High-Efficiency SiC Polishing: Exploring Advanced Polishing Techniques
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Silicon carbide semiconductor has the characteristics of high thermal conductivity, wide bandgap, high breakdown electric field, and high electron mobility, making it one of the semiconductor materials currently being researched and developed. However, in practical applications, silicon carbide is very hard, with a Mohs hardness of about 9.5, close to diamond. The current chemical reaction polishing technology represented by CMP is an important means of processing SiC substrates, but the processing efficiency is very low, and the material removal rate can only reach about 0.5 µ m/h. Therefore, researchers have studied the wafer polishing process of the superhard material, the details as follows:
1. SiC Substrate Polished by Metal Friction Induced Reaction Grinding Technology
The metal friction induced reaction grinding technology is mainly based on the principle of metal friction induced chemical action, and achieves high-speed removal of silicon carbide in the cyclic process of continuous generation and removal of the reaction modified layer.
Although SiC wafer has a very high Mohs hardness, it is not suitable for processing black metals because SiC decomposes at high temperatures, and carbon and silicon atoms diffuse into the metal to form metal silicides and unstable metal carbides. During the cooling process, it gradually decomposes, causing extremely severe wear. Based on this characteristic, it is inferred that pure metals can undergo chemical reactions with silicon carbide under certain conditions.
During the experimental process, the carbon(C) surface of the SiC substrate often has a nearly undamaged surface, while the silicon(Si) surface has a large number of crystal defects such as cracks, dislocations, stacking faults, and lattice distortions. The removal rate of carbon surface material on SiC substrate by iron friction can reach 330 µ m/h. The removal rate of Si surface material on SiC substrate rubbed with pure nickel is 534 µ m/h.
At present, there is relatively little research on this method, mainly focusing on the processing of small-sized SiC. However, it has great potential in the grinding and polishing of SiC substrates and the thinning of SiC chips.
2. Sol Gel Polishing Technology on SiC Substrate
Sol gel polishing technology is a green and efficient polishing method. Through the use of semi consolidated abrasives and flexible substrates, and by virtue of the flexible characteristics of soft substrates, the “containment” effect of abrasive particles is achieved to achieve ultra smooth and low defect density surfaces on extremely hard semiconductor substrates. This method combines chemical and mechanical actions to effectively polish extremely hard semiconductor substrates without causing severe surface or subsurface damage.
Compared with the traditional CMP, the sol gel polishing technology can significantly reduce the surface roughness in a short time, and achieve a higher material removal rate; Due to its good flexibility, soft substrates can work under lower polishing pressures, reducing the pressure requirements on workpieces and equipment, minimizing wear and detachment of abrasives, and extending the service life of abrasives.
Precursor substances (usually metal organic compounds) are converted into sol, and gel is formed through hydrolysis and condensation reaction. In the sol gel polishing pad, abrasive particles are partially fixed in the gel matrix, which can provide a certain mechanical strength while maintaining the activity of abrasive particles. Scholars have used this technology to process the (111) surface of HTHP single crystal diamond. After polishing for 22 hours, the surface roughness decreased from 230nm to 1.3nm.
3. Grinding and Polishing Technology for Inducing Silicon Carbide Water Reaction Through Abrasive Grain Scratching
The grinding and polishing technology induced by abrasive scratching and water reaction of SiC is an advanced material processing technology, mainly used for precision machining of hard and brittle materials such as SiC.
This technology utilizes the scratching effect of abrasive particles on the SiC surface during processing, combined with water reaction to improve the removal efficiency and surface quality of the material. By controlling the inclusion effect of abrasive particles to maintain them at the same height, amorphous SiC is induced to form on the SiC surface through abrasive scratching. Amorphous SiC can react with water to produce soft silica, and then the deteriorated layer of silica is removed through abrasive scratching.
At the nanoscale, the surface of SiC substrate will be induced to become amorphous silicon carbide under repeated mechanical action of diamond pressure head. The influencing factors of the reaction between amorphous silicon carbide and water to generate silicon dioxide include load, contact state, speed, and temperature. By rational utilization of this process, the processing efficiency and surface quality of SiC substrates can be significantly improved, and the generation of cracks can be reasonably avoided.
These processing technologies are expected to achieve wider applications in improving the processing efficiency and surface quality of hard semiconductor substrates, especially in the processing of large-sized SiC substrates, demonstrating enormous potential. With the advancement of intelligent manufacturing and materials science, these technologies may be further optimized, driving the development of fields such as semiconductors and optoelectronics.
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