Sapphire is one of the important substrate materials for LED, and the surface of the sapphire wafer as the substrate of LED must be ultra-smooth without damage. The research shows that the quality of the device relies heavily on the surface processing technology of the substrate, so the processing technology that how to make sapphire wafer with super smoothness and little or no damage has become an urgent problem to be solved in the industry. At present, there are many polishing methods for sapphire wafers, but only chemical mechanical polishing technology can obtain a lower surface roughness and a higher material removal rate with rather low cost. Next, we will analyze the effects of different abrasives on chemical mechanical polishing of sapphire wafers.
The surface quality of sapphire wafers before polishing is very poor. But, after polishing with different abrasives, the surface roughness of sapphire wafer is slightly different. The surface roughness of sapphire wafers after polishing with silica sol is the lowest with smooth surface without obvious fluctuation. However, the surface quality after polishing with carbonization or alumina abrasive polishing solution is relatively poor, silicon carbide polished surface scratches are more, alumina polished surface has obvious fluctuations.
The removal rate of silica sol is the highest (MRR=34.1nm/min), silicon carbide is the second (MRR=24.0nm/min), and alumina is the lowest (MRR=20.2nm/min). This may be because under the condition of the same mass concentration of abrasive, the larger the particle size is, the less the number of effective particles involved in grinding will be. Meanwhile, under the same polishing pressure, the greater the pressure of a single particle will have. After polishing, the surface roughness Ra is proportional to the average cutting depth.
Alumina has the largest particle size, followed by silicon carbide, and silica sol is the smallest. Therefore, at the same concentration, silica sol has the most effective particles in grinding, and the single particle bears less pressure, so the surface roughness is the lowest and the removal rate is the highest. Moreover, the Mohs hardness of silicon carbide is the biggest, and the greater the hardness is, the greater the mechanical effect is, which means the more serious the damage is, so the surface roughness of silicon carbide polished is the highest.
Conclusion: After three different abrasives (SiC, Al2O3, SiO2) are used for chemical mechanical polishing of sapphire wafers, it is found that the removal rate of silica sol is the highest (MRR= 34.1nm /min), and the surface roughness is the lowest Ra=1.7nm.