A method of forming a semiconductor device includes forming an opening having a sidewall in a substrate and forming a first epitaxial layer in the opening. The first epitaxial layer is formed in a first portion of the sidewall without growing in a second portion of the sidewall. A second epitaxial layer is formed in the opening after forming the first epitaxial layer. The second epitaxial layer is formed in the second portion of the sidewall. The first epitaxial layer is removed after forming the second epitaxial layer.