Temperature sensitivity and thermal expansion coefficient of benzocyclobutene thin films studied with ellipsometry

Temperature induced changes in thickness and refractive index of thin films of benzocyclobutene (BCB) have been studied with ellipsometry in the temperature range 22-190 degrees C. The ellipsometric parameters psi and Delta, which depend on both the thickness and the optical constants of the BCB films, change significantly with temperature with short response times. The temperature sensitivity, resolution, and dynamic range depend on film thickness and wavelength. For a film with thickness 4.73 mu m, a sensitivity of 0.2 degrees/degrees C with a resolution of 0.25 degrees C is achieved within a range of 170 degrees C. Thermal expansion coefficients (TEC) of BCB films with different thicknesses evaluated from spectroscopic ellipsometric measurements are in the range 6.1-6.5X10(-5)/degrees C. Based on the findings here, a real-time detection system for remote optical monitoring of surface temperature variation can be developed. A technique for the determination of TEC of some organic films is also feasible. (C) 1994 American Institute of Physics.