Before being used for a LPCVD device, a tool is washed first and on the surface of the tool a TEOS-NSG film, which is the film to be formed on a semiconductor substrate and whose etching speed is faster than that of a nitride film, is coated in advance. If the tool coated in the abovementioned manner is used to form a film on the semiconductor substrate, the nitride film formed on the substrate is also adhered to and deposited on the tool and if wet etching is applied to the tool, the TEOS-NSG film underlying the nitride film is exposed at the portions where the nitride film is thinner than at other portions. Since the etching time of the TEOS-NSG film is faster than that of the nitride film, the TEOS-NSG film is selectively etched. When the TEOS-NSG film is being removed, the nitride film left on the TEOS-NSG film is also peeled and removed at the same time. Thereby, reproduction can be achieved by etching without damage.
