The present disclosure provides a method including providing a semiconductor substrate and forming a first layer and a second layer on the semiconductor substrate. The first layer is patterned to provide a first element, a second element, and a space interposing the first and second elements. Spacer elements are then formed on the sidewalls on the first and second elements of the first layer. Subsequently, the second layer is etched using the spacer elements and the first and second elements as a masking element.