Evaluation of a heat-resistant photoimageable polyimide

A photosensitive, fully imidized, solvent-soluble polyimide system, Probimide 400, which demonstrates very broad processing latitudes in both photolithographic and thermal aspects is studied. A statistical experimental design was used to evaluate the effect of coating parameters on the coating quality of this system. This resulted in an optimal set of coating parameters for the best process latitude. Variables monitored were spin time, spin acceleration, spread cycle time, and exhaust velocity. Experiments at various spin speeds and solution viscosities using the refractive index as a probe supported the hypothesis that such high-molecular-weight polymers undergo chain alignment during the spin coating process. The degree of alignment depended on solution viscosity as well as spin speed. The photolithographic evaluation of Probimide 400 as a 5-μm film showed a very broad exposure latitude, with less than ±5% CD deviation for an 8-μm structure over an exposed range of 75%. The effective dose, measured at 3675 nm, centers at 100 mJ/cm²/μm of thickness. The material exhibits excellent thermal and tensile properties