The present disclosure provides a 3D memory structure such as 3D Flash memory structure applying for 3D AND flash memory and a method of forming the same. An etching stop layer is formed on a substrate including active elements. A stacked layer is formed on the etching stop layer. The stacked layer includes insulation layers and sacrificed layers stacked alternatively on the etching stop layer. A patterning process is performed on the stacked layer to form a first stacked structure above the active elements, a second stacked structure surrounding the first stacked structure, and a trench pattern separating the first stacked structure and the second stacked structure and exposing the etching stop layer. The trench pattern includes asymmetric inner sidewalls and outer sidewalls. The inner sidewalls define sidewalls of the first stacked structure. The outer sidewalls define sidewalls of the second stacked structure that face the first stacked structure.