| 摘要 |
A highly integrated DRAM is provided. A circuit for driving a memory cell array is formed over a substrate, a bit line is formed thereover, and a semiconductor region, word lines, and a capacitor are formed over the bit line. Since the bit line is located below the semiconductor region, and the word lines and the capacitor are located above the semiconductor region, the degree of freedom of the arrangement of the bit line is high. When an open-bit-line DRAM is formed, an area per memory cell less than or equal to 6F2, or when a special structure is employed for a cell transistor, an area per memory cell less than or equal to 4F2 can be achieved.
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