Three-dimensional memory and preparation method thereof

The invention provides a three-dimensional memory and a preparation method thereof. The preparation method of the three-dimensional memory comprises the following steps: forming a laminated structure comprising stacked dummy gate layers and interlayer insulating layers on one side of a substrate, forming a plurality of stepped steps by each adjacent dummy gate layer and interlayer insulating layer, and exposing at least one part of the interlayer insulating layer of each stepped step; forming a buffer layer covering the step; removing the part, covering the side wall of the stepped step, of the buffer layer to form a plurality of interval grooves; forming a dielectric layer filling the interval groove and covering the step; and forming a contact hole which penetrates through the dielectric layer and the buffer layer and extends to the dummy gate layer farthest from the substrate.