Preparation of organic soluble polyimides and their applications in KrF excimer laser LIGA process

In this study two organic soluble polyimides were successfully synthesized via polycondensation of a hexafluoropropyl group contained dianhydride with two kinds of diamines. These two polyimides (DMDB/6FDA, OT/6FDA) can be dissolved in most aprotic solvents (for example, NMP, DMAc) and many other common solvents (for example. THF, DMSO). The soluble polyimides also show good thermal stability and high absorption at the KrF excimer laser wavelength (λ = 248 nm). (The absorption coefficients of DMDB/6FDA and OT/6FDA were 1.26 × 10⁵ cm^-1 and 1.49 × 10^-1, respectively.) The photoablation properties of the polyimides were studied in detail. Due to incorporating the hexafluoropropyl group into the chemical structure, these two polyimides have higher etching rates than Kapton (a conmercial PI film). The effects of exposure parameters on linewidth and taper-angle of polyimides with different chemical structure were also investigated here. Under the proper control of exposure conditions, good precision patterns with near-vertical side wall can be produced. The 300 mm thick comb-shape and Fresnel patterns with 10 mm linewidth have been made. Moreover. the complementary metallic microstructures have also been realized in the following electroforming procedure. The results showed that these two soluble polyimides were very suitable for KrF Laser LIGA process.