System and method for monitoring laser implicit cutting depth in real time based on laser ultrasound

Abstract

The invention discloses a laser implicit cutting depth real-time monitoring system and method based on laser ultrasound, and the system comprises a laser transmitting module which is used for generating and outputting cutting laser; the vibration measurement module is used for generating vibration measurement laser and receiving a vibration signal from the surface of the sample; the optical beam combining and focusing module is used for combining the cutting laser and the vibration measuring laser and jointly focusing the cutting laser and the vibration measuring laser to the same target position on the surface of a sample; the moving carrying table is used for carrying and driving a to-be-cut sample to move; and the control and data processing unit is in communication connection with the laser emission module, the vibration measurement module and the moving platform deck, and is used for controlling the operation of each module and reflecting the implicit cutting depth in real time according to the vibration signal. The implicit cutting device has the advantages that the implicit cutting depth of the wafer by the cutting laser can be sensed in real time through the vibration measurement module, the damage risk in the wafer cutting process is reduced, and the implicit cutting effect of the wafer is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductors, in particular to a system and method for real-time monitoring of laser stealth cutting depth based on laser ultrasound. BACKGROUND

[0002] Laser stealth cutting, also known as laser invisible cutting, is an advanced precision cutting technology applied to brittle materials such as semiconductor wafers, glass, and ceramics. This technology uses high-power, short-pulse laser beams to focus on specific depths within the material through precise optical systems, forming a so-called "modified layer" or "invisible cutting layer". This modified layer, composed of micro-cracks or changes in crystal lattice structure, is located in the subsurface of the material and does not appear on the material surface before cutting is completed. Subsequently, by applying a controllable force through external stress sources (such as tape expansion, mechanical bending, etc.), the material will precisely separate along the pre-formed modified layer, achieving high-quality and low-damage cutting results.

[0003] However, a significant limitation of current laser stealth cutting technology in practical application is its insufficient online real-time monitoring capability, especially in terms of real-time feedback and control of cutting depth. There is no mature and reliable monitoring method. Cutting depth, as a key parameter affecting cutting quality and yield, its instability or deviation from the expected will directly affect device performance and process consistency. Therefore, developing a method that can accurately monitor the stealth cutting depth in real time is of great significance to improve process controllability and yield.

[0004] In this context, laser ultrasound technology shows its application potential in real-time monitoring of laser stealth cutting depth. Laser ultrasound technology combines the advantages of laser excitation and laser vibration measurement, and belongs to the category of non-contact, high-precision non-destructive testing. Its basic principle is: when a laser pulse is irradiated onto the material surface, part of the energy is absorbed and converted into transient thermal energy, causing local thermal expansion of the material, and then exciting a wideband stress pulse. This stress pulse propagates in the material in the form of ultrasonic waves, and when it encounters interfaces, defects, or structural changes (such as stealth cutting modified layers), it will produce reflection, scattering, or mode conversion. Through optical detection means such as laser interferometer, nanoscale vibration signals caused by ultrasonic wave propagation on the material surface can be captured, and then ultrasonic characteristics including transit time, frequency component, amplitude attenuation, etc. can be extracted. However, the stealth cutting depth cannot be detected by laser vibration measurement during the current laser stealth cutting process.

[0005] For example, the laser hidden cutting equipment disclosed in the publication No. CN219598424U, wherein: the laser emitted by the laser emits two beams of light after passing through the isolator and the first coupler, the first light beam enters the fourth coupler after being modulated by two acousto-optic frequency shifters, and the second light beam is divided into a correction light beam and a signal light beam after passing through the third coupler; the correction light beam enters the second coupler after passing through the intensity phase modulator; the signal light beam irradiates the surface of the target to be measured through the optical transceiver system, and enters the second coupler after passing through the circulator; the signal light beam and the correction light beam are mixed in the second coupler, and the mixed light beam enters the fourth coupler and interferes with the reference light, and then enters the balanced detection system; the Doppler vibration of the target to be measured is obtained through the demodulation algorithm, and finally the vibration information of the target to be measured is obtained. The above-mentioned device uses a polarization beam splitter prism to divide a part of the light beam for power detection, and based on the detection result, the transmittance of the laser is dynamically adjusted by a stepping motor driving optical element (such as a glass sheet), so as to stabilize the output power, so as to adapt to the processing requirements of wafers of different thicknesses. However, the device lacks real-time, online and accurate monitoring means for the hidden cutting depth (i.e. the internal modification layer depth), which is the core parameter of the cutting process. Even if the laser power is stably controlled, the actual hidden cutting depth will deviate from the preset target due to factors such as material non-uniformity, laser focusing state drift, stage movement error and the like during the processing. This depth deviation cannot be directly reflected or corrected by single power monitoring, and finally directly affects the quality of the cutting surface, the device performance and the process consistency.

[0006] Therefore, it is necessary to provide a system and method for real-time monitoring of laser hidden cutting depth based on laser ultrasound. SUMMARY

[0007] The system and method for real-time monitoring of laser hidden cutting depth based on laser ultrasound provided by the present application effectively solve the existing problems.

[0008] The technical scheme adopted by the present application is: a system for real-time monitoring of laser hidden cutting depth based on laser ultrasound, comprising a laser emission module for generating and outputting cutting laser; a vibration measurement module for generating vibration measurement laser and receiving vibration signals from the surface of a sample; an optical beam combining and focusing module for combining and focusing the cutting laser and the vibration measurement laser to the same target position on the surface of the sample; a moving stage for carrying and driving the sample to be cut to move; a control and data processing unit in communication connection with the laser emission module, the vibration measurement module and the moving stage, for controlling the operation of each module, and reflecting the hidden cutting depth in real time according to the vibration signals.

[0009] Further, the optical beam combining and focusing module comprises a mirror, a beam combining device and a focusing objective, the mirror is used to reflect the vibration measurement laser emitted by the vibration measurement module to the beam combining device, the beam combining device is used to combine the vibration measurement laser emitted by the vibration measurement module and the cutting laser emitted by the laser emission module, and the focusing objective is used to focus the cutting laser and the vibration measurement laser on the wafer, and the beam combining device is one of a dichroic mirror, a polarization beam splitter prism or a half-transmission half-reflection mirror.

[0010] Further, the vibration measurement module comprises a non-contact optical head, a laser and a photoelectric detection unit, the laser is used to emit the vibration measurement laser, the non-contact optical head is used to transmit the vibration measurement laser to the optical beam combining and focusing module and receive the light signal carrying vibration information from the sample surface returned from the optical beam combining and focusing module, and the photoelectric detection unit is used to receive the light signal from the non-contact optical head and convert it into a corresponding vibration electric signal and transmit it to the control and data processing unit.

[0011] The method for monitoring the laser hidden cutting depth in real time based on laser ultrasound comprises the following steps: S1, calibration: ensuring that the vibration measurement initial position coincides with the cutting initial position; S2, fixing the wafer on a motion stage; S3, driving the wafer to feed by the motion stage, and emitting the high-frequency cutting laser by the laser emission module to focus on the wafer interior and form a modified layer below the wafer surface; S4, emitting the high-frequency vibration measurement laser by the vibration measurement module to measure the vibration signal at the irradiation position of the wafer surface cutting mechanism; S5, sending the vibration signal to the control and data processing unit by the vibration measurement module, and monitoring the wafer hidden cutting depth in real time by the control and data processing unit.

[0012] Further, the method for measuring the vibration signal at the irradiation position of the wafer surface cutting mechanism in S4 comprises at least one of continuous frequency modulation wave, interference method, speckle effect and triangulation method.

[0013] Further, the frequency of the vibration measurement laser is greater than 5 times the frequency of the cutting laser.

[0014] Further, the wavelength of the cutting laser is 1000 nm-1400 nm, the wavelength of the vibration measurement laser is 650 nm-1550 nm, and the difference between the wavelength of the cutting laser and the wavelength of the vibration measurement laser is 50 nm-600 nm.

[0015] Further, the frequency of the cutting laser is 80 Hz-140 KHz, and the frequency of the vibration measurement laser is 320 Hz-1.25 MHz.

[0016] Further, the pulse width of the cutting laser is 20 ns-500 ns.

[0017] Further, the power of the cutting laser is 1W-4W.

[0018] Advantages of the application: 1. The vibration measurement module can sense the hidden cutting depth of the wafer in real time, reduce the damage risk in the wafer cutting process, and improve the effect of wafer hidden cutting.

[0019] 2. The frequency of the vibration measurement laser is 5 times that of the cutting laser, which can avoid confusion of the two laser signals, facilitate subsequent filtering process, improve the anti-interference ability of the system, and the vibration measurement laser as a collection laser has a frequency 5 times that of the cutting laser, which means that the sampling interval time is shorter and can track the change of the ultrasonic signal in the hidden cutting process more accurately.

[0020] 3. The structure design of the optical beam combining and focusing module can realize beam combining of the two beams (cutting laser beam and vibration measurement laser beam), ensure that the vibration measurement laser irradiates the same position on the wafer surface irradiated by the cutting laser, capture the nanometer vibration signal on the wafer surface caused by ultrasonic propagation, and then extract the ultrasonic characteristics including transit time, frequency component, amplitude attenuation, etc., so as to determine the effect of wafer hidden cutting.

[0021] 4. The structure design of the vibration measurement module can realize the emission, shaping and reception of the vibration measurement laser, and ensure the smooth vibration measurement on the wafer surface. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A simple schematic diagram of the system for real-time monitoring of laser hidden cutting depth based on laser ultrasonic provided by the embodiments of the application.

[0023] Figure 2 A flowchart of the method for real-time monitoring of laser hidden cutting depth based on laser ultrasonic provided by the embodiments of the application.

[0024] Figure 3 A signal waveform diagram collected by the vibration measurement module.

[0025] Figure 4 The change of the pulse area of the cutting laser with the cutting laser power and the cutting depth.

[0026] In the figure, 1 is a laser emission module, 2 is a vibration measurement module, 3 is an optical beam combining and focusing module, 4 is a motion platform, 5 is a control and data processing unit, 31 is a mirror, 32 is a beam combining device, 33 is a focusing objective lens, and 100 is a wafer. DETAILED DESCRIPTION

[0027] In order to make the above objectives, characteristics and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the drawings.

[0028] As shown in Figure 1 The first embodiment provided by the present application is a system for real-time monitoring of laser hidden cutting depth based on laser ultrasound, which comprises a laser emission module 1 for generating and outputting cutting laser; a vibration measurement module 2 for generating vibration measurement laser and receiving vibration signals from the sample surface; an optical beam combining and focusing module 3 for combining and focusing the cutting laser and the vibration measurement laser to the same target position on the sample surface; a motion platform 4 for carrying and driving the sample to be cut to move; and a control and data processing unit 5 in communication connection with the laser emission module 1, the vibration measurement module 2 and the motion platform 4, for controlling the operation of each module and reflecting the hidden cutting depth in real time according to the vibration signals.

[0029] It should be noted that the geometric size (thickness, side length) of the wafer 100 to be cut has unclear influence on the signal, and the processing parameters, especially the laser power and the instantaneous cutting depth, have significant and regular influence on the time domain characteristics (such as pulse height and pulse area) of the collected ultrasonic pulse signal. The motion platform 4 can be an air floating motion platform to realize the fixation of the wafer 100 by vacuum adsorption.

[0030] In actual use, after the wafer 100 is fixed by the motion platform 4, the wafer 100 is driven to feed by the motion platform 4, and the wafer 100 is emitted with high-frequency pulse cutting laser by the laser emission module 1. The high-frequency pulse cutting laser is focused in the predetermined cutting path region of the wafer 100 by the optical beam combining and focusing module 3, and the focal point is in the cutting region. The laser energy is selectively absorbed by the material, and a modified layer with a permanently changed structure is formed in the subsurface layer of the wafer 100 through photothermal or photochemical action. The vibration measurement module 2 emits high-frequency vibration measurement laser, and the beam of the high-frequency vibration measurement laser is focused on the irradiation region of the cutting laser on the surface of the wafer 100 after being combined with the cutting laser by the optical beam combining and focusing module 3. Then, the vibration measurement module 2 captures and analyzes the slight vibration of the wafer 100 surface caused by internal ultrasonic disturbance, and converts the mechanical vibration into electronic signals for analysis in real time. The control and data processing unit 5 performs noise reduction and feature extraction on the signals, separates the ultrasonic characteristic parameters closely related to the hidden cutting depth, and the computer inverses these characteristic parameters into the current hidden cutting depth value according to the preset acoustic physical model.

[0031] In the above design, the vibration measurement module 2 can realize real-time sensing of the hidden cutting depth of the wafer 100 by the cutting laser, reduce the damage risk in the cutting process of the wafer 100, and improve the effect of the hidden cutting of the wafer 100.

[0032] Specifically: as Figure 1As shown, the optical beam combining and focusing module 3 includes a reflector 31, a beam combining device 32, and a focusing objective lens 33. The reflector 31 reflects the vibration measurement laser emitted by the vibration measurement module 2 to the beam combining device 32. The beam combining device 32 combines the vibration measurement laser emitted by the vibration measurement module 2 with the cutting laser emitted by the laser emitting module 1. The focusing objective lens 33 focuses the cutting laser and the vibration measurement laser onto the wafer 100. The beam combining device 32 is one of a dichroic mirror, a polarizing beam splitter, or a semi-transparent mirror. In this application, a dichroic mirror is used.

[0033] In actual use, the cutting laser is reflected by the dichroic mirror to the focusing objective 33 and then focused inside the wafer 100. The reflecting mirror 31 emits the vibration measurement laser to the dichroic mirror and then to the surface of the wafer 100, where it is focused by the focusing objective 33 onto the area irradiated by the cutting laser.

[0034] In the above design, the structure of the optical beam combining and focusing module 3 can combine the two beams (cutting laser beam and vibration measurement laser beam) to ensure that the vibration measurement laser irradiates the same position on the surface of wafer 100 that is irradiated by the cutting laser, capture the nanoscale vibration signal on the surface of wafer 100 caused by ultrasonic wave propagation, and then extract ultrasonic features including transit time, frequency components, amplitude attenuation, etc., so as to determine the effect of wafer 100 slicing.

[0035] Specifically: the vibration measurement module 2 includes a non-contact optical head, a laser, and a photoelectric detection unit. The laser is used to emit a vibration measurement laser. The non-contact optical head is used to transmit the vibration measurement laser to the optical beam combining and focusing module 3 and to receive the light signal carrying vibration information from the sample surface returned from the optical beam combining and focusing module 3. The photoelectric detection unit is used to receive the light signal from the non-contact optical head and convert it into a corresponding vibration electrical signal, which is then transmitted to the control and data processing unit 5.

[0036] In practical use, a vibration-measuring laser is emitted by a laser, shaped by a non-contact optical head, and then transmitted to an optical beam combining and focusing module 3. This combined laser beam is then focused onto the cutting laser irradiation area on the product surface. The module also receives light signals carrying vibration information from the sample surface, such as those returned from the optical beam combining and focusing module 3. Figure 3 ).

[0037] In the above design, the structure of the vibration measurement module 2 is designed to realize the emission, shaping and reception of the vibration measurement laser, ensuring the smooth vibration measurement of the wafer 100 surface.

[0038] like Figure 2As shown, the second embodiment provided in this application is a method for real-time monitoring of laser hidden cutting depth based on laser ultrasound. The system for real-time monitoring of laser hidden cutting depth based on laser ultrasound includes the following steps: S1, calibration: ensuring that the initial vibration measurement position coincides with the initial cutting position; S2, fixing the wafer 100 on the motion stage 4; S3, the motion stage 4 drives the wafer 100 to feed, and the laser emission module 1 emits a high-frequency cutting laser focused into the interior of the wafer 100, forming a modified layer below the surface of the wafer 100; S4, the vibration measurement module 2 emits a high-frequency vibration measurement laser to measure the vibration signal at the irradiation point of the cutting mechanism on the surface of the wafer 100; S5, the vibration measurement module 2 sends the vibration signal to the control and data processing unit 5, and the control and data processing unit 5 monitors the hidden cutting depth of the wafer 100 in real time.

[0039] The above design enables the use of a vibration-measuring laser to detect the cutting area during the laser dicing process of wafer 100, and the depth of the dicing can be determined by analyzing the vibration signals collected during the vibration measurement process.

[0040] Specifically, the method for measuring the vibration signal at the irradiation point of the wafer 100 surface cutting mechanism in S4 includes at least one of continuous frequency modulation wave, interferometry, speckle effect, and triangulation measurement.

[0041] Specifically, the frequency of the vibration-measuring laser is greater than 5 times the frequency of the cutting laser.

[0042] In the above design, the frequency of the vibration measurement laser is more than 5 times that of the cutting laser, which can avoid confusion between the two laser signals, facilitate filtering in subsequent analysis, and improve the anti-interference capability of the system. At the same time, the vibration measurement laser, as the acquisition laser, has a frequency that is more than 5 times that of the cutting laser, indicating that its sampling interval is shorter and can more accurately track the changes in the ultrasonic signal during the hidden cutting process.

[0043] Specifically: the wavelength of the cutting laser is 1000nm~1400nm, specifically 1000nm, the wavelength of the vibration measuring laser is 650nm~1550nm, specifically 1310nm, and the wavelength difference between the cutting laser and the vibration measuring laser is 50nm~600nm.

[0044] It should be noted that the dichroic mirrors in the optical beam combiner and focusing module operate on wavelength selectivity, and the center wavelengths of the cutting laser and the vibratory laser must have a sufficiently large gap (typically >50nm). If the wavelengths are too close (e.g., differing by only 10nm), it will result in a significant loss of light energy.

[0045] In the above design, for semiconductor materials such as silicon (Si) and silicon carbide (SiC), the 1000nm~1400nm wavelength range is a crucial optical absorption window. Within this range, laser energy can be efficiently absorbed by the material and converted into heat energy at the internal focal point, thereby precisely forming an internal modified layer and achieving "invisible" cutting. This ensures sufficient penetration depth, allowing the focal point to be located inside the material rather than on its surface. Furthermore, the wavelength of the vibratory laser can be effectively distinguished from the interfering spectra of the cutting laser, such as strong plasma emission and thermal radiation.

[0046] Specifically, the frequency of the cutting laser is 80Hz~140KHz, and the frequency of the vibration measuring laser is 320Hz~1.25MHz.

[0047] In the above design, the frequencies of the vibration measurement laser and the vibration measurement laser are such that the frequencies of the two lasers are easy to distinguish.

[0048] Specifically, the pulse width of the cutting laser is 20ns to 500ns.

[0049] In the above design, the pulse width of the cutting laser can effectively localize the energy deposition in the focal region inside the material, forming a clearly defined modified layer through a controllable thermo-mechanical effect. Specifically, the power of the cutting laser is 1W to 4W.

[0050] In the above design, such as Figure 4 As shown, the average power range of 1W to 4W, combined with pulse width and frequency, can provide just the right amount of flexible and adjustable pulse energy for 100 stealth dicing of semiconductor wafers, ensuring precise and consistent formation of the modified layer inside the material, rather than surface damage.

[0051] In further detail, it should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for real-time monitoring of laser concealment depth based on laser ultrasound, characterized in that: The system includes a laser emitting module (1) for generating and outputting a cutting laser; a vibration measuring module (2) for generating a vibration measuring laser and receiving vibration signals from the sample surface; an optical beam combining and focusing module (3) for combining the cutting laser and the vibration measuring laser and focusing them together to the same target position on the sample surface; a motion stage (4) for carrying and driving the sample to be cut to move; and a control and data processing unit (5) for communicating with the laser emitting module (1), the vibration measuring module (2) and the motion stage (4), for controlling the operation of each module and reflecting the hidden cutting depth in real time according to the vibration signals.

2. The system for real-time monitoring of laser concealment depth based on laser ultrasound according to claim 1, characterized in that: The optical beam combining and focusing module (3) includes a reflector (31), a beam combining device (32), and a focusing objective (33). The reflector (31) is used to reflect the vibration measurement laser emitted by the vibration measurement module (2) to the beam combining device (32). The beam combining device (32) is used to combine the vibration measurement laser emitted by the vibration measurement module (2) with the cutting laser emitted by the laser emission module (1). The focusing objective (33) is used to focus the cutting laser and the vibration measurement laser onto the wafer (100). The beam combining device (32) is one of a dichroic mirror, a polarizing beam splitter, or a semi-transparent mirror.

3. The system for real-time monitoring of laser concealment depth based on laser ultrasound according to claim 1, characterized in that: The vibration measurement module (2) includes a non-contact optical head, a laser, and a photoelectric detection unit. The laser is used to emit a vibration measurement laser. The non-contact optical head is used to transmit the vibration measurement laser to the optical beam combining and focusing module (3) and receive the light signal carrying vibration information from the sample surface returned from the optical beam combining and focusing module (3). The photoelectric detection unit is used to receive the light signal from the non-contact optical head and convert it into a corresponding vibration electrical signal, which is then transmitted to the control and data processing unit (5).

4. A method for real-time monitoring of laser concealment depth based on laser ultrasound, employing the system for real-time monitoring of laser concealment depth based on laser ultrasound as described in any one of claims 1 to 3, characterized in that: The process includes the following steps: S1, Calibration: Ensure that the initial position of vibration measurement coincides with the initial position of cutting; S2, Fix the wafer (100) on the motion stage (4); S3, The motion stage (4) drives the wafer (100) to feed, and the laser emission module (1) emits a high-frequency cutting laser that is focused into the interior of the wafer (100) to form a modified layer below the surface of the wafer (100); S4, The vibration measurement module (2) emits a high-frequency vibration measurement laser to measure the vibration signal at the irradiation point of the cutting mechanism on the surface of the wafer (100); S5, The vibration measurement module (2) sends the vibration signal to the control and data processing unit (5), and the control and data processing unit (5) monitors the hidden cutting depth of the wafer (100) in real time.

5. The method for real-time monitoring of laser concealment depth based on laser ultrasound according to claim 4, characterized in that: The method for measuring the vibration signal at the irradiation point of the wafer (100) surface cutting mechanism in S4 includes at least one of continuous frequency modulation wave, interferometry, speckle effect, and triangulation.

6. The method for real-time monitoring of laser concealment depth based on laser ultrasound according to claim 4, characterized in that: The frequency of the vibration-measuring laser is more than 5 times that of the cutting laser.

7. The method for real-time monitoring of laser concealment depth based on laser ultrasound according to claim 4, characterized in that: The wavelength of the cutting laser is 1000nm~1400nm, the wavelength of the vibration measuring laser is 650nm~1550nm, and the wavelength difference between the cutting laser and the vibration measuring laser is 50nm~600nm.

8. The method for real-time monitoring of laser concealment depth based on laser ultrasound according to claim 4, characterized in that: The frequency of the cutting laser is 80Hz~140KHz, and the frequency of the vibration measuring laser is 320Hz~1.25MHz.

9. The method for real-time monitoring of laser concealment depth based on laser ultrasound according to claim 4, characterized in that: The pulse width of the cutting laser is 20ns to 500ns.

10. The method for real-time monitoring of laser concealment depth based on laser ultrasound according to claim 4, characterized in that: The power of the cutting laser is 1W to 4W.

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