Photosensitive fluorinated polyimides with a low dielectric constant based on reaction development patterning

The fluorinated polyimide PK6FDA/HFBAPP) was prepared by the reaction of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP) in l-methyl-2-pyrrolidone/toluene A multiblock copolyimide with both fluorinated and rigid-rod segments, PI(6FDA/HFBAPP)(BPDA/2-DMB), was prepared by the addition of a second dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and a second diamine, 2,2′-dimethylbenzidine (2-DMB), to the polyimide main chain. The potential lithographic performance of photosensitive polyimides composed of nonphotosensitive fluorine-containing polyimides and photosensitive diazonaphthoquinone (DNQ) was studied on the basis of a new imaging principle recently proposed by our laboratory, that is, reaction development patterning. Neat PI(6FDA/HFBAPP) showed a low dielectric constant (ε) of 2.41 and a low dissipation factor (tan δ) of 0.0027 at 20 GHz, and a 10-μm resolution of the fluorinated polyimide/DNQ system was demonstrated with reactive development with a solution including ethanolamine after ultraviolet exposure. Although slight changes in the dielectric properties were observed in the presence of DNQ residues, these values (ε = 2.63 and tan δ = 0.0033 at 20 GHz) were low enough for use in microelectronic applications. However, PI(6FDA/HFBAPP)(BPDA/2-DMB), having a lower coefficient of thermal expansion (CTE; 33 ppm/°C) than PK6FDA/HFBAPP) (49 ppm/°C), exhibited good positive photosensitivity, whereas the relatively low-CTE multiblock copolyimide displayed a much higher e value (3.48 at 1 MHz) than the highly fluorinated polyimide (2.88 at 1 MHz). A film consisting of PK6FDA/HFBAPPXBPDA/2-DMB) and the remaining DNQ derivatives showed a CTE value comparable to that of the neat polyimide film.