Research of lithograph process of polyimide photo resist for passivation thick films

Polyimide has been applied in semiconductor field for a long time. For its stable chemical characteristics, it's usually used as the passivation layer on the chip. In this paper, litho process was setup to research the influence of polyimide as photo resist. Several experiments were performed to solve the spin coating uniformity, polyimide resist residue and the edge bead removal (EBR). Optimization of the develop recipe were carried on step by step, ultimately, existing problems were solved by modifying several parameters, such as, soft baking time and temperature, spin speed, spin time, exposure time and develop time. Smooth and compact 43 μm thick polyimide films were prepared under the parameters below: soft baking under 100oC for 90 s, spin time of 25 s, spin speed of 2500 rpm, 50 μm approximate-mode exposure, exposure time of 100 s, develop time of 80 s. The forming polyimide films were applied on the power (insulated gate bipolar transistor) IGBT chip as passivation layer.