Grinding control method and system suitable for ultrathin wafer thinning

Abstract

The invention relates to the technical field of wafer production, in particular to a grinding control method and system suitable for ultrathin wafer thinning, and the method comprises the steps: dividing a thinning process into a coarse grinding stage and a fine grinding stage based on the initial thickness of a wafer and the target thickness of the wafer, and determining the stage thinning thicknesses corresponding to the coarse grinding stage and the fine grinding stage; based on the stage thinning thickness, stepping division is conducted on the rough grinding stage and the accurate grinding stage, and a plurality of stepping units are obtained; within the preset time before each stepping unit ends, the grinding state characteristics and the grinding process characteristics of the stepping unit are obtained; and process correction is conducted on the grinding process characteristics based on the grinding state characteristics, the grinding process characteristics corresponding to the next step unit are obtained, and therefore the grinding operation of the next step unit is controlled. The defects of hidden cracks, scratches and the like caused by mismatching of process parameters can be reduced, and the wafer yield is improved.

Description

Technical Field

[0001] This invention relates to the field of wafer manufacturing technology, and in particular to a grinding control method and system suitable for thinning ultrathin wafers. Background Technology

[0002] As the semiconductor industry rapidly develops towards high-density integration and miniaturization, wafer thinning technology can achieve 3D stacked packaging and improve the optoelectronic performance and mechanical strength of devices. In particular, for fan-out stacked ultra-thin EMC (epoxy molding compound) wafers, the thickness needs to be reduced to within 120μm and the silicon layer needs to be exposed to meet the size and performance requirements of advanced packaging.

[0003] In existing grinding control methods, a simple segmentation of coarse grinding and fine grinding is often used without fine division of each stage. Furthermore, the grinding process parameters for each stage are based on empirical presets, making it difficult to dynamically adjust the grinding process parameters according to the real-time status of the wafer. The coarse grinding stage relies on empirically set rotation speed and feed pressure, which may lead to microcracks in the fine grinding stage if the stress generated by rapid thinning is not released in time. In the fine grinding stage, if the parameters are still fixed values ​​when approaching the target thickness, even small deviations may exceed the accuracy requirement of ±20μm, which may seriously affect the product yield. Summary of the Invention

[0004] This invention provides a grinding control method and system suitable for ultrathin wafer thinning, which can effectively solve the problems in the background art.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a grinding control method suitable for ultrathin wafer thinning, comprising: Based on the initial wafer thickness and the target wafer thickness, the thinning process is divided into a rough grinding stage and a fine grinding stage, and the corresponding stage thinning thickness is determined for the rough grinding stage and the fine grinding stage. Based on the stage thinning thickness, the coarse grinding stage and the fine grinding stage are divided into steps to obtain multiple step units; Within a preset time before the end of each stepping unit, the grinding state characteristics and grinding process characteristics of that stepping unit are acquired; Based on the grinding state characteristics, the grinding process characteristics are modified to obtain the grinding process characteristics corresponding to the next step unit, and the grinding operation of the next step unit is controlled accordingly.

[0006] In conjunction with the first aspect, in one possible design, the polishing state characteristics include wafer surface temperature characteristics, surface roughness characteristics, and polishing current characteristics. The grinding process features include grinding wheel rotation speed, axial feed pressure, and axial feed speed.

[0007] In conjunction with the first aspect, in one possible design, the grinding process characteristics corresponding to the first step unit of the rough grinding stage are determined based on the initial characteristics of the grinding wheel and the initial structural characteristics of the wafer; The grinding process characteristics corresponding to the first step unit of the fine grinding stage are determined based on the real-time structural characteristics of the wafer and the real-time characteristics of the grinding wheel after the last step unit of the rough grinding stage is completed.

[0008] In conjunction with the first aspect, in one possible design, the thinning process is divided into a rough grinding stage and a fine grinding stage, including: Based on the target wafer thickness and the initial wafer thickness, and constrained by stress buffering and accuracy redundancy, the thinning process is divided into a rough grinding stage and a fine grinding stage, and the corresponding thinning thickness for each stage is determined.

[0009] In conjunction with the first aspect, in one possible design, the method for dividing the rough grinding stage into steps includes: Calculate the rough grinding risk coefficient based on the thinning thickness during the rough grinding stage; The rough grinding step interval is determined based on the rough grinding risk coefficient; The coarse grinding stage is divided into steps based on the coarse grinding step interval.

[0010] In conjunction with the first aspect, in one possible design, the method for dividing the finishing grinding stage into steps includes: Based on the materials mechanics model, the relative stiffness of the wafer at different thicknesses is calculated; Based on the preset rigidity descent rate threshold and the thinning thickness of the fine grinding stage, the fine grinding stage is divided to ensure that the rigidity descent rate in each stepping unit of the fine grinding stage is within the preset rigidity descent rate threshold range.

[0011] In conjunction with the first aspect, in one possible design, the wafer surface temperature characteristics are acquired by an infrared temperature sensor array; local high temperature characteristics are extracted during the rough grinding stage, and temperature stability characteristics are extracted during the fine grinding stage. The grinding current characteristics are collected by a current sensor. The peak current characteristics are extracted during the coarse grinding stage, and the current stability characteristics are extracted during the fine grinding stage.

[0012] In conjunction with the first aspect, in one possible design, the process modification for the rough grinding stage includes: The axial feed pressure correction of the next stepping unit is determined based on the current axial feed pressure reference value, temperature characteristic parameters, current characteristic parameters, and roughness characteristic parameters of the current stepping unit. The speed correction amount of the next stepping unit is determined based on the current stepping unit's speed reference value, roughness characteristic parameters, and current characteristic parameters; The axial feed rate correction of the next stepper unit is determined based on the current axial feed rate reference value, temperature characteristic parameters, and roughness characteristic parameters of the stepper unit.

[0013] In conjunction with the first aspect, in one possible design, the process modification for the finishing grinding stage includes: The axial feed pressure correction of the next stepping unit is determined based on the current axial feed pressure reference value, roughness characteristic parameters, current stability characteristic parameters, and temperature fluctuation characteristic parameters of the current stepping unit. The speed correction amount of the next stepping unit is determined based on the current stepping unit's speed reference value, thickness characteristic parameters, and roughness characteristic parameters; The axial feed rate correction of the next stepping unit is determined based on the current axial feed rate reference value, thickness characteristic parameters, current stability characteristic parameters, and roughness characteristic parameters of the current stepping unit.

[0014] Secondly, the present invention also provides a grinding control system suitable for ultra-thin wafer thinning, comprising: The stage division module is used to divide the thinning process into a rough grinding stage and a fine grinding stage based on the initial thickness and target thickness of the wafer, and to determine the stage thinning thickness corresponding to the rough grinding stage and the fine grinding stage. The stepping unit division module is used to divide the coarse grinding stage and the fine grinding stage into multiple stepping units based on the stage thinning thickness. The parameter acquisition module is used to acquire the grinding state characteristics and grinding process characteristics of each stepping unit within a preset time before the end of each stepping unit. The process correction module is used to correct the grinding process features based on the grinding state features, obtain the grinding process features corresponding to the next step unit, and control the grinding operation of the next step unit accordingly.

[0015] The technical solution of this invention can achieve the following technical effects: by further dividing the coarse grinding and fine grinding stages into multiple stepping units, the grinding process is brought down from the stage-level control to the unit level, providing finer-grained control nodes for precise adjustment and solving the problem that traditional segmentation cannot capture subtle state changes; the grinding process parameters are corrected based on the real-time grinding state characteristics of each stepping unit, so that the grinding process parameters change from fixed values ​​to adaptive values, avoiding stress accumulation and accuracy deviation caused by the mismatch between empirical parameters and real-time state. Attached Figure Description

[0016] Figure 1 This is a logic flowchart of the grinding control method applicable to ultra-thin wafer thinning in this invention; Figure 2This is a structural block diagram of the grinding control system applicable to ultra-thin wafer thinning in this invention. Detailed Implementation

[0017] This application will now be described with reference to the accompanying drawings.

[0018] like Figure 1 As shown, the grinding control method of the present invention for ultra-thin wafer thinning specifically includes the following steps: Step S100: Based on the initial thickness of the wafer and the target thickness of the wafer, the thinning process is divided into a rough grinding stage and a fine grinding stage, and the corresponding stage thinning thickness of the rough grinding stage and the fine grinding stage is determined. Step S200: Based on the stage thinning thickness, the coarse grinding stage and the fine grinding stage are divided into steps to obtain multiple step units; Step S300: Within a preset time before the end of each stepping unit, acquire the grinding state characteristics and grinding process characteristics of that stepping unit; the grinding state characteristics include wafer surface temperature characteristics, surface roughness characteristics, and grinding current characteristics; the grinding process characteristics include grinding wheel rotation speed, axial feed pressure, and axial feed speed; the grinding process characteristics corresponding to the first stepping unit in the rough grinding stage are determined based on the initial characteristics of the grinding wheel and the initial structural characteristics of the wafer, and the grinding process characteristics corresponding to the first stepping unit in the fine grinding stage are determined based on the real-time structural characteristics of the wafer and the real-time characteristics of the grinding wheel after the last stepping unit in the rough grinding stage is completed; Step S400: Based on the grinding state characteristics, perform process correction on the grinding process characteristics to obtain the grinding process characteristics corresponding to the next step unit, and control the grinding operation of the next step unit accordingly.

[0019] In this embodiment, by further dividing the coarse grinding and fine grinding stages into multiple stepping units, the grinding process is controlled from the stage level down to the unit level, providing finer-grained control nodes for precise adjustments and solving the problem that traditional segmentation cannot capture subtle state changes; the grinding process parameters are corrected based on the real-time grinding state characteristics of each stepping unit, so that the grinding process parameters change from fixed values ​​to adaptive values, avoiding stress accumulation and accuracy deviations caused by the mismatch between empirical parameters and real-time state. Specifically, by combining fine division of stepper units with real-time state correction, the stress in the rough grinding stage can be gradually released within each stepper unit through parameter fine-tuning, rather than accumulating into the fine grinding stage. At the same time, the parameter settings in the fine grinding stage, based on the real-time state of the rough grinding, avoid the superposition of rough grinding stress and new stress in the fine grinding. Compared with simple segmented thinning or static parameter optimization, this more thoroughly solves the problem of microcracks and improves the adaptability to the fragile characteristics of ultra-thin wafers. The rough grinding stage ensures thinning efficiency through stepper units with larger thickness intervals, quickly approaching the target thickness. The fine grinding stage achieves precision control through stepper units with smaller thickness intervals, finely adjusting to within the precision requirements. Real-time parameter correction provides a smooth transition between prioritizing efficiency and prioritizing precision, thereby resolving the inherent contradiction in existing methods where efficiency improvement inevitably sacrifices precision. This allows ultra-thin wafer thinning to meet both mass production efficiency requirements and consistently achieve the required precision.

[0020] In some embodiments of the present invention, if the stress generated by rapid thinning during rough grinding is not released through reasonable stage division, it will be concentrated and erupt during the fine grinding stage due to the thickness approaching the target value and the wafer rigidity dropping sharply, causing microcracks. At the same time, if the thinning thickness in the fine grinding stage is too high, the wear accumulation caused by the continuous operation of the grinding wheel will make it difficult to control the accuracy. Therefore, it is necessary to balance efficiency and accuracy by scientifically dividing the stages and determining the thinning thickness.

[0021] Specifically, with a target silicon exposure thickness of 120μm, and considering the initial wafer thickness, the rough grinding stage and the fine grinding stage are divided into two dimensions based on stress buffering and precision redundancy, along with the corresponding thinning thickness for each stage. The specific implementation is as follows: A target thickness benchmark was defined, with 120μm as the end point of the fine grinding stage. This target thickness was determined based on the size requirements and accuracy threshold of the ultra-thin EMC wafer package. The endpoint of the rough grinding stage is set as the target thickness plus the fine grinding allowance, where the fine grinding allowance is 30μm, that is, the thickness at the end of the rough grinding stage is 150μm. Therefore, the thickness reduction in the rough grinding stage is the initial thickness of the wafer minus 150μm. The fine grinding stage starts at the end of the rough grinding stage at 150μm and ends at the target thickness of 120μm; the fine grinding stage reduces the thickness by 30μm to ensure that the grinding wheel completes the final precision control in a fine working range with less wear. If the initial thickness is ≤180μm, the thickness reduction during the rough grinding stage is compressed to the initial thickness minus 150μm, with a minimum of 20μm. The fine grinding stage still maintains a thickness reduction of 30μm. If the initial thickness is >1000μm, the rough grinding stage can be divided into two steps: pre-rough grinding and main rough grinding. The total thickness reduction remains the initial thickness minus 150μm, ensuring that the 150μm starting point for the fine grinding stage remains unchanged.

[0022] In this embodiment, the rough grinding stage is mainly used for the rapid removal of the main part of the silicon substrate on the wafer, while the fine grinding stage is used for fine grinding of the remaining part. The small allowance design in the fine grinding stage can reduce the impact of grinding wheel wear on accuracy and ensure that the final thickness deviation is within the required range. By dividing the wafer into stages of rough grinding to 150μm and fine grinding to 120μm and designing a 30μm fine grinding allowance, stress can be released in stages. The rough grinding stage rapidly thins the wafer to 150μm while retaining a certain rigidity, and most of the stress can be released through stepping unit correction. The fine grinding stage only handles a 30μm thinning. Although the wafer is already ultra-thin, the small thinning amount and low stress accumulation, combined with dynamic parameter correction, reduce the probability of microcracks and solve the problem of stress being directly transferred to the ultra-thin fine grinding stage in traditional rough grinding.

[0023] As a preferred embodiment of the above, during the step unit division process in the rough grinding stage and the fine grinding stage, if the division is based solely on a fixed interval, the larger the thinning thickness in the rough grinding stage, the greater the single-step thinning amount will lead to the accumulation of grinding stress. Although the thinning thickness in the fine grinding stage is fixed at 30 μm, even a small step may cause microcracks due to wafer brittleness when approaching the target thickness. Therefore, it is necessary to consider the risk of the step interval and the thinning amount based on the respective thinning thicknesses of the two stages, so that the step interval size adapts to the characteristics of the stage thinning thickness.

[0024] The rough grinding stage is divided into steps, and the specific implementation is as follows: Let the thickness reduction during the rough grinding stage be H1. Calculate the rough grinding risk coefficient K1 = H1 ÷ 100. When H1 ≤ 100 μm, K1 ≤ 1; when H1 > 100 μm, K1 > 1. Determine the rough grinding step interval D1 = 5 μm × (1 + K1), where 5 μm is the base interval and K1 is used for dynamic adjustment. For example, when H1=50μm, K1=0.5, D1=5×(1+0.5)=7.5μm, the number of stepping units=H1÷D1=50÷7.5≈7 units. The number of stepping units is rounded up to ensure that the total removal amount covers H1; when H1=150μm, K1=1.5, D1=5×(2.5)=12.5μm, the number of stepping units=150÷12.5=12 units.

[0025] In the step division process of the above-mentioned rough grinding stage, the step interval D1 is increased as H1 increases by dynamically relating the rough grinding risk coefficient K1 to the thinning thickness H1. This avoids the inefficiency caused by too many step units when H1 is too large, and also prevents stress accumulation caused by too large intervals when H1 is small. This achieves a balance between efficient thickness removal with large thinning amounts and precise stress control with small thinning amounts. The calculation is based solely on the thinning thickness H1 of the rough grinding stage itself, without relying on external parameters. By combining the basic interval with the risk coefficient correction formula, the interval size is adapted to the rapid removal characteristics of silicon material, ensuring that while achieving efficient thickness removal, a stable stress release space is reserved for fine grinding.

[0026] The fine grinding stage is divided into steps, and the specific implementation is as follows: Based on the principle in materials mechanics that the rigidity of a thin plate is proportional to the cube of its thickness, a model for calculating the relative rigidity of a wafer is constructed. Taking the rigidity at the end of rough grinding with a thickness of 150 μm as the baseline value, i.e., 100%, the relative rigidity value for any thickness h is calculated as (h / 150)³ × 100%. For example, the relative rigidity value at a thickness of 120 μm is (120 / 150)³ × 100% = 51.2%, and the relative rigidity value at a thickness of 130 μm is approximately (130 / 150)³ × 100% ≈ 65.1%. Based on historical data verification, the rigidity drop rate threshold is set so that each step cell does not exceed the preset rigidity drop rate threshold, that is, the difference in rigidity value between adjacent step cells is ≤ the preset rigidity drop rate threshold, ensuring that the rigidity change within the cell is within the stress range that the wafer can withstand. Starting from the thickness at the end of the coarse grinding, the thickness range of each stepping unit is calculated backward according to the rigidity descent rate threshold to obtain each stepping unit in the fine grinding stage.

[0027] During the step division process in the above-mentioned fine grinding stage, the relative rigidity value is calculated based on the material mechanics model to ensure that the step unit division conforms to the wafer rigidity decrease law. By limiting the rigidity difference between adjacent units, it is ensured that the rigidity change within each unit is within the stress range that the wafer can withstand, thus solving the risk of microcracks caused by a sudden drop in rigidity when grinding approaches the target thickness. In view of the brittle characteristics of the wafer, the thickness range is calculated in reverse so that the step interval automatically decreases as the rigidity decreases, achieving more precise control in the silicon exposure critical range and avoiding the problem that traditional fixed intervals cannot match the nonlinear change in rigidity.

[0028] In some embodiments of the present invention, in order to ensure the continuity of the grinding operation, data needs to be collected in advance within a preset time before the end of each stepping unit. This provides a buffer for the correction of process parameters in the next stepping unit, ensuring that the process characteristics can adapt to changes in state characteristics in real time. By collecting the grinding state characteristics and grinding process characteristics of the current stepping unit and performing correction processing, the grinding process parameters of the next stepping unit can be corrected.

[0029] The grinding state characteristics include wafer surface temperature characteristics, surface roughness characteristics, and grinding current characteristics. The method for obtaining the grinding state characteristics of the current stepper unit is as follows: Step S301: Based on the temperature characteristics of the wafer surface, the temperature distribution of the corresponding area of ​​each stepping unit is collected by an infrared temperature sensor array to generate a temperature gradient curve. The local high temperature characteristics caused by friction are extracted in the rough grinding stage, and the temperature stability characteristics during the grinding process are extracted in the fine grinding stage. Step S302: Based on the surface roughness characteristics, a laser profilometer is used to scan the wafer surface to calculate the surface roughness Ra value in the rough grinding stage and the surface roughness Rz value in the fine grinding stage. Step S303: Based on the characteristics of the grinding current, the current fluctuation of the grinding wheel motor is recorded in real time by the current sensor of the grinding equipment. The current peak value in the coarse grinding stage reflects the removal resistance, and the current stability in the fine grinding stage reflects the uniformity of the grinding resistance.

[0030] The grinding process features include grinding wheel rotation speed, axial feed pressure, and axial feed speed; the grinding wheel rotation speed is monitored in real time by installing an encoder on the grinding wheel spindle; the axial feed pressure is monitored in real time by installing a pressure sensor in the feeding system of the grinding machine; and the axial feed speed is monitored in real time by using an encoder or grating ruler of the grinding machine.

[0031] In this embodiment, data is collected within a preset time before the stepping unit ends, reserving analysis time for process correction of the next stepping unit and avoiding the lag in data collection after the stepping unit ends. For example, if local overheating is found in the temperature characteristics of a certain stepping unit during the rough grinding stage, the feed pressure of the next stepping unit can be reduced in advance to prevent thermal stress on the wafer due to high temperature. If slight fluctuations occur in the current characteristics during the fine grinding stage, the rotation speed can be adjusted in time to avoid uneven grinding. Different state characteristics are collected for different stages of rough grinding and fine grinding. For example, rough grinding focuses on the efficiency correlation between temperature and current, while fine grinding focuses on the correlation between roughness and current accuracy. These characteristics are then correlated with process characteristics such as high feed pressure in rough grinding and low rotation speed in fine grinding, making the adjustment of grinding process parameters more targeted.

[0032] As a preferred embodiment of the above embodiments, the grinding process characteristics corresponding to the first step unit of the coarse grinding stage are determined based on the initial characteristics of the grinding wheel, such as the initial grit size and wear state, and the initial structural characteristics of the wafer, such as the initial thickness and initial stress distribution, to meet the requirements of rapid removal. Specifically: Step S311: Use a laser particle size analyzer to measure the abrasive particle size distribution of the grinding wheel and obtain the particle size distribution curve; a grinding wheel with a wider particle size distribution has a stronger material removal capacity and is suitable for rapid grinding; while a grinding wheel with a narrower particle size distribution can provide a more uniform grinding effect. Step S312: Observe the initial wear state of the grinding wheel using a laser scanning confocal microscope, analyze the wear morphology and degree of the abrasive grains, estimate the average wear amount of the abrasive grains, and evaluate the initial wear state of the grinding wheel; the grinding wheel with less wear has sharper abrasive grains and higher grinding efficiency; the grinding wheel with more wear needs to adjust the grinding parameters appropriately to ensure grinding quality. Step S313: Use a high-precision optical thickness gauge to measure the initial thickness of the wafer at multiple points and take the average value as the initial thickness value of the wafer; determine the initial feed amount of the grinding wheel based on the initial thickness of the wafer to avoid excessive grinding or stress concentration due to excessive feed amount; Step S314: Use an X-ray diffractometer to detect the initial stress distribution of the wafer, analyze the stress state of the wafer at different locations, and determine the stress concentration areas; for the stress concentration areas, adjust the speed and feed pressure of the grinding wheel appropriately during the grinding process to avoid microcracks caused by excessive stress. Step S315: Based on the initial characteristics of the grinding wheel and the initial structural characteristics of the wafer, establish a grinding wheel speed optimization model; the model takes maximizing the material removal rate and minimizing the grinding stress as the objective functions, and the abrasive particle size distribution, wear state, initial wafer thickness and initial stress distribution of the grinding wheel as constraints, and optimizes the grinding wheel speed through a genetic algorithm; Step S316: Taking into account the initial characteristics of the grinding wheel and the initial structural characteristics of the wafer, an axial feed pressure adjustment model is established. The model is based on the grinding force balance principle, taking into account the contact area between the grinding wheel and the wafer, the cutting force of the abrasive grains and the stress distribution of the wafer. The grinding effect under different axial feed pressures is calculated by finite element analysis to determine the optimal axial feed pressure. Step S317: Based on the optimization results of the grinding wheel rotation speed and axial feed pressure, and combined with the initial wafer thickness and the abrasive wear characteristics of the grinding wheel, establish an axial feed speed planning model. The model aims to maximize grinding efficiency and optimize the grinding surface quality. It uses a dynamic programming algorithm to optimize the axial feed speed to ensure efficient material removal while meeting the grinding quality requirements.

[0033] On the other hand, the grinding process characteristics corresponding to the first step unit of the fine grinding stage are determined based on the real-time structural characteristics of the wafer, such as surface flatness and residual stress, after the last step unit of the coarse grinding stage, as well as the real-time characteristics of the grinding wheel, such as actual wear and particle size change after wear, to meet the needs of fine grinding. Specifically: Step S321: Use an optical interferometer to perform high-precision detection on the surface flatness of the wafer after rough grinding, and obtain microscopic morphology data of the wafer surface; based on the surface flatness detection results, analyze the undulation and unevenness of the wafer surface, and determine the areas that need to be ground in particular. Step S322: Measure the residual stress distribution of the wafer after rough grinding using deep X-ray diffraction technology to obtain the stress state at different depths inside the wafer; analyze the magnitude and distribution law of the residual stress to evaluate the internal stress generated in the wafer during rough grinding. Step S323: Measure the mass loss of the grinding wheel after coarse grinding by gravimetric method, and calculate the actual wear of the grinding wheel by combining the density and volume changes of the grinding wheel; at the same time, observe the wear morphology of the grinding wheel using a laser scanning confocal microscope, analyze the wear degree and shedding of abrasive particles, and evaluate the wear state of the grinding wheel. Step S324: Use a laser particle size analyzer to measure the particle size distribution of the grinding wheel after coarse grinding again, and compare it with the initial particle size distribution of the grinding wheel to determine the particle size change after wear; based on the particle size change, evaluate the changes in the cutting ability and grinding performance of the grinding wheel. Step S325: Based on the real-time structural characteristics of the wafer, such as surface flatness and residual stress distribution, as well as the real-time characteristics of the grinding wheel, such as the actual wear amount and particle size change after wear, an optimization model for the grinding wheel speed in the fine grinding stage is established. The model takes minimizing the surface roughness and residual stress as the objective function, while considering the cutting ability of the grinding wheel and the characteristics of the wafer. The grinding wheel speed is optimized and solved by the particle swarm optimization algorithm. Step S326: Taking into account the real-time structural characteristics of the wafer and the real-time characteristics of the grinding wheel, an axial feed pressure adjustment model is established. The model is based on the principle of minimizing the force balance and grinding damage of the wafer during the grinding process. Through mechanical analysis and numerical simulation methods, the grinding effect and wafer stress distribution under different axial feed pressures are calculated to determine the optimal axial feed pressure. Based on the surface flatness and residual stress distribution of the wafer, as well as the real-time characteristics of the grinding wheel and the grinding process requirements, an axial feed speed planning model is established. The model aims to achieve high-precision grinding and avoid brittle fracture of the wafer. A fuzzy control algorithm is used to dynamically adjust the axial feed speed to ensure that the unevenness and stress remaining from the rough grinding can be effectively removed during the fine grinding process, while also ensuring the integrity and surface quality of the wafer.

[0034] In this embodiment, by analyzing the initial and real-time characteristics of the grinding wheel and the wafer, the grinding process characteristics of the rough grinding and fine grinding stages are determined, which can match the actual needs of the grinding process and improve grinding accuracy and stability. In the rough grinding stage, the main thickness of the wafer silicon substrate can be quickly removed and the stress distribution can be controlled. In the fine grinding stage, fine grinding can be performed to ensure precise control of the final wafer thickness and optimization of surface quality. Based on the initial stress distribution of the wafer and the residual stress distribution after rough grinding, the grinding process parameters are reasonably adjusted to avoid microcracks caused by stress concentration. At the same time, in the fine grinding stage, by precisely controlling the axial feed pressure and the grinding wheel speed, the grinding damage to the wafer is reduced, further reducing the risk of microcracks and improving the wafer yield.

[0035] In some embodiments of the present invention, the rough grinding stage needs to control wafer stress accumulation while efficiently removing thickness, and the fine grinding stage needs to avoid brittle fracture while ensuring accuracy. If a uniform correction logic is used, the rough grinding stage will reduce efficiency due to excessive pursuit of stress release, or the fine grinding stage will ignore wafer damage due to emphasis on efficiency. Therefore, it is necessary to design differentiated correction logic for the two stages to enable the process characteristics to adapt to the state changes in real time and avoid insufficient adaptability caused by a single correction rule.

[0036] Specifically, methods for process modification in the rough grinding stage include: Regarding the axial feed pressure correction, the axial feed pressure correction amount for the next stepper unit is determined based on the current stepper unit's axial feed pressure reference value, temperature characteristic parameters, current characteristic parameters, and surface roughness characteristic parameters; the specific calculation formula is as follows: ; Wherein, P1 represents the axial feed pressure correction amount of the next feed unit, with positive values ​​increasing and negative values ​​decreasing; P 01 This indicates the reference value of the axial feed pressure of the current stepper unit; k t,p This indicates the influence coefficient of temperature on feed pressure, for example, a value of -0.3 to -0.1. A negative sign indicates that the pressure needs to be reduced when the temperature rises, and reducing the pressure avoids excessive cutting. T i This indicates the highest measured temperature of the current stepper unit; T o This indicates the safe grinding temperature threshold for wafers; k i,p This indicates the coefficient of influence of current on feed pressure, for example, a value of -0.2 to -0.05. The negative sign indicates that the pressure needs to be reduced when the current increases. The current reflects the cutting resistance. When the resistance is high, the pressure is reduced to reduce stress. I i Indicates the current peak current of the stepper cell; I o This indicates the current reference value, which is the set value of the initial stepping unit; k r,p This represents the influence coefficient of surface roughness on feed pressure. For example, a value of 0.1 to 0.2 indicates that when the surface roughness exceeds the limit, the pressure needs to be increased to improve the cutting force and flatness. Ra i Ra represents the surface roughness Ra value of the current step unit wafer; o This represents the target value for wafer surface roughness.

[0037] For the correction of the grinding wheel speed, the speed correction amount of the next stepping unit is determined based on the current stepping unit's speed reference value, roughness characteristic parameters, and current characteristic parameters; the specific calculation formula is as follows: ; Wherein, N1 represents the speed correction amount of the next feed unit; N 01 This indicates the current speed reference value of the stepper unit; k r,N This represents the influence coefficient of roughness on the grinding wheel speed. For example, it can be 0.05 to 0.1. A positive value indicates that when the roughness exceeds the limit, the speed should be increased to enhance the uniformity of cutting. k i,N This represents the influence coefficient of current on the grinding wheel speed. For example, it can be 0.03 to 0.08. A positive value indicates that the speed should be increased when the current is too low to compensate for insufficient cutting force.

[0038] For axial feed rate correction, the axial feed rate correction amount for the next stepper unit is determined based on the current stepper unit's axial feed rate reference value, temperature characteristic parameters, and surface roughness characteristic parameters; the specific calculation formula is as follows: ; Where V1 represents the axial feed rate correction of the next feed unit, with positive values ​​increasing and negative values ​​decreasing; V 01 This indicates the reference value of the axial feed rate of the current stepper unit; k t,v This represents the influence coefficient of temperature on the axial feed rate, for example, a value of 0.1 to 0.2. A positive value indicates that the speed can be increased when the temperature is below the threshold. k r,v This represents the influence coefficient of roughness on axial feed rate, for example, a value of -0.15 to -0.05. The negative sign indicates that when the roughness exceeds the limit, the speed is reduced, and the surface quality is improved by extending the grinding time.

[0039] On the other hand, methods for process modification in the finishing grinding stage include: For axial feed pressure correction, the axial feed pressure correction amount for the next stepper unit is determined based on the current stepper unit's axial feed pressure reference value, surface roughness characteristic parameters, current stability characteristic parameters, and temperature fluctuation characteristic parameters; the specific calculation is as follows: ; Where P2 represents the axial feed pressure correction amount of the next feed unit; P 02 This indicates the reference value of the axial feed pressure of the current stepper unit; k rz,p This represents the influence coefficient of surface roughness on axial feed pressure, with a value ranging from -0.4 to -0.2. A negative sign indicates that the pressure should be reduced when Rz exceeds the limit to avoid brittle damage to the wafer. Rz i This represents the current roughness Rz value of the stepping element; Rz0 represents the target Rz value. k i,s This coefficient represents the influence of current stability on axial feed pressure. For example, it can be -0.3 to -0.1. A negative sign indicates that the pressure is reduced when the current fluctuates greatly, thus reducing uneven grinding. S i S0 represents the standard deviation of the current in the current stepper unit, which reflects the degree of current fluctuation; S0 represents the current stability threshold. k t' This represents the influence coefficient of temperature fluctuation on axial feed pressure, with a value ranging from -0.2 to -0.1. A negative sign indicates that the pressure is reduced when the temperature fluctuation exceeds the limit, thus alleviating stress concentration. ΔT i ΔT0 represents the maximum temperature fluctuation of the current stepper unit; ΔT0 represents the temperature stability threshold.

[0040] For the correction of the grinding wheel speed, the speed correction amount of the next stepping unit is determined based on the current stepping unit's speed reference value, thickness characteristic parameters, and roughness characteristic parameters; the specific calculation is as follows: ; Where N2 represents the speed correction amount of the next feed unit; N 02 This indicates the current speed reference value of the stepper unit; k h This represents the coefficient of influence of thickness on the grinding wheel speed, for example, a value of -0.5 to -0.3. The negative sign indicates that the speed is reduced when approaching the target thickness. h0 is the target thickness, and h... i For the current thickness, ensure final accuracy; k rz' This represents the influence coefficient of roughness on the grinding wheel speed, for example, a value of -0.2 to -0.1. The negative sign indicates that the speed is reduced when Rz exceeds the limit, thereby reducing wafer tearing.

[0041] For axial feed rate correction, the axial feed rate correction amount for the next stepper unit is determined based on the current stepper unit's axial feed rate reference value, thickness characteristic parameters, current stability characteristic parameters, and surface roughness characteristic parameters; the specific calculation is as follows: ; Where V2 represents the axial feed rate correction of the next feed unit; V 02 This indicates the reference value of the axial feed rate of the current stepper unit; k h,v This represents the influence coefficient of thickness on axial feed rate, for example, a value of -0.4 to -0.2. The negative sign indicates that the speed is reduced when approaching the target thickness to ensure the final dimensional accuracy. k s,v The coefficient representing the influence of current stability on axial feed speed, for example, a value of 0.05~0.1. A positive value indicates that the speed can be increased when the current fluctuation is small, thus improving efficiency by utilizing grinding stability. k rz,v This represents the influence coefficient of roughness on axial feed rate, for example, a value of -0.2 to -0.1. The negative sign indicates that the speed is reduced when Rz exceeds the limit, thereby reducing wafer surface tearing.

[0042] It should be noted that the coefficients in the above formulas are determined by comprehensively considering the influence of grinding stage characteristics, the physical and mechanical properties of the material being ground, and the process objectives, and by relating the grinding state characteristics to the process characteristics. Specifically, the degree and direction of the influence of different state characteristics such as temperature, current, roughness, and thickness on process characteristics such as feed pressure, rotation speed, and feed rate can be quantified through experimental data fitting, simulation analysis, process experience accumulation, or machine learning, forming a coefficient range suitable for the corresponding stage. The positive or negative sign of the coefficient reflects the direction of influence. For example, when the temperature increases, the pressure needs to be reduced, and the corresponding coefficient is negative; when the roughness exceeds the tolerance, the rotation speed needs to be increased, and the corresponding coefficient is positive. The value range of the coefficients is dynamically adjusted according to the differences in material properties, the sensitivity of process parameters, and the target control accuracy to ensure that the correction logic is compatible with the stage requirements, material properties, and process objectives.

[0043] In this embodiment, the rough grinding correction prioritizes efficiency and controllable stress. By using synergistic parameters of temperature, current, and roughness, it can quickly remove the main thickness of the wafer while avoiding excessive cutting or stress accumulation. The fine grinding correction prioritizes accuracy and minimizes damage. It focuses on introducing parameters such as thickness characteristics and current stability to adapt to the high brittleness of the wafer and avoid microcracks or surface tearing. The rough grinding axial feed pressure correction is simultaneously linked to temperature, current, and roughness to avoid misjudgment of a single parameter. The fine grinding axial feed speed correction integrates thickness, current stability, and roughness to ensure that even when the current is stable, the speed will actively decrease due to thickness characteristics when approaching the target thickness, thus ensuring the final dimensional accuracy.

[0044] like Figure 2 As shown, the present invention also provides a grinding control system suitable for ultra-thin wafer thinning, specifically including the following modules; The stage division module is used to divide the thinning process into a rough grinding stage and a fine grinding stage based on the initial thickness and target thickness of the wafer, and to determine the stage thinning thickness corresponding to the rough grinding stage and the fine grinding stage. The stepping unit division module is used to divide the coarse grinding stage and the fine grinding stage into multiple stepping units based on the stage thinning thickness. The parameter acquisition module is used to acquire the grinding state characteristics and grinding process characteristics of each stepping unit within a preset time before the end of each stepping unit. The process correction module is used to correct the grinding process features based on the grinding state features, obtain the grinding process features corresponding to the next step unit, and control the grinding operation of the next step unit accordingly.

[0045] In this embodiment, the process is first clearly divided into rough grinding and fine grinding stages by the stage division module, and the corresponding thinning thickness is determined. The step unit division module then further subdivides each stage into step units, so that the control granularity is reduced from the stage level to the unit level. This allows the system to capture more subtle state changes during wafer thinning, providing more detailed control nodes for precise adjustments and avoiding the problem that traditional simple segmentation cannot respond to subtle state differences. The parameter acquisition module collects grinding state characteristics and process characteristics in real time before the end of each step unit. The process correction module dynamically corrects the process parameters based on the real-time state characteristics, so that the process parameters of the next step unit can adapt to the real-time state of the wafer, avoiding problems such as stress accumulation and accuracy deviation caused by the mismatch between traditional experience-based preset parameters and actual state. Through the continuous division of step units and dynamic correction of parameters, the process parameters of the rough grinding stage can be gradually adjusted with the wafer state, avoiding excessive stress accumulation, eliminating process breaks and stress superposition caused by traditional independent stage settings, reducing the risk of microcracks as a whole, and ensuring the accuracy control of the fine grinding stage.

[0046] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A grinding control method suitable for ultra-thin wafer thinning, characterized in that, include: Based on the initial wafer thickness and the target wafer thickness, the thinning process is divided into a rough grinding stage and a fine grinding stage, and the corresponding stage thinning thickness is determined for the rough grinding stage and the fine grinding stage. Based on the stage thinning thickness, the coarse grinding stage and the fine grinding stage are divided into steps to obtain multiple step units; Within a preset time before the end of each stepping unit, the grinding state characteristics and grinding process characteristics of that stepping unit are acquired; Based on the grinding state characteristics, the grinding process characteristics are modified to obtain the grinding process characteristics corresponding to the next step unit, and the grinding operation of the next step unit is controlled accordingly.

2. The grinding control method for ultrathin wafer thinning according to claim 1, characterized in that, The grinding state characteristics include wafer surface temperature characteristics, surface roughness characteristics, and grinding current characteristics; The grinding process features include grinding wheel rotation speed, axial feed pressure, and axial feed speed.

3. The grinding control method for ultrathin wafer thinning according to claim 2, characterized in that, The grinding process characteristics corresponding to the first step unit of the rough grinding stage are determined based on the initial characteristics of the grinding wheel and the initial structural characteristics of the wafer. The grinding process characteristics corresponding to the first step unit of the fine grinding stage are determined based on the real-time structural characteristics of the wafer and the real-time characteristics of the grinding wheel after the last step unit of the rough grinding stage is completed.

4. The grinding control method for ultrathin wafer thinning according to claim 1, characterized in that, The thinning process is divided into a rough grinding stage and a fine grinding stage, including: Based on the target wafer thickness and the initial wafer thickness, and constrained by stress buffering and accuracy redundancy, the thinning process is divided into a rough grinding stage and a fine grinding stage, and the corresponding thinning thickness for each stage is determined.

5. The grinding control method for ultrathin wafer thinning according to claim 4, characterized in that, Methods for dividing the rough grinding stage into steps include: Calculate the rough grinding risk coefficient based on the thinning thickness during the rough grinding stage; The rough grinding step interval is determined based on the rough grinding risk coefficient; The coarse grinding stage is divided into steps based on the coarse grinding step interval.

6. The grinding control method for ultrathin wafer thinning according to claim 5, characterized in that, Methods for dividing the finishing grinding stage into steps include: Based on the materials mechanics model, the relative stiffness of the wafer at different thicknesses is calculated; Based on the preset rigidity descent rate threshold and the thinning thickness of the fine grinding stage, the fine grinding stage is divided to ensure that the rigidity descent rate in each stepping unit of the fine grinding stage is within the preset rigidity descent rate threshold range.

7. The grinding control method for ultrathin wafer thinning according to claim 2, characterized in that, The surface temperature characteristics of the wafer are acquired by an infrared temperature sensor array; local high temperature characteristics are extracted during the rough grinding stage, and temperature stability characteristics are extracted during the fine grinding stage. The grinding current characteristics are collected by a current sensor. The peak current characteristics are extracted during the coarse grinding stage, and the current stability characteristics are extracted during the fine grinding stage.

8. The grinding control method for ultrathin wafer thinning according to claim 7, characterized in that, The process modifications in the rough grinding stage include: The axial feed pressure correction of the next stepping unit is determined based on the current axial feed pressure reference value, temperature characteristic parameters, current characteristic parameters, and roughness characteristic parameters of the current stepping unit. The speed correction amount of the next stepping unit is determined based on the current stepping unit's speed reference value, roughness characteristic parameters, and current characteristic parameters; The axial feed rate correction of the next stepper unit is determined based on the current axial feed rate reference value, temperature characteristic parameters, and roughness characteristic parameters of the stepper unit.

9. The grinding control method for ultrathin wafer thinning according to claim 7, characterized in that, The process modifications during the fine grinding stage include: The axial feed pressure correction of the next stepping unit is determined based on the current axial feed pressure reference value, roughness characteristic parameters, current stability characteristic parameters, and temperature fluctuation characteristic parameters of the current stepping unit. The speed correction amount of the next stepping unit is determined based on the current stepping unit's speed reference value, thickness characteristic parameters, and roughness characteristic parameters; The axial feed rate correction of the next stepping unit is determined based on the current axial feed rate reference value, thickness characteristic parameters, current stability characteristic parameters, and roughness characteristic parameters of the current stepping unit.

10. A grinding control system suitable for ultra-thin wafer thinning, characterized in that, include: The stage division module is used to divide the thinning process into a rough grinding stage and a fine grinding stage based on the initial thickness and target thickness of the wafer, and to determine the stage thinning thickness corresponding to the rough grinding stage and the fine grinding stage. The stepping unit division module is used to divide the coarse grinding stage and the fine grinding stage into multiple stepping units based on the stage thinning thickness. The parameter acquisition module is used to acquire the grinding state characteristics and grinding process characteristics of each stepping unit within a preset time before the end of each stepping unit. The process correction module is used to correct the grinding process features based on the grinding state features, obtain the grinding process features corresponding to the next step unit, and control the grinding operation of the next step unit accordingly.

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