Wafer thinning equipment and thinning methods

Abstract

This invention provides wafer thinning equipment and a thinning method. The wafer thinning method includes: determining the amount of grinding water used for thinning based on the passivation degree of the grinding wheel and / or the shear force in the through-silicon via (TSV) region, to reduce thermal damage in the TSV region and reduce the overall usage of grinding water for thinning; wherein the passivation degree is characterized by the rate of change of the total grinding force of the grinding wheel, and the shear force in the TSV region is characterized by the rate of change of the grinding force in the horizontal direction of the grinding wheel; the grinding water includes two independent streams for cooling the wafer and for cooling the grinding wheel. The wafer thinning equipment and method provided by this invention can reduce thermal damage in the TSV region, reduce surface damage to the thinned wafer, improve the surface quality of the thinned wafer, increase wafer yield, reduce the overall usage of grinding water for thinning, and reduce equipment operating costs.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor equipment, in particular to a wafer thinning equipment and a thinning method. BACKGROUND

[0002] Three-dimensional integrated circuit (3D IC) is an important technical path for the semiconductor industry to continue Moore's law and improve chip performance and integration. The core idea is to stack multiple chips or functional layers in the vertical direction, and realize electrical connection between layers through Through-Silicon Via (TSV) interconnection technology, so as to realize higher functional density in limited space.

[0003] Wafer thinning is a key supporting process in 3D IC manufacturing, and its main purpose is to thin the wafer from the original thickness to a super-thin state suitable for vertical integration. The super-thin wafer is the physical basis for realizing three-dimensional stacking, and is crucial for optimizing electrical performance and thermal management. With the increase of the number of 3D IC stacking layers, the requirement for the thinning thickness of a single wafer is increasingly stringent. At the same time, 3D IC puts forward very high requirements on the surface quality of the thinned wafer, including excellent Total Thickness Variation (TTV) and extremely low Roughness Average (Ra), to ensure the accuracy, consistency and stability of the subsequent bonding process.

[0004] To achieve the above thinning target, the wafer thinning equipment usually uses the physical grinding action of the grinding wheel to process the super-thin wafer. Such equipment must precisely design and control its grinding structure and grinding process, so as to meet the requirements of super-thin wafer processing (such as thickness ≤10μm, TTV ≤1.5μm and Ra ≤5nm), while taking into account the manufacturing cost and production efficiency.

[0005] In the prior art, the thinning process uses fixed water quantity for cooling. For wafers with heterogeneous materials in 3D IC technology (such as wafers for Cu / SiO2 hybrid bonding), when grinding the copper pillars in the TSV area of the wafer, the grinding dust is difficult to discharge due to structural limitations, and the grinding dust is easy to adhere and block the air holes of the grinding wheel, thereby rapidly passivating the grinding wheel, reducing the effective cutting action, and rapidly increasing the grinding heat, resulting in thermal damage due to heat accumulation in the TSV area, and deepening of the damage layer on the wafer surface as a whole, and significantly increasing the wafer surface roughness. Fixed water quantity cannot effectively inhibit wafer thermal damage and maintain stable wafer thinning process. Therefore, precisely controlling the grinding water quantity in the wafer thinning process to reduce the thermal stress of heterogeneous material thinning is a key to further improve the precision and quality of wafer thinning. SUMMARY

[0006] In view of the problems in the prior art, the embodiments of the present application provide a wafer thinning device and a thinning method, which can at least partially solve or alleviate the problems in the prior art.

[0007] In a first aspect, the present application provides a wafer thinning method, comprising:

[0008] The amount of grinding water used for thinning is determined according to the passivation degree of the grinding wheel and / or the shear force condition of the through silicon via area, so as to reduce thermal damage of the through silicon via area and reduce the overall use amount of the grinding water used for thinning; wherein the passivation degree is represented by the change rate of the total grinding force of the grinding wheel, and the shear force condition of the through silicon via area is represented by the change rate of the horizontal grinding force of the grinding wheel;

[0009] The grinding water includes two independent grinding waters for cooling the wafer and for cooling the grinding wheel.

[0010] On the basis of the above-mentioned embodiments, further, before determining the amount of grinding water used for thinning according to the passivation degree of the grinding wheel and / or the shear force condition of the through silicon via area, the wafer thinning method provided by the embodiments of the present application further comprises:

[0011] The horizontal grinding force and the normal grinding force of the grinding wheel are collected, and the total grinding force of the grinding wheel is calculated.

[0012] On the basis of the above-mentioned embodiments, further, the wafer thinning method provided by the embodiments of the present application further comprises:

[0013] The grinding water is provided to the wafer and the grinding wheel respectively.

[0014] Further, determining the amount of grinding water used for thinning according to the passivation degree of the grinding wheel comprises:

[0015] If the change rate of the total grinding force of the grinding wheel is greater than a first threshold value, it is determined that the grinding wheel is passivated, and the use amount of the two independent grinding waters for cooling the wafer and for cooling the grinding wheel is increased by a first water amount mode, so as to enhance cooling.

[0016] Further, determining the amount of grinding water used for thinning according to the shear force condition of the through silicon via area of the grinding wheel comprises:

[0017] If the change rate of the horizontal grinding force of the grinding wheel is greater than a second threshold value, it is determined that the shear force of the through silicon via area causes thermal damage of the through silicon via area, and the use amount of the two independent grinding waters for cooling the wafer and for cooling the grinding wheel is increased by a first water amount mode, so as to enhance cooling.

[0018] Further, the first water amount mode comprises:

[0019] The usage of grinding water for cooling the wafer is increased to a first range, and the usage of grinding water for cooling the grinding wheel is increased to a second range, wherein the first range and the second range are determined based on a regular water amount.

[0020] Further, in the first water amount mode, the increase range of the usage of grinding water for cooling the grinding wheel is smaller than the increase range of the usage of grinding water for cooling the wafer, so as to prevent the water flow fluctuation of the grinding water from inducing the vibration of the grinding wheel.

[0021] Further, the wafer thinning method provided by the embodiment of the present application further comprises:

[0022] If the change rate of the total grinding force of the grinding wheel is less than a third threshold value and lasts for a first preset time length, the first water amount mode is exited, and the usage of two independent grinding waters for cooling the wafer and the grinding wheel is reduced through a second water amount mode, so as to maintain the basic cooling of the wafer and the grinding wheel and reduce the hydraulic vibration and the temperature fluctuation.

[0023] Further, the wafer thinning method provided by the embodiment of the present application further comprises:

[0024] If the change rate of the horizontal direction grinding force is less than a fourth threshold value and lasts for a second preset time length, the usage of two independent grinding waters for cooling the wafer and the grinding wheel is adjusted through a third water amount mode, so as to reduce the hydraulic vibration and the temperature fluctuation.

[0025] Further, the second water amount mode comprises:

[0026] The usage of grinding water for cooling the wafer is reduced to a first water amount, and the usage of grinding water for cooling the grinding wheel is adjusted to a second water amount, wherein the first water amount and the second water amount are determined based on a regular water amount.

[0027] Further, the amount of grinding water for thinning is determined according to the passivation degree of the grinding wheel, and the passivation degree of the grinding wheel comprises:

[0028] If the change rate of the total grinding force of the grinding wheel is less than a fifth threshold value, the usage of two independent grinding waters for cooling the wafer and the grinding wheel is reduced through a fourth water amount mode, so as to suppress the hydraulic vibration and maintain the thermal stability of the grinding spindle.

[0029] Further, the wafer thinning method provided by the embodiment of the present application further comprises:

[0030] If the change rate of the total grinding force of the grinding wheel is greater than or equal to the fifth threshold value, the fourth water amount mode is exited, and the usage of two independent grinding waters for cooling the wafer and the grinding wheel is adjusted through a third water amount mode, so as to avoid the thermal accumulation.

[0031] Further, the fourth water amount mode comprises:

[0032] reducing the usage amount of the grinding water for cooling the wafer to a third range; and reducing the usage amount of the grinding water for cooling the grinding wheel to a fourth range; wherein the third range and the fourth range are determined based on the regular water amount.

[0033] Further, determining the amount of the grinding water for thinning according to the dullness degree of the grinding wheel comprises:

[0034] if the change rate of the total grinding force of the grinding wheel is greater than or equal to a fifth threshold value and less than or equal to a sixth threshold value, adjusting the usage amount of the two independent grinding waters for cooling the wafer and for cooling the grinding wheel by a third water amount mode to balance the cooling of the wafer and the stability of the grinding performance.

[0035] Further, the third water amount mode comprises:

[0036] adjusting the usage amount of the grinding water for cooling the wafer according to the change rate of the total grinding force of the grinding wheel being within a fifth range; and adjusting the usage amount of the grinding water for cooling the grinding wheel according to the change rate of the total grinding force of the grinding wheel being within a sixth range; wherein the fifth range and the sixth range are determined based on the regular water amount.

[0037] In a second aspect, the present application provides a wafer thinning apparatus for performing the wafer thinning method according to any one of the above embodiments, comprising:

[0038] a worktable, on which a plurality of chuck turntables are arranged, the worktable being configured to rotate around a vertical central axis thereof to drive the plurality of chuck turntables to rotate as a whole so as to switch the chuck turntables between different stations, the chuck turntables being used to hold and rotate the wafer;

[0039] a grinding device, comprising a grinding wheel arranged at a lower portion thereof, and configured to grind the wafer by the grinding wheel to thin the wafer;

[0040] a detection device, configured to obtain the grinding force of the grinding wheel in the horizontal direction and the grinding force of the grinding wheel in the normal direction during the wafer thinning process;

[0041] a control apparatus, configured to determine the change rate of the total grinding force of the grinding wheel based on the grinding force of the grinding wheel in the horizontal direction and the grinding force of the grinding wheel in the normal direction during the wafer thinning process, and determine the amount of the grinding water for thinning based on the grinding force of the grinding wheel in the horizontal direction during the wafer thinning process.

[0042] Further, the detection device comprises a three-axis force ring sensor arranged on the worktable to detect the reaction force of the grinding force of the worktable in the horizontal direction and the reaction force of the grinding force of the worktable in the normal direction.

[0043] The wafer thinning device and the wafer thinning method provided by the embodiment of the present application can determine the amount of grinding water used for thinning according to the dullness degree of the grinding wheel and / or the shear force condition of the through silicon via area, so as to reduce the overall usage amount of the grinding water used for thinning; wherein the dullness degree is characterized by the change rate of the total grinding force of the grinding wheel, and the shear force condition of the through silicon via area is characterized by the change rate of the grinding force in the horizontal direction of the grinding wheel; the grinding water includes two independent grinding water used for cooling the wafer and the grinding wheel, so as to reduce the thermal damage of the through silicon via area; since the amount of the grinding water used for thinning is adjusted according to the dullness degree of the grinding wheel and / or the shear force condition of the through silicon via area, the cooling of the wafer and the grinding wheel is respectively performed by the two independent grinding water, so as to reduce the thermal damage of the through silicon via area, reduce the surface damage of the thinned wafer, improve the surface quality of the thinned wafer, improve the wafer yield, reduce the overall usage amount of the grinding water used for thinning, and reduce the operation cost of the device. BRIEF DESCRIPTION OF DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description only show some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort. In the drawings:

[0045] Figure 1 FIG. 1 is a structural schematic diagram of a wafer thinning device provided by an embodiment of the present application.

[0046] Figure 2 FIG. 2 is a schematic diagram of providing grinding water in a wafer thinning process provided by an embodiment of the present application.

[0047] Figure 3 FIG. 3 is an installation position schematic diagram of a detection device provided by an embodiment of the present application.

[0048] Figure 4 FIG. 4 is an installation position schematic diagram of a detection device provided by another embodiment of the present application.

[0049] Figure 5 FIG. 5 is a schematic diagram of multi-point measurement of a three-axis force ring sensor provided by an embodiment of the present application.

[0050] Figure 6 FIG. 6 is a flow schematic diagram of a wafer thinning method provided by an embodiment of the present application.

[0051] Figure 7 FIG. 7 is a schematic diagram of the processing surface of a copper pillar in a TSV area of a thinned wafer according to a conventional scheme provided by an embodiment of the present application.

[0052] Figure 8 This is a schematic diagram of the copper pillar processing surface of the TSV region after wafer thinning according to an embodiment of the present invention.

[0053] Figure 9 This is a schematic diagram comparing the Ra of a traditional solution provided in an embodiment of the present invention with that of the solution in this application after wafer thinning.

[0054] Figure 10 This is a schematic diagram comparing the copper ion concentration after wafer thinning in a conventional scheme provided by an embodiment of the present invention with that of the scheme in this application. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. The acquisition, storage, use, and processing of data in the technical solutions of this application all comply with the relevant provisions of laws and regulations. The user information in the embodiments of this application is obtained through legal and compliant means, and the acquisition, storage, use, and processing of user information have been agreed upon by the customer.

[0056] To facilitate understanding of the technical solution provided in this application, the relevant content of the technical solution in this application will be explained below.

[0057] As a cutting-edge technology in the packaging field, hybrid bonding has been widely used in high-end 3D integrated circuits (i.e., 3D ICs, such as high-bandwidth memory HBM stacked structures) and wafer-to-wafer (W2W) bonding scenarios. This technology places stringent requirements on process precision; the surface roughness of the bonding interface should be less than or equal to 0.5 nm. This indicator dictates that the control precision in the thinning process must reach an extremely high level to achieve high-precision thinning processing.

[0058] Meanwhile, in the TSV region, the significant differences in grinding force between the constituent materials lead to differences in the grinding thermal field: copper (Cu) has high thermal conductivity, while silicon dioxide (Cu / SiO2) is a typical high-hardness insulating material. This causes nonlinear changes in grinding force and heat accumulation effects to easily occur in the TSV region during thinning. Under the same grinding process parameters, the temperature of the Cu material region in the TSV region is significantly higher than that of the silicon substrate region. This local temperature imbalance makes it difficult to meet the system-level heat dissipation requirements of advanced packaging, further highlighting the necessity of heat dissipation through hybrid bonding technology.

[0059] In the wafer thinning process, it is difficult to discharge the grinding dust during the grinding of the TSV area, and it is easy to form blockage and adhesion, so that the grinding wheel is rapidly passivated in a short time. During the wafer thinning process, the grinding wheel surface will gradually be passivated as the grinding proceeds. The passivation of the grinding wheel is specifically manifested as that the cutting edges of the abrasive grains are worn, broken or blunt, resulting in the weakening of the effective cutting ability of the wafer. Due to the decrease of the effective cutting effect, the abrasive grains cannot efficiently remove the wafer surface material, and the grinding dust is difficult to be smoothly discharged through the air hole channel of the grinding wheel surface, and then the grinding dust is accumulated in the air hole of the grinding wheel and on the surface of the grinding wheel, causing the air hole blockage problem to be aggravated. The blockage of the grinding wheel air hole will further worsen the grinding area discharge condition and the heat dissipation environment, on the one hand, the friction resistance between the abrasive grains and the wafer and the grinding dust is increased, resulting in a significant increase in the grinding force; on the other hand, the heat generated by friction cannot be dissipated in time, so that the heat in the grinding area continuously accumulates, and finally the grinding heat is increased. The increase of the grinding heat will cause the heat accumulation in the TSV area, and then the thermal damage of the TSV area occurs. The passivation of the grinding wheel will also cause the damage layer of the wafer surface to be deepened, so that the surface roughness (Ra) of the wafer is significantly increased.

[0060] In the prior art, the thinning process uses fixed water amount for cooling, and cannot accurately control the grinding water amount according to the demand. In the 3D IC scene, the thermal stress protection of the TSV heterogeneous interface cannot be realized, the fixed water amount during coarse grinding is easy to induce the copper column micro-vibration fatigue of the TSV area, the fixed water amount during fine grinding cannot cope with the local high temperature of the TSV area. Also, the damage layer depth of the ultra-thin wafer cannot be controlled, the damage layer thickness caused by the wafer thinning will be greater than 2.5 μm by using the fixed water amount, but for the ultra-thin wafer, it cannot bear the above loss. In addition, the fixed water amount cannot effectively inhibit the grinding wheel blockage, which will further aggravate the damage layer depth of the wafer surface. Therefore, in the development of 3D IC technology, the control of the thermal stress of the heterogeneous material thinning and the accurate control of the thinning water amount become the key bottleneck restricting the further development.

[0061] In view of the above problems, the present application provides a wafer thinning device and a thinning method, which are used for thinning the bonded wafer of 3D IC, and the amount of grinding water used for thinning is regulated and controlled. The grinding wheel passivation state and / or the shear force condition of the through silicon via area can be dynamically identified based on the grinding force change rate. Through independent control of the two water paths for cooling the wafer and for cooling the grinding wheel, the water amount mode can be automatically switched, the thermal damage of the heterogeneous TSV area in the 3D IC can be accurately protected, and the wafer surface quality can be improved, and the process adaptability of multiple materials or structures can be improved.

[0062] Figure 1 is a structural schematic diagram of a wafer thinning device provided by an embodiment of the present application, as Figure 1 shown, the wafer thinning device provided by the embodiment of the present application comprises:

[0063] A worktable 1 is provided with a plurality of chuck turntables 11, and the worktable 1 is configured to rotate around a vertical central axis thereof to drive the plurality of chuck turntables 11 to rotate as a whole so as to switch the chuck turntables 11 between different stations, and the chuck turntables 11 are used to hold wafers and drive the wafers to rotate;

[0064] A grinding device 2 is provided with a grinding wheel 3 at a lower portion thereof, and the grinding wheel 3 is used to grind the wafer to thin the wafer;

[0065] A detection device (not shown in the figure) is used to collect the grinding force of the grinding wheel 3 in the horizontal direction and the grinding force of the grinding wheel 3 in the normal direction during the wafer thinning process;

[0066] A control device (not shown in the figure) is used to determine the change rate of the total grinding force of the grinding wheel based on the grinding force of the grinding wheel in the horizontal direction and the grinding force of the grinding wheel in the normal direction during the wafer thinning process, determine the change rate of the grinding force of the grinding wheel in the horizontal direction based on the grinding force of the grinding wheel in the horizontal direction during the wafer thinning process, and determine the amount of grinding water used for thinning.

[0067] The grinding device 2 is provided with a grinding wheel 3 at a lower portion thereof, and the grinding wheel 3 is used to grind the wafer to thin the wafer. The grinding process is to press the grinding wheel against the surface of the wafer and rotate to grind off a certain thickness. The grinding wheel 3 generates grinding heat during the wafer thinning process, and needs to be cooled by grinding water. As shown in Figure 2 During the process of grinding the wafer 5 by the grinding wheel 3, the grinding water is continuously injected into the grinding area through the water channel 4 for cooling the wafer and the water channel 6 for cooling the grinding wheel, so as to carry away the heat generated by grinding and wash away the debris generated by grinding.

[0068] A detection device is used to obtain the grinding force of the grinding wheel 3 in the horizontal direction and the grinding force of the grinding wheel 3 in the normal direction during the wafer thinning process, as shown in Figure 5 The horizontal direction can include X and Y directions, and the X and Y directions are perpendicular to each other, and the normal direction can be represented as the Z direction which is perpendicular to the horizontal direction. The detection device is arranged below the chuck turntable 11, and accurately collects the grinding force of the grinding wheel in the horizontal direction and the grinding force of the grinding wheel in the normal direction. Since the wafer is vacuum adsorbed on the chuck turntable 11, the chuck turntable 11 is fixed relative to the adsorption, and thus the collected grinding force of the chuck turntable 11 is equivalent to the grinding force received by the wafer.

[0069] The control device can determine the change rate of the total grinding force of the grinding wheel according to the horizontal direction grinding force and the normal direction grinding force of the grinding wheel in the wafer thinning process. The control device can also determine the change rate of the horizontal direction grinding force of the grinding wheel according to the horizontal direction grinding force of the grinding wheel in the wafer thinning process. The control device can perform the wafer thinning method provided by the embodiments of the present application to determine the amount of grinding water used for thinning. The grinding water includes two independent grinding water used for cooling the wafer and used for cooling the grinding wheel. After determining the amount of grinding water used for thinning, the amount of grinding water used for cooling the wafer and the amount of grinding water used for cooling the grinding wheel can be adjusted respectively through the flow adjustment valves of the two independent grinding water.

[0070] The wafer thinning device provided by the embodiments of the present application can dynamically identify the change state of the grinding wheel and the thermal damage state of the wafer in real time through the change rate of the grinding force, and adjust the amount of the two independent grinding water used for cooling the wafer and used for cooling the grinding wheel, so as to reduce the thermal damage of the through silicon via area, reduce the surface damage of the thinned wafer, improve the surface quality of the thinned wafer, improve the wafer yield, and reduce the overall use amount of the grinding water used for thinning, and reduce the operation cost of the device.

[0071] As shown in Figure 3 and 4 On the basis of the above embodiments, further, the detection device includes a three-axis ring sensor 7 arranged below the chuck table 11 to detect the reaction force of the grinding force in the horizontal direction and the reaction force of the grinding force in the normal direction received by the chuck table 11. The three-axis ring sensor can accurately measure three vertical components of the grinding force, including the normal direction grinding force and the horizontal direction grinding force. The horizontal direction grinding force can include the first direction grinding force (i.e. the X direction grinding force) and the second direction grinding force (i.e. the Y direction grinding force), and the first direction is perpendicular to the second direction. The normal direction grinding force is the force perpendicular to the workpiece machining surface.

[0072] When the grinding wheel 3 grinds the wafer, the grinding force of the grinding wheel is transmitted to the wafer, and the grinding force is transmitted to the chuck table 111 holding the wafer after the wafer is stressed, and the chuck table 11 provides the reaction force of the grinding force. The three-axis ring sensor 7 arranged below the chuck table 11 can detect the reaction force of the grinding force, i.e. the reaction force of the grinding force in the horizontal direction and the reaction force of the grinding force in the normal direction received by the chuck table 11. The reaction force of the grinding force in the horizontal direction received by the chuck table 11 is equal in size and opposite in direction to the horizontal direction grinding force of the grinding wheel; the reaction force of the grinding force in the normal direction received by the chuck table 11 is equal in size and opposite in direction to the normal direction grinding force of the grinding wheel.

[0073] To more accurately measure the reaction force of the grinding force on the chuck turntable 11 in the horizontal direction and the reaction force of the grinding force in the normal direction, multiple triaxial force ring sensors 7 can be installed. For example, such as... Figure 4 As shown, three triaxial force ring sensors 7 are evenly arranged around the central axis of the chuck turntable 11. During the grinding process of the wafer, the three triaxial force ring sensors 7 detect the reaction force of the grinding force on the chuck turntable 11 in the horizontal direction and the reaction force of the grinding force on the normal direction, such as... Figure 5 As shown. The three triaxial force ring sensors 7 detect the reaction forces of the grinding force on the chuck turntable 11 in the normal direction and the reaction forces of the grinding force on the chuck turntable 11 in the horizontal direction, respectively. The reaction forces of the grinding force on the chuck turntable 11 in the normal direction detected by the three triaxial force ring sensors 7 are respectively expressed as F. 1z F 2z and F 3z The grinding force corresponds to the normal direction of the grinding wheel. The reaction force of the grinding force on the chuck turntable 11 in the horizontal direction includes the reaction force of the grinding force on the chuck turntable 11 in the first direction and the reaction force of the grinding force on the chuck turntable 11 in the second direction. The reaction force of the grinding force on the chuck turntable 11 in the first direction corresponds to the grinding force of the grinding wheel in the first direction, and the reaction force of the grinding force on the chuck turntable 11 in the second direction corresponds to the grinding force of the grinding wheel in the second direction. The reaction force of the grinding force on the chuck turntable 11 in the first direction detected by the three triaxial force ring sensors 7 is expressed as F. 1x F 2x and F 3x The reaction force of the grinding force on the chuck turntable 11 in the second direction, detected by the three triaxial force ring sensors 7, is expressed as F. 1y F 2y and F 3y The average value of the reaction force of the grinding force on the chuck turntable 11 in the normal direction, detected by the three triaxial force ring sensors 7, is calculated as the reaction force of the grinding force on the chuck turntable 11 in the normal direction. The average value of the reaction force of the grinding force on the chuck turntable 11 in the first direction, detected by the three triaxial force ring sensors 7, is calculated as the reaction force of the grinding force on the worktable 1 in the first direction. The average value of the reaction force of the grinding force on the chuck turntable 11 in the second direction, detected by the three triaxial force ring sensors 7, is calculated as the reaction force of the grinding force on the chuck turntable 11 in the second direction.

[0074] Since the grinding force cannot be accurately through the geometric center of the chuck table 11 in the wafer thinning process, the average value of the grinding force reaction in the horizontal direction and the average value of the grinding force reaction in the normal direction of the chuck table 11 are measured by multi-point measurement, which can average the local error and improve the accuracy of the collected data.

[0075] Figure 6 is a flowchart of a wafer thinning method provided by an embodiment of the present application, as shown in the figure, the wafer thinning method provided by the embodiment of the present application comprises: Figure 6

[0076] S601, determine the amount of grinding water for thinning according to the passivation degree of the grinding wheel and / or the shear force condition of the TSV area, so as to reduce the thermal damage of the TSV area and reduce the total amount of grinding water for thinning; wherein the passivation degree is characterized by the change rate of the total grinding force of the grinding wheel, and the shear force condition of the TSV area is characterized by the change rate of the grinding force in the horizontal direction of the grinding wheel; the grinding water includes two independent grinding waters for cooling the wafer and the grinding wheel.

[0077] In a specific embodiment, before step S601, it can further comprise: S600, collecting the grinding force in the horizontal direction and the grinding force in the normal direction of the grinding wheel, and calculating the total grinding force of the grinding wheel; and after step S601, it can further comprise: S602, providing grinding water to the wafer and the grinding wheel respectively.

[0078] Specifically, the present application characterizes the passivation degree of the grinding wheel by the change rate of the total grinding force of the grinding wheel, the greater the change rate of the total grinding force of the grinding wheel, the more serious the passivation degree of the grinding wheel, and the more likely to cause thermal damage in the TSV area. The change rate of the grinding force in the horizontal direction of the grinding wheel is used to characterize the shear force condition of the TSV area, the greater the change rate of the grinding force in the horizontal direction of the grinding wheel, the more likely to cause thermal damage in the TSV area.

[0079] The change rate of the total grinding force of the grinding wheel can be obtained by taking the derivative of the total grinding force of the grinding wheel with respect to time, which is represented as dF / dt in the present application. The total grinding force of the grinding wheel can be obtained by synthesizing the grinding force in the normal direction of the grinding wheel, the grinding force in the first direction of the grinding wheel and the grinding force in the second direction of the grinding wheel. wherein F represents the total grinding force of the grinding wheel, F x represents the grinding force in the first direction of the grinding wheel, F y represents the grinding force in the second direction of the grinding wheel, and F z represents the grinding force in the normal direction of the grinding wheel. The grinding force in the normal direction of the grinding wheel, the grinding force in the first direction of the grinding wheel and the grinding force in the second direction of the grinding wheel can be collected by a detection device.

[0080] ​The rate of change of the horizontal direction grinding force of the grinding wheel includes the rate of change of the first direction grinding force of the grinding wheel and the rate of change of the second direction grinding force of the grinding wheel. The rate of change of the first direction grinding force of the grinding wheel can be obtained by taking the derivative of the first direction grinding force of the grinding wheel with respect to time, denoted as dF x / dt in the present application; the rate of change of the second direction grinding force of the grinding wheel can be obtained by taking the derivative of the second direction grinding force of the grinding wheel with respect to time, denoted as dF y / dt in the present application. The rate of change of the normal direction grinding force of the grinding wheel can be obtained by taking the derivative of the normal direction grinding force of the grinding wheel with respect to time, denoted as dF z / dt in the present application.

[0081] The normal direction grinding force of the grinding wheel is the vertical pressing force between the grinding wheel and the wafer. The rate of change of the normal direction grinding force of the grinding wheel affects the stability of the material removal rate and is directly related to the degree of grinding wheel passivation. The instantaneous fluctuation of the material removal rate (MRR) will directly manifest as the mutation of the normal direction grinding force F z of the grinding wheel. In an ideal grinding state, stable grinding removes the material of the wafer, F z fluctuates little, and the rate of change of the grinding force dF z / dt is small. When grinding wheel passivation occurs, the wear of the cutting edge of the abrasive grains of the grinding wheel exceeds the threshold, the number of effective abrasive grain cutting edges decreases, the effective cutting effect is weakened, the proportions of “cutting - extrusion - sliding” in the grinding process are imbalanced, the proportions of extrusion or sliding increase, the enhancement of extrusion and sliding effects leads to the continuous accumulation of the contact load between the grinding wheel and the wafer, resulting in the continuous rise of F z and the intensification of the fluctuation of dF z / dt.

[0082] The first direction grinding force of the grinding wheel and the second direction grinding force of the grinding wheel are the shear work between the grinding wheel and the wafer. The rate of change of the horizontal direction grinding force of the grinding wheel, i.e. the rate of change of the first direction grinding force of the grinding wheel dF x / dt and the rate of change of the second direction grinding force of the grinding wheel dF y / dt, reflects the mutation of the shear force of the micro area of the TSV area metal column (such as a copper column). The TSV area of the wafer has high ductility of metal (such as copper) and significantly lower shear strength than the surrounding brittle material, and there is a mechanical performance mutation interface between the metal column and the silicon matrix. At the moment when the grinding wheel cuts into the metal column, due to the sudden drop of the material yield strength, the shear force F x and / or F y drops sharply, resulting in a significant negative peak of dF x / dt and / or dF y / dt, and the peak signal reflects F x , Fy Maximum rate of change over time. At the instant the grinding wheel cuts into the metal column: material strength increases sharply, F x and / or F y Rises sharply, causing dF x / dt and / or dF y / dt to form a significant positive spike.

[0083] The rate of change of total grinding force dF / dt of the grinding wheel can be used to characterize the overall passivation degree of the grinding wheel. This parameter has stronger robustness to interference such as TSV area mutation or vibration compared to the grinding force component.

[0084] In the wafer thinning process, the amount of grinding water used for thinning is determined according to the passivation degree of the grinding wheel in the embodiments of the present application, that is, the amount of grinding water used for cooling the wafer and the amount of grinding water used for cooling the grinding wheel are adjusted independently. When the grinding wheel is passivated, the amount of grinding water used for thinning is increased to enhance cooling and reduce thermal damage to the through-silicon via area. When the grinding wheel is not passivated, the amount of grinding water used for thinning is reduced to suppress the unstable grinding state caused by hydrodynamic vibration. In the embodiments of the present application, the amount of grinding water used for thinning is determined according to the shear force of the through-silicon via area, that is, when it is determined that the shear force of the through-silicon via area causes thermal damage to the through-silicon via area, the amount of grinding water used for thinning is increased to enhance cooling and reduce thermal damage to the through-silicon via area. Since the embodiments of the present application can adjust the amount of grinding water used for thinning according to the passivation degree of the grinding wheel and / or the shear force of the through-silicon via area, the thermal damage to the through-silicon via area is reduced while the overall use amount of grinding water used for thinning is also reduced, thereby reducing the grinding cost.

[0085] The grinding water used for cooling the wafer, also known as worktable cooling water, is used to cool the wafer, especially the through-silicon via area of the wafer. The grinding water used for cooling the grinding wheel, also known as spindle-grinding wheel cooling water, can cool the grinding wheel and the spindle to avoid thermal deformation of the grinding wheel and the spindle. The worktable cooling water and the spindle-grinding wheel cooling water are managed independently.

[0086] The wafer thinning method provided by the embodiment of the present application determines the amount of grinding water used for thinning according to the passivation degree of the grinding wheel and / or the shear force condition of the through silicon via area, so as to reduce the thermal damage of the through silicon via area and reduce the overall usage amount of the grinding water used for thinning; wherein the passivation degree is characterized by the change rate of the total grinding force of the grinding wheel, and the shear force condition of the through silicon via area is characterized by the change rate of the grinding force in the horizontal direction of the grinding wheel; the grinding water includes two independent grinding waters used for cooling the wafer and the grinding wheel respectively, and since the amount of the grinding water used for thinning is adjusted based on the passivation degree of the grinding wheel and / or the shear force condition of the through silicon via area, the cooling of the wafer and the grinding wheel is respectively performed by the two independent grinding waters, so as to reduce the thermal damage of the through silicon via area, reduce the surface damage of the thinned wafer, improve the surface quality of the thinned wafer, improve the wafer yield, and reduce the overall usage amount of the grinding water used for thinning, thereby reducing the equipment operation cost.

[0087] On the basis of the above-mentioned embodiments, further comprising, before step S601:

[0088] S600, collecting the grinding force in the horizontal direction and the grinding force in the normal direction of the grinding wheel, and calculating the total grinding force of the grinding wheel.

[0089] Specifically, the grinding force in the horizontal direction and the grinding force in the normal direction of the grinding wheel can be collected by a detection device, the grinding force in the horizontal direction of the grinding wheel includes the grinding force in the first direction and the grinding force in the second direction, and the total grinding force of the grinding wheel is calculated according to the grinding force in the first direction, the grinding force in the second direction and the grinding force in the normal direction of the grinding wheel.

[0090] On the basis of the above-mentioned embodiments, further comprising, after step S601:

[0091] S602, providing grinding water to the wafer and the grinding wheel respectively.

[0092] Specifically, after determining the amount of grinding water used for thinning according to the passivation degree of the grinding wheel and / or the shear force condition of the through silicon via area, the amount of grinding water used for cooling the wafer and the amount of grinding water used for cooling the grinding wheel can be determined. Then, the grinding water is provided to the wafer through the water path used for cooling the wafer according to the amount of grinding water used for cooling the wafer, and the grinding water is provided to the grinding wheel through the water path used for cooling the grinding wheel according to the amount of grinding water used for cooling the grinding wheel.

[0093] On the basis of the above-mentioned embodiments, further comprising, determining the amount of grinding water used for thinning according to the passivation degree of the grinding wheel includes:

[0094] If the change rate of the total grinding force of the grinding wheel is greater than a first threshold value, it is determined that the grinding wheel is blunted, and the amount of use of the two independent grinding water for cooling the wafer and for cooling the grinding wheel is increased through the first water amount mode to enhance the cooling.

[0095] Specifically, the change rate of the total grinding force of the grinding wheel is compared with the first threshold value, if the change rate of the total grinding force of the grinding wheel is greater than the first threshold value, it is determined that the grinding wheel is blunted, and the amount of grinding water for thinning is adjusted through the first water amount mode, that is, the amount of use of the two independent grinding water for cooling the wafer and for cooling the grinding wheel is increased to enhance the cooling of the wafer and the grinding wheel. The first threshold value is set according to actual experience, for example, 5N / s, which is not limited in the embodiments of the present application.

[0096] On the basis of the above embodiments, further, the amount of grinding water for thinning is determined according to the shear force of the through silicon via area of the grinding wheel, including:

[0097] If the change rate of the grinding force in the horizontal direction of the grinding wheel is greater than a second threshold value, it is determined that the shear force of the through silicon via area causes thermal damage to the through silicon via area, and the amount of use of the two independent grinding water for cooling the wafer and for cooling the grinding wheel is increased through the first water amount mode to enhance the cooling.

[0098] Specifically, the change rate of the grinding force in the horizontal direction of the grinding wheel is compared with the second threshold value, if the change rate of the grinding force in the horizontal direction of the grinding wheel is greater than the second threshold value, it is determined that the shear force of the through silicon via area causes thermal damage to the through silicon via area, and the amount of grinding water for thinning is adjusted through the first water amount mode, that is, the amount of use of the two independent grinding water for cooling the wafer and for cooling the grinding wheel is increased to enhance the cooling of the wafer and the grinding wheel. The second threshold value is set according to actual experience, for example, 3N / s, which is not limited in the embodiments of the present application.

[0099] The change rate of the grinding force in the horizontal direction of the grinding wheel includes the change rate of the grinding force in the first direction of the grinding wheel and the change rate of the grinding force in the second direction of the grinding wheel, and the change rate of the grinding force in the horizontal direction of the grinding wheel being greater than the second threshold value means that the change rate of the grinding force in the first direction of the grinding wheel is greater than the second threshold value, or the change rate of the grinding force in the second direction of the grinding wheel is greater than the second threshold value.

[0100] In the wafer thinning process, the amount of grinding water used for thinning is adjusted by the first water amount mode, the use amount of grinding water used for cooling the wafer is increased, the grinding dust generated in the grinding area can be efficiently removed, and the accumulation of grinding dust on the surface of the grinding wheel and in the air hole is avoided. The efficient removal of grinding dust can create good exposure conditions for the abrasive particles of the grinding wheel: on the one hand, it can reduce the abnormal wear of the cutting edge of the abrasive particles caused by the extrusion of the grinding dust, and on the other hand, it can make the abrasive particles on the surface of the grinding wheel more easily crack or fall off under the action of cutting force, thereby promoting the grinding wheel to achieve efficient self-sharpening and maintaining its continuous and stable cutting performance. The improvement of the self-sharpening of the grinding wheel can effectively inhibit the decline of the cutting ability, so that the cutting resistance between the abrasive particles and the wafer in the grinding process is suppressed, and the increase of the grinding force is slowed down. Thus, the change rate of the total grinding force of the grinding wheel is reduced. Increasing the use amount of grinding water used for cooling the wafer can enhance the cooling of the TSV area of the wafer, inhibit the temperature of the TSV area, and due to the efficient removal of grinding, the Ra of the wafer surface can be reduced.

[0101] In the wafer thinning process, the amount of grinding water used for thinning is adjusted by the first water amount mode, the use amount of grinding water used for cooling the wafer is increased, the grinding dust generated in the grinding area can be efficiently removed, and the accumulation of grinding dust on the surface of the grinding wheel and in the air hole is avoided. The efficient removal of grinding dust can create good exposure conditions for the abrasive particles of the grinding wheel: on the one hand, it can reduce the abnormal wear of the cutting edge of the abrasive particles caused by the extrusion of the grinding dust, and on the other hand, it can make the abrasive particles on the surface of the grinding wheel more easily crack or fall off under the action of cutting force, thereby promoting the grinding wheel to achieve efficient self-sharpening and maintaining its continuous and stable cutting performance. The improvement of the self-sharpening of the grinding wheel can effectively inhibit the decline of the cutting ability, so that the cutting resistance between the abrasive particles and the wafer in the grinding process is suppressed, and the increase of the grinding force is slowed down. Thus, the change rate of the total grinding force of the grinding wheel is reduced. Increasing the use amount of grinding water used for cooling the wafer can enhance the cooling of the TSV area of the wafer, inhibit the temperature of the TSV area, and due to the efficient removal of grinding, the Ra of the wafer surface can be reduced.

[0102] In addition, the first water amount mode is triggered to enhance cooling when the change rate of the total grinding force of the grinding wheel is greater than a first threshold or the change rate of the grinding force in the horizontal direction of the grinding wheel is greater than a second threshold, which can compress the cooling response time and cool the wafer and the grinding wheel in time.

[0103] On the basis of the above embodiments, further, the first water amount mode comprises:

[0104] The use amount of grinding water used for cooling the wafer is increased to a first range, and the use amount of grinding water used for cooling the grinding wheel is increased to a second range; wherein the first range and the second range are determined based on the conventional water amount.

[0105] Specifically, the first water amount mode comprises increasing the use amount of grinding water used for cooling the wafer to a first range to enhance the cooling effect of the wafer, and increasing the use amount of grinding water used for cooling the grinding wheel to a second range to enhance the cooling effect of the grinding wheel. Wherein the first range and the second range are determined based on the conventional water amount. The conventional water amount can adopt the fixed grinding water amount used in the thinning process in the prior art, or it can be a fixed value of the grinding water set according to actual experience.

[0106] It can be understood that when the amount of grinding water used for thinning is in the first mode, the use amount of grinding water used for cooling the wafer is within the first range, and the use amount of grinding water used for cooling the grinding wheel is within the second range.

[0107] In some embodiments, the first range is 150-200% of the regular water amount, and the second range is 100-120% of the regular water amount.

[0108] On the basis of the above-mentioned embodiments, further, in the first water amount mode, the increase range of the usage amount of the grinding water for cooling the grinding wheel is smaller than the increase range of the usage amount of the grinding water for cooling the wafer, so as to prevent the flow fluctuation of the grinding water from inducing the vibration of the grinding wheel.

[0109] Specifically, by increasing the usage amount of the two independent grinding waters for cooling the wafer and the grinding wheel in the first water amount mode, the increase range of the usage amount of the grinding water for cooling the grinding wheel is smaller than the increase range of the usage amount of the grinding water for cooling the wafer, so as to prevent the flow fluctuation of the grinding water from inducing the vibration of the grinding wheel.

[0110] On the basis of the above-mentioned embodiments, further, the wafer thinning method provided by the embodiments of the present application further comprises:

[0111] If the change rate of the total grinding force of the grinding wheel is smaller than the third threshold value and lasts for the first preset time length, the first water amount mode is exited, and the usage amount of the two independent grinding waters for cooling the wafer and the grinding wheel is reduced in the second water amount mode, so as to maintain the basic cooling of the wafer and the grinding wheel and reduce the hydraulic vibration and the temperature fluctuation.

[0112] Specifically, the amount of the grinding water for thinning is compared with the third threshold value in the first water amount mode. If the change rate of the total grinding force of the grinding wheel is smaller than the third threshold value and lasts for the first preset time length, it is indicated that the amount of the grinding water for thinning does not need to be maintained in the first water amount mode, the first water amount mode can be exited, and the usage amount of the two independent grinding waters for cooling the wafer and the grinding wheel is reduced in the second water amount mode. The amount of the grinding water for thinning in the second water amount mode is a temporary state, the second water amount mode is used to realize the transition between the first water amount mode and the third water amount mode, can maintain the basic cooling of the wafer and the grinding wheel and reduce the hydraulic vibration and the temperature fluctuation, and avoid the overcooling or micro-cracks of the non-TSV area of the wafer.

[0113] The third threshold value and the first preset time length are set according to actual experience, and are not limited by the embodiments of the present application. For example, the third threshold value is 3N / s, and the first preset time length is 10 seconds.

[0114] On the basis of the above-mentioned embodiments, further, the wafer thinning method provided by the embodiments of the present application further comprises:

[0115] If the rate of change of the horizontal grinding force is less than a fourth threshold value and lasts for a second preset time length, the usage of the two independent grinding water for cooling the wafer and for cooling the grinding wheel is adjusted by a third water amount mode to reduce the hydraulic vibration and temperature fluctuation.

[0116] Specifically, the amount of grinding water for thinning in the second water amount mode compares the rate of change of the total grinding force of the grinding wheel with the fourth threshold value, if the rate of change of the total grinding force of the grinding wheel is less than the fourth threshold value and lasts for a second preset time length, it indicates that the amount of grinding water for thinning does not need to be maintained in the second water amount mode, the second water amount mode can be exited, and the usage of the two independent grinding water for cooling the wafer and for cooling the grinding wheel is reduced by the third water amount mode. In the embodiment of the present application, the amount of grinding water for thinning does not directly change from the first water amount mode to the third water amount mode, but passes through the second water amount mode to enter the third water amount mode, which can reduce the hydraulic vibration and temperature fluctuation, and avoid overcooling or microcracks in the non-TSV area of the wafer.

[0117] Wherein, the fourth threshold value and the second preset time length are set according to actual experience, which is not limited in the embodiment of the present application. For example, the fourth threshold value is 2N / s, and the second preset time length is 5 seconds.

[0118] On the basis of the above-mentioned embodiments, further, the second water amount mode comprises:

[0119] The usage of the grinding water for cooling the wafer is reduced to a first water usage, and the usage of the grinding water for cooling the grinding wheel is adjusted to a second water usage; wherein the first water usage and the second water usage are determined based on the conventional water amount.

[0120] Specifically, the second water amount mode comprises reducing the usage of the grinding water for cooling the wafer to the first water usage to maintain the basic cooling of the wafer, and adjusting the usage of the grinding water for cooling the grinding wheel to the second water usage to maintain the basic cooling of the grinding wheel. Wherein the first water usage and the second water usage are determined based on the conventional water amount.

[0121] In some embodiments, the first water usage is 120% of the conventional water amount, and the second water usage is 110% of the conventional water amount.

[0122] On the basis of the above-mentioned embodiments, further, determining the amount of grinding water for thinning according to the passivation degree of the grinding wheel comprises:

[0123] If the rate of change of the total grinding force of the grinding wheel is less than a fifth threshold value, the usage of the two independent grinding water for cooling the wafer and for cooling the grinding wheel is reduced by a fourth water amount mode to suppress the hydraulic vibration and maintain the thermal stability of the grinding spindle.

[0124] Specifically, the rate of change of the total grinding force of the grinding wheel is compared with a fifth threshold value, if the rate of change of the total grinding force of the grinding wheel is less than the fifth threshold value, it indicates that the contact between the grinding wheel and the wafer is unstable, and the grinding wheel has not been passivated, then the amount of grinding water used for thinning is reduced through the fourth water amount mode, that is, the amount of grinding water used for cooling the wafer and the grinding wheel is reduced independently. The fifth threshold value is set according to actual experience, for example, it is set to 2N / s, and the embodiments of the present application are not limited thereto.

[0125] In the wafer thinning process, the amount of grinding water used for thinning is adjusted through the fourth water amount mode, and the amount of grinding water used for cooling the wafer is reduced, which can inhibit hydraulic vibration and avoid excessive impact load when the grinding wheel re-contacts the wafer, so as to prevent micro-cracks from being induced in the TSV area.

[0126] In the wafer thinning process, the amount of grinding water used for thinning is adjusted through the fourth water amount mode, and the amount of grinding water used for cooling the wafer is reduced, which can inhibit hydraulic vibration and avoid excessive impact load when the grinding wheel re-contacts the wafer, so as to prevent micro-cracks from being induced in the TSV area.

[0127] On the basis of the above-mentioned embodiments, further, the wafer thinning method provided by the embodiments of the present application further comprises:

[0128] If the rate of change of the total grinding force of the grinding wheel is greater than or equal to the fifth threshold value, the fourth water amount mode is exited and the amount of grinding water used for cooling the wafer and the grinding wheel is adjusted through the third water amount mode, so as to avoid heat accumulation.

[0129] Specifically, the amount of grinding water used for thinning in the fourth water amount mode is compared with the fifth threshold value, if the rate of change of the total grinding force of the grinding wheel is greater than or equal to the fifth threshold value, it indicates that the amount of grinding water used for thinning does not need to be maintained in the fourth water amount mode, and the fourth water amount mode can be exited, and the amount of grinding water used for cooling the wafer and the grinding wheel is adjusted through the third water amount mode. After the amount of grinding water used for thinning exits the fourth water amount mode, it directly enters the third water amount mode without transition, so as to avoid heat accumulation.

[0130] On the basis of the above-mentioned embodiments, further, the fourth water amount mode comprises:

[0131] The amount of grinding water used for cooling the wafer is reduced to a third range, and the amount of grinding water used for cooling the grinding wheel is reduced to a fourth range; wherein the third range and the fourth range are determined based on a conventional water amount.

[0132] Specifically, the fourth water amount mode comprises reducing the usage amount of the grinding water for cooling the wafer to a third range to suppress the hydrodynamic vibration, and reducing the usage amount of the grinding water for cooling the grinding wheel to a fourth range to maintain the spindle thermal stability. The third range and the fourth range are determined based on the conventional water amount.

[0133] It can be understood that when the amount of the grinding water for thinning is in the fourth mode, the usage amount of the grinding water for cooling the wafer is in the third range, and the usage amount of the grinding water for cooling the grinding wheel is in the fourth range.

[0134] In some embodiments, the third range is 60-70% of the conventional water amount, and the fourth range is 80-100% of the conventional water amount.

[0135] On the basis of the above-mentioned embodiments, further, the amount of the grinding water for thinning is determined according to the dulling degree of the grinding wheel, comprising:

[0136] If the change rate of the total grinding force of the grinding wheel is greater than or equal to the fifth threshold value and less than or equal to the sixth threshold value, the usage amounts of the two independent grinding waters for cooling the wafer and for cooling the grinding wheel are adjusted by the third water amount mode to balance the cooling of the wafer and the thermal stability of the grinding spindle.

[0137] Specifically, the change rate of the total grinding force of the grinding wheel is compared with the fifth threshold value and the sixth threshold value respectively. If the change rate of the total grinding force of the grinding wheel is greater than or equal to the fifth threshold value and less than or equal to the sixth threshold value, it indicates that the self-sharpening of the grinding wheel is good, and the grinding wheel has not been dulled. Then, the usage amounts of the two independent grinding waters for cooling the wafer and for cooling the grinding wheel can be adjusted by the third water amount mode to balance the cooling of the wafer and the stability of the grinding performance.

[0138] When the self-sharpening of the grinding wheel is good, it indicates that the gradually dulled abrasive grains on the surface of the grinding wheel due to cutting during the wafer thinning process can timely crack, fall off or micro-fracture under reasonable cutting force or heat, thereby continuously exposing new abrasive grains with sharp cutting edges on the surface of the grinding wheel. The dynamic self-renewing ability of the grinding wheel can effectively avoid the cutting ability decline of the grinding wheel due to excessive dulling of the abrasive grains, ensure the stability of the cutting performance during the grinding process, and reduce the occurrence of adverse phenomena such as excessive increase of the grinding force and excessive accumulation of the grinding heat.

[0139] On the basis of the above-mentioned embodiments, further, the third water amount mode comprises:

[0140] adjusting the usage amount of the grinding water for cooling the wafer according to the rate of change of the total grinding force of the grinding wheel in a fifth range; and adjusting the usage amount of the grinding water for cooling the grinding wheel according to the rate of change of the total grinding force of the grinding wheel in a sixth range; wherein the fifth range and the sixth range are determined based on the regular water amount.

[0141] In particular, the third water amount mode comprises adjusting the usage amount of the grinding water for cooling the wafer according to the rate of change of the total grinding force of the grinding wheel in a fifth range, and adjusting the usage amount of the grinding water for cooling the grinding wheel according to the rate of change of the total grinding force of the grinding wheel in a sixth range, so that the grinding wheel has good self-sharpening. Wherein the fifth range and the sixth range are determined based on the regular water amount.

[0142] The adjusting the usage amount of the grinding water for cooling the wafer according to the rate of change of the total grinding force of the grinding wheel in a fifth range comprises: determining the usage amount of the grinding water for cooling the wafer according to a first linear adaptive adjustment relationship between the rate of change of the total grinding force and the usage amount of the grinding water for cooling the wafer, the usage amount of the grinding water for cooling the wafer being in the fifth range; the first linear adaptive adjustment relationship is a linear relationship between the rate of change of the total grinding force and the usage amount of the grinding water for cooling the wafer in the fifth range, and is established in advance.

[0143] The adjusting the usage amount of the grinding water for cooling the wafer according to the rate of change of the total grinding force of the grinding wheel in a fifth range comprises: determining the usage amount of the grinding water for cooling the wafer according to a first linear adaptive adjustment relationship between the rate of change of the total grinding force and the usage amount of the grinding water for cooling the wafer, the usage amount of the grinding water for cooling the wafer being in the fifth range; the first linear adaptive adjustment relationship is a linear relationship between the rate of change of the total grinding force and the usage amount of the grinding water for cooling the wafer in the fifth range, and is established in advance.

[0144] It can be understood that when the amount of grinding water for thinning is in the third mode, the usage amount of the grinding water for cooling the wafer is in the fifth range, and the usage amount of the grinding water for cooling the grinding wheel is in the sixth range.

[0145] In some embodiments, the fifth range is 80-120% of the regular water amount, and the sixth range is 90-110% of the regular water amount.

[0146] In some embodiments, the wafer thinning method provided by the embodiments of the present application comprises:

[0147] The first step is to collect the grinding force of the grinding wheel. The normal direction grinding force and the horizontal direction grinding force of the grinding wheel are collected by a detection device. The normal direction grinding force of the grinding wheel is represented as F z , and the horizontal direction grinding force of the grinding wheel comprises a first direction grinding force F x and a second direction grinding force F y .

[0148] Second step, calculating the rate of change of grinding force. The normal direction of the grinding force of the grinding wheel, the first direction of the grinding force of the grinding wheel and the second direction of the grinding force of the grinding wheel are calculated to obtain the total grinding force of the grinding wheel. The total grinding force of the grinding wheel is calculated to obtain the rate of change of the total grinding force of the grinding wheel dF / dt. The first direction of the grinding force of the grinding wheel is calculated to obtain the rate of change of the first direction of the grinding force of the grinding wheel dF x / dt, and the second direction of the grinding force of the grinding wheel is calculated to obtain the rate of change of the second direction of the grinding force of the grinding wheel dF y / dt.

[0149] Third step, judging the rate of change of the total grinding force. dF / dt is compared with the first threshold value 5 N / s and the fifth threshold value 2 N / s respectively, if dF / dt is greater than 5 N / s, it is determined that the grinding wheel is dull, then it goes to the fifth step; if dF / dt is less than 2 N / s, it goes to the tenth step; if dF / dt is greater than or equal to 2 N / s and less than or equal to 5 N / s, it goes to the ninth step.

[0150] Fourth step, judging the rate of change of the horizontal direction of the grinding force of the grinding wheel. dF x / dt is compared with the second threshold value 3 N / s, and dF y / dt is compared with the second threshold value 3 N / s, if dF x / dt is greater than 3 N / s or dF y / dt is greater than 3 N / s, it is determined that the shear force of the through silicon via area causes thermal damage to the through silicon via area, then it goes to the fifth step.

[0151] Fifth step, entering the first water amount mode. The use amount of the two independent grinding water for cooling the wafer and for cooling the grinding wheel is increased through the first water amount mode, that is, the use amount of the grinding water for cooling the wafer is increased to 150-200% of the regular water amount, and the use amount of the grinding water for cooling the grinding wheel is increased to 100-120% of the regular water amount.

[0152] Sixth step, judging the rate of change of the total grinding force. It is judged whether dF / dt is less than the third threshold value 3 N / s and lasts for a first preset time length 10 seconds, if yes, it goes to the seventh step; if not, the amount of the grinding water for thinning remains in the first water amount mode, and it goes back to the fifth step.

[0153] Seventh step, entering the second water amount mode. The use amount of the two independent grinding water for cooling the wafer and for cooling the grinding wheel is reduced through the second water amount mode, that is, the use amount of the grinding water for cooling the wafer is reduced to 120% of the regular water amount, and the use amount of the grinding water for cooling the grinding wheel is adjusted to 110% of the regular water amount.

[0154] The eighth step is to determine the change rate of the grinding force in the horizontal direction of the grinding wheel. Determine whether dF / dt is less than the fourth threshold value 2 N / s and lasts for a second preset time length 5 seconds. x dF / dt is less than the fourth threshold value 2 N / s and lasts for a second preset time length 5 seconds, if yes, go to the ninth step; if no, the amount of grinding water for thinning will remain in the second water amount mode, and return to the seventh step. y dF / dt is less than the fourth threshold value 2 N / s and lasts for a second preset time length 5 seconds, if yes, go to the ninth step; if no, the amount of grinding water for thinning will remain in the second water amount mode, and return to the seventh step.

[0155] The ninth step is to enter the third water amount mode. Through the third water amount mode, the usage amount of the two independent grinding waters for cooling the wafer and for cooling the grinding wheel is reduced, that is, the usage amount of the grinding water for cooling the wafer is adjusted within the conventional water amount of 80-120% according to the change rate of the total grinding force of the grinding wheel; and the usage amount of the grinding water for cooling the grinding wheel is adjusted within the conventional water amount of 90-110% according to the change rate of the total grinding force of the grinding wheel.

[0156] The tenth step is to enter the fourth water amount mode. Through the fourth water amount mode, the usage amount of the two independent grinding waters for cooling the wafer and for cooling the grinding wheel is reduced, that is, the usage amount of the grinding water for cooling the wafer is reduced to 60-70% of the conventional water amount; and the usage amount of the grinding water for cooling the grinding wheel is reduced to 80-100% of the conventional water amount.

[0157] The eleventh step is to determine the change rate of the total grinding force. Determine whether dF / dt is greater than or equal to the fifth threshold value 2 N / s, if yes, exit the current fourth water amount mode and enter the ninth step; if no, the amount of grinding water for thinning will remain in the fourth water amount mode, and return to the tenth step.

[0158] In the prior art, the wafer thinning process with fixed water amount is prone to grinding wheel passivation. After the grinding wheel passivation, the friction heat between the grinding wheel and the wafer increases dramatically, and the TSV area of the wafer is prone to heat accumulation due to the high thermal conductivity of the metal (such as Cu), which causes the temperature of the TSV area to rise rapidly. The wafer thinning method of the present application determines whether the grinding wheel is passivated through the change rate of the total grinding force of the grinding wheel. After determining that the grinding wheel is passivated, the usage amount of the two independent grinding waters for cooling the wafer and for cooling the grinding wheel is increased through the first water amount mode to enhance cooling and maintain the temperature of the TSV area stable, thereby reducing the thermal damage of the TSV area. In addition, the change rate of the grinding force in the horizontal direction of the grinding wheel is used to determine the shear force condition of the through silicon via area. In the case that the shear force of the through silicon via area causes thermal damage to the through silicon via area, the usage amount of the two independent grinding waters for cooling the wafer and for cooling the grinding wheel is increased through the first water amount mode to enhance cooling and reduce the thermal damage of the TSV area.

[0159] The wafer thinning method provided in this invention (i.e., the solution of this application) has the following advantages over the existing wafer thinning process using a fixed amount of water (i.e., the conventional solution):

[0160] (1) Thermal protection of the TSV region: The solution in this application dynamically controls the amount of grinding water used for thinning by adjusting the rate of change of grinding force, thus solving the problem of deformation and damage to the metal pillars caused by localized instantaneous high temperatures due to CTE (Coefficient of Thermal Expansion) mismatch between the metal pillars and Si in the TSV region of the wafer in the prior art. A wafer has multiple TSV regions, each with copper pillars. In the prior art, a wafer thinning process with a fixed water volume (i.e., the traditional solution) is used. The surface of the copper pillars in the TSV region after wafer thinning is imaged using an electron microscope, as shown in the image. Figure 7 As shown, Figure 7 The lighter-colored areas represent the machined surface of the copper pillar. Due to excessively high temperatures during the grinding process, the surface of the copper pillar showed obvious deformation and damage. For example... Figure 8 As shown, using the wafer thinning method of this application, the copper pillar processing surface of the TSV region obtained after wafer thinning is imaged using an electron microscope. Figure 8 As shown, Figure 8 The light-colored area represents the machined surface of the copper pillar. Since no or almost no thermal damage occurred in the TSV zone, the degree of deformation damage to the copper pillar is minimal, and the machined surface of the copper pillar is circular.

[0161] (2) Optimization of wafer surface roughness: Using the scheme of this application, in the passivated state of the grinding wheel, the amount of grinding water used for thinning is increased to strongly cool and reduce the temperature, suppress thermal damage to the wafer surface, and enhance lubrication to reduce friction, thereby reducing the surface roughness Ra of the wafer. Figure 9 As shown, wafers 1, 2, and 3 were thinned using the conventional method and the wafer thinning method of this application, respectively. Ra measurements were performed on each wafer at its center, the middle (0.5 times the wafer radius from the center), and the edge (10 mm from the outer edge). The results are shown below. Figure 9 As shown, Figure 9 The unit of surface roughness is nm. For the thinned wafers 1, 2, and 3, the Ra at the same location is superior to the conventional solution at all locations except the middle location of wafer 3.

[0162] (3) Reducing Cu ion contamination: In this application, when wheel passivation occurs, the temperature in the grinding zone is lowered by increasing the amount of grinding water used for thinning, thus reducing the copper oxidation reaction rate in the TSV zone and effectively inhibiting the generation of Cu metal ions, thereby reducing Cu metal ion contamination. For example... Figure 10As shown, 10 wafers are thinned by using the conventional scheme and the scheme of the present application respectively, and the Cu metal ion concentration is measured after thinning, and the unit of Cu metal ion concentration is atoms / cm 2 Except for No. 3 and No. 10 wafers, the Cu metal ion concentration of the wafers thinned by using the scheme of the present application is obviously lower than that of the wafers thinned by using the conventional scheme.

[0163] Those skilled in the art will understand that embodiments of the present application can be provided as methods, systems, or computer program products. Accordingly, the present application can be embodied in the form of complete hardware embodiments, complete software embodiments, or embodiments combining software and hardware aspects. Furthermore, the present application can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage, etc.) having computer usable program code embodied thereon.

[0164] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing apparatus to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing apparatus generate a means for implementing the functions specified in the flow Figure 1 one or more flows and / or blocks Figure 1 an apparatus that implements the functions specified in the flow

[0165] These computer program instructions can also be stored in a computer-readable memory that can direct the computer or other programmable data processing apparatus to work in a specific manner, so that the instructions stored in the computer-readable memory produce a manufactured product including instruction apparatus, which implements the functions specified in the flow Figure 1 one or more flows and / or blocks Figure 1 an apparatus that implements the functions specified in the flow

[0166] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus, so that a series of operation steps are performed on the computer or other programmable data processing apparatus to produce a computer-implemented process, so that the instructions executed on the computer or other programmable data processing apparatus provide steps for implementing the functions specified in the flow Figure 1 one or more flows and / or blocks Figure 1 Figure 1 an apparatus that implements the functions specified in the flow

[0167] In the description of the present specification, the description of the terms "one embodiment", "one specific embodiment", "some embodiments", "for example", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Also, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in one or more embodiments or examples.

[0168] The specific embodiments described above further illustrate the purposes, technical solutions and beneficial effects of the present application. It should be understood that the above description is only for specific embodiments of the present application and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A wafer thinning method, characterized by, The application comprises: determining the amount of grinding water for thinning according to the dulling degree of the grinding wheel and / or the shear force condition of the through silicon via area, so as to reduce the thermal damage of the through silicon via area and reduce the overall use of grinding water for thinning; wherein the dulling degree is characterized by the change rate of the total grinding force of the grinding wheel, and the shear force condition of the through silicon via area is characterized by the change rate of the horizontal grinding force of the grinding wheel; the grinding water comprises two independent grinding water for cooling the wafer and for cooling the grinding wheel; wherein if the change rate of the total grinding force of the grinding wheel is greater than a first threshold value, it is determined that the grinding wheel is dull; if the change rate of the horizontal grinding force of the grinding wheel is greater than a second threshold value, it is determined that the shear force of the through silicon via area causes thermal damage to the through silicon via area, and the use of the two independent grinding water for cooling the wafer and for cooling the grinding wheel is increased by a first water amount mode to enhance cooling; in the first water amount mode, the increase amplitude of the use of the grinding water for cooling the grinding wheel is less than the increase amplitude of the use of the grinding water for cooling the wafer, so as to prevent the water flow fluctuation of the grinding water from inducing grinding wheel vibration.

2. The wafer thinning method according to claim 1, wherein Before determining the amount of grinding water for thinning according to the dulling degree of the grinding wheel and / or the shear force condition of the through silicon via area, the application further comprises: collecting the horizontal grinding force and the normal grinding force of the grinding wheel, and calculating the total grinding force of the grinding wheel.

3. The wafer thinning method of claim 1, wherein The application further comprises: respectively providing the wafer and the grinding wheel with grinding water.

4. The wafer thinning method of claim 1, wherein Determining the amount of grinding water for thinning according to the dulling degree of the grinding wheel comprises: after determining that the grinding wheel is dull, increasing the use of the two independent grinding water for cooling the wafer and for cooling the grinding wheel by a first water amount mode to enhance cooling.

5. The wafer thinning method according to claim 1 or 4, wherein The first water amount mode comprises: increasing the use of the grinding water for cooling the wafer to a first range; and increasing the use of the grinding water for cooling the grinding wheel to a second range; wherein the first range and the second range are determined based on the conventional water amount.

6. The wafer thinning method according to claim 1 or 4, wherein The application further comprises: if the change rate of the total grinding force of the grinding wheel is less than a third threshold value and lasts for a first preset time length, exiting the first water amount mode and reducing the use of the two independent grinding water for cooling the wafer and for cooling the grinding wheel by a second water amount mode to maintain the basic cooling of the wafer and the grinding wheel, and reduce the water force vibration and temperature fluctuation.

7. The wafer thinning method according to claim 6, wherein The application further comprises: if the change rate of the horizontal grinding force is less than a fourth threshold value and lasts for a second preset time length, adjusting the use of the two independent grinding water for cooling the wafer and for cooling the grinding wheel by a third water amount mode to reduce the water force vibration and temperature fluctuation.

8. The wafer thinning method of claim 6, wherein, The second water amount mode comprises: reducing the use of the grinding water for cooling the wafer to a first water consumption; and adjusting the use of the grinding water for cooling the grinding wheel to a second water consumption; wherein the first water consumption and the second water consumption are determined based on the conventional water amount.

9. The wafer thinning method of claim 1, wherein Determining the amount of grinding water for thinning according to the dulling degree of the grinding wheel comprises: If the rate of change of the total grinding force of the grinding wheel is less than a fifth threshold value, the usage amount of the two independent grinding waters for cooling the wafer and for cooling the grinding wheel is reduced by a fourth water amount mode to suppress water-induced vibration and maintain grinding spindle thermal stability.

10. The wafer thinning method according to claim 9, wherein Further comprising: If the rate of change of the total grinding force of the grinding wheel is greater than or equal to the fifth threshold value, the fourth water amount mode is exited and the usage amount of the two independent grinding waters for cooling the wafer and for cooling the grinding wheel is adjusted by a third water amount mode to avoid thermal accumulation.

11. The wafer thinning method of claim 9, wherein, The fourth water amount mode comprises: The usage amount of the grinding water for cooling the wafer is reduced to a third range; and the usage amount of the grinding water for cooling the grinding wheel is reduced to a fourth range; wherein the third range and the fourth range are determined based on a regular water amount.

12. The wafer thinning method of claim 1, wherein Determining the amount of grinding water for thinning according to the degree of passivation of the grinding wheel comprises: If the rate of change of the total grinding force of the grinding wheel is greater than or equal to a fifth threshold value and less than or equal to a sixth threshold value, the usage amount of the two independent grinding waters for cooling the wafer and for cooling the grinding wheel is adjusted by a third water amount mode to balance the cooling of the wafer and the stability of the grinding performance.

13. The wafer thinning method according to claim 10 or 12, wherein The third water amount mode comprises: The usage amount of the grinding water for cooling the wafer is adjusted according to the rate of change of the total grinding force of the grinding wheel within a fifth range; and the usage amount of the grinding water for cooling the grinding wheel is adjusted according to the rate of change of the total grinding force of the grinding wheel within a sixth range; wherein the fifth range and the sixth range are determined based on a regular water amount.

14. A wafer thinning apparatus for performing the wafer thinning method of any one of claims 1 to 13, characterized by, Comprising: A worktable on which a plurality of chuck tables are arranged, the worktable being configured to rotate about a vertical central axis thereof to drive the plurality of chuck tables to rotate as a whole so as to switch the chuck tables between different stations, the chuck tables being used to hold and rotate wafers; A grinding device comprising a grinding wheel arranged at a lower portion thereof, the grinding device being used to grind the wafers by the grinding wheel to thin the wafers; A detection device used to obtain the grinding force of the grinding wheel in a horizontal direction and the grinding force of the grinding wheel in a normal direction during the thinning of the wafers; A control device used to determine the rate of change of the total grinding force of the grinding wheel based on the grinding force of the grinding wheel in the horizontal direction and the grinding force of the grinding wheel in the normal direction during the thinning of the wafers, and determine the amount of grinding water for thinning based on the grinding force of the grinding wheel in the horizontal direction during the thinning of the wafers.

15. The wafer thinning apparatus of claim 14, wherein, The detection device comprises a three-axis ring sensor arranged below the chuck table to detect the reaction force of the grinding force of the chuck table in the horizontal direction and the reaction force of the grinding force of the chuck table in the normal direction.

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