The "resist poisoning", development defect of photo-resist pattern, has become more serious problem in via-first dual damascene process for 65-nm technology node and beyond. Suppression of the resist poisoning using by novel gap fill (GF) materials is investigated and the influence of GF material's properties on the poisoning is also clarified. It is concluded that the poisoning suppression is associated with chemical reaction between functional groups in the GF film and basic contamination causing the poisoning. On the other hand, the film properties such as film density and hardness do not influence on the poisoning. A mechanism for the poisoning generation is proposed that the GF material can capture the poisoning-contamination in polymer matrix during cross-linking reaction. The capture-reaction can prevent the contamination from diffusion into the photo-resist. Finally, a new GF material, sample-D, suppresses the poisoning to the same level as a process with annealing treatment.