| 摘要 |
PURPOSE:To reudce the value of adverse bias voltage, by forming a partial region of a semiconductor substrate right under a photodiode with a semiconductor region which has the conduction type opposite to a well region and high density of impurity. CONSTITUTION:An n type semiconductor region 22 added with an impurity of high density is formed at a partial region right under a photodiode of an n type semiconductor substrate 21. At the same time, an n type semiconductor layer 23 is formed on the substrate 21 by an epitaxial growing process, for example. Then p wells 2 and 3 are formed on the layer 23, and an n type semiconductor region 5 which forms a photodiode is formed on the well 3. Here if the adverse bias voltage increases, the layer 23 right under the region 25 is completely depleted. Then the edge of the depletion layer finally reaches the region 22. Thus the depletion layer does not extend easily since the region 22 has high density, and the adverse bias voltage contributes to extending the depletion layer toward the well 3. As a result, the adverse bias voltage can modulate effecitvely the potential of the well 3, and the value of the adverse bias voltage is reduced. |
