PURPOSE: To obtain a highly sensitive solid state image pick-up element, by making the impurity concentration in a P well lower than that on the side of an N-type substrate at a P-N junction part with an N+ layer, thereby effectively utilizing optical signal charge.
CONSTITUTION: On an N-type silicon substrate 1, a P well 2, N+ layers 3 and 4 and a signal line 5 are formed. The N+ layers 3 and 4 and a gate electrode 7 form an MOS transistor. The P well 2 and the layer 3 form a photodiode. The MOS transistor acts as a switching element, which reads signal charge stored in the layer 3. The P well 2 is formed as follows. At first, a P+ layer 21 is formed on the substrate 21. Then, a P-type epitaxial layer 22 is formed. Thereafter, the N+ layer 3 is formed. Electrons, which are generated in the P well, are drifted to a P-N junction part with the N+ layer 3, i.e., to the photodiode and effectively utilized as a signal.
MATSUMOTO KATSUMI
MAKI MASAHIRO
HITACHI DEVICE ENG