Flexible self-supporting vertical optical waveguide array and preparation method and application thereof

Abstract

The invention relates to the technical field of microelectronic devices, and provides a flexible self-supporting vertical optical waveguide array and a preparation method and application thereof. According to the flexible self-supporting vertical optical waveguide array and the preparation method thereof, an ultraviolet-curable SU-8 polymer is used as an optical waveguide material, a vertical optical waveguide array is prepared on a substrate by using simple coating, photoetching and ICP etching processes, then a flexible supporting layer is prepared, and the substrate is removed, so that the flexible self-supporting vertical optical waveguide array is obtained. The flexible self-supporting vertical optical waveguide array provided by the invention can solve the photoelectric crosstalk problem of an image sensor, improves the detection sensitivity in a weak light environment, has excellent flexibility, and can realize conformal fitting with the surface of the image sensor; moreover, the flexible self-supporting vertical optical waveguide array does not depend on the pixel size of the image sensor, the preparation process is independent of the preparation process of the image sensor, the universality is high, and the flexibility is good.

Description

Technical Field

[0001] The present invention relates to the technical field of microelectronic devices, and in particular to a flexible self-supporting vertical optical waveguide array and a preparation method and application thereof. Background Art

[0002] With the advent of the era of artificial intelligence and 5G, the image sensor industry for multiple application scenarios such as the Internet of Things and intelligent unmanned systems has developed rapidly, while also putting forward higher demands on the imaging quality and miniaturization of image sensors.

[0003] The improvement of spatial resolution of modern image sensors is mainly achieved by reducing pixel size. However, as the pixel size is reduced to below micrometers, the amount of light entering the pixel will be significantly reduced, which will seriously affect the detection sensitivity of the sensor in low light. At the same time, due to the diffraction and scattering of light, serious optical crosstalk will occur between adjacent pixels of the image sensor, which is not conducive to achieving high-resolution and high-fidelity imaging.

[0004] The general solution to overcome the above problems is to increase the amount of light entering the pixel by integrating on-chip lenses and use deep trench isolation technology within the pixel to reduce photoelectric crosstalk. However, these processes require the use of complex and expensive thick film growth equipment, deep etching equipment, etc., and their preparation and integration processes are complex and the production cost is high. In addition, these technologies are usually applied in the manufacturing process of image sensors, have a strong dependence on pixel size, low versatility, and cannot improve the performance of existing old image sensors.

[0005] Therefore, it is of great significance to develop a low-cost and versatile structural array that can be externally integrated on the surface of image sensors. Summary of the invention

[0006] In view of this, the present invention provides a flexible self-supporting vertical optical waveguide array and a preparation method and application thereof. The flexible self-supporting vertical optical waveguide array provided by the present invention can solve the photoelectric crosstalk problem of the image sensor, improve the detection sensitivity in a weak light environment, and has excellent flexibility. It can be conformally bonded to the surface of the image sensor through simple external integration, and is independent of the pixel size of the image sensor. The preparation process is independent of the preparation process of the sensor, and has strong versatility and good flexibility.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] A flexible self-supporting vertical optical waveguide array comprises a flexible supporting layer and a SU-8 one-dimensional vertical optical waveguide array; the SU-8 one-dimensional vertical optical waveguide array is composed of a plurality of SU-8 one-dimensional optical waveguide units, and the SU-8 one-dimensional optical waveguide units are perpendicular to the flexible supporting layer; each of the SU-8 one-dimensional optical waveguide units is partially embedded in the flexible supporting layer, and the end of the exposed part presents a hemispherical convex surface; the SU-8 one-dimensional vertical optical waveguide array is prepared by SU-8 ultraviolet negative photoresist.

[0009] Preferably, the height of the SU-8 one-dimensional vertical optical waveguide unit is ≥10 μm and the diameter is ≤5 μm; the density of the SU-8 one-dimensional optical waveguide unit in the flexible self-supporting vertical optical waveguide array is ≤2.5×10 5 Pieces / mm 2 .

[0010] Preferably, the flexible supporting layer is polyimide; the thickness of the flexible supporting layer is 8-25 μm.

[0011] The present invention also provides a method for preparing the flexible self-supporting vertical optical waveguide array described in the above scheme, comprising the following steps:

[0012] A positive photoresist is coated on the surface of the substrate, and then pre-baking, first mask exposure and development are performed in sequence to obtain a patterned photoresist layer;

[0013] The substrate having a patterned photoresist layer on the surface is isotropically etched by inductively coupled plasma etching to form a hemispherical concave structure in the area of ​​the substrate not protected by the photoresist layer, and then the patterned photoresist layer on the surface of the substrate is removed to obtain a hemispherical end face template;

[0014] SU-8 ultraviolet negative photoresist is coated on the surface of the hemispherical end face template, and then pre-baking, second mask exposure, intermediate baking, development and post-baking are performed in sequence to obtain a SU-8 one-dimensional vertical optical waveguide array on the surface of the hemispherical end face template; the mask used in the first mask exposure and the second mask exposure is provided with a hollow structure array corresponding to the target SU-8 one-dimensional vertical optical waveguide array structure, and the hollow structure array is aligned with the hemispherical concave structure of the hemispherical end face template when the second mask exposure is performed;

[0015] After coating the surface of the SU-8 one-dimensional vertical optical waveguide array with a flexible polymer precursor solution, a cross-linking curing reaction is performed to obtain a flexible supporting layer supporting the SU-8 one-dimensional vertical optical waveguide array, and then the substrate is removed to obtain the flexible self-supporting vertical optical waveguide array.

[0016] Preferably, the conditions for the isotropic etching include: a pressure of 150 to 550 mTorr, an etching gas of SF6, a flow rate of the etching gas of 50 to 200 sccm, a temperature in the reaction chamber of 5 to 25°C, a power of the plasma generator of 200 to 500 W, a substrate bias power of 5 to 50 W, and an etching time of 5 to 10 min.

[0017] Preferably, the radius of the hemispherical concave structure is 1.7-7.7 μm, and the depth of the bottom of the concave is 300-400 nm.

[0018] Preferably, the coating thickness of the SU-8 UV negative photoresist is 10 to 30 μm.

[0019] Preferably, the first mask exposure and the second mask exposure are ultraviolet mask exposure.

[0020] Preferably, the flexible polymer precursor is a polyimide precursor; the temperature of the cross-linking and curing reaction is 300-350° C., and the time is 2-5 hours; and the cross-linking and curing reaction is carried out under a protective atmosphere.

[0021] The present invention also provides the use of the flexible self-supporting vertical optical waveguide array described in the above scheme or the flexible self-supporting vertical optical waveguide array prepared by the preparation method described in the above scheme in an image sensor.

[0022] The present invention provides a flexible self-supporting vertical optical waveguide array, comprising a flexible support layer and a SU-8 one-dimensional vertical optical waveguide array; the SU-8 one-dimensional vertical optical waveguide array is composed of a plurality of SU-8 one-dimensional optical waveguide units, and the SU-8 one-dimensional optical waveguide units are perpendicular to the flexible support layer; each of the SU-8 one-dimensional optical waveguide units is partially embedded in the flexible support layer, and the end of the exposed part presents a hemispherical convex surface; the SU-8 one-dimensional vertical optical waveguide array is prepared by SU-8 ultraviolet negative photoresist. The optical waveguide can confine the light inside it through total internal reflection in the spatial dimension, thereby realizing low-loss and efficient transmission of optical signals. The optical waveguide with a one-dimensional linear structure is vertically integrated into the surface of the image sensor pixel, and the incident light can be coupled from the top of the vertical waveguide and transmitted efficiently with low loss, and then efficiently absorbed by the pixel of the image sensor at the bottom of the waveguide, thereby hopefully solving the problem of small amount of light entering the pixel of the image sensor and large photoelectric crosstalk between pixels. The flexible self-supporting vertical optical waveguide array provided by the present invention is made of all-polymer, which can solve the problem of photoelectric crosstalk, improve the detection sensitivity in weak light environment, and is independent of the pixel size of the image sensor. By adjusting the diameter and length of the optical waveguide array, the imaging performance of image sensors with different pixel specifications can be improved without changing the pixel structure of the image sensor, and it has strong versatility and flexibility. In addition, the flexible self-supporting vertical optical waveguide array provided by the present invention has excellent flexibility and can achieve surface deformation with a minimum curvature radius of 10 mm. Therefore, the conformal bonding of the waveguide array and the image sensor surface can be achieved through simple external integration means. The incident light from the outside can be directionally collected and transmitted to the surface of the image sensor element through the optical waveguide unit, thereby reducing the crosstalk problem between the image sensor pixels, improving the detection sensitivity of the pixels, and achieving the improvement of the imaging performance of the image sensor. It has great application prospects in the field of flexible electronic device integration. Furthermore, the flexible self-supporting vertical optical waveguide array provided by the present invention has high density (up to 2.5×10 5 Pieces / mm 2 ), large aspect ratio (5-6), small feature size (≤5μm), steep side walls, flat surface and low optical loss.

[0023] The present invention also provides a method for preparing the flexible self-supporting vertical optical waveguide array described in the above scheme. The present invention uses UV-curable SU-8 UV negative photoresist as the optical waveguide material, and uses simple coating, photolithography and ICP etching processes to efficiently prepare a polymer optical waveguide array with steep side walls, flat surface and low light loss, and then prepares a flexible support layer and removes the substrate to obtain a flexible self-supporting vertical optical waveguide array. The processing technology of the flexible self-supporting vertical optical waveguide array of the present invention is independent of the preparation process of the sensor, and is simpler and cheaper than the prior art, and has the advantages of low-cost batch production, high quality consistency within the batch, high precision and low surface roughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the process of preparing a flexible self-supporting vertical optical waveguide array provided by the present invention;

[0025] Figure 2 The schematic diagram (left) and scanning electron microscope image (right) of the SU-8 one-dimensional vertical optical waveguide array obtained on the original silicon substrate;

[0026] Figure 3 This is the test result of the surface deformation ability of the flexible self-supporting vertical optical waveguide array;

[0027] Figure 4 The imaging capability of the sensor changes after the flexible self-supporting vertical optical waveguide array is integrated, wherein the left side shows the imaging result of the sensor without the flexible self-supporting vertical optical waveguide array integrated, and the right side shows the imaging result of the sensor with the flexible self-supporting vertical optical waveguide array prepared in the integrated embodiment. DETAILED DESCRIPTION

[0028] The invention provides a flexible self-supporting vertical optical waveguide array, comprising a flexible supporting layer and a SU-8 one-dimensional vertical optical waveguide array; the SU-8 one-dimensional vertical optical waveguide array is composed of a plurality of SU-8 one-dimensional optical waveguide units, and the SU-8 one-dimensional optical waveguide units are perpendicular to the flexible supporting layer; each of the SU-8 one-dimensional optical waveguide units is partially embedded in the flexible supporting layer, and the end of the exposed part presents a hemispherical convex surface; the SU-8 one-dimensional vertical optical waveguide array is prepared by SU-8 ultraviolet negative photoresist.

[0029] In the present invention, the height of the SU-8 one-dimensional vertical optical waveguide unit is ≥10 μm, preferably 10 to 30 μm, and the diameter is ≤5 μm, preferably 1 to 5 μm; the density of the SU-8 one-dimensional optical waveguide unit in the flexible self-supporting vertical optical waveguide array is ≤2.5×10 5 Pieces / mm 2 , preferably 4×10 4 ~2.5×10 5Pieces / mm 2 The aspect ratio of the SU-8 one-dimensional vertical optical waveguide unit is preferably 5-6.

[0030] In the present invention, the flexible supporting layer is preferably polyimide; the thickness of the flexible supporting layer is preferably 8 to 25 μm.

[0031] The present invention also provides a method for preparing the flexible self-supporting vertical optical waveguide array described in the above scheme, comprising the following steps:

[0032] A positive photoresist is coated on the surface of the substrate, and then pre-baking, first mask exposure and development are performed in sequence to obtain a patterned photoresist layer;

[0033] The substrate having a patterned photoresist layer on the surface is isotropically etched by inductively coupled plasma etching to form a hemispherical concave structure in the area of ​​the substrate not protected by the photoresist layer, and then the patterned photoresist layer on the surface of the substrate is removed to obtain a hemispherical end face template;

[0034] SU-8 ultraviolet negative photoresist is coated on the surface of the hemispherical end face template, and then pre-baking, second mask exposure, intermediate baking, development and post-baking are performed in sequence to obtain a SU-8 one-dimensional vertical optical waveguide array on the surface of the hemispherical end face template; the mask template used in the first mask exposure and the second mask exposure is provided with a hollow structure array corresponding to the target SU-8 one-dimensional vertical optical waveguide array structure, and the hollow structure array is aligned with the hemispherical concave structure of the hemispherical end face template when the second mask exposure is performed;

[0035] After coating the surface of the SU-8 one-dimensional vertical optical waveguide array with a flexible polymer precursor solution, a cross-linking curing reaction is performed to obtain a flexible supporting layer supporting the SU-8 one-dimensional vertical optical waveguide array, and then the substrate is removed to obtain the flexible self-supporting vertical optical waveguide array.

[0036] Figure 1 The process diagram of the method for preparing the flexible self-supporting vertical optical waveguide array provided by the present invention is shown below in combination with Figure 1 Provide detailed explanation.

[0037] The present invention coats a positive photoresist on the surface of a substrate, and then sequentially performs pre-baking (referred to as the first pre-baking), first mask exposure and development (referred to as the first development) to obtain a patterned photoresist layer. In the present invention, the substrate is preferably a hard substrate, more preferably a silicon substrate, specifically a silicon wafer, the surface of the silicon wafer contains a silicon dioxide layer, and the thickness of the silicon dioxide layer is preferably 90 to 300 nm, more preferably 300 nm. Before the coating, the substrate is preferably pretreated, and the pretreatment preferably includes: washing the substrate with acetone, isopropanol and deionized water in sequence, and then drying it with dry nitrogen; the time for the acetone washing, isopropanol washing and deionized water washing is preferably 5 minutes; the positive photoresist is preferably AZ-5214E ​​positive photoresist; the method of coating the positive photoresist is preferably spin coating, the spin coating speed is preferably 3000rpm, the spin coating time is preferably 30s, and a photoresist layer is obtained after spin coating, and the thickness of the photoresist layer is preferably 1-20μm, more preferably 1-10μm; the temperature of the first pre-bake is preferably 95-120℃, more preferably 100℃; the time of the first pre-bake is preferably 90-300s, more preferably 90-20 0s; the first mask exposure is preferably ultraviolet mask exposure, and the ultraviolet wavelength of the ultraviolet mask exposure is preferably 365nm; the mask plate used for the first mask exposure is provided with a hollow structure array corresponding to the target SU-8 one-dimensional vertical optical waveguide array structure; in a specific embodiment of the present invention, the optical waveguide in the vertical optical waveguide array is cylindrical, and the corresponding hollow structure on the mask plate is circular; in a specific embodiment of the present invention, the first mask exposure is performed using an ultraviolet mask exposure machine; the developer used in the first development is preferably NMD-3 developer; the present invention dissolves the photoresist at the processing area of ​​each vertical optical waveguide through development, thereby exposing the substrate, while the area between the vertical optical waveguide units continues to be covered by the photoresist, that is, a patterned photoresist layer is formed on the substrate surface.

[0038] After obtaining a substrate with a patterned photoresist layer on the surface, the present invention uses an inductively coupled plasma etching method to isotropically etch the substrate with a patterned photoresist layer on the surface, forming a hemispherical concave structure in the area of ​​the substrate not protected by the photoresist layer, and then removing the patterned photoresist layer on the surface of the substrate to obtain a hemispherical end surface template. In the present invention, the conditions of the isotropic etching preferably include: a pressure of 150 to 550 mTorr, preferably 250 to 350 mTorr, an etching gas of SF6, a flow rate of the etching gas of 50 to 200 sccm, preferably 50 to 150 sccm, a temperature in the reaction chamber of 5 to 25° C., preferably 10 to 15° C., a power of a plasma generator of 200 to 500 W, preferably 300 to 500 W, a substrate bias power of 5 to 50 W, preferably 5 to 20 W, and an etching time of 5 to 10 min, more preferably 5 to 8 min. The present invention etches isotropically the area on the substrate not protected by the photoresist by inductively coupled plasma etching to form a hemispherical concave structure, which is then used as a hemispherical end face template when making a vertical waveguide array; the radius of the hemispherical concave structure is preferably 1.7 to 7.7 μm, and the depth of the bottom of the concave is preferably 300 to 400 nm.

[0039] In the present invention, a degumming liquid is preferably used to remove the patterned photoresist layer on the surface of the substrate, and the degumming liquid is preferably N-methylpyrrolidone (NMP) degumming liquid; after removing the patterned photoresist layer, an etched substrate is obtained, which is the hemispherical end face template of the present invention; the present invention preferably cleans the hemispherical end face template and then blows it dry; the cleaning is preferably carried out using acetone, isopropanol and deionized water in sequence.

[0040] After obtaining the hemispherical end face template, the present invention coats SU-8 ultraviolet negative photoresist on the surface of the hemispherical end face template, and then sequentially performs pre-baking (referred to as the second pre-baking), mask exposure (referred to as the second mask exposure), intermediate baking, development (referred to as the second development) and post-baking to obtain a SU-8 one-dimensional vertical optical waveguide array on the surface of the hemispherical end face template. The present invention has no special requirements for the source of the SU-8 ultraviolet negative photoresist, and the one familiar to those skilled in the art can be used; in the present invention, the coating is specifically applied on the etched surface of the hemispherical end face template; the coating method is preferably spin coating; the spin coating speed is preferably 1200-4500rpm, more preferably 1200-3000rpm, and the spin coating time is preferably 30s; after spin coating, a SU-8 film is obtained, and the thickness of the SU-8 film is preferably ≥10μm, more preferably 10-30μm, and the thickness of the SU-8 film is calculated based on the thickness on the substrate plane; the temperature of the second pre-bake is preferably 95-120℃, more preferably 95-110℃, and the second pre-bake time is 3-5min; the second mask exposure is preferably ultraviolet mask exposure; the ultraviolet wavelength of the ultraviolet mask exposure is preferably 365nm; the mask used in the second mask exposure is the same as the first The mask used for mask exposure is the same and will not be repeated here; when performing the second mask exposure, the hollow structure array of the mask is aligned with the hemispherical recessed structure of the hemispherical end face template; the temperature of the intermediate baking is preferably 95-120°C, more preferably 95-110°C, and the time of the intermediate baking is preferably 3-5min; the developer used in the second development is preferably propylene glycol methyl ether acetate (PGMEA), and the time of the second development is preferably 5-7min. The present invention dissolves the SU-8 film in the unexposed area through development to form a vertical array structure; after the second development is completed, it is preferably used to rinse the residual glue with isopropyl alcohol and deionized water in sequence, and then post-bake; the temperature of the post-bake is preferably 150-200°C, more preferably 150-180°C, and the time of the post-bake is preferably 15-30min, more preferably 15-20min; after the post-bake is completed, the SU-8 one-dimensional vertical optical waveguide array is obtained.

[0041] After obtaining the SU-8 one-dimensional vertical optical waveguide array, the present invention coats the surface of the SU-8 one-dimensional vertical optical waveguide array with a flexible polymer precursor solution and then performs a cross-linking curing reaction to obtain a flexible support layer supporting the SU-8 vertical array, and then removes the substrate to obtain the flexible self-supporting vertical optical waveguide array. In the present invention, the flexible polymer precursor is preferably a polyimide precursor; the coating method is preferably spin coating; the spin coating speed is preferably 4000-7000rpm, more preferably 6000-7000rpm, and the spin coating time is preferably 30s; the cross-linking curing reaction temperature is preferably 300-350℃, and the time is preferably 2-5h; the cross-linking curing reaction is preferably carried out under a protective atmosphere, and the protective atmosphere is preferably nitrogen; the thickness of the flexible support layer is preferably 8-25μm; in a specific embodiment of the present invention, the thickness of the flexible support layer is based on being able to completely cover the SU-8 one-dimensional vertical optical waveguide array on the substrate surface.

[0042] In the present invention, the method of removing the substrate is preferably a chemical etching method; the etchant used in the chemical etching is preferably a buffered oxide etchant (BOE); the components of the buffered oxide etchant preferably include NH4F and HF, and the mass ratio of the NH4F and HF is preferably 10:1; in a specific embodiment of the present invention, it is preferred to immerse the substrate with the SU-8 one-dimensional vertical optical waveguide array and the flexible support layer in the buffered oxide etchant for etching, and the etching time is preferably 3 to 5 hours; the buffered oxide etchant of the present invention etches the silicon dioxide layer on the surface of the silicon substrate, thereby separating the substrate from the SU-8 one-dimensional vertical optical waveguide array and the flexible support layer. After the etching is completed, it is preferred to use a polytetrafluoroethylene substrate to fish out the flexible self-supporting vertical optical waveguide array.

[0043] The present invention also provides the application of the flexible self-supporting vertical optical waveguide array described in the above scheme or the flexible self-supporting vertical optical waveguide array prepared by the preparation method described in the above scheme in an image sensor; the present invention has no special requirements for the application method, and the method familiar to those skilled in the art can be used; in a specific embodiment of the present invention, it is preferred to conformally bond the flexible self-supporting vertical optical waveguide array to the surface of the image sensor.

[0044] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Example 1

[0046] A preparation method of a flexible self-supporting vertical optical waveguide array, the specific steps are as follows:

[0047] 1. Prepare the raw materials: 20mm×20mm silicon wafer (including 300nm thick silicon dioxide layer), AZ-5214E ​​positive photoresist, SU-8 UV negative photoresist, polyimide (PI) liquid precursor solution;

[0048] 2. Spin-coat AZ-5214E ​​positive photoresist as an etching mask layer: A silicon wafer with a side length of 20mm×20mm was cleaned with acetone, isopropanol and deionized water for 5 minutes, and then blown dry with dry nitrogen. Then, 0.5mL of AZ-5214E ​​positive photoresist was transferred using a pipette gun and slowly dripped on the surface of the silicon wafer, and then spin-coated at a speed of 3000rmp for 30s to evenly spin-coat the photoresist on the sample surface to obtain an AZ-5214E ​​photoresist layer with a thickness of 1μm. Pre-bake at 100℃ for 90s, use a UV mask exposure machine to expose according to the pre-designed optical waveguide array mask, and use NMD-3 developer for development. In this process, the photoresist in the processing area of ​​each vertical waveguide is dissolved, thereby exposing the silicon substrate, while the area between the vertical waveguides continues to be covered by the photoresist.

[0049] 3. Preparation of spherical end face template by isotropic etching using inductively coupled plasma etching (ICP-RIE): Place the developed silicon wafer inside the ICP-RIE chamber, evacuate to 250mTorr, introduce 200sccm of SF6 gas to isotropically etch the silicon wafer, control the temperature in the reaction chamber to 10°C, the power of the plasma generator to 500W, the substrate bias power to 5W, and the etching time to 5min. The purpose of this step is to isotropically etch the area not protected by the photoresist through the ICP-RIE process to form a spherical concave structure, which can then be used as a hemispherical end face template when making a polymer vertical waveguide.

[0050] 4. Preparation of polymer vertical waveguide array by UV mask exposure: Use N-methylpyrrolidone (NMP) degumming solution to treat the etched silicon wafer to remove the residual photoresist layer; use acetone, isopropanol and deionized water to clean the silicon wafer in turn and blow it dry, then add about 1 mL of SU-8 UV negative photoresist on the etched surface of the silicon wafer and spin coat it at 1200 rpm for 30 seconds to obtain a SU-8 film with a thickness of about 10 μm. After the silicon wafer coated with SU-8 film was pre-baked at 95°C for 3 min, the same optical waveguide array mask was aligned with the etched hemispherical recessed structure array using a 365nm wavelength UV exposure machine and exposed for 3 min; then, it was mid-baked on a 95°C hot plate for 3 min. After cooling to room temperature, it was developed with propylene glycol methyl ether acetate (PGMEA) for 5 min. Then, it was rinsed with isopropyl alcohol and deionized water to remove the residual glue. Finally, it was post-baked at 150°C for 15 min to obtain a SU-8 one-dimensional vertical optical waveguide array with a height of 10 μm and a diameter of 2 μm. The density of the optical waveguide was 2.5×10 5 Pieces / mm 2 .

[0051] 5. Prepare a flexible support layer for the vertical optical waveguide array by spin coating: Add the PI liquid precursor to the surface of the sample obtained in step 4 and spin coat it at 7000 rpm for 30 seconds to evenly coat the sample surface; then put it into an oven at 300°C and keep it warm for 2 hours under a nitrogen atmosphere for cross-linking and curing reaction to obtain a PI film with a thickness of about 8 to 9 μm, which serves as a flexible support layer to support the vertical optical waveguide array after removing the original silicon substrate.

[0052] 6. Low-damage stripping of flexible vertical optical waveguide array: Place the sample obtained in step 5 in a buffered oxide etchant (BOE) to etch the SiO2 layer on the surface of the substrate. The etchant composition is NH4F:HF=10:1 (mass ratio), and the etching time is 3h. After the etching is completed, use a polytetrafluoroethylene substrate to obtain a flexible self-supporting vertical optical waveguide array.

[0053] Characterization and Testing:

[0054] Figure 2 The schematic diagram (left) and scanning electron microscope image (right) of the SU-8 one-dimensional vertical optical waveguide array obtained on the original silicon substrate. Figure 2 It can be seen that the vertical optical waveguide array prepared by the present invention has steep sidewalls and a flat surface. According to tests, the single waveguide diameter error in the optical waveguide array prepared by the present invention is less than 10%, the sidewall angle is 85-89°, and the root mean square roughness is 0.119nm.

[0055] Surface deformation ability test: The flexible self-supporting vertical optical waveguide array prepared in this embodiment is bonded to a spherical glass substrate to observe the degree of bonding. Figure 3 This is the test result of the surface deformation ability of the flexible self-supporting vertical optical waveguide array. Figure 3 It can be seen that the flexible self-supporting vertical optical waveguide array of the present invention can be completely attached to the curved surface and has excellent flexibility. When the side length of the array is 12-14 mm, the maximum depth after bending can reach 2.2 mm, and the minimum curvature radius can reach 10-11.8 mm.

[0056] Sensor imaging capability test: Use parallel light to illuminate a photomask with a specific pattern, and project the specific pattern on the mask onto the surface of the sensor integrated with an optical waveguide array for testing. The sensor control unit reads the electrical signal and reconstructs the image through a computer. The photomask is prepared using a metal mask through a laser etching process. Figure 4 To integrate the flexible self-supporting vertical optical waveguide array, the imaging capability of the sensor changes. Figure 4 The left side shows the imaging result of the sensor without the integrated flexible self-supporting vertical optical waveguide array, and the right side shows the imaging result of the sensor with the integrated flexible self-supporting vertical optical waveguide array prepared in the embodiment. Figure 4 It can be seen that after integrating the flexible self-supporting vertical optical waveguide array of the present invention, the imaging performance of the sensor is significantly improved.

[0057] In summary, the present invention uses UV-cured SU-8 polymer as an optical waveguide material, and after a concave hemispherical template is etched on the surface of the substrate by means of ICP technology, the in-situ preparation of the microlens at the end of the waveguide can be realized. At the same time, only a fast mask exposure and curing process is required to obtain a large-area vertical optical waveguide structure; and the preparation process of the present invention is independent of the preparation process of the image sensor, and has the advantages of batch low-cost production, high quality consistency within the batch, high precision and low surface roughness; the flexible vertical optical waveguide array prepared by the present invention not only has the characteristics of high density, large aspect ratio, small feature size, etc., but also has excellent flexibility, can realize surface deformation with a minimum curvature radius of 10 mm, can realize conformal bonding between the waveguide array and the image sensor surface through simple external integration means, thereby reducing the crosstalk problem between the image sensor pixels and improving the detection sensitivity of the pixels, and has extremely strong flexibility and versatility, and has broad application prospects.

[0058] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A flexible self-supporting vertical optical waveguide array, characterized in that: It comprises a flexible support layer and a SU-8 one-dimensional vertical optical waveguide array; the SU-8 one-dimensional vertical optical waveguide array is composed of a plurality of SU-8 one-dimensional optical waveguide units, and the SU-8 one-dimensional optical waveguide units are perpendicular to the flexible support layer; each of the SU-8 one-dimensional optical waveguide units is partially embedded in the flexible support layer, and the end of the exposed part presents a hemispherical convex surface; the SU-8 one-dimensional vertical optical waveguide array is prepared by SU-8 ultraviolet negative photoresist.

2. The flexible self-supporting vertical optical waveguide array according to claim 1, characterized in that: The height of the SU-8 one-dimensional vertical optical waveguide unit is ≥10 μm and the diameter is ≤5 μm; the density of the SU-8 one-dimensional optical waveguide unit in the flexible self-supporting vertical optical waveguide array is ≤2.5×10 5 Pieces / mm 2 .

3. The flexible self-supporting vertical optical waveguide array according to claim 1, characterized in that: The flexible supporting layer is polyimide; the thickness of the flexible supporting layer is 8-25 μm.

4. The method for preparing the flexible self-supporting vertical optical waveguide array according to any one of claims 1 to 3, characterized in that: The following steps are involved: A positive photoresist is coated on the surface of the substrate, and then pre-baking, first mask exposure and development are performed in sequence to obtain a patterned photoresist layer; The substrate having a patterned photoresist layer on the surface is isotropically etched by inductively coupled plasma etching to form a hemispherical concave structure in the area of ​​the substrate not protected by the photoresist layer, and then the patterned photoresist layer on the surface of the substrate is removed to obtain a hemispherical end face template; SU-8 ultraviolet negative photoresist is coated on the surface of the hemispherical end face template, and then pre-baking, second mask exposure, intermediate baking, development and post-baking are performed in sequence to obtain a SU-8 one-dimensional vertical optical waveguide array on the surface of the hemispherical end face template; the mask used in the first mask exposure and the second mask exposure is provided with a hollow structure array corresponding to the target SU-8 one-dimensional vertical optical waveguide array structure, and the hollow structure array is aligned with the hemispherical concave structure of the hemispherical end face template when the second mask exposure is performed; After coating the surface of the SU-8 one-dimensional vertical optical waveguide array with a flexible polymer precursor solution, a cross-linking curing reaction is performed to obtain a flexible supporting layer supporting the SU-8 one-dimensional vertical optical waveguide array, and then the substrate is removed to obtain the flexible self-supporting vertical optical waveguide array.

5. The preparation method according to claim 4, characterized in that: The conditions for the isotropic etching include: a pressure of 150 to 550 mTorr, an etching gas of SF6, a flow rate of the etching gas of 50 to 200 sccm, a temperature in the reaction chamber of 5 to 25°C, a power of the plasma generator of 200 to 500 W, a substrate bias power of 5 to 50 W, and an etching time of 5 to 10 min.

6. The preparation method according to claim 4, characterized in that: The radius of the hemispherical concave structure is 1.7-7.7 μm, and the depth of the bottom of the concave is 300-400 nm.

7. The preparation method according to claim 4, characterized in that: The coating thickness of the SU-8 ultraviolet negative photoresist is 10 to 30 μm.

8. The preparation method according to claim 4, characterized in that: The first mask exposure and the second mask exposure are ultraviolet mask exposure.

9. The preparation method according to claim 4, characterized in that: The flexible polymer precursor is a polyimide precursor; the temperature of the cross-linking curing reaction is 300-350° C., and the time is 2-5 hours; and the cross-linking curing reaction is carried out under a protective atmosphere.

10. Use of the flexible self-supporting vertical optical waveguide array according to any one of claims 1 to 4 or the flexible self-supporting vertical optical waveguide array prepared by the preparation method according to any one of claims 5 to 9 in an image sensor.

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