Method for efficiently modifying silicon carbide substrate through in-situ liquid phase assisted laser

Abstract

A method for in-situ liquid phase assisted laser efficient modification of a silicon carbide substrate comprises the following steps: modifying under a laser liquid phase, placing a to-be-modified SiC substrate on an objective table under the liquid phase for fixing, and irradiating the surface of the to-be-modified SiC substrate by using a picosecond laser to realize local and global ablation / modification; the objective table device can freely ascend and descend and is used for controlling the focusing position of the laser beam; deionized water or a free abrasive system can be adopted in a liquid phase, kinetic energy is generated under the rotation effect of a magnet, the kinetic energy is used for reducing sputtering and surface / subsurface hot cracks of the SiC substrate under the high-temperature effect, and a laser-modified recast layer and chippings can be effectively removed; a laser beam vertically irradiates the surface of the SiC substrate; laser catalysis: laser can be used for catalyzing chemical reagents in the solution, so that the solution is catalyzed while modification is carried out, the mechanical property of SiC is improved, and the modification efficiency is remarkably improved.

Description

Technical Field

[0001] The invention relates to a silicon carbide substrate processing technology, in particular to a silicon carbide substrate laser modification technology, specifically to a method for in-situ liquid phase assisted laser efficient modification of silicon carbide substrates. Background Art

[0002] As third-generation semiconductor materials, silicon carbide, gallium nitride, etc. have superior physical properties in terms of bandgap width, breakdown electric field strength, thermal conductivity, etc. They are in great demand in the fields of national defense, military, aerospace, 5G communications, artificial intelligence, automotive electronics, and LED lighting, and have important application value and broad development prospects. In addition, it is used in semiconductor materials due to its superior capabilities caused by high temperature and high frequency. Under normal circumstances, SiC is mostly used for device epitaxy. Since the quality (defects) of the substrate surface will directly affect the quality of epitaxy and the service life of the device. Therefore, the quality of the substrate surface plays a vital role in the field of electronic integrated manufacturing. However, SiC has high mechanical hardness (Mohs hardness 9.4) and strong chemical stability (decomposition temperature 1700K, SiC melting temperature 3100K, C melting temperature 4000K), which makes it difficult to achieve high removal rates by conventional technical means.

[0003] Compared with traditional processing methods, the laser transient power density can be as high as 10 13 W / cm 2 , can oxidize, melt and evaporate any material, so laser can be used as the most effective method for modifying SiC slices. This is a modification technology that selectively melts and evaporates materials by setting corresponding laser parameters. Its advantages are non-contact, no tool wear, high flexibility, good modification quality, controllable modification depth, small heat-affected zone, etc., which has aroused great interest in laser processing at home and abroad. In addition, the laser beam can be focused on the spot diameter of micrometer to submicrometer through the optical system, so the laser can be used for local or global fine modification of SiC slices to prepare microscopic feature components and functional texture structures with special functions. This laser texture modification technology does not require the use of any chemical reagents, is green and harmless to the environment, has no subsequent processing steps, greatly improves processing efficiency and reduces processing costs, and is an effective method for efficient modification of SiC. However, compared with ultrashort pulses, continuous pulses have more intuitive efficiency, but it is inevitable that high-precision texture structures cannot be obtained. Therefore, how to improve the efficiency of ultrashort pulse modification / ablation and obtain high-quality modification is the key to realizing large-scale industrial application of semiconductor substrates.

[0004] Among the existing pretreatment technologies, picosecond laser assisted chemical mechanical polishing (CMP) achieves efficient processing of SiC substrates. However, this method alone can only achieve a material removal rate of 3.67μm / h within the first 45 minutes, and the structure caused by picosecond laser modification cannot be completely removed. In addition, a chemical mechanical polishing method for silicon carbide crystals based on liquid phase laser technology has also been proposed in the prior art. It can be seen from the examples that it cannot take into account both efficiency and surface quality. It can be seen that the chemical mechanical polishing method for silicon carbide crystals using the currently known laser assisted CMP and liquid phase laser technology cannot solve the problems of low efficiency of existing ultrashort pulse pretreatment and low utilization of underwater laser energy. Summary of the invention

[0005] The purpose of the invention is to invent a method for in-situ liquid-phase assisted laser efficient modification of silicon carbide substrates in order to address the problems that the existing ultrashort pulse processing efficiency is low and efficient removal and surface quality cannot be satisfied simultaneously.

[0006] The technical solution of the present invention is:

[0007] A method for in-situ liquid phase assisted laser efficient modification of silicon carbide substrate, characterized in that it comprises the following steps:

[0008] Step 1, cleaning the SiC substrate 10;

[0009] Step 2: Using the driving motor 8 to rotate the ball screw 2, driving the nut pair 7 to raise the stage 9 to the outside of the liquid medium container 1;

[0010] Step 3, the cleaned SiC substrate 10 is heated by a laboratory heating table, and the surface bonded to the stage 9 is evenly coated with paraffin wax, and then the SiC substrate 10 is placed at the center of the stage 9, and the SiC substrate 10 is cooled to room temperature and solidified on the stage 9;

[0011] Step 4, adding deionized water or free abrasive solution into the liquid medium container 1 to 2 / 3 of the capacity of the liquid medium container 1;

[0012] Step 5, the operation process is reversed to step 2, so that the stage 9 is lowered to within 1-10 mm below the horizontal plane of the liquid medium;

[0013] Step 6: The magnetic stirrer 4 is rotated, and the rotor connected to the magnetic disk 3 drives the magnet 11 to rotate to obtain kinetic energy, thereby driving the magnetic stirrer 4 to stir the deionized water or free abrasive solution in the liquid medium container 1;

[0014] In step 7, the spot of the laser beam 6 is focused on the surface of the SiC substrate 10 through deionized water or free abrasive solution; the laser parameters are set as follows: laser power 60-80W, pulse width 1-10ps, laser scanning speed 80-200mm / s, laser repetition frequency 100-200kHz; the laser beam scanning path is modified / ablated according to the matching pattern of the picosecond laser.

[0015] In short, the modification method of the present invention is to modify the SiC substrate by laser in liquid phase, the SiC substrate to be modified is placed on a stage in liquid phase and fixed, a picosecond laser is used to irradiate the surface of the SiC substrate to be modified, and local and global ablation / modification are achieved; the stage device can be freely raised and lowered to achieve the control of the focusing position of the laser beam; the liquid phase rotation system can use deionized water or a free abrasive system in the liquid phase to generate kinetic energy under the action of magnet rotation, which is used to reduce sputtering and surface / subsurface thermal cracks of the SiC substrate under high temperature, and can effectively remove the recast layer and debris after laser modification; the laser beam is vertically irradiated on the surface of the SiC substrate; laser catalysis, the laser can catalyze the chemical reagents in the solution, so as to catalyze the solution while modifying, improve the mechanical properties of SiC, and achieve a significant improvement in the modification efficiency.

[0016] in:

[0017] The lifting and lowering of the stage device is controlled by a ball screw, which is equipped with a limit device and started and stopped by a servo motor.

[0018] The maximum position of the stage upper limit is 1 mm beyond the liquidus plane, and the lower limit is 10 mm below the liquidus plane.

[0019] The liquid phase rotating system can obtain different rotation levels of kinetic energy through the magnet under the action of the magnetic stirrer.

[0020] The liquid phase rotating system can reduce the sputtering and thermal impact of the material during the modification process through the rotational kinetic energy, and prevent the generation of surface / subsurface thermal cracks.

[0021] The liquid phase rotation system can effectively remove the recast layer and debris after laser modification through rotational kinetic energy.

[0022] The laser beam of a picosecond laser has a Gaussian distribution.

[0023] The laser beam of the picosecond laser is vertically irradiated on the surface of the SiC substrate to be processed.

[0024] The liquid medium is deionized water or a free abrasive system.

[0025] If the liquid medium is free abrasive, the catalysts that can be selected are H2O2, NaOH, and KMnO4.

[0026] If the liquid medium is a free abrasive, a chemical reaction will occur under the high temperature of the laser.

[0027] Liquid medium improves the mechanical properties of SiC under the action of laser high temperature catalysis and improves the efficiency of laser modification / ablation.

[0028] The beneficial effects of the present invention are:

[0029] The present invention uses laser direct writing technology to achieve surface modification / ablation removal. At the same time, the mechanical properties of SiC are changed through laser high-temperature catalytic liquid phase medium, further improving the efficiency of picosecond laser modification / ablation. In addition, deionized water / free abrasives can effectively reduce material sputtering and surface / subsurface thermal cracks under the action of rotational kinetic energy, and can remove recast layers and debris. In-situ efficient, high-quality, low surface / subsurface damage modification / ablation of SiC substrates can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the in-situ liquid phase assisted laser efficient modification of SiC substrate of the present invention.

[0031] Figure 2 The invention relates to a ball screw mechanism for in-situ liquid phase assisted laser efficient modification of SiC substrates.

[0032] Figure 3 The invention discloses a magnetic stirrer for in-situ liquid phase assisted laser efficient modification of SiC substrate.

[0033] Figure 4 It is a schematic diagram of the three-dimensional structure of the in-situ liquid phase assisted laser high-efficiency modification device of the present invention.

[0034] Figure 5 This is a TEM morphology image of a SiC substrate after in-situ liquid phase assisted laser efficient modification of the present invention.

[0035] In the figure: 1 is a liquid medium container, 2 is a ball screw, 3 is a magnetic disk, 4 is a magnetic stirrer, 5 is a screw base, 6 is a laser beam, 7 is a nut pair, 8 is a driving motor, 9 is a stage, 10 is a substrate material, and 11 is a magnet. DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention are further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] A SiC substrate in-situ modification / ablation processing method, comprising the following steps:

[0038] Step 1, cleaning the SiC substrate 10;

[0039] In the second step, the ball screw 2 is rotated by the driving motor 8, and the driving nut pair 7 is used to raise the stage 9 to the outside of the liquid medium container 1.

[0040] Step 3, heat the cleaned SiC substrate 10 on a heating table in the laboratory, evenly apply paraffin wax on the surface bonded to the stage 9, then place the SiC substrate 10 at the center of the stage 9, and wait for the SiC substrate 10 to cool to room temperature and solidify on the stage 9.

[0041] Step 4: Add liquid medium into the liquid medium container 1 to 2 / 3 of the capacity of the liquid medium container 1.

[0042] Step 5, the operation process is reversed to step 2, so that the stage 9 is lowered to within 1-10 mm below the horizontal plane of the liquid medium.

[0043] Step 6: Set the corresponding rotation level (1, 2, 3) according to the magnetic stirrer 4, usually the 1st level speed is 350-500 rpm, the 2nd level speed is 500-1000 rpm, and the 3rd level speed is 1000-1800 rpm; the magnet size range is 20-30 mm; rotate clockwise, and the rotor connected to the disk 3 drives the magnet 11 to rotate to obtain kinetic energy.

[0044] Step 7, the spot of the laser beam 6 is focused on the surface of the SiC substrate 10 through the liquid medium. The laser parameters are set as follows: laser power 60-80W, pulse width 1-10ps, laser scanning speed 80-200mm / s, laser repetition frequency 100-200kHz. The laser beam scanning path is modified / ablated according to the graphics designed in the picosecond laser supporting software.

[0045] In specific implementation, the liquid medium can be deionized water or free abrasive (using the abrasive of the following formula (mass percentage, propylene glycol: 1%, H2O2: 3%, NaOH: 0.5%, diamond powder (W5: domestic micron grade): 1-3%, the balance is deionized water). According to the pressure level that the object needs to withstand underwater (10 meters underwater corresponds to 1 bar / 14.7 psi), the material removal rate when the workpiece is 2 mm underwater and the level 2 rotation speed is 800 rpm can be calculated by the following formula.

[0046] MRR=KPV

[0047] Where MRR—material removal rate;

[0048] K—Preston coefficient;

[0049] P—corresponds to the water pressure at 2mm, which is 0.00294psi after calculation;

[0050] V—speed.

[0051] In the specific processing process, after the SiC substrate 10 has been processed in steps 1 to 3 above, deionized water or free abrasive is added to the liquid medium container 7 to 2 / 3 of the capacity of the liquid medium container 1, and steps 5 to 6 are repeated. The ball screw 2 is driven by the driving motor 8 to rotate, and the nut pair 7 is driven downward / upward to drive the stage 9 downward / upward to achieve the focus (positive focus / negative focus, relative to the focus position of the SiC substrate surface) modification / ablation of the laser beam, and the laser parameters are set as follows: laser power 60-80W, pulse width 1-10ps, laser scanning speed 80-200mm / s, laser repetition frequency 100-200kHz.

[0052] Example 1.

[0053] This example uses a TruMicro5050 infrared (1064) picosecond laser made by TRUMPF. The laser power is 1-100W and the frequency is 1-200kHz. The picosecond laser modification / ablation of SiC substrate is performed underwater. The parameters of the picosecond laser used are shown in Table 1. The microgroove profile of the SiC substrate surface obtained by the present invention is clearer, and no obvious sputtered particles and cracks appear on the surface.

[0054] Table 1

[0055]

[0056] Example 2.

[0057] This example uses the TruMicro5050 infrared (1064) picosecond laser produced by TRUMPF of the United States. The laser power is 1 to 100W, the frequency is 1-200kHz, and the picosecond laser modification / ablation of the SiC substrate is performed underwater. The parameters of the picosecond laser used are shown in Table 2. The microgrooves on the surface of the SiC substrate obtained by the present invention are deeper, indicating a greater material removal efficiency. No obvious sputtered particles and recast layers appear on the surface, and there are no obvious cracks on the subsurface. In addition, the surface sputtered particles and recast layers (the main components after laser modification / ablation are single crystal Si and SiO2 (the hydroxyl groups produced by the laser high-temperature catalysis of the free abrasive are washed away under the action of the kinetic energy of the liquid phase, and on the other hand, the catalyzed hydroxyl groups react with single crystal Si and SiO2 under the action of high temperature during the laser modification / ablation process to achieve material removal; and the SiC substrate is corroded simultaneously)) and the microcracks caused by thermal cycles on the subsurface are eliminated. Figure 5It can be seen that the in-situ modification / ablation efficiency is improved while the surface quality is guaranteed.

[0058] Table 2

[0059]

[0060] Example 3.

[0061] This example uses the TruMicro5050 infrared (1064) picosecond laser produced by TRUMPF. The laser power is 1-100W, the frequency is 1-200kHz, and the picosecond laser modification / ablation of SiC substrate is performed underwater. The parameters of the picosecond laser used are shown in Table 3. Using a defocusing amount of +1mm (i.e., the distance from the liquid phase layer to the SiC substrate is 2mm), the SiC substrate obtained by the present invention has no surface sputtered particles, and the surface quality is improved.

[0062] Table 3

[0063]

[0064] Example 4:

[0065] This example uses the TruMicro5050 infrared (1064) picosecond laser produced by TRUMPF. The laser power is 1-100W, the frequency is 1-200kHz, and the picosecond laser modification / ablation of the SiC substrate is performed underwater. The parameters of the picosecond laser used are shown in Table 4. Using a defocusing amount of +1mm (i.e., the distance from the liquid phase layer to the SiC substrate is 2mm), the SiC substrate obtained by the present invention has no surface sputtered particles and recast layers, and a greater profile depth is obtained compared to Example 3. The in-situ improvement of the modification / ablation efficiency is achieved while ensuring the surface quality.

[0066] Table 4

[0067]

[0068] The present invention does not involve parts that are the same as the prior art or can be implemented by using the prior art.

Claims

1. A method for in-situ liquid phase assisted laser efficient modification of silicon carbide substrate, characterized in that: The following steps are involved: Step 1, cleaning the SiC substrate (10); Step 2: Using a driving motor (8) to rotate the ball screw (2) and drive the nut pair (7) to raise the stage (9) to the outside of the liquid medium container (1); Step 3, heating the cleaned SiC substrate (10) on a heating table in the laboratory, evenly coating the surface bonded to the stage (9) with paraffin wax, then placing the SiC substrate (10) at the center of the stage (9), and waiting for the SiC substrate (10) to cool to room temperature and solidify on the stage (9); Step 4, adding deionized water or free abrasive solution into the liquid medium container (1) to 2 / 3 of the capacity of the liquid medium container (1); Step 5, performing the operation process opposite to step 2, so that the stage (9) is lowered to within 1-10 mm below the horizontal plane of the liquid medium; Step 6, the magnetic stirrer (4) is rotated, and the rotor connected to the magnetic disk (3) drives the magnet (11) to rotate to obtain kinetic energy, thereby driving the magnetic stirrer (4) to stir the deionized water or free abrasive solution in the liquid medium container (1); In step 7, the spot of the laser beam (6) is focused on the surface of the SiC substrate (10) through deionized water or a free abrasive solution; the laser parameters are set as follows: laser power 60-80 W, pulse width 1-10 ps, ​​laser scanning speed 80-200 mm / s, laser repetition frequency 100-200 kHz; the laser beam scanning path is modified / ablated according to the matching pattern of the picosecond laser.

2. The method according to claim 1, characterized in that: The ball screw (2) is driven to rotate by a driving motor (8), and the nut pair (7) is driven to move the stage (9) downward / upward to achieve defocus modification / ablation of the laser beam. The laser parameters are set as follows: laser power 60-80W, pulse width 1-10ps, laser scanning speed 80-200mm / s, and laser repetition frequency 100-200kHz.

3. The method according to claim 1, characterized in that: The lifting and lowering of the loading platform device is controlled by a ball screw equipped with a limit device, and is started and stopped by a servo motor.

4. The method according to claim 1, characterized in that: The upper limit position of the stage lifting is 1 mm above the liquid phase plane, and the lower limit position is 10 mm below the liquid phase plane.

5. The method according to claim 1, characterized in that: The liquid phase rotation system can obtain kinetic energy of different rotation levels through a magnet under the action of a magnetic stirrer; the liquid phase rotation system can reduce the sputtering and thermal impact of the material during the modification process through the rotational kinetic energy, and prevent the generation of surface / subsurface thermal cracks; the liquid phase rotation system can effectively remove the recast layer and debris after laser modification through the rotational kinetic energy.

6. The method according to claim 1, wherein the laser beam of the picosecond laser presents a Gaussian distribution, and the laser beam is vertically irradiated on the surface of the SiC substrate to be processed.

7. The method for in-situ liquid phase assisted laser efficient modification of silicon carbide substrate according to claim 1, characterized in that: The liquid medium is deionized water or a free abrasive system.

8. The method according to claim 1, characterized in that: If the liquid medium is free abrasive, H2O2, NaOH, or KMnO4 is selected as the catalyst.

9. The method according to claim 1, characterized in that: If the liquid medium is free abrasive, a chemical reaction occurs under the action of high temperature of the laser.

10. The method according to claim 1, characterized in that: The liquid phase medium improves the mechanical properties of SiC under the high-temperature catalytic effect of laser, thereby increasing the laser modification / ablation efficiency.

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