Swelling behavior of thin anisotropic polymer layers

The swelling of thin anisotropic aromatic polymer films in microelectronic devices and micromechanical systems can lead to significant reliability pro blems. Polymer swelling is caused by the reversible sorption of gas molecul es such as water or volatile organic compounds in the polymer. In this pape r, we investigate the relationship between the number of sorbed molecules a nd the resulting anisotropic volume expansion, with particular focus on in- plane-stress and out-of-plane expansion. Based on analytical and phenomenol ogical studies of the polymer-gas interactions we have developed a model de scribing the microphysical mechanisms of sorption and swelling. The model i s valid for a variety of gases and polymers, the chemical and structural pr operties of which are available in the literature or may be measured direct ly. (C) 1999 Elsevier Science S.A. All rights reserved.