A multi-parameter layer-by-layer laser hidden cutting method and device for ultra-thin wafers

Abstract

The application provides a multi-parameter layer-by-layer laser hidden cutting method and device for ultrathin wafers, relates to the field of laser cutting, and comprises the following steps: a hidden cutting strategy for hidden cutting of a wafer to be cut is configured according to a laser hidden cutting model, wherein the laser hidden cutting model comprises a mapping relationship between wafer parameters and hidden cutting parameters; the wafer to be cut is hidden cut based on the hidden cutting strategy, comprising the following steps: the wafer to be cut is divided into a surface layer, an intermediate layer and a bottom layer from top to bottom; the position of a laser focal point is automatically adjusted so as to be focused on the surface layer, the intermediate layer and the bottom layer respectively; different hidden cutting parameters are adopted to cut the surface layer, the intermediate layer and the bottom layer at least three times in sequence; wherein the thickness of the surface layer and the bottom layer is the same, and the thickness of the intermediate layer is greater than that of the surface layer and the bottom layer. The application realizes the collaborative adjustment of laser power, pulse frequency, scanning speed and other parameters, and provides an optimal parameter scheme for different processing requirements through the interaction between different parameters.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser processing, in particular, to a multi-parameter layer-by-layer laser stealth cutting method and device for ultra-thin wafers. BACKGROUND

[0002] Ultra-thin wafers (typically referring to wafers with a thickness less than 50 μm) are key basic materials for modern semiconductor device miniaturization and high performance, widely used in advanced packaging, three-dimensional integrated chips, micro-electro-mechanical systems (MEMS), and flexible electronics, etc. With the continuous reduction of semiconductor technology nodes and the continuous improvement of device integration, the demand for ultra-thin wafers is increasing. However, the mechanical strength of ultra-thin wafers is significantly reduced, and they are more prone to deformation and cracking, which poses extremely high requirements on subsequent cutting and separation processes.

[0003] Laser stealth cutting technology is an advanced processing method that forms a modified layer inside the wafer by focusing pulsed laser inside the wafer, and then separates the die through processes such as film expansion. Most of the laser stealth cutting equipment on the market currently adopts a fixed parameter processing strategy, i.e., using the same laser power, pulse frequency and scanning speed throughout the cutting process. This single parameter method has significant limitations when dealing with ultra-thin wafers:

[0004] Inadequate control of heat-affected zone: Fixed parameters are difficult to adapt to changes in material properties at different depths inside the wafer. Studies have shown that the interaction efficiency of laser with semiconductor materials changes nonlinearly with depth, which is due to the interface refraction effect and material heterogeneity. In ultra-thin wafer cutting, a single energy parameter often produces excessive heat accumulation at certain depths, leading to an enlarged heat-affected zone, and even causing micro-cracks to extend to the active area of the chip, severely affecting device reliability and yield.

[0005] Inaccurate crack propagation control: The modified layer formed inside the ultra-thin wafer needs to guide the crack to propagate along the predetermined direction. The fixed parameter strategy is difficult to achieve precise control of the crack, which can easily lead to irregular crack propagation or even bifurcation. Especially near the back of the wafer, excessive energy can cause the crack to extend to the back, resulting in back edge collapse, while insufficient energy can lead to incomplete separation, requiring additional mechanical dicing operations, which in turn increases the risk of chipping.

[0006] Lack of adaptive ability: Existing technologies lack the ability to make real-time adjustments according to the actual state of the wafer. Variations such as wafer warping, uneven thickness, and material property fluctuations can significantly affect the cutting effect. The fixed parameter strategy cannot adapt to these changes, resulting in unstable cutting quality. Especially for high-end chips such as RFID, CIS (CMOS image sensor), this instability can cause the dispersion of electrical performance parameters, directly affecting product yield and performance consistency.

[0007] Efficiency vs. quality contradiction: In order to improve the cutting quality, the traditional method often adopts a conservative low parameter strategy and multiple repeated scanning, which significantly reduces the processing efficiency. This problem is particularly prominent for thick wafers (such as SiC wafers) that require multiple cuts.

[0008] Therefore, the present application proposes a multi-parameter layer-by-layer laser hidden cutting method and device for ultra-thin wafers to solve one or several of the above technical problems. SUMMARY

[0009] The present application aims to provide a multi-parameter layer-by-layer laser hidden cutting method and device for ultra-thin wafers, which can solve at least one of the above technical problems. The specific scheme is as follows:

[0010] According to the specific embodiment of the present application, a multi-parameter layer-by-layer laser hidden cutting method for ultra-thin wafers comprises:

[0011] S101: configuring a hidden cutting strategy for hidden cutting of a to-be-cut wafer according to a laser hidden cutting model, wherein the laser hidden cutting model comprises a mapping relationship between wafer parameters and hidden cutting parameters;

[0012] S102: hidden cutting of the to-be-cut wafer based on the hidden cutting strategy, comprising: dividing the to-be-cut wafer from top to bottom into a surface layer, an intermediate layer and a bottom layer; automatically adjusting the position of the laser focal point to focus on the surface layer, the intermediate layer and the bottom layer respectively; and using different hidden cutting parameters to cut the surface layer, the intermediate layer and the bottom layer at least three times in turn;

[0013] Wherein, the thickness of the surface layer and the bottom layer is the same, and the thickness of the intermediate layer is greater than the thickness of the surface layer and the bottom layer.

[0014] In some embodiments, the hidden cutting parameters include laser power, laser pulse frequency, laser energy density and scanning speed; wherein the laser pulse frequency of the intermediate layer is greater than the laser pulse frequency of the surface layer and the bottom layer.

[0015] In some embodiments, the laser power and laser energy density of the surface layer, the intermediate layer and the bottom layer increase in turn.

[0016] In some embodiments, the scanning speed of the surface layer, the intermediate layer and the bottom layer decreases in turn.

[0017] In some embodiments, the intermediate layer comprises a plurality of sub-layers, and the same hidden cutting parameters are used for hidden cutting of each sub-layer.

[0018] In some embodiments, the thickness of the to-be-cut wafer is less than 50 microns, wherein the thickness of the surface layer and the bottom layer is less than 15 microns, and the thickness of the intermediate layer is greater than 20 microns.

[0019] In some embodiments, the laser is a picosecond laser or a femtosecond laser.

[0020] In some embodiments, the automatic adjustment of the position of the laser focus point to focus on the surface layer, the middle layer and the bottom layer respectively comprises:

[0021] The surface state of the wafer to be cut is detected in real time by a distance measuring component;

[0022] Based on the surface state, the position of the laser focus point is automatically adjusted by a first focusing component to focus on the surface layer, the middle layer and the bottom layer respectively.

[0023] In some embodiments, the first focusing component comprises a piezoelectric ceramic driver for realizing nanoscale movement of the laser focus point.

[0024] Embodiments of the present application further provide a multi-parameter layer-by-layer laser hidden cutting device for ultra-thin wafers for realizing the above method, which comprises:

[0025] A laser cutting unit comprising a light source component and a first focusing component, the light source component focuses the laser on the surface of the wafer, and the first focusing component adjusts the position of the focus point of the laser so that the focus point is maintained in the surface layer, the middle layer or the bottom layer;

[0026] A distance measuring component for detecting in real time the height of the surface of the wafer to be cut in front of the focus point along the cutting direction at a preset distance from the first focusing component;

[0027] A controller connected to the laser cutting unit and the distance measuring component, receiving the detection results of the distance measuring component and controlling the first focusing component according to the detection results so that the position of the focus point is maintained in the surface layer, the middle layer or the bottom layer.

[0028] The above scheme of the embodiments of the present application has at least the following beneficial effects compared with the prior art:

[0029] The multi-parameter layer-by-layer laser stealth cutting method and device for ultra-thin wafers realize the coordinated adjustment of laser power, pulse frequency, scanning speed and other parameters through the mapping relationship between wafer parameters and stealth cutting parameters, and find the global optimal parameter combination through the interaction between different parameters. The method constructs a closed-loop intelligent decision system of "process parameters-material response-cutting quality", instead of the traditional single-parameter independent adjustment. The wafer to be cut is divided into a surface layer, an intermediate layer and a bottom layer from top to bottom, and based on the stealth strategy, a "depth-laser parameter" relationship database covering various semiconductor materials is used to dynamically adjust the laser parameters in real time, which can provide the optimal parameter scheme for different processing requirements. By integrating a high-dynamic focusing system with nanometer precision and a high-speed position comparison output function, the laser focus is configured to focus on the surface layer, the intermediate layer and the bottom layer respectively, so as to realize the accurate control of the three-dimensional machining track, especially the focus cutting at the warping position, which can more quickly and accurately adjust the focus height to match the warping height. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one embodiment consistent with the present application and, together with the description, serve to explain the principles of the application. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained from these drawings without creative labor for those skilled in the art. In the drawings:

[0031] Figure 1 A multi-parameter layer-by-layer laser stealth cutting method for ultra-thin wafers is provided for the embodiments of the present application;

[0032] Figure 2 A multi-parameter layer-by-layer laser stealth cutting device for ultra-thin wafers is provided for the embodiments of the present application.

[0033] Figure 3 A multi-parameter layer-by-layer laser stealth cutting device for ultra-thin wafers is provided for the embodiments of the present application.

[0034] Legend of the drawings: 1, laser cutting unit, 111, laser, 112, beam expander, 113, prism, 114, focusing mirror, 115, beam splitter, 12, first focusing assembly, 2, distance measuring assembly, 21, distance measuring sensor, 22, rotating galvanometer, 23, dichroic mirror, 3, controller, 4, monitoring assembly, 41, camera, 42, second focusing assembly, 5, motion platform, 51, wafer to be cut. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the article or device that includes said element.

[0037] like Figure 1 As shown, a multi-parameter layer-by-layer laser slicing method for ultrathin wafers includes:

[0038] S101: Configure a hidden cutting strategy for the wafer 51 to be cut according to the laser hidden cutting model. The laser hidden cutting model includes the mapping relationship between wafer parameters and hidden cutting parameters, including the material of the wafer, the depth and the numerical relationship between laser power, laser pulse frequency, laser energy density and scanning speed, as shown in Table 1.

[0039] For example, when the depth of the ultrathin wafer is 15μm, the laser power is 1W, the laser pulse frequency is 40KHz, the laser energy density is 1.2J / cm², and the scanning speed is 400mm / s.

[0040] Table 1 shows the mapping relationship between wafer parameters and hidden cutting parameters.

[0041]

[0042] S102: The wafer 51 to be cut is hidden-cut based on the hidden-cutting strategy, including: dividing the wafer 51 to be cut into a surface layer, an intermediate layer and a bottom layer from top to bottom; automatically adjusting the position of the laser focus so that it is focused on the surface layer, the intermediate layer and the bottom layer respectively; using different hidden-cutting parameters to cut the surface layer, the intermediate layer and the bottom layer at least three times in sequence, injecting a lower energy each time, the total heat input is controlled, which can effectively reduce the accumulation of thermal stress, thereby suppressing cracks and edge chipping;

[0043] The surface layer and the bottom layer have the same thickness, and the thickness of the intermediate layer is greater than the thickness of the surface layer and the bottom layer.

[0044] In some embodiments, the hidden cutting parameters include: laser power, laser pulse frequency, laser energy density and scanning speed; wherein the laser pulse frequency of the intermediate layer is greater than the laser pulse frequency of the surface layer and the bottom layer, mainly for the following reasons: 1. Ensure the continuity of the modification: the internal modification layer must be continuous to ensure that the crack propagation path is controllable and consistent. High pulse frequency means that the overlap rate of adjacent spots is very high when the laser beam is scanned at a certain speed. In this way, the modified area generated by each pulse can fully overlap with the modified areas of the previous and next pulses, seamlessly connected, thereby forming a complete and uniform "cutting line". 2. Utilize controllable heat accumulation effect: contrary to the surface layer, in the intermediate layer, we need a certain degree of controllable heat accumulation. At a higher frequency, the interval time between pulses is short, and the heat generated by the previous pulse has not yet completely dissipated before the energy of the next pulse arrives. This selective heat accumulation can promote the material to absorb laser energy more effectively (especially for transparent or semi-transparent materials, their absorption rate will increase with temperature, thereby achieving deeper modification with lower single-pulse energy, reducing nonlinear side effects. 3. Improve processing efficiency: under the condition of ensuring the scanning speed, high pulse frequency is the only way to achieve high overlap rate, thereby maintaining or improving the processing tempo without sacrificing quality. The surface layer and the bottom layer have lower frequency to minimize the thermal impact on the functional materials of the surface layer, prevent metal melting, dielectric layer peeling or thermal-induced cracking, and prevent energy from being released explosively; the bottom layer is the "exit" of laser action, if the frequency here is too high and the heat accumulation is too strong, it may cause the material to undergo a sudden phase change or stress release, forming a larger edge collapse. In this embodiment, the laser pulse frequency of the intermediate layer is 40-60 kHz, the laser pulse frequency of the surface layer is 30-40 kHz, and the laser pulse frequency of the bottom layer is 20-40 kHz. Selecting different laser pulse frequencies at different positions not only ensures the hidden cutting efficiency, but also avoids continuous irradiation causing thermal damage and micro-cracks to the wafer to be cut 51. The intermediate layer is far from the upper and lower surfaces of the wafer to be cut 51, and a higher laser pulse frequency is needed to ensure that the processing forms a continuous and effective modified layer during the hidden cutting process, avoiding uneven separation in the subsequent expansion step.

[0045] In some embodiments, the laser power and laser energy density of the surface layer, intermediate layer and bottom layer increase in turn. Low energy input of the surface layer can effectively avoid surface edge collapse and thermal damage of the wafer to be cut 51, while ensuring the accurate formation of the modified layer starting point. For example, the laser power of the surface layer can be 0.5-1 W; the intermediate layer gradually increases the laser power and laser energy, which can realize the continuity and uniformity of the modified layer, providing an ideal guide path for crack propagation. For example, the laser power of the intermediate layer can be 1-1.5 W; the higher input of the bottom layer ensures that the modified layer can extend to the back of the wafer to be cut, realizing complete separation. For example, the laser power of the bottom layer can be 1.5-2 W.

[0046] In some embodiments, the scanning speed of the surface layer, the intermediate layer and the bottom layer decreases in turn. The hidden cutting of the surface layer takes a higher scanning speed, which enables short energy deposition time and relatively small heat-affected zone. The high speed means that the laser beam stays at each point for a very short time. This greatly reduces the time for heat to spread to the surrounding sensitive areas, controls the heat-affected zone to the minimum range, and avoids material performance degradation or structural failure. The surface layer has a small amount of material removal, and usually does not require high single-pulse energy. Therefore, a higher speed can be tolerated without causing insufficient processing. The relatively slow speed of the intermediate layer is to ensure sufficient energy deposition. A high enough energy density is required to induce nonlinear absorption (such as multi-photon absorption) inside the material. Reducing the scanning speed is equivalent to extending the effective time of laser-material interaction, allowing each point to absorb more cumulative energy (combined with high pulse frequency) to achieve sufficient modification depth. At the same time, it ensures the continuity of the modification, and the hidden cutting requires the modified layer to be connected like a "dotted line" to a solid line. The combination of slower speed and higher pulse frequency can achieve a very high pulse overlap rate (e.g., > 90%), ensuring that the adjacent pulse areas overlap sufficiently to form a continuous modification band with uniform mechanical strength. This is the key to obtaining clean chips. The hidden cutting of the bottom layer takes a lower scanning speed to ensure sufficient energy deposition in the depth direction. The bottom layer is the most complex stress and the most prone to failure area. The residual stress inside the material, the thermal stress introduced by laser processing, and the presence of the back free surface make it prone to explosive energy release, leading to large-scale collapse. The extremely low scanning speed allows the system to release these stresses one pulse at a time, in a fine "knife work" and progressive manner, guiding the crack to extend to the surface in a controllable manner. In this embodiment, the scanning speed of the surface layer is 300-400 mm / s, the scanning speed of the intermediate layer is 200-300 mm / s, and the scanning speed of the bottom layer is 100-200 mm / s.

[0047] In some embodiments, the intermediate layer includes a plurality of sub-layers, and each sub-layer is hidden cut using the same hidden cutting parameters. When the thickness of the wafer 51 to be cut is greater than 50 μm, the thickness of the intermediate layer is greater than 20 μm, and the hidden cutting strategy does not match the current intermediate layer thickness, a plurality of sub-layers are arranged in the intermediate layer, and the layers are processed one by one to achieve the hidden cutting strategy, ensuring the continuity and uniformity of the modified layer, solving the uncontrollable risk brought by "one-time high-energy penetration", and instead using a "progressive and relay" modification method to achieve the optimal balance between quality and efficiency in depth.

[0048] In some embodiments, the thickness of the wafer to be cut 51 is less than or equal to 50 μm, which belongs to an ultra-thin wafer. The mechanical strength of the ultra-thin wafer is low, and it is more prone to deformation and cracking, which puts high requirements on the cutting and separation process. When cutting an ultra-thin wafer, a single energy parameter is easy to cause cracks to extend to the surface or back. The present application selects an ultra-thin silicon wafer with a thickness of 50 μm as an example. The ultra-thin silicon wafer is divided into a surface layer, an intermediate layer and a bottom layer in the thickness direction, wherein the thickness of the surface layer and the bottom layer is less than 15 μm, and the thickness of the intermediate layer is less than or equal to 20 μm, and the most suitable laser parameter combination is customized for each region. This division is based on the physical mechanism of laser and material interaction: at different depths, the laser energy deposition efficiency, thermal diffusion effect and stress distribution characteristics are significantly different. The surface layer region is 15 μm away from the surface of the ultra-thin silicon wafer. This region is closest to the surface of the wafer and is prone to thermal damage and micro-cracks. The intermediate region is 35 μm away from the surface of the ultra-thin silicon wafer. This region is the main area for the formation of the modified layer and requires sufficient and uniform energy input. The bottom layer region is 50 μm away from the surface of the ultra-thin silicon wafer. This region is close to the back of the wafer and needs to ensure complete separation without damaging the carrier film.

[0049] In some embodiments, the laser is a picosecond laser or a femtosecond laser. The wavelength range is 1000-1400 nm (such as 1064 nm or 1342 nm), which has appropriate penetration depth and absorption characteristics inside the wafer to be cut 51. In the present embodiment, a femtosecond laser is used, with a pulse width < 120 fs. Its cold processing characteristics can control the heat-affected zone to be below 0.8 μm, and the multi-photon absorption effect is dominant, which can maximize the inhibition of melting and thermal stress, thereby significantly reducing the edge collapse and dark cracks. The modified layer is formed inside the wafer to be cut 51 without excessive damage to the surface.

[0050] In some embodiments, the position of the laser focus is automatically adjusted to focus on the surface layer, the intermediate layer and the bottom layer, respectively, including:

[0051] The surface state of the wafer to be cut is detected in real time by the distance measuring assembly, whether the current layer cutting is achieved, and whether there are special conditions such as warping and irregular shape. When performing a laser cutting task, the measurement spot is aligned with the position in front of the cutting laser spot. The height of the cutting position is measured before cutting. Through the height deviation of the object to be cut, the cutting laser focus is adjusted in time, so that the cutting laser focus always remains on the surface of the object to be cut during the laser cutting process, even when passing through uneven surfaces, to solve the technical problem of accurate cutting in special conditions such as warping and irregular shape of the object to be cut.

[0052] Based on the surface state, the position of the laser focus point is automatically adjusted by the first focusing assembly to focus on the surface layer, the middle layer and the bottom layer respectively, the focal length is adjusted in real time, and the positions at different depths inside the wafer to be cut 51 can be accurately tracked.

[0053] In some embodiments, the first focusing assembly includes a piezoelectric ceramic driver for realizing nanoscale movement of the laser focus point.

[0054] As shown in Figure 2 The embodiment of the present application further provides a multi-parameter layer-by-layer laser hidden cutting device for ultra-thin wafers, which is used to realize the above method, and the device comprises: a laser cutting unit 1, a distance measuring assembly 2 and a controller 3. The laser cutting unit 1 comprises a light source assembly and a first focusing assembly 12, the light source assembly focuses laser on the surface of the wafer to be cut, and the first focusing assembly 12 adjusts the position of the focus point of the laser so that the focus point is maintained in the surface layer, the middle layer or the bottom layer; the distance measuring assembly 2 is used to detect in real time the height of the surface of the wafer to be cut to the first focusing assembly 12 at a preset distance in front of the focus point along the cutting direction; the controller 3 is connected with the laser cutting unit 1 and the distance measuring assembly 2, receives the detection result of the distance measuring assembly 2 and controls the first focusing assembly 12 according to the detection result, so that the position of the focus point is maintained in the surface layer, the middle layer or the bottom layer of the wafer to be cut 51.

[0055] Optionally, as shown in Figure 3 The light source assembly comprises a laser 111, a beam expander 112, a prism 113 and a focusing lens 114; the laser 111 selects femtosecond laser as needed, continuous laser with a wavelength range of 1000-1400 nm, and the laser emitted by the laser 111 is expanded and / or shaped by the beam expander 112 to form cutting laser. The cutting laser is reflected by the prism 113 and then irradiates the focusing lens 114, and the focusing lens 114 focuses the cutting laser in a preset range of the wafer to be cut 51.

[0056] Optionally, the first focusing assembly 12 is connected with the focusing lens 114 and is used to adjust the position of the focusing lens 114 to adjust the position of the laser focus point. Specifically, the first focusing assembly 12 comprises a driving device such as a piezoelectric ceramic, the focusing lens 114 is assembled with the piezoelectric ceramic driver, the driving realizes nanoscale bidirectional movement of the optical path axis direction of the focusing lens 114, so as to adjust the focusing depth of the cutting laser focus point.

[0057] In some embodiments, the distance measuring assembly 2 comprises a distance measuring sensor 21 for emitting and receiving distance measuring laser, a rotating galvanometer 22 for adjusting the direction of the distance measuring laser to adjust the position of the distance measuring laser on the wafer to be cut 51. A dichroic mirror 23 is arranged between the prism 113 and the focusing mirror 114, for transmitting the cutting laser emitted by the laser 111 to the wafer to be cut 51, and reflecting the distance measuring laser in the same direction as the cutting laser to the wafer to be cut 51. In this embodiment, since the distance measuring laser is emitted in a direction substantially perpendicular to the wafer to be cut 51, most of the reflected light can be received, thereby improving the distance measuring accuracy of the distance measuring assembly 2. In addition, by rotating the rotating galvanometer 22, the position of the distance measuring laser entering the dichroic mirror 23 can be adjusted, thereby adjusting the positional relationship between the distance measuring laser and the cutting laser. When changing the cutting direction, the angle of the rotating galvanometer 22 can be adjusted to ensure that the distance measuring laser is always located in front of the cutting laser to achieve the purpose of detecting first and cutting later. It can be understood that by adjusting the angle of the rotating galvanometer 22, the distance measuring laser can be located at any position around the cutting laser, so that no matter the cutting direction, by adjusting the angle of the rotating galvanometer 22, the distance measuring laser can be always located in front of the cutting laser to achieve the purpose of detecting first and cutting later. When the distance measuring laser is incident on the warped position of the wafer to be cut 51, the reflected light is reflected back to the distance measuring sensor 21 through the dichroic mirror 23 and the rotating galvanometer 22, and the distance measuring sensor 21 sends detection information to the controller 3, and the first focusing assembly 12 adjusts the focal position of the focusing mirror 114, and adjusts the hidden cutting strategy of the laser cutting unit 1 acting on the warped position to match the warped height, thereby ensuring the cutting quality. That is, when performing the laser cutting task, the measurement spot of the distance measuring sensor 21 is aligned with the front position of the cutting laser spot, and the height of the position to be cut is measured by the distance measuring sensor 21 before cutting, to ensure that the distance measuring sensor 21 can timely feedback the surface height deviation of the wafer to be cut 51, and the first focusing assembly 12 and the focusing mirror 114 can timely respond to the height deviation and adjust the cutting laser focal length, thereby ensuring that the cutting laser focal point always remains on the surface of the wafer to be cut 51 during the laser cutting process. To solve the technical problem of precise cutting under special conditions such as warping and special-shaped of the wafer to be cut 51.

[0058] In some embodiments, the multi-parameter layer-by-layer laser hidden cutting device for ultra-thin wafers further comprises a monitoring assembly 4 for monitoring the cutting state of the wafer to be cut 51; the monitoring assembly 4 comprises: a camera 41 for obtaining a cutting image of the surface of the wafer to be cut; and a second focusing assembly 42 for adjusting the focal length of the camera 41 to achieve clear imaging. The cutting effect can be observed through the monitoring assembly 4, such as observing whether there is a broken line during cutting, and real-time detection of changes in cutting path width, whether there is edge collapse or slag accumulation, etc., to further assist in monitoring the laser cutting process and achieve the purpose of precise monitoring. In addition, since the camera 41 monitors the reflected light path of the cutting laser used, when the first focusing assembly 12 is adjusted in real time to achieve clear imaging of the camera 41, the focal length of the second focusing assembly 42 needs to be adjusted at the same time.

[0059] In some embodiments, the light source assembly further comprises a beam splitter 115 disposed on the light exit side of the beam expander 112, which is used to transmit the cutting laser emitted by the laser 111 to the wafer to be cut 51, and at the same time reflect the reflected light from the surface of the wafer to be cut 51 to the camera 41.

[0060] In some embodiments, the multi-parameter layer-by-layer laser hidden cutting device for ultra-thin wafers further comprises a motion platform 5 for carrying the wafer to be cut 51 and moving the wafer to be cut 51 in a predetermined direction. For example, the wafer to be cut 51 is adsorbed by a wafer adsorption platform, and the wafer to be cut 51 is controlled to move in XYZ directions. Optionally, the Z-axis direction motion is realized by a piezoelectric ceramic driver with a nanometer-level resolution, and the wafer to be cut 51 is driven to move along the Z-axis direction by the piezoelectric ceramic driver, which together with the first focusing assembly 12 ensures that the laser focal point can accurately track the position of different depths inside the wafer, so as to adjust the focusing depth of the cutting laser focal point.

[0061] Finally, it should be noted that: the embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts of each embodiment can be referred to. For the system or device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant part can be referred to the method part.

[0062] The above embodiments are only used to illustrate the technical solutions of the present application, but not limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for some technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A multi-parameter layer-by-layer laser stealth dicing method for ultra-thin wafers, characterized in that, The method comprises: S101: configuring a hidden cutting strategy for cutting a wafer to be cut according to a laser hidden cutting model, wherein the laser hidden cutting model comprises a mapping relationship between wafer parameters and hidden cutting parameters; S102: performing hidden cutting on the wafer to be cut based on the hidden cutting strategy, comprising: dividing the wafer to be cut into a surface layer, an intermediate layer and a bottom layer from top to bottom; automatically adjusting the position of the laser focal point to focus on the surface layer, the intermediate layer and the bottom layer respectively; and performing at least three times of cutting on the surface layer, the intermediate layer and the bottom layer in turn using different hidden cutting parameters. The thickness of the surface layer and the bottom layer is the same, and the thickness of the intermediate layer is greater than the thickness of the surface layer and the bottom layer.

2. A multi-parameter layer-by-layer laser stealth dicing method for ultra-thin wafers according to claim 1, characterized in that, The hidden cutting parameters comprise laser power, laser pulse frequency, laser energy density and scanning speed; wherein the laser pulse frequency of the intermediate layer is greater than the laser pulse frequency of the surface layer and the bottom layer.

3. A multi-parameter layer-by-layer laser stealth dicing method for ultra-thin wafers according to claim 2, characterized in that, The laser power and laser energy density of the surface layer, the intermediate layer and the bottom layer increase in turn.

4. The method of claim 2, wherein, The scanning speed of the surface layer, the intermediate layer and the bottom layer decreases in turn.

5. The method of claim 1, wherein, The intermediate layer comprises a plurality of sub-layers, and each sub-layer is hidden cut using the same hidden cutting parameters.

6. The method of claim 5, wherein, The thickness of the wafer to be cut is less than 50 microns, wherein the thickness of the surface layer and the bottom layer is less than 15 microns, and the thickness of the intermediate layer is greater than 20 microns.

7. The method of claim 1, wherein, The laser is a picosecond laser or a femtosecond laser.

8. The method of claim 1, wherein, The automatic adjustment of the position of the laser focal point to focus on the surface layer, the intermediate layer and the bottom layer comprises: detecting the surface state of the wafer to be cut in real time by a distance measuring component; based on the surface state, automatically adjusting the position of the laser focal point to focus on the surface layer, the intermediate layer and the bottom layer by a first focusing component.

9. The method of claim 8, wherein, The first focusing component comprises a piezoelectric ceramic driver for realizing nanoscale movement of the laser focal point.

10. A multi-parameter layer-by-layer laser stealth dicing device for ultra-thin wafers, for implementing a multi-parameter layer-by-layer laser stealth dicing method for ultra-thin wafers according to any one of claims 1-9, characterized in that, The device comprises: a laser cutting unit comprising a light source component and a first focusing component, the light source component focuses the laser on the wafer surface, and the first focusing component adjusts the focal position of the laser so that the focal point is maintained in the surface layer, the intermediate layer or the bottom layer; a distance measuring component for detecting the height of the wafer surface to the first focusing component at a preset distance in front of the focal point along the cutting direction in real time; a controller connected with the laser cutting unit and the distance measuring component, receiving the detection result of the distance measuring component and controlling the first focusing component according to the detection result, so that the position of the focal point is maintained in the surface layer, the intermediate layer or the bottom layer.

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