CN116500857A - Preparation method of thin-film lithium niobate photonic device - Google Patents

Abstract

The invention relates to a preparation method of a thin-film lithium niobate photonic device, and relates to the field of micro-nano processing. Including: spin-coating photoresist on the surface of thin-film lithium niobate, using a photolithography machine to expose and develop; depositing a layer of titanium film and a layer of chromium film successively by electron beam evaporation or magnetron sputtering; wet removal of photoresist The resist is stripped to obtain a metal hard mask composed of titanium and chromium; the lithium niobate material in the unmasked area of the mask is removed by dry etching; the metal mask is etched by wet method. The hard mask of the present invention adopts a double-layer thin film structure of titanium and chromium, which can effectively avoid the cracking of the chromium mask. At the same time, a better stripping effect can be achieved in the densely patterned area of the device, and the mask can be effectively avoided during the stripping process. The damage of debris to the mask structure improves the quality of the etching mask and improves the performance of photonic devices.

Description

A kind of preparation method of thin film lithium niobate photonic device

technical field

The present invention relates to the field of micro-nano processing, more specifically, to a preparation method of a thin-film lithium niobate photonic device, in particular to a preparation method of a thin-film lithium niobate micro-nano device.

Background technique

With the advent of the fourth industrial revolution and the rapid development of emerging application scenarios such as cloud services, big data and industrial Internet of Things, there is an urgent need for new optoelectronic devices with ultra-large bandwidth, high speed, low power consumption and large-scale integration. Similar to the application of silicon in the field of microelectronics, lithium niobate has been widely used in the field of optoelectronics due to its advantages such as large second-order nonlinear coefficient, wide optical transparent window and high refractive index. Especially with the maturity of thin film lithium niobate (Thin-film lithium niobate, TFLN) preparation technology based on ion cutting and wafer bonding technology, it is possible to prepare an electro-optical device with the integration characteristics of optical waveguide and excellent lithium niobate. , acousto-optic and nonlinear optoelectronic devices become possible. At the same time, thin-film lithium niobate materials have shown a wide range of application scenarios in the fields of low power consumption, large bandwidth and highly integrated optoelectronics.

In the fields of electro-optic modulators, optical sensors, and fiber optic gyroscopes, traditional lithium niobate materials have been very maturely applied, and related optoelectronic devices are prepared by ion diffusion or proton exchange methods. However, these two processes have a low degree of modification of the refractive index of lithium niobate and the temperature requirements of the ion diffusion process exceed the maximum temperature that the thin-film lithium niobate material can withstand, so the above processes are no longer suitable for thin-film lithium niobate micro-nano Device processing. At present, dry etching based on inductively coupled plasma etching is the mainstream process for the preparation of thin-film lithium niobate micro-nano devices. Due to the high hardness of lithium niobate, chromium and nickel metal waveguides prepared by metal stripping or etching are often used as etching masks in dry etching to achieve higher selective etching. Dry etching will transfer the roughness and other characteristics of the metal mask to the thin-film lithium niobate waveguide, thereby affecting the loss of the final optical waveguide. Therefore, the optimization of the quality of the metal mask is an urgent problem to be solved in the current dry etching thin film lithium niobate process based on the metal mask.

Contents of the invention

In view of the existing technical problems, the purpose of the present invention is to provide a method for processing and preparing thin-film lithium niobate micro-nano devices. The invented hard mask adopts a titanium-chromium double-layer film structure, which can effectively improve the chromium film due to photolithography. The problem of fragmentation caused by uneven glue can solve the problem of rough edges of mask patterns caused by single-layer metal peeling and difficult metal peeling in pattern-intensive areas.

According to the purpose of the present invention, a kind of preparation method of thin film lithium niobate photonic device is provided, comprises the following steps:

(1) Form a titanium conductive layer on the surface of thin-film lithium niobate, spin-coat electron beam photoresist on the surface of the titanium conductive layer, and develop after exposure;

(2) deposit titanium film and chromium film successively on the photoresist after step (1) development;

(3) Remove the photoresist by a wet method, and peel off the metal on the photoresist to obtain a metal mask composed of a titanium film and a chromium film;

(4) using a dry etching method to remove the part of the titanium conductive layer not covered by the metal mask and the lithium niobate below;

(5) Removing the mask and the remaining part of the conductive layer of the titanium film by wet etching to obtain a thin-film lithium niobate photonic device.

According to another aspect of the present invention, a method for preparing a thin-film lithium niobate photonic device is provided, comprising the following steps:

(1) Spin-coat UV photoresist on the surface of thin-film lithium niobate, develop after exposure;

(2) deposit titanium film and chromium film successively on the photoresist after step (1) development;

(3) Remove the photoresist by a wet method, and peel off the metal on the photoresist to obtain a metal mask composed of a titanium film and a chromium film;

(4) using a dry etching method to remove lithium niobate not covered by the metal mask;

(5) The mask is removed by wet etching to obtain a thin-film lithium niobate photonic device.

Preferably, the thickness of the titanium film is 10nm-20nm, and the thickness of the chromium film is 90nm-120nm.

Preferably, the thickness of the lithium niobate thin film is 300nm-900nm.

Preferably, the deposition in step (2) is electron beam evaporation or magnetron sputtering.

Preferably, in step (3), the wet removal of the photoresist is specifically: immersing the thin film lithium niobate deposited with a titanium film and a chromium film in N-methylpyrrolidone, acetone or N-ethylpyrrolidone solution, and then wash.

Preferably, in step (5), removing the mask object by wet etching is as follows: using chromium etching solution and titanium etching solution in sequence to remove the remaining mask after dry etching.

Preferably, in step (1), the lithium niobate thin film is located on the upper surface of the buried oxide layer, and the buried oxide layer is located on the upper surface of the substrate layer.

Preferably, the material of the substrate layer is lithium niobate or silicon, and the material of the buried oxide layer is silicon dioxide.

Preferably, the substrate layer has a thickness of 400 μm˜500 μm, and the buried oxide layer has a thickness of 1 μm˜4 μm.

Preferably, the dry etching method in step (4) is reactive ion etching, inductively coupled plasma etching or magnetic neutral discharge plasma etching.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:

(1) The hard mask of the present invention adopts a titanium-chromium double-layer metal film structure to replace the traditional single-layer chromium metal film, which can effectively improve the cracking problem of the metal film in the single-layer chromium film.

(2) The hard mask of the present invention replaces the traditional single-layer chromium metal film with a titanium-chromium double-layer metal film structure, which can achieve faster and more effective stripping effects in metal stripping, avoiding the traditional single-layer chromium metal Ultrasonic operation of the film during metal stripping reduces damage to the metal mask.

(3) The double-layer film structure combined with titanium and chromium adopted in the present invention, compared with the traditional single-layer chromium metal film, achieves a better peeling effect in the device structure dense area, reduces the process requirements, and obtains better metal mask.

Description of drawings

Fig. 1 is a flow chart of the method for preparing micro-nano devices on the surface of thin-film lithium niobate disclosed in Example 1 of the present invention.

FIG. 2 is a process diagram of the method for preparing micro-nano devices on the surface of thin-film lithium niobate disclosed in Example 1 of the present invention.

Fig. 3 is a flow chart of the method for preparing micro-nano devices on the surface of thin-film lithium niobate disclosed in Example 2 of the present invention.

FIG. 4 is a process diagram of the method for preparing micro-nano devices on the surface of thin-film lithium niobate disclosed in Example 2 of the present invention.

5 is a flow chart of a method for preparing a micro-nano device on a thin-film lithium niobate surface according to a comparative example of the present invention.

Fig. 6 is a process diagram of a method for preparing a micro-nano device on a thin-film lithium niobate surface according to a comparative example of the present invention.

FIG. 7 is a microscope image of the metal surface after depositing a single-layer chromium metal film in Example 2 of the present invention.

FIG. 8 is a microscope image of the metal surface after depositing a titanium-chromium metal film in Example 1 of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

The invention provides a method for preparing a thin-film lithium niobate micro-nano device. The flow chart of the method is shown in FIG. 3 , which includes the following steps:

S1: cleaning and drying the thin film lithium niobate wafer;

S2: Spin-coat photoresist on the surface of the thin-film lithium niobate wafer, use a photolithography machine to expose and develop;

S3: successively depositing a layer of titanium film and a layer of chromium film on the patterned photoresist;

S4: remove the photoresist by wet method, peel off the metal on the glue, and obtain a metal mask composed of titanium and chromium;

S5: Removing the lithium niobate material in the unshielded area of the metal mask by means of dry etching;

S6: Wet etching the metal mask.

The thin-film lithium niobate micro-nano device obtained by the present invention comprises a substrate layer, a buried oxygen layer, and a waveguide layer (thin-film lithium niobate) from bottom to top.

In some embodiments, the thickness of the sunken bottom layer of the thin film lithium niobate material is 400 μm-500 μm, the thickness of the buried oxide layer is 1-4 μm, and the thickness of the waveguide layer is 300 nm-900 nm.

In some embodiments, the substrate layer material of the thin film lithium niobate material is lithium niobate or silicon, the material of the buried oxide layer is silicon dioxide, and the material of the waveguide layer is lithium niobate.

In some embodiments, the photolithography includes one of electron beam exposure or ultraviolet exposure.

In some embodiments, when the photolithography is electron beam exposure, a layer of titanium film may be formed on the surface of the lithium niobate film first, and then the photoresist is spin-coated. A titanium film is used as a conductive layer to improve exposure.

In some embodiments, the titanium film thickness of the conductive layer is 10-20 nm.

In some embodiments, the method of forming the titanium film or the chromium film is one of electron beam evaporation or magnetron sputtering.

In some embodiments, the thickness of the titanium film is 10-20 nm, and the thickness of the chromium film is 90-120 nm.

Example 1

The thin film lithium niobate material is X-cut thin film lithium niobate, the substrate layer 110 is 500 μm silicon, the buried oxide layer 120 is 2.7 μm silicon dioxide, and the waveguide layer 130 is 600 nm thick X-cut lithium niobate. The flow chart and process diagram of the processing technology of micro-nano devices on the surface of thin-film lithium niobate in this case are shown in Figure 1 and Figure 2 respectively, and the specific implementation steps include:

S1, cleaning the thin-film lithium niobate; first, soak the thin-film lithium niobate in the room temperature solution of acetone and isopropanol successively and ultrasonically for 5 minutes, secondly, rinse with deionized water, and finally blow dry with nitrogen;

S2. Forming a titanium film 140 with a thickness of 15nm on the surface of the thin film lithium niobate 130 by means of electron beam evaporation, which is used as a conductive layer to enhance the effect of electron beam exposure;

S3, uniformly spin-coat electron beam photoresist (such as: ARP6200.13) on the surface of titanium film 140 to form photoresist layer 150, and complete exposure under suitable acceleration voltage, exposure metering, and exposure current, and finally expose The final photoresist layer 150 is developed and dried;

S4. Forming a 10nm titanium film 160 and a 90nm chromium film 170 on the surface of the photoresist 150 successively by using an electron beam evaporation process.

S5. The photoresist is removed by a wet method, and the metal on the photoresist is stripped. At room temperature, the lithium niobate thin film deposited with titanium and chromium was soaked in N-methylpyrrolidone solution for about 30 minutes, rinsed with deionized water and dried.

S6, using dry etching based on inductively coupled plasma etching, removing the part of the conductive layer of the titanium film not covered by the metal mask, and the part of the conductive layer of the titanium film not covered corresponds to the lithium niobate directly below;

S7. The mask is removed by wet etching to obtain the designed thin-film lithium niobate optical waveguide. The etching solution uses chromium etching solution and titanium etching solution in sequence to ensure that the remaining mask after dry etching can be completely removed.

Example 2

The thin film lithium niobate material is X-cut thin film lithium niobate, the substrate layer 110 is 500 μm lithium niobate, the buried oxide layer 120 is 2.7 μm silicon dioxide, and the waveguide layer 130 is 600 nm thick X-cut lithium niobate. The flow chart and process diagram of the processing technology of micro-nano devices on the surface of thin-film lithium niobate in this case are shown in Figure 3 and Figure 4 respectively, and the specific implementation steps include:

S1: Clean the thin-film lithium niobate; first, soak the thin-film lithium niobate in the room temperature solution of acetone and isopropanol successively and ultrasonically for 5 minutes, secondly, rinse with deionized water, and finally blow dry with nitrogen;

S2: Uniformly spin-coat a photoresist layer 150 on the surface of lithium niobate film at a certain rotational speed, specifically ultraviolet photoresist, and perform exposure under a suitable acceleration voltage, exposure metering, and exposure current, and finally perform exposure on the exposed light The resist layer 150 is developed and dried;

S3: A 20nm titanium film 160 and a 90nm chromium film 170 are successively formed on the surface of the photoresist layer 150 after photolithography by means of magnetron sputtering.

S4: The photoresist is removed by a wet method, and the metal on the photoresist is stripped. At room temperature, the lithium niobate thin film deposited with titanium and chromium was soaked in N-methylpyrrolidone solution for about 30 minutes, rinsed with deionized water and dried.

S5: removing the lithium niobate material not covered by the mask by dry etching based on plasma etching.

S6: The hard mask is removed by wet etching to obtain the designed thin-film lithium niobate optical waveguide. The etching solution uses a chromium etching solution and a titanium etching solution in sequence to ensure that the remaining hard mask of the dry etching can be completely removed.

comparative example

The thin film lithium niobate material is X-cut thin film lithium niobate, the substrate layer 110 is 500 μm silicon, the buried oxide layer 120 is 2.7 μm silicon dioxide, and the waveguide layer 130 is 600 nm thick X-cut lithium niobate. The flow chart and process diagram of the processing technology of micro-nano devices on the surface of thin-film lithium niobate in this case are shown in Figure 5 and Figure 6 respectively, and the specific implementation steps include:

S1, cleaning the thin-film lithium niobate; first, soak the thin-film lithium niobate in the room temperature solution of acetone and isopropanol successively and ultrasonically for 5 minutes, secondly, rinse with deionized water, and finally blow dry with nitrogen;

S2. Forming a titanium film 140 with a thickness of 15nm on the surface of the thin film lithium niobate 130 by means of electron beam evaporation, which is used as a conductive layer to enhance the effect of electron beam exposure;

S3, uniformly spin-coat electron beam photoresist (such as: ARP6200.13) on the surface of titanium film 140 to form photoresist layer 150, and complete exposure under suitable acceleration voltage, exposure metering, and exposure current, and finally expose The final photoresist layer 150 is developed and dried;

S4, forming a 90 nm chromium film 160 on the surface of the photoresist 150 by using an electron beam evaporation process.

S5. The photoresist is removed by a wet method, and the metal on the photoresist is stripped. At room temperature, the lithium niobate thin film deposited with titanium and chromium was soaked in N-methylpyrrolidone solution for about 30 minutes, rinsed with deionized water and dried.

S6, using dry etching based on inductively coupled plasma etching, removing the part of the conductive layer of the titanium film not covered by the metal mask, and the part of the conductive layer of the titanium film not covered corresponds to the lithium niobate directly below;

S7. The mask is removed by wet etching to obtain the designed thin-film lithium niobate optical waveguide. The etching solution uses chromium etching solution and titanium etching solution in sequence to ensure that the remaining mask after dry etching can be completely removed.

Figure 7 is a microscope image of the metal surface after the deposition of a single-layer chromium metal film. Compared with the surface of the titanium-chromium double-layer metal film deposited in Figure 8, it is not difficult to find that the traditional single-layer chromium metal film will cause large-scale cracks on the surface.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (10)

1. The preparation method of the thin film lithium niobate photonic device is characterized by comprising the following steps:

(1) Forming a titanium conductive layer on the surface of the thin film lithium niobate, spin-coating electron beam photoresist on the surface of the titanium conductive layer, exposing and developing;

(2) Sequentially depositing a titanium film and a chromium film on the photoresist after the development in the step (1);

(3) Removing the photoresist by adopting a wet method, and stripping metal on the photoresist to obtain a metal mask formed by the titanium film and the chromium film;

(4) Removing the part of the titanium conductive layer uncovered by the metal mask and lithium niobate below the titanium conductive layer by adopting a dry etching method;

(5) And removing the mask and the residual titanium film conducting layer part through wet etching to obtain the thin film lithium niobate photonic device.

2. The preparation method of the thin film lithium niobate photonic device is characterized by comprising the following steps:

(1) Spin-coating ultraviolet photoresist on the surface of the film lithium niobate, and developing after exposure;

(2) Sequentially depositing a titanium film and a chromium film on the photoresist after the development in the step (1);

(3) Removing the photoresist by adopting a wet method, and stripping metal on the photoresist to obtain a metal mask formed by the titanium film and the chromium film;

(4) Removing lithium niobate uncovered by the metal mask by adopting a dry etching method;

(5) And removing the mask through wet etching to obtain the thin film lithium niobate photonic device.

3. The method of manufacturing a thin film lithium niobate photonic device according to claim 1 or 2, wherein the thickness of the titanium film is 10nm to 20nm, and the thickness of the chromium film is 90nm to 120nm.

4. The method of making a thin film lithium niobate photonic device of claim 1 or 2, wherein the thin film lithium niobate has a thickness of 300nm to 900nm.

5. The method of making a thin film lithium niobate photonic device of claim 1 or 2, wherein the deposition of step (2) is electron beam evaporation or magnetron sputtering.

6. The method for manufacturing a thin film lithium niobate photonic device according to claim 1 or 2, wherein in the step (3), the wet photoresist removal is specifically: the thin film lithium niobate deposited with the titanium film and the chromium film is soaked in N-methyl pyrrolidone, acetone or N-ethyl pyrrolidone solution and then washed.

7. The method of manufacturing a thin film lithium niobate photonic device according to claim 1 or 2, wherein in step (5), the mask removal by wet etching is specifically: and sequentially adopting chromium corrosive liquid and titanium corrosive liquid to remove the residual mask after dry etching.

8. The method of making a thin film lithium niobate photonic device of claim 1 or 2, wherein in step (1), the thin film lithium niobate is located on an upper surface of an oxygen buried layer, and the oxygen buried layer is located on an upper surface of a substrate layer.

9. The method of manufacturing a thin film lithium niobate photonic device of claim 8, wherein the substrate layer material is lithium niobate or silicon, and the oxygen-buried layer material is silicon dioxide;

preferably, the thickness of the substrate layer is 400-500 μm, and the thickness of the buried oxide layer is 1-4 μm.

10. The method of manufacturing a thin film lithium niobate photonic device according to claim 1 or 2, wherein the dry etching method in step (4) is reactive ion etching, inductively coupled plasma etching or magnetic neutral line discharge plasma etching.