Hybrid polishing of mm-TSVs using laser cavitation-driven micro-abrasive erosion and laser-enhanced electrochemical corrosion

H Zhu and WJ Zhang and WB Xie and ZY Zhang and J Wang and YX Ye and K Xu and M Chen and Y Liu and JQ Wu and JT Wang, JOURNAL OF MANUFACTURING PROCESSES, 155, 1113-1132 (2025).

DOI: 10.1016/j.jmapro.2025.10.070

Laser drilling shows significant potential for processing large-sized through silicon vias (TSV). However, its application is often limited by associated thermal damage and poor surface roughness. This study proposes a hybrid polishing method for millimeter-sized TSV (mm-TSV), combining laser cavitation-driven micro-abrasive erosion and laser- enhanced electrochemical corrosion (ECC) effects. Specifically, the electrical conductivity of silicon (Si) is locally enhanced through laser-induced thermal and photoconductive effects, strengthening ECC on the inner walls and forming a soft oxide layer. Simultaneously, the laser-induced cavitation effect drives suspended micro-abrasives to erode the softened inner wall. In this way, the abrasive erosion and ECC effects can be coupled and reinforce each other, realizing green polishing of mm-TSV in a neutral NaNO3 electrolyte. Experiments on laser-enhanced ECC of Si were firstly conducted, and surface morphology observations and nano-indentation tests demonstrated that increasing laser power or external voltage promotes localized ECC, resulting in reduced surface hardness and Young's modulus. In addition, polishing tests for mm-TSV were performed, comparing the polishing results caused by various combinations of laser irradiation, micro-abrasives and ECC. Results indicated that the synergistic involvement of three factors achieved the most significant polishing effect, reducing surface roughness from an initial 2950 nm to 311 nm with a reduction of 89.5 %, while the surface oxide content was also decreased. Moreover, temperature field modeling was conducted to quantitatively analyze the enhancement of inner wall conductivity by laser irradiation, and theoretical calculations of laser-induced breakdown in liquid was carried out, estimating a threshold of around 11.94 GW/cm2 in this study and hence guaranteeing laser cavitation phenomenon. Furthermore, molecular dynamics (MD) simulation of a single abrasive erosion of Si surface revealed multiple rebound oscillation stages, in which the erosion area, subsurface amorphous zone, and the impact caused stress and strain evolve dynamically. Meanwhile, the influences of impact velocity and angle on the erosion results were quantitatively discussed, and characterizations of experimental scratching results were also conducted, demonstrating consistent variation trends in ratios of erosion depth/width to particle size between experimental tests and MD predictions.

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