Laser lift-off system and laser lift-off method

Abstract

The application discloses a laser stripping system and a laser stripping method, and the laser stripping system is applied to stripping a functional chip from a substrate, and the laser stripping system comprises a laser output module, a bearing table, a stress monitoring module and a processing and control unit. The laser output module is used for outputting a first laser beam. The bearing table is used for bearing a wafer and is located on an exit light path of the laser output module, and the first laser beam can be focused on the wafer and is used for separating the functional chip from the substrate. The relative motion between the bearing table and the laser output module is generated, and the first laser beam fully covers and scans the functional chip. The stress monitoring module is used for acquiring an actual stress value borne by a functional chip area irradiated by the first laser beam in real time when the first laser beam is focused on the functional chip. The processing and control unit is in communication connection with the stress monitoring module, the laser output module and the bearing table respectively, is configured to receive the actual stress value of the stress monitoring module, control output parameter adjustment of the laser output module and / or relative speed adjustment between the bearing table and the laser output module, and improves a stripping yield.

Description

Technical Field

[0001] This invention relates to the field of laser ablation, and more particularly to a laser ablation system and laser ablation method. Background Technology

[0002] Micro-LED (Micro Light Emitting Diode), also known as micro LED, is widely used in cutting-edge fields such as high-end automotive displays, AR / VR near-eye displays, ultra-high-definition large screens, and medical imaging displays due to its advantages such as high brightness, high contrast, low power consumption, and fast response speed.

[0003] Laser lift-off (LLO) technology is a core process in Micro-LED chip manufacturing to separate the epitaxial layer from the temporary substrate, which is commonly made of sapphire or SiC. The principle of LLO is to use a laser of a specific wavelength to penetrate the interface region between the temporary substrate and the epitaxial layer. Under the influence of laser energy, the semiconductor material at the interface undergoes thermal decomposition, thereby breaking the interfacial bonding force and achieving separation of the epitaxial layer from the temporary substrate.

[0004] Traditional laser lift-off processes employ fixed parameter modes, setting uniform parameters such as laser energy density, scanning speed, and pulse frequency for the entire wafer. In actual production, unavoidable microscopic inhomogeneities exist between the temporary substrate and the epitaxial layer: thickness fluctuations in the sapphire substrate, deviations in the doping concentration of the epitaxial layer, and differences in microstructures such as dislocations and defects.

[0005] During laser stripping, the duration of the laser pulse is usually in the nanosecond to microsecond range. The instantaneous thermal shock can cause the temperature of the epitaxial layer to rise to over 1000°C in a very short time. The thermal conductivity of the temporary substrate is low, and the heat cannot dissipate quickly, resulting in a huge temperature gradient between the epitaxial layer and the temporary substrate, which causes significant thermal stress. As the size of the Micro LED chip gradually decreases, its stress resistance and fracture strength become weaker.

[0006] As mentioned above, using fixed parameters for laser ablation and thermal stress runaway can lead to insufficient laser energy in some areas, resulting in adhesion and incomplete ablation between the epitaxial layer and the temporary substrate, while excessive laser energy in other areas can cause damage to the epitaxial layer such as ablation, edge cracking, and internal microcracks. Summary of the Invention

[0007] One of the objectives of this invention is to provide a laser lift-off system that at least solves the technical problem in the prior art where epitaxial layer adhesion or damage occurs during laser lift-off due to fixed laser output parameters, resulting in low lift-off yield.

[0008] To achieve one of the above-mentioned objectives, one embodiment of the present invention provides a laser lift-off system for removing functional chips from a substrate of a wafer, the functional chips being disposed on the substrate. The laser lift-off system includes:

[0009] The laser output module outputs the first laser beam; A support stage is used to support the wafer and is located in the output optical path of the laser output module, so that the first laser beam can be focused on the wafer and used to separate the functional chip from the substrate; relative motion is generated between the support stage and the laser output module to achieve full coverage scanning of the functional chip by the first laser beam; The stress monitoring module is used to acquire the stress value of the functional chip area irradiated by the first laser beam in real time when the first laser beam is focused on the functional chip. The processing and control unit is communicatively connected to the stress monitoring module, the laser output module, and the support platform, respectively. The processing and control unit is configured to receive the stress value from the stress monitoring module and output control commands based on the stress value. The control commands are used to adjust the output parameters of the laser output module and / or the relative speed between the support platform and the laser output module.

[0010] As a further improvement of one embodiment of the present invention, a plurality of the functional chips are arranged in an array along a first direction and a second direction, the support platform is movably disposed along the first direction and the second direction, and the support platform drives the wafer to move relative to the first laser beam along the first direction or the second direction.

[0011] As a further improvement of one embodiment of the present invention, the laser output module includes a laser emitter and an optical system; The laser emitter emits a first laser beam; The optical system, disposed on the output optical path of the laser emitter, is used for shaping and scanning the first laser beam. It includes a galvanometer, a focusing lens, and a spot shaper. The support stage is disposed on the output optical path of the optical system. The first laser beam can form a stripping spot with preset parameters on the wafer surface. The size of the stripping spot covers at least one of the functional chips.

[0012] As a further improvement of one embodiment of the present invention, the stress monitoring module includes a laser interferometer, which emits a second laser beam. The energy of the second laser beam is less than that of the first laser beam. The second laser beam can form a probe spot on the wafer surface. The size of the probe spot is smaller than that of the stripping spot. The probe spot and the stripping spot maintain a preset fixed distance on the wafer surface.

[0013] As a further improvement of one embodiment of the present invention, the pulse frequency of the first laser beam is 45-55 Hz, and the sampling frequency of the second laser beam is 1-5 MHz.

[0014] As a further improvement of one embodiment of the present invention, the processing and control unit takes a first time from acquiring the stress value to outputting the control command, and the interval between adjacent pulses of the first laser beam is a second time, wherein the first time is shorter than the second time.

[0015] As a further improvement of one embodiment of the present invention, the processing and control unit has a built-in ideal stress reference model and a feedback control algorithm. The ideal stress reference model presets an optimal stress window, and the feedback control algorithm generates control commands based on the deviation between the stress value and the optimal stress window.

[0016] As a further improvement of one embodiment of the present invention, the ideal stress reference model presets a lower stress threshold and an upper stress threshold, and the optimal stress window is located between the lower stress threshold and the upper stress threshold. When the stress value is higher than the upper limit of the stress threshold, the control command controls the laser output module to reduce the laser energy density, and / or controls the relative motion speed between the support platform and the laser output module to increase; When the stress value is lower than the lower limit of the stress threshold, the control command controls the laser output module to increase the laser energy density, and / or controls the relative motion speed between the support platform and the laser output module to decrease.

[0017] As a further improvement of one embodiment of the present invention, the adjustment range of the laser energy density of the laser output module is between 5% and 20%, and the adjustment range of the relative motion speed between the support platform and the laser output module is between 10% and 30%.

[0018] To achieve one of the above-mentioned objectives, an embodiment of the present invention provides a laser lift-off method, comprising the steps of: providing a wafer and placing it on a support stage, wherein the wafer includes a substrate and a plurality of functional chips, and the plurality of functional chips are disposed on the substrate; The laser output module is activated, and the relative movement between the support platform and the laser output module is initiated; the laser output module outputs a first laser beam, and the support platform is disposed on the output optical path of the laser output module. The first laser beam scans the wafer and is used to separate the functional chip and the substrate. The stress monitoring module and the processing and control unit are activated; when the first laser beam scans the functional chip area of ​​the wafer, the stress monitoring module acquires the stress value borne by the functional chip area in real time; the processing and control unit receives the stress value and controls the laser output module to adjust the output parameters according to the stress value, and / or controls the support stage and the laser output module to adjust the relative speed between them.

[0019] As a further improvement of one embodiment of the present invention, the support platform is movable; Initiating the relative movement between the support platform and the laser output module includes the following steps: initiating the support platform; Controlling the relative speed between the support platform and the laser output module includes the steps of: controlling the movement speed of the support platform; And / or, the laser stripping method includes the steps of: repeatedly performing the stress value acquisition step of the stress monitoring module and the dynamic adjustment step of the processing and control unit until the full coverage scan of the entire wafer is completed.

[0020] As a further improvement of one embodiment of the present invention, the wafer includes a first region and a second region, wherein the thickness of the first region is thinner than the thickness of the second region; the processing and control unit presets a lower stress threshold and an upper stress threshold. The first region moves to the scanning path of the first laser beam, the stress monitoring module obtains the first stress value, the processing and control unit receives the first stress value, determines that the first stress value is greater than the upper limit of the stress threshold, controls the laser output module to reduce the laser energy density, and / or controls the relative movement speed between the support platform and the laser output module to increase; The second region moves to the scanning path of the first laser beam, the stress monitoring module obtains the second stress value, the processing and control unit receives the second stress value, determines that the second stress value is less than the lower limit of the stress threshold, controls the laser output module to increase the laser energy density, and / or controls the relative movement speed between the support stage and the laser output module to decrease.

[0021] Compared with the prior art, the present invention provides a laser stripping system, including a stress monitoring module and a processing and control unit. The stress monitoring module can acquire the actual stress value of the irradiated functional chip area in real time after the first laser beam irradiates and strips the chip. The processing and control unit dynamically adjusts the output parameters of the laser output module according to the actual stress value, or adjusts the relative speed between the support platform and the laser output module, so as to realize closed-loop adaptive adjustment of stress value and reduce poor stripping caused by excessively high or low stress values. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a laser ablation system according to one embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of a wafer according to one embodiment of the present invention.

[0024] Figure 3 This is a flowchart illustrating the steps of a laser ablation method according to an embodiment of the present invention. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the scope of protection of the present invention.

[0026] It should be noted that the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Furthermore, the terms "first," "second," "third," "fourth," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0027] The terms “connection,” “connected to,” or any other variations are intended to encompass various relative positions where a connection exists, including both direct and indirect connections. A direct connection can be formed through a pneumatic conduit, while an indirect connection can be formed through devices such as valves or sensors, through pneumatic components such as brake control units, or through any other medium such as air.

[0028] Please see Figure 1 This is a schematic diagram of a laser lift-off system 100 provided in an embodiment of the present invention, which is used to lift the functional chip 210 of a wafer 200 from the substrate 220 of the wafer, wherein the functional chip 210 is disposed on the substrate 220.

[0029] The laser ablation system 100 includes: Laser output module 10 outputs the first laser beam; The support stage 30 is used to support the wafer and is located in the output optical path of the laser output module 10 so that the first laser beam can be focused on the wafer 200 and used to separate the functional chip 210 from the substrate 220; the support stage 30 and the laser output module 10 generate relative motion to achieve full coverage scanning of the functional chip 210 by the first laser beam. The stress monitoring module 50 is used to acquire the stress value of the functional chip area irradiated by the first laser beam in real time when the first laser beam is focused on the functional chip 210. The processing and control unit 60 is communicatively connected to the stress monitoring module 50, the laser output module 10, and the support platform 30, respectively. The processing and control unit 60 is configured to receive the stress value from the stress monitoring module 50 and output control commands based on the stress value. The control commands are used to adjust the output parameters of the laser output module 10 and / or the relative speed between the support platform 30 and the laser output module 10. This achieves closed-loop adaptive control of the stress value, reducing poor peeling caused by excessively high or low stress values.

[0030] In one specific embodiment, the wafer 200 sequentially includes a substrate 220, a laser absorption layer, and a gallium nitride-based epitaxial layer. The substrate 220 is a temporary substrate, preferably a sapphire substrate. The laser absorption layer is a TiN or AlN thin film. The epitaxial layer typically includes a buffer layer, an N-type GaN layer, a multiple quantum well light-emitting layer, and a P-type GaN layer. An array of functional chips 210 is formed on the epitaxial layer using photolithography and etching processes.

[0031] The functional chip 210 has a size of 20-100μm, and the spacing between adjacent functional chips 210 is 2-5μm. It can be understood that the laser lift-off system 100 is used for the mass transfer of functional chips 210, which is to peel the functional chips 210 from the current substrate 220 and transfer them to a new substrate.

[0032] During the laser stripping process, the functional chip 210 on the wafer 200 can be divided into a stripping completed area, a stripping in progress area, and a stripping to be stripped area according to the stripping state. The stripping in progress area is equivalent to the area where the first laser beam irradiates the corresponding functional chip area. In other words, it is the laser action area. The actual stress value detected in this application is the actual stress value corresponding to the stripping in progress area of ​​the functional chip 210.

[0033] The actual stress borne by the functional chip 210 in this application mainly originates from the instantaneous thermal shock effect of the first laser beam. Specifically, when the first laser beam is focused onto the interface between the functional chip 210 and the substrate 220, the energy of the first laser beam is absorbed by the material in the interface region and rapidly converted into heat energy, causing the temperature in the interface region to rise sharply to over 1000°C within a nanosecond timescale. At the same time, the substrate 220, such as a sapphire substrate, has a low thermal conductivity, and the heat cannot diffuse sufficiently to the substrate 220 within the same timescale, resulting in a significant temperature gradient between the functional chip 210 and the substrate 220.

[0034] The aforementioned temperature gradient directly induces significant thermal stress within the functional chip 210 and near the bonding interface. Understandably, the amplitude of this thermal stress is related to the output parameters of the first laser beam, such as energy density and pulse width, and is also affected by the duration of irradiation of the first laser beam on the functional chip 210. By adjusting the output parameters of the first laser beam and / or the irradiation time of the first laser beam on the functional chip 210, the actual stress value that the functional chip in the area to be peeled off can be adjusted, thereby achieving a better peeling effect.

[0035] In a specific embodiment, adjusting the output parameters of the laser output module 50 means adjusting the output parameters of the first laser beam, including energy density, pulse width, etc. Adjusting the relative speed between the support platform 30 and the laser output module 10 means adjusting the irradiation time of the functional chip 210 by the first laser beam. A faster relative speed between the support platform 30 and the laser output module 10 results in a shorter irradiation time for the functional chip 210, while a slower relative speed results in a longer irradiation time for the functional chip 210.

[0036] It should be clarified that when the first laser beam is focused on the functional chip, the stress value borne by the irradiated functional chip area is acquired in real time. This means that the application detects the actual stress value of the functional chip area during the peeling process. The timing of stress monitoring is that the stress monitoring module 50 and the irradiation process of the first laser beam are basically synchronized in time; or, after the first laser beam completes the irradiation and peeling of the current functional chip area, the stress monitoring module 50 detects the same functional chip area during peeling within a very short time window, such as microseconds.

[0037] The pulse width of the first laser beam is extremely short. As soon as the first laser beam stops irradiating the stripped area, the deformation information such as out-of-plane displacement and vibration of the functional chip area caused by thermal shock is still retained. The stress monitoring module 50 obtains the actual stress value borne by the functional chip area during the stripping by capturing the deformation data and performing inversion calculation.

[0038] The actual stress value borne by the functional chip 210 during the laser lift-off process has a clear physical correspondence with the lift-off effect and can serve as a key quantitative indicator characterizing the lift-off quality. Specifically, if the actual stress value borne by the functional chip 210 is too small, it indicates that the output energy of the first laser beam is insufficient or the action time is too short, the interface material between the functional chip 210 and the substrate 220 is not fully decomposed, the bonding force between the functional chip 210 and the substrate 220 is not completely destroyed, and defects such as local adhesion and epitaxial layer residue appear in the functional chip 210, indicating incomplete lift-off.

[0039] The actual stress value borne by the functional chip 210 is too large, indicating that the output energy of the first laser beam is excessive or the action time is too long. The functional chip 210 is subjected to thermal stress impact that exceeds the fracture strength of its material, which may cause different degrees of mechanical damage such as microcracks, edge fragmentation or overall fracture inside the functional chip 210.

[0040] In summary, this application establishes a stress monitoring module 50 and a processing and control unit 60 to construct a closed-loop stress control mechanism during the laser peeling process. The stress monitoring module 50 can monitor the actual stress value of the functional chip area after irradiation by the first laser beam in real time, thereby obtaining a quantitative index characterizing the peeling quality of that area. After receiving the actual stress value, the processing and control unit 60 adjusts the output parameters of the first laser beam and / or the irradiation time of the first laser beam on the functional chip 210, thereby adjusting the actual stress value of the functional chip in the next peeling area to ensure a good peeling effect in the next peeling area.

[0041] Several functional chips 210 are arranged in an array along a first direction and a second direction. The support stage 30 is movable along the first direction and the second direction. The support stage 30 drives the wafer to move relative to the first laser beam along the first direction or the second direction. In this way, the support stage 30 moves while the laser output module 10 is fixed in position, so as to realize the movement of the support stage 30 relative to the laser output module 10.

[0042] Specifically, the moving direction of the support stage 30 is consistent with the array arrangement direction of the functional chips 210, which makes it easier to align and overlap the scanning trajectory of the first laser beam with the arrangement of the functional chips 210.

[0043] The stage 30 moves the wafer along a first direction, such as from left to right, in conjunction with the pulsed first laser beam output by the laser output module 10, to complete the scanning and stripping of the current row of functional chips. After one row is scanned, the stage 30 steps forward a preset distance along a second direction, and then continues to move the wafer 200 along the first direction, such as from right to left, to scan and strip the next row of functional chips.

[0044] By alternating the linkage of the support stage 30 in the first and second directions, the first laser beam can cover all the functional chips 210 arranged in an array on the wafer in a serpentine or bow-shaped scanning path sequence, achieving full coverage of the entire wafer and complete stripping without omission.

[0045] The stage 30 adopts an air-floating XY motion platform, capable of moving along either the first or second vertical direction. The stage 30 has a positioning accuracy of less than or equal to 1 μm and a repeatability of less than or equal to 0.5 μm. It can drive the wafer 200 to move at a constant speed of 50-150 mm / s, supporting both constant speed scanning and step scanning modes. The stage 30 incorporates an encoder and a position feedback unit, enabling real-time transmission of the wafer 200's position information to the processing and control unit 60, achieving precise synchronization between the scanning of the laser output module 10 and the movement of the stage 30.

[0046] The laser output module 10 includes a laser emitter 11 and an optical system 13; Laser emitter 11 emits the first laser beam; Optical system 13 is disposed on the output optical path of laser emitter 11 and is used for shaping and scanning the first laser beam. It includes a galvanometer, a focusing lens and a spot shaper. The support stage 30 is disposed on the output optical path of optical system 13. The first laser beam can form a stripping spot with preset parameters on the wafer surface. The size of the stripping spot covers at least one functional chip 210. It provides an energy source for the laser stripping system.

[0047] In one specific embodiment, the laser emitter 11 is an ultraviolet pulsed laser, such as a KrF excimer laser, with an output wavelength of 248 nm. This wavelength corresponds to the strong absorption band of gallium nitride-based materials, which enables the energy of the first laser beam to be efficiently absorbed at the interface between the functional chip 210 and the substrate 220, and then converted into heat energy to achieve thermal decomposition of the interface material.

[0048] The output parameters of the laser emitter 11 refer to the output parameters of the first laser beam, which typically include energy density, pulse frequency, and pulse width. These parameters can be dynamically adjusted in real time via control commands from the processing and control unit 60 to achieve precise control of the stress value during the stripping process. For example, the energy density of the first laser beam can be set to 500-600 mJ / cm², the pulse width to 10-50 ns, the pulse frequency to 50 Hz, and the initial stripping spot diameter to 50-100 μm.

[0049] It is understandable that when the size of the functional chip 210 is 100μm and the initial spot diameter is 100μm, the stripping spot just covers one functional chip 210, realizing the scanning stripping of a single functional chip 210, without the stripping spot overlapping, which would cause the functional chip 210 to be subjected to repeated thermal shock.

[0050] The optical system 13 includes, but is not limited to, a galvanometer scanning unit, a focusing lens, and a spot shaper. The optical system 13 can focus the first laser beam onto a stripping spot with preset parameters and achieve high-speed scanning under the drive of the galvanometer, thus completing a full-coverage scan of the entire wafer 200 in conjunction with the stage 30.

[0051] The stress monitoring module 50 includes a laser interferometer that emits a second laser beam. The energy of the second laser beam is less than that of the first laser beam. The second laser beam can form a probe spot on the wafer surface. The size of the probe spot is smaller than the size of the stripping spot. The probe spot and the stripping spot maintain a preset fixed distance on the wafer surface. This is used to collect the stress state of the functional chip 210 after thermal shock by the stripping spot.

[0052] Specifically, the stress monitoring module 50 is used to acquire deformation data of the functional chip area irradiated by the first laser beam in real time, and calculate the stress value borne by the functional chip area based on the deformation data.

[0053] The detection direction of the laser interferometer is parallel to the direction of the laser stripping beam. In other words, the first laser beam is incident perpendicularly to the wafer surface, and the second laser beam is also incident perpendicularly to the wafer surface. After being reflected by the surface, the second laser beam interferes with the reference beam, forming interference fringes that carry deformation information of the functional chip 210 region.

[0054] When the functional chip 210 undergoes nanoscale out-of-plane displacement, vibration, or other deformation due to thermal stress generated by laser peeling, the phase, spacing, and contrast of the interference fringes will change accordingly. By acquiring the change signal of the interference fringes and combining it with phase demodulation algorithms or Doppler frequency shift analysis, the actual stress value borne by the functional chip 210 during the peeling process can be calculated.

[0055] Laser interferometers have significant advantages such as non-contact operation, high sensitivity, and high sampling rate. They can capture the instantaneous deformation response caused by thermal shock within a microsecond timescale, making them suitable for high-speed, transient process monitoring scenarios such as laser ablation.

[0056] The first laser beam is a high-energy ultraviolet pulsed laser, for example, with an energy density of 500-600 mJ / cm². Sufficient energy is injected into the bonding interface to drive the thermal decomposition of the material. The second laser beam is a low-energy continuous or low-frequency pulsed laser, with an energy density typically in the range of several mJ / cm² to tens of mJ / cm², only one-hundredth or even one-thousandth of that of the first laser beam. This ensures that when the second laser beam irradiates the functional chip 210, it is only used for detection purposes and will not generate perceptible thermal stress on the functional chip 210.

[0057] The size of the probe spot is smaller than that of the stripping spot. The diameter of the stripping spot ranges from 50 to 100 μm, while the diameter of the probe spot is 10 to 20 μm. The smaller probe spot can be precisely aligned with a specific location within the area of ​​action of the stripping spot, such as the central area of ​​the surface of a single functional chip 210, thereby obtaining stress deformation information at the local location.

[0058] The relative spatial position of the detection spot and the stripping spot is kept at a preset fixed distance of less than or equal to 100μm, so as to realize synchronous scanning stripping or sequential scanning stripping, and ensure stress monitoring of the functional chip area and its adjacent area during stripping.

[0059] The pulse frequency of the first laser beam is 45-55 Hz, and the sampling frequency of the second laser beam is 1-5 MHz. In other words, the time interval between adjacent pulses of the first laser beam is 18ms-22ms, the sampling time interval of the second laser beam is 0.2μs-1μs, and the pulse width of the first laser beam is 10-50ns. With an adjacent pulse interval of 18ms-22ms for the first laser beam, the second laser beam continuously probes at a sampling frequency of 1-5MHz within this time interval, achieving the detection of tens of thousands of data points, demonstrating the high sensitivity and high sampling rate of the stress monitoring module 50.

[0060] The processing and control unit 60 takes a first time from acquiring the stress value to outputting the control command, and the interval between adjacent pulses of the first laser beam is a second time. The first time is shorter than the second time, ensuring that the processing and control unit 60 has sufficient running time.

[0061] Specifically, during the laser stripping process, the first laser beam pulse frequency is 50Hz, meaning that a laser pulse is output approximately every 20ms. Once the stress monitoring module 50 acquires the stress value of the current functional chip area, if adjustments to the laser parameters of the next or subsequent pulses are required, the adjustment command must be output and take effect stably before the arrival of the next pulse.

[0062] The first time is the adjustment response time of the processing and control unit 60, which is usually less than or equal to 10μs, much smaller than the interval between adjacent pulses of 18ms-22ms. The processing and control unit 60 can quickly complete all calculations and output control commands before the next pulse arrives.

[0063] The processing and control unit 60 has a built-in ideal stress reference model and feedback control algorithm. The ideal stress reference model presets an optimal stress window, and the feedback control algorithm generates control commands based on the deviation between the stress value and the optimal stress window.

[0064] The processing and control unit 60 adopts an industrial-grade embedded computer, equipped with a high-speed processor and a real-time operating system, and has a built-in ideal stress reference model library, covering model parameters and feedback control algorithms for different functional chip sizes and epitaxial layer structures.

[0065] The signal input terminal of the processing and control unit 60 is connected to the stress monitoring module 50 and the laser output module 10, and the signal output terminal is connected to the laser output module 10 and the support platform 30 to realize the coordinated control of multiple components.

[0066] The ideal stress reference model is used to provide the optimal stress window that the functional chip 210 should withstand during the peeling process. It can be understood that if the stress value of the functional chip 210 is lower or higher than the optimal stress window, it is equivalent to a deviation between the stress value and the optimal stress window. The feedback control algorithm will generate control commands based on the deviation to adjust the output parameters of the first laser beam and / or the duration of the first laser beam irradiation on the functional chip, so as to ensure that the stress value that the functional chip in the next peeling area should withstand is within the optimal stress window.

[0067] The ideal stress reference model presets a lower stress threshold and an upper stress threshold, and the optimal stress window is located between the lower stress threshold and the upper stress threshold. When the stress value is higher than the upper limit of the stress threshold, the control command controls the laser output module 10 to reduce the laser energy density, and / or controls the relative motion speed between the support platform 30 and the laser output module 10 to increase. When the stress value is lower than the lower limit of the stress threshold, the control command controls the laser output module 10 to increase the laser energy density, and / or controls the relative movement speed between the support stage 30 and the laser output module 10 to decrease; thereby realizing real-time adjustment of the stress value borne by the functional chip in the next stripping area.

[0068] In one specific embodiment, the upper limit of the stress threshold is 150 MPa and the lower limit of the stress threshold is 100 MPa. The optimal stress window is 100-150 MPa. When the actual stress value falls within 100-150 MPa, the characterization chip 210 achieves the desired peeling effect.

[0069] When the actual stress value borne by the functional chip 210 in the current stripping area is higher than the upper limit of the stress threshold, for example, the actual stress value is 165 MPa, it indicates that the input energy of the first laser beam is excessive or the action time is too long. Adjust the energy density of the first laser beam and / or control the support stage 30 to increase the movement speed to reduce the time the first laser beam acts on the functional chip. In this way, the actual stress value borne by the functional chip 210 in the next stripping area can be adjusted to be reduced, for example, reduced to 145 MPa, falling into the optimal stress window.

[0070] When the actual stress value of the functional chip 210 in the current stripping area is lower than the lower limit of the stress threshold, for example, the actual stress value is 95 MPa, it indicates that the input energy of the first laser beam is insufficient or the action time is too short. Adjust the energy density of the first laser beam and / or control the movement speed of the support stage 30 to reduce the time of the first laser beam acting on the functional chip. In this way, the actual stress value of the functional chip 210 in the next stripping area can be adjusted to increase, for example, to 105 MPa, falling into the optimal stress window.

[0071] When the relative deviation between the actual stress values ​​of five consecutive functional chips 210 and the optimal stress window exceeds 10%, for example, when the actual stress values ​​of five consecutive functional chips 210 exceed 165 MPa or are lower than 90 MPa, it is determined that the material uniformity of the functional chip area being scanned and stripped is poor. A sampling composite adjustment method can be used, specifically including simultaneously adjusting the laser energy density and pulse frequency of the first laser beam.

[0072] The laser energy density of the laser output module 10 can be adjusted between 5% and 20%, and the relative motion speed between the support platform 30 and the laser output module 10 can be adjusted between 10% and 30%. The specific adjustment range can be determined according to the deviation of the actual stress value to ensure that the stress value of the subsequent functional chip falls back to the optimal stress window.

[0073] Specifically, when the actual stress value borne by the functional chip 210 in the current stripped area is higher than the upper limit of the stress threshold, the energy density of the first laser beam is reduced by 5%-20%, and / or the movement speed of the support stage 30 is increased by 10%-30%.

[0074] When the actual stress value borne by the functional chip 210 in the current stripping area is lower than the upper limit of the stress threshold, the energy density of the first laser beam is increased by 5%-15%, and / or the movement speed of the support stage 30 is reduced by 10%-20%.

[0075] In summary, by adjusting the stress value, defects such as failure to peel off, microcracks, breakage, and warping of the functional chip 210 caused by mismatched laser energy are effectively eliminated. In the peeling test of the 10-100μm functional chip 210, the breakage rate of the functional chip 210 is reduced from more than 10% in the traditional process to less than 1%, improving the overall peeling yield.

[0076] During the scanning process of the entire wafer 200, the stress monitoring module 50 continuously collects data, and the processing and control unit 60 adjusts in real time until the laser output module 10 scans and covers the entire wafer 200, completing the adaptive laser stripping of all functional chips 210.

[0077] After the stripping is completed, the functional chip 210 is subjected to subsequent testing, including stripping integrity check, chip damage rate statistics, stress residue detection, etc., to form stripping quality feedback data, which is used to optimize the ideal stress reference model, feedback control algorithm, and the settings of the output parameters of the initial laser output module 10 and the parameters of the support stage 30, so as to realize the continuous iterative upgrade of the process.

[0078] The laser lift-off system 100 also includes a cooling system, a cleaning system, and an optical microscope, among other things. Specifically, the cooling system includes a water-cooled laser cooler and a wafer air-cooling device to ensure stable laser emission and uniform temperature of the wafer 200. The cleaning system includes plasma cleaning or ultrasonic cleaning equipment for pre-processing and post-lift cleaning of the wafer 200 and its functional chips 210. The optical microscope is used for damage detection and yield statistics of the functional chips 210 after lift-off.

[0079] This application also protects a laser ablation method applied to the laser ablation system in any of the above-mentioned technical solutions. The laser ablation method includes the following steps: S1: Provide a wafer 200 and place it on a support stage 30. The wafer 200 includes a substrate 220 and multiple functional chips 210, with the multiple functional chips 210 disposed on the substrate 220. S2: Start the laser output module 10 and start the relative movement between the support platform 30 and the laser output module 10; the laser output module 10 outputs a first laser beam, the support platform 30 is disposed on the output optical path of the laser output module 10, the first laser beam scans the wafer 200 and is used to separate the functional chip 210 and the substrate 220. S3: Start the stress monitoring module 50 and the processing and control unit 60; when the first laser beam scans the peeling area of ​​the wafer 200, the stress monitoring module 50 acquires the stress value of the peeling area in real time; the processing and control unit 60 receives the stress value and controls the laser output module 10 to adjust the output parameters according to the stress value, and / or controls the carrier stage 30 and the laser output module 10 to adjust the relative speed between them; stress fluctuations are reduced during the peeling process and the peeling yield is improved.

[0080] In step S1, the wafer 200 provided includes a pre-processed wafer 200, which cleans the surface of the wafer 200 to remove impurities such as oil and particles, thus avoiding affecting the peeling effect and stress monitoring accuracy. In a specific embodiment, the functional chip size is 100μm and the array spacing is 3μm.

[0081] In step S2, before starting the laser output module 10, the steps include initializing the output parameters of the laser output module 10. In a specific embodiment, the initial energy density of the laser emitter 11 is set to 600 mJ / cm², the pulse width is 30 ns, and the pulse frequency is 50 Hz.

[0082] In one specific embodiment, the support platform 30 is movable; Initiating the relative movement between the support platform 30 and the laser output module 10 includes the following steps: initiating the support platform 30; in a specific embodiment, before initiating the support platform 30, the initial movement speed of the support platform 30 is set to 100 mm / s, and the initial movement direction is the row direction; The steps for controlling the relative speed between the support platform 30 and the laser output module 10 include: controlling the movement speed of the support platform 30.

[0083] Before initiating the relative motion between the support platform 30 and the laser output module 10, the steps include initializing the relative speed and direction of motion between the support platform 30 and the laser output module 10.

[0084] In step S3, the stress monitoring module 50 is activated, and the stress monitoring module 50 collects and obtains the stress value borne by the peeling area; the processing and control unit 60 is activated, and the processing and control unit 60 receives the stress value and outputs control commands according to the stress value to adjust the output parameters of the laser output module 10 and / or adjust the movement speed parameters of the support platform 30.

[0085] The laser stripping method also includes step S4: repeatedly executing the stress value acquisition step of the stress monitoring module 50 and the dynamic adjustment step of the processing and control unit 60 until the full coverage scan of the entire wafer is completed.

[0086] The wafer 200 includes a first region 201 and a second region 202, wherein the thickness of the first region 201 is thinner than the thickness of the second region 202; the processing and control unit 60 presets a lower limit and an upper limit of the stress threshold. The first region 201 moves to the scanning path of the first laser beam, the stress monitoring module 50 obtains the first stress value, the processing and control unit 60 receives the first stress value, determines that the first stress value is greater than the upper limit of the stress threshold, controls the laser output module 10 to reduce the laser energy density, and / or controls the relative movement speed between the support stage 30 and the laser output module 10 to increase. The second region 202 moves to the scanning path of the first laser beam, the stress monitoring module 50 obtains the second stress value, the processing and control unit 60 receives the second stress value, determines that the second stress value is less than the lower limit of the stress threshold, controls the laser output module 10 to increase the laser energy density, and / or controls the relative movement speed between the support stage 30 and the laser output module 10 to decrease.

[0087] In one specific embodiment, the optimal stress window is between 100-150 MPa.

[0088] The laser output module 10 scans the first region 201, such as the edge region of a wafer, which is thin. The stress monitoring module 50 obtains a first stress value of 165 MPa. Within 10 μs, the processing and control unit 60 outputs a control command to reduce the laser energy density of the first laser beam by 15% and simultaneously increase the movement speed of the support stage 30 by 20%. After adjustment, the stress value of the next functional chip is monitored to quickly drop back to 140 MPa and stabilize within the optimal stress window. Ultimately, the functional chip 210 in the first region 201 is free from damage such as breakage or microcracks, achieving 100% peel integrity.

[0089] The laser output module 10 scans the second region 202, for example, the central region of the wafer, which is thick. The stress monitoring module 50 obtains a second stress value of 85 MPa. Within 10 μs, the processing and control unit 60 outputs a control command to increase the laser energy density of the first laser beam by 10% and simultaneously reduce the movement speed of the support stage 30 by 15%. After adjustment, the stress value of the next functional chip is monitored to rise rapidly to 110 MPa and stabilize within the optimal stress window. Ultimately, the functional chip 210 in the second region 202 suffers very little damage such as breakage and microcracks, achieving a peel integrity of 99%.

[0090] The beneficial effects of the present invention are as follows: the stress monitoring module 50 can monitor the actual stress value of the functional chip area after the first laser beam irradiation in real time. After receiving the actual stress value, the processing and control unit 60 adjusts the output parameters of the first laser beam and / or the irradiation time of the functional chip 210 under the first laser beam, thereby adjusting the actual stress value of the functional chip in the next irradiation area and ensuring a good peeling rate.

[0091] This can be formed by referring to any of the technical solutions provided above, and will not be elaborated here.

[0092] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0093] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A laser lift-off system for removing functional chips from a substrate of a wafer, the functional chips being disposed on the substrate, characterized in that, The laser ablation system includes: The laser output module outputs the first laser beam; A support stage is used to support the wafer and is located in the output optical path of the laser output module, so that the first laser beam can be focused on the wafer and used to separate the functional chip from the substrate; relative motion is generated between the support stage and the laser output module to achieve full coverage scanning of the functional chip by the first laser beam; The stress monitoring module is used to acquire the stress value of the functional chip area irradiated by the first laser beam in real time when the first laser beam is focused on the functional chip. The processing and control unit is communicatively connected to the stress monitoring module, the laser output module, and the support platform, respectively. The processing and control unit is configured to receive the stress value from the stress monitoring module and output control commands based on the stress value. The control commands are used to adjust the output parameters of the laser output module and / or the relative speed between the support platform and the laser output module.

2. The laser ablation system according to claim 1, characterized in that, A plurality of the functional chips are arranged in an array along a first direction and a second direction, and the support platform is movable along the first direction and the second direction. The support platform drives the wafer to move relative to the first laser beam along the first direction or the second direction.

3. The laser ablation system according to claim 1, characterized in that, The laser output module includes a laser emitter and an optical system; The laser emitter emits a first laser beam; The optical system, disposed on the output optical path of the laser emitter, is used for shaping and scanning the first laser beam. It includes a galvanometer, a focusing lens, and a spot shaper. The support stage is disposed on the output optical path of the optical system. The first laser beam can form a stripping spot with preset parameters on the wafer surface. The size of the stripping spot covers at least one of the functional chips.

4. The laser ablation system according to claim 3, characterized in that, The stress monitoring module includes a laser interferometer that emits a second laser beam. The energy of the second laser beam is less than that of the first laser beam. The second laser beam can form a probe spot on the wafer surface. The size of the probe spot is smaller than the size of the stripping spot. The probe spot and the stripping spot maintain a preset fixed distance on the wafer surface.

5. The laser ablation system according to claim 4, characterized in that, The pulse frequency of the first laser beam is 45-55 Hz, and the sampling frequency of the second laser beam is 1-5 MHz.

6. The laser ablation system according to claim 1, characterized in that, The processing and control unit takes a first time from acquiring the stress value to outputting the control command, and the interval between adjacent pulses of the first laser beam is a second time, wherein the first time is shorter than the second time.

7. The laser ablation system according to claim 1, characterized in that, The processing and control unit incorporates an ideal stress reference model and a feedback control algorithm. The ideal stress reference model presets an optimal stress window, and the feedback control algorithm generates control commands based on the deviation between the stress value and the optimal stress window.

8. The laser ablation system according to claim 7, characterized in that, The ideal stress reference model presets a lower stress threshold and an upper stress threshold, and the optimal stress window is located between the lower stress threshold and the upper stress threshold. When the stress value is higher than the upper limit of the stress threshold, the control command controls the laser output module to reduce the laser energy density, and / or controls the relative motion speed between the support platform and the laser output module to increase; When the stress value is lower than the lower limit of the stress threshold, the control command controls the laser output module to increase the laser energy density, and / or controls the relative motion speed between the support platform and the laser output module to decrease.

9. The laser ablation system according to claim 8, characterized in that, The laser energy density of the laser output module can be adjusted within the range of 5%-20%, and the relative motion speed between the support platform and the laser output module can be adjusted within the range of 10%-30%.

10. A laser ablation method, characterized in that, Including the following steps: A wafer is provided and placed on a support stage, the wafer including a substrate and a plurality of functional chips disposed on the substrate; The laser output module is activated, and the relative movement between the support platform and the laser output module is initiated; the laser output module outputs a first laser beam, and the support platform is disposed on the output optical path of the laser output module. The first laser beam scans the wafer and is used to separate the functional chip and the substrate. The stress monitoring module and the processing and control unit are activated; when the first laser beam scans the functional chip area of ​​the wafer, the stress monitoring module acquires the stress value borne by the functional chip area in real time; the processing and control unit receives the stress value and controls the laser output module to adjust the output parameters according to the stress value, and / or controls the support stage and the laser output module to adjust the relative speed between them.

11. The laser ablation method according to claim 10, characterized in that, The support platform is movable. Initiating the relative movement between the support platform and the laser output module includes the following steps: initiating the support platform; Controlling the relative speed between the support platform and the laser output module includes the steps of: controlling the movement speed of the support platform; And / or, the laser stripping method includes the steps of: repeatedly performing the stress value acquisition step of the stress monitoring module and the dynamic adjustment step of the processing and control unit until the full coverage scan of the entire wafer is completed.

12. The laser ablation method according to claim 10, characterized in that, The wafer includes a first region and a second region, wherein the thickness of the first region is thinner than the thickness of the second region; the processing and control unit presets a lower stress threshold and an upper stress threshold. The first region moves to the scanning path of the first laser beam, the stress monitoring module obtains the first stress value, the processing and control unit receives the first stress value, determines that the first stress value is greater than the upper limit of the stress threshold, controls the laser output module to reduce the laser energy density, and / or controls the relative movement speed between the support platform and the laser output module to increase; The second region moves to the scanning path of the first laser beam, the stress monitoring module obtains the second stress value, the processing and control unit receives the second stress value, determines that the second stress value is less than the lower limit of the stress threshold, controls the laser output module to increase the laser energy density, and / or controls the relative movement speed between the support stage and the laser output module to decrease.

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