Three-dimensional flat NAND memory device having high mobility channels and methods of making the same

A method of forming a three-dimensional memory device, comprising:

• forming alternating stacks of insulating strips and spacer material strips located over a semiconductor substrate, wherein the alternating stacks are laterally spaced apart among one another by line trenches laterally extending along a first horizontal direction, and wherein the spacer material strips are formed as, or are subsequently replaced with, electrically conductive strips;
• forming line trench fill structures within the line trenches, wherein each line trench fill structure fills a respective one of the line trenches, and each line trench fill structure comprises a pair of memory film layers and a sacrificial semiconductor material layer;
• forming a two-dimensional array of dielectric pillar structures through the line trench fill structures to form an alternating two-dimensional array of the dielectric pillar structures and remaining portions of the line trench fill structures;
• forming channel cavities by removing the sacrificial semiconductor material layers;
• and
• forming vertical semiconductor channels in the channel cavities by selectively growing replacement semiconductor channel layers from physically exposed surfaces of the semiconductor substrate.