Wafer processing method for suppressing backside grinding damage

Abstract

The application relates to the technical field of semiconductor manufacturing, in particular to a wafer processing method for inhibiting back surface grinding damage, which comprises the following steps: a femtosecond laser beam is incident from the front surface of a wafer, the femtosecond laser beam is focused to a preset depth inside a material layer to be removed on the back surface of the wafer through focusing positioning, the material layer is scanned in a direction parallel to the wafer surface, and a modified layer parallel to the surface is formed inside the wafer; rough grinding is performed on the back surface of the wafer to remove most of the material above the modified layer, and a residual material layer is reserved above the modified layer; fine grinding processing is performed on the residual material layer, and a shearing force parallel to the wafer surface is applied at the same time, so that the residual material layer is peeled off along the whole modified layer; and modified material marks possibly remaining on the back surface of the wafer after the modified layer is peeled off are removed, thereby obtaining a wafer back surface with low damage. Therefore, the problems of subsurface damage, high processing cost, and the difficulty in compatibility between low damage and high efficiency and low cost in the prior art are solved.

Description

Technical Field

[0001] This application relates to the field of semiconductor manufacturing technology, and in particular to a wafer processing method for suppressing back-side grinding damage. Background Technology

[0002] Backside thinning of wafers is a critical step in semiconductor packaging processes. Its purpose is to remove excess material from the back side of the wafer to achieve the target thickness, meeting the requirements for chip stacking, heat dissipation, and thinning. Currently, the mainstream thinning method is grinding with diamond wheels. Because wafers are brittle materials, the mechanical action of the abrasive grains during traditional grinding processes can cause defects such as microcracks, residual stress, and lattice damage on the back side of the wafer, severely affecting wafer processing yield and finished product performance. The processing damage problem is particularly prominent for ultra-thin wafers.

[0003] To address grinding damage, existing technologies optimize grinding process parameters or employ non-mechanical thinning processes such as chemical or plasma methods by reducing grinding feed rate, decreasing grinding pressure, and using higher-grit ultrafine grinding wheels. While simply optimizing grinding parameters can mitigate the mechanical effects of abrasive grains and reduce surface damage to some extent, it significantly lengthens processing time and drastically reduces production line capacity, failing to balance processing quality and production efficiency. Non-mechanical thinning processes generally suffer from slow material removal rates and long production cycles. Furthermore, the chemical reagents and process waste gases and liquids impose stringent environmental treatment requirements, resulting in high raw material and maintenance costs, making them unsuitable for large-scale industrial production. Summary of the Invention

[0004] This application provides a wafer processing method to suppress back-side grinding damage, thereby solving problems such as subsurface damage, high processing cost, and the incompatibility between low damage and high efficiency and low cost in the prior art.

[0005] The first aspect of this application provides a wafer processing method for suppressing back-side grinding damage, comprising the following steps: a femtosecond laser beam is incident from the front side of the wafer; the femtosecond laser beam is focused at a preset depth inside the material layer to be removed on the back side of the wafer by focusing and positioning; the material layer is scanned along a direction parallel to the wafer surface to form a modified layer parallel to the surface inside the wafer; the lattice bonding strength of the modified layer is reduced but the overall structure of the wafer remains intact; a grinding wheel is used to rough grind the back side of the wafer to remove most of the material above the modified layer, and the remaining thickness of the back side of the wafer after rough grinding is monitored in real time; when the remaining thickness reaches a preset threshold, the rough grinding is stopped at a preset distance from the modified layer, leaving a residual material layer above the modified layer; the residual material layer is finely ground, and a shearing force parallel to the wafer surface is applied simultaneously to peel off the residual material layer along the entire modified layer; and any residual modified material traces that may remain on the back side of the wafer after the modified layer is peeled off are removed, resulting in a wafer back side with low damage.

[0006] Optionally, the preset depth inside the material layer to be removed satisfies Where d is the preset depth inside the material layer to be removed. This represents the total thickness of the material layer to be removed from the back side of the wafer. The thickness of the residual material layer.

[0007] Optionally, the process parameters of the incident femtosecond laser beam are: laser pulse width less than 500 fs, single pulse energy of 0.1~10 μJ, focused spot diameter of 0.5~3 μm, and scanning spacing of 3~15 μm; the lattice bonding strength of the modified layer formed by the femtosecond laser is reduced to 30%~70% of the original strength, ensuring that the modified layer forms a uniform weak bonding interface.

[0008] Optionally, the pressure used in the fine grinding process is 20% to 60% of the pressure used in the rough grinding process, and the grinding wheel grit size is #3000 to #8000.

[0009] Optionally, the shear force parallel to the wafer surface is provided by one or more of the following methods: a horizontal oscillating mechanism of the grinding spindle, an eccentric rotation mechanism of the chuck carrying the wafer, or directional injection of high-pressure fluid from the side.

[0010] Optionally, the process also includes an in-situ monitoring step: during the fine grinding and peeling process, the torque signal and / or acoustic emission signal of the grinding spindle are collected in real time; the collected signals are compared with a preset peeling feature library to obtain the comparison result, wherein the peeling feature library includes at least one of the following features: torque reduction feature when the modified layer peels off completely, and acoustic emission burst feature; when the comparison result shows that the signal feature changes from continuous grinding mode to intermittent peeling mode, it is determined that the residual material layer has begun to peel off completely, and the feed rate of the grinding wheel is reduced.

[0011] A second aspect of this application provides a wafer processing system for suppressing back-side grinding damage, comprising: a femtosecond laser processing module, a grinding spindle and a grinding wheel, a shear force application module, a control unit, and an in-situ monitoring module. The femtosecond laser processing module is used to incident a femtosecond laser beam from the front side of the wafer, focusing the femtosecond laser beam at a predetermined depth within the material layer to be removed on the back side of the wafer, and scanning the material layer along a direction parallel to the wafer surface to form a modified layer parallel to the surface inside the wafer. The grinding spindle and grinding wheel are used to perform rough grinding and fine grinding on the wafer surface. The shear force application module is used to apply a shear force parallel to the surface of the wafer during the fine grinding process to assist the residual material layer to peel off along the modified layer in its entirety. The control unit is electrically connected to the femtosecond laser processing module, the grinding execution module, and the shear force application module, respectively, and is used to uniformly control the working sequence, start and stop status, and process parameters of each module. The in-situ monitoring module is connected to the control unit and is used to collect the torque signal and / or acoustic emission signal of the grinding spindle in real time during the fine grinding and peeling process, and feed the collected signals back to the control unit.

[0012] Optionally, the shear force application module is a functional mechanism capable of generating shear force parallel to the wafer surface, including one or more of a horizontal swing mechanism, an eccentric rotating chuck, or a high-pressure fluid nozzle.

[0013] Optionally, the femtosecond laser processing module and the grinding spindle and grinding wheel are integrated on the same processing platform. The processing platform also includes a wafer transfer mechanism for automatically transferring wafers between the laser processing station and the grinding station, and maintaining the spatial orientation of the wafer and the spatial positional relationship of the modified layer unchanged during the transfer process.

[0014] A third aspect of this application provides a computer program product storing a computer program that, when executed by a processor, implements a wafer processing method for suppressing back-side grinding damage as described in the above embodiments.

[0015] The beneficial effects of using the present invention are as follows: (1) In this application, a modified layer is pre-formed inside the wafer using a femtosecond laser. The lattice bonding strength of the modified layer is reduced but the overall structure of the wafer is maintained. During the fine grinding stage, a shearing force parallel to the wafer surface is applied to peel off the residual material layer along the modified interface, rather than relying on the mechanical pressing of abrasive grains for removal. This fundamentally changes the material removal method, avoids the extension of microcracks, dislocations and residual stress to the retained layer, significantly suppresses back-side grinding damage, and improves wafer processing quality. (2) In the process of rough grinding and fine grinding, this application monitors the remaining thickness in real time and controls the stop position of rough grinding to ensure that the remaining material layer is removed by peeling. Since the peeling process generates almost no mechanical impact force and the shear force direction is parallel to the wafer surface, it avoids the bending stress of the axial pressure on the ultrathin wafer in traditional grinding, which is suitable for ultrathin wafer processing and reduces the risk of fragmentation. (3) This application adopts a mature grinding wheel process, which has a processing speed much higher than non-mechanical thinning methods such as chemical etching and plasma etching. The pretreatment process of femtosecond laser is short and stable, and it is smoothly connected with the grinding process. The overall production cycle can meet the requirements of mass production lines. At the same time, it does not require a large amount of chemical reagents or complex environmental protection equipment, effectively controlling production and maintenance costs. (4) This application is equipped with an in-situ monitoring mechanism to collect torque and acoustic emission signals in real time and compare them with the feature library. It can accurately determine the peeling state of the residual layer and adjust the grinding feed rate in time to realize closed-loop control of the processing process, avoid human operation error and process fluctuation, and ensure uniform and stable processing quality of batch products. (5) The laser parameters, grinding process and shear force application method used in this application can be flexibly adjusted according to the wafer specifications, material and target thickness. It can be applied to conventional semiconductor wafers and can also meet the back-side thinning requirements of special wafers such as power devices and sensors. The solution has wide compatibility and strong applicability, and is easy to promote and apply in the industry.

[0016] This solves the problems of subsurface damage, high processing costs, and the incompatibility between low damage and high efficiency and low cost in existing technologies.

[0017] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0018] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a flowchart of a wafer processing method for suppressing back-side grinding damage according to an embodiment of this application; Figure 2This is a schematic diagram of a wafer processing system for suppressing back-side grinding damage according to an embodiment of this application. Detailed Implementation

[0019] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0020] A wafer processing method for suppressing back-side grinding damage according to an embodiment of this application is described below with reference to the accompanying drawings.

[0021] Specifically, Figure 1 This is a schematic flowchart of a wafer processing method for suppressing back-side grinding damage, provided in an embodiment of this application.

[0022] like Figure 1 As shown, the wafer processing method for suppressing back-side grinding damage includes the following steps: In step S101, a femtosecond laser beam is incident from the front side of the wafer. By focusing and positioning, the femtosecond laser beam is focused to a preset depth inside the material layer to be removed on the back side of the wafer. The material layer is scanned along a direction parallel to the wafer surface, forming a modified layer inside the wafer that is parallel to the surface. The lattice bonding strength of the modified layer is reduced, but the overall structure of the wafer is maintained.

[0023] In this design, semiconductor device structures are already fabricated on the front side of the wafer. When a femtosecond laser beam is incident from the front side of the wafer, it passes through the passive regions between the device structures or through a dielectric layer transparent to the laser wavelength to avoid damaging the device structures. Femtosecond lasers have extremely short pulse widths and extremely high peak power densities. When they interact with materials, they produce localized modification in the focal region through multiphoton absorption and nonlinear ionization mechanisms, without significantly affecting the surrounding areas. Therefore, the formation of the modified layer is a cold processing procedure, without a melt-resolidification layer and without thermal stress accumulation.

[0024] Specifically, the lattice bonding strength of the modified layer is reduced to 30%–70% of its original strength, but the wafer as a whole still maintains its structural integrity. This strength reduction ensures that the modified layer becomes the preferred fracture surface during the subsequent peeling process, while also preventing premature delamination of the wafer due to mechanical loads during the rough grinding stage. The modified layer is continuously distributed in a plane parallel to the wafer surface, ensuring the integrity and consistency of the peeling interface.

[0025] It is understood that the depth of the modified layer in this embodiment determines the thickness of the subsequent peel-off layer. If the modified layer is too deep (close to the front side of the wafer), the residual material layer will be too thick, increasing the surface roughness after peeling; if the modified layer is too shallow (close to the back side of the wafer), the rough grinding process may directly touch the modified layer, causing premature delamination. Therefore, the depth of the modified layer needs to be precisely set according to the target removal thickness.

[0026] In this embodiment of the application, the preset depth inside the material layer to be removed satisfies Where d is the preset depth inside the material layer to be removed. This represents the total thickness of the material layer to be removed from the back side of the wafer. The thickness of the residual material layer.

[0027] in, The value is selected based on the wafer material, diameter, and final thickness requirements. For silicon wafers, Preferably 5~15μm; for hard and brittle materials such as silicon carbide, The preferred size is 8~20μm.

[0028] For example, when the target thinning thickness is 100 μm, the thickness of the residual material layer is set. When the thickness is 10 μm, the preset depth inside the material layer to be removed, i.e., the modified layer depth d = =100-10=90μm.

[0029] Specifically, the depth of the modified layer is determined using a focusing system. This system includes a confocal microscope or a white light interferometer, used to monitor the position of the femtosecond laser focus relative to the wafer surface and back side in real time. Before laser scanning, the front side of the wafer is focused to determine the reference plane. Then, based on the total thickness of the material layer to be removed on the back side of the wafer and the preset residual layer thickness, the target depth is calculated. The focus is then precisely moved to this depth position using a motorized displacement stage.

[0030] Understandably, a thicker residual material layer helps protect the modified interface from damage during rough grinding, but it increases the burden on subsequent fine grinding and peeling. A thinner residual material layer, on the other hand, requires higher precision in controlling the stop position of rough grinding.

[0031] In this embodiment, the process parameters of the incident femtosecond laser beam are: laser pulse width less than 500 fs, single pulse energy of 0.1~10 μJ, focused spot diameter of 0.5~3 μm, and scanning spacing of 3~15 μm; the lattice bonding strength of the modified layer formed by the femtosecond laser is reduced to 30%~70% of the original strength, ensuring that the modified layer forms a uniform weak bonding interface.

[0032] The preferred values ​​for the above parameter range are: pulse width 300~350 fs, single pulse energy 3~8 μJ, spot diameter 1.0~2.0 μm, and scanning spacing 6~12 μm. Within this parameter range, the modified layer exhibits the best uniformity and the most stable intensity reduction. It should be noted that the optimal parameters may vary slightly for different materials, such as silicon, silicon carbide, and gallium nitride, but all fall within the above range.

[0033] Specifically, the scanning path adopts a raster scanning method, that is, scanning line by line along the first direction, stepping one scan interval after completing a line, and then scanning the next line in the opposite direction, and so on. The scanning area covers the entire projected area of ​​the material layer to be removed on the back of the wafer, ensuring complete coverage of the modified layer in the horizontal direction.

[0034] It is understood that the embodiments of this application solve the problems of unevenness, easy damage, and uncontrollable interface in traditional laser modification by defining a precise laser process window and a bonding strength weakening range, thus providing stable interface conditions for the subsequent overall, stable, and tear-free peeling of the residual layer.

[0035] In step S102, a grinding wheel is used to rough grind the back side of the wafer to remove most of the material above the modified layer, and the remaining thickness of the back side of the wafer after rough grinding is monitored in real time. When the remaining thickness reaches a preset threshold, the rough grinding is stopped at a preset distance from the modified layer, leaving a layer of residual material above the modified layer.

[0036] Specifically, throughout the rough grinding process, a capacitive thickness sensor continuously and in real-time collects the remaining thickness data on the back side of the wafer and feeds the real-time data back to the control unit, achieving closed-loop monitoring of the grinding process. The control unit compares the measured thickness with a preset threshold in real time. When the remaining thickness on the back side of the wafer reaches the preset threshold, it immediately controls the grinding wheel to stop feeding and lift the tool, terminating the rough grinding process, and finally leaving a uniform residual material layer above the modified layer.

[0037] It is understood that the embodiments of this application efficiently remove most of the material above the modified layer through coarse grinding, reducing the driving force required for subsequent shearing and peeling, and avoiding wafer breakage caused by the large stress impact generated by directly peeling off thick material.

[0038] In step S103, the residual material layer is finely ground, and a shearing force parallel to the wafer surface is applied simultaneously to peel off the residual material layer along the entire modified layer.

[0039] In this process, the precision grinding uses a cutting depth below the critical value for brittle fracture. The purpose of reducing the precision grinding pressure is to decrease the axial penetration depth of the abrasive grains into the residual material layer, thus avoiding the introduction of new damage before it peels off. The depth of cut in a single pass is controlled below 50 nm, which is far below the critical cutting depth for brittle materials to undergo brittle fracture, ensuring that material removal is mainly achieved through plastic flow or small-scale fracture.

[0040] In the embodiments of this application, the pressure used for fine grinding is 20% to 60% of the pressure used for rough grinding, and the grinding wheel grit size is #3000 to #8000.

[0041] Understandably, the fine grinding pressure is set to 20%~60% of the coarse grinding pressure, employing a low-pressure grinding mode to reduce the compressive and impact stresses of the abrasive grains on the wafer substrate, thus avoiding brittle fracture and microcrack formation. High-mesh ultrafine grinding wheels (#3000~#8000) are selected, with fine abrasive grains and uniform cutting, enabling ultra-fine micro-cutting and reducing surface roughness.

[0042] In the embodiments of this application, the shear force parallel to the wafer surface is provided by one or more of the following methods: a horizontal oscillating mechanism of the grinding spindle, an eccentric rotation mechanism of the chuck carrying the wafer, or directional injection of high-pressure fluid from the side.

[0043] Specifically, when a horizontal oscillating mechanism is used, the grinding spindle makes a small reciprocating oscillation in a plane perpendicular to the spindle axis, with an oscillation amplitude of 0.5~2mm and an oscillation frequency of 5~20Hz, so that the grinding wheel and the wafer generate periodic lateral relative motion, thereby forming a shear stress component at the contact interface.

[0044] When an eccentric rotary chuck is used, the vacuum chuck carrying the wafer is eccentrically positioned relative to the rotation center of the grinding spindle, with an eccentricity of 0.1~1mm. As the chuck rotates, the edge of the wafer undergoes periodic tangential motion relative to the grinding wheel, generating shearing force.

[0045] When a high-pressure fluid nozzle is used, a high-pressure fluid, such as deionized water or compressed air, is sprayed from the side of the wafer at an angle of 5° to 30° to the wafer surface. The fluid impacts the wafer edge, generating a tangential thrust and thus a shearing force. The pressure of the high-pressure fluid is preferably 0.5 to 5 MPa.

[0046] The three methods described above can be used independently or in combination. For ordinary silicon wafers, the eccentric rotating chuck method is sufficient; for high-hardness materials such as silicon carbide, it is recommended to use a combination of a horizontal oscillating mechanism and a high-pressure fluid nozzle to provide stronger shearing force.

[0047] It is understandable that the key inventive point is the synergistic mechanism of simultaneous application of fine grinding and shear force in the embodiments of this application. In conventional grinding, the residual material layer is removed piece by piece by the axial indentation of abrasive grains, resulting in a large indentation depth and deep damage. In this application, the modified layer has become a weak bonding interface, and the introduction of shear force causes the residual material layer to slide and separate along this interface as a whole. Fine grinding plays two main roles in this process: first, it removes the microscopic protrusions on the surface of the residual material layer, reducing the peeling resistance; second, it introduces initial microcracks at the modified interface, providing a crack initiation point for the whole-layer peeling under the action of shear force.

[0048] In this embodiment of the application, the in-situ monitoring step is as follows: During the fine grinding and peeling process, the torque signal and / or acoustic emission signal of the grinding spindle are collected in real time; The collected signals are compared with a preset peeling feature library to obtain the comparison results. The peeling feature library contains at least one of the following features: torque reduction feature when the modified layer peels off completely, and acoustic emission burst feature. When the comparison results show that the signal characteristics have changed from continuous grinding mode to intermittent peeling mode, it is determined that the residual material layer has begun to peel off completely, and the feed rate of the grinding wheel should be reduced.

[0049] Among them, the torque signal reflects the tangential resistance between the grinding wheel and the wafer during the grinding process and is a direct physical quantity characterizing the material removal state. The acoustic emission signal reflects the elastic stress waves released when microscopic fractures occur inside the material and is highly sensitive to crack initiation and propagation. The two signals complement each other; the torque signal is sensitive to changes in the macroscopic removal state, while the acoustic emission signal is sensitive to microscopic fracture events. Using them together can improve the accuracy and robustness of spalling determination.

[0050] The method for establishing the peeling feature library is as follows: A test wafer of the same material and size as the wafer to be processed is used. Pre-processing is performed using the same femtosecond laser modification and rough grinding processes, followed by fine grinding and shear force peeling experiments. During the experiments, signals are simultaneously acquired at high sampling rates of ≥1kHz for torque signals and ≥100kHz for acoustic emission signals. The actual moment of peeling occurrence is simultaneously observed using a high-speed microscope or side-mounted camera system. The signal features corresponding to the observed peeling initiation moment are labeled and extracted to form a positive sample feature set. Simultaneously, normal grinding signals without peeling are collected as negative samples. The above samples are trained using a machine learning classification algorithm to obtain a classification model capable of determining the peeling state in real time during operation. This model and its parameters constitute the peeling feature library.

[0051] The spalling process is divided into continuous grinding mode and intermittent spalling mode. The signal characteristics of continuous grinding mode and intermittent spalling mode differ as follows: For torque signals: the signal characteristics of continuous grinding mode are smooth or slow fluctuations with relatively stable amplitude. The signal characteristics of intermittent stripping mode are often accompanied by sudden drops and sawtooth fluctuations.

[0052] For acoustic emission signals: the signal characteristics of continuous grinding mode are a continuous spectrum distribution with low energy levels. The signal characteristics of intermittent stripping mode are often accompanied by bursts of pulses, with amplitudes increasing sharply by 5 to 20 times compared to the background noise, and high-frequency components appearing in the spectrum.

[0053] When the comparison results show that the signal characteristics have changed from continuous grinding mode to intermittent peeling mode, it is determined that the residual material layer has begun to peel off completely. The control unit reduces the feed rate of the grinding wheel from the current value to 30%~60% of the initial feed rate. The purpose of reducing the feed rate is to reduce the axial load during the grinding process and prevent the grinding wheel from continuing to press down at high speed when the residual material layer has begun to peel off, which could cause damage to the modified interface or new damage to the back side of the wafer.

[0054] In some preferred embodiments, when the peeling signal is strong and stable, the control unit may choose to reduce the feed rate to zero, that is, stop the downward feed, and only keep the shear force application module working continuously, so that the residual material layer can be peeled off completely under pure shear action.

[0055] It is understood that the embodiments of this application convert the invisible peeling process into quantifiable electrical signal changes by collecting torque and acoustic emission signals, and then achieve automatic judgment and response through feature comparison, thereby realizing the intelligentization and automation of the fine grinding and peeling process.

[0056] In step S104, any traces of modified material that may remain on the back side of the wafer after the modified layer is peeled off are removed to obtain a wafer back side with low damage.

[0057] Specifically, the back side of the wafer after the modified layer has been removed can be treated using methods such as chemical mechanical polishing (CMP) or plasma etching. When using CMP, the polishing time is controlled at 30–60 seconds, the polishing pressure is 30%–50% of the conventional pressure, and a commercially available slurry compatible with the wafer material is used. When using plasma etching, the etching gas is selected from… , , One or more of them with The mixed gas was used to etch a depth of 30-50 nm.

[0058] It is understood that the processing steps in the embodiments of this application are not essential. For some application scenarios where surface quality requirements are not high, such as back-side thinning of power devices, the quality of the wafer back side after peeling in step S103 is sufficient to meet the requirements.

[0059] Next, referring to the accompanying drawings, a wafer processing system for suppressing back-side grinding damage according to an embodiment of this application is described.

[0060] Figure 2 This is a schematic diagram of the structure of a wafer processing system for suppressing back-side grinding damage according to an embodiment of this application.

[0061] like Figure 2 As shown, the wafer processing system 10 for suppressing back-side grinding damage includes: a femtosecond laser processing module 100, a grinding spindle and grinding wheel 200, a shear force application module 300, a control unit 400, and an in-situ monitoring module 500.

[0062] The system includes a femtosecond laser processing module 100, which directs a femtosecond laser beam from the front of the wafer, focuses the beam at a preset depth inside the material layer to be removed on the back of the wafer, and scans the material layer along a direction parallel to the wafer surface to form a modified layer parallel to the surface inside the wafer. A grinding spindle and grinding wheel 200 are used to perform rough and fine grinding on the wafer surface. A shearing force application module 300 applies a shearing force parallel to the wafer surface during fine grinding to assist in peeling off the residual material layer along the modified layer. A control unit 400 is electrically connected to the femtosecond laser processing module, the grinding execution module, and the shearing force application module to uniformly control the working sequence, start / stop status, and process parameters of each module. An in-situ monitoring module 500 is connected to the control unit to collect torque signals and / or acoustic emission signals from the grinding spindle in real time during fine grinding and peeling, and feeds the collected signals back to the control unit.

[0063] In this embodiment, the shear force application module is a functional mechanism capable of generating shear force parallel to the wafer surface, including one or more of a horizontal swing mechanism, an eccentric rotating chuck, or a high-pressure fluid nozzle.

[0064] Specifically, the horizontal oscillation mechanism is connected to the grinding spindle, causing the grinding spindle to oscillate slightly in a plane perpendicular to its axis. The oscillation amplitude is 0.5~2mm, and the oscillation frequency is 5~20Hz. When the spindle rotates and feeds downwards, the horizontal oscillation causes periodic lateral relative motion between the grinding wheel and the wafer, forming a shear stress component at the contact interface. The advantages of this method are its compact structure, ease of integration, and suitability for upgrading conventional grinding equipment.

[0065] The structural feature of an eccentric rotary chuck is that the rotation center of the vacuum chuck carrying the wafer is eccentrically positioned relative to the rotation center of the grinding spindle, with an eccentricity of 0.1~1mm. When the chuck rotates in the same direction as the spindle, the wafer edge generates a periodic tangential motion relative to the grinding wheel, forming a shearing force. This method does not change the motion pattern of the grinding spindle; it can be implemented simply by replacing the eccentric chuck, resulting in the lowest modification cost.

[0066] The high-pressure fluid nozzle is positioned on the side of the wafer, with the nozzle axis forming an angle of 5° to 30° with the wafer surface. The nozzle exit is 5 to 15 mm from the wafer edge. During operation, deionized water or compressed air is sprayed at a pressure of 0.5 to 5 MPa. The fluid impacts the wafer edge, generating tangential thrust and shearing force. The advantage of this method is that it avoids mechanical contact with the wafer, thus avoiding the risk of scratches that may result from hard contact. It is particularly suitable for ultra-thin wafers or applications requiring extremely high surface quality.

[0067] The three shear force generation methods mentioned above can be used independently or in combination depending on the wafer material, thickness, and processing requirements.

[0068] It is understood that the specific selection of the shear force application module in the embodiments of this application depends on the characteristics of the wafer material, equipment configuration, and process requirements. Regardless of the implementation method, its core function is to apply a shear force parallel to the wafer surface to the residual material layer during the grinding process, causing the residual material layer to peel off completely along the weakened modified interface. Therefore, any mechanism or device capable of achieving this function falls within the protection scope of the embodiments of this application.

[0069] In this embodiment, the femtosecond laser processing module and the grinding spindle and grinding wheel are integrated on the same processing platform. The processing platform also includes a wafer transfer mechanism for automatically transferring wafers between the laser processing station and the grinding station, and maintaining the spatial orientation of the wafer and the spatial positional relationship of the modified layer unchanged during the transfer process.

[0070] It is understood that the embodiments of this application integrate the femtosecond laser processing module and the grinding module on the same platform, reducing the number of times the wafer is loaded and unloaded between different devices, reducing the risk of particle contamination and scratches; eliminating the steps of secondary clamping and repositioning, avoiding the problem of misalignment between the modified layer and the grinding position due to repeated positioning errors; shortening the waiting time of the wafer between processes, and improving production efficiency.

[0071] It should be noted that the foregoing explanation of an embodiment of a wafer processing method for suppressing back-side grinding damage also applies to a wafer processing system for suppressing back-side grinding damage in this embodiment, and will not be repeated here.

[0072] This application also provides a computer program product that stores a computer program that, when executed by a processor, implements the wafer processing method described above for suppressing back-side grinding damage.

[0073] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0074] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "N" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0075] Any process or method described in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more N executable instructions for implementing custom logic functions or processes, and the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as should be understood by those skilled in the art to which embodiments of this application pertain.

[0076] It should be understood that the various parts of this application can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, the N steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0077] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

Claims

1. A wafer processing method for suppressing back-side grinding damage, characterized in that, Includes the following steps: A femtosecond laser beam is incident from the front side of the wafer. By focusing and positioning, the femtosecond laser beam is focused to a preset depth inside the material layer to be removed on the back side of the wafer. The material layer is scanned along a direction parallel to the wafer surface, forming a modified layer inside the wafer that is parallel to the surface. The lattice bonding strength of the modified layer is reduced, but the overall structure of the wafer is maintained. A grinding wheel is used to rough grind the back side of the wafer to remove most of the material above the modified layer. The remaining thickness of the back side of the wafer after rough grinding is monitored in real time. When the remaining thickness reaches a preset threshold, the rough grinding is stopped at a preset distance from the modified layer, leaving a layer of residual material above the modified layer. The residual material layer is finely ground, and a shearing force parallel to the wafer surface is applied simultaneously to peel off the entire residual material layer along the modified layer. Remove any traces of modified material that may remain on the back side of the wafer after the modified layer is peeled off, to obtain a wafer back side with low damage.

2. The wafer processing method for suppressing back-side grinding damage according to claim 1, characterized in that, The preset depth inside the material layer to be removed satisfies Where d is the preset depth inside the material layer to be removed. This represents the total thickness of the material layer to be removed from the back side of the wafer. The thickness of the residual material layer.

3. The wafer processing method for suppressing back-side grinding damage according to claim 1, characterized in that, The process parameters of the incident femtosecond laser beam are: laser pulse width less than 500 fs, single pulse energy of 0.1~10 μJ, focused spot diameter of 0.5~3 μm, and scanning spacing of 3~15 μm; the lattice bonding strength of the modified layer formed by the femtosecond laser is reduced to 30%~70% of the original strength, ensuring that the modified layer forms a uniform weak bonding interface.

4. A wafer processing method for suppressing back-side grinding damage according to claim 1, characterized in that, The pressure used in the fine grinding process is 20% to 60% of the pressure used in the rough grinding process, and the grinding wheel grit size is #3000 to #8000.

5. A wafer processing method for suppressing back-side grinding damage according to claim 1, characterized in that, The shear force parallel to the wafer surface is provided by one or more of the following methods: a horizontal oscillating mechanism of the grinding spindle, an eccentric rotation mechanism of the chuck carrying the wafer, or directional injection of high-pressure fluid from the side.

6. A wafer processing method for suppressing back-side grinding damage according to claim 1, characterized in that, It also includes in-situ monitoring steps: During the fine grinding and peeling process, the torque signal and / or acoustic emission signal of the grinding spindle are collected in real time; The collected signals are compared with a preset peeling feature library to obtain the comparison results. The peeling feature library includes at least one of the following features: torque reduction feature when the modified layer peels off completely, and acoustic emission burst feature. When the comparison results show that the signal characteristics have changed from continuous grinding mode to intermittent peeling mode, it is determined that the residual material layer has begun to peel off completely, and the feed rate of the grinding wheel should be reduced.

7. A wafer processing system for suppressing back-side grinding damage, which can implement the wafer processing method for suppressing back-side grinding damage as described in any one of claims 1-6, characterized in that, include: The system includes a femtosecond laser processing module, a grinding spindle and grinding wheel, a shearing force application module, a control unit, and an in-situ monitoring module. The femtosecond laser processing module is used to incident a femtosecond laser beam from the front side of the wafer, focus the femtosecond laser beam to a preset depth inside the material layer to be removed on the back side of the wafer, scan the material layer in a direction parallel to the wafer surface, and form a modified layer inside the wafer that is parallel to the surface. The grinding spindle and grinding wheel are used to perform rough grinding and fine grinding on the wafer surface; The shear force application module is used to apply a shear force parallel to the surface of the wafer during the fine grinding process to assist the residual material layer to peel off along the entire modified layer. The control unit is electrically connected to the femtosecond laser processing module, the grinding execution module, and the shearing force application module, respectively, and is used to uniformly control the working sequence, start and stop status and process parameters of each module. The in-situ monitoring module is connected to the control unit and is used to collect the torque signal and / or acoustic emission signal of the grinding spindle in real time during the fine grinding and peeling process, and to feed back the collected signals to the control unit.

8. A wafer processing system for suppressing back-side grinding damage according to claim 7, characterized in that, The shear force application module is a functional mechanism capable of generating shear force parallel to the wafer surface, including one or more of a horizontal swing mechanism, an eccentric rotating chuck, or a high-pressure fluid nozzle.

9. A wafer processing system for suppressing back-side grinding damage according to claim 7, characterized in that, The femtosecond laser processing module and the grinding spindle and grinding wheel are integrated on the same processing platform. The processing platform also includes a wafer transfer mechanism for automatically transferring wafers between the laser processing station and the grinding station, and maintaining the spatial orientation of the wafer and the spatial positional relationship of the modified layer unchanged during the transfer process.

10. A computer program product, comprising a computer program or instructions, characterized in that, When the computer program or instructions are executed, they implement a wafer processing method for suppressing back-side grinding damage as described in any one of claims 1-6.

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