CN102730629B - Microlens preparation method and its product - Google Patents

Abstract

The invention discloses a method for preparing a microlens and its products. The method comprises: performing a photolithography process on a substrate to form a convex platform structure with a diameter equal to the designed diameter of the microlens; performing etching on the formed convex platform structure. Etching process and cleaning off the photoresist to form a boss structure composed of substrate material; perform photolithography process again on the substrate and boss structure to form a cylindrical shape with a diameter smaller than the diameter of the boss structure on the boss structure structure; the obtained product is placed in an acetone vapor environment, and the cylindrical structure is corroded by acetone vapor to form a microlens with a spherical cap structure; and the photoresist material is formed by an etching process or an inversion process The microlenses are transferred to form the final microlens products accordingly. The present invention can effectively avoid the defects of insufficient contact angle and large lens spherical surface error existing in the photoresist hot-melt method, and prepare microlens products with high quality, small contact angle and larger size.

Description

A kind of preparation method of microlens and product thereof

technical field

The invention belongs to the field of micro-optics technology, and more specifically relates to a preparation method of a micro-lens and corresponding products thereof.

Background technique

With the development of micro-nano manufacturing technology, modern optical devices are developing towards lighter weight and smaller volume. Microlenses and their arrays, as representative micro-optical devices, play an important role in optical communication systems, micro-opto-electromechanical systems and other fields. The so-called microlenses (microlenses) refer to optical lenses with a clear aperture and a relief depth of microns. The array of these small lenses is called a microlens array. The methods currently used to make microlenses include photoresist hot-melt method, photosensitive glass thermoforming method, ion exchange method, photoelectric reaction etching method, focused ion beam etching and deposition method, etc.

Photoresist hot-melt method is one of the most commonly used microlens fabrication methods. The principle of using the photoresist hot-melt method to make microlenses is: coating a certain thickness of photoresist on the substrate, performing ultraviolet exposure under the shield of a circular mask, and then developing a cylindrical photoresist structure. The photoresist is heated to a molten state, and its surface tension allows the conventional transformation of the cylindrical structure into a smooth spherical crown structure; then, the microlens of the photoresist material can be transferred or replicated to the silicon through an etching process or an inversion process. Or on a sheet made of glass material, thus finally forming a microlens product of silicon or glass material.

The advantage of the photoresist hot-melt method is that it is simple and easy to implement, but after research, it mainly has the following defects: 1. In the process of heating to form a spherical crown structure, due to the limitation of the wetting angle, usually only the contact angle greater than 20 can be produced. ° of the microlens, when the contact angle is less than 20 °, the center of the microlens is prone to depression, and because the contact angle is large, the design diameter of the microlens is limited; 3, in the prior art, the photoresist material on the substrate is often directly The formed cylindrical structure performs heating, so that during the heating process, due to the evaporation of the photoresist material solvent, the photoresist on the outer layer of the cylindrical structure is solidified earlier than the photoresist inside the cylindrical structure, and the Before the spherical surface of the lens is formed, the outer layer of photoresist has been solidified and formed, which easily causes a large spherical surface error when making a larger-sized microlens; 4. During the heating process, due to the cylindrical structure When the internal photoresist solvent evaporates, bubbles will be formed inside the microlens structure. Since the outer layer of photoresist solidifies first, the bubbles will be trapped inside the microlens structure and cannot be eliminated. On the one hand, the performance of the photoresist will be unstable and easily deformed. On the other hand, the adhesion between the photoresist and the substrate is reduced, and it is easy to fall off; 5. The heating causes the denaturation of the photoresist material, and the possibility of subsequent photolithography process is lost.

Contents of the invention

In view of the defects and technical demands of the prior art, the object of the present invention is to provide a method for preparing a microlens and its products, which perform the spherical surface molding process of the microlens by replacing the heating method with acetone vapor corrosion, Correspondingly, microlens products with high quality, small contact angle and larger size can be prepared.

According to one aspect of the present invention, a kind of preparation method of microlens is provided, and this method comprises the following steps:

(1) Coating photoresist on the substrate and performing a photolithography process using a circular mask. After development, a convex platform structure composed of photoresist material and whose diameter is equal to the designed diameter of the microlens is formed on the substrate ;

(2) Perform an etching process on the boss structure formed in step (1), and then wash off the photoresist, thereby forming a boss made of substrate material and having a diameter equal to the designed diameter of the microlens on the substrate structure;

(3) Coating photoresist on the entire substrate and the boss structure after step (2), and performing a photolithography process on the boss structure with a circular mask, after development , forming a cylindrical structure made of photoresist material and having a diameter smaller than the diameter of the boss on the boss structure;

(4) placing the product obtained in step (3) in an acetone vapor environment, and corroding the cylindrical structure by acetone vapor, thereby forming a microlens with a spherical cap structure;

(5) Transfer the microlens made of photoresist material through etching process or inversion process, and form the final microlens product accordingly.

Through the above ideas, since the acetone corrosion method is used to replace the heating method, as the acetone vapor rises, a chemical reaction can be continuously produced on the cylindrical structure of the photoresist material, that is, the corrosion process, and correspondingly, a smaller contact angle can be formed. And the surface is smoother spherical crown surface. In addition, since the micro-lens is formed by using a boss structure and performing a photoresist process on it, on the one hand, the position and diameter of the final formed micro-lens can be guaranteed, and random diffusion will not occur; on the other hand, it is compatible with direct Compared with the method of molding the spherical cap surface on the substrate, it is easy to control its registration error and convenient to operate.

As a further preference, the substrate is a silicon substrate or a glass substrate, and when the substrate is a silicon substrate, an inductively coupled plasma etching process is used to perform the etching process in step (2); when the substrate When it is a glass substrate, the etching process is performed by using a reactive ion etching process in step (2).

The etching process is performed by selecting inductively coupled plasma etching technology or reactive ion etching process according to different substrate materials, which can adapt to the characteristics of the substrate material itself, and can be performed quickly and with high quality The transfer of the boss and the formation of products that meet the process requirements.

As a further preference, during the process of corroding the cylindrical structure with acetone vapor in step (4), the ambient temperature is 20° C. to 70° C., and the corresponding corrosion time is 30 minutes to 1 minute.

Under the process conditions of the above numerical range, the acetone vapor can fully perform the corrosion process on the cylindrical structure, ensure the molding of the spherical cap surface of the microlens, and at the same time be suitable for operation in most occasions and provide processing efficiency.

As a further preference, in the process of corroding the cylindrical structure with acetone vapor in step (4), the ambient temperature is 30° C. to 40° C., and the corresponding corrosion time is 10 minutes to 2 minutes.

If the etching time is less than 1 minute, it is too short, the control precision is low, and the repeatability is poor; if the etching time is more than 15 minutes, it is too long, which affects the production efficiency. Many studies and practices have shown that by limiting the process parameters of the acetone vapor etching process to the above numerical ranges, microlens products that meet the requirements can be produced with high efficiency and high quality in practice.

As a further preference, in step (4), the product obtained in step (3) is placed on a ring-shaped carrier with a bracket with the cylindrical structure facing down, and then placed together in an acetone vapor environment In this method, a microlens with a spherical cap structure is formed by etching the cylindrical structure with acetone vapor.

Through the above ideas, since the cylindrical structure is placed downward in the acetone vapor environment, on the one hand, it is convenient to contact with the rising acetone vapor, which promotes the corrosion. On the other hand, for the cylindrical structure with a large diameter , the photoresist material will contribute to the rapid prototyping of the spherical cap surface due to its own gravity. In addition, positioning and transfer of products in an acetone vapor environment can be realized with a simple structure, and it is easy to handle.

As a further preference, the designed diameter of the microlens is 10 μm˜1 mm, preferably 300 μm˜1 mm.

Tests and practices have shown that the preparation method of the present invention is suitable for preparing microlenses with a wider diameter range such as 10 μm to 1 mm; in addition, the microlenses with a diameter of less than about 300 μm have negligible effects of gravity due to their small mass. Microlenses around 300 μm enhance the fluidity of the photoresist due to gravity, which is helpful for spherical cap molding.

As a further preference, after step (4), an annealing step may be performed on the microlens made of photoresist material, thereby further stabilizing the performance of the photoresist.

By performing an annealing step, the photoresist solvent is further evaporated and the photoresist material becomes stronger. In addition, during the photolithography process and the etching process, bubbles are easily formed inside the photoresist. By performing an annealing step to remove these air bubbles, the adhesion of the photoresist material to the substrate is enhanced and the sensitivity of the photoresist material to the environment is reduced. Correspondingly, when the microlens made of photoresist material is transferred by etching process or reverse molding process, a microlens product with a more stable overall shape, especially the spherical cap surface, which meets design standards can be obtained.

According to another aspect of the present invention, a corresponding microlens product is provided, characterized in that the final microlens product has a contact angle of 1°-20° and a diameter of 10 μm-1 mm.

Compared with the prior art, according to the method for making microlens of the present invention and products thereof, its main advantages are:

1. The contact angle of the final prepared microlens product is small, ranging from 1° to 20°; in addition, this method is suitable for preparing microlens products with a diameter of 10 μm to 1 mm, especially for a diameter of 300 μm to 1 mm. 1mm microlens;

2. Compared with the traditional hot-melt method, the surface error of the prepared microlens is smaller, which can ensure the characteristics of the spherical cap surface; since it does not need to be heated to a temperature above 100°C during the preparation process, the photoresist is avoided. Denaturation, which preserves the possibility to perform further photolithographic processes;

3. The microlens made of photoresist material has good adhesion to the substrate, good stability, is not sensitive to the environment, is not easy to deform or denature, and is beneficial to the subsequent microlens transfer or inversion process.

Description of drawings

Fig. 1 is the process flow chart that the present invention is used to prepare microlens;

Fig. 2 is the structural representation of the sample prepared according to the preparation method of the present invention;

Fig. 3 is the schematic diagram that utilizes acetone vapor to form the spherical profile of microlens according to the present invention;

Fig. 4 is the structural representation of the annular carrier for carrying microlens sample;

Figure 5a is a schematic diagram of the microlens profile and spherical fitting curve prepared according to Example 1 of the present invention;

Figure 5b is a schematic diagram of a microlens profile and a spherical fitting curve prepared according to Example 2 of the present invention;

Fig. 5c is a schematic diagram of a microlens profile and a spherical fitting curve prepared according to Example 3 of the present invention.

Throughout the drawings, the same reference numerals are used to designate the same elements or structures, wherein:

1 Substrate 2 Boss structure 3 Cylindrical structure 4 Container 5 Support 6 Acetone

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.

Considering the shortcomings of the photoresist hot-melt method and other microlens preparation methods in the prior art, the present invention expects to propose an improved preparation method, and correspondingly obtain a contact angle of 1-20 degrees, and a diameter of 10μm~1mm microlens products.

The method for producing the microlens according to the present invention will be specifically described below.

First, a photoresist is coated on a substrate such as a silicon substrate or a glass substrate, and a photolithography process is performed using a circular mask. After developing in this way, a boss structure made of photoresist material and whose diameter is equal to the designed diameter of the microlens (for example, 10 μm to 1 mm) is formed on the substrate;

Next, performing an etching process on the formed boss structure, and then cleaning off the photoresist, thereby forming a boss structure made of substrate material and having a diameter equal to the designed diameter of the microlens on the substrate;

Then, coat photoresist again on the entire substrate and the raised platform processed through the above steps, and perform a photolithography process on the raised platform using a circular mask. In this way, the corresponding product as shown in Figure 1 can be obtained after development, that is, a cylindrical structure made of photoresist material and whose diameter is smaller than the diameter of the boss is formed on the boss structure;

Then, the obtained product is placed in an acetone vapor environment, the ambient temperature is, for example, 20°C to 70°C, preferably 30°C to 40°C, and the cylindrical structure is corroded by the acetone vapor to form a spherical cap structure. microlens, wherein the corresponding etching time is, for example, 30 minutes to 1 minute, and 10 minutes to 2 minutes.

Finally, the microlens made of the photoresist material is transferred through an etching process or an inversion process to form a final microlens product accordingly.

Through the above method, the contact angle of the finally prepared microlens product is 1 degree to 20 degrees, and the diameter is 10 μm to 1 mm.

In a preferred embodiment, as an improvement of the present invention, after forming a cylindrical structure made of photoresist material and having a diameter smaller than the diameter of the protrusion on the protrusion structure, an annealing step may be performed on it. By performing an annealing step, the photoresist solvent is further evaporated and the photoresist material becomes stronger. On the other hand, during the photolithography process and the etching process, bubbles are easily formed inside the photoresist. By performing an annealing step to remove these air bubbles, the adhesion of the photoresist material to the substrate is enhanced and the sensitivity of the photoresist material to the environment is reduced.

In another preferred embodiment, a specific structure can be used to perform the acetone vapor etching process of the cylindrical structure. As shown in FIG. 3 , the upper part of the annular carrier for carrying the microlens sample is, for example, ring-shaped, and the lower part has, for example, three supports. When performing etching of a cylindrical structure with acetone vapor, the article obtained in the previous steps can be placed on a ring-shaped carrier with a stand with the cylindrical structure facing down, and then placed together in an acetone vapor environment. On the one hand, this facilitates the contact with the rising acetone vapor and promotes the corrosion. On the other hand, for cylindrical structures with a diameter larger than 300 μm, the photoresist material will contribute to the spherical cap shape due to its own gravity. rapid prototyping.

The following are some specific embodiments of the present invention.

Example 1

The first step is to clean the substrate 1 made of silicon material, spin-coat a photoresist with a thickness of about 1 μm on the substrate 1, and then make a photoresist material through a photolithography process, and its diameter is equal to the microlens design diameter of 1mm circular boss.

In the second step, the silicon substrate 1 is etched by inductively coupled plasma etching technology, thereby forming a boss structure 2 made of silicon material on the silicon substrate, and then cleaning the photoresist material with acetone and ethanol. The correspondingly formed boss structures have a diameter of 1 mm and a height of about 1 μm.

The third step is to spin-coat photoresist on the entire silicon substrate and the boss structure 2, and produce a cylindrical structure 3 concentric with the boss structure, composed of photoresist material and with a diameter of about 600 μm by photolithography . During this process, the photoresist was spin-coated with a thickness of about 33.5 μm.

The fourth step is to place a carrier such as a plastic ring with a bracket 5 in a container 4 such as a beaker, and pour acetone 6 so that the liquid level of the acetone 6 is slightly lower than the upper surface of the carrier. Then, the sample prepared through the above steps was placed face down (that is, with the cylindrical structure 3 facing down) on the carrier, so that the columnar photoresist on the surface of the sample was fully exposed to the acetone vapor. Under the environment of 30C°, after 10 minutes of acetone vapor corrosion, a microlens made of photoresist material can be made.

The fifth step is to place the molded microlens in the air and slowly heat it to 160°C at a speed of 2°C/min. Hold at 160°C for 20 minutes. Then cool naturally to 25°C. Complete the annealing step.

The sixth step is to transfer the microlens made of photoresist material to the silicon substrate by inductively coupled plasma etching technology to form a microlens product made of silicon material. After measurement, the diameter of the finished microlens is 1mm, and the contact angle is about 6.2°.

Example 2

The first step is to clean the substrate 1 of the glass material, spin-coat a photoresist with a thickness of about 1 μm on the glass substrate 1, and then make a photoresist material with a diameter equal to the design diameter of the microlens of 150 μm through a photolithography process circular boss.

In the second step, the substrate 1 is etched by a reactive ion etching process to form a boss structure 2 made of glass material on the glass substrate, and then the photoresist material is washed away with acetone and ethanol. The correspondingly formed mesa structures have a diameter of 150 μm and a height of about 1 μm.

The third step is to spin-coat a photoresist with a thickness of about 11 μm on the boss structure, and produce a cylindrical structure 3 made of photoresist material through a photolithography process, and the diameter of the cylindrical structure 3 is about 140 μm.

The fourth step is to place a carrier such as a plastic ring with a bracket 5 in a container 4 such as a beaker, and pour acetone 6 so that the liquid level of the acetone 6 is slightly lower than the upper surface of the carrier. The sample prepared through the above steps is placed face down on the carrier, so that the columnar photoresist on the surface of the sample is fully exposed to the acetone vapor. Under the environment of 40 degrees centigrade, after 2 minutes of acetone vapor corrosion, the microlenses made of photoresist material are made.

The fifth step is to place the molded microlens in the air and slowly heat it to 160°C at a speed of 2°C/min. Hold at 160°C for 20 minutes. Then cool naturally to 25°C.

The sixth step is to transfer the microlens made of photoresist material to the glass substrate 1 by reactive ion etching process, thereby forming a microlens product made of glass material. After measurement, the diameter of the finished microlens is 150 μm, and the contact angle is 15°.

Example 3

The first step is to clean the substrate 1 made of silicon material, spin-coat a photoresist with a thickness of about 1 μm on the substrate 1, and then make a circular boss made of photoresist material through a photolithography process.

In the second step, the substrate 1 is etched by the inductively coupled plasma etching technique to form a boss structure 2 made of silicon material on the substrate, and then the photoresist material is washed away with acetone and ethanol. The resulting mesa structures have a diameter of 630 μm and a height of about 1 μm.

The third step is to spin-coat a photoresist with a thickness of about 33.5 μm on the boss structure 2, and produce a cylindrical structure 3 made of photoresist material concentric with the boss structure through a photolithography process. The diameter of the structures is approximately 500 μm.

The fourth step is to place a carrier such as a plastic ring with a bracket 5 in a container 4 such as a beaker, and pour acetone 6 so that the liquid level of the acetone 7 is slightly lower than the upper surface of the bracket 6 . Place the sample face down on the support 6, so that the columnar photoresist on the surface of the sample is fully exposed to the acetone vapor. Under the environment of 35°C, after 3 minutes and 30 seconds of acetone vapor corrosion, a microlens made of photoresist material is made.

The fifth step is to place the molded microlens in the air and slowly heat it to 160°C at a speed of 2°C/min. Hold at 160°C for 20 minutes. Then cool naturally to 25°C.

Step 6: Coating a layer of vacuum-treated polydimethylsiloxane on the surface of the microlens made of photoresist material, and baking polydimethylsiloxane at 70°C for 1 hour to achieve After curing, and then peeling off the polydimethylsiloxane, an inverted mold of a microlens with a diameter of 630 μm and a contact angle of 18.5° can be obtained. Bake the SU8 photoresist under the condition of 120°C for 1 hour to the molten state, then pour the SU8 photoresist in the molten state into the polydimethylsiloxane inverted mold, and place it Put it in a ventilated place and wait for the SU8 photoresist to solidify. Finally, the polydimethylsilane inverted mold was removed to obtain a finished microlens made of SU8 material with a diameter of 630 μm and a contact angle of 18.5°.

Referring to Figures 4a, 4b and 4c respectively, the relationship between the profile of the microlens prepared according to the present invention and the spherical fitting curve is shown. It can be seen from these figures that microlens products with high quality, small contact angle and larger size can be prepared by the microlens preparation method of the present invention.

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 (1)

1. A method for preparing a microlens with a diameter of 300 μm to 1 mm and a contact angle of 1 to 20 degrees, characterized in that the method may further comprise the steps: (1) Coating photoresist on a substrate made of silicon or glass, and using a circular mask to perform a photolithography process. After development, a microlens made of photoresist material and whose diameter is the same as the microlens is formed on the substrate. Design boss structures with equal diameters; (2) Carry out an etching process to the boss structure formed in step (1), and then clean off the photoresist, thereby forming a boss made of substrate material and having a diameter equal to the design diameter of the microlens on the substrate structure; (3) Coating photoresist again on the entire substrate and the boss structure after step (2), and adopting a circular mask to perform photolithography process on the boss structure, after developing , forming a cylindrical structure made of photoresist material and having a diameter smaller than the diameter of the boss on the boss structure; (4) The product obtained in step (3) is placed on the ring-shaped carrier with the support in the manner of the cylindrical structure facing down, and then it is placed together in the acetone vapor environment, thereby the acetone vapor is used for the cylinder. Forming microlenses with a spherical cap structure by corroding a spherical structure. During this process, the ambient temperature is set at 30°C to 40°C, and the corrosion time is set at 10 minutes to 2 minutes; (5) Place the molded microlens in the air, heat it to 160°C at a rate of 2°C/min, keep it at this temperature for 20 minutes, and then cool it naturally to 25°C; (6) Transfer the microlens made of photoresist material through etching process or inversion process, and correspondingly form the final microlens product.