A method of forming a thin layer including providing a first single-crystalline silicon layer partially exposed through an opening in an insulation pattern and forming an epitaxial layer on the first single-crystalline silicon layer and forming an amorphous silicon layer on the insulation pattern, the amorphous silicon layer having a first portion adjacent the epitaxial layer and a second portion spaced apart from the first portion, wherein the amorphous silicon layer is formed on the insulation pattern at substantially the same rate at the first portion and at a second portion. The amorphous silicon layer may be formed to a uniform thickness without a thinning defect.