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 problems. Polymer swelling is caused by the reversible sorption of gas molecules such as water or volatile organic compounds in the polymer. In this paper, we investigate the relationship between the number of sorbed molecules and the resulting anisotropic volume expansion, with particular focus on in-plane-stress and out-of-plane expansion. Based on analytical and phenomenological studies of the polymer-gas interactions we have developed a model describing the microphysical mechanisms of sorption and swelling. The model is valid for a variety of gases and polymers, the chemical and structural properties of which are available in the literature or may be measured directly.