Large-size wafer thinning and polishing device and method based on dynamic line beams

Abstract

The invention discloses a large-size wafer thinning and polishing device and method based on a dynamic line beam, and the device comprises a dynamic beam generation module, a rotary bearing module and a closed-loop control module, and the dynamic beam generation module comprises a laser, a polaroid, a line beam shaping assembly, a reflector, a hollow conical lens and a lifting module. The linear beam shaping assembly is used for shaping a laser beam into a line-shaped linear beam, the hollow conical lens is a hollow conical lens with an open end face and is used for shaping the line-shaped linear beam into an arc-shaped linear beam, and the hollow conical lens is installed on the lifting module to generate a dynamic arc-shaped linear beam; the rotary bearing module is used for fixing and driving a wafer to rotate; and the closed-loop control module is used for controlling the lifting of the lifting module and the movement of the rotary bearing module. The polishing speed can be greatly increased, the polishing uniformity and the polishing quality are also improved, a plurality of wafers can be thinned and polished at the same time, and the polishing device can adapt to wafers of different sizes and shapes.

Description

Technical Field

[0001] The present invention relates to the field of laser processing technology, and in particular 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 new energy vehicles, rail transit, consumer electronics and other industries, the market has higher and higher performance and demand 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. 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, high-stability and non-destructive surface processing of large-size wafers can be achieved by using ultra-fine-grained diamond wheels and high-stability ultra-precision thinning equipment. Chemical mechanical polishing (CMP) technology uses a combination of chemical corrosion and mechanical friction to achieve global flatness of the wafer surface, which is crucial for the front-end process of advanced integrated circuit manufacturing and advanced packaging. However, the existing CMP technology still has the following problems: low process efficiency (<0.5 mm² / s), processing stress causes wafer warping (Bow>10μm), and chemical waste liquid pollution. Traditional laser polishing has problems such as low material removal rate in point beam scanning mode (<0.1 mm² / s), heat-affected zone depth>50μm, and surface roughness Ra>1nm. Especially when large-area wafers need to be polished, traditional methods are difficult to meet the needs of industrial production. The power density of the line beam is relatively low. Using a line beam to polish the wafer surface can overcome the shortcomings of the traditional Gaussian distribution point spot that has a thermal impact on the material due to energy concentration. However, the existing line beam polishing technology lacks dynamic matching, resulting in low edge removal rate of the wafer, poor surface consistency, and low processing efficiency. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the above-mentioned 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 the device, so as to achieve coordinated optimization of wafer thinning and polishing efficiency and quality.

[0005] The present invention is achieved through the following technical solutions: A large-size wafer thinning and polishing device based on a dynamic line beam comprises a dynamic beam generating module, a rotating bearing module and a closed-loop control module, wherein the dynamic beam generating module comprises a laser, a polarizing plate, a line beam shaping component, a reflector, a hollow conical lens and a lifting module, wherein the laser is used to generate a Gaussian laser beam, the line beam shaping component is used to shape the laser beam into a straight line beam, the polarizing plate is arranged between the laser and the line beam shaping component, the hollow conical lens is a hollow conical lens with an open end face, and the wall thickness is uniform, and is used to shape the straight line beam into an arc Line beam, the hollow conical lens is installed on the lifting module with its end face opening facing upward and its cone angle facing downward, and moves up and down under the drive of the lifting module to generate a dynamic arc line beam, the reflector is arranged between the line beam shaping component and the hollow conical lens, the laser beam generated by the laser reaches the line beam shaping component through the polarizer, is shaped into a straight line beam, and then is reflected by the reflector, enters the inner cone surface of the hollow conical lens, and is emitted from the outer cone surface of the hollow conical lens to form an arc line beam, which is used for thinning and polishing the wafer, and the arc line beam adjusts its position and shape with the lifting module.

[0006] The rotating bearing module is used to fix and drive the wafer to rotate, and the closed-loop control module is respectively connected to the lifting module and the rotating bearing module to control the lifting of the lifting module and the movement of the rotating bearing module.

[0007] Furthermore, it also includes a detection module, which includes a white light interferometer and an infrared thermal imager arranged above the rotating carrying 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 of the wafer during laser thinning and polishing. 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 rotating carrying module according to the real-time detection data.

[0008] Furthermore, the line beam shaping assembly 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 to expand the laser beam, and the laser beam is expanded by the beam expander and then shaped into a line beam by the line beam shaping mirror; A line beam focusing mirror is also arranged between the hollow conical lens and the wafer, and the arc line beam is focused by the line beam focusing mirror and reaches the surface of the wafer to process the wafer; 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 cooperate with the effective incident light beam of the reflector and adjust the incident angle as the angle of the reflector is adjusted.

[0009] Furthermore, the cone 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 quartz (n=1.458, high ultraviolet transmittance), and the wall thickness is 1.5-2.0 mm; The rotating supporting module includes a disc, a vacuum adsorption device, an air bearing and a rotating 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 ≥200mm. The rotating driving component drives the disc to rotate through the air bearing.

[0010] A large-size wafer thinning and polishing method based on a dynamic line beam, using the large-size wafer thinning and polishing device based on a dynamic line beam, comprises the following steps: S1. Vacuum adsorb multiple wafers to be processed on a disc on a rotating carrying module, and arrange the multiple wafers 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; S2. According to the material, size and surface polishing requirements of the wafer, refer to the pre-stored mapping table of materials (silicon carbide, gallium nitride, etc.), sizes and polishing parameters, preliminarily set the laser power, arc length of the arc line beam, angle of the reflector, initial position of the lifting module and 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 line beam generated by the dynamic beam generation module falls on the outermost or innermost processing layer of the wafer; S3, start the rotating bearing module to rotate the disk at a certain speed, so that the arc line light beam can perform thinning and polishing processing on all the wafers on the disk in sequence as the disk rotates; at the same time, control the lifting module to drive the hollow conical lens to rise and fall at a certain speed program, so that the dynamic arc line light beam takes the rotation center of the disk as the center to perform thinning and polishing processing on all the wafers on the disk from the outside to the inside or from the inside to the outside; 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 of the wafer processing area is monitored in real time through a thermal imager. The closed-loop control module dynamically adjusts the rotation speed of the disc, the driving speed of the lifting module, the laser power and the arc length of the arc line beam in real time according to the acquired surface data and temperature distribution data of the wafer, so that the total thickness deviation TTV of the wafer is less than 1μm and the depth of the heat affected zone of laser processing is less than 5μm.

[0011] Furthermore, a post-processing step is also included, and the method is: using megasonic cleaning (frequency 950kHz) to remove residual particles on the surface of the wafer, and then using atomic force microscopy AFM to finally inspect the surface roughness.

[0012] Furthermore, in step S3, the hollow conical lens is continuously lowered or raised at a certain speed program, so that the arc line beam scans on the disk to form a spiral track 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 track covers all wafers. If the hollow conical lens is lowered at a constant speed, a spiral track is formed from the outside to the inside, and vice versa, if the hollow conical lens is raised at a constant speed, a spiral track is formed from the outside to the inside.

[0013] 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 distance between two 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 light beam on the hollow conical lens.

[0014] Furthermore, in step S3, the hollow conical lens intermittently steps down or up, 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 multiple concentric circles with the rotation center of the disk as the center, and the stepping amount between two adjacent concentric circles is equal or unequal, and the concentric circle trajectory covers all wafers; if the hollow conical lens intermittently steps down, concentric circles are formed from the outside to the inside in sequence, and vice versa, if the hollow conical lens intermittently steps up, concentric circles are formed from the inside to the outside in sequence. The diameter of the concentric circle is related to the position of the hollow conical lens, and the distance between two adjacent concentric circles is related to the stepping amount when the hollow conical lens is lowered or raised.

[0015] The residence time T of the hollow conical lens at different step heights is controlled according to the following formula: T=k1·h; wherein 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 light beam on the hollow conical lens.

[0016] Furthermore, the arc length of the arc-shaped line light beam output by the hollow conical lens is 0.2-8 mm, the line width is less than 0.1 mm, the arc is less than π / 4, and the uniformity is greater than 90%; the output power of the laser is 300-500 W, and the rotation speed of the disk is 100-200 rpm.

[0017] Furthermore, in step S4, the dynamic adjustment method of the rotating bearing module is: a. When it is detected that the material removal rate of the wafer surface is less than the set value M, the arc length of the arc 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%; b. When it is detected that the material removal rate on the wafer surface is greater than the set value N, it automatically switches to the safe polishing mode; c. When it is detected that the local temperature exceeds the set threshold value P (such as 150°C), if the current laser is in continuous laser mode, it will switch to pulse laser mode, set the duty cycle to 30%-50%, and trigger the cooling air curtain; if the current laser is in pulse laser mode, it will automatically switch to safe polishing mode; the safe polishing mode is: reduce the laser power to 50%-70% of the current value, and trigger the ultrasonic assisted polishing mechanism for local finishing.

[0018] The present invention arranges a line beam shaping component to first shape the laser beam into a straight line beam, and then shapes the straight line beam into an arc line beam through a hollow conical lens, and arranges the hollow conical lens on the lifting module. When the hollow conical lens is lifted, a dynamic arc line beam is generated, and the wafers are laser processed in coordination 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, and the uniform energy distribution of the line beam improves the uniformity of polishing, reduces the thermal impact on the wafer, and improves the polishing quality. The ingenious combination design of the hollow conical lens and the lifting module can generate a dynamic arc line beam. Compared with the conventional mode of generating a dynamic beam or moving the beam by changing the angle of the light, the position of the output line beam is kept constant during the processing because the incident angle remains unchanged. It can be accurately predicted that the energy density of the laser beam can always remain stable and will not change due to changes in angles. Therefore, the processing process is controllable and the processing quality can be guaranteed. The movement of the dynamic arc line beam can match the rotation of the wafer on the disc. As the disc rotates, multiple wafers can be thinned and polished at the same time, further improving the processing efficiency. Through the placement of the wafer on the disc, the rotation speed of the wafer, 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-size wafers can be achieved. At the same time, with the real-time monitoring of the white light interferometer and the infrared thermal imager, the shape, energy and operation mode of the line beam can be dynamically adjusted to further improve the polishing efficiency and ensure the polishing quality. It can adapt to wafers of different sizes and shapes, especially large-size wafers. Practice has proved that the material removal rate of the present invention reaches 8mm² / s, which is 300 times higher than that of the traditional spot beam, and the single wafer processing cycle is shortened to 42min; in terms of precision, the TTV of the processed wafer is less than 1μm, Bow is less than 3μm, the surface Ra is less than 0.5nm, there are no microcracks on the surface, the depth of the heat-affected zone is less than 5μm, and the lattice distortion rate is reduced to less than 0.05%; it can support 8-12 inch wafer mixed line production, the process switching time is less than 10min, and the equipment utilization rate is greater than 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1It is a schematic diagram of the framework structure of the thinning and polishing device according to an embodiment of the present invention.

[0020] Figure 2 It is a schematic diagram of the three-dimensional structure of the hollow conical lens in the thinning and polishing device according to an embodiment of the present invention.

[0021] Figure 3 The schematic diagram of the generation principle of the dynamic arc line beam in the thinning and polishing device according to the embodiment of the present invention is shown in FIG. Figure 3 (a) 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 3 (b) is a schematic diagram of the arc-shaped line beam falling on the disk when the hollow conical lens is in a low position.

[0022] Figure 4 The figure is a flow chart of the working principle of the thinning and polishing device according to an embodiment of the present invention.

[0023] Figure 5 4 is a control framework diagram of an embodiment of the present invention.

[0024] Figure 6 Schematic diagram of the cone angle, height position of the incident light, and incident angle of the hollow conical lens in an embodiment of the present invention.

[0025] Figure 7 Schematic diagram of an arc line light beam falling on a disk in an embodiment of the present invention.

[0026] Figure 8 The figure is a schematic diagram of a laser trajectory formed on a circular disk by an arc-shaped line light beam as the circular disk rotates in an embodiment of the present invention.

[0027] Fig. 9 The figure is a schematic diagram of a trajectory of processing multiple wafers on a disk by an arc line light beam as the disk rotates in an embodiment of the present invention.

[0028] Fig.10 Schematic diagram of another laser trajectory formed by an arc-shaped line light beam on a disk as the disk rotates in an embodiment of the present invention.

[0029] Fig.11 It is another schematic diagram of the trajectory of processing multiple wafers on a disk by an arc line light beam as the disk rotates in an embodiment of the present invention.

[0030] Figure numerals: 1-laser; 2-polarizer; 3-line beam shaping assembly; 4-first reflector; 5-hollow conical lens; 6-lifting module; 7-line beam focusing mirror; 8-disc; 9-wafer; 10-second reflector; 11-third reflector; 12-horizontal linear module; 13-arc-shaped line beam; 14-laser trajectory; 31-line beam shaping mirror; 32-beam expander; 81-rotation center. DETAILED DESCRIPTION

[0031] A large-size wafer thinning and polishing device based on dynamic line beam, such as Figure 1 As shown, it includes a dynamic beam generating module, a rotating bearing module, a closed-loop control module and a detection module.

[0032] like Figure 1 The dynamic beam generation module includes a laser 1, a polarizer 2, a second reflector 10, a third reflector 11, a line beam shaping component 3, a first reflector 4, a hollow conical lens 5, a lifting module 6 and a line beam focusing mirror 7. The laser 1 is used to generate a Gaussian laser beam. The line beam shaping component 3 is used to shape the laser beam into a straight line beam. The polarizer 2, the second reflector 10, the third reflector 11 and the line beam shaping component 3 are arranged in sequence. The polarizer 2 can ensure the polarization state of the laser output. The second reflector 10 and the third reflector 11 are parallel to each other, which changes the optical path of the laser beam, which is beneficial to the spatial layout of the equipment, such as Figure 2 As shown, the hollow conical lens 5 is a conical lens with a hollow interior and an open end face, and has a uniform wall thickness, and is used to shape a straight line beam into an arc line beam 13. The hollow conical lens 5 is installed on the lifting module 6 with the end face opening facing upward and the cone angle facing downward, and moves up and down under the drive of the lifting module 6, as shown in FIG. Figure 5 , to generate a dynamic arc line beam 13, the first reflector 4 is arranged between the line beam shaping component 3 and the hollow conical lens 5, the laser beam generated by the laser 1 reaches the line beam shaping component 3 through the polarizer 2, is shaped into a straight line beam, and then reflects through the first reflector 4, enters the inner conical surface of the hollow conical lens 5, and is emitted through the outer conical surface of the hollow conical lens 5 to form an arc line beam 13, the arc line beam 13 adjusts its position and shape with the lifting module 6. The line beam focusing mirror 7 is arranged at the rear end of the hollow conical lens 5, and the arc line beam 13 reaches the surface of the wafer 9 after being focused by the line beam focusing mirror 7 to perform thinning and polishing on the wafer 9. The line beam focusing mirror 7 is an aspherical mirror or a cylindrical mirror.

[0033] The lifting module 6 can be an existing linear module, such as an electric slide rail, a pneumatic drive component, etc., preferably an electric slide rail, and its displacement accuracy is ≤±0.1μm.

[0034] The formation principle of dynamic arc line beam can be as follows Figure 3 As 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, the incident angle remains unchanged, and thus the angle of the outgoing light does not change. However, due to the change of the incident point, the position of the outgoing light will also change, thereby forming a dynamic arc line beam. Figure 3 As shown, when the hollow conical lens 5 is Figure 3 The position in (a) drops to Figure 3After the position in (b) is reached, the incident point of the laser changes accordingly, and the line 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.

[0035] The rotating support module is used to fix and drive the wafer 9 to rotate. Figure 5 The closed-loop control module is respectively connected to the lifting module 6 and the rotating bearing module to control the lifting of the lifting module 6 and the movement of the rotating bearing module.

[0036] like Figure 4 As shown, the working principle of the thinning and polishing device of the present invention is as follows: the laser generates a Gaussian beam, which enters the line beam shaping component through the reflection of the reflector to form a line beam, and the uniform line beam enters the specific position of the hollow conical lens through the reflector to form an arc line beam of a specific arc length. The hollow conical lens can be lifted and reciprocated during operation, and 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 line beam is generated as the hollow conical lens is lifted and lowered; when the wafer rotates on the disc around the rotation center of the disc, the dynamic arc line beam is fed along the rotation radius, and the movement of the hollow conical lens corresponds to the feeding of the arc beam. The specific direction is that when the hollow conical lens descends, the arc line beam is fed in the direction of the rotation center. The present invention mainly uses an arc line beam for polishing. Due to the energy dispersion and balancing effect of the line beam, a higher power laser can be used. Also, because the range of the curvature radius of the arc line beam should not be too large, the present invention is suitable for the processing of large-sized wafers.

[0037] The detection module includes a white light interferometer and an infrared thermal imager arranged above the rotating bearing module. The white light interferometer is used to detect the processing surface of the wafer 9, and the infrared thermal imager is used to detect the temperature of the wafer 9 during the laser thinning and polishing process. Figure 5 The white light interferometer and the infrared thermal imager are respectively connected to the closed-loop control module to transmit the detection data. The closed-loop control module adjusts the movement of the lifting module 6 and the rotating bearing module according to the real-time detection data. The white light interferometer monitors the wafer 9 surface shape in real time with a resolution of 0.1nm and controls TTV≤1μm. The thermal imager detects the temperature of the polishing area with an accuracy of ±1℃.

[0038] The function of the line beam shaping component 3 is to convert a 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 to expand 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 a collimated point laser beam into a straight line beam with a line width of less than 0.1 mm and a uniformity of more than 90%.

[0039] As one of the implementation modes, the lifting module 6 is installed on a 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 cooperate with the first reflector 4 to effectively incident the line beam, and adjust the incident angle to adapt to the processing of wafers 9 with different materials, sizes and surface morphologies. The horizontal linear module 12 can adopt a combination of a conventional X-axis linear moving module and a Y-axis linear moving module. In this embodiment, in order to further realize automation, the first reflector 4 is connected to a swing module for controlling the angle of the first reflector 4, thereby adjusting the incident angle of the line beam, such as Figure 5 The closed-loop control module is also connected to the horizontal linear module 12 and the swing module respectively to control the angle of the first reflector 4 and the horizontal position of the hollow conical lens 5.

[0040] As one implementation manner, the cone angle of the hollow conical lens 5 is 30°-120°, preferably 15°-45°, and 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.

[0041] As one of the embodiments, the rotating bearing module includes a disc 8, a vacuum adsorption device, an air bearing and a rotating drive component. The vacuum adsorption device is arranged on the disc 8 and is used to fix the wafer 9 on the disc 8 by vacuum adsorption. The diameter of the disc 8 is ≥200mm, and the rotating drive component drives the disc 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 <1μm, thereby improving the processing accuracy. The vacuum adsorption pressure can be controlled at 0.1-0.5MPa, and can support the rapid clamping of 45-200mm wafers 9 (taking time <30 seconds). The electrostatic clamping mode can also be set at the same time to achieve switching with the vacuum adsorption dual mode.

[0042] A large-size wafer thinning and polishing method based on a dynamic line beam, using the large-size wafer thinning and polishing device based on a dynamic line beam, comprises the following steps: S1. Wafer clamping: vacuum adsorb multiple wafers 9 to be processed on the disc 8 on the rotating carrying module, and arrange the multiple wafers 9 in a ring with the rotation center 81 of the disc 8 as the center, so that the wafers 9 can rotate around the rotation center 81 of the disc 8; select a suitable hollow conical lens 5 and fix it on the lifting module 6. The position of the wafer 9 can be determined according to the size of the wafer and the disc.

[0043] The selection of the cone angle of the hollow conical lens 5 should take into account the position of the wafer 9, which is related to the required radius of curvature of the arc line beam 13. When the position of the wafer 9 is relatively close to the rotation center 81, the required radius of curvature of the arc line beam 13 is relatively small, 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 line beam 13 is relatively large, and a hollow conical lens 5 with a large cone angle can be selected, such as a cone angle of 90°-120°.

[0044] S2. Parameter preset: According to the material, size and surface polishing requirements of the wafer, refer to the pre-stored material (silicon carbide, gallium nitride, etc.), size and polishing parameter mapping table, preliminarily set the laser power, the arc length of the arc line beam 13, the angle of the first reflector 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 line beam 13 generated by the dynamic beam generation module falls on the outermost or innermost processing layer of the wafer 9.

[0045] 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 avoid total reflection of the light beam on the one hand, and control the distortion of the refracted light spot on the other hand. The incident angle of the line light beam on the hollow conical lens 5 can be adjusted by adjusting the angle of the first reflector 4.

[0046] 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 position close to 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. When 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. When the initial position of the lifting module 6 is determined, the horizontal linear module 12 will not move again. During the processing, it is only necessary to drive the height of the hollow conical lens 5 to change through the lifting module 6. This can avoid the problem of affecting the energy density of the laser due to the change of the incident angle, thereby affecting the processing quality and processing efficiency.

[0047] Specifically, the arc length of the arc line beam 13 output by the hollow conical lens 5 is 0.2-8 mm, the line width is less than 0.1 mm, the arc is less than π / 4, and the uniformity is greater than 90%. The output power of the laser 1 is 300-500 W, and the rotation speed of the disk 8 is 100-200 rpm.

[0048] S3, dynamic polishing: start the rotating supporting module to rotate the disk 8 at a certain speed, so that the arc line light beam 13 can thin and polish all the wafers 9 on the disk 8 in turn as the disk 8 rotates; at the same time, control the lifting module 6 to drive the hollow conical lens 5 to rise and fall at a certain speed program, so that the dynamic arc line light beam 13 takes the rotation center 81 of the disk 8 as the center to perform thinning and polishing on all the wafers 9 on the disk 8 from the outside to the inside or from the inside to the outside.

[0049] When the cone angle θ of the hollow conical lens 5 is constant and the hollow conical lens 5 moves up and down, according to the curvature radius R∝h⋅cot(θ / 2) of the arc line beam 13, as Figure 6 As the height h of the incident position of the line light 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 line light beam 13 also changes accordingly. The higher the height, the larger the radius, and the lower the height, the smaller the radius. Correspondingly, when the hollow conical lens 5 is located at a high place, the arc line light beam 13 falls at a position far away from the rotation center 81 of the disk 8, and the outer layer of the wafer 9 is processed. As the hollow conical lens 5 descends, the arc line light beam 13 gradually moves toward the rotation center 81 of the disk 8, and the wafer 9 is processed from the outside to the inside.

[0050] The length of the straight line beam is determined by the parameters of the line beam shaping component 3, that is, by the beam expander 32 and the cylindrical lens. After the parameters of the line beam shaping component 3 are fixed, when the specification, position and height of the hollow conical lens 5 are fixed, the arc length L of the arc line beam 13 is also fixed. Therefore, after the hollow conical lens 5 is installed and fixed, the arc length L of the arc line beam 13 is determined by the height of the hollow conical lens 5, and the height change is driven by the lifting module 6. The height position of the hollow conical lens 5 also determines the radius of the arc line beam 13. This is a continuation of the relationship. 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 light beam 13 gradually becomes shorter, the curvature radius gradually becomes smaller, and gradually moves toward the rotation center of the disk.

[0051] The diameter of the wafer determines the lifting range of the hollow conical lens 5, and the minimum value R of the arc line beam 13 min and the maximum value R max It is determined by the distance from the inner and outer edges of the wafer to the rotation center 81.

[0052] It is also necessary to control the overlap rate of adjacent scanning tracks to 20%-40% to avoid low surface roughness due to accumulation of remelted materials.

[0053] S4. Real-time control: 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 of the processing area of ​​the wafer 9 is monitored in real time through a 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 line beam 13 in real time according to the real-time surface morphology data and temperature distribution data of the wafer 9, so that the total thickness deviation TTV of the wafer 9 is less than 1μm, and the depth of the heat affected zone of the laser processing is less than 5μm.

[0054] S5, post-processing: Use megasonic cleaning (frequency 950kHz) to remove residual particles on the surface of wafer 9, and then use atomic force microscopy AFM to finally inspect the surface roughness.

[0055] Generally speaking, under normal circumstances, the rotational angular velocity ω of the disk 8 remains constant, and the arc length L of the arc line light beam 13 changes with the change of the curvature radius. The closer to the rotation center 81, the shorter the arc length. However, the total energy Q of the arc line light beam is constant. The change of the arc length L will cause its energy density E to 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 line light beam 13 at the corresponding arc length according to the arc length L of the arc line light beam 13. The longer the arc length, the smaller the energy density, and the longer the duration is required. The shorter the arc length, the greater the energy density, and the shorter the duration is.

[0056] like Figure 7 , from the formula L=2R⋅α, we can know the relationship between the arc length L, the radius of curvature R and the center angle α of the arc line beam 13, and the center angle α of the arc 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 constant, the center angle α of the arc line beam 13 is also a constant. Therefore, the arc length L of the arc line beam 13 is linearly related to the radius of curvature R. According to the radius of curvature R∝h⋅cot(θ / 2) of the arc line beam 13, it can be obtained that the arc length L of the arc line beam 13∝h⋅cot(θ / 2), thereby the movement mode of the arc line beam 13 or the hollow conical lens 5 can be controlled according to the trajectory of the arc line beam 13 or the height of the hollow conical lens 5.

[0057] The laser track 14 formed by the arc line light beam 13 can be designed according to needs, and the laser track 14 can be controlled by regulating the rotation of the disc and the movement of the lifting module.

[0058] As one of the implementation methods, Figure 8, the laser trajectory 14 is a concentric circle. Accordingly, in step S3, the hollow conical lens 5 intermittently steps down or up, and the generated arc line light beam 13 remains at the corresponding position for a certain period of time to complete the processing at the curvature radius and then steps to the next position, so that the arc line light beam 13 scans from the outside to the inside or from the inside to the outside on the disk 8 to form a plurality of concentric circles with the rotation center 81 of the disk 8 as the center. The stepping amount between two adjacent concentric circles can be the same or different, forming a laser trajectory 14 in the form of concentric circles. If the hollow conical lens 5 intermittently steps down, concentric circles are formed in sequence from the outside to the inside. Conversely, if the hollow conical lens 5 intermittently steps up, concentric circles are formed in sequence from the inside to the outside. The diameter of the concentric circle is related to the height position of the hollow conical lens 5, and the distance between two adjacent concentric circles is closely related to the stepping amount when the hollow conical lens 5 descends or rises. As Fig. 9 When a plurality of wafers 9 are arranged on the disk 8 and the plurality of wafers 9 are arranged in a ring shape with the rotation center 81 of the disk 8 as the center, the laser track 14 can cover all the wafers 9, thereby polishing the plurality of wafers 9 at the same time.

[0059] When the lifting module 6 drives the hollow conical lens 5 to lift intermittently in steps, 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; wherein h is the height of the hollow conical lens 5, 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. When the cone angle θ of the hollow conical lens 5 and the incident angle β of the line beam are constant, k1 is a constant. The formula can be used to control the movement program of the hollow conical lens 5, thereby controlling the residence time of the arc line beam at each curvature radius R, and balancing the energy density of the arc line beam in turn 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.

[0060] As another implementation method, Fig.10 , the laser trajectory 14 is a spiral line. Accordingly, in step S3, the hollow conical lens 5 continuously descends or ascends at a certain speed program, so that the arc line beam 13 scans on the disk 8 to form a spiral trajectory 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. 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 toward the top or end of the cone at a speed v, forming a spiral laser trajectory 14. If the hollow conical lens 5 descends at a constant speed, a spiral trajectory from the outside to the inside is formed. Conversely, if the hollow conical lens 5 rises at a constant speed, a spiral trajectory from the outside to the inside is formed. Similarly, if Fig.11When a plurality of wafers 9 are arranged on the disk 8 and the plurality of wafers 9 are arranged in a ring with the rotation center 81 of the disk 8 as the center, the spiral laser track 14 can cover all the wafers 9, thereby polishing the plurality of wafers 9 at the same time.

[0061] 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 trajectory (including the radius of the spiral and the distance 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 constant, k2 is a constant. The energy density of the arc line beam is balanced by controlling the lifting speed of the hollow conical lens 5. When the hollow conical lens 5 moves from top to bottom, the speed gradually increases, so that the residence time of the arc line beam on the wafer gradually becomes shorter, thereby ensuring the uniformity of wafer processing.

[0062] In step S4, the dynamic adjustment method of the rotating bearing module is: 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 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.

[0063] 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 automatically switches to the safe polishing mode; c. When it is detected that the local temperature exceeds the set threshold value P (such as 150°C), if the current laser is in continuous laser mode, it will switch to pulse laser mode, set the duty cycle to 30%-50%, and trigger the cooling air curtain; if the current laser is in pulse laser mode, it will automatically switch to safe polishing mode; The safe polishing mode is: reducing the laser power to 50%-70% of the current value, and triggering the ultrasonic assisted polishing mechanism for local finishing.

[0064] Take 6-inch silicon carbide wafer 9 as an example: Initial state: thickness 675μm, TTV=8μm, Ra=1.2nm; Polishing parameters: laser power 400W, rotation speed 150rpm, slide rail speed 2mm / s; Processing results: The thickness is reduced to 100 μm, TTV = 0.8 μm, Bow = 2.5 μm; Ra=0.38nm, no thermal damage layer on the surface; The overall yield rate reaches 96.5% (82% for traditional processes).

[0065] In summary, the technical effects of the present invention are as follows: Efficiency breakthrough: The material removal rate reaches 8mm² / s, which is 300 times higher than that of traditional spot beams, and the single wafer 9 processing cycle is shortened to 42 minutes.

[0066] Improved accuracy: Surface accuracy: TTV<1μm, Bow<3μm; Surface quality: Ra<0.5nm, no microcracks; Damage control: The depth of heat-affected zone is less than 5μm, and the lattice distortion rate is reduced to less than 0.05%; Industrial adaptation: Supports 8-12 inch wafer 9 mixed line production, process switching time <10 minutes, equipment utilization rate >95%.

[0067] The above detailed description is a specific description of a feasible embodiment of the present invention. The embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not deviate from the present invention should be included in the patent scope of this case.

Claims

1. A large-size wafer thinning and polishing device based on dynamic line beam, characterized in that: The invention comprises a dynamic beam generating module, a rotating bearing module and a closed-loop control module, wherein the dynamic beam generating module comprises a laser, a polarizing plate, a line beam shaping component, a reflector, a hollow conical lens and a lifting module, wherein the laser is used to generate a Gaussian laser beam, the line beam shaping component is used to shape the laser beam into a straight line beam, the polarizing plate is arranged between the laser and the line beam shaping component, the hollow conical lens is a hollow conical lens with an open end face, and the wall thickness is consistent, and is used to shape the straight line beam into an arc line beam, and the hollow conical lens end The laser beam is installed on the lifting module with the opening facing upward and the cone angle facing downward, and moves up and down under the drive of the lifting module to generate a dynamic arc line beam. The reflector is arranged between the line beam shaping component and the hollow conical lens. After the laser beam generated by the laser reaches the line beam shaping component through the polarizer, it is shaped into a straight line beam, and then after being reflected by the reflector, it 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 line beam for thinning and polishing the wafer. The arc line beam adjusts its position and shape with the lifting module. The rotating bearing module is used to fix and drive the wafer to rotate, and the closed-loop control module is respectively connected to the lifting module and the rotating bearing module to control the lifting of the lifting module and the movement of the rotating bearing module.

2. The large-size wafer thinning and polishing device based on dynamic line beam according to claim 1 is characterized in that: It also includes a detection module, which includes a white light interferometer and an infrared thermal imager arranged above the rotating carrying 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 of the wafer during laser thinning and polishing. The white light interferometer and the infrared thermal imager are respectively connected to the closed-loop control module to transmit detection data. The closed-loop control module controls the movement of the lifting module and the rotating carrying module according to the real-time detection data.

3. The large-size wafer thinning and polishing device based on dynamic line beam according to claim 1 is characterized in that: The line beam shaping assembly 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 to expand the laser beam. After the laser beam is expanded by the beam expander, it is shaped into a line beam by the line beam shaping mirror. A line beam focusing mirror is also arranged between the hollow conical lens and the wafer, and the arc line beam is focused by the line beam focusing mirror and reaches the surface of the wafer to process the wafer; 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.

4. The large-size wafer thinning and polishing device based on dynamic line beam according to claim 1 is characterized in that: The cone 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 supporting module includes a disc, a vacuum adsorption device, an air bearing and a rotating 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 ≥200mm. The rotating driving component drives the disc to rotate through the air bearing.

5. A method for thinning and polishing a large-size wafer based on a dynamic line beam, using the large-size wafer thinning and polishing device based on a dynamic line beam as claimed in any one of claims 1 to 4, characterized in that: The steps include: S1. Vacuum adsorb multiple wafers to be processed on a disc on a rotating carrying module, and arrange the multiple wafers 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; S2. According to the material, size and surface polishing requirements of the wafer, refer to the pre-stored mapping table of materials, sizes and polishing parameters, preliminarily set the laser power, arc length of the arc line beam, angle of the reflector, initial position of the lifting module and 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 line beam generated by the dynamic beam generation module falls on the outermost or innermost processing layer of the wafer; S3, start the rotating bearing module to rotate the disk at a certain speed, so that the arc line light beam can perform thinning and polishing processing on all the wafers on the disk in sequence as the disk rotates; at the same time, control the lifting module to drive the hollow conical lens to rise and fall at a certain speed program, so that the dynamic arc line light beam takes the rotation center of the disk as the center to perform thinning and polishing processing on all the wafers on the disk from the outside to the inside or from the inside to the outside; 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 of the wafer processing area is monitored in real time through a thermal imager. The closed-loop control module dynamically adjusts the rotation speed of the disc, the driving speed of the lifting module, the laser power and the arc length of the arc line beam in real time according to the acquired surface data and temperature distribution data of the wafer, so that the total thickness deviation TTV of the wafer is less than 1μm and the depth of the heat affected zone of laser processing is less than 5μm.

6. The method for thinning and polishing a large-size wafer based on a dynamic line beam according to claim 5, characterized in that: The method also includes a post-processing step, which includes: using megasonic cleaning to remove residual particles on the surface of the wafer, and then using an atomic force microscope (AFM) to perform a final surface roughness inspection.

7. The method for thinning and polishing a large-size wafer based on a dynamic line beam according to claim 5, characterized in that: In step S3, the hollow conical lens intermittently steps down or up, 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, and the stepping amount between two adjacent concentric circles is equal or unequal, and the concentric circle track covers all wafers; The residence time T of the hollow conical lens at different step heights is controlled according to the following formula: T=k1·h; wherein 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 light beam on the hollow conical lens.

8. The method for thinning and polishing a large-size wafer based on a dynamic line beam according to claim 5, characterized in that: In step S3, the hollow conical lens is continuously lowered or raised at a certain speed program, so that the arc line beam scans on the disk to form a spiral track 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 track covers all the wafers; The lifting speed v of the hollow conical lens is 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 light beam on the hollow conical lens.

9. The method for thinning and polishing a large-size wafer based on a dynamic line beam according to claim 5, characterized in that: The arc length of the arc line beam output by the hollow conical lens is 0.2-8mm, the line width is less than 0.1mm, the arc is less than π / 4, and the uniformity is greater than 90%; the output power of the laser is 300-500W, and the rotation speed of the disk is 100-200rpm.

10. The method for thinning and polishing a large-size wafer based on a dynamic line beam according to claim 5, characterized in that: In step S4, the dynamic adjustment method of the rotating bearing module is: a. When it is detected that the material removal rate of the wafer surface is less than the set value M, the arc length of the arc 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%; b. When it is detected that the material removal rate on the wafer surface is greater than the set value N, it automatically switches to the safe polishing mode; c. When it is detected that the local temperature exceeds the set threshold value P, if the current laser is in continuous laser mode, it will switch to pulse laser mode, set the duty cycle to 30%-50%, and trigger the cooling air curtain; if the current laser is in pulse laser mode, it will automatically switch to safe polishing mode; The safe polishing mode is: reducing the laser power to 50%-70% of the current value, and triggering the ultrasonic assisted polishing mechanism for local finishing.

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