A few phenomena on the fully depleted CCDs at the engineering observation of Hyper Suprime-Cam

We report the non-uniformity of quantum efficiency (QE) and concentric ring patterns on the images of the CCDs used in Hyper Suprime-Cam (HSC) mounted on Subaru Telescope. The non-uniformity of QE is seen as gradient patterns along the direction of the vertical resistor especially in images obtained with the g, r, and i-band filters. This is explained by non-uniformity of QE on the CCDs caused by non-uniformity of thickness of the anti-reflective coating. We confirmed this phenomena by using laboratory QE data; with the g-band filter, QE increases 1.5 % from the horizontal resistor side to vertical resistor while it decreases with the i-band filter. The concentric ring pattern is seen on uniformly illuminated images. This is caused by inhomogeneous of impurity in high resistivity silicon wafer. The fluctuation is ±0.3 % of the signal levels with the g, r, i, z, and Y-band filters.