Research on the synergistic effect of megasonic and particles in through mask electrochemical etching process

Through-mask electrochemical etching (TMEE) is one of the main methods to fabricate metal microstructures array in large scale. In deep metal microstructure etching process, lateral corrosion problem seriously affects the etching localization. In this paper, megasonic and particle combined through mask electrochemical etching (MP-TMEE) method was proposed to improve the etching localization in TMEE process. Experimental results show that the etching factor (EF) was greatly improved by MP-TMEE method compared to traditional TMEE. With the use of MP-TMEE, when the feature size of the mask was 100 μm, the average diameter and depth of the etched micro pits were 148.7 μm and 59.9 μm. The use of MP-TMEE instead of TMEE leads to an increase in EF from 1.58 to 2.50. Besides, the mechanism of the synergistic effect of megasonic and the particles in MP-TMEE process was investigated. An erosion theoretical model of passivation film was established and verified by electrochemical impedance spectroscopy (EIS) method. The measurement results of EIS show that the micro pit depth and the passivation film resistance have the opposite variation trend, and the passivation film resistance measurement results are consistent with the trend of the theoretical model. Finally, microstructure arrays involving stainless steel micro pit array and micro pillar array, copper micro pit array and micro pillar array were fabricated using MP-TMEE method.