High-precision lossless cutting method and system based on laser implicit cutting and laser thermal stress control fracture cutting technology

Abstract

The invention discloses a high-precision lossless cutting method and system based on a laser implicit cutting technology and a laser thermal stress control fracture cutting technology, the system combines the laser implicit cutting technology and the laser thermal stress control fracture cutting technology, and a modified area is formed in a silicon wafer through high-power laser emitted by a laser according to set parameters. Then, a continuous laser light source emits low-power laser to form a thermal stress induction area on the surface of the material, low-temperature gas is rapidly blown and cooled near the area, and the wafer is cut through thermal stress. The problems that according to a laser thermal stress control fracture cutting technology, due to the fact that stress field distribution is complex, thermal distribution is difficult to control, cutting precision is low, and increasingly-developing industry requirements are difficult to meet are solved.

Description

TECHNICAL FIELD

[0001] The application relates to the field of wafer cutting, in particular to a high-precision non-destructive cutting method and system based on laser hidden cutting and laser thermal stress controlled fracture cutting technology of an efficient energy-saving drip irrigation system. BACKGROUND

[0002] With the development of semiconductor devices towards miniaturization and high integration, the wafer cutting process has increasingly stringent requirements for precision, efficiency and cross-section quality. The traditional laser hidden cutting technology forms a modified layer inside the wafer by focusing laser, and realizes separation by using thermal stress, which has the advantages of non-contact and small edge collapse. However, the exponential decay of laser energy with depth results in low modification efficiency in deep layer: in order to meet the needs of thick wafer cutting, the laser energy often needs to be increased, which is easy to cause thermal damage to the material; while reducing the energy leads to discontinuous modified layer, and the cutting integrity is difficult to guarantee. Another laser thermal stress controlled fracture cutting technology induces thermal stress to realize crack by continuously heating the surface of the material with laser and auxiliary cooling. Although this method is suitable for thick material cutting, the distribution of thermal stress field is complex, and the control of temperature gradient and cooling rate is difficult, which is easy to cause crack propagation path deviation and edge collapse size exceeding the standard (usually > 10 μm), and it is difficult to meet the needs of advanced packaging for cutting precision (edge collapse < 5 μm).

[0003] In view of these problems, the prior art proposes some improvement schemes, but there are still certain limitations, for example, the patent with publication number CN119549902A discloses a wafer laser hidden cutting positioning method, which determines the laser focusing position by three-dimensional scanning of the wafer and model training and fitting of the scanning data, but there are still some deficiencies: it is difficult to solve the problem that the complex stress inside the laser hidden cutting leads to difficulty in completely meeting the current situation in calculation, so as to ensure the integrity of the cutting. SUMMARY

[0004] (I) Technical problems solved In view of the problems of the prior art, the present application aims to provide a high-precision non-destructive cutting method and system based on laser hidden cutting and laser thermal stress controlled fracture cutting technology, which solves the problems existing in the prior art and overcomes the problem of difficulty in deep modification caused by the exponential decay of laser energy with depth. The traditional method needs to increase the energy (easy to cause thermal damage) or sacrifice the cutting efficiency and integrity (the modified layer is discontinuous). The present system reduces the stringent requirements for single hidden cutting technology to achieve complete penetration and high energy threshold modification layer by combining thermal stress fracture technology. The analyzer analyzes the fracture surface after each cutting to obtain key quality indicators such as edge collapse size, position, morphology (sawtooth, layered peeling) and crack characteristics (bifurcation, inclined expansion). The computing device uses the preset fault diagnosis logic to feed back the optimized parameters to the controller for real-time adjustment in the next cutting process according to the actual unqualified result data provided by the analyzer. This closed-loop feedback system does not need to rely on a perfect initial calculation model. It senses the deviation caused by internal complex stress and other factors through the actual cutting result, and automatically and continuously adjusts the parameters for compensation and optimization. This fundamentally solves the problem of "difficulty in completely meeting the complex status through calculation", significantly improves the robustness of the cutting process, and finally reliably ensures the integrity and high precision (edge collapse size qualification rate) of the cutting.

[0005] (Two) Technical solutions To achieve the above object, the present application provides the following technical solutions: a high-precision non-destructive cutting method based on laser hidden cutting and laser thermal stress controlled fracture cutting technology, the cutting method comprising the following steps: S1 input the initial wafer thickness parameter through the controller, set the initial hidden cutting laser parameter and the parameter of the continuous laser light source by the controller; S2 generate high-power laser by the laser; S3 adjust the pulse frequency and scanning speed of the high-power laser by the optical system; S4 focus the laser adjusted by the optical system to the specified depth of the wafer through the focusing lens to form a modified region inside the wafer; S5 the continuous laser light source emits low-power laser to form a thermal stress induced region at the position corresponding to the modified region on the wafer surface; S6 the cooling device rapidly blows gas to cool the thermal stress induced region, and the wafer is fractured along the modified region by thermal stress to realize cutting; S7 take out the cut wafer, analyze its fracture surface by the analyzer, and judge whether the edge collapse size is qualified; if qualified, output the current cutting parameter to the storage; S8If not qualified, the morphology, location and crack characteristics of the chipped edge are input into a computing device, and the computing device calculates optimized hidden cutting laser parameters and continuous laser source parameters based on the characteristics, which are fed back to the controller, and steps S1-S6 are repeated for re-cutting.

[0006] Preferably, in step S1, the initial hidden cutting laser parameters include a focal depth, a pulse frequency and a scanning speed.

[0007] Preferably, in step S1, the parameters of the continuous laser source include a power and a spot diameter.

[0008] Preferably, in step S3, the optical system controls the laser generated by the laser to form a continuous modification region inside the wafer by adjusting the pulse frequency and the scanning speed of the laser.

[0009] Preferably, the pulse frequency of the laser ranges from 100 kHz to 500 kHz, and the scanning speed ranges from 50 mm / s to 200 mm / s.

[0010] Preferably, in step S2, the high-power laser generated by the laser has a power ranging from 50 W to 200 W, which is used to form a modification region inside the wafer through nonlinear absorption, and the depth of the modification region is 30%-50% of the thickness of the wafer.

[0011] Preferably, in step S5, the low-power laser emitted by the continuous laser source has a power ranging from 10 W to 50 W, which is used to form a thermal stress-induced region on the surface of the wafer along the projection path of the modification region, and the temperature gradient of the region is 50-200 ℃ / mm.

[0012] Preferably, in step S4, the focusing lens adjusts the distance from the wafer through the controller to control the focal depth of the laser to be 30%-50% of the thickness of the wafer, and the focal position is aligned with the projection path of the thermal stress-induced region in step S5.

[0013] Preferably, the modification region formed in step S4 corresponds in space to the thermal stress-induced region formed in step S5, the axis of the modification region deviates from the center line of the thermal stress-induced region by ≤5 μm, and the length of the thermal stress-induced region covers the length of the modification region, so that the wafer is broken along the modification region through the synergistic effect of thermal stress and the modification region, and the deviation of the breaking path is ≤3 μm.

[0014] Preferably, the system of the high-precision non-destructive cutting method of the laser hidden cutting and laser thermal stress controlled fracture cutting technology comprises a ceramic stage for placing the wafer to be cut; a laser for generating a laser beam; an optical system for controlling the laser generated by the laser; Focusing lens: it is used to focus the laser emitted by the optical system to the specified depth of the wafer; Continuous laser source: it is used to emit laser to form a thermal stress induced area on the material surface; Cooling device: it is used to blow high-speed cold air; Analyzer: it is used to measure and analyze the size, position, morphology and crack characteristics of the edge collapse; Computing device: it is used to calculate new laser trimming parameters and parameters of the continuous laser source by using the unqualified edge collapse size data measured by the analyzer; Storage: it is used to store qualified data.

[0015] (Three) beneficial effects The present application aims to provide a high-precision non-destructive cutting method and system based on laser trimming and laser thermal stress controlled fracture cutting technology, which innovatively combines laser trimming technology with laser thermal stress controlled fracture cutting technology, effectively overcoming the bottleneck of traditional single technology. On the one hand, a modified area is formed inside the wafer by a high-power laser, and a low-power continuous laser source and a cooling device are used to induce thermal stress on the surface, which not only reduces the dependence on the high energy threshold of the trimming technology and avoids the problems of low efficiency and thermal damage in the deep modification, but also solves the problem of insufficient precision of traditional thermal stress cutting by using controllable thermal stress distribution, achieving high-precision and non-destructive wafer cutting effect. On the other hand, the analyzer and the computing device provided by the device form a closed-loop feedback system, which can automatically optimize the laser parameters according to the actual data such as the edge collapse size, morphology and crack characteristics of the wafer after cutting and feedback to the controller, forming a dynamic calibration mechanism of "detection-computation-adjustment", which can adapt to complex stress environment without relying on perfect initial model, significantly improving the robustness of the cutting process. The device not only controls the edge collapse size within the industry's strict standards (qualified edge collapse < 5 μm), but also greatly improves the cutting integrity and production efficiency through parameter self-optimization, meeting the urgent needs of high-precision cutting process for the miniaturization and high-integration development of semiconductor devices, and having significant technical advancement and engineering application value. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The system schematic diagram of the present application is shown in the figure; Figure 2 The schematic diagram of the feedback method in the present application is shown in the figure; In the figure: 1-controller, 2-laser, 3-optical system, 4-focusing lens, 5-continuous laser source, 6-cooling device, 7-wafer, 8-ceramic stage, 9-analyzer, 10-computing device, 11-storage. DETAILED DESCRIPTION

[0017] The specific embodiments of the present application will be described below with reference to the accompanying drawings of the examples of the present application. Figure 1-Appendix Figure 2 The technical solutions in the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0018] Example 1: This invention provides a technical solution: a high-precision non-destructive cutting method based on laser hidden cutting and laser thermal stress controlled fracture cutting technology, the cutting method comprising the following steps: S1 inputs the initial wafer thickness parameters through controller 1, and controller 1 sets the initial hidden laser parameters and the parameters of the continuous laser source 5; S2 generates laser light through laser 2; S3 controls the laser generated by laser 2 through optical system 3; S4 focuses the laser emitted from the optical system 3 onto the wafer 7 at a specified depth using the focusing lens 4; S5 continuous laser source 5 emits laser light onto the surface of wafer 7; The S6 cooling device 6 rapidly blows air onto the workpiece surface to cool it, increasing the stress on the wafer 7 and thus enabling the wafer 7 to be cut. S7 takes out the cut wafer 7 and uses the analyzer 9 to analyze its cross-section to determine whether the chipping size is qualified. If it is qualified, the parameters are output to the storage 11. The defective chipping morphology, location, and crack features of S8 are input into the computing device 10, calculated by the computing device 8, and then input into the controller 1 for recutting.

[0019] Detailed explanation of the effects of each step S1-S8: S1: Input the initial wafer thickness parameters 7 through controller 1, and set the initial hidden laser parameters and continuous laser source 5 parameters.

[0020] Effect: This is the "initialization" step of the entire cutting process. It defines the basis of the operation: Wafer thickness parameter 7: Informs the system of the physical properties (thickness) of the wafer being cut.

[0021] Initial hidden laser parameters include focusing depth, pulse frequency, and scanning speed. These parameters determine the depth, morphology, and continuity of the modified layer formed inside the wafer.

[0022] Initial continuous laser source parameters 5: primarily laser power. This determines the heating intensity that forms the thermal stress-induced region on the surface of wafer 7.

[0023] Regarding the focusing depth of the laser Calculation According to a typical case of 300mm silicon wafer, the focusing depth is linearly related to the thickness: ; In the case of T=300μm, , the proportionality coefficient 0.4 corresponds to a back modification layer depth of 40% of the thickness, avoiding excessive depth leading to backside edge collapse.

[0024] Pulse frequency Calculation Pulse frequency The calculation of pulse frequency is related to the energy density. The initial setting needs to consider both cutting efficiency and thermal damage: Derivation basis: when T=300μm , the frequency decreases by the square root as the thickness decreases to maintain the energy density.

[0025] Scan speed Calculation The scan speed is positively related to the square root of the focusing depth, ensuring stable energy input per unit length: Substitute , we get: S2: Generate laser light through laser 2.

[0026] Effect: Execute the high-power laser parameters set in S1 to generate a high-power pulsed laser beam for stealth cutting.

[0027] This is the energy source generation action for physically executing the stealth cutting step. Without laser generation, subsequent steps cannot proceed.

[0028] S3: Control the laser generated by laser 2 through the optical system.

[0029] Accurately control the properties of the laser beam generated by S2, mainly the pulse frequency and scan speed. This directly determines the precision and efficiency of the laser scanning to form the modification layer inside the wafer. Ensure that the stealth cutting laser acts on the specified depth inside the wafer 7 according to the preset mode (such as scan path, pulse interval).

[0030] S4: Focus the laser emitted by the optical system to the specified depth of the wafer 7 through the focusing lens.

[0031] Accurately focus the laser beam controlled by S3 to the specified depth inside the wafer 7 (the depth is set based on the wafer thickness parameter input by S1). At the focal point, the laser energy density reaches the highest, sufficient to induce nonlinear absorption inside the wafer 7, forming a modification layer (the core of stealth cutting).

[0032] This is a key step to realize the "laser stealth dicing" technology. Only when the laser is precisely focused to the target depth, an effective modification region can be formed inside as the guide path for subsequent fracture. Depth setting error will directly lead to poor cutting quality (such as the edge collapse morphology problem analyzed in S6) S5: The continuous laser light source 5 emits laser light on the wafer surface.

[0033] Effect: Execute the low-power continuous laser parameters set in S1 to form a local heating area (thermal stress-induced area) on the wafer surface (usually along the predetermined cutting line).

[0034] This is a key input to realize the "laser thermal stress controlled fracture dicing" technology. Surface heating creates a temperature gradient for rapid cooling in the next step (S6). The heating intensity must be matched with the wafer material, thickness, and the state of the modification layer formed by stealth dicing.

[0035] Through the input thickness T data, the controller 1 is used to control the power, spot diameter, and offset distance of the continuous laser light source emitting laser light.

[0036] 1. Power Calculation The power is linearly related to the thickness, taking into account the need for thermal stress-induced crack propagation: Deduction basis: T=300μm in the case , This coefficient controls the heat-affected zone (HAZ) to .

[0037] 2. Spot diameter Calculation The spot diameter is linearly related to the thickness to ensure uniform energy density distribution: Deduction basis: T=300μm is 15μm, adjusted to 17.25μm after expansion by 1.15 times, meeting the requirement of dispersed energy density (energy density ).

[0038] 3. Offset distance Calculation The offset distance is linearly related to the thickness to match the initial crack propagation angle Deduction basis: T=300μm , corresponds to .

[0039] S6: The cooling device 6 rapidly blows air cooling to the workpiece surface to increase the stress of the wafer and realize the cutting of the wafer.

[0040] Rapid cooling is performed near the heating region formed in S5. This results in a large temperature gradient and thermal stress between the material below the heating region (expanded by heat) and the surface layer material that is rapidly cooled. This thermal stress will guide the crack to initiate from the internal modification layer (weak zone) formed in S4 and expand along the predetermined cutting path. Eventually, the thermal stress overcomes the material strength, causing the wafer to break cleanly along the modification path and the direction guided by the thermal stress. This is the execution step for the final separation using thermal stress. S5 and S6 together constitute the "thermal stress breaking" technique. The timing, location, and rate of cooling are crucial to the initiation and expansion direction of the crack.

[0041] S7: The cut wafer 7 is taken out and analyzed by an analyzer to determine whether the chipping size is qualified. If qualified, the parameters are output to the storage 11. Quality detection and evaluation of the cutting result: the analyzer 9 (optical microscope, scanning electron microscope SEM, etc.) is used to measure the chipping size (Chipping Size) with high precision, observe the chipping position (front / back), chipping morphology (sawtooth, layered peeling), and crack characteristics (bifurcation, inclined expansion). The measured chipping size is compared with the preset standard (<5 μm). If the cutting quality is qualified, it means that the current S1 parameters (including initial settings and any feedback-optimized parameters) are effective for the wafer 7 of this thickness, and they are stored in the storage 11 as a reference or starting point for future cutting of the same type of wafer 7. This is a key step for quality control and knowledge accumulation. Only after detection can it be known whether the cutting is successful and the parameters are appropriate. Qualified parameters are stored to form an experience database, improving the efficiency of subsequent cutting.

[0042] S8: Unqualified chipping morphology, position, and crack characteristics are input into the computing device, which calculates and inputs them into the controller for re-cutting. Handle the case of cutting failure: input defect information: input the unqualified chipping characteristics (position, morphology, crack characteristics) obtained by S7 analysis into the computing device.

[0043] The cutting method is used in a cutting system, and the sequence of operation of the devices in the cutting system is as follows: The ceramic stage 8 places the wafer 7 to be cut; The laser 2 is used to generate a laser beam; The optical system 3 is used to control the laser generated by the laser 2; The focusing lens 4 focuses the laser emitted by the optical system 3 to a specified depth of the wafer 7; The continuous laser light source 5 emits laser light to form a thermal stress-induced region on the material surface; The cooling device 6 blows high-speed cold air; analyzer 9 for measuring and analyzing the size, position, morphology and crack feature of the chipping edge; The computing device 10 uses the unqualified chipping edge size data measured by the analyzer 9 to calculate new laser parameters and parameters of the continuous laser source 5; The storage 11 is used to store qualified data for next use.

[0044] The optical system 3 is used to control the pulse frequency and scanning speed of the laser 2.

[0045] The laser 2 is a high-power laser.

[0046] The continuous laser source 5 is a low-power laser source.

[0047] The focusing lens 4 changes the depth of the focal point in the wafer 7 by changing the distance between the wafer 7.

[0048] The analysis method of the analyzer 9 for unqualified wafers 7 is as follows: S1 judges whether the chipping edge position is mainly back chipping edge or front chipping edge, if it is mainly back chipping edge, it enters S2, if S2 judges the chipping edge morphology, if it is jagged, the laser depth is too deep, if it is layered peeling, the laser depth is too shallow, and the input computing device 10.

[0049] S3 judges the crack feature, if the crack feature is bifurcation, the thermal stress is too large, if it is inclined expansion, the thermal stress is uneven, and the input computing device 10.

[0050] When the chipping edge is unqualified (less than 5 microns is qualified), the analyzer 9 inputs the measurement parameters to the computing device 10, and the computing device recalculates the laser parameters according to the preset fault diagnosis logic (such as S1-S3 judgment logic): 1. Back chipping edge is mainly jagged -> laser depth is too deep The main adjustment is the focusing depth and the pulse frequency, The focusing depth adjustment formula is: The difference between the chipping edge greater than 5 and the root of the chipping edge (chipping edge length) Through experiments on different thickness silicon wafers (such as ), it is found that when , reducing the focusing depth can effectively control the chipping edge within the target range.

[0051] The pulse frequency adjustment formula is: This formula is derived experimentally. In the experiment, a 300µm thick wafer 7 was cut, and the initial parameters were... Collapsed edge (The back side accounts for 70%). After adjustment: (KHz) Effects: The modified layer depth was reduced by about 6%, the back stress was reduced, and the edge chipping was reduced from 8.2μm to 4.1μm.

[0052] 2. Mainly chipping on the back edge + layered peeling -> the hidden cut depth is too shallow. This can be addressed by increasing the depth of focus and changing the scanning speed. The formula for adjusting focus depth is: Insufficient formation of modified layer When the focusing depth is too shallow, the modified layer does not completely penetrate the wafer, leading to incomplete material separation and layered peeling. Increasing D allows the modified layer to extend to the back side, promoting complete fracture. Stress distribution optimization. A suitable depth of focus can create a symmetrical stress distribution within the wafer: upper layer: compressive stress (laser incident side); lower layer: tensile stress (back side). This allows cracks to propagate stably along the modified layer, preventing layered spalling. The physical meaning of the exponential function. The nonlinear effect of material fracture toughness on the adjustment amount was simulated. When the edge breakage is large, the number of internal defects in the material increases, and the required adjustment amount tends to saturate (asymptotic characteristic of exponential function).

[0053] In the experiment, for The wafer with thickness 7 is cut. initial parameters , (Layered peeling edge breakage). Calculate adjustment amount: After adjustment: the focusing depth increased from 110μm to 116.4μm, and the edge chipping decreased to 4.3μm.

[0054] Scan speed In the experiment, for 275 Initial parameters for cutting wafers of thickness 7 , After adjustment (See previous example). Calculate the new scan rate: Results: After adjustment, the pulse overlap rate changed from 82% to 80%, the width of the modified layer remained at 12μm±1μm, and the edge chipping decreased from 7.5μm to 4.3μm.

[0055] 3. Predominantly chipped edges + forked cracks -> Excessive thermal stress The power and spot diameter of the continuous laser source 5 are adjusted according to the situation, The power adjustment formula is: The stress laser generates a temperature gradient by local heating, inducing thermal stress to separate the material along the kerf. Excessive power will cause: The temperature gradient exceeds the critical value Crack propagation is out of control, forming bifurcated cracks or shell-like patterns.

[0056] In the experiment: for a wafer 7 with a thickness of 300 μm, the continuous laser source 5 should be 25 W, and the edge collapse =8.2 μm (65% on the front side, bifurcated crack characteristics). The adjustment amount is calculated: The adjusted power is: The heat-affected zone decreases from 3.8 μm to 2.3 μm, and the edge collapse decreases to 4.1 μm.

[0057] The adjustment formula for the spot diameter is: By measuring the system output corresponding to different d values through experiments, it is found that when d increases by 15%, the system meets certain indicators (such as minimum error, highest efficiency), thereby inducing .

[0058] 4. When the front edge collapse is dominant, and there are inclined cracks and uneven thermal stress The offset distance Δx is optimized in this case The offset distance Δx formula is In the experimental process, cutting a 300 μm thick wafer will produce front edge collapse and inclined cracks, and the measured expansion angle of the inclined cracks is 3°. After entering the empirical formula, =30.5, the crack is greatly reduced after re-cutting.

[0059] Generate new parameters: based on the diagnosis results, the calculation device 10 calculates new kerf laser parameters (affecting S2-S4) and continuous laser parameters (affecting S5).

[0060] Controller 1: input the optimized parameters into the controller.

[0061] Second cutting: the controller 1 uses the new parameters to start a new round of cutting (from S1, but the new parameters are input).

[0062] Working principle: The controller 1 sets the focus depth, pulse frequency and other parameters of the hidden cutting laser and the power and other parameters of the continuous laser according to the input wafer thickness. The laser 2 generates laser, which is precisely focused to the inside of the wafer 7 by the focusing lens 4 to form a modified layer after being regulated by the optical system 3; the continuous laser light source 5 synchronously heats the surface, and the cooling device 6 rapidly cools the induced thermal stress to make the wafer 7 break along the modified layer. After cutting, the analyzer 9 detects the size, position and crack characteristics of the edge collapse: if it is qualified, the parameters are stored in the storage 11 for subsequent cutting of the same type of wafer; if it is not qualified, the computing device 10 re-calculates the optimized parameters according to the edge collapse characteristics (such as back sawtooth-shaped edge collapse indicating that the hidden cutting depth is too deep, and front bifurcated crack indicating that the thermal stress is too large), and feeds back to the controller to start a new round of cutting until it is qualified.

[0063] Comparative example 1: Traditional laser hidden cutting technology (cutting 300 μm thick silicon wafer as an example) The traditional laser hidden cutting technology only focuses high-power pulsed laser inside the wafer to form a modified layer, relies on the stress concentration effect of the modified layer itself, and cooperates with external mechanical force (such as film stretching machine stretching) to make the wafer break along the modified layer without thermal stress assistance and closed-loop feedback adjustment.

[0064] The specific process is as follows: after inputting the wafer thickness of 300 μm, set the laser power to 250 W (which needs to meet the energy requirement of deep layer modification), the pulse frequency to 300 kHz, the scanning speed to 80 mm / s, and the focus depth to 200 μm (which needs to be close to the bottom of the wafer to ensure penetration); then the high-power pulsed laser forms a modified layer inside the wafer after focusing, and relies on the laser energy to directly penetrate the material to form a continuous modified path; after cutting, the wafer is separated by applying mechanical tension with the film stretching machine; finally, the detection shows that the front edge collapse size reaches 8-12 μm, and the back edge collapse size reaches 10-15 μm (because the laser energy decays exponentially with depth, the deep layer modification is insufficient, and the mechanical tension easily leads to edge tearing), the path deviation is 6-10 μm (crack bifurcation easily occurs at the discontinuous part of the modified layer, and the mechanical force cannot accurately guide), 15% of the wafer surface appears burnt or micro-cracks (high-power laser leads to local overheating), and the single cutting qualified rate is only 58% (which needs to be adjusted multiple times for trial cutting, and the efficiency is low).

[0065] Taking the same 300 μm thick silicon wafer as the cutting object, in terms of edge collapse size, the traditional technology causes insufficient deep layer modification due to the decay of laser energy with depth, and the non-uniform effect of mechanical tension, the front edge collapse reaches 8-12 μm, and the back edge collapse reaches 10-15 μm; while the present application can control the front edge collapse within 3 μm and the back edge collapse within 4 μm through the synergistic effect of internal modified layer (weak area) and surface thermal stress (directional driving force) and real-time optimization of focus depth, thermal stress intensity and other parameters with the closed-loop feedback system, avoiding edge tearing caused by mechanical force.

[0066] In the aspect of path deviation, the traditional technology is prone to discontinuity of the modification layer, and the mechanical tension cannot accurately guide the crack propagation, with a path deviation of 6-10 μm; the present application strictly controls the deviation (≤5 μm) between the axis of the modification layer and the center line of the thermal stress inducing area, ensures stress concentration in the modification layer, and uses uniform thermal stress to avoid crack branching, so that the path deviation is stabilized within 2 μm.

[0067] In the aspect of thermal damage, the traditional technology uses a 250W high-power laser to ensure deep modification, resulting in 15% of the wafers appearing burnt or micro-cracks; the present application reduces the dicing laser power to 150W (without the need for separate through modification), and cooperates with a 30W low-power continuous laser and rapid cooling control to completely avoid thermal damage, with a thermal influence area controlled within 5 μm.

[0068] In the aspect of cutting efficiency, the traditional technology lacks a real-time optimization mechanism, with a single cutting qualified rate of only 58%, and multiple trial cuts are required to adjust the parameters; the present application uses a closed-loop feedback system of "cutting-detection-optimization", directly optimizes the parameters based on the actual edge collapse characteristics, with a first cutting qualified rate of 82%, and after secondary optimization, the qualified rate can be increased to more than 95%, greatly reducing the number of trial cuts.

[0069] In the aspect of applicable thickness range, the traditional technology is limited by the exponential decay of laser energy with depth, and is only applicable to thin wafers below 200 μm, and thick wafers are prone to insufficient modification; the present application reduces the dependence on "complete penetration" of the dicing layer through thermal stress assisted fracture, and can stably cut wafers with a thickness of 100-500 μm, significantly widening the applicable range.

[0070] In summary, the present application combines laser dicing and thermal stress fracture technology, and uses closed-loop feedback parameter optimization to overcome the limitations of traditional laser dicing technology in precision, efficiency, thermal damage and applicable range, and provides a better solution for thick wafer high-precision non-destructive cutting. Although embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A high-precision non-destructive cutting method based on laser stealth cutting and laser thermal stress controlled fracture cutting technology, characterized in that, The cutting method comprises the following steps: S1, inputting an initial wafer thickness parameter through a controller (1), setting initial hidden cutting laser parameters and parameters of a continuous laser light source (5) by the controller (1); S2, generating high-power laser by a laser (2); S3, adjusting the pulse frequency and scanning speed of the high-power laser by an optical system (3); S4, focusing the laser adjusted by the optical system (3) to a specified depth of the wafer (7) by a focusing lens (4), and forming a modified region inside the wafer (7); S5, emitting low-power laser by the continuous laser light source (5), and forming a thermal stress induction region on the wafer (7) surface corresponding to the modified region; S6, rapidly blowing and cooling the thermal stress induction region by a cooling device (6), and making the wafer (7) crack along the modified region by thermal stress to realize cutting; S7, taking out the cut wafer (7), analyzing the cross section of the wafer (7) by an analyzer (9), and judging whether the edge collapse size is qualified; if qualified, outputting the current cutting parameters to a storage (11); S8, if not qualified, inputting the morphology, position and crack characteristics of the edge collapse into a computing device (10), calculating the optimized hidden cutting laser parameters and continuous laser light source (5) parameters based on the characteristics by the computing device (10), feeding back to the controller (1), and repeating steps S1-S6 to cut again.

2. The high-precision non-destructive cutting method based on the laser hidden cutting and laser thermal stress controlled fracture cutting technology according to claim 1, characterized in that, In step S1, the initial hidden cutting laser parameters include: focusing depth, pulse frequency and scanning speed.

3. The high-precision non-destructive cutting method based on the laser stealth cutting and laser thermal stress controlled fracture cutting technology according to claim 1, characterized in that, In step S1, the parameters of the continuous laser light source (5) include power and spot diameter.

4. The high-precision non-destructive cutting method based on the laser stealth cutting and laser thermal stress controlled fracture cutting technology according to claim 1, characterized in that, In step S3, the optical system (3) adjusts the pulse frequency and scanning speed of the laser to control the laser generated by the laser (2) to form a continuous modified region inside the wafer (7).

5. The high-precision non-destructive cutting method based on the laser stealth cutting and laser thermal stress controlled fracture cutting technology according to claim 4, characterized in that, The pulse frequency of the laser ranges from 100 kHz to 500 kHz, and the scanning speed ranges from 50 mm / s to 200 mm / s.

6. The high-precision non-destructive cutting method based on the laser stealth cutting and laser thermal stress controlled fracture cutting technology according to claim 1, characterized in that, In step S2, the high-power laser generated by the laser (2) has a power ranging from 50 W to 200 W, which is used to form a modified region inside the wafer (7) through nonlinear absorption, and the depth of the modified region is 30%-50% of the wafer thickness.

7. The high-precision non-destructive cutting method based on the laser stealth cutting and laser thermal stress controlled fracture cutting technology according to claim 1, characterized in that, In step S5, the low-power laser emitted by the continuous laser light source (5) has a power ranging from 10 W to 50 W, which is used to form a thermal stress induction region on the wafer surface along the projection path of the modified region, and the temperature gradient of the region is 50-200 ℃ / mm.

8. The high-precision non-destructive cutting method based on the laser stealth cutting and laser thermal stress controlled fracture cutting technology according to claim 1, characterized in that, In step S4, the focusing lens (4) adjusts the distance from the wafer by the controller (1), and controls the laser focal point depth to be 30%-50% of the wafer thickness, and the focal point position is aligned with the projection path of the thermal stress induction region in step S5.

9. The high-precision non-destructive cutting method based on the laser stealth cutting and laser thermal stress controlled fracture cutting technology according to claim 1, characterized in that, The modified region formed in step S4 corresponds in space to the thermal stress induction region formed in step S5, the axis of the modified region deviates from the center line of the thermal stress induction region by ≤5 μm, and the length of the thermal stress induction region covers the length of the modified region, so that the wafer cracks along the modified region through the synergistic effect of thermal stress and the modified region, and the cracking path deviation is ≤3 μm.

10. A system for performing a high precision non-destructive cutting method based on the laser stealth dicing and laser thermal stress controlled fracture dicing technique according to any one of claims 1-9, characterized in that, It comprises a ceramic carrier (8) for placing the wafer (7) to be cut; a laser (2) for generating a laser beam; Optical system (3): for controlling the laser generated by the laser (2); Focusing lens (4): for focusing the laser emitted by the optical system (3) to a specified depth of the wafer (7); Continuous laser source (5): for emitting laser to form a thermal stress induced area on the material surface; Cooling device (6): for blowing high-speed cold air; Analyzer (9): for measuring and analyzing the size, position, morphology and crack characteristics of the edge collapse; Computing device (10): for calculating new parameters of the hidden cutting laser and the continuous laser source (5) using the unqualified edge collapse size data measured by the analyzer (9); Storage (11): for storing qualified data.

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