A method is provided for fabricating a semiconductor structure. The method includes providing a semiconductor substrate, forming an epitaxial layer on a top surface of the semiconductor substrate and having a predetermined thickness, and forming a plurality of trenches in the epitaxial layer. The trenches are formed in the epitaxial layer and have a predetermined depth, top width, and bottom width. Further, the method includes performing a first trench filling process to form a semiconductor layer inside of the trenches using a mixture gas containing at least silicon source gas and halogenoid gas, stopping the first trench filling process when at least one trench is not completely filled, and performing a second trench filling process, different from the first trench filling process, to fill the plurality of trenches completely.