Grinding control method and system suitable for ultra-thin wafer thinning

Abstract

The present application relates to the technical field of wafer production, and particularly relates to a grinding control method and system suitable for ultra-thin wafer thinning, comprising the following steps: based on wafer initial thickness and wafer target thickness, thinning process is divided into coarse grinding stage and fine grinding stage, and stage thinning thickness corresponding to the coarse grinding stage and the fine grinding stage is determined; based on the stage thinning thickness, the coarse grinding stage and the fine grinding stage are respectively step-divided to obtain a plurality of step units; within a preset time before the end of each step unit, grinding state features and grinding process features of the step unit are acquired; based on the grinding state features, the grinding process features are corrected to obtain grinding process features corresponding to the next step unit, and the grinding operation of the next step unit is controlled. The present application can reduce defects such as hidden cracks and scratches caused by mismatched process parameters, and improve wafer yield.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wafer production, and particularly to a grinding control method and system suitable for ultra-thin wafer thinning. BACKGROUND

[0002] With the rapid development of the semiconductor industry towards high-density integration and miniaturization, wafer thinning process can realize 3D stacked packaging, improve the photoelectric performance and mechanical strength of devices; especially for fan-out stacked ultra-thin EMC (epoxy plastic encapsulant) wafers, their thickness needs to be thinned to within 120μm and the silicon layer is exposed to meet the size and performance requirements of advanced packaging.

[0003] In the existing grinding control method, simple segmentation of coarse grinding and fine grinding is often used, and each stage is not finely divided, and the grinding process parameters of each stage are preset based on experience, which makes it difficult to dynamically adjust the grinding process parameters according to the real-time state of the wafer; the speed and feed pressure in the coarse grinding stage are set based on experience, and the stress generated by rapid thinning may not be released in time, which may cause hidden cracks in the fine grinding stage; if the parameters are still fixed when the fine grinding stage approaches the target thickness, the small deviation may exceed the accuracy requirement of ±20μm, which seriously affects the product yield. SUMMARY

[0004] The present application provides a grinding control method and system suitable for ultra-thin wafer thinning, which can effectively solve the problems in the background art.

[0005] In order to achieve the above purpose, in a first aspect, the present application provides a grinding control method suitable for ultra-thin wafer thinning, comprising:

[0006] Based on the initial thickness of the wafer and the target thickness of the wafer, the thinning process is divided into a coarse grinding stage and a fine grinding stage, and the stage thinning thickness corresponding to the coarse grinding stage and the fine grinding stage is determined;

[0007] Based on the stage thinning thickness, the coarse grinding stage and the fine grinding stage are respectively step-divided to obtain a plurality of step units;

[0008] Within a preset time before the end of each step unit, the grinding state feature and the grinding process feature of the step unit are obtained;

[0009] Based on the grinding state feature, the grinding process feature is corrected to obtain the grinding process feature corresponding to the next step unit, and the grinding operation of the next step unit is controlled.

[0010] In a possible design, the grinding state feature includes wafer surface temperature feature, surface roughness feature and grinding current feature.

[0011] The grinding process features include grinding wheel rotation speed, axial feed pressure, and axial feed speed.

[0012] In combination with the first aspect, in a possible design, the grinding process features corresponding to the first step unit of the coarse grinding stage are determined based on initial characteristics of the grinding wheel and initial structure characteristics of the wafer;

[0013] The grinding process features corresponding to the first step unit of the fine grinding stage are determined based on real-time structure characteristics of the wafer and real-time characteristics of the grinding wheel after the last step unit of the coarse grinding stage ends.

[0014] In combination with the first aspect, in a possible design, the thinning process is divided into a coarse grinding stage and a fine grinding stage, including:

[0015] According to the wafer target thickness and the wafer initial thickness, the thinning process is divided into a coarse grinding stage and a fine grinding stage with stress buffering and precision redundancy as constraints, and the corresponding thinning thickness of each stage is determined.

[0016] In combination with the first aspect, in a possible design, the method for stepwise division of the coarse grinding stage includes:

[0017] Based on the thinning thickness of the coarse grinding stage, a coarse grinding risk coefficient is calculated;

[0018] Based on the coarse grinding risk coefficient, a coarse grinding step interval is determined;

[0019] Based on the coarse grinding step interval, the coarse grinding stage is stepwise divided.

[0020] In combination with the first aspect, in a possible design, the method for stepwise division of the fine grinding stage includes:

[0021] Based on a material mechanics model, a relative rigidity value of the wafer at different thicknesses is calculated;

[0022] Based on a preset rigidity drop rate threshold and the thinning thickness of the fine grinding stage, the fine grinding stage is divided to ensure that the rigidity drop rate in each step unit of the fine grinding stage is within the preset rigidity drop rate threshold range.

[0023] In combination with the first aspect, in a possible design, the wafer surface temperature features are collected by an infrared temperature sensor array; local high-temperature features are extracted in the coarse grinding stage, and temperature stability features are extracted in the fine grinding stage;

[0024] The grinding current features are collected by a current sensor, current peak features are extracted in the coarse grinding stage, and current smoothness features are extracted in the fine grinding stage.

[0025] In combination with the first aspect, in a possible design, the process correction of the coarse grinding stage includes:

[0026] The axial feed pressure correction amount of the next step unit is determined based on the axial feed pressure reference value of the current step unit, the temperature characteristic parameter, the current characteristic parameter and the roughness characteristic parameter;

[0027] The rotational speed correction amount of the next step unit is determined based on the rotational speed reference value of the current step unit, the roughness characteristic parameter and the current characteristic parameter;

[0028] The axial feed speed correction amount of the next step unit is determined based on the axial feed speed reference value of the current step unit, the temperature characteristic parameter and the roughness characteristic parameter.

[0029] With reference to the first aspect, in a possible design, the process correction of the fine grinding stage includes:

[0030] The axial feed pressure correction amount of the next step unit is determined based on the axial feed pressure reference value of the current step unit, the roughness characteristic parameter, the current smoothness characteristic parameter and the temperature fluctuation characteristic parameter;

[0031] The rotational speed correction amount of the next step unit is determined based on the rotational speed reference value of the current step unit, the thickness characteristic parameter and the roughness characteristic parameter;

[0032] The axial feed speed correction amount of the next step unit is determined based on the axial feed speed reference value of the current step unit, the thickness characteristic parameter, the current smoothness characteristic parameter and the roughness characteristic parameter.

[0033] The second aspect, the present application also provides a kind of grinding control system suitable for ultra-thin wafer thinning, including:

[0034] Stage division module, for based on wafer initial thickness and wafer target thickness, thinning process is divided into coarse grinding stage and fine grinding stage, and the stage thinning thickness corresponding to coarse grinding stage and fine grinding stage is determined;

[0035] Step unit division module, for based on the stage thinning thickness, respectively, coarse grinding stage and fine grinding stage are step-divided, and a plurality of step units are obtained;

[0036] Parameter acquisition module, for in the preset time before each the step unit ends, the grinding state characteristic and the grinding process characteristic of this step unit are acquired;

[0037] Process correction module, for based on the grinding state characteristic process correction the grinding process characteristic, the grinding process characteristic corresponding to the next step unit is obtained, and the next step unit is controlled by grinding operation.

[0038] The technical scheme of the present application can realize the following technical effects: by further dividing the coarse grinding and fine grinding stages into multiple stepping units, the grinding process is controlled from the stage level to the unit level, providing more fine-grained control nodes for accurate adjustment, solving the problem that traditional segmentation cannot capture subtle state changes; based on the real-time grinding state characteristics of each stepping unit, the grinding process parameters are corrected, so that the grinding process parameters change from fixed values to adaptive values, avoiding stress accumulation and precision deviation caused by mismatch between experience parameters and real-time state. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 A logic flowchart of the grinding control method suitable for ultra-thin wafer thinning in the present application;

[0040] Figure 2 A structure block diagram of the grinding control system suitable for ultra-thin wafer thinning in the present application. DETAILED DESCRIPTION

[0041] The present application will be described below in conjunction with the drawings in the present application.

[0042] As shown in Figure 1 The grinding control method suitable for ultra-thin wafer thinning of the present application specifically includes the following steps:

[0043] Step S100, based on the initial thickness of the wafer and the target thickness of the wafer, the thinning process is divided into a coarse grinding stage and a fine grinding stage, and the stage thinning thickness corresponding to the coarse grinding stage and the fine grinding stage is determined;

[0044] Step S200, based on the stage thinning thickness, the coarse grinding stage and the fine grinding stage are respectively step-divided to obtain multiple stepping units;

[0045] Step S300, within a preset time before the end of each stepping unit, the grinding state characteristics and grinding process characteristics of the stepping unit are obtained; 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 of the coarse 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 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 stepping unit of the coarse grinding stage ends;

[0046] Step S400, based on the grinding state characteristics, the grinding process characteristics are corrected to obtain the grinding process characteristics corresponding to the next stepping unit, and the grinding operation of the next stepping unit is controlled based on the grinding process characteristics.

[0047] In the embodiment, by further dividing the rough grinding and fine grinding stages into multiple step units, the grinding process is controlled from the stage level to the unit level, providing more fine-grained control nodes for precise adjustment, solving the problem that traditional segmentation cannot capture subtle state changes; based on the real-time grinding state characteristics of each step unit, the grinding process parameters are corrected, so that the grinding process parameters change from fixed values to adaptive values, avoiding stress accumulation and precision deviation caused by mismatch between experience parameters and real-time state;

[0048] Specifically, after the fine division of the step unit and the real-time state correction, the stress in the rough grinding stage can be gradually released in each step unit through parameter fine-tuning, rather than accumulated to the fine grinding stage; at the same time, based on the parameter setting of the real-time state of the rough grinding stage, the superposition of the rough grinding stress and the new stress in the fine grinding stage is avoided, which more thoroughly solves the hidden crack problem than simply segmenting the thinning or optimizing the static parameters, and improves the adaptability of the fragile characteristics of the ultra-thin wafer; the rough grinding stage ensures the thinning efficiency through step units with large thickness intervals, and quickly approaches the target thickness; the fine grinding stage realizes precision control through step units with small thickness intervals, and fine-tunes to meet the precision requirements; real-time parameter correction provides a smooth transition in the switching between efficiency priority and precision priority, thereby solving the inherent contradiction that efficiency improvement must sacrifice precision in existing methods, so that ultra-thin wafer thinning can meet the efficiency requirements of mass production and also meet the precision requirements.

[0049] In some embodiments of the present application, if the stress generated by rough grinding is not released by reasonable stage division, it will concentrate and burst in the fine grinding stage due to the close proximity to the target thickness and the sudden drop in wafer rigidity, causing hidden cracks; at the same time, if the thinning thickness ratio in the fine grinding stage is too high, it will be difficult to control the precision due to the accumulation of wear caused by continuous operation of the grinding wheel; therefore, the stages need to be divided scientifically and the thinning thickness needs to be determined to balance efficiency and precision.

[0050] Specifically, taking 120μm as the target thickness of the exposed silicon, combining the initial thickness of the wafer, dividing the rough grinding stage and the fine grinding stage according to the stress buffer and precision redundancy, and determining the corresponding thinning thickness of each stage, the specific implementation is as follows:

[0051] The target thickness is determined based on the size requirements of the ultra-thin EMC wafer package and the precision threshold, and 120μm is taken as the end point of the fine grinding stage;

[0052] The end point of the rough grinding stage is set to the target thickness plus the fine grinding allowance, where the fine grinding allowance is 30μm, i.e. the rough grinding end point thickness is 150μm, and the rough grinding stage thinning thickness is the initial thickness of the wafer minus 150μm;

[0053] The starting point of the fine grinding stage is the end point of the coarse grinding stage of 150 pm, and the end point is the target thickness of 120 pm; the thickness reduction of the fine grinding stage is 30 pm, which ensures that the grinding wheel completes the final precision control in the fine work area with less wear;

[0054] If the initial thickness is less than or equal to 180 pm, the thickness reduction of the coarse grinding stage is compressed to the initial thickness minus 150 pm, and the minimum is not less than 20 pm, and the fine grinding stage still maintains a thickness reduction of 30 pm; if the initial thickness is greater than 1000 pm, the coarse grinding stage can be divided into two steps of pre-coarse grinding and main coarse grinding, and the total thickness reduction still maintains the initial thickness minus 150 pm, to ensure that the starting point of 150 pm in the fine grinding stage remains unchanged.

[0055] In the embodiment, the coarse grinding stage is mainly used for fast removal of the main part of the wafer silicon substrate, and the fine grinding stage is used for fine grinding of the remaining part. The small excess amount design of the fine grinding stage can reduce the influence of the grinding wheel wear on the precision, and ensure that the final thickness deviation is within the required range. Through the stage division of coarse grinding to 150 pm and fine grinding to 120 pm and the design of 30 pm fine grinding excess amount, the stress can be released in stages. The coarse grinding stage is quickly thinned to 150 pm, and a certain rigidity is reserved, which can correct and release most of the stress through the stepping unit. The fine grinding stage only processes a thickness reduction of 30 pm. Although the wafer is already very thin, the probability of hidden cracks is reduced due to the small thickness reduction and the small stress accumulation, and the problem of direct transmission of stress from the coarse grinding stage to the fine grinding ultra-thin stage is solved.

[0056] As a preferred embodiment of the above embodiment, during the stepping unit division process of the coarse grinding stage and the fine grinding stage, if only the fixed interval is used for division, the larger the thickness reduction of the coarse grinding stage, the larger the single stepping thickness reduction, which leads to the accumulation of grinding stress. Although the thickness reduction of the fine grinding stage is fixed at 30 pm, when the target thickness is approached, even a small stepping amount may cause hidden cracks due to the brittleness of the wafer. Therefore, based on the thickness reduction of each stage, the risk of the stepping interval and the thickness reduction is associated, and the size of the stepping interval is self-adapted according to the characteristics of the thickness reduction of the stage.

[0057] The coarse grinding stage is divided by stepping, and the implementation is as follows:

[0058] Let the thickness reduction of the coarse grinding stage be H1, and calculate the coarse grinding risk coefficient K1=H1÷100. When H1≤100 pm, K1≤1; when H1>100 pm, K1>1; determine the coarse grinding stepping interval D1=5 pm×(1+K1), wherein 5 pm is the basic interval, and K1 is used for dynamic adjustment:

[0059] 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, 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.

[0060] In the step-by-step division process of the above coarse grinding stage, by dynamically associating the coarse grinding risk coefficient K1 with the thinning thickness H1, the step interval D1 is increased as H1 increases, which not only avoids the low efficiency caused by too many stepping units when H1 is too large, but also prevents stress accumulation caused by too large interval when H1 is small, achieving a balance between high-efficiency thickness reduction and precise stress control for small thickness reduction; only based on the thinning thickness H1 of the coarse grinding stage itself for calculation, without relying on external parameters, through the formula of basic interval combined with risk coefficient correction, the interval size is adapted to the rapid removal characteristics of silicon material, ensuring efficient thickness reduction while reserving stable stress release space for fine grinding.

[0061] The fine grinding stage is divided by steps, and the specific implementation is as follows:

[0062] Based on the principle that the rigidity of a thin plate is proportional to the cube of the thickness in material mechanics, a wafer relative rigidity value calculation model is constructed; taking the rigidity at the coarse grinding endpoint thickness of 150μm as the reference value, i.e. 100%, then the relative rigidity value corresponding to any thickness h=(h / 150)³×100%; for example, the relative rigidity value when the thickness is 120μm=(120 / 150)³×100%=51.2%, and the relative rigidity value when the thickness is 130μm≈(130 / 150)³×100%≈65.1%;

[0063] Through historical data verification, the rigidity drop rate threshold is set to not more than a preset rigidity drop rate threshold per stepping unit, i.e. the difference between the rigidity values of adjacent stepping units≤the preset rigidity drop rate threshold, to ensure that the rigidity change in the unit is within the stress range that the wafer can withstand;

[0064] Starting from the coarse grinding endpoint thickness, the thickness interval of each stepping unit in the fine grinding stage is calculated in reverse according to the rigidity drop rate threshold.

[0065] In the step-by-step division process of the above fine grinding stage, the relative rigidity value is calculated based on a material mechanics model, so that the step-by-step unit division conforms to the wafer rigidity decline law, and by limiting the rigidity difference between adjacent units, the rigidity change in each unit is ensured to be within the stress range that the wafer can withstand, thereby solving the risk of hidden cracks caused by sudden rigidity drop when the grinding approaches the target thickness; according to the brittle characteristics of the wafer, the thickness interval is calculated reversely, so that the step interval automatically decreases with the rigidity drop, and more precise control is realized in the critical interval of exposing the silicon, thereby avoiding the problem that the traditional fixed interval cannot match the nonlinear change of rigidity.

[0066] In some embodiments of the present application, 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 step unit, so as to reserve a buffer for the process parameter correction of the next step unit, and ensure that the process characteristics can adapt to the changes of the state characteristics in real time. By collecting the grinding state characteristics and grinding process characteristics of the current step unit and performing correction processing, the grinding process parameter correction of the next step unit is realized.

[0067] The grinding state characteristics include wafer surface temperature characteristics, surface roughness characteristics and grinding current characteristics, and the acquisition method of the grinding state characteristics of the current step unit is as follows:

[0068] Step S301, for the wafer surface temperature characteristics, the temperature distribution of the region corresponding to each step unit is collected by an infrared temperature sensor array, a temperature gradient curve is generated, the local high temperature characteristics generated by friction in the rough grinding stage are extracted, and the temperature stability characteristics in the grinding process in the fine grinding stage are extracted.

[0069] Step S302, for the surface roughness characteristics, a laser profilometer is used to scan the wafer surface, and the surface roughness Ra value in the rough grinding stage and the surface roughness Rz value in the fine grinding stage are calculated.

[0070] Step S303, for the grinding current characteristics, 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 rough grinding stage reflects the removal resistance, and the current stability in the fine grinding stage reflects the uniformity of the grinding resistance.

[0071] The grinding process characteristics include the grinding wheel rotating speed, the axial feed pressure and the axial feed speed; the grinding wheel rotating 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 feed system of the grinding machine; and the axial feed speed is monitored in real time by the encoder or grating ruler of the grinding machine.

[0072] In the embodiment, by collecting data within a preset time before the end of the stepping unit, analysis time is reserved for process correction of the next stepping unit, avoiding the lag of data collected after the end of the stepping unit; for example, if local overheating is found in the temperature characteristics of a certain stepping unit in the rough grinding stage, the feed pressure of the next stepping unit can be reduced in advance to prevent thermal stress of the wafer due to high temperature; if a slight fluctuation occurs in the current characteristics in the fine grinding stage, the speed can be adjusted in time to avoid uneven grinding; different state characteristics are collected for different stages of rough grinding and fine grinding, such as the efficiency correlation of temperature and current in rough grinding, and the precision correlation of roughness and current in fine grinding, and the correlation analysis with process characteristics such as high feed pressure in rough grinding and low speed in fine grinding, so that the grinding process parameter adjustment is more targeted.

[0073] As a preferred embodiment of the above embodiment, the grinding process characteristics corresponding to the first stepping unit in the rough grinding stage are determined based on the initial particle size, wear state and other initial characteristics of the grinding wheel, and the initial thickness, initial stress distribution and other initial structural characteristics of the wafer, to adapt to the rapid removal requirement, specifically:

[0074] In step S311, a laser particle size analyzer is used to measure the particle size distribution of the grinding wheel, and a particle size distribution curve is obtained; a grinding wheel with a wider particle size distribution has stronger material removal capability and is suitable for rapid grinding; while a grinding wheel with a narrower particle size distribution can provide more uniform grinding effect;

[0075] In step S312, the initial wear state of the grinding wheel is observed by a laser scanning confocal microscope, the wear morphology and wear degree of the abrasive particles are analyzed, the average wear amount of the abrasive particles is estimated, and the initial wear state of the grinding wheel is evaluated; a grinding wheel with less wear has sharper abrasive particles and higher grinding efficiency; a grinding wheel with more wear needs to adjust the grinding parameters appropriately to ensure the grinding quality;

[0076] In step S313, a high-precision optical thickness gauge is used to measure the initial thickness of the wafer at multiple points, and the average value is taken as the initial thickness value of the wafer; the initial feed amount of the grinding wheel is determined according to the initial thickness of the wafer, to avoid excessive grinding or stress concentration due to excessive feed amount;

[0077] In step S314, the initial stress distribution of the wafer is detected by an X-ray diffractometer, the stress state of the wafer at different positions is analyzed, and the stress concentration area is determined; the speed and feed pressure of the grinding wheel are adjusted appropriately during grinding for the stress concentration area to avoid hidden cracks caused by excessive stress;

[0078] Step S315, according to the initial characteristics of the grinding wheel and the initial structural characteristics of the wafer, a grinding wheel speed optimization model is established; the model takes the maximum material removal rate and the minimum grinding stress as the objective function, and takes the abrasive grain size distribution, the wear state of the grinding wheel, the initial thickness of the wafer and the initial stress distribution as the constraint condition, and the grinding wheel speed is optimized and solved by genetic algorithm;

[0079] Step S316, considering 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 principle of grinding force balance, and the contact area between the grinding wheel and the wafer, the cutting force of the abrasive grain and the stress distribution of the wafer are used as the basis, the grinding effect under different axial feed pressures is calculated by finite element analysis method, and the optimal axial feed pressure is determined;

[0080] Step S317, according to the optimization results of the grinding wheel speed and the axial feed pressure, combining the initial thickness of the wafer and the abrasive wear characteristics of the grinding wheel, an axial feed speed planning model is established; the model takes the maximum grinding efficiency and the optimal grinding surface quality as the goal, and uses dynamic programming algorithm to optimize the axial feed speed, so as to realize efficient material removal under the premise of meeting the grinding quality requirements.

[0081] 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, and the real-time characteristics of the grinding wheel such as actual wear and particle size change after wear, which adapts to the demand of fine grinding, specifically:

[0082] Step S321, the surface flatness of the wafer after coarse grinding is detected with high precision by using an optical interferometer, and the micro-topography data of the wafer surface is obtained; according to the surface flatness detection result, the undulating condition and uneven degree of the wafer surface are analyzed, and the area needing to be grinded is determined;

[0083] Step S322, the residual stress distribution of the wafer after coarse grinding is measured by using deep X-ray diffraction technology, and the stress state of the wafer at different depth positions is obtained; the size and distribution law of the residual stress are analyzed, and the internal stress condition of the wafer generated in the coarse grinding process is evaluated;

[0084] Step S323, the mass loss of the grinding wheel after coarse grinding is measured by weight method, the actual wear of the grinding wheel is calculated by combining the density and volume change of the grinding wheel, and the wear state of the grinding wheel is evaluated by observing the wear morphology of the grinding wheel by using laser scanning confocal microscope and analyzing the wear degree and shedding of abrasive grains;

[0085] Step S324, the particle size distribution of the abrasive grains of the grinding wheel after the coarse grinding is measured again by using the laser particle size analyzer, and compared with the initial particle size distribution of the grinding wheel to determine the particle size change after the wear; according to the particle size change, the cutting ability and the change of the grinding performance of the grinding wheel are evaluated;

[0086] Step S325, based on the real-time structural characteristics of the wafer such as the surface flatness and the residual stress distribution, and the real-time characteristics of the grinding wheel such as the actual wear amount and the particle size change after the wear, a grinding wheel speed optimization model for the fine grinding stage is established; the model takes the minimization of the grinding surface roughness and the residual stress as the objective function, and simultaneously considers the cutting ability of the grinding wheel and the wafer characteristics, and the grinding wheel speed is optimized and solved by using the particle swarm optimization algorithm;

[0087] Step S326, considering 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 takes the force balance of the wafer and the minimization of the grinding damage as the principle during the grinding process, and the grinding effect and the wafer stress distribution under different axial feed pressures are calculated by using the mechanical analysis and numerical simulation method, and the optimal axial feed pressure is determined;

[0088] According to the surface flatness and the residual stress distribution of the wafer, and the real-time characteristics of the grinding wheel and the grinding process requirements, an axial feed speed planning model is established; the model takes the realization of high-precision grinding and the avoidance of wafer brittle fracture as the target, and the fuzzy control algorithm is used to dynamically adjust the axial feed speed, so as to ensure that the unevenness and stress remaining after the coarse grinding can be effectively removed in the fine grinding process, and the integrity and surface quality of the wafer can be ensured.

[0089] In the embodiment, by analyzing the initial and real-time characteristics of the grinding wheel and the wafer, the grinding process characteristics of the coarse grinding and the fine grinding stages are determined, which can match the actual needs of the grinding process, and improve the grinding precision and stability; in the coarse 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 the accurate control of the final thickness of the wafer and the optimization of the surface quality; according to the initial stress distribution of the wafer and the residual stress distribution after the coarse grinding, the grinding process parameters are reasonably adjusted to avoid hidden cracks caused by stress concentration; at the same time, in the fine grinding stage, the axial feed pressure and the grinding wheel speed are accurately controlled to reduce the grinding damage of the wafer, further reduce the risk of hidden cracks, and improve the yield of the wafer.

[0090] In some embodiments of the present application, the rough grinding stage needs to control wafer stress accumulation while efficiently reducing thickness, and the fine grinding stage needs to avoid brittle fracture while ensuring accuracy; if the unified correction logic is used, it will lead to a decrease in efficiency in the rough grinding stage due to excessive pursuit of stress release, or neglect of wafer damage in the fine grinding stage due to emphasis on efficiency; therefore, differentiated correction logic needs to be designed for the two stages to adapt to the state changes in real time, avoiding the lack of adaptability caused by a single correction rule.

[0091] Specifically, the method for process correction in the rough grinding stage includes:

[0092] For axial feed pressure correction, the axial feed pressure correction amount of the next step unit is determined based on the axial feed pressure reference value of the current step unit, the temperature characteristic parameter, the current characteristic parameter, and the roughness characteristic parameter; the specific calculation formula is:

[0093] ;

[0094] Wherein, P1 represents the axial feed pressure correction amount of the next step unit, a positive value means increasing, and a negative value means decreasing;

[0095] P 01 represents the axial feed pressure reference value of the current step unit;

[0096] k t,p represents the influence coefficient of temperature on feed pressure, for example, the value is-0.3~-0.1, the negative sign means that the pressure needs to be reduced when the temperature rises, and reducing the pressure avoids excessive cutting;

[0097] T i represents the highest temperature actually measured by the current step unit; T o represents the wafer safe grinding temperature threshold;

[0098] k i,p represents the influence coefficient of current on feed pressure, for example, the value is-0.2~-0.05, the negative sign means that the pressure needs to be reduced when the current rises, and the current reflects the cutting resistance, so the pressure is reduced to reduce the stress when the resistance is large;

[0099] I i represents the current peak value of the current step unit; I o represents the current reference value, which adopts the set value of the initial step unit;

[0100] k r,p represents the influence coefficient of roughness on feed pressure, for example, the value is 0.1~0.2, the positive value means that the pressure needs to be increased when the roughness exceeds the limit, and the cutting force is improved to improve the flatness;

[0101] Ra i represents the wafer surface roughness Ra value of the current step unit; Rao represents the target value of wafer surface roughness.

[0102] For the speed correction of the grinding wheel, the speed correction amount of the next step unit is determined based on the speed reference value of the current step unit, the roughness characteristic parameter and the current characteristic parameter; the specific calculation formula is:

[0103] ;

[0104] wherein N1 represents the speed correction amount of the next step unit;

[0105] N 01 represents the speed reference value of the current step unit;

[0106] k r,N represents the influence coefficient of roughness on the speed of the grinding wheel, for example, the value is 0.05~0.1, and the positive value means to increase the speed when the roughness is out of limit, and to enhance the cutting uniformity;

[0107] k i,N represents the influence coefficient of current on the speed of the grinding wheel, for example, the value is 0.03~0.08, and the positive value means to increase the speed when the current is too low, and to compensate the insufficient cutting force.

[0108] For the speed correction of the axial feed, the speed correction amount of the next step unit is determined based on the speed reference value of the current step unit, the temperature characteristic parameter and the roughness characteristic parameter; the specific calculation formula is:

[0109] ;

[0110] wherein V1 represents the speed correction amount of the next step unit, and the positive value means to increase, and the negative value means to decrease;

[0111] V 01 represents the speed reference value of the current step unit;

[0112] k t,v represents the influence coefficient of temperature on the speed of the axial feed, for example, the value is 0.1~0.2, and the positive value means to increase the speed when the temperature is lower than the threshold value;

[0113] k r,v represents the influence coefficient of roughness on the speed of the axial feed, for example, the value is -0.15~-0.05, and the negative sign means to decrease the speed when the roughness is out of limit, and to improve the surface quality by prolonging the grinding time.

[0114] On the other hand, the method for process correction in the fine grinding stage comprises:

[0115] For the axial feed pressure correction, the axial feed pressure correction amount of the next stepping unit is determined based on the axial feed pressure reference value of the current stepping unit, the roughness characteristic parameter, the current stability characteristic parameter and the temperature fluctuation characteristic parameter; the specific calculation is as follows:

[0116] ;

[0117] Wherein, P2 represents the axial feed pressure correction amount of the next stepping unit;

[0118] P 02 represents the axial feed pressure reference value of the current stepping unit;

[0119] k rz,p represents the influence coefficient of roughness on axial feed pressure, the value is-0.4~ -0.2, the negative sign represents reducing the pressure when Rz exceeds the limit, avoiding wafer brittle damage;

[0120] Rz i represents the roughness Rz value of the current stepping unit; Rz0 represents the Rz target value;

[0121] k i,s represents the influence coefficient of current stability on axial feed pressure, for example, the value is-0.3~ -0.1, the negative sign represents reducing the pressure when the current fluctuates greatly, reducing uneven grinding;

[0122] S i represents the current standard deviation of the stepping unit, which is used to reflect the fluctuation degree of the current; S0 represents the current stability threshold;

[0123] k t' represents the influence coefficient of temperature fluctuation on axial feed pressure, the value is-0.2~ -0.1, the negative sign represents reducing the pressure when the temperature fluctuation exceeds the limit, relieving stress concentration;

[0124] ΔT i represents the maximum temperature fluctuation value of the current stepping unit; ΔT0 represents the temperature stability threshold.

[0125] For the grinding wheel speed correction, the speed correction amount of the next stepping unit is determined based on the speed reference value of the current stepping unit, the thickness characteristic parameter and the roughness characteristic parameter; the specific calculation is as follows:

[0126] ;

[0127] Wherein, N2 represents the speed correction amount of the next stepping unit;

[0128] N 02 represents the speed reference value of the current stepping unit;

[0129] k hh0 is the target thickness, h i h is the current thickness, ensuring the final accuracy;

[0130] k rz' k is the influence coefficient of roughness on the rotation speed of the grinding wheel, for example, the value is -0.2~ -0.1, the negative sign indicates that the rotation speed is reduced when Rz exceeds the limit, and the wafer tearing is reduced.

[0131] For the axial feed speed correction, the axial feed speed correction amount of the next step unit is determined based on the axial feed speed reference value of the current step unit, the thickness characteristic parameter, the current smoothness characteristic parameter and the roughness characteristic parameter; The specific calculation is as follows:

[0132] ;

[0133] V2 represents the axial feed speed correction amount of the next step unit;

[0134] V 02 V represents the axial feed speed reference value of the current step unit;

[0135] k h,v k is the influence coefficient of thickness on the axial feed speed, for example, the value is -0.4~ -0.2, the negative sign indicates that the speed is reduced when approaching the target thickness, and the final size accuracy is ensured;

[0136] k s,v k is the influence coefficient of current smoothness on the axial feed speed, for example, the value is 0.05~0.1, the positive value indicates that the speed can be increased when the current fluctuates, and the grinding stability is used to improve the efficiency;

[0137] k rz,v k is the influence coefficient of roughness on the axial feed speed, for example, the value is -0.2~ -0.1, the negative sign indicates that the speed is reduced when Rz exceeds the limit, and the wafer surface tearing is reduced.

[0138] It should be noted that the coefficients in the above formula are determined based on the grinding stage characteristics, the physical and mechanical properties of the material to be ground, and the process target, by correlating the influence law of the grinding state characteristics and the process characteristics; Specifically, the influence degree and direction of different state characteristics such as temperature, current, roughness, and thickness on process characteristics such as feed pressure, rotation speed, and feed speed can be quantified through experimental data fitting, simulation analysis, process experience accumulation, or machine learning, etc. Form a coefficient interval suitable for the corresponding stage; Among them, the positive and negative of the coefficient reflect the direction of influence, for example, the coefficient is negative when the temperature rises and the pressure needs to be reduced, the coefficient is positive when the roughness is out of tolerance and the rotation speed needs to be increased, and the value range of the coefficient is dynamically adjusted according to the difference of material characteristics, process parameter sensitivity and target control accuracy, to ensure that the correction logic is adapted to the stage requirements, material properties and process targets.

[0139] In this embodiment, the coarse grinding correction takes efficiency priority and controllable stress as the principle, through the coordinated parameters of temperature, current and roughness, to avoid excessive cutting or stress accumulation while quickly removing the main thickness of the wafer; The precision priority and minimum damage principle is adopted in the fine grinding correction, and parameters such as thickness characteristics and current smoothness are introduced to adapt to the characteristics of high wafer brittleness and avoid hidden cracks or surface tearing; The coarse grinding axial feed pressure correction is related to temperature, current and roughness to avoid single parameter misjudgment; The fine grinding axial feed speed correction integrates thickness, current smoothness and roughness to ensure that even if the current is smooth, the speed will be reduced due to the thickness characteristics when the target thickness is approached, and the final size accuracy is ensured.

[0140] As shown in Figure 2 The present application also provides a grinding control system suitable for ultra-thin wafer thinning, which specifically comprises the following modules:

[0141] A stage division module is used to divide the thinning process into a coarse grinding stage and a fine grinding stage based on the initial thickness of the wafer and the target thickness of the wafer, and to determine the stage thinning thickness corresponding to the coarse grinding stage and the fine grinding stage;

[0142] A step unit division module is used to divide the coarse grinding stage and the fine grinding stage into multiple step units based on the stage thinning thickness;

[0143] A parameter acquisition module is used to acquire the grinding state characteristics and grinding process characteristics of each step unit within a preset time before the end of the step unit;

[0144] A process correction module is used to correct the grinding process characteristics based on the grinding state characteristics, to obtain the grinding process characteristics corresponding to the next step unit, and to control the grinding operation of the next step unit.

[0145] In the embodiment, the process is first divided into coarse grinding and fine grinding stages and the corresponding thinning thicknesses are determined by the stage division module, and then the step units division module further splits out step units in each stage, so that the control granularity is lowered from the stage level to the unit level, so that the system can capture more subtle state changes in the wafer thinning process, provide more detailed control nodes for precise adjustment, and avoid the problem that the traditional simple segmentation cannot respond to subtle state differences; the parameter acquisition module collects the 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 the problems of stress accumulation, precision out-of-tolerance and the like caused by the mismatch between the traditional experience preset parameters and the actual state; through the continuous division of step units and the dynamic correction of parameters, the process parameters of the coarse grinding stage can be adjusted gradually according to the wafer state, avoiding excessive stress accumulation, eliminating the process faults and stress superposition caused by the traditional independent setting of stages, and reducing the risk of hidden cracks as a whole, and ensuring the precision control in the fine grinding stage.

[0146] The basic principles, main features and advantages of the present application are shown and described above. It should be understood by those skilled in the art that the present application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method of polishing control suitable for ultra-thin wafer thinning, characterized by, The method comprises the following steps: Based on the wafer initial thickness and the wafer target thickness, the thinning process is divided into a coarse grinding stage and a fine grinding stage, and the corresponding stage thinning thicknesses of the coarse grinding stage and the fine grinding stage are determined; Based on the stage thinning thicknesses, the coarse grinding stage and the fine grinding stage are respectively step-divided to obtain a plurality of step units; Within a preset time before the end of each step unit, the grinding state characteristics and the grinding process characteristics of the step unit are obtained; Based on the grinding state characteristics, the grinding process characteristics are corrected to obtain the grinding process characteristics corresponding to the next step unit, and the grinding operation of the next step unit is controlled; 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 method for step-dividing the coarse grinding stage comprises the following steps: Based on the thinning thickness of the coarse grinding stage, a coarse grinding risk coefficient is calculated; Based on the coarse grinding risk coefficient, a coarse grinding step interval is determined; Based on the coarse grinding step interval, the coarse grinding stage is step-divided; The method for step-dividing the fine grinding stage comprises the following steps: Based on a material mechanics model, the relative rigidity values of the wafer at different thicknesses are calculated; Based on a preset rigidity drop rate threshold and the thinning thickness of the fine grinding stage, the fine grinding stage is divided to ensure that the rigidity drop rate in each step unit in the fine grinding stage is within the preset rigidity drop rate threshold range.

2. The polishing control method for ultra-thin wafer thinning according to claim 1, wherein 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 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 coarse grinding stage ends.

3. The method of claim 1, wherein the method is applied to ultra-thin wafer thinning. The method for dividing the thinning process into a coarse grinding stage and a fine grinding stage comprises the following steps: Based on the wafer target thickness and the wafer initial thickness, the thinning process is divided into a coarse grinding stage and a fine grinding stage with stress buffering and precision redundancy as constraints, and the corresponding thinning thicknesses of each stage are determined.

4. The method of claim 1, wherein the method is applied to ultra-thin wafer thinning. The wafer surface temperature characteristics are collected by an infrared temperature sensor array; local high-temperature characteristics are extracted in the coarse grinding stage, and temperature stability characteristics are extracted in the fine grinding stage; The grinding current characteristics are collected by a current sensor; current peak value characteristics are extracted in the coarse grinding stage, and current smoothness characteristics are extracted in the fine grinding stage.

5. The polishing control method for ultra-thin wafer thinning according to claim 4, wherein The process correction of the coarse grinding stage comprises the following steps: The axial feed pressure correction amount of the next step unit is determined based on the axial feed pressure reference value, the temperature characteristic parameter, the current characteristic parameter, and the roughness characteristic parameter of the current step unit; The rotation speed correction amount of the next step unit is determined based on the rotation speed reference value, the roughness characteristic parameter, and the current characteristic parameter of the current step unit; The axial feed speed correction amount of the next step unit is determined based on the axial feed speed reference value, the temperature characteristic parameter, and the roughness characteristic parameter of the current step unit.

6. The polishing control method for ultra-thin wafer thinning according to claim 4, wherein The process correction of the fine grinding stage comprises the following steps: The axial feeding pressure correction amount of the next step unit is determined based on the axial feeding pressure reference value of the current step unit, the roughness characteristic parameter, the current stability characteristic parameter and the temperature fluctuation characteristic parameter; The rotation speed correction amount of the next step unit is determined based on the rotation speed reference value of the current step unit, the thickness characteristic parameter and the roughness characteristic parameter; The axial feeding speed correction amount of the next step unit is determined based on the axial feeding speed reference value of the current step unit, the thickness characteristic parameter, the current stability characteristic parameter and the roughness characteristic parameter.

7. A polishing control system suitable for ultra-thin wafer thinning, the system being applied to the polishing control method suitable for ultra-thin wafer thinning according to claim 1, characterized by, The system comprises: The stage division module is configured to divide the thinning process into a coarse grinding stage and a fine grinding stage based on the wafer initial thickness and the wafer target thickness, and determine stage thinning thicknesses corresponding to the coarse grinding stage and the fine grinding stage; The step unit division module is configured to perform step division on the coarse grinding stage and the fine grinding stage respectively based on the stage thinning thicknesses, and obtain a plurality of step units; The parameter acquisition module is configured to acquire the grinding state characteristic and the grinding process characteristic of each step unit within a preset time before the end of the step unit; The process correction module is configured to perform process correction on the grinding process characteristic based on the grinding state characteristic, obtain grinding process characteristics corresponding to the next step unit, and control the grinding operation of the next step unit based on the grinding process characteristics.

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