Developing novel photoresists: microstructuring of triazene containing copolyester films

The growing field of microtechnology induces an increasing demand for affordable functional materials. Several strategies exist for improving the ablation behaviour of standard polymers, e.g., doping with a chromophore. Another possibility is the synthesis of copolymers containing photosensitive moieties besides standard monomers. The specialty polymers investigated in this study contain a triazene group (Ph-N=N-NR(2)) as the photosensitive unit; a polyester with varying contents of triazene groups is presented. These units can be situated in either the main chain or in the side chain. Under irradiation the photosensitive chromophores are cleaved fast and irreversibly. Spectroscopic evidence shows the loss of nitrogen to be the initial photochemical decomposition step. For a comparison of the performance of copolymers with different fractions of triazene groups in the backbone, we have determined the threshold fluences and the effective absorption coefficients. With respect to these ablation parameters, only small differences were found within the set of copolymers investigated. From atomic force microscopy (AFM) and scanning electron microscopy (SEM) it becomes evident that a minimum content of triazene groups in the main chain is necessary for defined microstructures with sharp edges, whereby a resolution in the sub-mu m scale has been achieved. At lower concentrations no sharp structures are formed; at high concentrations bubbles impair the quality of the structures. (C) 1998 Elsevier Science B.V.