US Patent 11393844 Methods for forming three-dimensional memory devices

Embodiments of 3D memory devices and methods for forming the same are disclosed. In an example, a method for forming a 3D memory device is disclosed. A stop layer, a first polysilicon layer, a sacrificial layer, a second polysilicon layer, and a dielectric stack are sequentially formed at a first side of a substrate. A channel structure extending vertically through the dielectric stack, the second polysilicon layer, the sacrificial layer, and the first polysilicon layer, stopping at the stop layer, is formed. An opening extending vertically through the dielectric stack and the second polysilicon layer, stopping at the sacrificial layer to expose part of the sacrificial layer, is formed. The sacrificial layer is replaced, through the opening, with a third polysilicon layer between the first and second polysilicon layers. The substrate is removed from a second side opposite to the first side of the substrate, stopping at the stop layer.