Abstract: A method of cleaning a film-forming apparatus to remove at least a part of a silicon-based material deposited on a constituent member of the film-forming apparatus after used to form thin films includes introducing a first-gas including fluorine gas and a second gas including nitrogen monoxide gas into the film-forming apparatus, and heating the constituent member. The constituent member includes quartz or silicon carbide, and the silicon-based material includes silicon nitride.

Abstract: A cleaning agent comprising a mixture of a propylene glycol alkyl ether compatible with water any ratio, a propylene glycol alkyl ether compatible with water only at ratios of 50% by volume or less, and water, for example, the mixture having such a composition that each of 15% by volume or more of dipropylene glycol monomethyl ether, 10% by volume or more of dipropylene glycol monopropyl ether, and 15% by volume or more of water is uniformly dissolved in the other two components. This cleaning agent has high detergency on oily matter, has a characteristic that it is easy to separate the oily matter because the oily matter is not dissolved in the cleaning agent, and is low toxic.