A method for forming a memory device, including: forming several overlapping composite
layers on the surface of a substrate, with a
mask layer on the surface of the composite layer, and the composite layer includes an insulating layer and a device layer located on the surface of the insulating layer; A reinforcement layer is formed on the side wall surface, and the reinforcement layer exposes the top surface of the
mask layer and part of the side wall surface; using the reinforcement layer as a
mask, the exposed side wall surface of the
mask layer is etched, exposing part of the top composite layer surface; then, use the
mask layer and strengthening layer as a mask to etch the exposed composite layer, and the
etching thickness of the composite layer is greater than or equal to the thickness of the single-layer device layer; then, repeat the
etching mask once or several times The steps of film layer sidewalls and
etching the composite layer are until the projected
pattern size of several device
layers is gradually reduced in at least one direction from the bottom to the top layer, so that the several device
layers form a ladder shape that decreases layer by layer from the bottom layer to the top layer. The formed storage device has low space occupation rate, high bit density and low bit cost.