UV-laser-induced surface topology changes in polyimide

Surface topology changes in polyimide induced by single UV-laser pulses with pulse durations between 140 ns and 5 mu s are investigated by means of atomic force microscopy. With increasing fluence three different regimes are found: (a) real material removal (ablation), (b) swelling of the irradiated area above the level of the untreated surface (hump formation) and (c) lowering of the irradiated area below the level of the untreated surface (dent formation). A detailed description of these topology changes is given and different formation processes are discussed.