A method for forming a memory, comprising: providing a semiconductor substrate, wherein a plurality of separate active regions are formed on the semiconductor substrate and isolated through an isolation layer; forming a word line trench in the active regions and the isolation layer by etching, wherein the word line trench comprises a first partial word line trench located in the active regions and a second partial word line trench located in the isolation layer, the first partial word line trench is interconnected with the second partial word line trench, and a width and a depth of the second partial word line trench are greater than a width and a depth of the first partial word line trench respectively; and forming a word line structure in the word line trench, wherein the word line structure comprises a first partial word line structure located in the first partial word line trench and a second partial word line structure located in the second partial word line trench, the first partial word line structure is interconnected with the second partial word line structure, and a width and a depth of the second partial word line structure are greater than a width and a depth of the first partial word line structure respectively, wherein a forming process of the word line trench comprises: forming a mask layer on the active regions and the isolation layer, wherein the mask layer has a plurality of parallel openings, an extending direction of the openings and an extending direction of the active regions form an angle, and both a partial surface of the active regions and a partial surface of the isolation layer are exposed from each of the openings; and etching the active regions and the isolation layer along the openings, to form the word line trench both in the active regions and the isolation layer, characterized in that, lateral etching the isolation layer is added during the etching, wherein the etching comprises: adding an isotropic dry plasma etching step in an anisotropic dry plasma etching step, wherein the isotropic dry plasma etching step is used for laterally etching the isolation layer. providing a semiconductor substrate, wherein a plurality of separate active regions are formed on the semiconductor substrate and isolated through an isolation layer; forming a word line trench in the active regions and the isolation layer by etching, wherein the word line trench comprises a first partial word line trench located in the active regions and a second partial word line trench located in the isolation layer, the first partial word line trench is interconnected with the second partial word line trench, and a width and a depth of the second partial word line trench are greater than a width and a depth of the first partial word line trench respectively; and forming a word line structure in the word line trench, wherein the word line structure comprises a first partial word line structure located in the first partial word line trench and a second partial word line structure located in the second partial word line trench, the first partial word line structure is interconnected with the second partial word line structure, and a width and a depth of the second partial word line structure are greater than a width and a depth of the first partial word line structure respectively, wherein a forming process of the word line trench comprises: forming a mask layer on the active regions and the isolation layer, wherein the mask layer has a plurality of parallel openings, an extending direction of the openings and an extending direction of the active regions form an angle, and both a partial surface of the active regions and a partial surface of the isolation layer are exposed from each of the openings; and etching the active regions and the isolation layer along the openings, to form the word line trench both in the active regions and the isolation layer, characterized in that, lateral etching the isolation layer is added during the etching, wherein the etching comprises: adding an isotropic dry plasma etching step in an anisotropic dry plasma etching step, wherein the isotropic dry plasma etching step is used for laterally etching the isolation layer. forming a mask layer on the active regions and the isolation layer, wherein the mask layer has a plurality of parallel openings, an extending direction of the openings and an extending direction of the active regions form an angle, and both a partial surface of the active regions and a partial surface of the isolation layer are exposed from each of the openings; and etching the active regions and the isolation layer along the openings, to form the word line trench both in the active regions and the isolation layer, characterized in that, lateral etching the isolation layer is added during the etching, wherein the etching comprises: adding an isotropic dry plasma etching step in an anisotropic dry plasma etching step, wherein the isotropic dry plasma etching step is used for laterally etching the isolation layer.