PURPOSE: To prevent dark currents due to charges implanted from a substrate back by forming an impurity layer in concentration higher than a channel stopper to a region forming a sub-line of an IC chip.

CONSTITUTION: Sections among the aluminum of the sub-line 2 and the P+ layer 12 in high concentration and a P type substrate 1a can be ohmic-connected because the P+ layer 12 is formed between the sub-line 2 and the P type substrate 1a. Accordingly, the internal potential of the substrate 1a is equalized to that of a substrate voltage source 8 because the voltage of the substrate voltage source 8 applied to the sub-line 2 is applied to the substrate 1a through a resistor 9 of linear characteristics completely ohmic-connected to the P+ layer 12. The voltage is applied to a diode 11 parasitized between the substrate 1a and a bed 5 through a second substrate resistor 10 between the sub-line 2 and the substrate back. Since substrate voltage is applied to the bed 5 from the substrate voltage source 8, on the other hand, a section between both electrodes of the diode 11 is brought to the same potential and cut off. Electrons are implanted from the back of the substrate 1a, and dark currents are prevented.