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technical paper
Study of Selective Laser Etching Process With Various Etchants
keywords:
chemical etching
selectivity
bessel beam
through glass via
selective laser etching
As emerging of IoT devices, the ICs should be fast. To fulfill the fast performance, 3D ICs has been adopted. A 3D IC has relatively shorter connection electrode than conventional 2D ICs. And it is achieved by interposer. A interposer has via holes which are filled with conducting materials. In previous studies, various researchers have been suggested glass interposer, so called through glass via (TGV). Since glass has low electric permittivity, thus it is suitable for interposer. Also, glass can match its thermal expansion coefficient with silicon and it can suppress a warpage of wafer. Therefore, we have been studying of TGV for last few years. There are many methods which can generate via holes in the glass. Among them, recently, selective laser etching is emerging as a good candidate for mass production. It consists with two steps for generating TGV. Which is laser local modification and chemical etching. With previous study, we could enhance a process speed with Bessel beam shaping and picosecond interval pulses. In this study, we are focused on chemical etching process. In order to enhance the etching rate, 4 different etchants are tested. Which is HF, KOH, NaOH, and NH4F. Each etchant has its own optimal etching conditions, such as temperature and molar concentration. Here, we compare their etching results. The main criteria of comparison is selectivity. In our study, NH4F shows the best selectivity. Thus, we claim that NH4F can be a good candidate etchant for mass production of Glass interposer.