Investigation of low-cost through glass vias formation on borosilicate glass by picosecond laser-induced selective etching

This paper reports selective etching process of borosilicate glass by laser-induced deep etching (LIDE) for through glass via (TGV) applications. Picosecond laser is used to modify the glass substrate, and then, with the help of the laser-induced selective etching (LISE), the modified glass samples are etched by hydrofluoric acid (HF) solution to complete the manufacture of TGV in the present experiments. Here we experimentally study the micro mechanism of LISE on borosilicate glass. At the laser affected zone (LAZ), a series of nanovoids along the path of laser beam propagating are observed, which contribute to enhanced etchability of LAZ when the glass sample is immersed in HF solution. Further, the mechanism of the fabrication of TGV is investigated, and the effect of key factors, including laser pulses, the concentration of HF solution and the chemical composition of borosilicate glass on TGV profile are studied. When compared with laser pulses, the effect of concentration of HF solution and the chemical composition on TGV profile is more remarkable. Optimized results show that vertical vias (~ 90  $$^\circ$$ ) can be achieved on borosilicate glass.