A method of manufacturing a silicon layer includes pretreating a surface of a silicon nitride layer formed on a substrate through a plasma enhanced chemical vapor deposition method using a first reaction gas including at least one of silicone tetrafluoride (SiF4) gas, a nitrogen trifluoride (NF3) gas, SiF4—H2 gas and a mixture thereof. Then, a silicon layer is formed on the pretreated silicon nitride layer through the plasma enhanced chemical vapor deposition method using a second reaction gas including a mixture of gas including silicon tetrafluoride (SiF4), hydrogen (H2) and argon (Ar).