A method of manufacturing a non-volatile memory device includes forming a gate insulation layer on a semiconductor substrate having a source layer. The method also includes forming a silicon nitride layer having a buffer-treated upper surface on the gate insulation layer, wherein the buffer-treated upper surface of the silicon nitride layer has a hardness higher than a hardness of the silicon nitride layer. The method further includes forming a silicon oxide layer on the buffer-treated upper surface of the silicon nitride layer. The method additionally includes alternately forming additional silicon nitride layers and additional silicon oxide layers on the silicon oxide layer to form a stack structure.