Abstract
The broad applications of sapphire substrates in many fields warrants an urgent demand for a highly efficient and high precision polishing method for the sapphire substrates. The authors proposed a novel sapphire substrate polishing method that is based on the dielectrophoresis (DEP) effect. The principle of dielectrophoresis polishing (DEPP) is described. A non-uniform electric field was added in the polishing area to drive abrasives moving in the direction towards the plate by the DEP force. The amount of abrasives that participates in the polishing action increases as the distribution of polishing slurry on sapphire surface changes, leading towards the improvement of sapphire polishing both in quality and efficiency. Comparative experiments between DEPP and traditional chemical mechanical polishing (CMP) were carried out. It was found that the maximum increase of sapphire MRR for DEPP is 71%, reaching 13 mg/h, and the minimum increase was 9.5%, reaching 4.6 mg/h. The surface roughness of the sapphire substrate decreases faster and more uniform with DEPP. The final surface roughness of the sapphire substrate after DEPP was Ra 0.87 nm and the flatness was 0.3078 waves (RMS value), which is better than 0.6863 waves (RMS value) of sapphire substrate with traditional CMP polishing.
Highlights
Sapphire has many special characteristics such as high hardness, great thermal stability, good light transmission, excellent electrical insulation and chemical inertness [1]
In the same time, polishing slurry that follows the abrasives tends to move towards the sapphire non-uniform electric field, and the abrasives are polarized subject to force, as shown in Figure being electrically charged, and the direction of the force points towards the electrode
The simulation results show that the abrasive can still move towards the surface of the workpiece when it is subjected to both DEP force and centrifugal force, which indicates that the idea of using the DEP effect of abrasive to assist polishing is feasible
Summary
Sapphire has many special characteristics such as high hardness, great thermal stability, good light transmission, excellent electrical insulation and chemical inertness [1]. It is widely used in mechanics, optics, electronics, light emitting diodes (LEDs) industry and other fields [2]. When growing thin film on sapphire substrates with a poor surface quality, the film tends to grow preferentially in scratches. The authors apply a non-uniform electric field to produce a DEP effect on polishing slurry consisting of abrasive particles in the polishing area of the traditional polishing machine.
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