Glass micro-lens array and preparation method thereof

Abstract

According to the glass micro-lens array and the preparation method thereof provided by the invention, the glass micro-lens array of which the size and the rise both break through the limitation of a traditional process is successfully prepared by combining a molding process with a local hot reflux process, and the local hot reflux process can soften surface molecules of a glass substrate, so that the surface of the glass substrate is more uniform. In addition, the depth and the curvature radius of the second concave cavity are controlled by controlling the time of the two times of deep silicon etching processes, so that the high controllability of the morphology of a single micro lens is realized, and the optical transmission efficiency and the imaging quality are remarkably improved. According to the invention, the first substrate and the glass substrate are bonded by using the MEMS technology, later reassembly is not needed, and wafer-level batch preparation is supported, so that the uniformity of the glass micro-lens array can be guaranteed, and the preparation cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of micro-nano fabrication technology, and in particular to a glass microlens array and its fabrication method. Background Technology

[0002] Microlenses, as fundamental optical components, have wide applications in imaging sensing, photovoltaics, and displays. Their core function is to modulate incident light through diffusion, shaping, distribution, or focusing, thereby enhancing key optical performance aspects such as wide-angle imaging, low optical distortion, and extended depth of field. Microlens arrays refer to a series of microlenses with diameters ranging from micrometers to millimeters, arranged periodically or aperiodically. By adjusting parameters such as the geometry, arrangement, duty cycle, and focal length of the microlenses, specific optical functions can be achieved, improving the integration and performance of optical systems. With the rapid development of miniaturized optical systems, microlens arrays have become a core component for improving system integration and overall performance, thus placing higher demands on their fabrication precision and large-scale production capabilities.

[0003] Traditional methods for fabricating microlens arrays include direct and indirect methods. The direct method eliminates the need for hard masks and relies on changes in the material's physical state (e.g., placing the material in a thermoplastic or liquid state) to utilize the surface tension effect of the molten polymer to form microlenses. While direct methods produce microlens arrays with very low surface roughness, the geometry of the microlenses is affected by thermodynamic parameters (softening temperature, pressure field, cooling rate) and interfacial characteristics (substrate wettability), making precision control difficult and resulting in poor morphological consistency. The indirect method uses molds for compression molding and injection molding to form microlenses. Precision molds allow for accurate control of lens morphology, making it more suitable for mass production of microlens arrays. However, the indirect method is more complex, and the surface quality of the microlenses is limited by the roughness of the mold (typically in the 10-50 nm range), significantly increasing scattering loss. Furthermore, mold manufacturing is expensive, especially for large-aperture or large-size microlens arrays, where the mold processing difficulty increases exponentially.

[0004] Currently, commonly used methods for fabricating microlenses include inkjet printing, laser direct writing, thermal embossing, and photolithography. Inkjet printing involves spraying polymer liquid material onto a substrate surface through a printhead, where it solidifies to form a microlens. Its advantages include the elimination of photomasks, compatibility with flexible substrates, and low surface roughness. However, the droplet spreading dynamics are difficult to control precisely, leading to morphological deviations. Furthermore, it is limited by fluid viscosity, making it unsuitable for high-refractive-index optical glass materials. Laser direct writing utilizes femtosecond / picosecond lasers to induce refractive index changes or surface ablation within a transparent medium. It can achieve submicron resolution and flexible topology design. However, the single-point scanning mode results in low processing efficiency, and the unit size is less than 100 μm, making it difficult to meet the requirements of large-aperture optical systems. Photolithography involves fabricating photoresist pillars on a substrate, thermally melting these pillars to form the desired microlens shape, and then transferring the photoresist pattern onto the substrate using dry etching to form a microlens array. It boasts mature technology and low cost, but the curvature control range of the thermally melted photoresist is limited, resulting in a small sag. Nano-thermal embossing technology uses a silicon / glass mold to hot-press and cure UV adhesive, which is currently the mainstream large-scale fabrication method. Although it meets the requirements of high efficiency and high surface quality, the rigid structure of the mold limits the improvement of lens sagitta, and the micro-nano fabrication cost of the glass mold is extremely high.

[0005] Therefore, how to develop large-size, high-angle, wafer-level glass microlens arrays for mass production while reducing the surface roughness of the microlenses to meet the needs of miniaturized optical systems has become an urgent problem to be solved. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a glass microlens array and its preparation method, which solves the problems of small size, small sag, high surface roughness, and inability to mass-produce glass microlens arrays obtained by existing glass microlens array preparation methods.

[0007] To achieve the above and other related objectives, the present invention provides a method for fabricating a glass microlens array, the method comprising at least the following steps:

[0008] A first substrate is provided, the first substrate including a front side and a back side disposed opposite to each other, a first oxide layer is formed on the front side of the first substrate, and a second oxide layer is formed on the back side of the first substrate;

[0009] Photoresist is spin-coated onto the surface of the first oxide layer, and the first opening is formed by exposure and development.

[0010] Using the first oxide layer as a mask, isotropic deep silicon etching is performed on the first substrate at the first opening to form a first cavity;

[0011] The first oxide layer and the second oxide layer are removed by wet etching process, and the first cavity is modified again by maskless deep silicon etching process to form the second cavity and obtain the mold.

[0012] A glass substrate is provided, and the mold is bonded to the glass substrate by an anodic bonding process to form a bonding structure;

[0013] The bonding structure is heated to a first temperature and held for a certain period of time until the glass substrate completely fills the second cavity in the mold.

[0014] The bonded structure is immersed in TMAH solution for demolding to obtain a wafer-level glass microlens array.

[0015] Optionally, before immersing the bonded structure in the TMAH solution for demolding, the process further includes a step of thinning and polishing the glass substrate using a CMP process.

[0016] Optionally, the thickness of the first oxide layer is 1 to 2 μm, and the thickness of the first oxide layer is equal to the thickness of the second oxide layer.

[0017] Optionally, the width of the first opening is 100 to 2000 μm.

[0018] Optionally, the sagittal height of the second cavity is 150–260 μm.

[0019] Optionally, the radius of curvature of the second cavity is at least 300 μm.

[0020] Optionally, the glass substrate is a BF33 glass substrate, and the holding time after heating the bonding structure to the first temperature is 20 to 30 minutes.

[0021] Optionally, after immersing the bonded structure in a TMAH solution for demolding, the process further includes a step of performing a localized hot reflow process on the glass microlens array.

[0022] Optionally, the temperature for performing the localized hot reflow process on the glass microlens array is 520–560°C.

[0023] The present invention also provides a glass microlens array, which is obtained by the glass microlens array preparation method described above.

[0024] As described above, the glass microlens array and its fabrication method of the present invention have the following beneficial effects: by combining molding process with local hot reflow process, a glass microlens array with dimensions and height exceeding the limitations of traditional processes is successfully fabricated. Moreover, the local hot reflow process can soften the surface molecules of the glass substrate, thereby significantly reducing the surface roughness of the microlens and significantly improving optical transmission efficiency and imaging quality. In addition, by controlling the time of the two deep silicon etching processes to control the depth and radius of curvature of the second cavity, a high degree of controllability of the morphology of a single microlens is achieved. The present invention uses MEMS process to bond the first substrate to the glass substrate, eliminating the need for subsequent reassembly and supporting wafer-level batch fabrication, thereby ensuring the uniformity of the glass microlens array and reducing the fabrication cost. Attached Figure Description

[0025] Figure 1 The diagram shown is a process flow chart of the method for fabricating the glass microlens array of the present invention.

[0026] Figure 2 The diagram shown is a cross-sectional view of the first substrate provided in the preparation method of the present invention.

[0027] Figure 3 The diagram shown is a cross-sectional view of the first opening formed in the preparation method of the present invention.

[0028] Figure 4 The diagram shown is a cross-sectional view of the first cavity formed in the preparation method of the present invention.

[0029] Figure 5 The diagram shown is a cross-sectional view of the second concave cavity formed in the preparation method of the present invention.

[0030] Figure 6 The diagram shows a cross-sectional structure of the first substrate and the glass substrate after bonding in the preparation method of the present invention.

[0031] Figure 7 The diagram shows a cross-sectional structure of the glass substrate after it has completely filled the second cavity in the preparation method of the present invention.

[0032] Figure 8 The diagram shows a cross-sectional structure of the glass substrate after CMP processing in the preparation method of the present invention.

[0033] Figure 9 The diagram shown is a cross-sectional view of the glass microlens array formed in the preparation method of the present invention.

[0034] Figure 10 The image shown is a SEM image of the glass microlens array formed in the preparation method of the present invention.

[0035] Figure 11The image shown is a profilometer test result of the second concave cavity formed in the preparation method of the present invention.

[0036] Component designation explanation

[0037] 101. First substrate; 102. First oxide layer; 103. Second oxide layer; 104. First opening; 105. First cavity; 106. Second cavity; 107. Glass substrate; 108. Bonding structure; 109. Microlens; S1-S7. Steps. Detailed Implementation

[0038] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0039] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for devices in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or there may be one or more layers in between.

[0040] It should be understood that the use of terms such as "first" and "second" to define the components is merely for the purpose of distinguishing the aforementioned components. Unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0041] Please see Figures 1 to 11 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0042] This embodiment provides a method for fabricating a glass microlens array. Please refer to [link to relevant documentation]. Figure 1 The diagram shows the process flow of this preparation method, which includes the following steps:

[0043] S1: A substrate is provided, the substrate including a front side and a back side disposed opposite to each other, a first oxide layer 102 is formed on the front side of the substrate, and a second oxide layer 103 is formed on the back side of the substrate;

[0044] S2: Photoresist is spin-coated onto the surface of the first oxide layer 102, and the first opening 104 is formed by exposure and development;

[0045] S3: Using the first oxide layer 102 as a mask, isotropic deep silicon etching is performed on the substrate at the first opening 104 to form the first cavity 105.

[0046] S4: Remove the first oxide layer 102 and the second oxide layer 103 by wet etching process, and use maskless deep silicon etching process to modify the first cavity 105 again to form the second cavity 106 and obtain the mold.

[0047] S5: A glass substrate 107 is provided, and the mold is bonded to the glass substrate 107 by an anodic bonding process to form a bonding structure 108;

[0048] S6: Heat the bonding structure 108 to a first temperature and hold it for a certain time until the glass substrate 107 completely fills the second cavity 106 in the mold;

[0049] S7: The bonding structure 108 is immersed in TMAH solution for demolding to obtain a wafer-level glass microlens array 109.

[0050] The fabrication method of the glass microlens array 109 in this embodiment will be described in detail below with reference to the specific accompanying drawings.

[0051] like Figure 2 As shown, in step S1, a first substrate 101 is provided. The first substrate 101 includes a front side and a back side disposed opposite to each other. A first oxide layer 102 is formed on the front side of the first substrate 101, and a second oxide layer 103 is formed on the back side of the first substrate 101.

[0052] Specifically, in this embodiment, the first substrate 101 includes one of a silicon substrate, a germanium substrate, a silicon-germanium substrate, or a silicon-on-insulator (SOI) substrate, etc. Before performing subsequent processes, the first substrate 101 can be cleaned, for example, by sequentially cleaning with an organic solvent such as acetone and deionized water to remove contaminants from the surface of the first substrate 101, followed by drying; or by first removing the natural oxide layer on the surface of the first substrate 101 with a diluted acid solution, followed by cleaning with deionized water, and finally drying; or by performing multiple cleaning operations using the aforementioned methods. It should be noted that in this embodiment, if... Figure 2The diagram shown is a cross-sectional view of the first substrate 101, which is a silicon substrate.

[0053] Furthermore, the first substrate 101 includes a front side and a back side disposed opposite to each other. A first oxide layer 102 is formed on the front side of the first substrate 101. The first oxide layer 102 covers the surface of the substrate and can prevent damage to the substrate during subsequent isotropic deep silicon etching of the first substrate 101. Specifically, the first oxide layer 102 can be a single layer or a stack of more than one dielectric material. The dielectric material can include silicon oxide or a material with a high dielectric constant, such as silicon nitride (SiN), silicon oxynitride (SiON), hafnium oxide (HfO2), or aluminum oxide (Al2O3). In addition, a second oxide layer 103 is formed on the back side of the first substrate 101.

[0054] Preferably, in this embodiment, the thickness of the first oxide layer 102 is 1-2 μm, and the thickness of the first oxide layer 102 is equal to the thickness of the second oxide layer 103. The first oxide layer 102 and the second oxide layer 103 can be silicon oxide layers obtained by thermo-oxidative growth. Compared with silicon oxide layers obtained by chemical vapor deposition (CVD), silicon oxide layers obtained by thermo-oxidative growth have a higher density and are less susceptible to corrosion.

[0055] like Figure 3 As shown, in step S2, photoresist is spin-coated onto the surface of the first oxide layer 102, and the first opening 104 is formed by exposure and development.

[0056] Specifically, photoresist is coated on the surface of the first oxide layer 102 to form a photoresist mask layer; after exposure and development, a first opening 104 is formed in the photoresist mask layer to form a patterned first oxide layer 102. The width of the first opening 104 is 100-2000 μm, for example, the width of the first opening 104 is 100 μm, 500 μm, 1000 μm, 1500 μm or 2000 μm. The width of the first opening 104 can be used to define the width of the second cavity 106 formed subsequently, thereby determining the size of the microlenses in the final glass microlens array 109. Compared with the existing process, the size of a single microlens in the glass microlens array 109 obtained in this embodiment is greatly improved.

[0057] like Figure 4 As shown, in step S3, using the first oxide layer 102 as a mask, isotropic deep silicon etching is performed on the substrate at the first opening 104 to form the first cavity 105.

[0058] Specifically, using the patterned first oxide layer 102 as a mask layer, an isotropic deep silicon etching process is performed on the substrate to form a plurality of first cavities 105 of equal size in the substrate, wherein the first cavities 105 do not penetrate the first substrate 101.

[0059] like Figure 5 As shown, in step S4, the first oxide layer 102 and the second oxide layer 103 are removed by wet etching process, and the first cavity 105 is modified again by maskless deep silicon etching process to form the second cavity 106, and the mold is obtained.

[0060] Specifically, such as Figure 5 As shown, the first oxide layer 102 on the front side of the first substrate 101 and the second oxide layer 103 on the back side of the first substrate 101 are first removed by a wet etching process. The wet etching process has different selectivity ratios for the first oxide layer 102, the second oxide layer 103 and the first substrate 101. By controlling the etching rate of the wet etching process, the first oxide layer 102 and the second oxide layer 103 can be completely removed without damaging the first substrate 101. Then, the radius of curvature of the first cavity 105 is trimmed by a maskless deep silicon etching process so that the radius of curvature of the second cavity is at least 300 μm. For example, the radius of curvature of the second cavity 106 is 300 μm, 1000 μm, 1500 μm, or 2000 μm. In this case, the first substrate 101 with the second cavity 106 serves as the mold for the subsequently formed wafer-level glass microlens array 109. Furthermore, the sagitta of the second cavity 106 is 150–260 μm, for example, 150 μm, 200 μm, or 260 μm. No excessive limitation is imposed here. In this embodiment, a surface profilometer is used to measure the sagitta of the second cavity 106. Figure 11 As shown, the sagittal height of the second cavity 106 is greater than 200μm.

[0061] like Figure 6 As shown, in step S5, a glass substrate 107 is provided, and the mold is bonded to the glass substrate 107 by an anodic bonding process to form a bonding structure 108.

[0062] Specifically, in this embodiment, such as Figure 6As shown, a glass substrate 107 is provided. The glass substrate 107 is a BF33 glass substrate 107. The BF33 glass substrate 107 includes a first surface and a second surface disposed opposite to each other. The first surface of the BF33 glass substrate 107 is bonded to the front side of the first substrate 101. Since the first substrate 101 is a silicon substrate and the glass substrate 107 is a BF33 glass substrate 107, the bonding process between the BF33 glass substrate 107 and the first substrate 101 can be an anodic bonding process. That is, the BF33 glass substrate 107 and the first substrate 101 form a close contact and a strong Si-O-Si chemical bond is formed at the contact interface, thereby forming a bonding structure 108.

[0063] like Figure 7 As shown, step S6 is performed, in which the bonding structure 108 is heated to a first temperature and held for a certain period of time until the glass substrate 107 completely fills the second cavity 106 in the mold.

[0064] Specifically, the bonding structure 108 is placed in a high-temperature furnace and heated until the temperature inside the furnace reaches a first temperature, which is the softening point temperature of the BF33 glass substrate 107. After heating the bonding structure 108 to the first temperature, it is held for a period of time, specifically 20-30 minutes, for example, 20 minutes, 25 minutes, or 30 minutes. After holding at the softening point temperature for the aforementioned time, under the influence of the pressure difference between the inside and outside of the high-temperature furnace and the softening point temperature, as... Figure 7 As shown, this allows the BF33 glass substrate 107 to soften and completely fill the second cavity 106 in the mold.

[0065] like Figure 8 and Figure 9 As shown, in step S7, the bonding structure 108 is immersed in TMAH solution for demolding to obtain a wafer-level glass microlens array 109.

[0066] As an example, the bonding structure 108 further includes a step of thinning and polishing the glass substrate 107 using a CMP process before it is immersed in the TMAH solution for demolding.

[0067] Specifically, such as Figure 8 As shown, since the subsequent hot reflow process will make the surface of the glass substrate 107 away from the second cavity rough and uneven, before demolding the bonding structure 108, the glass substrate 107 of the bonding structure 108 is thinned and polished by CMP process, so as to control the total thickness and back surface roughness of the subsequently formed glass microlens array 109.

[0068] Specifically, the demolding process for the bonding structure 108 is as follows: the bonding structure 108 is immersed in a TMAH solution, and the temperature of the TMAH solution is maintained at 80-90°C. Since the TMAH solution has different selectivity ratios for silicon and silicon oxide, it will not have a significant impact on the surface of the glass substrate 107 until the silicon substrate is completely etched.

[0069] As an example, after the bonding structure 108 is immersed in TMAH solution for demolding, the process further includes a step of performing a localized thermal reflow process on the wafer-level glass microlens array 109.

[0070] Specifically, since the glass substrate 107 and the second cavity 106 of the silicon substrate are in contact, the deep silicon etching process will greatly increase the roughness of the inner surface of the second cavity 106. The final surface roughness of the microlens largely depends on the roughness of the inner surface of the second cavity 106. Therefore, in order to further reduce the surface roughness of the microlens, after the bonding structure 108 is immersed in a TMAH solution for demolding, a localized thermal reflow process is used to reduce the roughness of the wafer-level glass microlens array 109. In this embodiment, as... Figure 10 As shown, it is a microlens array 109 with different sizes. As can be seen from the figure, after the above-mentioned local thermal reflow process, the wafer-level glass microlens array 109 all exhibit good morphological characteristics, and its roughness can be reduced to within 10nm.

[0071] Specifically, the glass microlens array 109 obtained after demolding the bonding structure 108 is placed in a high-temperature furnace and heated until the temperature in the high-temperature furnace reaches the temperature requirement of the local hot reflow process. In this embodiment, the temperature for the local hot reflow process of the wafer-level glass microlens array 109 is 520-560°C, which is the annealing point temperature of the BF33 glass substrate. At this temperature range, the rough surface of the BF33 glass substrate undergoes local softening and reflow due to the increased molecular mobility caused by heating. At the same time, the viscosity decreases, allowing surface tension to play a role, ultimately making the surface of the BF33 glass substrate smoother, thereby greatly reducing the roughness of the glass microlens array 109.

[0072] In another embodiment of the present invention, a glass microlens array is also provided, wherein the glass microlens array is obtained by the glass microlens array fabrication method described above, such as... Figure 10 As shown, the glass microlens array includes multiple glass microlenses of equal size.

[0073] In summary, the glass microlens array and its fabrication method of this invention, by combining molding and localized reflow processes, successfully fabricate glass microlens arrays with dimensions and heights that break through the limitations of traditional processes. Furthermore, the localized reflow process softens the surface molecules of the glass substrate, significantly reducing the surface roughness of the microlenses and substantially improving optical transmission efficiency and imaging quality. In addition, by controlling the timing of the two deep silicon etching processes to control the depth and radius of curvature of the second cavity, a high degree of controllability in the morphology of individual microlenses is achieved. This invention uses MEMS technology to bond the first substrate to the glass substrate, eliminating the need for subsequent reassembly and supporting wafer-level batch fabrication. This ensures the uniformity of the glass microlens array and reduces fabrication costs. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial applicability.

[0074] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for fabricating a glass microlens array, characterized in that, The preparation method includes at least the following steps: A first substrate is provided, the first substrate including a front side and a back side disposed opposite to each other, a first oxide layer is formed on the front side of the first substrate, and a second oxide layer is formed on the back side of the first substrate; Photoresist is spin-coated onto the surface of the first oxide layer, and the first opening is formed by exposure and development. Using the first oxide layer as a mask, isotropic deep silicon etching is performed on the first substrate at the first opening to form a first cavity; The first oxide layer and the second oxide layer are removed by wet etching process, and the first cavity is modified again by maskless deep silicon etching process to form the second cavity and obtain the mold. A glass substrate is provided, and the mold is bonded to the glass substrate by an anodic bonding process to form a bonding structure; The bonding structure is heated to a first temperature and held for a certain period of time until the glass substrate completely fills the second cavity in the mold. The bonded structure is immersed in a TMAH solution for demolding to obtain a wafer-level glass microlens array.

2. The method for fabricating a glass microlens array according to claim 1, characterized in that: Before the bonding structure is immersed in TMAH solution for demolding, the glass substrate is thinned and polished using a CMP process.

3. The method for fabricating a glass microlens array according to claim 1, characterized in that: The thickness of the first oxide layer is 1 to 2 μm, and the thickness of the first oxide layer is equal to the thickness of the second oxide layer.

4. The method for fabricating a glass microlens array according to claim 1, characterized in that: The width of the first opening is 100–2000 μm.

5. The method for fabricating a glass microlens array according to claim 1, characterized in that: The sagittal height of the second cavity is 150–260 μm.

6. The method for fabricating a glass microlens array according to claim 1, characterized in that: The radius of curvature of the second cavity is at least 300 μm.

7. The method for fabricating a glass microlens array according to claim 1, characterized in that: The glass substrate is a BF33 glass substrate, and the holding time after heating the bonding structure to the first temperature is 20 to 30 minutes.

8. The method for fabricating a glass microlens array according to claim 1, characterized in that: After the bonded structure is immersed in TMAH solution for demolding, the process also includes a step of performing a localized hot reflow process on the glass microlens array.

9. The method for fabricating a glass microlens array according to claim 8, characterized in that: The temperature for the local hot reflow process of the glass microlens array is 520–560°C.

10. A glass microlens array, characterized in that: The glass microlens array is obtained by the fabrication method of any one of claims 1 to 9.

Images