A Highly Ultraviolet Light Sensitive and Highly Robust Image Sensor Technology Based on Flattened Si Surface

Photodiode (PD) light sensors, PD arrays and image sensors with a wide spectral response, including ultraviolet light (UV-light) waveband of 200-380 nm, are strongly required in the fields of various spectrophotometric analysis, biological phenomena analysis, environmental assessment and space vision1)~4). For the image sensor development, an improvement of UV-light sensitivity and an improvement of sensitivity robustness to UVlight exposure have been challenges5) 6). Especially, due to the short penetration depth of UV-light in Si, an atomic scale control of the dopant profile of the light incident side Si surface region to form a photo-generated carrier drift layer is required7). UV-light sensitive backside illuminated (BSI)-CCD, BSI-CMOS with additional backside surface treatment process, and detector-on-Si type CMOS imagers with UV-light sensitive materials as detector have been reported4) 7) 8). In this paper, a PD technology based on an atomically flattened Si surface for the formation of the thin surface high concentration layer with a steep dopant profile uniformly is summarized, and its application to a CMOS image sensor in-pixel PD is demonstrated. In the next section, the PD concept, experimental results and discussions of n+pn and p+np PDs are shown. In addition, evaluation results of the electrical characteristics of SiO2 /Si system at various UV-light irradiation times are summarized to discuss the origin of sensitivity change due to UV-light exposure. In section 3, a 5.6 μm pixel pitch front-side-illuminated (FSI) CMOS image sensor with the developed PD technology is demonstrated.