Deep-ultraviolet-induced damage of charge coupled device sensors

In order to facilitate the inspection of deep-submicron features, a generation of semiconductor inspection systems are being pushed to image using deep-ultraviolet (UV) sensitive cameras at increasingly shorter wavelengths. In this article, we present a deep-UV sensitive thinned front-illuminated linear charge coupled device (CCD) image sensor structure and investigate its behavior after exposure to F2 (λ=157 nm) excimer laser. Two key manifestations of radiation damage are observed: (1) Extrinsic quantum efficiency drifts with increasing 157 nm exposure, and (2) dark current increases almost exponentially with 157 nm exposure. These fluctuations in CCD parameters can be caused by several factors including UV-induced color center formation in the oxide, charge generation in the oxide, interface modification, and structural rearrangement. These UV-induced effects alter the optical and electrical properties of the oxide and Si–SiO2 interface, resulting in both temporal and permanent shifts in device performance. The experimental results suggest that careful control of the oxide thickness and the Si–SiO2 interface quality are critical for realizing CCD sensors with high responsivity and stability for deep-UV imaging.