A method for the determination of the thermally induced optical and structural changes of polymers used to fabricate lightpipes integrated in CMOS image sensor arrays

In this article, we will present a method to be able to determine the thermally induced optical and structural changes of polymers used to realize lightpipes integrated in CMOS image sensor pixel arrays. The reduction of the pixel size to the visible wavelength scale increases the diffraction of the transmitted light, and lightpipes can compensate this effect by improving light confinement in each pixel enhancing the resulting device external quantum efficiency. Thus, the measurements of the polymer structural and optical changes are the key parameters for the optimization of the guiding and transmission properties of the lightpipe. Spectroscopic ellipsometric measurements allow users to determine the variations of the polymer film refractive index and thickness as a function of the thermal budgets for temperatures ranging from 250 °C to 500 °C. On the other hand, thermogravimetric analysis permits users to relate the variations of these parameters to the polymer structural modifications as a function of the increasing temperature.