs. The first layer is marked as a square with the side length larger than 4 mu m or a cross with the width larger than 4 mu m, wherein the cross is a cross-shaped pattern, specifically a horizontal line and a vertical line, and the width of the line is larger than 4 mu m. The first layer mark is used for focusing in the second electron beam exposure.

Step 2, cleaning and drying the lithium niobate substrate, comprising: and repeatedly cleaning the lithium niobate substrate with ethanol, acetone and deionized water, and drying in an oven for 15-20 min.

And 3, manufacturing a metal conducting layer with the thickness of 10-50 nm on the lithium niobate substrate by adopting magnetron sputtering, wherein the metal conducting layer is metal which does not react with an alkaline developing solution, such as chromium.

And 4, spin-coating electron beam glue polymethyl methacrylate (PMMA) on the metal conducting layer of the lithium niobate substrate at the rotating speed of 2000r/min, and placing on a hot plate at the temperature of 170 ℃ for drying for 15 minutes after spin-coating, wherein the thickness of the electron beam glue film is 700-800 nm.

And 5, conveying the lithium niobate substrate into an electron beam exposure machine to manufacture a first layer of mark, wherein the electron beam exposure machine has the voltage of 80kV and the beam current of 0.6-6.8 nA, and the exposure dose is 4-8C/m²Preferably 6C/m²。

And 6, developing and fixing. The developing solution is an electronic grade and is a mixed solution of methyl isobutyl ketone (MIBK) and Isopropanol (IPA), the volume ratio of the MIBK to the IPA is 1:3, and the developing time is 60-180 s; the fixer is electronic grade, and the fixer is rinsed for 30s by using ethanol and then the sample is dried by using nitrogen.

And 7, manufacturing a metal mark on the lithium niobate substrate by magnetron sputtering metal, wherein the manufacturing of the metal mark can ensure that the subsequent electron beam glue HSQ focusing value is accurate, the thickness of the metal mark is 60-200 nm, and the metal can be chromium or aluminum.

Step 8, ultrasonically removing electron beam glue and stripping a metal-masked pattern in acetone, wherein the ultrasonic power is 2-10W, and the ultrasonic time is 5-10 minutes; and cleaning the lithium niobate substrate by using ethanol and deionized water, and drying by using nitrogen to prepare the lithium niobate sheet with the metal protrusion marks.

And 9, covering the lithium niobate sheet with the metal protrusion marks with high-temperature adhesive tapes at two diagonally opposite corners, spin-coating the electron beam adhesive HSQ at the rotating speed of 2000r/min, wherein the thickness of the electron adhesive film is 300-500 nm, and placing the electron adhesive film on a hot plate at 150 ℃ for baking for 2 minutes after spin-coating. The high-temperature adhesive tape covered by the lithium niobate sheet diagonally opposite to the two corners can be attached to a subsequent conductive adhesive tape to form a conductive path in order to ensure that the two corners are not covered by the electron beam adhesive.

And step 10, replacing the high-temperature adhesive tape of the lithium niobate sheet diagonally opposite to two corners with a conductive adhesive tape, and then putting the conductive adhesive tape into the electron beam exposure machine again, wherein the lithium niobate sheet can be fixed on the electron beam exposure machine by using the conductive adhesive tape, and the conductivity of the sample is ensured. Attaching the lithium niobate sheet to a metal tray of an electron beam exposure machine, wherein the electron beam exposure machine has 80kV voltage and 0.6-6.5 nA beam current, and the exposure dose is 0.7-4C/m²Preferably 2C/m²And measuring the resistance between the lithium niobate sheet and the metal tray by a multimeter to be below 100k omega.

Step 11, development and fixing. Wherein the developing solution is MF319, and the developing time is 2 minutes; the fixation is soaking for 2 minutes by using deionized water and washing for 30 seconds.

And step 12, carrying out pattern transfer, such as etching, stripping, electroplating and the like, and forming a micro-nano structure.

In this embodiment, the purpose of the first electron beam exposure is to make a metal mark used for focusing of the second electron beam exposure, so that a positive electron beam resist, i.e., PMMA (which is removed when the exposed part is developed and is not left by the exposed part) is used to expose and develop the pattern at the mark position to form a groove, and then subsequent sputtering and stripping processes are performed to make a protruding metal mark. The purpose of the second electron beam exposure is to manufacture a micro-nano pattern on the surface of the lithium niobate, in order to ensure short exposure time, negative electron beam glue HSQ (exposed parts are left during development and unexposed parts are removed) is preferably selected, only the area with the micro-nano pattern needs to be exposed, the large area of the residual sample surface does not need to be exposed, and the exposure time is saved; the etching resistance of the negative electron beam resist HSQ is also an important reason for selecting the negative electron beam resist HSQ for the second exposure.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.