A method for manufacturing a semiconductor structure, comprising: providing a substrate, an isolation trench being formed on the substrate; forming a silicon-rich isolation layer in the isolation trench, the silicon-rich isolation layer covering an inner surface of the isolation trench; characterized in that the method further comprises: forming a second oxide layer in the isolation trench, the second oxide layer covering the silicon-rich isolation layer, wherein the silicon-rich isolation layer is oxidized by an in-situ steam generation process, after the in-situ steam generation process is finished, at least part of the silicon-rich isolation layer has been oxidized into the first oxide layer; forming a third oxide layer in the isolation trench, the third oxide layer covering the second oxide layer, wherein after the third oxide layer is formed, the silicon-rich isolation layer has been completely oxidized into the first oxide layer, and the first oxide layer, the second oxide layer, and the third oxide layer serving as the first isolation oxide layer; and forming a second isolation oxide layer in the isolation trench, the second isolation oxide layer covering the first isolation oxide layer, and the first isolation oxide layer and the second isolation oxide layer serving as the isolation oxide layer, wherein, the isolation oxide layer fills up the isolation trench. providing a substrate, an isolation trench being formed on the substrate; forming a silicon-rich isolation layer in the isolation trench, the silicon-rich isolation layer covering an inner surface of the isolation trench; characterized in that the method further comprises: forming a second oxide layer in the isolation trench, the second oxide layer covering the silicon-rich isolation layer, wherein the silicon-rich isolation layer is oxidized by an in-situ steam generation process, after the in-situ steam generation process is finished, at least part of the silicon-rich isolation layer has been oxidized into the first oxide layer; forming a third oxide layer in the isolation trench, the third oxide layer covering the second oxide layer, wherein after the third oxide layer is formed, the silicon-rich isolation layer has been completely oxidized into the first oxide layer, and the first oxide layer, the second oxide layer, and the third oxide layer serving as the first isolation oxide layer; and forming a second isolation oxide layer in the isolation trench, the second isolation oxide layer covering the first isolation oxide layer, and the first isolation oxide layer and the second isolation oxide layer serving as the isolation oxide layer, wherein, the isolation oxide layer fills up the isolation trench. forming a second oxide layer in the isolation trench, the second oxide layer covering the silicon-rich isolation layer, wherein the silicon-rich isolation layer is oxidized by an in-situ steam generation process, after the in-situ steam generation process is finished, at least part of the silicon-rich isolation layer has been oxidized into the first oxide layer; forming a third oxide layer in the isolation trench, the third oxide layer covering the second oxide layer, wherein after the third oxide layer is formed, the silicon-rich isolation layer has been completely oxidized into the first oxide layer, and the first oxide layer, the second oxide layer, and the third oxide layer serving as the first isolation oxide layer; and forming a second isolation oxide layer in the isolation trench, the second isolation oxide layer covering the first isolation oxide layer, and the first isolation oxide layer and the second isolation oxide layer serving as the isolation oxide layer, wherein, the isolation oxide layer fills up the isolation trench.