Evaluation of bis (perfluorophenyl azide)s as cross-linkers for a soluble polyimide

Abstract

A soluble polyimide has been synthesized and its potential as a negative resist evaluated using bis(perfluorophenyl azide)s (bis-PFPAs) ethylene l,2-bis(4′-azido-2′,3′,5′,6′-tetrafluorobenzoate)1, l,5-bis(4′-azido-2′,3′,5′,6′-tetrafluorophenyl)penta-l,4-diene-3-one 2 and 2,6-bis(4′-azido-2′,3′,5′,6′-tetrafluorophenylmethylene)-4-methylcyclohexanone 3. Retention of over 70% has been achieved with ca. 10 mass% of either 1 or 2 as the cross-linking reagent under our development conditions. With the long-wavelength cross-linker 2, irradiation was carried out at 350 nm, which enabled films with a thickness of several microns to be crosslinked. Deep-UV lithography was performed with the polyimide and 11 mass% of bis-PFPA 1. It was found that the resist has a deep-UV sensitivity of 30–35 mJ cm–2 while the polyimide itself has a deep UV sensitivity of 350–400 nil cm –2. Feature sizes of 0.5 µm were resolved.