US Patent 11430811 3D NAND memory device with select gate cut

A memory device includes a stack of alternating word line layers and insulating layers over a substrate. The word line layers includes a bottom select gate (BSG) positioned over the substrate. The memory device includes first dielectric trenches that are formed in the BSG of the word line layers and extend in the length direction of the substrate to separate the BSG into a plurality of sub-BSGs. The memory device also includes a first common source region (CSR) that is formed over the substrate and extends in the length direction of the substrate. The first CRS further extends through the word line layers and the insulating layers in a height direction of the substrate, where the first CSR is arranged between two adjacent first dielectric trenches of the first dielectric trenches.