Three-dimensional memory device and method of forming the same

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

• forming a plurality of insulating layers and a plurality of sacrificial layers alternatively stacked on a substrate;
• forming at least one first opening through the insulating layers and the sacrificial layers;
• forming a plurality of protection layers on surfaces of the sacrificial layers exposed by a sidewall of the first opening;
• forming a charge storage layer on the sidewall of the first opening, the charge storage layer covering the protection layers;
• forming a channel layer on the charge storage layer;
• and
• replacing the sacrificial layers and the protection layers with a plurality of electrode layers,
• wherein each of the protection layers has a curved surface.