Influence of ion-beam induced chemical and structural modification in polymers on moisture uptake

Polyimide thin films are a promising material for microelectronics and aero space applications. In particular, they are sensitive to moisture and gas u ptake. This leads to film swelling which may be monitored by a correspondin g change in piezoresistance caused by plate bending of a polymer-silicon do uble-layer or bimorphic sensor, respectively. However, the expansion of the polymer, induced by moisture or gas uptake, can usually be influenced by s urface ion-beam modification. By this, the selectivity to a partial gas may be enhanced or decreased. In this work, the influence of ion-beam induced surface modification on both polymer structure and moisture uptake of polyi mide and polyethersulfone is investigated. To modify the polymer layer surf ace boron ions were implanted with energies from 50 to 180 keV and irradiat ion doses between 10(13) and 10(16) B+/cm(2). It could be shown that increa se of irradiation dose leads partly to a destruction of the imide and aroma tic groups. The aromatic structure is degraded by hydrogen abstraction. Thi s corresponds to the creation of a new amorphous and graphite-like structur e, which increases the modified surface film conductivity by several orders of magnitude, and which decreases the Freundlich's coefficient of the mois ture-uptake behaviour. (C) 2001 Elsevier Science B.V. All rights reserved.