| 摘要 |
PURPOSE:To increase the surge withstanding voltage of a protective circuit, and to improve the reliability of a semiconductor element by forming the protective circuit so that a reverse conduction type impurity concentration constituting the protective circuit is made thinner than other sections. CONSTITUTION:Well regions 26a-26d having a second conduction type are shaped to one main surface of a semiconductor substrate having a first conduction type, and protective resistance circuit sections 24 consisting of a first conduction type impurity layer into the well regions. In such a constitution, a protective circuit section 24 is formed in n<+>-p<->-n three layer structure in which the concentration of the well region 26c is made thinner than the impurity concentration of the well region 26d in a light-receiving section 21. Consequently, when a surge is applied to an Al wiring 2, currents id' uniformly flow toward the n-type silicon substrate 4 from a plane section in an n<+> diffusion layer 6 before they flow through an Al wiring 15 for grounding. Current density at that time is brought to value of two figures or less, thus largely improving a margin to the breakdown of a p-n junction. |
