An image sensor and a manufacturing method thereof are provided to improve the electric charge accumulation ability by forming the effective potential barrier. An isolation insulating layer(121) is formed within a substrate. A separation impurity region(122a) of the first conductivity type is formed under the isolation insulating layer into multilayer. An impurity region(122b) of the second conductive type is formed with multilayer within the substrate. The deep well of the first conductivity type is formed within the substrate. The separation impurity region formed with multilayer contacts to the deep well. The impurity of the first conductivity type is ion-implanted into the substrate at the plurality of times. The separation impurity region of multilayer is formed in the isolation insulating layer.
