A multi-step etching method is provided. First, a substrate including a gate over the substrate and a spacer over the gate is provided. Then, an anisotropic etching step is performed for etching a first region and a second region in the substrate at two sides of the gate. Thereafter, an isotropic etching step is performed for etching a first external region under the spacer and adjacent to the first region, and etching a second external region under the spacer and adjacent to the second region. Then, a filling step is performed for filling a material into the first region, the first external region, the second region and the second external region.