A silicon carbide ingot pre-processing process method

Abstract

The present invention discloses a method for pre-processing a silicon carbide ingot, which belongs to the technical field of ingot pre-processing, and includes the following steps: S1, placing the ingot in a material preparation tray, scanning the surface of the ingot using a three-dimensional topography scanner, and obtaining point cloud data of the ingot surface topography error; S2, reconstructing the ingot surface error model through a Delaunay triangulation algorithm based on the obtained point cloud data; S3, setting a calculation program based on the ingot surface error model and basic optical principles, and calculating the distance that the objective lens holder at different points of the ingot should be adjusted in the vertical direction relative to the calibration position; S4, performing laser processing based on the result obtained in S3. The present invention realizes adaptive control of the laser focus through an ingot topography error detection and reconstruction algorithm, and pre-processes the ingot surface, thereby reducing the influence of the ingot three-dimensional topography on the subsequent peeling quality.

Description

Technical Field

[0001] The invention relates to the technical field of crystal ingot pre-processing, and in particular to a silicon carbide crystal ingot pre-processing process method. Background Art

[0002] As the main representative of the third generation of semiconductor materials, silicon carbide has the advantages of large bandgap, large critical breakdown electric field, high thermal conductivity, high electron saturation drift rate, high electron mobility and stable chemical properties. It plays an important role in many fields of modern industry and has broad application prospects and huge market potential. However, silicon carbide has the characteristics of high hardness, high brittleness, strong corrosion resistance, and is very sensitive to mechanical external forces, so processing and etching silicon carbide has become a problem.

[0003] At present, the new technology for processing silicon carbide wafers is mainly laser processing. Pulsed laser is commonly used for laser processing of silicon carbide. Pulsed laser has a very short pulse time and high peak power. The irradiated material will be ablated immediately without increasing the temperature, which reduces the impact of surface burns and spatter caused by the accumulation of thermal effects on the material. Therefore, pulsed laser is usually used for precision processing of brittle and hard materials. At this stage, picosecond lasers are often used as the basic device for processing silicon carbide wafers.

[0004] At the beginning of the production of the crystal ingot, the temperature changes and residual stress will cause a certain wafer curvature and total thickness deviation on the surface of the crystal ingot. When using laser processing, if the laser Z-axis direction maintains a uniform height, the laser will be focused on horizontal planes at different depths inside the crystal ingot, affecting the flatness and uniformity of the modified layer. The first layer of peeling surface will be uneven. If not handled in time, the surface error will accumulate, seriously affecting the subsequent wafer processing quality.

[0005] In the invention patent with publication number CN113465554A and patent name "A wafer morphology measurement device and its use method", the measurement platform is supported by shock-absorbing support blocks, filling films and gas shock-absorbing springs. However, since the materials used for the filling films and gas shock-absorbing springs are relatively soft, their durability is relatively poor. The measurement sensor uses infrared interference measurement to collect data on the wafer surface. Infrared interference technology has relatively high environmental requirements. Measurement using infrared interference technology requires complex optical systems and signal processing algorithm support, which increases the complexity of the equipment and increases maintenance and servicing costs.

[0006] Therefore, for the SiC ingot ultrafast laser stripping system, it is very important to perform pre-processing on the ingot before the laser stripping process. Summary of the invention

[0007] The purpose of the present invention is to provide a silicon carbide ingot pre-processing process method, which realizes laser focus adaptive control through ingot morphology error detection and reconstruction algorithm, and pre-processes the ingot surface, thereby reducing the influence of the ingot three-dimensional morphology on the subsequent stripping quality.

[0008] To achieve the above object, the present invention provides a silicon carbide ingot pre-processing process method, comprising the following steps:

[0009] S1. Place the ingot in a material preparation tray, and use a three-dimensional topography scanner to scan the surface of the ingot to obtain point cloud data of the ingot surface topography error;

[0010] S2. Reconstructing the ingot surface error model through Delaunay triangulation algorithm based on the obtained point cloud data;

[0011] S3. Based on the ingot surface error model and basic optical principles, a calculation program is set, and according to the set calculation program, the distance that the objective lens holder at different points of the ingot should be adjusted in the vertical direction relative to the calibration position is calculated;

[0012] S4. Based on the result obtained in S3, laser processing is performed.

[0013] Preferably, in S1, 3D structured light imaging technology is used, a light source is used to project light onto the surface of the ingot, reflection information is captured by a camera, and the position and depth information of each location of the ingot is calculated using triangulation to generate point cloud data.

[0014] Preferably, in S2, the point cloud data is first projected into the XY two-dimensional plane through the normal, and then the projected point cloud is triangulated in the plane to obtain the topological connection relationship of each point in the plane projection, determine the topological connection between each original three-dimensional point, and obtain the reconstructed ingot surface error model.

[0015] Preferably, the calculation procedure of S3 comprises the following steps:

[0016] 1) According to the highest point of the ingot surface at which the laser is vertically incident, the reference position of the calibration line on the objective lens frame is determined, and the reference working distance Z0 between the reference position and the ingot modification plane is calculated;

[0017] 2) Taking the highest point on the ingot surface as the reference plane and combining the obtained ingot surface error model, calculate the working distance Z at any point on the ingot surface when the laser is incident on the ingot surface;

[0018] 3) The distance ΔZ that the objective lens holder should be adjusted in the vertical direction relative to the calibration position at different points of the crystal ingot is obtained by calculation.

[0019] Preferably, Z0 is expressed as:

[0020] Z0=h+a+b;

[0021] Among them, h is the distance between the bottom surface of the objective lens and the surface of the ingot, a is the depth of the modified plane of the ingot, and b is the thickness between the calibration line and the bottom surface of the lens;

[0022] The calculation formula of h is:

[0023]

[0024]

[0025] r is the radius of the light beam at the bottom of the lens, γ is the incident angle of the laser on the surface of the ingot, β is the refraction angle of the laser on the surface of the ingot, and f is the focal length of the lens;

[0026] When the laser is incident vertically on the surface of the ingot, the refractive index n of the silicon carbide ingot is:

[0027]

[0028] According to calculation

[0029]

[0030] The Z is represented by:

[0031] Z=h′+a+b

[0032] When the ingot surface is tilted at an angle of α, the incident angle of the laser optical axis on the ingot surface is also α, and the refractive index n of the silicon carbide ingot is:

[0033]

[0034] Wherein, β0 is the refraction angle of the laser optical axis on the surface of the ingot at this time;

[0035]

[0036] or

[0037]

[0038] Among them, β1 and β2 are the refraction angles on the left and right sides respectively.

[0039] Preferably, the ΔZ is expressed as:

[0040] ΔZ=Z-Z0.

[0041] Based on the method, the present invention provides a device for laser modification of silicon carbide ingots, comprising a material preparation tray, a three-dimensional topography scanner, a four-axis SCARA manipulator, an error data processor, a processing platform, a pulsed picosecond laser, an optical path system and a CCD observation system, wherein the material preparation tray is arranged at the lower end of the four-axis SCARA manipulator, the four-axis SCARA manipulator has four degrees of freedom of translation in the X, Y, and Z axes and rotation around the Z axis, and a vacuum suction cup is installed at the end effector position to pick up and transfer the ingot by adsorption force;

[0042] The three-dimensional shape scanner and the processing platform are respectively arranged on both sides of the four-axis SCARA manipulator, the three-dimensional shape scanner is connected to the data processor signal on the same side, and the error processor is program-set according to the pre-processing process method provided by the present invention;

[0043] The upper end of the processing platform is provided with a motion panel, and the processing platform has five degrees of freedom: translation of the X and Y axes and rotation around the X, Y and Z axes; the motion panel is installed on the gantry;

[0044] The pulse picosecond laser is arranged on the other side of the processing platform. An optical path system is arranged on the optical path of the pulse picosecond laser. The optical path system includes a total reflection mirror combination, a dichroic beam splitter and a focusing lens arranged in sequence along the optical path. The last reflection mirror on the total reflection mirror combination is arranged in parallel with the dichroic beam splitter. The CCD observation system includes an eyepiece and a CCD camera which are arranged vertically on the upper end of the dichroic beam splitter in sequence. The CCD observation system is electrically connected to the display.

[0045] The laser output from the picosecond laser is transmitted to the surface of the dichroic beam splitter 14 through the reflection effect of the total reflection mirror combination arranged along the optical path. The dichroic beam splitter adopts a short-wave light-transmitting plate, and the light in the short-wave band passes through and reflects the light in the long-wave band. Therefore, the picosecond laser is reflected and finally focused vertically on the processing surface of the ingot through the focusing lens.

[0046] The dichroic beam splitter, the last reflector of the total reflector combination, the condenser lens, the eyepiece, and the CCD camera are all fixed on the motion panel.

[0047] Therefore, the present invention provides a method for pre-processing a silicon carbide ingot, which utilizes a three-dimensional topography scanner to scan the three-dimensional surface of the ingot to obtain surface morphology parameters of the silicon carbide ingot; uses a Delaunay triangulation algorithm to process point cloud data, and reconstructs a surface error model of the ingot; based on the ingot surface error model and basic optical principles, the distance ΔZ that should be adjusted in the vertical direction relative to the calibrated position of the objective lens holder at different points of the ingot is calculated to ensure that the laser can be focused on the same horizontal plane inside the ingot for direct writing processing, thereby reducing the processing errors caused by morphology differences at different positions of the same ingot or ingots from different batches. In this way, the modified layer obtained by laser scanning has better flatness, so the roughness of the wafer after peeling is smaller, which can reduce the material loss in the subsequent grinding process.

[0048] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A schematic diagram of the structure of a device for reforming a crystal ingot according to an embodiment of the present invention;

[0050] Figure 2 This is a schematic diagram of the 3D structured light imaging technology of an embodiment of the present invention;

[0051] Figure 3 A schematic diagram of a focusing lens structure and laser focusing according to an embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram of a laser incident on the highest point on the surface of a crystal ingot and focused inside the crystal ingot according to an embodiment of the present invention;

[0053] Figure 5 This is a schematic diagram of focusing of any incident point of laser light inside a crystal ingot according to an embodiment of the present invention;

[0054] Reference numerals:

[0055] 1. Material preparation tray; 2. 3D topography scanner; 3. Four-axis SCARA manipulator; 4. Data processor; 5. Processing platform; 6. Motion panel; 7. Pulsed picosecond laser; 8. Total reflection mirror combination; 9. Dichroic beam splitter; 10. Focusing lens; 11. Eyepiece; 12. CCD camera; 13. Display. DETAILED DESCRIPTION

[0056] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0057] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0058] The present invention provides a silicon carbide ingot pre-processing process method, comprising the following steps:

[0059] 1) placing the ingot in a preparation tray, scanning the surface of the ingot using a 3D topography scanner, and obtaining point cloud data of the ingot surface topography error;

[0060] 2) Based on the obtained point cloud data, the ingot surface error model is reconstructed by using the Delaunay triangulation algorithm;

[0061] 3) According to the highest point of the laser vertically incident on the ingot surface, determine the reference position of the calibration line on the objective lens frame, and calculate the reference working distance Z0 between the reference position and the ingot modified plane;

[0062] 4) Taking the highest point on the ingot surface as the reference plane and combining the obtained ingot surface error model, calculate the working distance Z at any point on the ingot surface when the laser is incident on the ingot surface;

[0063] 5) The distance ΔZ that the objective lens holder should be adjusted in the vertical direction relative to the calibration position at different points of the crystal ingot is obtained by calculation.

[0064] 6) The algorithm is used to set the program, and laser processing is performed based on the result obtained in S3.

[0065] Based on the above method, the present invention provides a device for laser modification of silicon carbide ingots, such as Figure 1 As shown, it includes a material preparation tray 1, a three-dimensional shape scanner 2, a four-axis SCARA manipulator 3, an error data processor 4, a processing platform 5, a pulsed picosecond laser 7, an optical path system and a CCD observation system. The material preparation tray 1 is arranged at the lower end of the four-axis SCARA manipulator 3. The four-axis SCARA manipulator has four degrees of freedom of translation in the X, Y, and Z axes and rotation around the Z axis. A vacuum suction cup is installed at the end effector position to pick up and transfer the ingot by adsorption force.

[0066] The three-dimensional morphology scanner 2 and the processing platform 5 are respectively arranged on both sides of the four-axis SCARA manipulator 3. The three-dimensional morphology scanner 2 is signal-connected to the data processor 4 on the same side. Its function is to scan the surface of the crystal ingot, obtain the crystal ingot surface morphology error point cloud data, and transmit it to the error data processor; the error data processor 4, based on the acquired point cloud data, reconstructs the error model through the Delaunay triangulation algorithm to obtain the three-dimensional morphology characteristics of the surface of the crystal ingot to be processed.

[0067] A motion panel 6 is provided at the upper end of the processing platform 5, and the processing platform 5 has five degrees of freedom: translation along the X and Y axes and rotation around the X, Y and Z axes; the motion panel 6 is installed on the gantry and can translate along the Z axis; the movement direction and movement speed of the processing platform 5 and the motion panel 6 can be controlled by the controller and the motor drive, so as to realize the adjustment of the silicon carbide processing parameters. During the entire processing process, the silicon carbide ingot is fixed by the vacuum adsorption effect of the processing platform 5.

[0068] A pulsed picosecond laser 7 is arranged on the other side of the processing platform 5. An optical path system is arranged on the optical path of the pulsed picosecond laser 7. The optical path system includes a total reflection mirror combination 8, a dichroic beam splitter 9 and a focusing lens 10 arranged in sequence along the optical path. The last reflection mirror on the total reflection mirror combination 8 is arranged parallel to the dichroic beam splitter 9. The CCD observation system includes an eyepiece 11 and a CCD camera 12 which are vertically arranged on the upper end of the dichroic beam splitter 9 in sequence. The CCD observation system is electrically connected to a display 13; it is used to directly observe the shape and size of the light spot irradiated by the laser on the surface of the ingot.

[0069] The laser output from the pulsed picosecond laser 7 is transmitted to the surface of the dichroic beam splitter 14 through the reflection effect of the total reflection mirror combination 8 arranged along the optical path. The dichroic beam splitter 14 adopts a short-wave light-passing plate, and the light in the short-wave band passes through, and reflects the light in the long-wave band. Therefore, the picosecond laser is reflected and finally focused vertically on the processing surface of the ingot through the focusing lens 10.

[0070] The dichroic beam splitter 14, the last reflector of the total reflector assembly 8, the focusing lens 10, the eyepiece 11, and the CCD camera 12 are all fixed on the motion panel, the processing platform 5, the motion panel 6, the data processor 4, and the four-axis SCARA robot 3 are all electrically connected to the controller, and the processing platform 5 and the motion panel 6 are both driven by a motor, and the motor is electrically connected to the controller. The controller drives the motor and adjusts the position of the motion panel 6 in the Z-axis direction to achieve the control of the laser focus depth.

[0071] Example

[0072] This embodiment pre-treats a silicon carbide ingot that needs to be laser-modified, and specifically includes the following steps:

[0073] (1) placing a silicon carbide ingot on a preparation tray 1, scanning the surface of the ingot with a three-dimensional topography scanner 2, and obtaining point cloud data of the ingot surface topography error;

[0074] The 3D shape scanner 2 uses 3D structured light imaging technology, such as Figure 2As shown, the basic principle is that the light source projects light with a special structure onto the surface of the ingot, the camera captures the reflected information, and the triangulation method is used to calculate the position and depth information of the ingot and generate point cloud data.

[0075] (2) The point cloud data is processed by using the Delaunay triangulation algorithm in the data processor 4. The point cloud is first projected into the XY two-dimensional plane through the normal line, and then the projected point cloud is triangulated in the plane to obtain the topological connection relationship of each point. Finally, the topological connection between the original three-dimensional points is determined according to the topological connection relationship of the projected points in the plane. The obtained triangulated mesh is the reconstructed ingot surface error model.

[0076] (3) Program setting method:

[0077] Based on the ingot surface error model and basic optical principles, the distance ΔZ that the objective lens holder should be adjusted in the vertical direction relative to the calibration position at different points of the ingot is calculated, and the control program is designed based on this calculation method;

[0078] like Figure 3 , 4 As shown in the figure, when the laser is incident vertically on the highest point on the ingot surface and focused inside the ingot, the reference position of the calibration line on the objective lens frame is determined by this highest point, the depth of the ingot modified plane is a, the thickness between the calibration line and the bottom surface of the lens is b, the focal length of the lens is f, the beam diameter of the bottom surface of the lens is 2r, and the incident angle and refraction angle of the laser on the ingot surface are represented by γ and β respectively. After analysis and calculation, we get

[0079]

[0080] The refractive index n of silicon carbide ingot is:

[0081]

[0082] According to the basic optical principles and geometric relationships, the reference position of the calibration line on the lens frame at the highest point on the ingot surface can be determined, and the reference working distance Z0 between the reference position and the ingot modification plane can be calculated:

[0083]

[0084] Then, the highest point on the ingot surface is used as the reference plane, and combined with the obtained ingot surface error model, the distance ΔZ that the objective lens frame should be adjusted in the vertical direction relative to the calibration position at the remaining points is obtained;

[0085] Take laser focusing at any point of the ingot as an example. Figure 5As shown, the inclination angle of the ingot surface is α, and the other parameters remain unchanged; α is the incident angle of the laser optical axis on the ingot surface, β0 is the refraction angle of the laser optical axis on the ingot surface, the incident angles on the left and right sides are α-γ and α+γ respectively, and β1 and β2 are the corresponding refraction angles respectively;

[0086] Combination Figure 5 The refractive index of the silicon carbide ingot at this time is obtained as follows:

[0087]

[0088] According to the above formula and geometric relationship, the distance h between the bottom of the objective lens and the surface of the ingot can be calculated. ′ :

[0089]

[0090] or

[0091]

[0092] Thus, the working distance at this point is obtained (the distance between the calibration line on the objective lens frame and the modified plane:)

[0093] Z=h′+a+b

[0094] The distance that the objective lens holder should be adjusted in the vertical direction relative to the calibration position at this point is:

[0095] ΔZ=Z-Z0

[0096] The control program is designed in the above manner to calculate the distance ΔZ that the objective lens frame at other different points should be adjusted in the vertical direction relative to the calibrated position.

[0097] (4) Based on the result obtained in step (3), the controller sends a control signal to each component, and the four-axis SCARA manipulator 3 absorbs the scanned ingot, controls the rotation angle of each joint of the manipulator through the program, keeps the coordinate system unchanged during the three-dimensional morphology scanning, and translates the ingot to the processing platform 5 and fixes the ingot by vacuum adsorption. The pulsed picosecond laser 7 is turned on, and the picosecond laser is vertically focused downward on a preset horizontal plane inside the ingot through the reflection of multiple reflectors, dichroic beam splitter 9 and the action of focusing lens 10, and controls the moving speed and distance of the processing platform 5 in the X and Y directions and the moving panel 6 in the Z direction, so that the two cooperate during the pre-processing process to ensure that the laser can be focused on the same horizontal plane inside the ingot for direct writing processing. After the processing is completed, the pulsed picosecond laser 7 is turned off, and the four-axis SCARA manipulator 3 transfers the silicon carbide ingot for subsequent peeling process.

[0098] Therefore, the present invention provides a silicon carbide ingot pre-processing process method, which realizes adaptive control of laser focus through ingot morphology error detection and reconstruction algorithm, and performs pre-processing on the ingot surface, thereby reducing the influence of the ingot three-dimensional morphology on the subsequent stripping quality.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A silicon carbide ingot pre-processing process, characterized in that: The following steps are involved: S1. Place the ingot in a material preparation tray, and use a three-dimensional topography scanner to scan the surface of the ingot to obtain point cloud data of the ingot surface topography error; S2. Based on the obtained point cloud data, the ingot surface error model is reconstructed by using the Delaunay triangulation algorithm. Specifically, the point cloud data is first projected into the XY two-dimensional plane through the normal line, and then the projected point cloud is triangulated in the plane to obtain the topological connection relationship of each point in the plane projection, and the topological connection between each original three-dimensional point is determined to obtain the reconstructed ingot surface error model. S3, based on the ingot surface error model and the basic optical principle, a calculation program is set to calculate the distance that the objective lens holder at different points of the ingot should be adjusted in the vertical direction relative to the calibration position; comprising the following steps: 1) According to the highest point of the ingot surface at which the laser is incident vertically, determine the reference position of the calibration line on the objective lens frame, and calculate the reference working distance between the reference position and the ingot modification plane ; ； in, is the distance between the bottom of the objective lens and the surface of the ingot, is the depth of the ingot modification plane, is the thickness between the calibration line and the bottom surface of the lens; h The calculation formula is: ； ； r is the radius of the light beam at the bottom of the lens, γ is the incident angle of the laser on the surface of the ingot, β is the refraction angle of the laser on the surface of the ingot, is the focal length of the lens; When the laser is incident vertically on the surface of the ingot, the refractive index of the silicon carbide ingot is n for: ； According to calculation ； 2) Take the highest point on the ingot surface as the reference plane, and combine the obtained ingot surface error model to calculate the working distance at any point on the ingot surface when the laser is incident on that point. ; ； When the ingot surface is tilted at an angle of α, the incident angle of the laser light axis on the ingot surface is also α. The refractive index of the silicon carbide ingot is n for: ； in, This is the refraction angle of the laser optical axis on the surface of the ingot; ； or ； in, , are the refraction angles on the left and right sides respectively; 3) By calculating, the distance that the objective lens holder should be adjusted in the vertical direction relative to the calibration position at different points of the crystal ingot is obtained ; It is expressed as: ； S4. Based on the results obtained in S3, the controller sends control signals to each component, and the four-axis SCARA manipulator absorbs the scanned ingot, controls the rotation angle of each joint of the manipulator through the program, keeps the coordinate system unchanged during the three-dimensional morphology scanning, translates the ingot to the processing platform and fixes the ingot through vacuum adsorption; the pulsed picosecond laser is turned on; Wherein, an optical path system is arranged on the optical path of the pulsed picosecond laser, and the optical path system includes a total reflection mirror combination, a dichroic beam splitter and a focusing lens arranged in sequence along the optical path, and the last reflection mirror on the total reflection mirror combination is arranged in parallel with the dichroic beam splitter; the laser output from the picosecond laser is transmitted to the surface of the dichroic beam splitter through the reflection effect of the total reflection mirror combination arranged along the optical path, and the dichroic beam splitter adopts a short-wave light-passing plate, and the light in the short-wave band passes through and reflects the light in the long-wave band, and the picosecond laser is reflected and finally vertically focused on the processing surface of the ingot through the focusing lens; The picosecond laser is focused vertically downward on a preset horizontal plane inside the ingot through the reflection of multiple mirrors, dichroic beam splitters and the action of a focusing lens, controlling the movement speed and distance of the processing platform in the X and Y directions and the motion panel in the Z direction, so that the two can cooperate during the pre-processing process to ensure that the laser can be focused on the same horizontal plane inside the ingot for direct writing processing; after the processing is completed, the pulsed picosecond laser is turned off, and the four-axis SCARA robot transfers the silicon carbide ingot for subsequent peeling process.

2. The method for pre-processing a silicon carbide ingot according to claim 1, characterized in that: In S1, 3D structured light imaging technology is used to project light onto the surface of the ingot using a light source, and the reflected information is captured by a camera. The position and depth information of each location of the ingot is calculated using triangulation and point cloud data is generated.

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