The invention relates to a formation method of a memory device. The method includes the following steps that: a multi-layer overlapped composite layer is formed on the surface of a substrate, the surface of the composite layer is provided with a
mask layer, the composite
layers include insulating
layers and device
layers arranged on the surfaces of the insulating layers; a strengthened layer is formed on a part of the side wall surface of the
mask layer, and the strengthened layer exposes the top surface and a part of the side wall surface of the
mask layer; with the strengthened layer adopted as a mask, the exposed side wall surface of the
mask layer is etched, so that a part of the surface of the composite layer at the top is exposed; with the
mask layer and the strengthened layer adopted as a mask, the exposed composite layer is etched, the
etching thickness of the composite layer is greater than or equal to the thickness of a single device layer; the steps in which the side wall of the
mask layer and the composite layer are etched are repeated for once or by a plurality of times until the size of the projection pattern of the plurality of device layers is gradually decreased from the bottom layer to the top layer along at least one direction, so that the plurality of device layers can form a steeped structure which is shrunk gradually from the bottom layer to the top layer. The memory device formed by the method of the invention has the advantages of low space
occupancy rate, high bit density and low bit cost.