Ridged word lines for increasing control gate lengths in a three-dimensional memory device

Abstract

After formation of a memory opening through an alternating stack of insulating layers and sacrificial material layers, a blocking dielectric having a greater thickness at levels of the insulating layers than at levels of the sacrificial material layers is formed around, or within, the memory opening. A memory stack structure is formed within the memory opening. Backside recesses are formed by removing the sacrificial material layers and surface portions of the blocking dielectric to form backside recesses including vertically expanded end portions. Electrically conductive layers are formed within the backside recesses. Each of the electrically conductive layers is a control gate electrode which includes a uniform thickness portion and a ridged end portion having a greater vertical extent than the uniform thickness region. The ridged end portion laterally surrounds the memory stack structure and provides a longer gate length for the control gate electrodes for the memory stack structure.