Water sorption properties of carbonized layers produced by controlled B+ bombardment of thin polyimide and polysulfone films.

Thin polyimide (PI) and polyethersulfone (PES) films are widely used as functional layers for microelectronic sensors. Ion implantation modifies the layer structure and morphology of these polymers and hence results in new mechanical and optical properties. However, ion-modified layers also show a change in sensitivity to moisture uptake under specific conditions. This is important for developing humidity sensors. Therefore, the water sorption ability of such modified polymer layers is studied by spectroscopic ellipsometry under definite relative humidity conditions (1-95%). Swelling data were obtained by fitting procedures based on changes of effective layer thickness and optical constants due to water uptake. Irradiation doses from 0.5 to 5x10(15) B+ cm(-2) at an energy of 180 keV were used for polymer modification. At irradiation doses from 0.5 to 0.7x10(15) B+ cm(-2), the maximum out-of-plane swelling is reached. At higher doses >2x10(15) B+ cm(-2), the swelling decreases and corresponds to values of the pure polymer layers. The wetting properties of the layer surfaces determined by contact angle measurements are important to explain this behavior.