Towards understanding uniformity of megasonic-assisted through-mask electrochemical micromachining based on bubble dynamics

In through-mask electrochemical micromachining (TMEMM), bubbles on the anode surface can lead to ohmic voltage drop and non-uniform conductivity distribution, resulting in lower etching accuracy. With the advantages of low cavitation effect, strong acoustic streaming and high acoustic intensity, megasonic facilitates the reduction of bubble accumulation on the anode surface, thus improving etching accuracy. In this paper, a multiphysics field simulation model is developed to predict the two-phase flow evolution and etching profile at the anode interface. The simulation results show that the gas content at the anode interface in the megasonic field is low, and the gas distribution is relatively uniform. The etching depth and etching uniformity of TMEMM are improved. Experiments demonstrate the accuracy of the proposed simulation model. In addition, micro pits array with CVdiameter and CVdepth of 2.28 % and 5.70 %, respectively, were prepared using the MA-TMEMM method. Visualization experiments systematically study the machining mechanism of MA-TMEMM. The underlying dynamic force balance on the gas bubble is analyzed to illustrate the mechanism and experimental observations. Finally, the advantage of megasonic in removing bubbles from the anode surface to improve etching uniformity was demonstrated by counting the detached bubble diameter and effective coverage.