In an embodiment, the first bit line contact structure 111 and the second bit line contact structure 211 each have a rectangular, T-shaped, or semicircular cross-section. The first bit line contact structure 111 and the second bit line contact structure 211 in the embodiment of FIG. 1 are rectangular bit line contact structures. FIG. 4 is a schematic diagram of a T-shaped bit line contact structure according to an embodiment. FIG. 5 is a schematic diagram of a semicircular bit line contact structure according to an embodiment. As shown in FIGS. 1, 4, and 5, the first bit line contact structure 111 and the second bit line contact structure 211 of any cross-sectional shape are suitable for the bit line structure. Therefore, the bit line contact structures of other cross-sectional shapes not shown in the present embodiment are also within the protection scope of the present embodiment.