Surface features in U-band of ITL devices for the LSST telescope

The LSST project (Large Survey for Space and Time), Vera Rubin Observatory is designed to observe the deep and wide Universe addressing the questions about dark matter as well as the near Universe with the study of the Milky Way. These observations are conducted by a high-resolution camera, which is made up of 189 4k×4k CCD sensors observing from the UV to the near-infrared. Some sensors supplied by ITL (Imaging Technology Laboratory), present a layer of cleaning residue or non-stoichiometric oxidized silicon adhering the surface after etching and create some non-uniformity in backside charging and irregularities inducing a variation of counting in UV and imprecise photometry. In this paper, we will present the camera and the particularities of the ITL sensors, then, the impact of this layer on the performances of the sensors and finally on the observed astronomical object.