CN106501884A - A kind of processing technology of sub-wavelength structure plano-convex microlens array - Google Patents

Abstract

The invention belongs to micronano optical and beam shaping field, specially a kind of processing technology of sub-wavelength structure plano-convex microlens array.The present invention is improved based on photoresist heat reflow method, by realizing the effective control to lenticule pattern to the exposure of positivity Other substrate materials, development, etching and accurate calculating technique duration, produce that radius of curvature is less, more crypto set microlens array on substrate, and then realize that lenticule beam collimation and Coupling power strengthen.The present invention has small volume, simple structure, processing technology maturation and experimental repeatability good, and can strengthen the output, realization of light source focusing, collimation to light source.

Description

Fabrication process of a plano-convex microlens array with subwavelength structure

technical field

The invention belongs to micro-nano optics and beam shaping, and in particular relates to a manufacturing process of a micro-lens, in particular to a manufacturing process of a plano-convex micro-lens array with a sub-wavelength structure.

Background technique

Lens is a very important optical element, which belongs to passive optical element and is used to converge and diverge light radiation in the optical system. Usually the lens volume is relatively large, and the human eye can see it. With the advancement of science and technology, instruments and equipment have developed towards the trend of optical, mechanical and electrical integration. Optical components manufactured by traditional methods are not only complicated in manufacturing process, but also have large size and heavy weight, which can no longer meet the needs of today's technological development. At present, it has been possible to produce lenses and lens arrays with very small diameters. Such lenses and lens arrays are usually not recognized by human eyes, and can only be observed with microscopes, scanning electron microscopes, atomic force microscopes and other equipment. This is a microlens. The microlens array has the advantages of small size, light weight, and easy integration and arraying. It is composed of lenses with a clear aperture and a relief depth of micron. It not only has the basic functions of traditional lenses such as focusing and imaging, but also has a unit size The characteristics of small size and high integration make it able to complete the functions that traditional optical components cannot complete, and can form many new optical systems. As a functional element, a denser microlens unit will strengthen the interference effect between the optical channels, and a smaller lens unit aperture will make the diffraction effect of light energy in the optical channel more obvious, which will eventually affect the uniformity of the optical system. Therefore, microlens arrays are widely used in various systems such as wavefront sensing, light concentration, and light shaping.

The photoresist thermal reflow method (melted photoresist method) was proposed by Poporie in 1988. The whole process can be divided into three steps: 1. Expose the photoresist on the substrate under the mask, and expose the pattern It is circular, rectangular or regular hexagonal; 2. Develop the exposed photoresist and clean the residual substances; 3. Place it on a heating platform for hot-melt molding. Because this method has the advantages of simple process, low requirements for materials and equipment, stable and easy-to-control process parameters, and easy replication, it is widely used in the manufacture of microlens arrays. However, the microlens array produced by this technology also has many disadvantages: 1. Due to the infiltration phenomenon of the photoresist on the substrate material, when the photoresist is in the molten state, the adhesion to the substrate is certain, so when the molten photoresist After the final molding of the glue, there is a wetting angle between the spherical contour of the microlens and the substrate, so that the edge of the microlens has a certain curvature, and the middle part is sunken; 2. Generally, the fill factor of the microlens array will not exceed 80%, and the light The resist is easy to stick after melting. Once the adjacent molten photoresist contacts, it will not form the surface shape of the lens. Due to the low filling factor, the incident light cannot be fully utilized and background noise will be caused; 3. Due to The mechanical and chemical properties of the photoresist itself are relatively poor, and the optical properties are not high, so it is not suitable as the final micro-lens or other micro-structure material.

The patent document with the notification number CN104614936A discloses "A Method for Making a Microlens Array", which uses the photoresist thermal reflow method to heat and reflow the negative photoresist layer, and realizes the microlens based on the designed pattern and the exposure process The planar structure of the negative photoresist is used to make the microlens array by heating and reflowing the negative photoresist. Since the pattern of the negative photoresist has expansion and contraction after development, the development effect is deformed, and the lens cannot maintain a good spherical shape, and it is adopted in this patent document The radius of curvature of the manufactured microlens is 640 μm, which is far from meeting the requirements of miniaturization and miniaturization.

The patent document with the notification number CN104423177A discloses the "Microlens Manufacturing Method", which uses the photoresist reflow method to form a microlens material and substrate; places a photomask above the microlens material, and uses a light beam to pass through the above-mentioned light The mask plate is irradiated on the micro-lens material to perform an exposure process, and then the micro-lens material is developed, and the micro-lens array is formed by a reflow process. Due to the limitation of the structure of the mask plate, the produced microlens array presents two specifications of lens structures, which are different in size and shape, and are arranged regularly. This invention makes full use of the gaps between the microlens units and increases the utilization rate of microlens materials, but the microlens array design of this structure does not achieve beam collimation and optical power coupling enhancement.

Contents of the invention

In view of the above existing problems or deficiencies, the present invention provides a manufacturing process of a plano-convex microlens array with a subwavelength structure, which is improved based on the thermal reflow method of photoresist, through exposing, developing, etching and Accurately calculate the process time to achieve effective control of the microlens morphology, and produce a denser microlens array with a smaller radius of curvature on the microlens substrate, thereby realizing microlens beam collimation and optical power coupling enhancement.

The technical solution of the present invention is a manufacturing process of a plano-convex microlens array with a subwavelength structure:

Step 1, cleaning the microlens substrate;

Step 2, in order to enhance the adhesion of the substrate to the photoresist, it is pretreated, that is, a bonding aid of an organic compound is coated on the insulating surface of the substrate;

Step 3. Calculate the thickness of the photoresist according to the refractive index of the photoresist and the size of the microlens to be designed, and then spin-coat the positive photoresist;

Step 4. Use ultraviolet exposure equipment to expose the substrate, and fully expose until the photoresist is deformed, showing a microlens array; exposure uses a mask that matches the required design of the microlens;

Step 5, hot-melt molding, heating to make the photoresist microlens array obtained in step 4 change from a cylindrical structure to a spherical cap structure;

Step 6. The shape of the photoresist microlens array obtained in step 5 is etched down and transferred to the substrate, and reactive ion etching (RIE) or inductively coupled ion etching (ICP) is used to finally obtain the required microlens array.

The invention is an improved microlens manufacturing process based on the photoresist reflow method, which mainly includes processes such as cleaning, pretreatment, gluing, photolithographic development, and hot-melt molding.

Further, the substrate is a silicon wafer, quartz or indium tin oxide-coated quartz (ITO).

Further, the positive photoresist material is AZ4620, AZ1500, AZ GXR601 or AZ9260 positive photoresist material.

Further, the bonding aid of the organic compound is HDMS.

The invention combines the micro-nano structure design capable of beam synthesis with the micro-lens manufacturing process, improves the micro-lens design process, and manufactures a micro-lens array with small curvature radius and high density. Such a design enhances the output power of the light source, and realizes focusing and collimation of the light source.

To sum up, the present invention has the advantages of small size, simple structure, mature manufacturing process and good experiment repeatability, and can enhance the output power of the light source and realize the focusing and collimation of the light source.

Description of drawings

Figure 1 is a schematic diagram of the size and structure of the photoresist before and after thermal melting;

Figure 2a is a schematic diagram of the pattern transfer of the embodiment, the upper part is photoresist, and the lower part is ITO glass; Figure 2b is the SEM photo of the embodiment, and the black bars on the figure are the scanning path of the step meter; Figure 2c is the step meter test of the embodiment result;

Fig. 3 is a comparison of output current-power curves before and after loading the microlens array of the embodiment.

detailed description

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

1) cleaning

Clean the microlens substrate (ITO glass) before fabrication to remove impurities, oil stains and other pollutants on the surface. In this example, we first ultrasonicated the ITO glass in acetone solution, absolute ethanol, and deionized water for 15 minutes in sequence. Finally, dry the ITO glass substrate with a nitrogen gun and set aside.

2) Pretreatment

After cleaning, the ITO substrate is pretreated, that is, a layer of HDMS (Hexamethyldisilazane, Chinese name: hexamethyldisilazane) is coated on the insulating surface of the ITO glass. attachment.

3) Glue

The designed microlens array has a height of 20 μm, a diameter of 120 μm, and a hemispherical curvature radius of 105 μm. According to this height, AZ4620 positive photoresist thick glue is used, and the photoresist is spin-coated on the ITO glass insulating surface substrate by using a glue leveler. Before gluing, calculate the required gluing thickness of 10 μm. Set the parameters of the homogenizer to spread the AZ4620 photoresist evenly at a speed of 600rad/s for 3s, and then spin-coat the photoresist to 10μm by rotating at a speed of 2000rad/s for 45s.

4) Photolithography and development

The ITO glass substrate spin-coated with AZ4620 photoresist was exposed under a mask plate using a KarlSuss MA6 UV lithography machine, and the mask plate matched the required design microlens. The parts not shielded by the mask plate are exposed to ultraviolet light, resulting in denaturation of the photoresist. Next, we put the exposed substrate into the developer solution, which is prepared by TMAH (Tetramethylammonium Hydroxide, Chinese name: Tetramethylammonium Hydroxide, Chinese name: Tetramethylammonium Hydroxide) and water at a ratio of 1:8. By soaking in the developer solution for 2 minutes, Dissolve the denatured photoresist in the photosensitive part completely. After the development is completed, continue to bake at 100° for 5 minutes to cure the photoresist. In order to verify that the above experimental process meets the previous design standards, we used a step tester to test the baked ITO glass substrate. The test results show that the cylindrical photoresist array has a diameter of 120 μm and a height of 12 μm.

5) Hot melt molding

The melting point of AZ4620 photoresist is between 100°C and 140°C. In order to use the colloidal surface tension to change the photoresist from a cylindrical structure to a spherical cap structure. In this embodiment, the above-mentioned cylindrical photoresist array is placed on a hot plate at 140° C. and heated for 10 minutes. The photoresist microlens array was obtained, and the test results were obtained using a step tester. As shown in Figure 2c, it can be seen that the shape and size are uniform, and the curvature of the spherical cap surface is good. According to the test results of the step tester, the height of the microlens is 12um, and the diameter is 120um.

6) Transfer etching

The shape of the photoresist microlens array obtained in step 5) is etched down and transferred to the ITO glass, thereby forming a glass microlens array. Since traditional ion beam etching produces the above-mentioned microlens array pattern structure, secondary effects such as redeposition will occur during the etching process, which will affect the final microlens array morphology. In this embodiment, reactive ion etching is used. (Reactive Ion Etching) method for microlens array etching process.

In the embodiment, we use the reactive ion plasma etching system (the model is Oxford PlasmaProNGP80RIE) to carry out the process. Since the ITO glass etching process is mainly removed by chemical reaction with F ^- ions, while the photoresist etching process relies on the reaction with O ₂ , so CHF ₃ and O ₂ are selected as etching gases during the etching process. In order to perfectly transfer the photoresist microlens to the ITO glass at 1:1, it is necessary to control the etching ratio during the pattern transfer process, that is, the ratio of the photoresist etching rate to the ITO glass etching rate. The key is to control the CHF ₃ and O ₂ ratio to meet the requirements, in this embodiment, CHF ₃ and O ₂ flow rates are 22sccm and 3sccm respectively, the chamber pressure is maintained at 30mTorr, and when the RF power of the reactive ion beam etching system is set to 200W, the etching ratio is the closest to 1 and the etching rate is relatively high. Finally, a microlens array with a diameter of 120 μm and a height of 12 μm was obtained on the insulating surface of ITO glass. Although the height of the microlens is slightly deviated, the diameter basically reaches the required size of the theoretical design calculation.

The microlens array prepared in this embodiment is shown in FIG. 2 . The diameter of the lens is 120 um and the height is 12 um. The prepared microlens array meets the basic requirements of miniaturization and miniaturization. In order to verify the light speed collimation and optical power coupling enhancement effect of the microlens, the experimental test compares the influence of the luminous power of the zinc oxide nanowire material covering the microlens array under the same voltage and current source input. Through experimental measurement and comparison of the current-power curve, it is found that the luminous power of the nanowire structure loaded with the microlens array is nearly doubled, reaching a maximum of 253uw. The experimental test results are shown in Figure 3. It can be seen that the microlens array designed in the present invention can realize light beam collimation, and can well realize optical power coupling enhancement.

Claims (4)

1. A manufacturing process of sub-wavelength structure plano-convex microlens array, comprising the following steps: Step 1, cleaning the microlens substrate; Step 2, in order to enhance the adhesion of the substrate to the photoresist, it is pretreated, that is, a bonding aid of an organic compound is coated on the insulating surface of the substrate; Step 3. Calculate the thickness of the photoresist according to the refractive index of the photoresist and the size of the microlens to be designed, and then spin-coat the positive photoresist; Step 4. Use ultraviolet exposure equipment to expose the substrate, and fully expose until the photoresist is deformed, showing a microlens array; exposure uses a mask that matches the required design of the microlens; Step 5, hot-melt molding, heating to make the photoresist microlens array obtained in step 4 change from a cylindrical structure to a spherical cap structure; Step 6. The shape of the photoresist microlens array obtained in step 5 is etched down and transferred to the substrate, and reactive ion etching (RIE) or inductively coupled ion etching (ICP) is used to finally obtain the required microlens array. 2. The manufacturing process of the plano-convex microlens array with sub-wavelength structure according to claim 1, characterized in that: the microlens substrate is a silicon wafer, quartz or ITO coated indium tin oxide quartz. 3. The manufacturing process of the sub-wavelength plano-convex microlens array according to claim 1, wherein the positive photoresist is AZ4620, AZ1500, AZ GXR601 or AZ9260. 4. The manufacturing process of the plano-convex microlens array with sub-wavelength structure according to claim 1, characterized in that: the bonding aid of the organic compound is HDMS.