Three-dimensional memory device and method for forming the same

In certain aspects, a method for forming a three-dimensional (3D) memory device is disclosed. A stacked structure including first dielectric layers and second dielectric layers that are alternated is formed. A channel structure extending through the first dielectric layers and the second dielectric layers is formed in a first region of the stack structure. Replacing all of the second dielectric layers in the first region of the stacked structure and a portion of each of the second dielectric layers in a second region of the stacked structure with conductive layers. Forming word line pickup structures extending to different depths through remaining portions of the first and second dielectric layers in the second region of the stacked structure such that the word line pickup structures are respectively electrically connected to the conductive layers in the second region of the stacked structure.