MODELING OF SUBSTRATE-INDUCED ANISOTROPY IN THROUGH-PLANE THERMAL-BEHAVIOR OF POLYMERIC THIN-FILMS

Polymeric thin films are widely used in microelectronic applications f or a variety of purposes. These films may possess completely isotropic material properties and yet still exhibit anisotropic effects due to the constraining influence of the substrate coupling into the film beh avior via the film Poisson ratio. A theoretical model of this effect o n the through-plane thermal properties of isotropic thin films for sin gle layer (thin film rigidly clamped) and bilayer (thin film on substr ate, e.g., silicon wafer) has been developed based on the assumption t hat the material follows Hooke's law in all directions. Finite element analyses using ANSYS 5.OA have also been performed to confirm theoret ical results both for singlelayer and bilayer models. In the case of P oisson ratio of 0.5, the effective coefficient of thermal expansion (C TE) in the thickness direction can be as high as three times that of t he unconstrained film. (C) 1996 John Wiley & Sons, Inc.