Embodiments of 3D memory devices and the fabrication methods to form the 3D memory devices are provided. A 3D memory device includes a substrate, a memory deck, and a memory string. The memory deck includes a plurality of interleaved conductor layers and dielectric layers on the substrate. The memory string extends vertically through the memory deck. A bottom conductor layer of the plurality of interleaved conductor layers and dielectric layers can intersect with and contact the memory string.