Transmission measurements of multilayer interference filters developed for a full integration on Complementary Metal Oxide Semiconductor chips

Abstract

We present in this paper a method to measure the transmission spectra of optical filters composed of Complementary Metal-Oxide-Semiconductor (CMOS) compatible materials thin layers in order to be fully integrated on various types of CMOS image sensors (ambient light sensors, proximity detection, red green blue colour imaging, etc.). As the filters have to be deposited on top of a CMOS device, a good approach in order to evaluate with accuracy their response on chip is (i) to achieve the stacks on Si wafers (as it is the case for the CMOS sensor) (ii) then to perform a direct bonding of the structure on glass wafers (iii) in the end to remove the entire bulk silicon. In this way, we show the measured spectral responses of multilayer interference filters and can check particularly the agreement of the transmission peak with the theoretical calculations and its reproducibility wafer to wafer. It enables to optimize the filters optical designs and to demonstrate that the developed filters fulfill typical CMOS requirements of integration and reliability.