Random microlens array and manufacturing method thereof

Abstract

The invention discloses a random microlens array and a manufacturing method thereof, and belongs to the technical field of semiconductor device manufacturing processes. Aiming at the problems that the structure is not real and random, the template dependence is strong, the morphology is difficult to continuously regulate and control, the process is complicated, the efficiency is low and the random micro-lens array is not suitable for large-area processing in the existing random micro-lens array preparation method, laser of an ultraviolet wave band is irradiated to the surface of a diffuser by utilizing a laser speckle gray scale photoetching system; forming a laser speckle pattern with statistical randomness, taking the intensity distribution of the laser speckle pattern as a natural gray level mask, and transferring the intensity distribution to the photoresist on the surface of the transparent substrate in a gray level exposure mode to form a three-dimensional free-form surface micro-lens morphology which is arranged in a non-periodic manner and has continuous change; therefore, a random micro-lens array preparation scheme which is real and random in structure, adjustable in height, free of a template and simple in process is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor device manufacturing technology, and in particular relates to a random microlens array and a manufacturing method thereof. Background Art

[0002] In recent years, the widespread application of lasers in fields such as illumination, detection, and communications has attracted significant attention from researchers. However, lasers typically exhibit a Gaussian intensity distribution, with high intensity at the center and weak intensity at the edges, which is unfavorable for certain applications requiring high intensity uniformity. To achieve the goal of shaping Gaussian beams into flat-top beams, various technical solutions have been proposed, including aspheric lens arrays, liquid crystal spatial light modulators (SLMs), diffractive optical elements (DOEs), and microlens arrays (MLAs).

[0003] Microlens arrays (MLAs) are considered one of the most commonly used homogenizing elements due to their high energy efficiency, flexible structure, and excellent homogenization. However, traditional MLAs typically have a periodic structure, which leads to interference coupling between microbeams. This easily creates interference fringes in the homogenized light spot, reducing the overall uniformity of the spot. To address this issue, researchers have proposed constructing random microlens arrays (RMLAs) by breaking the periodicity to effectively suppress interference effects and improve homogenization quality.

[0004] Currently, RMLA fabrication methods primarily include thermal reflow, template imprinting, polymer phase separation, laser direct writing, and wet / dry etching. However, these existing methods suffer from a lack of true randomness, difficulty in structural control, strong template dependence, complex processes, and low processing efficiency, making them unable to meet the multiple requirements of modern optical systems for miniaturization, integration, low cost, and structural tunability.

[0005] In contrast, grayscale lithography based on laser speckle patterns offers a new approach to constructing random microlens arrays. This method exploits the inherent statistical randomness of laser speckle patterns, controlling the exposure dose through grayscale patterns, thereby achieving continuous adjustment of the microlens height. Combined with standard photolithography processes, this approach offers advantages such as strong randomness, high structural controllability, the absence of templates, and suitability for large-area fabrication. This makes it an advanced fabrication method that combines high flexibility, high efficiency, and excellent reproducibility, with broad application prospects. Summary of the Invention

[0006] To address the problems of existing random microlens array preparation methods, such as non-truly random structure, strong template dependence, difficulty in continuous morphology control, complex process, low efficiency and unsuitability for large-area processing, the present invention provides a random microlens array and a method for its fabrication.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A random microlens array, comprising a transparent substrate and a photoresist structure on the surface of the transparent substrate; The transparent substrate is placed under the laser speckle field, and the height difference of the microlenses at different parts is achieved by controlling the laser exposure time; The photoresist structure is prepared by grayscale photolithography by irradiating a laser onto the surface of a diffuser to form a laser speckle pattern.

[0008] A method for manufacturing a random microlens array comprises the following steps: Step 1: Using a laser speckle grayscale lithography system, a laser in the ultraviolet band is irradiated onto the surface of the diffuser to form a laser speckle pattern with statistical randomness; The laser speckle grayscale lithography system includes a laser generator, a light transmission time control device, a reflector, and a scattering element. The laser generator generates coherent laser light, the exposure time is regulated by the light transmission time control device, and a speckle light field is formed through a diffuser. Laser generating device: used to provide coherent laser; Light-through time control device: controls the exposure time by controlling the light switch; Reflector: used to adjust the direction of the light path; Scattering element: used to form a speckle light field and adjust the uniformity of the light field.

[0009] Step 2: Using the intensity distribution of the laser speckle pattern as a natural grayscale mask, the pattern is transferred to the photoresist on the transparent substrate through grayscale exposure to form a non-periodic arrangement with a continuously changing three-dimensional free-form surface microlens morphology; Step 2.1: Spin-coating a multi-layer photoresist coating on the cleaned transparent substrate surface, wherein the total thickness of the photoresist coating is adjustable; Step 2.2: Place a transparent substrate coated with photoresist behind the diffuser and adjust the distance between the two to control the average aperture of the laser speckle pattern. Because the speckle pattern acts as a natural mask, the average size of the speckles can be approximately regarded as the average size of the random microlens array, thus achieving a random distribution of the random microlens array aperture. By adjusting the average size of the speckle particles in the speckle light field, the average size of the random microlens array produced by photolithography can be changed. The calculation formula for the average aperture of the laser speckle pattern is: ; in, is the incident laser wavelength, represents the distance between the photoresist coating surface and the engineered diffuser, Indicates the diameter of the laser spot on the engineered diffuser.

[0010] Step 2.3: Control the exposure time and laser intensity to achieve the target exposure dose, thereby controlling the average height of the microlens. The depth of the random microlens array is mainly determined by the exposure dose. The greater the exposure dose, the greater the depth. Because the light intensity of the speckle particles at different positions is different. Therefore, under the same exposure time conditions, the speckle particles at different positions will have different exposure doses, thereby achieving a random distribution of the height of the random microlens array. By controlling the exposure time, a suitable exposure dose is obtained so that the bright spot area of ​​the speckle will not penetrate the photoresist due to the high exposure dose, and the dark spot area can reach the photoreaction threshold through sufficient photon accumulation time for effective development. The exposure dose According to the formula of exposure dose: ; in, represents the exposure dose, Indicates light intensity, Indicates the photolithography time.

[0011] Step 2.4: After the exposure is completed, a development process is performed to obtain a random microlens array with continuously changing structural morphology.

[0012] Compared with the prior art, the present invention has the following advantages: 1. Truly random structure, significantly suppressing interference fringes. This invention uses laser speckle patterns as a natural grayscale mask, which exhibits statistical randomness in spatial distribution. This enables the construction of non-periodic, irregularly distributed microlens arrays. Compared to traditional regular microlens arrays, this invention effectively breaks the coherent interference condition, significantly reducing interference fringes in uniform light spots and improving uniform light quality.

[0013] 2. No template required, simplified process, and lower cost. Traditional methods (such as template imprinting and thermal reflow) rely on templates or complex micro-nano patterning processes. However, this invention uses the light field itself as a mask to achieve pattern transfer, eliminating the need for physical masks or master molds. This effectively reduces material costs and process complexity, making it suitable for industrialization.

[0014] 3. Continuously adjustable microlens morphology, offering a high degree of structural freedom. By controlling the laser speckle field characteristics (such as size and contrast) and the exposure dose, the present invention enables continuous adjustment of microlens parameters such as aperture and height, resulting in free-form structures with non-flat tops and bottoms, meeting the functional requirements of different optical systems for defocusing, shaping, and scattering.

[0015] 4. Suitable for large-area preparation with good repeatability and consistency. Based on standard photolithography technology, the present invention can complete the parallel exposure and development of random microlens array structures on the entire photoresist surface at one time, with good process repeatability, and is suitable for the preparation of large-area uniform structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a cross-sectional view of the photolithography topography; Figure 2 It is a top view of the photolithography topography; Figure 3 A schematic diagram of a three-dimensional image of the lithography topography; Figure 4 This is a diagram of the laser speckle grayscale lithography system; Figure 5 is the light field image behind the random microlens array; Figure 6 This is a real picture of a random microlens array. DETAILED DESCRIPTION

[0017] To gain a deeper understanding of the present invention, we will provide a comprehensive and detailed description thereof. However, the present invention has various implementations and is not limited to the specific examples listed herein. These examples are presented to enhance a comprehensive understanding of the present disclosure.

[0018] In order to better understand the technical solution of the present invention, the following describes the method for preparing a random microlens array of the present invention with reference to a specific example. It should be understood that this example is only used to illustrate a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention.

[0019] Materials and equipment used: Light source: UV laser with a wavelength of 360 nm; Scattering element: engineered diffuser (scattering angle 50°); Photoresist: positive photoresist SPR220-7.0, thickness 36 microns; Base material: soda-lime glass; Exposure system: projection type UV exposure system with light switch control; Measuring equipment: Scanning electron microscope (SEM).

[0020] Speckle light field generation and grayscale lithography process steps: Laser speckle generation: 360nm UV laser is vertically irradiated onto the surface of the engineered diffuser, forming a laser speckle light field with random intensity distribution behind it. By adjusting the distance Z (20mm) between the engineered diffuser and the photoresist, a speckle pattern with an average diameter of 10 microns can be obtained. Figure 2 Shown is a top view of speckle with an average size of 10 microns.

[0021] Photoresist coating preparation: Spin-coat two layers of SPR220-7.0 photoresist on the cleaned soda-lime glass transparent substrate. The thickness of each layer is about 18 μm, and the total thickness is about 36 μm. Figure 1The marked photoresist thickness shown is approximately 36 microns, with slight variations in different areas.

[0022] Grayscale exposure: Place the photoresist under the speckle light field and adjust the actual exposure dose by controlling the light switch on time. The intensity distribution of the speckle light field serves as a natural mask, and the grayscale image information is directly converted into spatial exposure dose distribution. Figure 1 As shown, different height distributions of microlenses at different positions are obtained by controlling the exposure dose.

[0023] Development: After exposure, develop with standard developer for approximately 6 minutes. Rinse with deionized water and dry.

[0024] Structural morphology: The microlens morphology was observed using SEM, and it was found that the obtained array was a continuous irregular structure, which was consistent with the expected grayscale response; as shown in the attached figure. Figure 1 , the microlens structure shown in 2 is continuous and there is no flat top or flat bottom area.

[0025] No interference fringes: After the laser irradiates the random microlens array, no obvious periodic interference fringes are observed in the light field behind it, indicating that the randomness is effective. Figure 5 After the laser illuminates the random microlens array, there are no obvious interference fringes in the light field behind it.

[0026] Any matters not described in detail in this specification are prior art known to those skilled in the art. Although the above description of the present invention is based on specific embodiments to facilitate understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the specific embodiments. As long as various modifications are within the spirit and scope of the present invention as defined and determined by the appended claims, such modifications will be obvious to those skilled in the art, and all inventions and creations utilizing the concepts of the present invention are protected.

Claims

1. A random microlens array, characterized in that: The random microlens array includes a transparent substrate and a photoresist structure on the surface of the transparent substrate; The transparent substrate is placed under the laser speckle field, and the height difference of the microlenses at different parts is achieved by controlling the laser exposure time; The photoresist structure is prepared by grayscale photolithography by irradiating a laser onto the surface of a diffuser to form a laser speckle pattern.

2. A method for manufacturing a random microlens array, characterized in that: The following steps are involved: Step 1: Using a laser speckle grayscale lithography system, a laser in the ultraviolet band is irradiated onto the surface of the diffuser to form a laser speckle pattern with statistical randomness; Step 2: Using the intensity distribution of the laser speckle pattern as a natural grayscale mask, the pattern is transferred to the photoresist on the transparent substrate through grayscale exposure to form a non-periodic arrangement with a continuously changing three-dimensional free-form surface microlens morphology; Step 2.1: Spin-coating a multi-layer photoresist coating on the cleaned transparent substrate surface, wherein the total thickness of the photoresist coating is adjustable; Step 2.2: Place the transparent substrate coated with photoresist behind the diffuser and adjust the distance between the two to control the average aperture of the laser speckle pattern; Step 2.3: Control the exposure time and laser intensity to achieve the target exposure dose, thereby controlling the average height of the microlenses; Step 2.4: After the exposure is completed, a development process is performed to obtain a random microlens array with continuously changing structural morphology.

3. The method for manufacturing a random microlens array according to claim 2, wherein: The laser speckle grayscale lithography system in step 1 includes a laser generator, a light transmission time control device, a reflector, and a scattering element. The laser generator generates coherent laser light, the exposure time is controlled by the light transmission time control device, and a speckle light field is formed by a diffuser. Laser generating device: used to provide coherent laser; Light-through time control device: controls the exposure time by controlling the light switch; Reflector: used to adjust the direction of the light path; Scattering element: used to form a speckle light field and adjust the uniformity of the light field.

4. The method for manufacturing a random microlens array according to claim 3, wherein: The calculation formula for the average aperture of the laser speckle pattern in step 2.2 is: ; in, is the incident laser wavelength, represents the distance between the photoresist coating surface and the engineered diffuser, Indicates the diameter of the laser spot on the engineered diffuser.

5. The method for manufacturing a random microlens array according to claim 4, wherein: The exposure dose in step 2.3 According to the formula of exposure dose: ; in, represents the exposure dose, Indicates light intensity, Indicates the photolithography time.

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