Thermal deformation takes place when a polyimide(PI) film, which is a common dielectic material used in electronic devices, is cooled down to a room temperature after being coated on silicon(Si) substrate at high temperature. This phenomenon is due to CTE difference between PI and Si, and this thermal deformation results in thermal stress. The thermal deformation and its induced thermal stress have a negative effect in manufacturing process and sometimes cause the structure to fail.
In this study, the thermal deformation is measured by a curvature measurement method using laser scanning, and the residual stress is calculated by an analytic model. Since PI film shows visco-elastic behavior, the modulus of the film varies with time and temperature, we analyze the residual stress by measuring the relaxation modulus of the PI film, taking into account the visco-elastic behavior of the PI film. From the comparison between the measured value and the elastic solution, we find that the residual stress in PI film has relaxed by an amount of 6.4% at 100℃ and 8.8% at 150℃ two hours after manufacturing.
