A method for improving surface roughness of laser lift-off

Abstract

The present invention provides a method for improving the surface roughness of laser stripping, which belongs to the technical field of laser cutting. The method for improving the surface roughness of laser stripping includes: S10: measuring the deflection angle θ of the surface of a wafer to be processed, and determining the normal line of the surface of the wafer to be processed; S20: taking a wafer sample, the material of the wafer sample is the same as the material of the wafer to be processed, hitting the wafer sample with a laser stripper, and determining the spot diameter A of the laser stripper; S30: calculating the scanning interval B: B=A / tanθ; S40: determining the projection line of the normal line of the surface of the wafer to be processed on the XY plane, adjusting the emission direction of the laser in the laser stripper to be perpendicular to the projection line, and stripping the surface of the wafer to be processed under the condition of the scanning interval B. The method for improving the surface roughness of laser stripping provided by the present invention takes the deflection angle of the wafer into consideration in the setting of parameters in laser stripping, thereby improving the efficiency of stripping.

Description

Technical Field

[0001] The invention belongs to the technical field of laser cutting, and in particular relates to a method for improving the surface roughness of laser peeling. Background Art

[0002] Silicon carbide, as a widely used third-generation semiconductor material, has excellent properties such as high hardness, high melting point, high wear resistance, high corrosion resistance, high thermal conductivity, and high electrical conductivity. It is difficult to process. Cutting is an important process in crystal processing. The commonly used cutting method in production is reciprocating multi-wire cutting. However, the cost of silicon carbide materials is high, and the ingot length is short. Several ingots need to be bonded together for multi-wire cutting. The production efficiency is low, the cutting loss is large, the surface orientation of the chip is difficult to control, and the stability of the equipment is required to be high.

[0003] The application of laser lift-off technology in third-generation semiconductor materials is gradually increasing. It can avoid the shortcomings of long multi-wire cutting processing cycle and large cutting loss, and has the advantages of flexible single-chip processing and easy surface curve adjustment.

[0004] Laser peeling is a combination of laser precision processing technology and crystal peeling technology. A modified layer with weaker bonding force is pre-manufactured at a specific position in the crystal, which is conducive to forming a certain crystal fracture position in the peeling process, thereby improving the controllability of the peeling process and the consistency of chip thickness. This is especially important for the processing of high-strength, high-brittleness, and high-cost single crystal materials such as silicon carbide.

[0005] The surface of laser peeling is flat, but there is a certain amount of modified layer remaining on the surface. In the traditional laser peeling process, the scanning spacing is gradually increased, and the roughness of the laser peeling surface is improved through continuous experiments. This process is cumbersome and has high losses. Summary of the invention

[0006] The embodiment of the present invention provides a method for improving the surface roughness of laser lift-off, aiming to solve the technical problem that the traditional laser lift-off method for improving the surface roughness requires gradual adjustment of the scanning spacing for verification, and the process is cumbersome and has high loss.

[0007] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for improving the surface roughness of laser lift-off, comprising:

[0008] S10: measuring the deflection angle θ of the surface of the wafer to be processed, and determining the normal line of the surface of the wafer to be processed;

[0009] S20: taking a wafer sample, the material of the wafer sample being the same as the material of the wafer to be processed, hitting the wafer sample with a laser stripper, and determining the spot diameter A of the laser stripper;

[0010] S30: Calculate the scanning distance B:

[0011] B = A / tanθ;

[0012] S40: determining the projection line of the normal line of the surface of the wafer to be processed on the XY plane, adjusting the emission direction of the laser in the laser stripper to be perpendicular to the projection line, and stripping the surface of the wafer to be processed under the condition of a scanning interval B.

[0013] In a possible implementation, the step S10 includes:

[0014] S11: Measure the X-axis direction of the wafer to be processed <0001> The angle of the face α;

[0015] S12: Measure the Y-axis direction of the wafer to be processed <0001> The angle of the face β;

[0016] S13: Calculate the deflection angle θ of the surface of the wafer to be processed by the formula:

[0017] (tanα) 2 + (tan β) 2 = (tanθ) 2 ;

[0018] S14: Calculate the angle φ between the projection line and the X-axis using the formula:

[0019] tanφ=tanβ / tanα.

[0020] In a possible implementation, the angle α in step S11 and the angle β in step S12 are both measured by an X-ray orientation instrument.

[0021] In a possible implementation, the wafer to be processed is placed on a rotatable stage, and after the measurement in step S11 is completed, the stage is rotated 90° to perform the measurement in step S12.

[0022] In a possible implementation, the loading platform is driven to rotate by a motor, a position sensor is provided on the periphery of the loading platform, and the position sensor is communicatively connected with the motor.

[0023] In a possible implementation, a positioning ring is provided on the stage, the positioning ring, the output shaft of the motor and the stage are all coaxial, and the wafer to be processed is placed on the inner ring of the positioning ring.

[0024] In a possible implementation, after the angle α and the angle β of the wafer to be processed are measured on the stage, the stage is rotated by an angle φ, and a laser stripper is used to strip the surface of the wafer to be processed.

[0025] Compared with the prior art, the solution shown in the embodiment of the present application takes the wafer deflection angle into consideration when setting the parameters in laser stripping. By measuring and calculating the wafer deflection angle and the direction of the deflection angle projection, the scanning spacing of the laser stripper is determined in combination with the size of the light spot. Compared with the traditional method of obtaining a suitable scanning spacing through multiple experiments, this method is more convenient. Moreover, since the scanning spacing takes the wafer deflection angle into consideration, it can ensure that the projection of the crystal direction on the XY plane is perpendicular to the laser scanning direction during laser stripping, thereby improving the stripping efficiency and reducing the surface roughness after stripping. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of the spot size and scanning spacing in the laser lift-off method used in an embodiment of the present invention;

[0027] Figure 2 Schematic diagrams of two implementation methods of wafers to be processed according to embodiments of the present invention, wherein Figure 2 (a) is an embodiment in which the positioning edge is a flat edge, Figure 2 (b) is an embodiment in which the positioning edge is an arc edge;

[0028] Figure 3 It is a schematic diagram of the main structure of the stage and the position sensor used in the embodiment of the present invention;

[0029] Figure 4 It is a schematic diagram of the top view of the structure of the object carrier used in the embodiment of the present invention.

[0030] Description of reference numerals:

[0031] 10- stage; 11- positioning ring; 12- first positioning point; 13- second positioning point;

[0032] 20-wafer to be processed; 21-positioning edge;

[0033] 30-motor;

[0034] 40- Position sensor. DETAILED DESCRIPTION

[0035] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0036] In the claims, specification and the above drawings of the present invention, unless otherwise clearly defined, if the term "fixed connection" or "fixed connection" is used, it should be understood in a broad sense, that is, any connection method without a displacement relationship and relative rotation relationship between the two, that is to say, including non-detachable fixed connection, detachable fixed connection, integrated connection and fixed connection through other devices or elements.

[0037] In the claims, description and drawings of the present invention, if the terms "include", "have" and their variations are used, they are intended to mean "including but not limited to".

[0038] The method for improving the surface roughness of laser lift-off provided by the present invention is now described. The method for improving the surface roughness of laser lift-off comprises:

[0039] S10: measuring the deflection angle θ of the surface of the wafer 20 to be processed, and determining the normal line of the surface of the wafer to be processed;

[0040] S20: taking a wafer sample, the material of the wafer sample being the same as the material of the wafer 20 to be processed, hitting the wafer sample with a laser stripper, and determining the spot diameter A of the laser stripper;

[0041] S30: Calculate the scanning distance B:

[0042] B = A / tanθ;

[0043] S40: Determine the projection line of the normal line of the surface of the wafer to be processed on the XY plane, adjust the emission direction of the laser in the laser stripper to be perpendicular to the projection line, and strip the surface of the wafer 20 to be processed under the condition of scanning interval B.

[0044] It should be noted that the meaning of spot size and scanning spacing can be referred to Figure 1 ,and Figure 1 The angle between the crystal plane marked in and the modified layer is the deviation angle θ.

[0045] The principle of laser stripping is that the laser beam forms a spot at a certain depth inside the crystal by adjusting parameters such as energy, frequency, and focus. This spot realizes high-density light absorption inside the crystal, and physical and chemical processes such as chemical bond breaking, phase change, laser-induced ionization, and thermal cracking occur, ultimately achieving compression of the damaged layer parallel to the direction of laser propagation and crack extension perpendicular to the direction of laser propagation.

[0046] In this process, if the spacing of the laser beam scanning is set reasonably and the crack expansion is large enough, the chip can be peeled off from the crystal through thermal expansion and contraction or ultrasonic vibration.

[0047] Compared with the prior art, the method for improving the surface roughness of laser stripping provided in this embodiment takes the wafer deflection angle into consideration when setting the parameters in laser stripping, and determines the scanning spacing of the laser stripper by measuring and calculating the wafer deflection angle and the direction of the deflection angle projection, thereby combining the size of the light spot. Compared with the traditional method of obtaining a suitable scanning spacing through multiple experiments, this method is more convenient, and because the scanning spacing takes the wafer deflection angle into consideration, it can ensure that the projection of the crystal direction on the XY plane is perpendicular to the laser scanning direction during laser stripping, thereby improving the stripping efficiency and reducing the surface roughness after stripping.

[0048] In some embodiments, step S10 includes:

[0049] S11: Measure the X-axis direction of the wafer 20 to be processed <0001> The angle of the face α;

[0050] S12: Measure the Y-axis direction of the wafer 20 to be processed <0001> The angle of the face β;

[0051] S13: Calculate the deflection angle θ of the surface of the wafer 20 to be processed by the formula:

[0052] (tanα) 2 + (tan β) 2 = (tanθ) 2 ;

[0053] S14: Calculate the angle φ between the projection line and the X-axis using the formula:

[0054] tanφ=tanβ / tanα.

[0055] The angle α in step S11 and the angle β in step S12 are both measured by an X-ray orientation instrument.

[0056] Alternatively, when the angle α and the angle β are known in advance (such as when the wafer is fed with markings), the deflection angle θ can be directly calculated.

[0057] However, by re-measuring the angle α and the angle β through the X-ray orientation instrument, a certain difference between each wafer can be avoided, thereby ensuring that the calculation result of the deflection angle θ of the wafer 20 to be processed is more accurate.

[0058] In some embodiments, a specific measurement method of the above-mentioned wafer 20 to be processed can be as follows: Figure 3 to Figure 4 See the structure shown. Figure 3 to Figure 4 , the wafer 20 to be processed is placed on the rotatable stage 10. After the measurement in step S11 is completed, the stage 10 is rotated 90° to perform the measurement in step S12.

[0059] By measuring the angle α and the angle β with the aid of the stage 10, the center of the wafer can be made to coincide with the axis of the rotation shaft of the stage 10 when the wafer is placed. Furthermore, when the stage 10 is rotated, the center of the wafer can be kept stationary, thereby achieving measurement of the angle α and the angle β when the wafer rotates but the X-ray locator does not move, and the measurement result is more accurate.

[0060] In some embodiments, an improved implementation of the above-mentioned stage 10 can be as follows Figure 3 See the structure shown. Figure 3 The stage 10 is driven to rotate by the motor 30. A position sensor 40 is provided on the periphery of the stage 10. The position sensor 40 is in communication with the motor 30. Driven by the motor 30, the stage 10 can automatically rotate 90° after measuring the angle α, and then measure the angle β. The stage 10 is driven to rotate by the motor 30, which can improve the accuracy of the rotation angle of the stage 10. Compared with manual rotation, it is more accurate and labor-saving, and the corresponding measured angle α and angle β values ​​are also more accurate.

[0061] The specific working process of the position sensor 40 is as follows: the position sensor 40 starts the motor 30 to rotate the stage 10 to the initial position, and then the motor 30 is turned off for a preset time, during which the angle α can be measured; then the motor 30 is started to drive the stage 10 to rotate forward 90° and then is turned off for a preset time, during which the angle β can be measured; after the measurement is completed, the position sensor 40 starts the motor 30 to reverse 90° and return to the initial position.

[0062] It should be noted that the position sensor 40 can adopt the infrared principle, by setting positioning points on the periphery of the stage 10, and by identifying the positioning points on the periphery of the stage 10, the position of the stage 10 can be determined, thereby rotating and adjusting the stage 10.

[0063] In some embodiments, an improved implementation of the above-mentioned stage 10 can be as follows Figure 3 to Figure 4 See the structure shown. Figure 3 to Figure 4 , a positioning ring 11 is provided on the stage 10, and the positioning ring 11, the output shaft of the motor 30 and the stage 10 are all coaxial, and the wafer 20 to be processed is placed on the inner ring of the positioning ring 11. By providing the positioning ring 11, when the wafer is placed on the stage 10, the wafer is just in the inner ring of the positioning ring 11, and the positioning ring 11 abuts against the outer peripheral surface of the wafer, thereby ensuring that the axis of the wafer coincides with the axis of the rotation axis of the stage 10, ensuring that the center of the wafer remains unchanged after the stage 10 rotates, facilitating the positioning and installation of the wafer on the stage 10, and convenient operation, and improving the measurement efficiency of the angle α and the angle β.

[0064] Specifically, the positioning ring 11 can be connected to the stage 10 in a detachable manner. For example, a plurality of circles of sockets are arranged on the top surface of the stage 10 from the inside to the outside, and a plug block matching the sockets is arranged at the bottom of the positioning ring 11. By setting a plurality of circles of sockets, positioning rings 11 of different sizes can be easily replaced, thereby adapting to the measurement of wafers of different sizes.

[0065] It is easy to understand that after the wafer is placed on the stage 10 , the top surface of the positioning ring 11 is lower than the top surface of the wafer, which can ensure that the measurement process of the wafer deflection angle is not affected.

[0066] In some embodiments, after measuring the angle α and the angle β of the wafer 20 to be processed on the stage 10, the stage 10 is rotated by an angle φ, and the surface of the wafer to be processed is peeled using a laser stripper. By calculating the angle φ, the angle between the projection line of the normal line of the surface of the wafer 20 to be processed on the XY plane and the X-axis can be determined. In order to ensure that the laser emission path is perpendicular to the projection line, the stage 10 is directly rotated by an angle φ, and the laser emission path can be adjusted to be perpendicular to the projection line, which is convenient for adjustment and improves the efficiency of laser stripping.

[0067] In some embodiments, an improved implementation of the above-mentioned wafer 20 to be processed can be as follows Figure 2 and Figure 4 See the structure shown. Figure 2 and Figure 4 A positioning edge 21 is provided on the periphery of the wafer 20 to be processed, a line connecting the midpoint of the positioning edge 21 and the center of the wafer 20 to be processed is defined as the Y axis, and a direction perpendicular to the Y axis is defined as the X axis. By providing the positioning edge 21 on the periphery of the wafer 20 to be processed, it is convenient to quickly determine the X axis and the Y axis when measuring the deflection angle θ, shorten the debugging time, and improve the measurement efficiency.

[0068] In some implementations, an improved implementation of the above-mentioned stage 10 can be adopted as follows Figure 4 See the structure shown. Figure 4 The first positioning point 12 and the second positioning point 13 are provided on the periphery of the stage 10, and the line connecting the first positioning point 12 and the midpoint of the positioning edge 21 passes through the center of the wafer 20 to be processed. When the wafer is placed on the stage 10, it is ensured that the line connecting the midpoint of the positioning edge 21 and the first positioning point 12 passes through the center of the wafer. When the position sensor 40 detects the first positioning point 12 of the stage 10, it is the initial position. When the stage 10 rotates 90°, the position sensor 40 just corresponds to the second positioning point 13.

[0069] Optional, see Figure 2 In (a), the positioning edge 21 is a flat edge; see Figure 2 In (b), the positioning edge 21 may also be an arc edge, which can be selected according to the operation requirements.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the surface roughness of laser lift-off, characterized in that: include: S10: measuring the deflection angle θ of the surface of the wafer to be processed, and determining the normal line of the surface of the wafer to be processed; S20: taking a wafer sample, the material of the wafer sample being the same as the material of the wafer to be processed, hitting the wafer sample with a laser stripper, and determining the spot diameter A of the laser stripper; S30: Calculate the scanning distance B: B = A / tanθ; S40: determining a projection line of a normal line of the surface of the wafer to be processed on the XY plane, adjusting the emission direction of the laser in the laser stripper to be perpendicular to the projection line, and stripping the surface of the wafer to be processed under the condition of a scanning interval B; The step S10 includes: S11: Measure the X-axis direction of the wafer to be processed <0001> The angle of the face α; S12: Measure the Y-axis direction of the wafer to be processed <0001> The angle of the face β; S13: Calculate the deflection angle θ of the surface of the wafer to be processed by the formula: (tanα) 2 +(tanβ) 2 =(tanθ) 2 ; S14: Calculate the angle φ between the projection line and the X-axis using the formula: tanφ=tanβ / tanα; The wafer to be processed is placed on a rotatable stage. After the measurement in step S11 is completed, the stage is rotated 90° to perform the measurement in step S12; A first positioning point and a second positioning point are arranged on the periphery of the stage, a positioning edge is arranged on the periphery of the wafer to be processed, and a line connecting the midpoints of the first positioning point and the positioning edge passes through the center of the wafer to be processed.

2. The method for improving the surface roughness of laser lift-off according to claim 1, characterized in that: The loading platform is driven to rotate by a motor. A position sensor is provided on the periphery of the loading platform. The position sensor is communicatively connected with the motor.

3. The method for improving the surface roughness of laser lift-off according to claim 2, characterized in that: A positioning ring is provided on the stage, and the positioning ring, the output shaft of the motor and the stage are all coaxial, and the wafer to be processed is placed on the inner ring of the positioning ring.

4. The method for improving the surface roughness of laser lift-off according to claim 1, characterized in that: After the angle α and the angle β of the wafer to be processed are measured on the stage, the stage is rotated by an angle φ, and a laser stripper is used to strip the surface of the wafer to be processed.

Images