A method of manufacturing a backside illuminated image sensor includes providing a start material that has a layer of semiconductor material on a substrate. The layer of semiconductor material has a first face and a second, backside, face. The layer of semiconductor material is processed to form semiconductor devices in the layer adjacent the first face. At least a part of the substrate is removed to leave an exposed face. A passivation layer is formed on the exposed face, the passivation layer having negative fixed charges. The passivation layer can be Al2O3 (Sapphire). The passivation layer can have a thickness less than 5 μm, advantageously less than 1 μm, and more advantageously in the range 1 nm-150 nm. Another layer, or layers, can be provided on the passivation layer, including: an anti-reflective layer, a layer to improve passivation, a layer including a color filter pattern, a layer comprising a microlens.