Abstract: The present application discloses a method for forming a recess, which comprises the following steps: step 1: performing a dry etching process to a silicon substrate to form a U-shaped or ball-shaped recess; step 2: performing second etching to the recess by introducing HCl and GeH4 reaction gases in an epitaxial process chamber to form diamond-shaped recess. The present application further discloses a method for forming a recess and filling the recess with an epitaxial layer in situ. The disclosed etching changes U-shaped or ball-shaped reaction recess diamond-shaped recess by including reaction gases in the epitaxial process chamber, which is conducive to realizing the in-situ epitaxial filling process. This method reduces steps in the process loop of forming embedded epitaxial layer, thus decreasing defects from the process.