Semiconductor memory device having hierarchical bit line structure

摘要

A semiconductor memory device includes a semiconductor substrate, a plurality of sub bit line pairs formed on the semiconductor substrate, a main bit line pair formed at a layer above the plurality of sub bit line pairs, a plurality of selecting transistors, a plurality of word lines located to cross the sub bit line pairs, and a plurality of memory cells. Each selecting transistor is provided corresponding to one sub bit line and has one source/drain region connected to a corresponding sub bit line. At a layer above the other source/drain region of the selecting transistor, an intermediate layer is formed in the same layer as that of a storage node of memory cell. The intermediate layer is connected to the other source/drain region of the selecting transistor through a contact hole formed beneath it. The intermediate layer is further connected to the main bit line through another contact hole formed on the intermediate layer.