Experimental method for manufacturing through hole by using gray exposure

Abstract

The invention relates to an experimental method for manufacturing a through hole by using gray exposure, and aims to realize a through hole structure with a specific inclination angle and depth-to-width ratio through collaborative design of photoetching and etching processes. The method comprises the following steps: determining a through hole angle and a depth-to-width ratio, selecting an etching condition, designing a gray mask structure based on an etching rate selection ratio, implementing gray exposure to obtain a mask pattern, etching, removing residual photoresist and finally forming a target through hole. And by regulating and controlling the selection ratio k of the mask to the substrate material, the inclination angle beta of the through hole and the depth H, designing the gray-scale mask morphology conforming to the target structure. The gray mask can be constructed by adopting gray photoresist or an optical modulation mask, and the inclination morphology parameter, the etching time and the etching rate of the gray mask meet a specific relation, so that high-precision structure control is realized. The method is suitable for the fields of MEMS, micro-optical devices and the like with high requirements on the morphology precision of the through hole, and has the effects of good structure consistency and high process repeatability.

Description

Technical Field

[0001] The present application relates to the field of micro-nano manufacturing, and in particular to an experimental method for making through-holes using grayscale exposure. Background Art

[0002] Currently, inverted trapezoidal via etching technology primarily achieves structural control at specific angles by optimizing photolithography and etching process parameters. For example, in a double-layer aluminum interconnect process, by adjusting photoresist thickness and hard-bake temperature, combined with coordinated optimization of etching gas flow, chamber pressure, and plate power, a fixed-slope inverted trapezoidal via can be formed, significantly increasing the metal layer's step coverage at the via to over 90%. This technology has been applied to devices such as D / A converters, effectively improving yield.

[0003] However, existing technologies primarily optimize for a single fixed angle, relying on empirical parameter tuning. Flexible control of arbitrary angles is not yet possible. Control methods focus on mechanical adjustments to gas ratios and power, lacking dynamic closed-loop control of the angle formation mechanism. Slope adjustment requires re-optimization of the entire set of parameters, resulting in a narrow process window and angle tolerances typically exceeding ±5°. Furthermore, wafer-level etching uniformity is poor, with significant differences in through-hole angles between the edge and center regions, restricting mass production stability.

[0004] As advanced packaging evolves toward high-aspect-ratio structures like 3D NAND, etching technology for inverted trapezoidal vias (VAS) is facing physical limitations. Existing wet or plasma etching methods offer limited control over the sidewall morphology of high-aspect-ratio structures, easily leading to residual hole bottoms or uncontrolled sidewall tilt. While laser-induced etching can achieve high aspect ratios, it struggles to accommodate arbitrary-angle forming requirements.

[0005] Regarding the above-mentioned related technologies, the inventors believe that the inverted trapezoidal through-hole etching technology needs to break through core bottlenecks such as flexible angle control, surface quality control and high aspect ratio compatibility in order to adapt to the multi-dimensional integration requirements of the next generation of semiconductor devices. Summary of the Invention

[0006] In order to improve the inverted trapezoidal through-hole etching technology, it is necessary to break through technical problems such as flexible angle control, surface quality control and high aspect ratio compatibility. This application provides an experimental method for making through-holes using grayscale exposure.

[0007] The experimental method for forming a through hole using grayscale exposure provided in this application adopts the following technical solution: An experimental method for forming a through hole using grayscale exposure includes the following steps: Step 1: Determine the through hole angle and aspect ratio; Step 2: Select etching conditions; Step 3: Designing a grayscale mask structure based on the etching rate selection ratio; Step 4: Grayscale exposure to obtain a grayscale mask; Step 5: Etching; Step 6: Remove residual photoresist; Step 7: Obtain the target through-hole structure.

[0008] By adopting the above technical solution, the technical problem of constructing high-precision and high-control non-vertical through-hole structures in traditional photolithography processes has been effectively solved, which is specifically reflected in the following aspects: 1. By determining the inclination angle and aspect ratio of the through-hole in step one, the geometric morphology of the through-hole can be accurately set according to the actual application requirements, providing a clear target for subsequent processes, so that the final through-hole structure is more in line with the device design requirements, and is especially suitable for scenarios such as microlens arrays, conical electrodes, light guide cones or three-dimensional packaging through-holes (TSV) that require specific inclined structures; 2. In step two, appropriate etching conditions are selected, such as reactive ion etching (RIE) parameter setting, gas composition selection, cavity pressure control, etc., to ensure that the etching process has high anisotropy and stability, and combined with the etching selectivity ratio (mask / substrate) for adjustment, the graphic transfer accuracy between the mask and the substrate material is effectively improved to avoid Via distortion due to over- or under-etching. 3. In step 3, a grayscale mask structure is designed based on the etch rate selectivity (k). Combined with the target via depth H and tilt angle β, a mapping relationship between the mask thickness and the final structure is established. This process achieves precise conversion from a two-dimensional grayscale image to a three-dimensional tapered structure, ensuring a one-to-one correspondence between the photoresist steps and the via slopes during etching, improving structural consistency and reproducibility. 4. In step 4, a continuous thickness gradient structure is formed on the grayscale photoresist through grayscale exposure technology, resulting in a height variation in the photoresist layer that matches the designed grayscale image. Compared to traditional binary lithography, this technology significantly expands structural freedom and enables batch processing of non-flat cross-section structures, providing a crucial support for constructing arbitrary morphological micro- and nanostructures. 5. In steps 5 through 7, the spatial information of the grayscale mask is effectively transferred to the substrate material through etching and stripping steps, forming a via structure with a continuous slope. The entire process exhibits excellent dimensional control and repeatability, making it suitable for high-integration, high-throughput micro- and nanofabrication scenarios.

[0009] Optionally, after determining the inclination angle β of the through hole, the etching conditions are determined according to the etching rate selection ratio to ensure that the mask and the etched substrate material have a large selection ratio k, and then the grayscale mask morphology required for the design is calculated based on the selection ratio k, the through hole inclination angle β and the depth H.

[0010] By adopting the above technical solution, high-precision controllable processing of non-vertical through-hole structures is achieved. By first determining the inclination angle β of the target through-hole and then combining the etching selectivity ratio k between the mask and the substrate material, the etching conditions are reasonably set to ensure that the mask has sufficient etching resistance during the etching process, thereby ensuring the complete transmission of the through-hole morphology in the depth direction. According to the geometric relationship between the inclination angle β, depth H and the selectivity ratio k, the specific thickness distribution and morphology of the grayscale mask are calculated and designed, so that the final through-hole structure has the required angle and aspect ratio, realizing accurate mapping from two-dimensional grayscale images to three-dimensional structures, breaking through the limitations of traditional binary masks in structural freedom and sidewall control, and significantly improving the consistency, accuracy and repeatability of through-hole processing. It is widely applicable to the preparation needs of complex micro-nanostructure devices such as microlenses, conical electrodes, and optical waveguides.

[0011] Optionally, the tilt angle α, height h, and tilt angle width (x2-x1) of the grayscale mask satisfy a predetermined relationship under an etching condition with a selection ratio of k and an etching time of t, and the relationship expression is: By adopting the above technical solution, precise mapping control between the grayscale mask structure and the target through-hole morphology is achieved. By introducing parameters such as the mask tilt angle α, height h and tilt width (x2–x1), and combining the functional relationship between the selectivity ratio k and the etching time t, the final through-hole profile and tilt degree can be accurately predicted and controlled, thereby improving the processing accuracy and consistency of the through-hole structure.

[0012] Optionally, in step 1, the aspect ratio of the through hole is preferably between 1:1 and 10:1, and the inclination angle ranges from 30° to 85°.

[0013] By adopting the above technical solutions, effective control of the geometric parameters of the through-hole structure is achieved, ensuring that the through-hole has an adjustable aspect ratio and inclination angle range, which can adapt to the requirements of different application scenarios for through-hole conductivity, mechanical strength and heat dissipation capacity. The aspect ratio is controlled between 1:1 and 10:1, which helps to achieve high-depth or high-density structure processing, and the inclination angle is controlled between 30° and 85°, which improves the sidewall morphology quality and process compatibility of the structure, enhances the flexibility of process design and the diversity of through-hole functions.

[0014] Optionally, the etching conditions in step 2 include adopting a reactive ion etching (RIE) process, the etching gas is selected from SF6, O2 or a mixture thereof, and the gas flow, etching power and chamber pressure are adjusted according to the material type.

[0015] By adopting the above-mentioned technical solution, selecting the reactive ion etching (RIE) process, and flexibly adjusting the flow, power, and chamber pressure of etching gases such as SF6 and O2 according to the characteristics of the substrate material, the etching anisotropy and through-hole profile control capabilities are effectively improved, ensuring that the through-hole structure has smooth sidewalls and good dimensional consistency while achieving a high aspect ratio, meeting the requirements of refinement and high reliability of micro-nanostructure processing.

[0016] Optionally, the grayscale mask is implemented using grayscale photoresist or optical modulation mask, and its grayscale distribution is generated and precisely controlled by grayscale pattern design software.

[0017] By adopting the above technical solution, using grayscale photoresist or optical modulation mask as the mask material, and combining it with grayscale pattern design software to accurately model and control its grayscale distribution, a continuously changing mask thickness distribution can be achieved, thereby realizing multi-level, gradient depth microstructure processing in the subsequent etching process, improving the molding accuracy of the through-hole structure and the manufacturability of complex geometric contours.

[0018] Optionally, the selection ratio k is preferably between 3:1 and 10:1, and the desired etching selectivity is achieved by adjusting the combination of the mask material and the etching substrate material.

[0019] By employing this technical solution, the selectivity ratio k is controlled within a range of 3:1 to 10:1. By properly matching the mask material with the etching substrate material, the mask's corrosion resistance to the etching medium is effectively improved, ensuring that the mask is not excessively corroded during the etching process, thereby achieving precise etching of the substrate material. This highly selective etching technology ensures the accurate formation of through-hole morphology, improves the dimensional accuracy and edge quality of the structure, and meets the requirements of complex micro-nano fabrication.

[0020] Optionally, during the calculation process of designing the required grayscale mask morphology, two-dimensional geometric modeling and lithography-etching co-simulation software are used for auxiliary design to optimize the grayscale steps and mask thickness distribution.

[0021] By adopting the above technical solution and using two-dimensional geometric modeling combined with lithography-etching collaborative simulation software, it is possible to simulate the impact of mask thickness changes and grayscale steps on the shape of the through-hole during the etching process, predict the process results in advance and adjust the parameters, effectively improving accuracy and reliability, optimizing the structural distribution of the grayscale mask, and ensuring that the final through-hole size and inclination angle meet the expected requirements.

[0022] Optionally, where v1 is the etch rate of the mask, v2 is the etch rate of the substrate material, and k = v2 / v1. Then the inclination angle β and the depth H of the through hole satisfy the following relationship: ​Where t is the etching time, h is the mask thickness, k is the selectivity, and β is the target through-hole tilt angle.

[0023] By adopting the above technical solution, using the selectivity ratio k of the mask etching rate v1 and the substrate etching rate v2, combined with the etching time t and the mask thickness h, a mathematical relationship between the through-hole inclination angle β and the depth H is established to achieve accurate prediction and control of the through-hole morphology. The relationship helps to design a reasonable grayscale mask structure, ensure that the through-hole shape and inclination angle during the etching process reach the expected goals, improve the controllability and repeatability of the etching process, and optimize the processing quality of micro-nanostructures.

[0024] Optionally, the tilt width (x2–x1) of the grayscale mask is preferably 2 μm to 20 μm to ensure a sufficient tilt transition area to prevent a step effect during the etching process.

[0025] By adopting the above technical solution, the tilt angle width (x2–x1) of the grayscale mask is in the range of 2μm to 20μm, which can form a smooth grayscale transition area, effectively avoiding the step effect caused by the sudden change of the mask edge during the etching process, improving the uniformity of etching and the continuity of the through-hole morphology, ensuring the precise forming of the microstructure, improving the processing quality and the stability of device performance, and enhancing the repeatability and controllability of the process.

[0026] In summary, this application includes at least one of the following beneficial technical effects: 1. Flexible control of the inclination angle and depth of the etched through-hole is achieved. Compared with existing through-hole etching methods that rely on empirical parameter adjustment, this method has a larger process window and greater flexibility. 2. Compared with existing through-hole etching methods, this method only requires a stable vertical etching rate. During the etching process, the grayscale mask structure changes continuously, and the area of ​​lateral etching also changes continuously. This can effectively avoid the accumulation of lateral etching in a certain area under the mask in existing methods, greatly reducing the impact of lateral etching on the through-hole structure, and making the process conditions simpler and more controllable. 3. Compared with existing through-hole etching methods, where the etching rate ratio of the etching gas, mask material, and substrate material is relatively fixed and difficult to change, this method is compatible with a wider range of mask materials and substrate materials. For different etching selectivities of various materials, the inclination angle α of the grayscale mask can be adjusted to adapt to the changes in the etching rate ratio between different materials. This method is suitable for flexible control of through-hole structures of various materials with different selectivity ratios. 4. By combining grayscale exposure with a precisely designed grayscale mask, high-precision, controllable manufacturing of non-vertical via structures is achieved, overcoming the limitations of traditional binary lithography in terms of sidewall angle and morphology control. 5. Optimizing etching conditions by utilizing the mask / substrate etch rate selectivity significantly improves the selectivity between the mask and substrate materials, ensuring the mask's corrosion resistance during the etching process, effectively preventing over- or under-etching, and ensuring accurate transfer of through-hole structure morphology. 6. The use of 2D geometric modeling and lithography-etching collaborative simulation software to assist in design improves the design accuracy of the grayscale mask structure, ensures the precise matching of the through-hole inclination angle, depth, and step transition area, and realizes the efficient conversion of 2D grayscale images to 3D micro-nano structures. 7. By properly controlling the tilt angle width of the grayscale mask, discontinuity or edge defects in the through-hole morphology caused by the step effect during the etching process are effectively avoided, thereby improving the overall processing quality and repeatability of the micro-nano structure; 8. The use of reactive ion etching (RIE) technology and optimized etching gas ratio enhances the anisotropy and stability of the etching process, achieving high aspect ratio processing of through holes and smooth sidewall morphology, meeting the manufacturing requirements of high-performance devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of an experimental method for making through holes using grayscale exposure according to an embodiment of the present application.

[0028] Figure 2 This is a structural schematic diagram of the etching process of an experimental method for making through holes using grayscale exposure in an embodiment of the present application.

[0029] Figure 3 This is a diagram showing the structural changes during the etching process of an experimental method for making a through hole using grayscale exposure in an embodiment of the present application; Figure 4 It is a relational expression of an experimental method for making a through hole using grayscale exposure in an embodiment of the present application. DETAILED DESCRIPTION

[0030] The following is combined with Figure 1-3 This application is described in further detail.

[0031] The present application discloses an experimental method for making a through hole using grayscale exposure, referring to Figure 1 , including the following steps: Step 1: Determine the through hole angle and aspect ratio; Step 2: Select etching conditions; Step 3: Designing a grayscale mask structure based on the etching rate selection ratio; Step 4: Grayscale exposure to obtain a grayscale mask; Step 5: Etching; Step 6: Remove residual photoresist; Step 7: Obtain the target through-hole structure.

[0032] An experimental method for making through-holes based on grayscale exposure technology disclosed in the embodiment of the present application realizes the preparation of non-vertical through-hole structures with high precision and strong controllability through systematic design and process optimization, and has significant technical advantages and application potential. The specific technical effects are as follows: 1. This method determines the inclination angle and aspect ratio of the through-hole in step one, accurately sets the geometric morphology parameters of the target through-hole, provides a clear design basis for subsequent processes, meets the functional requirements of the through-hole structure in the device, and provides flexible parameter adjustment space for the personalized manufacturing of complex micro-nano structures. In high-end applications such as microlens arrays, light guide cones, conical electrodes and three-dimensional packaging through-holes (TSV), the sidewall inclination angle and depth ratio of the through-hole can be accurately controlled, effectively improving the optical performance, electrical performance and mechanical strength of the structure; 2. Select appropriate etching conditions through step two, especially the use of reverse etching. The reactive ion etching (RIE) process, combined with the ratio of gases such as SF6 and O2 and the precise adjustment of the chamber pressure, significantly improves the anisotropy and stability of the etching process, ensures the smoothness of the through-hole sidewalls, effectively reduces etching defects and surface roughness, greatly improves the structural integrity and consistency of the through-hole, and effectively improves the selectivity between the mask material and the substrate material, ensuring that the mask layer has good corrosion resistance during the etching process, avoiding excessive mask loss or failure, and thus ensuring the precise transfer of the through-hole structure; 3. In step 3, the grayscale is designed based on the etching rate selectivity (mask / substrate) The grayscale mask structure is constructed, and a mathematical mapping relationship between the grayscale mask thickness and the through-hole depth and inclination angle is established, which breaks through the plane limitation of the traditional binary mask and uses the continuous thickness change of the grayscale mask to achieve the precise forming of the three-dimensional conical structure. This transformation from a two-dimensional grayscale pattern to a three-dimensional through-hole structure not only improves the morphological accuracy of the through-hole, but also greatly expands the degree of freedom of micro-nanostructure design, providing a feasible path for the batch preparation of complex structures; 4. The grayscale exposure technology in step four forms a continuously changing thickness gradient on the grayscale photoresist or optical modulation mask, which greatly improves the processing accuracy and repeatability of the structure. Compared with traditional binary lithography, Grayscale exposure technology enables the creation of multi-level, gradient photoresist morphologies, providing an ideal morphological foundation for subsequent etching. This enables the fabrication of non-vertical sloped vias, improving the controllability and flexibility of micro-nanostructure fabrication and making it particularly suitable for batch processing of complex three-dimensional structures. 5. Steps 5 through 7 utilize high-precision etching and stripping processes to efficiently transfer the spatial information of the grayscale mask to the substrate material, ultimately resulting in a continuous, dimensionally precise via structure. This process exhibits excellent process stability and repeatability, making it suitable for high-integration, high-throughput manufacturing requirements and ensuring the consistency and reliability of the via structure in micro-nanofabrication. 6.Reasonable design of the grayscale mask's tilt angle width (2μm to 20μm) effectively avoids step effects during etching, improves the smoothness and structural integrity of sidewall transitions, and further enhances processing quality and device performance stability. The relationship between etching time, mask thickness, and selectivity provides a scientific basis for process parameters, enabling precise control of the via's tilt angle and depth, improving the scientific nature of the design and the predictability of the process. 7. The use of 2D geometric modeling and lithography-etching collaborative simulation software to aid design enables pre-simulation of the impact of grayscale mask topography on via structure during the design phase, optimizing grayscale step and mask thickness distributions, reducing experimental debugging times, and improving R&D efficiency and process reliability.

[0033] Reference Figure 2 , the tilt angle α, height h and tilt width (x2-x1) of the grayscale mask under the etching condition of the selection ratio k and the etching time t satisfy the following relationship, the relationship expression is as follows Figure 4 As shown in: Where v1 is the etching rate of the mask, v2 is the etching rate of the substrate material, and k=v2 / v1. Then the inclination angle β and depth H of the through hole satisfy the following relationship: Changes in the mask and substrate materials during the etching process Figure 3 shown.

[0034] In summary, according to the required inclination angle β, depth H of the etched through hole and the selection ratio of the etching conditions, the inclination angle α and height h of the grayscale mask can be calculated and designed, and the mask can be accurately made through grayscale exposure technology, and finally the inclination angle of the through hole can be flexibly controlled.

[0035] Furthermore, the mask described in this method is not limited to photoresist masks formed directly by grayscale exposure; it can also be used in hardmask etching and multi-layer hardmask etching. In hardmask technology, the hardmask is simply used as the etching material in the first step. The photoresist with a defined pattern through grayscale exposure is used as the mask for etching the hardmask material. The grayscale pattern can then be transferred to the hardmask. The hardmask layer is then used as a mask for etching the substrate material or the second hardmask layer, ultimately achieving flexible control of the tilt angle of the hardmask-etched through-hole.

[0036] The through-hole structure etched by this method is not limited to the inverted trapezoid. By utilizing the relationship between the mask tilt angle and the through-hole tilt angle, this method can also achieve flexible control of through-hole structures of various shapes, including but not limited to inverted truncated cone and inverted triangular pyramid.

[0037] Example 1: Constructing a tapered through-hole structure using a silicon-based substrate as an example In this example, the goal is to fabricate a set of tapered through-hole structures with a 45° inclination angle, a depth H of 30 μm, and an aperture of 15 μm. This is suitable for optical microstructuring of light-guiding structure arrays. The design phase begins with determining a 2:1 aspect ratio and a 45° inclination angle β based on the target through-hole geometric parameters.

[0038] Reactive ion etching (RIE) was selected for etching conditions. The etching chamber configuration was as follows: the etching gas was an SF6 / O2 mixture with a flow ratio of 20:5 sccm; the operating pressure was set at 20 mTorr, the RF power was 100 W, and the substrate temperature was maintained at 20°C. Based on experimentally measured etch rates, the grayscale photoresist etch rate v1 was approximately 0.25 μm / min, and the silicon substrate etch rate v2 was approximately 2.5 μm / min, resulting in a selectivity ratio k = v2 / v1 = 10.

[0039] The grayscale mask structure is designed based on the selectivity k=10, the target via depth H=30 μm, and the tilt angle β=45°, according to the following geometric relationship: H = k × h tanβ = (x2 - x1) / H Where h is the grayscale photoresist step height, and x2-x1 is the width of the grayscale change area.

[0040] From H = 30 μm and k = 10, we can get h = 3 μm. From tan45° = 1, we can get x2-x1 = H = 30 μm.

[0041] Finally, a linear grayscale change area is designed, whose thickness changes from 0 to 3 μm, corresponding to a width of 30 μm.

[0042] Grayscale mask production involves generating a continuous grayscale distribution pattern using grayscale mask design software (such as Grayscale LithoGen). This pattern is then imported into the photolithography system for exposure. SU-8-based grayscale photoresist is used as the mask material, with a spin-coated thickness of 4 μm. During exposure, the light intensity distribution is adjusted to match the grayscale pattern, maintaining an exposure energy between 80 mJ / cm² and 180 mJ / cm².

[0043] The photoresist was developed using a SU-8 developer for 90 seconds, with ultrasound assistance to enhance the clarity of grayscale step boundaries. After development, the grayscale mask was dried and hardened by baking.

[0044] During the etching process, a silicon wafer with a grayscale photoresist mask is placed in the RIE chamber and etched according to the conditions in step 2. The etching time is calculated to be 12 minutes, based on a silicon etch rate of 2.5 μm / min and a target depth of 30 μm. Etching progress is monitored to ensure the morphology remains consistent with expectations.

[0045] After stripping and post-etching, oxygen plasma was used to remove residual photoresist, followed by a wet clean (Piranha solution) to remove surface residues and passivate the structure. Scanning electron microscopy (SEM) observations revealed that the resulting via structure had continuous, smooth, tapered sidewalls with an inclination deviation within ±2° and excellent dimensional repeatability.

[0046] Example 2: Designing tapered through-hole structures with different inclination angles to verify universality To verify the universality of this method, through-holes with tilt angles β of 30°, 60°, 75°, and 85° were selected for experimental preparation. Based on the same silicon substrate, etching conditions, and photoresist, the grayscale mask structure design was changed: For β = 30°, tanβ ≈ 0.577, and if H = 30 μm, then x2-x1 ≈ 17.3 μm, corresponding to h = 3 μm For β = 60°, tanβ ≈ 1.732, x2-x1 ≈ 52 μm For β = 75°, tanβ ≈ 3.73, x2-x1 ≈ 112 μm For β = 85°, tanβ ≈ 11.43, x2-x1 ≈ 343 μm The grayscale mask's grayscale variation region was correspondingly widened, and the exposure energy gradient was proportionally adjusted to maintain step continuity and sidewall smoothness. Results showed that the resulting via angle error was controlled within ±3°, and the aspect ratio was kept between 1:1 and 10:1.

[0047] Example 3: Using collaborative simulation software to assist in designing grayscale masks To improve the efficiency and accuracy of grayscale mask design, lithography-etch co-simulation software (such as GENISYS BEAMER or S-LITHO) is introduced for parameter optimization. After inputting the grayscale pattern, exposure dose curve, photoresist response model, and etch selectivity, the software automatically outputs the required grayscale mask thickness distribution model. This model is used to derive the grayscale pattern and import it into the exposure system, ensuring that the grayscale mask thickness closely matches the target via slope. Simulations can predict the mask profile and the post-etch via structure morphology, significantly improving via consistency and manufacturing yield.

[0048] Example 4: Comparison with the traditional binary mask process to verify the superiority of the effect To verify the technical advantages of the grayscale mask method, traditional binary lithography and grayscale lithography were used to process the same target through-hole structure. The experimental comparison results are as follows: The traditional binary mask lacks continuous thickness control, resulting in a step effect on the edge of the through hole and an unclear tapered profile. The structure made by grayscale mask has a continuous and smooth sidewall curve, and the tilt angle control accuracy is higher; Binary lithography has poor repeatability and large topography errors between through holes; The grayscale mask method produces a highly consistent through-hole structure, and the processing yield is increased to over 95%.

[0049] The key technical points of this technical solution, an experimental method for making through-holes using grayscale exposure, are as follows: grayscale exposure technology is used to prepare a grayscale mask obtained through design and calculation, and different grayscale masks can be used to achieve flexible control of the inclination angle of the etched through-hole.

[0050] The technical protection point of this technical solution is an experimental method for making through holes using grayscale exposure: the photoresist grayscale mask required for etching is defined by grayscale exposure technology, including various grayscale hard mask etching technologies made using the photoresist grayscale mask defined by grayscale exposure.

[0051] This technical solution is an alternative to the experimental method of making through holes using grayscale exposure: 1. Reactive ion etching (RIE): This combines plasma ion bombardment with free radical reactions to achieve highly anisotropic etching. However, the etching aspect ratio is difficult to adjust, and the through-hole tilt angle cannot be flexibly controlled. 2. Laser-induced wet etching (LIWE): Combining femtosecond laser modification with hydrofluoric acid (HF) wet etching, it can achieve through-holes with a 100:1 aspect ratio and support sidewall angle control, but the process is complex and the equipment cost is high.

[0052] The implementation principle of an experimental method for forming a through hole using grayscale exposure in an embodiment of the present application is as follows: This application's "Experimental Method for Fabricating Via Holes Using Grayscale Exposure" is primarily based on the photoresist's response to grayscale light intensity and the selectivity (k) generated by the difference in etching rates between the mask and substrate materials. By precisely designing the spatial thickness distribution of the mask, the morphology of non-vertical via structures (such as inverted frustums, cones, and triangular prisms) can be controlled during the etching process. Its core principles include two aspects: grayscale exposure to form a continuous-thickness mask and mask-substrate collaborative etching to achieve three-dimensional structure construction; On the one hand, grayscale exposure technology utilizes the dose-thickness response relationship of photoresist and combines it with grayscale pattern design software to convert a two-dimensional grayscale image into a continuous thickness gradient structure on the photoresist surface. Unlike traditional binary exposure, grayscale exposure not only adjusts the dissolution depth of the photoresist by exposure intensity, but also achieves linear or nonlinear spatial height control. The grayscale pattern is loaded into the photolithography equipment through an optical modulation mask or digital micromirror device (DMD). Based on the precise control of the exposure energy distribution, the photoresist forms a microstructure layer with continuous thickness variation and smooth steps after development, namely the grayscale mask. On the other hand, the core of the etching stage lies in the decisive role of "mask thickness distribution" on the final through-hole morphology. Due to the difference in etching rates between the photoresist and the substrate material in plasma etching, when using reactive gases such as SF6 / O2 for plasma reactive ion etching (RIE), the mask layer and the substrate are etched simultaneously. However, due to the selectivity ratio k = v2 / v1 (v1 is the mask etching rate, v2 is the substrate etching rate), the mask is etched and consumed while the substrate is etched proportionally, thereby "projecting" or "extending" the mask thickness profile to the substrate to form a through-hole. Specifically, assuming the mask tilt angle is α, the height is h, and the corresponding mask projection width is (x2–x1), if the etching time is t, and the etching rates are v1 (mask) and v2 (substrate), then under the condition of k = v2 / v1, the final slope β and depth H of the through hole satisfy the following geometric relationship: H = k × h = v2 × t tanβ = (x2–x1) / H, that is, x2–x1 = H × tanβ The above formula can be used to infer the required mask thickness h and tilt angle α to meet the preparation requirements of the target through-hole tilt angle β and depth H. This mapping relationship essentially constructs a controllable three-dimensional structure construction method driven by mask design, which is the core control logic of this technical method. Figure 2 It reflects the functional relationship between the geometric parameters of the grayscale mask step (h, α, x2–x1) and the through-hole target morphology (H, β). Figure 3 The physical process of simultaneous consumption of mask and substrate materials and gradual formation of the structural sidewalls during the actual etching process is demonstrated. From grayscale exposure and development to plasma etching, each stage forms a continuous and coordinated through-hole structure transformation path with high predictability and process consistency. This method uses SU-8 and other high-thickness adjustable photoresists or other grayscale response materials as masks, introduces two-dimensional modeling and co-simulation in the pattern design stage, simulates the etching response in advance in the design stage, and further improves the mask accuracy and reliability of structure transfer. Furthermore, by controlling the tilt angle width of the grayscale mask within the range of 2μm to 20μm, the sidewall transition can be effectively smoothed, avoiding step effects and burrs during the etching process. Controlling the selectivity ratio k between 3:1 and 10:1 balances mask conformality and etching efficiency, making it suitable for structural designs with various aspect ratio requirements (1:1 to 10:1). By precisely adjusting the photolithography mask thickness and selectivity ratio, the construction of high-precision tapered structures or more complex structures can be achieved. Grayscale masks are not limited to soft masks made of photoresist. Grayscale pattern transfer technology can also be used in hard mask systems to form continuous step structures by etching in steps, thereby improving the through-hole structure's tolerance to harsh environments such as temperature and chemical corrosion, and expanding the scope of application of this method in TSV packaging, optoelectronic integration and other fields.

[0053] The above are all preferred embodiments of the present application, and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. An experimental method for making through-holes using grayscale exposure, characterized by: The following steps are involved: Step 1: Determine the through hole angle and aspect ratio; Step 2: Select etching conditions; Step 3: Designing a grayscale mask structure based on the etching rate selection ratio; Step 4: Grayscale exposure to obtain a grayscale mask; Step 5: Etching; Step 6: Remove residual photoresist; Step 7: Obtain the target through-hole structure.

2. The experimental method for forming a through hole using grayscale exposure according to claim 1, characterized in that: After determining the through-hole inclination angle β, the etching conditions are determined according to the etching rate selectivity to ensure a large selectivity k between the mask and the etched substrate material. Subsequently, the grayscale mask morphology required for the design is calculated based on the selectivity k, the through-hole inclination angle β, and the depth H.

3. The experimental method for forming a through hole using grayscale exposure according to claim 1, characterized in that: The tilt angle α, height h and tilt angle width (x2-x1) of the grayscale mask satisfy a predetermined relationship and have a predetermined relationship expression under the etching condition of a selection ratio of k and an etching time of t.

4. The method according to claim 1, wherein: In the step 1, the aspect ratio of the through hole is preferably between 1:1 and 10:1, and the inclination angle ranges from 30° to 85°.

5. The method according to claim 1, wherein: The etching conditions in step 2 include adopting a reactive ion etching (RIE) process, the etching gas is selected from SF6, O2 or a mixture thereof, and the gas flow rate, etching power and chamber pressure are adjusted according to the material type.

6. The method according to claim 1, wherein: The grayscale mask is realized by grayscale photoresist or optical modulation mask, and its grayscale distribution is generated and precisely controlled by grayscale pattern design software.

7. The method according to claim 2, wherein: The selectivity ratio k is preferably between 3:1 and 10:1, and the desired etching selectivity is achieved by adjusting the combination of the mask material and the etching substrate material.

8. The method according to claim 2, wherein: In the calculation process of designing the required grayscale mask morphology, two-dimensional geometric modeling and lithography-etching collaborative simulation software are used for auxiliary design to optimize the grayscale steps and mask thickness distribution.

9. The method according to claim 3, wherein: Where v1 is the etching rate of the mask, v2 is the etching rate of the substrate material, and k=v2 / v1. Then the inclination angle β and the depth H of the through hole satisfy the following relationship:    Where t is the etching time, h is the mask thickness, k is the selectivity, and β is the target through-hole tilt angle.

10. The method according to claim 3, wherein: The tilt width (x2–x1) of the grayscale mask is preferably 2 μm to 20 μm to ensure a sufficient tilt transition area to prevent a step effect during the etching process.

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