Large-sized wafer thinning and polishing device and method based on dynamic line light beam

Abstract

Large-size wafer thinning and polishing device and method based on a dynamic line beam, comprising a dynamic beam generation module, a rotating and carrying module, and a closed-loop control module. The dynamic beam generation module includes a laser, a polarizer, a line beam shaping component, a reflector, a hollow conical lens, and a lifting module. The line beam shaping component is used to shape the laser beam into a linear beam. The hollow conical lens is a conical lens that is hollow and has an open end face, and is used to shape the linear beam into an arc-shaped beam. The hollow conical lens is installed on the lifting module to generate a dynamic arc-shaped beam. The rotating and carrying module is used to fix and drive the wafer to rotate. The closed-loop control module is used to control the lifting of the lifting module and the movement of the rotating and carrying module. The present invention can greatly improve the polishing speed, and also improve the polishing uniformity and polishing quality. It can simultaneously perform thinning and polishing processing on multiple wafers, and can adapt to wafers of different sizes and shapes.

Description

Technical Field

[0001] The present invention relates to the technical field of laser processing, and particularly to a large-size wafer thinning and polishing device and method based on a dynamic line beam. Background Art

[0002] With the rapid development of industries such as new energy vehicles, rail transit, and consumer electronics, the market has increasingly higher performance and requirements for high-end chips and power devices. Wafer substrates such as silicon and silicon carbide are typical hard and brittle materials that are difficult to process, and their surface quality and surface accuracy determine the performance of semiconductor devices. Therefore, ultra-precision wafer thinning technology and polishing technology have become key technologies in the wafer manufacturing process.

[0003] In ultra-precision wafer thinning technology, high-precision, high-efficiency, and high-stability damage-free surface processing of large-size wafers can be achieved by using ultra-fine-grained diamond grinding wheels and ultra-precision thinning equipment with high stability. Chemical mechanical polishing (CMP) technology uses a process that combines chemical corrosion and mechanical friction to achieve global planarization of the wafer surface, which is crucial for the front-end processes of advanced integrated circuit manufacturing, advanced packaging, and other links. However, the existing CMP technology still has the following problems: low process efficiency (<0.5 mm² / s), wafer warping caused by processing stress (Bow > 10 μm), and chemical waste liquid pollution. Traditional laser polishing has problems such as low material removal rate (<0.1 mm² / s) in the point beam scanning mode, a thermal affected zone depth > 50 μm, and a surface roughness Ra > 1 nm. Especially when polishing large-area wafers, traditional methods are difficult to meet the requirements of industrial production. The power density of the line beam is relatively low. Using the line beam to polish the wafer surface can overcome the deficiency of the thermal influence on the material due to the energy concentration of the traditional Gaussian-distributed point spot. However, the existing line beam polishing technology lacks dynamic matching, resulting in low edge removal rate of the wafer, poor surface profile consistency, and low processing efficiency. Summary of the Invention

[0004] The object of the present invention is to overcome the above-mentioned shortcomings of the prior art and provide a large-size wafer thinning and polishing device based on a dynamic line beam, as well as a wafer thinning and polishing method using this device, to achieve the coordinated optimization of wafer thinning and polishing efficiency and quality.

[0005] The present invention is achieved by the following technical solutions:

[0006] A large-sized wafer thinning and polishing device based on a dynamic line beam, comprising a dynamic beam generation module, a rotary carrier module and a closed-loop control module. The dynamic beam generation module includes a laser, a polarizer, a line beam shaping component, a reflector, a hollow conical lens and a lifting module. The laser is used to generate a Gaussian laser beam. The line beam shaping component is used to shape the laser beam into a linear beam. The polarizer is arranged between the laser and the line beam shaping component. The hollow conical lens is a conical lens with a hollow interior and an open end face, and its wall thickness is uniform. It is used to shape the linear beam into an arc-shaped beam. The hollow conical lens is installed on the lifting module with its end face opening upwards and the conical angle downwards, and moves up and down under the drive of the lifting module to generate a dynamic arc-shaped beam. The reflector is arranged between the line beam shaping component and the hollow conical lens. After the laser beam generated by the laser passes through the polarizer and reaches the line beam shaping component, it is shaped into a linear beam, then reflected by the reflector and enters the inner conical surface of the hollow conical lens, and is emitted from the outer conical surface of the hollow conical lens to form an arc-shaped beam for wafer thinning and polishing. The arc-shaped beam adjusts its position and shape along with the lifting module.

[0007] The rotary carrier module is used to fix and drive the wafer to rotate. The closed-loop control module is respectively connected to the lifting module and the rotary carrier module to control the lifting of the lifting module and the movement of the rotary carrier module.

[0008] Furthermore, it further includes a detection module. The detection module includes a white light interferometer and an infrared thermal imager arranged above the rotary carrier module. The white light interferometer is used to detect the processing surface of the wafer. The infrared thermal imager is used to detect the temperature during the laser thinning and polishing process of the wafer. The white light interferometer and the infrared thermal imager are respectively connected to the closed-loop control module to transmit detection data, and the closed-loop control module adjusts the movement of the lifting module and the rotary carrier module according to the real-time detection data.

[0009] Furthermore, the line beam shaping component includes a beam expander and a line beam shaping mirror. The line beam shaping mirror is a cylindrical lens, a flat cylindrical lens, a Powell prism, a cylindrical lens array or a flat cylindrical lens array. The beam expander is used for beam expansion of the laser beam. After the laser beam is expanded by the beam expander, it is shaped into a linear beam by the line beam shaping mirror.

[0010] A line beam focusing mirror is further arranged between the hollow conical lens and the wafer. The arc-shaped beam reaches the wafer surface after being focused by the line beam focusing mirror for wafer processing.

[0011] The lifting module is installed on the horizontal linear module, and the horizontal linear module is used to drive the lifting module and the hollow conical lens thereon to move in the horizontal direction, so that the hollow conical lens can effectively cooperate with the mirror to incident the line beam, and adjust the incident angle as the angle of the mirror is adjusted.

[0012] Further, the conical angle of the hollow conical lens is 30°-120°, the hollow conical lens is made of BK7 optical glass (refractive index n = 1.516) or fused silica (n = 1.458, high ultraviolet transmittance), and the wall thickness is 1.5-2.0 mm;

[0013] The rotation and bearing module includes a disc, a vacuum adsorption device, an air floating bearing and a rotation driving component. The vacuum adsorption device is arranged on the disc and is used to fix the wafer on the disc by vacuum adsorption. The diameter of the disc is ≥200 mm, and the rotation driving component drives the disc to rotate through the air floating bearing.

[0014] A large-size wafer thinning and polishing method based on a dynamic line beam, using the above-mentioned large-size wafer thinning and polishing device based on a dynamic line beam, includes the following steps:

[0015] S1. Vacuum-adsorb multiple wafers to be processed on the disc of the rotation and bearing module, and the multiple wafers are arranged in a ring with the rotation center of the disc as the center, so that the wafers can rotate around the rotation center of the disc; select a suitable hollow conical lens and fix it on the lifting module;

[0016] S2. According to the material, size and surface polishing requirements of the wafer, referring to the pre-stored mapping table of each material (such as silicon carbide, gallium nitride, etc.), size and polishing parameters, initially set the laser power, the arc length of the arc-shaped line beam, the angle of the mirror, the initial position of the lifting module and the initial height of the hollow conical lens, so that the incident point of the line beam on the hollow conical lens is ≥4 mm away from the edge of the hollow conical lens, the incident angle range is 10°-30°, and the arc-shaped line beam generated by the dynamic beam generation module falls on the outermost layer or the innermost layer of the wafer processing;

[0017] S3. Start the rotation and bearing module to make the disc rotate at a certain speed, so that the arc-shaped line beam can sequentially perform thinning and polishing processing on all the wafers on the disc as the disc rotates; at the same time, control the lifting module to drive the hollow conical lens to lift and lower at a certain speed program, so that the dynamic arc-shaped line beam performs thinning and polishing processing on all the wafers on the disc from the outside to the inside or from the inside to the outside with the rotation center of the disc as the center;

[0018] S4. During the thinning and polishing process, the surface data of the wafer is obtained in real time by a white light interferometer, and the temperature distribution in the wafer processing area is monitored in real time by an infrared thermal imager. The closed-loop control module dynamically adjusts the rotation speed of the disk, the driving speed of the lifting module, the laser power, and the arc length of the arc-shaped line beam in real time according to the obtained surface data and temperature distribution data of the wafer, so that the total thickness variation (TTV) of the wafer < 1 μm, and the depth of the heat-affected zone of the laser processing < 5 μm.

[0019] Further, a post-processing step is also included, and the method is as follows: megasonic cleaning (frequency 950 kHz) is used to remove the residual particles on the wafer surface, and then the surface roughness is finally inspected by an atomic force microscope (AFM).

[0020] Further, in step S3, the hollow conical lens descends or ascends continuously at a certain speed program, so that the arc-shaped line beam scans on the disk to form a spiral trajectory centered on the rotation center of the disk, from the outside to the inside or from the inside to the outside, and the spiral trajectory covers all wafers. If the hollow conical lens descends at a constant speed, a spiral trajectory is formed from the outside to the inside; conversely, if the hollow conical lens ascends at a constant speed, a spiral trajectory is formed from the inside to the outside.

[0021] The lifting speed of the hollow conical lens is closely related to the shape of the spiral trajectory (including the radius of the spiral and the spacing between adjacent spirals). The lifting speed v of the hollow conical lens can be controlled according to the following formula: V = k2·h -1 / 2 , where h is the height of the hollow conical lens, and k2 is a constant, which is only related to the cone angle θ of the hollow conical lens and the incident angle β of the line beam on the hollow conical lens.

[0022] Further, in step S3, the hollow conical lens descends or ascends intermittently in a step-by-step manner, so that the arc-shaped line beam scans from the outside to the inside or from the inside to the outside on the disk to form a plurality of concentric circles centered on the rotation center of the disk. The step amount between adjacent concentric circles is equal or unequal, and the concentric circle trajectory covers all wafers; if the hollow conical lens descends intermittently in a step-by-step manner, concentric circles are formed in sequence from the outside to the inside; conversely, if the hollow conical lens ascends intermittently in a step-by-step manner, concentric circles are formed in sequence from the inside to the outside. The diameter of the concentric circle is related to the position of the hollow conical lens, and the distance between adjacent concentric circles is related to the step amount when the hollow conical lens descends or ascends.

[0023] The residence time T of the hollow conical lens at different step heights is controlled according to the following formula: T = k1·h; where h is the height of the hollow conical lens, and k1 is a constant, which is only related to the cone angle θ of the hollow conical lens 5 and the incident angle β of the line beam on the hollow conical lens.

[0024] Furthermore, the arc length of the arc-shaped line beam output by the hollow conical lens is 0.2 - 8 mm, the line width < 0.1 mm, the radian < π / 4, and the uniformity > 90%; the output power of the laser is 300 - 500 W, and the rotation speed of the disk is 100 - 200 rpm.

[0025] Furthermore, in step S4, the dynamic adjustment method of the rotation and bearing module is as follows:

[0026] a. When it is detected that the material removal rate on the surface of the wafer is less than the set value M, the arc length of the arc-shaped line beam is increased by 10% - 15% by adjusting the parameters of the line beam shaping component, and the rotation speed of the disk is increased by 5% - 10%;

[0027] b. When it is detected that the material removal rate on the surface of the wafer is greater than the set value N, automatically switch to the safe polishing mode;

[0028] c. When it is detected that the local temperature exceeds the set threshold P (such as 150 °C), if the current laser is in the continuous laser mode, then switch to the pulsed laser mode, set the duty cycle to 30% - 50%, and trigger the cooling air curtain to work; if the current laser is in the pulsed laser mode, then automatically switch to the safe polishing mode; the safe polishing mode is: reduce the laser power to 50% - 70% of the current value, and at the same time trigger the ultrasonic-assisted polishing mechanism to perform local trimming.

[0029] In the present invention, a line beam shaping component is provided to first shape the laser beam into a linear line beam respectively, and then a hollow conical lens is used to shape the linear line beam into an arc-shaped line beam. The hollow conical lens is arranged on a lifting module. When the hollow conical lens moves up and down, a dynamic arc-shaped line beam is generated, which is used to perform laser processing on the wafers in cooperation with the rotation of the wafers arranged on the disk. The continuous energy distribution of the line beam also greatly improves the polishing speed compared with the traditional point spot polishing. Moreover, due to the uniform energy distribution of the line beam, the polishing uniformity is improved, the thermal influence on the wafers is reduced, and the polishing quality is enhanced. The ingenious combination design of the hollow conical lens and the lifting module can generate a dynamic arc-shaped line beam. Compared with the conventional mode of generating a dynamic beam by changing the light angle or moving the beam, since the incident angle remains unchanged during the processing, the position of the output line beam can be accurately predicted, and the energy density of the laser beam can always be kept stable without changing due to the change of the angle. Therefore, the processing process is controllable, and the processing quality can be guaranteed. And the movement of the dynamic arc-shaped line beam can match the rotation of the wafers on the disk, and multiple wafers can be thinned and polished simultaneously as the disk rotates, further improving the processing efficiency. Through the matching among the placement position of the wafers on the disk, the rotation speed of the wafers, the parameters of the line beam shaping component, the cone angle of the hollow conical lens, the incident angle, the lifting speed, and the movement range, efficient and uniform polishing of large-sized wafers can be achieved. At the same time, with the real-time monitoring of a white light interferometer and an infrared thermal imager, the shape, energy, and operation mode of the line beam can be dynamically adjusted, further improving the polishing efficiency and ensuring the polishing quality, and it can adapt to wafers of different sizes and shapes, especially large-sized wafers. Practice has proved that the material removal rate of the present invention reaches 8 mm² / s, which is 300 times higher than that of the traditional point beam. The single-wafer processing cycle is shortened to 42 minutes. In terms of precision, the TTV of the processed wafers is < 1 μm, Bow < 3 μm, the surface Ra < 0.5 nm, there are no micro-cracks on the surface, the depth of the thermal influence zone is < 5 μm, and the lattice distortion rate is reduced to less than 0.05%. It can support the mixed-line production of 8-12-inch wafers, the process switching time is < 10 minutes, and the equipment utilization rate is > 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the frame structure of the thinning and polishing device according to an embodiment of the present invention.

[0031] Figure 2 It is a three-dimensional structure schematic diagram of the hollow conical lens in the thinning and polishing device according to an embodiment of the present invention.

[0032] Figure 3 It is a schematic diagram of the generation principle of the dynamic arc-shaped line beam in the thinning and polishing device according to an embodiment of the present invention. Among them, Figure 3 (a) in it is a schematic diagram of the arc-shaped line beam falling on the disk when the hollow conical lens is at a high position, Figure 3In (b), it is a schematic diagram of the arc-shaped line beam falling on the disc when the hollow conical lens is in the low position.

[0033] Figure 4 It is a flowchart of the working principle of the thinning and polishing device according to the embodiment of the present invention.

[0034] Figure 5 It is a control framework diagram according to the embodiment of the present invention.

[0035] Figure 6 It is a schematic diagram of the cone angle of the hollow conical lens, the height position of the incident light, and the incident angle in the embodiment of the present invention.

[0036] Figure 7 It is a schematic diagram of the arc-shaped line beam falling on the disc in the embodiment of the present invention.

[0037] Figure 8 It is a schematic diagram of a laser track formed by the arc-shaped line beam on the disc as the disc rotates in the embodiment of the present invention.

[0038] Figure 9 It is a schematic diagram of a track of the arc-shaped line beam for processing multiple wafers on the disc as the disc rotates in the embodiment of the present invention.

[0039] Figure 10 It is a schematic diagram of another laser track formed by the arc-shaped line beam on the disc as the disc rotates in the embodiment of the present invention.

[0040] Figure 11 It is a schematic diagram of another track of the arc-shaped line beam for processing multiple wafers on the disc as the disc rotates in the embodiment of the present invention.

[0041] Reference numerals: 1 - laser; 2 - polarizer; 3 - line beam shaping assembly; 4 - first reflector; 5 - hollow conical lens; 6 - lifting module; 7 - line beam focusing lens; 8 - disc; 9 - wafer; 10 - second reflector; 11 - third reflector; 12 - horizontal linear module; 13 - arc-shaped line beam; 14 - laser track; 31 - line beam shaping mirror; 32 - beam expander; 81 - rotation center. Detailed implementation manners

[0042] A large-sized wafer thinning and polishing device based on a dynamic line beam, as Figure 1 shown, includes a dynamic beam generation module, a rotating and carrying module, a closed-loop control module, and a detection module.

[0043] As Figure 1, the dynamic beam generation module includes a laser 1, a polarizer 2, a second mirror 10, a third mirror 11, a linear beam shaping component 3, a first mirror 4, a hollow conical lens 5, a lifting module 6, and a linear beam focusing lens 7. The laser 1 is used to generate a Gaussian laser beam. The linear beam shaping component 3 is used to shape the laser beam into a linear beam. The polarizer 2, the second mirror 10, the third mirror 11, and the linear beam shaping component 3 are arranged in sequence. The polarizer 2 can ensure the polarization state of the laser output. The second mirror 10 and the third mirror 11 are parallel to each other, changing the optical path of the laser beam, which is beneficial to the spatial layout of the device. As Figure 2 shown, the hollow conical lens 5 is a conical lens that is hollow and has an open end face. Its wall thickness is uniform. It is used to shape the linear beam into an arc-shaped beam 13. The hollow conical lens 5 is installed on the lifting module 6 with its open end face facing upward and the conical angle facing downward, and moves up and down under the drive of the lifting module 6. As Figure 5 , to generate a dynamic arc-shaped beam 13. The first mirror 4 is arranged between the linear beam shaping component 3 and the hollow conical lens 5. After the laser beam generated by the laser 1 reaches the linear beam shaping component 3 through the polarizer 2, it is shaped into a linear beam. After being reflected by the first mirror 4, it enters the inner conical surface of the hollow conical lens 5 and exits through the outer conical surface of the hollow conical lens 5 to form an arc-shaped beam 13. The arc-shaped beam 13 adjusts its position and shape along with the lifting module 6. The linear beam focusing lens 7 is arranged at the rear end of the hollow conical lens 5. The arc-shaped beam 13 is focused by the linear beam focusing lens 7 and then reaches the surface of the wafer 9 to perform thinning and polishing processing on the wafer 9. The linear beam focusing lens 7 is an aspherical mirror or a cylindrical mirror.

[0044] The lifting module 6 can be an existing linear module, such as an electric slide rail, a pneumatic driving component, etc. Preferably, it is an electric slide rail, and its displacement accuracy ≤ ±0.1 μm.

[0045] The formation principle of the dynamic arc-shaped beam can be as Figure 3 shown. The hollow conical lens 5 moves up and down under the drive of the lifting module 6. The direction of the incident light remains unchanged, and the incident angle remains unchanged. Therefore, the angle of the outgoing light will not change, but due to the change of the incident point, the position of the outgoing light will also change accordingly, thus forming a dynamic arc-shaped beam. As Figure 3 shown, when the hollow conical lens 5 descends from the position in (a) in Figure 3 to the position in (b) in Figure 3 , the incident point of the laser changes accordingly, and the linear beam moves from the outer layer of the wafer to the inner layer of the wafer, thereby processing the wafer from the outside to the inside.

[0046] The rotation and bearing module is used to fix and drive the wafer 9 to rotate. As Figure 5, the closed-loop control module is respectively connected to the lifting module 6 and the rotating and bearing module to control the lifting of the lifting module 6 and the movement of the rotating and bearing module.

[0047] As Figure 4 shown, the working principle of the thinning and polishing device of the present invention is as follows: The laser generates a Gaussian beam, and the Gaussian beam enters the line beam shaping component through the reflection of the mirror to form a line beam. The uniform line beam enters a specific position of the hollow conical lens through the mirror and can form an arc-shaped line beam with a specific arc length. The hollow conical lens can perform reciprocating lifting motion during the working process, and at the same time, the incident angle of the line beam remains unchanged. Therefore, when the line beam passes through the hollow conical lens from the inside, a dynamic arc-shaped line beam is generated as the hollow conical lens lifts and lowers; when the wafer rotates around the rotation center of the disk on the disk, the dynamic arc-shaped line beam advances along the rotation radius, and the movement of the hollow conical lens corresponds to the advancement of the arc-shaped beam. Specifically, when the hollow conical lens descends, the arc-shaped line beam advances in the direction of the rotation center. The present invention mainly uses the arc-shaped line beam for polishing processing. Due to the energy dispersion and equalization effect of the line beam, a laser with a higher power can be used. Also, since the range of change in the curvature radius of the arc-shaped line beam should not be too large, the present invention is suitable for processing large-sized wafers.

[0048] The detection module includes a white light interferometer and an infrared thermal imager arranged above the rotating and bearing module. The white light interferometer is used to detect the processed surface of the wafer 9, and the infrared thermal imager is used to detect the temperature during the laser thinning and polishing process of the wafer 9. As Figure 5 , the white light interferometer and the infrared thermal imager are respectively connected to the closed-loop control module to transmit detection data, and the closed-loop control module adjusts the movement of the lifting module 6 and the rotating and bearing module according to the real-time detection data. The white light interferometer monitors the surface shape of the wafer 9 in real time, with a resolution of 0.1 nm, controlling TTV ≤ 1 μm, and the thermal imager detects the temperature of the polishing area with an accuracy of ±1 °C.

[0049] The function of the line beam shaping component 3 is to convert the Gaussian beam into a linear beam. In this embodiment, the line beam shaping component 3 includes a beam expander 32 and a line beam shaping mirror 31. The beam expander 32 is used for expanding the laser beam. The line beam shaping mirror 31 is a cylindrical lens, a flat cylindrical lens, a Powell prism, a cylindrical lens array, or a flat cylindrical lens array. These mirrors or mirror arrays can convert the collimated dot-shaped laser beam into a one-dimensional line beam with a line width < 0.1 mm and a uniformity > 90%.

[0050] As one of the implementation manners, the lifting module 6 is installed on the horizontal linear module 12, and the horizontal linear module 12 is used to drive the lifting module 6 and the hollow conical lens 5 thereon to move in the horizontal direction, so that the hollow conical lens 5 can effectively cooperate with the first reflector 4 to irradiate the incident light beam and adjust the incident angle to adapt to the processing of wafers 9 of different materials, sizes and surface morphologies. The horizontal linear module 12 can adopt a combination form of a conventional X-axis linear movement module and a Y-axis linear movement module. In this embodiment, to further realize automation, the first reflector 4 is connected with a swing module for controlling the angle of the first reflector 4, so as to adjust the incident angle of the linear light beam, such as Figure 5 , the closed-loop control module is also respectively connected with the horizontal linear module 12 and the swing module to control the angle of the first reflector 4 and the horizontal position of the hollow conical lens 5.

[0051] As one of the implementation manners, the conical angle of the hollow conical lens 5 is 30° - 120°, preferably 15° - 45°. The hollow conical lens 5 is made of BK7 optical glass (refractive index n = 1.516) or fused quartz (n = 1.458, high ultraviolet transmittance), and the wall thickness is 1.5 - 2.0 mm.

[0052] As one of the implementation manners, the rotary bearing module includes a disk 8, a vacuum adsorption device, an air bearing and a rotary driving component. The vacuum adsorption device is arranged on the disk 8 and is used to fix the wafer 9 on the disk 8 by means of vacuum adsorption. The diameter of the disk 8 is ≥ 200 mm, and the rotary driving component drives the disk 8 to rotate through the air bearing. The air bearing can provide extremely high radial and axial rotation runout accuracy, and can make the radial runout error < 1 μm, thereby improving the processing accuracy. The vacuum adsorption pressure can be controlled within 0.1 - 0.5 MPa, and can support the rapid clamping (time-consuming < 30 seconds) of wafers 9 with a size of 45 - 200 mm. An electrostatic clamping mode can also be set simultaneously to realize the switching between the dual modes of vacuum adsorption.

[0053] A large-size wafer thinning and polishing method based on a dynamic linear light beam, adopting the above-mentioned large-size wafer thinning and polishing device based on a dynamic linear light beam, includes the following steps:

[0054] S1. Wafer clamping: A plurality of wafers 9 to be processed are vacuum-adsorbed on the disk 8 of the rotary bearing module, and the plurality of wafers 9 are arranged in a ring with the rotation center 81 of the disk 8 as the center, so that the wafers 9 can rotate around the rotation center 81 of the disk 8; Select a suitable hollow conical lens 5 and fix it on the lifting module 6. The position where the wafer 9 is placed can be determined according to the sizes of the wafer and the disk.

[0055] The cone angle of the hollow conical lens 5 should be selected considering the position where the wafer 9 is placed, which is related to the radius of curvature of the required arc-shaped line beam 13. When the position of the wafer 9 is relatively close to the rotation center 81, the radius of curvature of the required arc-shaped line beam 13 is smaller, and a hollow conical lens 5 with a small cone angle can be selected, such as a cone angle of 30° - 60°; when the position of the wafer 9 is far from the rotation center 81, the corresponding radius of curvature of the arc-shaped line beam 13 is larger, and a hollow conical lens 5 with a large cone angle can be selected, such as a cone angle of 90° - 120°.

[0056] S2. Parameter presetting: According to the material, size and surface polishing requirements of the wafer, referring to the mapping tables of various materials (such as silicon carbide, gallium nitride, etc.), sizes and polishing parameters stored in advance, initially set the laser power, the arc length of the arc-shaped line beam 13, the angle of the first mirror 4, the initial position of the lifting module 6 and the initial height of the hollow conical lens 5, so that the incident point of the line beam on the hollow conical lens 5 is ≥ 4 mm away from the edge of the hollow conical lens 5, the incident angle range is 10° - 30°, and the arc-shaped line beam 13 generated by the dynamic beam generation module falls on the outermost or innermost layer of the wafer 9 for processing.

[0057] According to Snell's law, a suitable incident angle on the hollow conical lens 5 can be selected. The size of the incident angle should, on the one hand, avoid total reflection of the beam, and on the other hand, control the spot distortion caused by refraction. The incident angle of the line beam on the hollow conical lens 5 can be adjusted by adjusting the angle of the first mirror 4.

[0058] The incident position of the line beam cannot be too close to the edge of the cone, including the upper edge of the port and the edge positions near the cone angle, to avoid edge diffraction and mechanical stress concentration. The incident position is related to the thickness of the hollow conical lens 5. The thickness of the hollow conical lens 5 is generally controlled within 2 mm. Therefore, the incident point is at least 4 mm away from the edge of the cone. After the incident angle is determined, the initial position of the incident point can be adjusted by the horizontal linear module 12 and the lifting module 6. After the initial position of the lifting module 6 is determined, the horizontal linear module 12 will no longer move. During the processing, only the height of the hollow conical lens 5 needs to be driven and changed by the lifting module 6, which can avoid the problem of affecting the energy density of the laser due to the change of the incident angle, thus affecting the processing quality and processing efficiency.

[0059] Specifically, the arc length of the arc-shaped line beam 13 output by the hollow conical lens 5 is 0.2 - 8 mm, the line width < 0.1 mm, the radian < π / 4, and the uniformity > 90%. The output power of the laser 1 is 300 - 500 W, and the rotation speed of the disk 8 is 100 - 200 rpm.

[0060] S3. Dynamic polishing: Start the rotating and bearing module to make the disk 8 rotate at a certain speed, so that the arc-shaped line beam 13 can successively perform thinning and polishing on all the wafers 9 on the disk 8 as the disk 8 rotates; at the same time, control the lifting module 6 to drive the hollow conical lens 5 to lift and lower at a certain speed program, so that the dynamic arc-shaped line beam 13 thins and polishes all the wafers 9 on the disk 8 from the outside to the inside or from the inside to the outside with the rotation center 81 of the disk 8 as the center.

[0061] When the cone angle θ of the hollow conical lens 5 is fixed, when the hollow conical lens 5 moves up and down, according to the curvature radius R of the arc-shaped line beam 13 ∝ h⋅cot(θ / 2), as Figure 6 , as the height h of the incident position of the line beam on the hollow conical lens 5 or the height h of the hollow conical lens 5 changes, the curvature radius R of the arc-shaped line beam 13 also changes accordingly. The higher the height, the larger the radius; the lower the height, the smaller the radius. Correspondingly, when the hollow conical lens 5 is at a high position, the arc-shaped line beam 13 falls at a position far from the rotation center 81 of the disk 8 to process the outer layer of the wafer 9. As the hollow conical lens 5 descends, the arc-shaped line beam 13 gradually moves towards the rotation center 81 of the disk 8 to process the wafer 9 from the outside to the inside.

[0062] The length of the linear-shaped line beam is determined by the parameters of the line beam shaping component 3, that is, determined by the beam expander 32 and the cylindrical lens. After the parameters of the line beam shaping component 3 are fixed, when the specifications, position, and height of the hollow conical lens 5 are fixed, the arc length L of the arc-shaped line beam 13 is also fixed. Therefore, after the hollow conical lens 5 is installed and fixed, the arc length L of the arc-shaped line beam 13 is determined by the height of the hollow conical lens 5, and its height change is realized by driving the lifting module 6. And the height position of the hollow conical lens 5 also determines the radius of the arc-shaped line beam 13. This is an interrelated relationship. From Figure 3 、 Figure 7 it can be seen that when the hollow conical lens 5 moves downward from high to low, the arc length L of the arc-shaped line beam 13 gradually becomes shorter, the curvature radius gradually becomes smaller, and it gradually moves towards the rotation center of the disk.

[0063] The diameter of the wafer determines the lifting range of the hollow conical lens 5. The minimum value R min and the maximum value R max of the arc-shaped line beam 13 are determined by the distances from the inner and outer edges of the wafer to the rotation center 81.

[0064] It is also necessary to control the overlap rate of adjacent scanning trajectories within 20% - 40% to avoid low surface roughness caused by the accumulation of remelting substances.

[0065] S4. Real-time regulation: During the thinning and polishing process, the surface data of the wafer 9 is obtained in real time through a white light interferometer, and the temperature distribution in the processing area of the wafer 9 is monitored in real time through an infrared thermal imager. The closed-loop control module dynamically adjusts the rotation speed of the disk 8, the driving speed of the lifting module 6, the laser power, and the arc length of the arc-shaped line beam 13 in real time according to the obtained real-time surface topography data and temperature distribution data of the wafer 9, so that the total thickness variation (TTV) of the wafer 9 is < 1 μm, and the depth of the heat-affected zone of the laser processing is < 5 μm.

[0066] S5. Post-processing: Megasonic cleaning (frequency 950 kHz) is used to remove the residual particles on the surface of the wafer 9, and then the surface roughness is finally inspected by an atomic force microscope (AFM).

[0067] Generally speaking, under normal circumstances, the angular velocity ω of the disk 8 remains constant, and the arc length L of the arc-shaped line beam 13 changes with the change of the radius of curvature. The closer it is to the rotation center 81, the shorter its arc length. However, the total energy Q of the arc-shaped line beam is certain. When the arc length L changes, its energy density E will change. The energy density E is inversely proportional to the arc length L. In order to maintain the uniformity of processing, it is necessary to adjust the duration of the arc-shaped line beam 13 at the corresponding arc length according to the arc length L of the arc-shaped line beam 13. The longer the arc length, the smaller the energy density, and the longer the required duration. The shorter the arc length, the greater the energy density, and the shorter the required duration.

[0068] As Figure 7 , from the formula L = 2R⋅α, the relationship between the arc length L, the radius of curvature R of the arc-shaped line beam 13, and the central angle α can be known. And the central angle α of the arc-shaped line beam 13 is related to the cone angle θ of the hollow conical lens 5 and the incident angle β of the line beam. When the cone angle θ of the hollow conical lens 5 and the incident angle β of the line beam are certain, the central angle α of the arc-shaped line beam 13 is also a fixed value. Therefore, the arc length L of the arc-shaped line beam 13 has a linear relationship with the radius of curvature R. And according to the radius of curvature R of the arc-shaped line beam 13 ∝ h⋅cot(θ / 2), it can be obtained that the arc length L of the arc-shaped line beam 13 ∝ h⋅cot(θ / 2). Thus, the movement mode of the arc-shaped line beam 13 or the hollow conical lens 5 can be controlled according to the trajectory of the arc-shaped line beam 13 or the height of the hollow conical lens 5.

[0069] The laser trajectory 14 formed by the arc-shaped line beam 13 can be designed as needed, and the laser trajectory 14 is controlled by regulating the rotation of the disk and the movement of the lifting module.

[0070] As one of the implementation manners, such as Figure 8, the laser track 14 is a set of concentric circles. Correspondingly, in step S3, the hollow conical lens 5 descends or ascends intermittently in a step-by-step manner. The generated arc-shaped line beam 13 persists at the corresponding position for a certain period of time to complete the processing at that radius of curvature and then steps to the next position, so that the arc-shaped line beam 13 scans from the outside to the inside or from the inside to the outside on the disk 8 to form a set of concentric circles centered on the rotation center 81 of the disk 8. The step amount between adjacent concentric circles can be the same or different, forming a concentric-circle-shaped laser track 14. If the hollow conical lens 5 descends intermittently in a step-by-step manner, concentric circles are formed in sequence from the outside to the inside. Conversely, if the hollow conical lens 5 ascends intermittently in a step-by-step manner, concentric circles are formed in sequence from the inside to the outside. The diameter of the concentric circles is related to the height position of the hollow conical lens 5, and the distance between adjacent concentric circles is closely related to the step amount when the hollow conical lens 5 descends or ascends. As Figure 9 , when there are multiple wafers 9 arranged on the disk 8 and the multiple wafers 9 are arranged in a ring centered on the rotation center 81 of the disk 8, the laser track 14 can cover all the wafers 9, thereby polishing the multiple wafers 9 simultaneously.

[0071] When the lifting module 6 drives the hollow conical lens 5 to descend or ascend intermittently in a step-by-step manner, the residence time T of the hollow conical lens 5 at different step heights can be controlled according to the following formula: T = k1·h; where h is the height of the hollow conical lens 5, and k1 is a constant that is only related to the cone angle θ of the hollow conical lens 5 and the incident angle β of the line beam. When the cone angle θ of the hollow conical lens 5 and the incident angle β of the line beam are fixed, k1 is a fixed value. The movement program of the hollow conical lens 5 can be controlled by this formula, thereby controlling the residence time of the arc-shaped line beam at each radius of curvature R, and sequentially balancing the energy density of the arc-shaped line beam to ensure the uniformity of wafer processing. The distance between adjacent concentric circles or the step amount of the hollow conical lens 5 can be determined by the surface condition of the wafer to be processed and the processing accuracy requirements.

[0072] As another implementation, such as Figure 10 , the laser track 14 is a spiral. Correspondingly, in step S3, the hollow conical lens 5 descends or ascends continuously at a certain speed program, so that the arc-shaped line beam 13 scans on the disk 8 to form a spiral track from the outside to the inside or from the inside to the outside centered on the rotation center 81 of the disk 8. That is, the disk 8 drives the wafer 9 to rotate at a constant angular velocity ω, and synchronously controls the lifting module 6 (such as an electric slide rail) to feed at a speed v towards the top or end of the cone, forming a spiral laser track 14. If the hollow conical lens 5 descends at a constant speed, a spiral track from the outside to the inside is formed. Conversely, if the hollow conical lens 5 ascends at a constant speed, a spiral track from the inside to the outside is formed. Similarly, as Figure 11, when multiple wafers 9 are arranged on the disk 8 and the multiple wafers 9 are arranged in a ring centered on the rotation center 81 of the disk 8, the spiral laser track 14 can cover all the wafers 9, so as to polish the multiple wafers 9 simultaneously.

[0073] When the lifting module 6 drives the hollow conical lens 5 to lift continuously, the lifting speed v of the hollow conical lens 5 is closely related to the shape of the spiral track (including the radius of the spiral and the spacing between two adjacent spirals). The lifting speed v of the hollow conical lens 5 can be controlled according to the following formula: V = k2·h -1 / 2 , where h is the height of the hollow conical lens 5, and k2 is a constant, which is only related to the cone angle θ of the hollow conical lens 5 and the incident angle β of the line beam. When the cone angle θ of the hollow conical lens 5 and the incident angle β of the line beam are fixed, k2 is a fixed value. By controlling the lifting speed of the hollow conical lens 5 to balance the energy density of the arc-shaped line beam, when the hollow conical lens 5 moves from top to bottom, the speed gradually increases, so that the residence time of the arc-shaped line beam on the wafer gradually becomes shorter, thus ensuring the uniformity of wafer processing.

[0074] In step S4, the dynamic adjustment method of the rotating and carrying module is as follows:

[0075] a. When it is detected that the material removal rate on the surface of the wafer 9 is less than the set value M, the arc length of the arc-shaped line beam 13 is increased by 10% - 15% by adjusting the parameters of the line beam shaping component 3, and the rotation speed of the disk 8 is increased by 5% - 10%; the material removal rate can be determined by the height difference before and after processing.

[0076] b. When it is detected that the material removal rate on the surface of the wafer 9 is greater than the set value N, it is automatically switched to the safe polishing mode;

[0077] c. When it is detected that the local temperature exceeds the set threshold P (such as 150 °C), if the current laser is in the continuous laser mode, it is switched to the pulsed laser mode, the duty cycle is set to 30% - 50%, and the cooling air curtain is triggered to work; if the current laser is in the pulsed laser mode, it is automatically switched to the safe polishing mode;

[0078] The safe polishing mode is: the laser power is reduced to 50% - 70% of the current value, and at the same time, the ultrasonic-assisted polishing mechanism is triggered for local trimming.

[0079] Taking a 6-inch silicon carbide wafer 9 as an example:

[0080] Initial state: thickness 675 μm, TTV = 8 μm, Ra = 1.2 nm;

[0081] Polishing parameters: laser power 400 W, rotation speed 150 rpm, slide rail speed 2 mm / s;

[0082] Processing result:

[0083] The thickness is reduced to 100 μm, TTV = 0.8 μm, Bow = 2.5 μm;

[0084] Ra = 0.38 nm, and there is no thermally damaged layer on the surface;

[0085] The overall yield reaches 96.5% (82% for the traditional process).

[0086] Generally speaking, the technical effects of the present invention are as follows:

[0087] Efficiency breakthrough: The material removal rate reaches 8 mm² / s, which is 300 times higher than that of the traditional point beam, and the processing cycle of a single wafer is shortened to 42 minutes.

[0088] Precision improvement:

[0089] Surface profile accuracy: TTV < 1 μm, Bow < 3 μm;

[0090] Surface quality: Ra < 0.5 nm, without microcracks;

[0091] Damage control: The depth of the heat-affected zone < 5 μm, and the lattice distortion rate is reduced to less than 0.05%;

[0092] Industrial adaptation: It supports the mixed-line production of 8 - 12-inch wafers, the process switching time < 10 minutes, and the equipment utilization rate > 95%.

[0093] The above detailed description is a specific description of the feasible embodiments of the present invention. These embodiments are not intended to limit the patent scope of the present invention. Any equivalent implementation or modification without departing from the present invention should be included in the patent scope of this case.

Claims

1. A large-sized wafer thinning and polishing device based on a dynamic line beam, characterized in that, It includes a dynamic beam generation module, a rotating carrier module and a closed-loop control module. The dynamic beam generation module includes a laser, a polarizer, a linear beam shaping component, a reflector, a hollow conical lens and a lifting module. The laser is used to generate a Gaussian laser beam. The linear beam shaping component is used to shape the laser beam into a linear beam. The polarizer is arranged between the laser and the linear beam shaping component. The hollow conical lens is a conical lens with a hollow interior and an open end face, and its wall thickness is uniform. It is used to shape the linear beam into an arc-shaped beam. The hollow conical lens is installed on the lifting module with its end face opening upward and the conical angle downward, and moves up and down under the drive of the lifting module to generate a dynamic arc-shaped beam. The reflector is arranged between the linear beam shaping component and the hollow conical lens. After the laser beam generated by the laser passes through the polarizer and reaches the linear beam shaping component, it is shaped into a linear beam, and then after being reflected by the reflector, it enters the inner conical surface of the hollow conical lens and exits from the outer conical surface of the hollow conical lens to form an arc-shaped beam for thinning and polishing the wafer. The arc-shaped beam adjusts its position and shape along with the lifting module; The rotating carrier module is used to fix and drive the wafer to rotate. The closed-loop control module is respectively connected to the lifting module and the rotating carrier module to control the lifting of the lifting module and the movement of the rotating carrier module; It further includes a detection module. The detection module includes a white light interferometer and an infrared thermal imager arranged above the rotating carrier module. The white light interferometer is used to detect the processing surface of the wafer, and the infrared thermal imager is used to detect the temperature during the laser thinning and polishing process of the wafer. The white light interferometer and the infrared thermal imager are respectively connected to the closed-loop control module to transmit detection data, and the closed-loop control module controls the movement of the lifting module and the rotating carrier module according to the real-time detection data.

2. The large-sized wafer thinning and polishing device based on a dynamic line light beam according to claim 1, characterized in that, The linear beam shaping component includes a beam expander and a linear beam shaping mirror. The linear beam shaping mirror is a cylindrical lens, a flat cylindrical lens, a Powell prism, a cylindrical lens array or a flat cylindrical lens array. The beam expander is used to expand the laser beam. After the laser beam is expanded by the beam expander, it is shaped into a linear beam by the linear beam shaping mirror; A linear beam focusing mirror is further arranged between the hollow conical lens and the wafer. The arc-shaped beam is focused by the linear beam focusing mirror and then reaches the wafer surface to process the wafer; The lifting module is installed on a horizontal linear module, and the horizontal linear module is used to drive the lifting module and the hollow conical lens thereon to move in the horizontal direction.

3. A large-sized wafer thinning and polishing device based on a dynamic line beam according to claim 1, characterized in that, The conical angle of the hollow conical lens is 30° - 120°. The hollow conical lens is made of BK7 optical glass or fused quartz, and the wall thickness of the hollow conical lens is 1.5 - 2.0 mm; The rotating carrier module includes a disk, a vacuum adsorption device, an air bearing and a rotation driving component. The vacuum adsorption device is arranged on the disk and is used to fix the wafer on the disk by vacuum adsorption. The diameter of the disk is ≥ 200 mm, and the rotation driving component drives the disk to rotate through the air bearing.

4. A large-size wafer thinning and polishing method based on a dynamic line beam, which uses the large-size wafer thinning and polishing device based on the dynamic line beam according to any one of claims 1 to 3, and is characterized in that, It includes the following steps: S1. Vacuum adsorb multiple wafers to be processed on the disk of the rotary carrier module, and arrange the multiple wafers in a circular pattern with the rotation center of the disk as the center, so that the wafers can rotate around the rotation center of the disk; select a suitable hollow conical lens and fix it on the lifting module; S2. According to the material, size and surface polishing requirements of the wafer, referring to the pre-stored mapping tables of various materials, sizes and polishing parameters, preliminarily set the laser power, the arc length of the arc-shaped line beam, the angle of the mirror, the initial position of the lifting module and the initial height of the hollow conical lens, so that the incident point of the line beam on the hollow conical lens is ≥4 mm away from the edge of the hollow conical lens, the incident angle range is 10°-30°, and the arc-shaped line beam generated by the dynamic beam generation module falls on the outermost layer or the innermost layer of the wafer processing; S3. Start the rotary carrier module to rotate the disk at a certain speed, so that the arc-shaped line beam can sequentially perform thinning and polishing processing on all the wafers on the disk as the disk rotates; at the same time, control the lifting module to drive the hollow conical lens to lift and lower at a certain speed program, so that the dynamic arc-shaped line beam performs thinning and polishing processing on all the wafers on the disk from the outside to the inside or from the inside to the outside with the rotation center of the disk as the center; S4. During the thinning and polishing process, the surface data of the wafer is obtained in real time through a white light interferometer, and the temperature distribution in the wafer processing area is monitored in real time through an infrared thermal imager. The closed-loop control module adjusts the rotation speed of the disk, the driving speed of the lifting module, the laser power and the arc length of the arc-shaped line beam in real time according to the obtained surface data and temperature distribution data of the wafer, so that the total thickness variation TTV of the wafer <1μm, and the depth of the heat affected zone of the laser processing <5μm; In step S4, the dynamic adjustment method of the rotation speed of the disk, the driving speed of the lifting module, the laser power and the arc length of the arc-shaped line beam is as follows: a. When it is detected that the material removal rate on the wafer surface is less than the set value M, increase the arc length of the arc-shaped line beam by 10%-15% by adjusting the parameters of the line beam shaping component, and increase the disk rotation speed by 5%-10%; b. When it is detected that the material removal rate on the wafer surface is greater than the set value N, automatically switch to the safe polishing mode; c. When it is detected that the local temperature exceeds the set threshold P, if the current laser is in the continuous laser mode, then switch to the pulsed laser mode, set the duty cycle to 30%-50%, and trigger the cooling air curtain to work; if the current laser is in the pulsed laser mode, then automatically switch to the safe polishing mode; The safe polishing mode is: reduce the laser power to 50%-70% of the current value, and at the same time trigger the ultrasonic-assisted polishing mechanism to perform local trimming.

5. A large-size wafer thinning and polishing method based on a dynamic line beam according to claim 4, characterized in that, It also includes a post-processing step, and the method is: use megasonic cleaning to remove the residual particles on the wafer surface, and then perform a final inspection of the surface roughness through an atomic force microscope AFM.

6. A large-size wafer thinning and polishing method based on a dynamic line beam according to claim 4, characterized in that In step S3, the hollow conical lens descends or ascends intermittently in a stepwise manner, so that the arc-shaped line beam scans from the outside to the inside or from the inside to the outside on the disk to form a plurality of concentric circles with the rotation center of the disk as the center. The step amount between adjacent two concentric circles is equal or unequal, and the concentric circle trajectory covers all the wafers; Control the residence time T of the hollow conical lens at different step heights according to the following formula: T = k1·h; where h is the height of the hollow conical lens, and k1 is a constant, which is only related to the cone angle θ of the hollow conical lens and the incident angle β of the line beam on the hollow conical lens.

7. A large-size wafer thinning and polishing method based on a dynamic line beam according to claim 4, characterized in that In step S3, the hollow conical lens descends or ascends continuously at a certain speed program, so that the arc-shaped line beam scans on the disk to form a spiral trajectory from the outside to the inside or from the inside to the outside with the rotation center of the disk as the center, and the spiral trajectory covers all wafers; Control the lifting speed v of the hollow conical lens according to the following formula: V = k2·h -1 / 2 , where h is the height of the hollow conical lens, and k2 is a constant that is only related to the cone angle θ of the hollow conical lens and the incident angle β of the line beam on the hollow conical lens.

8. A large-sized wafer thinning and polishing method based on a dynamic line light beam according to claim 4, characterized in that The arc length of the arc-shaped line beam output by the hollow conical lens is 0.2 - 8 mm, the line width < 0.1 mm, the radian < π / 4, and the uniformity > 90%; the output power of the laser is 300 - 500 W, and the rotation speed of the disk is 100 - 200 rpm.

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