To prevent a crystal defect-contg. photodiode from being formed by executing an ion implanting step separated in sub-steps for forming n-layers for photodiodes and N-annealing after each ion implanting sub-step.

In an ion implanting step, a first ion implanting is performed to form an n+-layer 10, then it is N-annealed, a second ion implanting is performed to form an n+-layer 10, then it is N-annealed, a second ion, another implanting is performed to form an p+-layer 11 and then it is N-annealed. Thus the ion implanting step is divided in several sub-steps to make point defects/ inter-lattice atom pairs caused at a high energy ion implanting step disappear by the N-anneal after each ion implanting sub-step before the point defects/inter- lattice atom pairs mutually combine into stable crystal defects.