Three-dimensional memory device including laterally-undulating memory material layers and methods for forming the same

A method of forming a memory device, comprising:

• forming an alternating stack of insulating layers and sacrificial material layers over a substrate;
• forming memory openings through the vertical repetition;
• forming lateral recesses at levels of the insulating layers around the memory opening by laterally recessing the insulating layers selective to the sacrificial material layers around the memory opening;
• forming a silicon oxide liner on physically exposed surfaces of the alternating stack around the memory opening;
• forming a vertical stack of outer insulating spacers by depositing an outer insulating spacer material in unfilled volumes of the lateral recesses;
• forming a vertical stack of inner insulating spacers by selectively growing an inner insulating spacer material from physically exposed surfaces of the vertical stack of outer insulating spacers while suppressing growth of the inner insulating spacer material from physically exposed surfaces of the silicon oxide liner;
• forming a memory opening fill structure in the memory opening, wherein the memory opening fill structure comprises the silicon oxide liner, the vertical stack of outer insulating spacers, the vertical stack of inner insulating spacers, a memory material layer and a vertical semiconductor channel that are sequentially formed over the vertical stack of inner insulating spacers;
• and
• replacing the sacrificial material layers with electrically conductive layers.