The present invention relates to a phase changeable structure having decreased amounts of defects and a method of forming the phase changeable structure. A stacked composite is first formed by (i) forming a phase changeable layer including a chalcogenide is formed on a lower electrode, (ii) forming an etch stop layer having a first etch rate with respect to a first etching material including chlorine on the phase changeable layer, and (iii) forming a conductive layer having a second etch rate with respect to the first etching material on the etch stop layer. The conductive layer of the stacked composite is then etched using the first etching material to form an upper electrode. The etch stop layer and the phase changeable layer are then etched using a second etching material that is substantially flee of chlorine to form an etch stop pattern and a phase changeable pattern, respectively.