Fabricating photosensitive polymer insulation layer by spin-coating for through silicon vias

Through silicon via (TSV) is an enabling technology for 3D interconnection. The insulation layer at the bottom of the via usually needs to be removed in order to expose the pad so that the electrical interconnection from the front side to the back side can be realized. This removal may be implemented by plasma etching, laser drilling, or photolithography. Compared with the other two methods, photolithography is considered having the merits of high efficiency, high reliability and low cost. In this study, we developed a photosensitive polymer insulation material that can be deposited with the spin-coating process. The photosensitive material at the bottom of the TSV was developed with potassium hydroxide (KOH) solution after exposure to thr 365 nm UV light. At last, the residual photosensitive polymer was cured via a preset heating procedure. The resulting polymer insulation layer exhibited excellent thermal stability, good chemical resistance, good adhesion and good thickness uniformity. Such a material may be considered a promising candidate for the insulation layer for the applications of CMOS image sensor (CIS) and fingerprint identification sensor with TSVs having a low aspect ratio.