Effects of Frequency on the Performance of Ultrasonic Vibration Assisted Chemical Mechanical Polishing for Sapphire

Sapphire (Al2O3) is renowned for its exceptional properties, yet its unique natural presents a surface processing challenge. To enhance the polishing quality and efficiency, the sapphire ultrasonic vibration assisted chemical mechanical polishing (UV-CMP) has been proposed. This paper employs computational fluid dynamics (CFD) simulation and polishing experiments to investigate the action and mechanism of ultrasonic frequency on sapphire UV-CMP. The CFD simulation reveals that an increase in frequency can effectively elevate the fluid velocity, pressure, and cavitation. The enhancement in pressure, Z-direction, and resultant velocity has a positive impact on the cutting ability and utilization rate of nano-abrasives. A high frequency can enhance the physical fields of slurry, but it suppresses the growth of cavitation bubbles, and is detrimental to the number and size of abrasive particles. The best processing performance of sapphire UV-CMP is obtained at 40 kHz due to coordinated physicochemical interactions. X-ray photoelectron spectroscpy proves the product of solid-solid chemical reaction between nano-SiO2 and sapphire is softer Al2Si2O7 instead of Al2SiO5, which is beneficial to the material removal. This article provides theoretical and practical guidance for sapphire UV-CMP.