Multi-piece thinning method for small-size and special-shaped pieces

Abstract

The invention discloses a multi-piece thinning method for small-size and special-shaped pieces, which comprises the following steps: preparing a circular mold by using an FR-4 material, the diameter of the mold is 8-10mm larger than the diameter of the actual adsorption surface of a sucker of a thinning machine, and the thickness of the mold is 50-100mu m lower than the target thickness after thinning; uniformly arranging through holes of which the diameter is 0.1-0.15 mm larger than that of the wafer to be thinned on the die; manufacturing an accompanying sheet by using an FR-4 material; then the mold is placed on a suction cup of a thinning machine, the center of the mold is aligned with the center of the suction cup, wafers to be thinned are sequentially placed in the through holes of the mold, the thinning faces are upward, when the number of the wafers to be thinned is smaller than the number of the through holes in the mold, the through holes in the mold are filled with accompanying pieces, vacuum adsorption is started, and the mold and the wafers are sucked on the suction cup at the same time; and thinning is started. According to the invention, a solution with technical advancement and engineering practicability is provided for large-scale thinning of small-size and special-shaped semiconductor substrates.

Description

Technical Field

[0001] This invention relates to a method for thinning multiple wafers of small size and irregular shape, belonging to the field of thinning technology for small size and irregular shape wafers. Background Technology

[0002] In semiconductor manufacturing, after wafers undergo preliminary processes such as dicing and grinding, a damage layer inevitably forms on their surface. If this damage layer is not removed, achieving a satisfactory surface quality in subsequent polishing stages becomes significantly more difficult. Thinning processes, with their ability to precisely remove material of specific thicknesses, can effectively remove portions containing the damage layer from the wafer surface, thus initially improving surface smoothness. This allows for more precise removal of minute imperfections and surface damage during polishing, ultimately resulting in a smoother, more even surface. This is because significant initial thickness variations or high surface roughness in wafers greatly increase the difficulty and time required for polishing, potentially negatively impacting the final surface quality. Pre-polishing thinning effectively avoids these problems, allowing subsequent polishing processes to focus on creating an ultra-smooth, damage-free surface, laying a solid foundation for the entire polishing process. This is the fundamental reason why thinning processes are increasingly favored by many semiconductor manufacturers.

[0003] Currently, single-wafer thinning machines are typically designed for wafers or components within a specific size range, and are only suitable for processing tasks within that size range. Once products exceeding this size range are involved, the equipment must be replaced or modified, which undoubtedly leads to increased costs and operational complexity. For example, most thinning machines on the market are optimized for semiconductor wafers with standard diameters of 100mm, 150mm, or 200mm. Their mechanical structure, grinding wheel dimensions, and especially key components such as suction cup specifications are all adapted and adjusted based on these common dimensions.

[0004] With the continuous development of semiconductor technology, the demand for small-sized and irregularly shaped substrates is increasing in many niche applications, and products with high production volumes have stringent requirements for thinning processes. However, traditional thinning methods are not well-suited for such substrates and cannot guarantee efficient and precise processing.

[0005] When processing wafers that are too small, forcibly using conventional equipment for direct adsorption and thinning operations may result in the chuck failing to secure the wafer effectively. Even if a secure hold is achieved, the wafer thinning process is subject to the combined effects of grinding force, adsorption force, and inertial force. This can lead to issues such as component displacement and breakage, as well as damage to the chuck and thinning blade.

[0006] Furthermore, given that current thinning machines are designed for specific wafer sizes, the wafer sizes they can thin are relatively fixed, typically only handling 4-inch, 6-inch, and 8-inch wafers. However, in actual thinning operations, it is common to encounter situations where wafers smaller than these sizes need to be thinned. For such cases, the current processing technology is as follows: First, the wafer to be thinned is placed face down, evenly within a template of the same size as the suction cup, with the wafer 5 mm from the outer edge of the template, arranged in a ring; then, random stainless steel retaining rings are placed on the outside of the template, ensuring the inner ring of the retaining ring overlaps with the outer ring of the template; next, a film laminating machine or manual film application is used to bond the wafer and retaining ring together using UV film. During this process, it is crucial to ensure that there are no air bubbles or particles between the film and the wafer; if such air bubbles or particles appear, the film must be removed and reapplied; after the film application is successful, excess film on the outer ring of the retaining ring is removed; select 8 In the thinning program, set the incoming wafer thickness and the final thickness, then lock the retaining ring into the clamping position of the equipment, and turn on the vacuum function of the suction cup. At this time, the entire film will be adsorbed onto the suction cup, and the wafer on the film will also be fixed onto the suction cup by the film. Then tighten the screws of the retaining ring fixing device to make the retaining ring press tightly around the suction cup. Then carry out the thinning operation according to the thinning program. After the thinning is completed, open the retaining ring fixing screws, remove the vacuum, remove the retaining ring, blow dry the water on the film and wafer, and use a UV lamp to irradiate for one minute to release the adhesion of the UV film. Finally, remove the wafer according to the loading order, put it into the clamping plug, and then you can carry out the thinning operation of the next set.

[0007] However, this processing method has many drawbacks, as follows:

[0008] Firstly, the cost is high. Currently, the market price of UV film is 2100 yuan per 100 meters. Each application requires approximately 0.45 meters of UV film. Taking a 3-inch wafer as an example, a maximum of 3 wafers can be placed per board. Therefore, the cost of UV film per 3-inch wafer is as high as 3.2 yuan. For 2-inch wafers, a maximum of 7 wafers can be placed per board, resulting in a cost of approximately 1.4 yuan per 2-inch wafer. Considering all factors, the overall cost is quite staggering.

[0009] Secondly, it requires a large amount of manual labor, and the operation process is complex and inefficient. The entire process involves multiple steps such as applying the film, securing the retaining ring, drying, and peeling off the film, which requires a high level of professional training for operators, greatly increasing labor and time costs.

[0010] Third, there is a risk of equipment damage. If the retaining ring fails to lock properly and protrudes from the suction cup, it could directly damage the thinning blade or the suction cup, leading to significant losses.

[0011] Fourth, the thickness control precision is insufficient. Because a film-coated thinning process is used, the film is involved in the thinning process. If the film bonding effect is poor, unevenness may occur on the wafer. Furthermore, when setting the thinning thickness, the film thickness needs to be taken into account and thickness compensation needs to be performed. Therefore, the final thinning thickness is actually an estimate, and its thickness error is usually controlled within 5 micrometers, making it difficult to achieve high precision requirements.

[0012] Fifth, there are potential safety hazards for personnel. When applying the film manually, it is necessary to shave off the excess film outside the retaining ring. During this process, operators are at risk of being cut by the blade.

[0013] Sixth, equipment selection is limited. This process requires the addition of a retaining ring positioning device to the equipment, which restricts equipment selection and makes it difficult to flexibly choose suitable equipment according to actual production needs. Summary of the Invention

[0014] This invention provides a multi-wafer thinning method for small-sized and irregularly shaped wafers, which systematically solves the multiple contradictions in traditional processes regarding cost, efficiency, precision, stability, safety, and equipment compatibility, and provides a solution that combines technological advancement and engineering practicality for the large-scale thinning of small-sized and irregularly shaped semiconductor substrates.

[0015] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0016] A method for thinning multiple sheets of small-sized and irregularly shaped sheets includes the following steps:

[0017] (1) A circular mold is prepared using FR-4 material (glass fiber reinforced epoxy resin composite material). The diameter of the mold is 8-10 mm larger than the actual adsorption surface diameter of the thinning machine suction cup to form an edge safety margin. The thickness of the mold is 50-100 μm lower than the target thickness after thinning. Through holes with a diameter 0.1-0.15 mm larger than the diameter of the wafer to be thinned are uniformly set on the mold.

[0018] (2) Use FR-4 material to make a die-off. The die-off is the same thickness as the mold. The diameter of the die-off is 0.1 to 0.15 mm smaller than the diameter of the through hole (used to fill the empty hole when the wafer is insufficient to fill the mold, to ensure sufficient vacuum adsorption force and avoid wafer displacement caused by uneven local force).

[0019] (3) Clean the thinning machine suction cup (rinse with backwash water, turn off the backwash water after cleaning), then place the mold on the thinning machine suction cup and align the center of the mold with the center of the suction cup. Place the wafers to be thinned into the through holes of the mold in sequence, with the thinning side facing up. When the number of wafers to be thinned is less than the number of through holes on the mold, use a spare wafer to fill the through holes on the mold. Check that all wafers are in the holes, and then turn on the vacuum suction. At this time, the vacuum pump generates a continuous vacuum suction force, so that the mold and wafers (including the wafers to be thinned and the spare wafers) are simultaneously suctioned onto the suction cup.

[0020] (4) Click the start button of the thinning machine to start the thinning process. During the thinning process, the grinding wheel and the suction cup rotate in opposite directions. The grinding wheel speed is 2500-3000 rpm and the suction cup speed is 200-300 rpm. The feed rate is divided into three steps: the first step is 0.8-1μm / s, and the amount of material removed is set according to the thickness of the wafer; the second step is 0.6-0.8μm / s, and the amount of material removed is 6-8μm; the third step is 0.4-0.6μm / s, and the amount of material removed is 4-6μm. After the thinning is completed, remove the vacuum and turn on the backwash water to separate the wafer to be thinned and the accompanying wafer from the suction cup. After taking out the wafer to be thinned and measuring the thickness, put it into the chuck and remove the mold to rinse it clean.

[0021] (5) Repeat steps (1), (3), and (4) until all wafers to be thinned are thinned.

[0022] In step (1) above, the thinning process is significantly simplified through the ingenious design of the mold. The shape of the cross-section of the through hole on the mold is the same as the shape of the cross-section of the wafer to be thinned. When the wafer to be thinned is placed in the corresponding through hole and the two axes coincide, the distance between the wafer to be thinned and the periphery of the through hole is 0.05 to 0.075 mm, more preferably 0.05 mm.

[0023] In step (1), FR-4 epoxy resin glass fiber board is used, which has excellent dimensional stability and insulation properties, avoiding electrostatic adsorption or material compatibility problems during the thinning process of semiconductor substrate.

[0024] In step (4), the feed rate is divided into three steps. The total thickness to be reduced minus the amount of material removed in the second and third steps is the amount of material removed in the first step.

[0025] The above method eliminates the need for UV film, thus avoiding the high costs associated with film application. It removes the complex processes of applying and removing film, optimizing the thinning process and increasing product profits. Simultaneously, it significantly reduces labor costs, simplifies operation, and improves overall work efficiency. The absence of blades during thinning eliminates the possibility of personnel injury. It allows for film-free wafer adhesion to the suction cup, ensuring no wafer displacement during the thinning process. The suction cups of the thinning machine virtually do not suck up particles generated during thinning (the gap between the wafer and the mold is very small), effectively reducing the risk of micropore blockage in the suction cups. It expands the range of equipment options, requiring only the selection of suction cups with appropriate diameters based on product size, eliminating the need for stainless steel retaining rings and related structures, thereby reducing equipment procurement costs. It completely resolves the instability and thickness error issues caused by film application during the thinning process, minimizing human interference and ensuring the stability of the thinning effect.

[0026] Wafer thinning is a critical process that directly impacts device performance, reliability, and miniaturization. However, current common wafer thinning methods and liquid formulations have many shortcomings in terms of stress relief, mechanical property optimization, and surface quality improvement, making it difficult to meet increasingly stringent industry demands.

[0027] To further improve wafer quality, in step (4), the thinning solution used during thinning includes: 17-19% succinic acid, 11-13% glutaric acid, 9-11% 1,1′-ferrocene di-bis(diphenylphosphine) (DPPF), 1-3% polyamide-amine dendritic polymer (PAMAM), 9-11% ammonium acetate, 4-6% triethanolamine, and the balance being solvent. The percentages are by mass.

[0028] The solvent mentioned above is ultrapure water, and the solvent contains 3%-5% glycerol, where % is a mass percentage.

[0029] Unless otherwise specified, all percentages of substance content in this application refer to mass percentages.

[0030] The aforementioned polyamide-amine dendritic polymer (PAMAM) is branded by Chenyuan and model number G0.

[0031] The use of the aforementioned thinning solution can effectively release stress, improve mechanical properties and surface quality. The inventors believe that the succinic acid (C4H6O4) and glutaric acid (C5H8O4) molecules can precisely bind with the atoms on the wafer surface, initiating a mild and uniform etching reaction. The smaller molecular structure of succinic acid allows it to quickly penetrate to the microscopic defects on the wafer surface, reacting first and initially opening the etching channels. Glutaric acid, with its slightly longer carbon chain structure, plays a stabilizing role in the reaction intermediate, allowing the etching reaction to proceed continuously and smoothly. Compared with traditional strong acid etchants, this combination of dicarboxylic acids significantly reduces the damage to the internal lattice structure of the wafer and effectively reduces stress concentration caused by uneven etching. The ferrocene unit in 1,1′-ferrocene di-bis(diphenylphosphine), (DPPF) has a unique sandwich structure that can form a flexible electron cloud buffer layer on the wafer surface. When the wafer is stressed due to the thinning process, the metal center in this complex can absorb and redistribute stress energy through the dynamic adjustment of coordination bonds, so that the stress is evenly distributed inside the wafer, avoiding wafer breakage caused by stress concentration. At the same time, the chemical bonding between the organophosphine part and the wafer surface can further stabilize the surface atomic structure and enhance the overall mechanical properties of the wafer. The polyamide-amine dendritic polymer (PAMAM) possesses a highly branched three-dimensional structure, which effectively encapsulates and carries other functional molecules, promoting their uniform distribution on the wafer surface. The long-chain fluoroalkyl groups on its outer layer impart extremely low surface energy, enabling the formation of an ultrathin, highly ordered molecular film between the liquid and the wafer surface. During etching, this molecular film reduces the adhesion of the liquid to the wafer surface, allowing reaction products to quickly detach and preventing redeposition that could cause surface defects. Furthermore, it allows for microscopic control of the etching process, filling tiny surface depressions and inhibiting further protrusion growth, thereby significantly reducing wafer surface roughness and improving surface finish. During wafer thinning, the etching reaction causes fluctuations in the pH of the liquid, which in turn affects the stability of the etching rate and the overall effect. The buffer system composed of ammonium acetate and triethanolamine can effectively resist pH changes within a certain range. When the acidity of the reaction system increases, the nitrogen atom in triethanolamine can accept protons, causing the pH value to rise. When the alkalinity of the system increases, the acetate ions in ammonium acetate can combine with hydrogen ions to maintain the relative stability of the pH value. The stable pH environment ensures that the core etchant and other components are always in the best active state, ensuring the uniformity and controllability of the etching process, which is beneficial to improving the quality consistency of wafer thinning and reducing the additional stress caused by pH fluctuations.Ultrapure water provides a pure and stable dispersion medium for all components, enabling them to mix thoroughly and disperse uniformly, thus effectively exerting a synergistic effect. The addition of glycerol significantly improves the liquid's solubility for other solutes, ensuring good dispersion of various functional components in the solution. Furthermore, the multiple hydroxyl groups in glycerol molecules can form hydrogen bond networks with water and other solute molecules, enhancing the liquid's stability and fluidity. During etching, this mixed solvent system helps remove the heat generated by the reaction, preventing localized overheating and thermal damage to the wafer. Simultaneously, during the cleaning stage, it can quickly and thoroughly remove reaction products and residual liquid from the wafer surface, ensuring wafer cleanliness and smooth subsequent processing. In addition, the synergistic effect among the components promotes improvements in wafer mechanical properties and surface quality.

[0032] Further preferred, in step (4), during thinning, a thinning liquid is used at the first and second feed rates, and ultrapure water is used at the third feed rate.

[0033] In step (1) above, the thickness of the mold is not less than 60% of the thickness of the wafer to be thinned.

[0034] In step (1) above, the outer edge of the mold is rounded.

[0035] In step (1) above, a serial number mark is engraved on the outside of each through hole so that the wafers can be loaded and unloaded in the order of the mark. The serial number mark can be engraved next to the outside of each through hole. The serial number mark can be a number or a letter in sequence. In step (3), the wafers to be thinned are placed into the through holes of the mold in the order of the serial number marks. In step (4), the wafers to be thinned and the accompanying wafers are separated from the suction cup. After the wafers are taken out in the order of loading and the thickness is measured and qualified, they are placed into the chuck.

[0036] The serial numbers in this application are laser-etched (font height 8mm, line width 4mm) and arranged in a clockwise order.

[0037] In step (2) above, if the number of through holes on the mold is n, then the number of auxiliary pieces is at least n-1 pieces.

[0038] This invention achieves precise control over the entire process of semiconductor substrate loading, adsorption, thinning, and unloading. Compared with traditional UV film processes, it achieves breakthrough improvements in cost, efficiency, precision, and safety, and is especially suitable for the mass production of small-sized and irregularly shaped substrates of 2 to 6 inches.

[0039] Generally, the size of the wafer to be processed should be less than 75% of the size of the suction cup.

[0040] In this invention, "small-sized" wafers refer to wafers with a diameter of less than 4 inches; "irregularly shaped" wafers refer to wafers with irregular shapes.

[0041] Any techniques not mentioned in this invention are based on existing technologies.

[0042] This application achieves thinning without using a UV film, utilizing a dedicated mold to achieve direct vacuum adsorption thinning, fundamentally solving multiple technical bottlenecks in the processing of small-sized and irregularly shaped substrates. The specific benefits are as follows:

[0043] 1. A revolutionary cost reduction through a fully membrane-free design: This invention utilizes a custom mold made of FR-4 material (density 1.8g / cm³). 3 This invention constructs a vacuum adsorption interface (with a hardness of HRB 100), replacing the UV film consumption of 2100 yuan / 100m. Taking a 3-inch wafer as an example, the cost of a single-chip UV film in the traditional process is 3.2 yuan, and the material expenditure exceeds 320,000 yuan when the annual output is 100,000 wafers. However, this invention only requires a one-time investment in mold preparation costs (single mold ≤ 50 yuan, lifespan ≥ 5000 cycles), achieving near-zero material costs in the thinning process. It is especially suitable for large-scale production scenarios with an annual output of millions of wafers, significantly improving product profit margins.

[0044] 2. Streamlined and efficient process, overcoming the bottleneck of manual operation: Traditional processes rely on complex steps such as "film application - edge trimming - retaining ring fixation - drying - film removal," with a single batch operation taking ≥19 minutes and requiring professional training (training period ≥20 hours) to control the film application bubble rate (target <0.5%). This invention directly couples the mold positioning hole (hole diameter accuracy ±0.05mm) with the suction cup vacuum system (adsorption pressure 60-80KPa), simplifying the operation process to four core steps: "film loading - adsorption - thinning - film removal," reducing the processing time per batch to less than 5 minutes. It also eliminates skill barriers such as film alignment and edge trimming, allowing ordinary operators to become proficient after 2 hours of training, significantly reducing labor and time costs.

[0045] 3. Intrinsically safe design, eliminating operational risks: Addressing the 1% risk of cutting injuries caused by blades during traditional processes, this invention fundamentally eliminates the need for blades by using a rounded mold edge design (R angle ≥ 1mm) and a film-free process. Wafer fixation relies on mold positioning holes and vacuum suction, avoiding the risk of physical contact caused by manual intervention. This meets the requirements of the ISO45001 Occupational Health and Safety Management System, achieving intrinsic safety in the thinning process.

[0046] 4. Precision positioning and adsorption ensure processing stability: The dedicated mold adopts a design where "positioning hole diameter = wafer diameter + 0.1mm", combined with the micron-level roughness of the suction cup surface (Ra≤0.2μm), to construct a dual fixing mechanism of "mechanical limiting + vacuum adsorption" (adsorption offset ≤5μm). Finite element analysis (FEA) verifies that under grinding force (radial 5-10N, axial 3-5N), the wafer displacement is reduced by 75% compared to traditional UV film processes (displacement ≥20μm), completely solving problems such as edge cracking and uneven thickness caused by poor film adhesion. This achieves a wafer thickness error of ≤±1μm after thinning, meeting the stringent requirements of 5G chips and power devices for TTV (total thickness variation) ≤3μm.

[0047] 5. Anti-fouling structural design enhances equipment reliability: This design mitigates the effects of traditional UV film edge cutting, which produces film debris (5-50μm in diameter) and Al2O3 particles (concentration 10) generated during grinding. 4 The presence of particles per mL (50-100 μm in diameter) easily clogs the micropores of the suction cup, leading to a decrease in adsorption efficiency (requiring 2-3 shutdowns per month for cleaning, with each shutdown lasting 4 hours). This invention employs an edge-closed mold structure (the mold diameter is 8-10 mm larger than the actual adsorption surface diameter of the thinning machine's suction cup; during vacuum adsorption, the excess mold presses against the solid ring at the edge of the suction cup, providing a sealing effect). The positioning hole depth is 50-150 μm lower than the wafer thickness, forming an isolated "adsorption chamber-processing area" design. This allows over 95% of grinding particles to be discharged with the cooling water, reducing suction cup clogging frequency by 80% and increasing equipment uptime from 75% to 92%, significantly reducing maintenance costs and downtime losses.

[0048] 6. Enhanced equipment compatibility and reduced hardware dependence: Breaking away from the traditional process's reliance on stainless steel retaining rings (inner diameter accuracy ±0.1mm) and customized positioning devices (modification cost ≥20,000 RMB / unit), this invention only requires selecting a universal chuck with a corresponding diameter based on the wafer size (e.g., an 8-inch chuck adapts to 2-8 inch wafers). Through standardized mold shape design (diameter = chuck adsorption area + 10mm), the same equipment can be used to process substrates from 2 inches (50.8mm) to 8 inches (200mm). No additional hardware modifications are required for equipment selection, increasing the capacity utilization rate of a single unit by 30% and reducing the procurement cost of additional functional hardware by 100%, significantly enhancing production line flexibility and return on investment.

[0049] 7. Dual Improvement in Precision and Stability: By eliminating the UV film thickness compensation step (traditional processes require compensation of 50±5μm), this invention directly uses the mold thickness (precision ±10μm) as the benchmark, combined with the closed-loop control of the grinding wheel feed system (resolution 0.1μm), achieving a thickness deviation of ≤±2μm from the target value after thinning, a 60% improvement in precision compared to traditional processes. Simultaneously, it eliminates the influence of human variables such as film-attached bubbles (occurrence rate 5-10%) and film stress (1-3MPa), improving the consistency of wafer surface flatness (Ra≤0.2μm) and thickness uniformity (TTV≤1μm) by 90% after thinning, providing an ideal ultra-precision machining benchmark for subsequent polishing processes.

[0050] 8. Improved wafer performance: The thinning liquid design effectively releases thinning stress, improving mechanical properties and surface quality. Attached Figure Description

[0051] Figure 1 A schematic diagram of a mold for a 2-inch wafer;

[0052] Figure 2 A schematic diagram of a mold for a 3-inch wafer;

[0053] Figure 3 A schematic diagram of a mold for a 5.5×5.5mm square sheet; Detailed Implementation

[0054] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0055] The directional terms used in this application, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," refer to the orientation or positional relationship in the usage state. They are used only for the convenience of describing this application and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0056] Example 1

[0057] A method for thinning multiple sheets of small-sized and irregularly shaped sheets includes the following steps:

[0058] (1) A circular mold is prepared using FR-4 material. The diameter of the mold is 10 mm larger than the actual adsorption surface diameter of the suction cup of the thinning machine to form an edge safety margin. The outer edge of the mold is rounded. The thickness of the mold is 50 μm lower than the target thickness after thinning. Through holes with a diameter 0.1 mm larger than the diameter of the wafer to be thinned are uniformly set on the mold. Arabic numerals (font height 8 mm, line width 4 mm) are laser-etched on the outside of each through hole as serial numbers, arranged in a clockwise direction.

[0059] (2) Use FR-4 material to make a die-off. The die-off is the same thickness as the mold. The diameter of the die-off is 0.1 mm smaller than the diameter of the through hole (to fill the empty hole when the wafer is not enough to fill the mold, to ensure that sufficient vacuum adsorption force is generated and to avoid wafer displacement caused by uneven local force).

[0060] (3) Using a Disco 810 device and an 8-inch suction cup, clean the thinning machine suction cup (rinse with backwash water, turn off the backwash water after cleaning), then place the mold on the thinning machine suction cup and align the center of the mold with the center of the suction cup (deviation ≤ 3mm). Place the wafers to be thinned into the through holes of the mold in the order marked with the serial number, with the thinning surface facing up. When the number of wafers to be thinned is less than the number of through holes on the mold, use a spare wafer to fill the through holes on the mold. Check that all wafers are in the holes and that the edges are not raised. Then turn on the vacuum suction. At this time, the vacuum pump generates a continuous vacuum suction force (80kPa), so that the mold and wafers (including the wafers to be thinned and the spare wafers) are simultaneously suctioned onto the suction cup.

[0061] (4) Input the initial wafer thickness (resolution ±1μm), safe cut thickness of 30μm, and target thickness into the equipment control system (accuracy 0.1μm). Select the corresponding 8-inch thinning program. The grinding wheel and suction cup rotate in opposite directions. Set the grinding wheel speed to 2500-3000rpm and the suction cup speed to 200-300rpm. The feed rate is divided into three steps: the first step is 0.8-1μm / s, and the amount of material removed is set according to the wafer thickness; the second step is 0.6-0.8μm / s, with a material removal of 6-8μm; the third step is 0.4-0.6μm / s, with a material removal of 4-6μm. The equipment measures the height of the mold surface using a laser rangefinder (accuracy ±1μm) and automatically compensates for the initial position of the grinding wheel to ensure that the thinning depth is controlled within the target value ±1μm range. Click the start button of the thinning machine. After the thinning is completed, remove the vacuum and turn on the backflushing water. The process utilizes the impact force of water flow to separate the mold from the suction cup, while preventing damage to the wafer due to residual adhesion. After the vacuum is broken, the backflushing water is turned off. Once the thinned wafer and its companion wafer have detached from the suction cup, the backflushing water is turned off again. The wafer and its companion wafer are then removed in the order of wafer loading. The wafer is placed in a PFA stopper and soaked in anhydrous ethanol with a volume content of ≥99% for 5 minutes to better remove thinning particles adhering to the wafer. After soaking, the wafer is rinsed clean and spun dry using a vertical rotary washing and drying machine. The thickness is then measured using a dial indicator. Qualified wafers (thickness error ≤±1μm) are placed in an anti-static stopper, while unqualified products are marked and reworked. The mold is removed, and the surface of the mold is rinsed with deionized water to remove grinding residue. The mold is then rinsed clean to ensure positioning accuracy for the next use (if not used continuously, it can be stored in a clean cabinet). Ultrapure water is used during the thinning process at a flow rate of 2.5L / min.

[0062] (5) Repeat steps (1), (3), and (4) until all wafers to be thinned are thinned.

[0063] The implementation used a Disco 810 device and 8-inch suction cups.

[0064] 8-inch suction cup specifications: effective suction area diameter 190mm, compatible mold diameter 200mm.

[0065] Chip layout design:

[0066] 2-inch wafer (50.8mm diameter): Six positioning holes are evenly distributed along the outer ring of the mold (the outermost ring of the holes is 12mm from the edge of the mold, with an included angle of 60°), and one positioning hole is set in the central area. The maximum loading capacity of a single mold is 7 wafers. The outer ring of the wafer is 0.1mm smaller than the mold holes to meet the requirements for uniform airflow in vacuum adsorption. See Figure 1 .

[0067] 3-inch wafer (76.2mm diameter): Three positioning holes are evenly distributed within the effective area of ​​the mold (the outermost ring of the hole is 12mm from the edge of the mold, with an included angle of 120°). The maximum loading capacity of a single mold is 3 wafers. The outer ring of the wafer is 0.1mm smaller than the mold hole to meet the requirements for uniform airflow in vacuum adsorption. See [link / details]. Figure 2 .

[0068] 5.5×5.5mm square wafers: Four positioning holes are evenly distributed within the effective area of ​​the mold (the outermost corner of the square hole is 12mm from the edge of the mold, with an included angle of 90°). The maximum loading capacity of a single mold is four wafers. The outer ring of the wafer is 0.1mm smaller than the mold hole to meet the requirements for uniform airflow in vacuum adsorption. See [link / details]. Figure 3 .

[0069] The following are experimental cases comparing three groups of subjects (single-crystal indium phosphide wafers, germanium wafers, and gallium arsenide wafers) in key dimensions such as thickness control, total thickness change (TTV), processing time, and cost between film-free thinning processes and traditional film-based thinning processes. The comparisons are detailed by group:

[0070] Group 1: 10,000 single-crystal indium phosphide wafers with a diameter of 50.8mm.

[0071] Experimental subject: 50.8mm diameter single crystal indium phosphide wafers, initial thickness 390μm→350μm, 7 wafers thinned in a single operation.

[0072] Parameter control: mold thickness 300μm; fixed grinding wheel speed 2700rpm, suction cup speed 250rpm, feed rate in three steps: first step 1μm / s, feed rate 30μm; second step 0.8μm / s, feed rate 6μm; third step 0.6μm / s, feed rate 4μm.

[0073]

[0074]

[0075] Second group: 10,000 germanium wafers, 76.2mm in diameter

[0076] Experimental subject: Germanium wafer with a diameter of 76.2 mm, initial thickness 340 μm → 300 μm, 3 wafers thinned in a single operation.

[0077] Parameter control: mold thickness 250μm; fixed grinding wheel speed 2700rpm, suction cup speed 250rpm, feed rate in three steps: first step 1μm / s, feed rate 30μm; second step 0.8μm / s, feed rate 6μm; third step 0.6μm / s, feed rate 4μm.

[0078]

[0079]

[0080]

[0081] Group 3: 10,000 5.5×5.5mm gallium arsenide square wafers

[0082] Experimental subject: 5.5×5.5mm gallium arsenide square sheet, initial thickness 390μm→350μm, 4 sheets thinned in one go.

[0083] Parameter control: mold thickness 300μm; fixed grinding wheel speed 2700rpm, suction cup speed 250rpm, feed rate in three steps: first step 1μm / s, feed rate 30μm; second step 0.8μm / s, feed rate 6μm; third step 0.6μm / s, feed rate 4μm.

[0084]

[0085]

[0086] Summary table of core indicators for large-scale production (10,000 pieces)

[0087]

[0088]

[0089] In summary, this application's film-free thinning process, through a complete film-removal design, systematically solves the core problems of traditional film-based thinning, including operational complexity, accuracy fluctuations, and cost dependence. Three sets of experimental data show that its thickness error is controlled within ±1μm, TTV ≤ 1μm, processing time is reduced by more than 83%, and consumable costs are reduced by more than 99.8%. Furthermore, its adaptability to irregularly shaped wafers has achieved a leap from "customized high cost" to "standardized zero threshold." In mass production, the overall cost per 10,000 wafers is only 0.1%-0.11% of the traditional process, and equipment uptime is increased by 75%-85%, providing the ultimate solution for semiconductor thinning with "high precision, high efficiency, and high cost-effectiveness."

[0090] Example 2

[0091] The difference from the second group in Example 1 is that a thinning solution was used at a flow rate of 2.5 L / min for the first and second feed steps, and ultrapure water was used at a flow rate of 2.5 L / min for the third feed step. The thinning solution consisted of 18% succinic acid, 12% glutaric acid, 10% 1,1′-ferrocene di-bis(diphenylphosphine) (DPPF), 2% polyamide-amine dendritic polymer (PAMAM), 10% ammonium acetate, 5% triethanolamine, 26% ultrapure water, and 17% glycerol (all percentages are by mass). The polyamide-amine dendritic polymer (PAMAM) was from Chenyuan, model G0. All other parameters were the same as in Example 1.

[0092] Example 3

[0093] The difference from Example 2 is that the DPPF in the thinning solution was replaced with ultrapure water. All other steps are the same as in Example 2.

[0094] Example 4

[0095] The difference from Example 2 is that PAMAM in the thinning solution was replaced with ultrapure water. All other steps were the same as in Example 2.

[0096] Each example processed 1000 single-crystal germanium wafers with a diameter of 76.2 mm, with an initial thickness of 340 μm → 300 μm, and a reduction of 7 wafers per pass. Parameter control: mold thickness 250 μm; grinding wheel speed 2700 rpm; chuck speed 250 rpm; feed rate in three steps: first step 1 μm / s, reduction 40 μm; second step 0.8 μm / s, reduction 6 μm; third step 0.6 μm / s, reduction 4 μm. The results for each example are as follows.

[0097] Example flexural strength TTV / micron shallow scratch rate Surface roughness Yield Example 1 27.8Ibf ≤1μm 7％ Ra = 0.0322 μm 99.5％ Example 2 33.8Ibf ≤1μm 2％ Ra = 0.0145 μm 99.8％ Example 3 21.8Ibf ≤1μm 5％ Ra = 0.0288 μm 99.6％ Example 4 24.8Ibf ≤1μm 4％ Ra = 0.0184 μm 99.7％

Claims

1. A method for thinning multiple sheets of small-sized and irregularly shaped sheets, characterized in that: Includes the following steps: (1) A circular mold is prepared using FR-4 material. The diameter of the mold is 8-10 mm larger than the actual adsorption surface of the suction cup of the thinning machine, and the thickness of the mold is 50-100 μm lower than the target thickness after thinning. Through holes with a diameter 0.1-0.15 mm larger than the diameter of the wafer to be thinned are evenly arranged on the mold. (2) Use FR-4 material to make a liner, the liner has the same thickness as the mold, and the diameter of the liner is 0.1 to 0.15 mm smaller than the diameter of the through hole; (3) Clean the thinning machine suction cup, then place the mold on the thinning machine suction cup and align the center of the mold with the center of the suction cup. Place the wafers to be thinned into the through holes of the mold in sequence, with the thinning side facing up. When the number of wafers to be thinned is less than the number of through holes on the mold, use a spare wafer to fill the through holes on the mold. Then turn on the vacuum suction so that the mold and the wafers are simultaneously suctioned onto the suction cup. (4) Start thinning. During thinning, the grinding wheel and the suction cup rotate in opposite directions. The grinding wheel speed is 2500-3000 rpm and the suction cup speed is 200-300 rpm. The feed rate is divided into three steps: the first step is 0.8-1 μm / s, and the amount of material removed is set according to the thickness of the wafer; the second step is 0.6-0.8 μm / s, and the amount of material removed is 6-8 μm; the third step is 0.4-0.6 μm / s, and the amount of material removed is 4-6 μm. After the thinning is completed, remove the vacuum and turn on the backflushing water to separate the wafer to be thinned and the accompanying wafer from the suction cup. After the wafer to be thinned and the accompanying wafer are taken out and the thickness is measured to be qualified, put in the chuck, remove the mold and rinse it clean. (5) Repeat steps (1), (3), and (4) until all wafers to be thinned are thinned.

2. The multi-piece thinning method for small-sized and irregularly shaped sheets according to claim 1, characterized in that: In step (4), the thinning solution used includes: 17-19% succinic acid, 11-13% glutaric acid, 9-11% 1,1′-ferrocene di-bis(diphenylphosphine), 1-3% polyamide-amine dendritic polymer, 9-11% ammonium acetate, 4-6% triethanolamine, and the remainder is solvent. The percentages are by mass.

3. The multi-piece thinning method for small-sized and irregularly shaped sheets according to claim 2, characterized in that: In step (4), the solvent is ultrapure water, and the solvent contains 3%-5% glycerol, where % is a mass percentage.

4. The method for thinning multiple sheets of small-sized and irregularly shaped sheets according to claim 2 or 3, characterized in that: In step (4), during the thinning process, a thinning solution is used at the first and second feed rates, and ultrapure water is used at the third feed rate.

5. The method for thinning multiple small-sized and irregularly shaped sheets according to any one of claims 1-3, characterized in that: In step (1), the thickness of the mold is not less than 60% of the thickness of the wafer to be thinned.

6. The method for thinning multiple sheets of small-sized and irregularly shaped sheets according to any one of claims 1-3, characterized in that: In step (1), the outer edge of the mold is rounded.

7. The method for thinning multiple sheets of small-sized and irregularly shaped sheets according to any one of claims 1-3, characterized in that: In step (1), serial number marks are engraved on the outside of each through hole. In step (3), the wafer to be thinned and the accompanying wafer are placed in the through hole of the mold in the order of the serial number marks. In step (4), the wafer to be thinned and the accompanying wafer are separated from the suction cup. After the wafer is taken out in the order of loading and the thickness is measured and qualified, it is placed into the chuck.

8. The method for thinning multiple sheets of small-sized and irregularly shaped sheets according to any one of claims 1-3, characterized in that: In step (2), if the number of through holes on the mold is n, then the number of supporting pieces is at least n-1.

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