CN114911003B - Optical waveguide preparation method based on cladding ultraviolet lithography - Google Patents

Abstract

The preparation method of the optical waveguide based on cladding ultraviolet lithography comprises the following steps: preparing a lower cladding layer on a substrate; pre-exposing the lower cladding, namely exposing the lower cladding in a large-area low-energy ultraviolet mode in a nitrogen or other inert gas environment; carrying out ultraviolet lithography on the pre-exposed lower cladding in a conventional air environment; developing the lower cladding layer subjected to the photoetching to obtain a groove corresponding to the optical waveguide; preparing a core layer on the developed lower cladding layer, and performing large-area exposure and ultraviolet curing on the core layer in a nitrogen or other inert gas environment; and preparing an upper cladding layer on the solidified core layer, and performing large-area exposure and ultraviolet curing on the upper cladding layer in a nitrogen or other inert gas environment. The invention solves the problem of oxygen polymerization inhibition in the direct ultraviolet lithography process, does not need to provide nitrogen or other inert gas atmosphere in the ultraviolet lithography process, reduces roughness, and has simple operation and high preparation efficiency.

Description

An optical waveguide preparation method based on cladding ultraviolet lithography

Technical field

The invention belongs to the fields of optical communication technology and microelectronics, and specifically relates to a method for preparing an optical waveguide.

Background technique

With the increasing demand for high-speed and high-density data transmission, short-distance optical interconnections have attracted widespread attention due to their advantages such as high bandwidth and integration density, low power consumption and cost, and immunity to electromagnetic interference. Polymer materials are widely used in the preparation of optical waveguides due to their low cost, good flexibility, and good compatibility with various substrates. Photosensitive fluorinated polymers based on acrylic acid have good optical properties, especially the material absorption loss in the 1310nm and 1550nm communication bands is relatively low. Commonly used preparation methods for this material include soft photolithography and reactive ion etching. For soft lithography, the preparation process includes preparing a master, preparing a PDMS mold, and preparing a waveguide. This method usually uses sharp tools to manually peel off the PDMS template. The operation process is complicated and the structure is easily damaged. For reactive ion etching, the equipment is expensive and the sidewall roughness is relatively large during the etching process. The UV lithography process is relatively simple compared to the above preparation process. However, due to the influence of oxygen inhibition, this material cannot complete the polymerization reaction in an air atmosphere. Therefore, UV lithography cannot prepare optical waveguides of this type of material in a conventional air environment.

Contents of the invention

Technical problems to be solved by the present invention: The present invention proposes an improved ultraviolet lithography process, aiming to solve the problem of oxygen inhibition, realize the preparation of optical waveguides based on cladding ultraviolet lithography in an air atmosphere, and simplify the preparation process of optical waveguides. .

In order to achieve the above objects, the present invention adopts the following technical solutions:

An optical waveguide preparation method based on cladding ultraviolet lithography, including:

S1: Preparing the lower cladding layer on the substrate;

S2: Pre-expose the lower cladding to form a thin layer on the surface of the lower cladding;

S3: Perform UV lithography on the lower cladding layer according to the designed optical waveguide line to prepare grooves;

S4: Develop the lower cladding layer that has completed UV lithography to obtain grooves;

S5: Prepare the core layer on the lower cladding layer and cure it;

S6: Prepare the upper cladding layer on the cured core layer and cure it.

In S2: The pre-exposure process is a large-area, low-energy UV exposure in a nitrogen or other inert gas environment. The surface of the lower cladding is not fully cured after the pre-exposure process.

In S3: Add a mask to the lower cladding layer, perform UV photolithography on the lower cladding layer according to the designed optical waveguide line, and prepare grooves.

Preparing the lower cladding layer in S1 means covering the surface of the substrate with a layer of polymer using processes such as spin coating, dipping and pulling, or a doctor blade method.

In S5 and S6: The core layer or upper cladding layer is prepared by processes such as spin coating, dipping and pulling, or scraper methods.

In S5 and S6: The core layer or upper cladding layer is cured by large-area UV exposure in a nitrogen or other inert gas environment.

Also includes S7, which is thermally cured as a whole

In S1: The substrate is cleaned, baked and plasma treated before preparing the lower cladding layer.

In S3: According to the characteristics of the selected glue, determine whether the mask plate is a positive plate or a negative plate.

The principle of the application of the present invention: by subjecting the lower cladding to large-area, low-energy ultraviolet exposure, the polymerization reaction rate is slowed down, thus forming a thin layer of high viscosity on the surface of the lower cladding, which can block the photolithography process. The influence of oxygen on the polymerization reaction allows the photolithography process to be performed in air.

Since the present invention adopts the above technical solutions, it has the following beneficial results:

1. By performing a large-area pre-exposure treatment on the lower cladding layer, the present invention enables the UV lithography process to be carried out in an air environment, without the need to provide nitrogen or other inert gas atmosphere during the UV lithography process, simplifying the preparation process and improving improve preparation efficiency.

2. The waveguide structure prepared by the present invention is parabolic, and because during the development process, the partially solidified thin layer on the surface of the lower cladding will sink as the development proceeds, thus forming a relatively smooth waveguide side wall, which is conducive to Reduce optical waveguide losses.

Description of the drawings

Figure 1 is a schematic flow chart of the optical waveguide preparation method of the present invention.

Figure 2 is a schematic diagram of preparing the lower cladding layer on the substrate.

Figure 3 is a schematic diagram of large-area pre-exposure of the lower cladding.

Figure 4 is a schematic diagram of masked UV lithography of the lower cladding layer.

Figure 5 is a schematic diagram of developing the lower cladding.

Figure 6 is a schematic diagram of preparing the core layer and the upper cladding layer on the surface of the lower cladding layer.

Implementation

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

Example

An optical waveguide preparation method based on cladding ultraviolet lithography, the process includes the following steps:

Step 1: Prepare the lower cladding layer on the substrate;

Step 2: Pre-expose the lower cladding layer;

Step 3: UV lithography is performed on the pre-exposed lower cladding layer;

Step 4: Develop the lower cladding layer after photolithography;

Step 5: Prepare the core layer on the surface of the lower cladding layer and expose it;

Step 6: Prepare the upper cladding layer on the surface of the core layer and expose it.

In step 1, the substrate can be made of a printed circuit board substrate, a glass substrate, a silicon substrate or other materials, and the preparation of the polymer lower cladding layer can be achieved by processes such as spin coating, dipping and pulling, or a scraper method.

In step 2, the pre-exposure treatment of the lower cladding is to perform large-area, low-energy UV exposure on the lower cladding in a nitrogen environment. The appropriate UV curing can be selected according to the thickness of the lower cladding. Energy and pre-exposure time. The entire pre-exposure process needs to be carried out in a nitrogen or other inert gas atmosphere.

In step 3, the photolithography process is carried out in a regular air atmosphere. Photolithography equipment such as a masked photolithography machine or a maskless photolithography machine can be used. The line width of the mask plate design and the photolithography energy will both affect the process. The depth of the groove.

The step 5 is to prepare a core layer on the surface of the lower cladding. The preparation of the core layer can be achieved by processes such as spin coating, dipping and pulling, and scraper methods. Afterwards, the core layer is exposed to large-area UV in a nitrogen or other inert gas environment. UV cured core layer.

The step 6 is to prepare the upper cladding layer on the surface of the core layer. The preparation of the upper cladding layer can be achieved by processes such as spin coating, dipping and pulling, and scraper methods. Afterwards, the core layer is subjected to large-area UV in a nitrogen or other inert gas environment. Exposure, UV curing of the upper cladding layer; finally, the prepared optical waveguide is thermally cured.

Example 2: Step S101, prepare a lower cladding layer on the substrate.

In this embodiment, a lower cladding layer is prepared on the FR-4 substrate of a clean printed circuit board, as shown in Figure 2. The cleaning process of FR-4 substrate 1 is as follows. First, clean it in hot acetone and hot alcohol in sequence. During the cleaning process, in order to prevent damage to the substrate surface, wipe it with a cotton ball, then put it into deionized water for ultrasonic cleaning, and finally blow it with nitrogen. Dry, place on the heating platform and bake at 120°C for 10 minutes. Before preparing the lower cladding layer 2, the substrate is subjected to plasma treatment. Finally, prepare the lower cladding layer 2 on the cleaned FR-4 board 1, as shown in Figure 2. In this embodiment, spin coating can be used to prepare the lower cladding layer, and the thickness of the lower cladding layer can be controlled by the spin coating speed. In this embodiment, the thickness of the lower cladding layer 2 is 26.8 μm.

In this embodiment, the material selected for the lower cladding layer is acrylic negative optical waveguide glue.

Step S102: Pre-expose the lower cladding layer.

In this embodiment, the pre-exposure process is as shown in Figure 3. The pre-exposure process involves large-area, low-energy ultraviolet exposure of the lower cladding layer in a nitrogen environment. The ultraviolet curing oven 4 that can pass nitrogen gas is the preferred equipment. According to the thickness of the lower cladding layer, appropriate ultraviolet curing energy is input into the preparation device, and a timer is used to time the pre-exposure time. Pre-exposed layer 3 is prepared.

In this embodiment, it is necessary to ensure that there is sufficient nitrogen in the exposure environment before pre-exposure.

Step S103: Perform ultraviolet photolithography on the pre-exposed lower cladding layer.

In this embodiment, the photolithography process can be performed in the air. A schematic diagram of the photolithography of the lower cladding layer is shown in Figure 4. A masked photolithography machine is the preferred equipment. According to the characteristics of the selected glue, it is determined whether the mask plate 8 is a positive plate or a negative plate. For example, the prepared photoresist is a negative resist, and the mask plate 8 is determined to be a positive plate, that is, most of the light is transmitted, the lines of the optical waveguide lines are opaque, the exposed part 5 of the lower cladding is cured by ultraviolet, and the unexposed parts There are pre-exposed layer 3 and unexposed layer 2.

In this embodiment, both the line width and photolithography energy designed in the mask plate 8 will affect the depth of the groove.

Step S104: Develop the lower cladding layer after photolithography.

In this embodiment, a schematic diagram of the development step is shown in Figure 5. Choose a suitable developer to develop the unexposed structure, and pay attention to controlling the development time during the development process. For example, acetone and alcohol are used to develop the unexposed structure in sequence, and the development time is 12 seconds respectively. Finally, deionized water is used to clean the developed lower cladding layer.

Steps S105 and S106, prepare a core layer and an upper cladding layer on the surface of the lower cladding layer to prepare a waveguide.

In this embodiment, as shown in FIG. 6 , a core layer 6 is prepared on the surface of the lower cladding layer, and then the core layer is exposed to large-area UV in a nitrogen environment to cure the core layer. Then, an upper cladding layer 7 is prepared on the core layer, and the upper cladding layer is also exposed to large-area ultraviolet light in a nitrogen environment to cure the upper cladding layer. Finally, the sample was placed on a hot plate for thermal curing.

In this embodiment, the core layer and the upper cladding layer are both made of acrylic negative optical waveguide glue.

In this embodiment, spin coating can be used to prepare the core layer and the upper cladding layer.

The present invention utilizes the pre-exposure treatment of the lower cladding layer so that the photolithography reaction can be carried out in an air environment. Specifically, through large-area low-energy exposure of the lower cladding layer, a thin layer of high viscosity is formed on the surface of the lower cladding layer, which can block the influence of oxygen on the polymerization reaction during the photolithography process. The invention eliminates the nitrogen supply device in the photolithography process and is simple to operate. In addition, during the development process of the present invention, the partially cured thin layer on the surface of the lower cladding layer will sink as the development proceeds, thus forming a relatively smooth waveguide side wall, which is beneficial to the preparation of low-loss waveguides.

Claims (8)

1. The preparation method of the optical waveguide based on cladding ultraviolet lithography is characterized by comprising the following steps:

s1: preparing a lower cladding layer on a substrate;

s2: pre-exposing the lower cladding, wherein the pre-exposure treatment process is to perform ultraviolet exposure in a nitrogen or other inert gas environment, proper ultraviolet curing energy and pre-exposure time are selected according to the thickness of the lower cladding, the surface of the lower cladding is in a state of not being fully cured after the pre-exposure treatment, and a thin layer with high viscosity is formed on the surface of the lower cladding;

s3: ultraviolet photoetching is carried out on the lower cladding according to the designed optical waveguide circuit, and a groove is prepared;

s4: developing the lower cladding after ultraviolet lithography to obtain a groove;

s5: preparing a core layer on the lower cladding layer and solidifying;

s6: preparing an upper cladding layer on the solidified core layer and solidifying;

the thin layer on the surface of the lower cladding layer can block the influence of oxygen on polymerization reaction in the photoetching process, and a nitrogen supply device in the photoetching process is omitted.

2. The method for preparing an optical waveguide based on cladding ultraviolet lithography according to claim 1, wherein in S3: and (3) covering a mask plate on the lower cladding layer for ultraviolet lithography, and obtaining the optical waveguide groove after development.

3. The method for manufacturing an optical waveguide based on cladding ultraviolet lithography according to claim 1, wherein the step of manufacturing the lower cladding in S1 means: and coating a layer of lower cladding polymer on the upper surface of the substrate by adopting a spin coating, dip-coating or doctor blade method process.

4. The method for manufacturing an optical waveguide based on cladding ultraviolet lithography according to claim 1, wherein in S5 and S6: the preparation of the core layer or the upper cladding layer is realized by adopting a spin coating, dip-coating or doctor blade method process.

5. The method for manufacturing an optical waveguide based on cladding ultraviolet lithography according to claim 1, wherein in S5 and S6: the curing of the core or upper cladding is by a large area uv exposure under nitrogen or other inert gas atmosphere.

6. The method for manufacturing an optical waveguide based on cladding ultraviolet lithography according to any one of claims 1 to 5, wherein: and S7, performing overall heat curing.

7. The method for manufacturing an optical waveguide based on cladding ultraviolet lithography according to any one of claims 1 to 5, wherein in S1: the lower cladding layer is prepared after the substrate is cleaned, baked and plasma treated.

8. The method for preparing an optical waveguide based on cladding ultraviolet lithography according to claim 2, wherein in S3: and determining whether the mask plate is a male plate or a female plate according to the characteristics of the selected glue.