Device for forming deposited film

A deposition film forming apparatus comprising:

• a reaction chamber for housing a substrate on which a deposition film is to be formed;
• starting gas introducing means including a plurality of mass flow controllers connected via gas lines to a plurality of starting gas sources for controlling the flow rates of starting gases from the plurality of starting gas sources, each mass flow controller corresponding to one of the plurality of starting gas sources;
• a first line for introducing the starting gases into the reaction chamber;
• a vent line;
• and a plurality of first three-way valves provided between said first line and said vent line and the plurality of mass flow controllers for selectively introducing the flow rate controlled starting gases either into said first line or into said vent line;
• a purge gas line for supplying a purge gas from a purge gas source to an upstream side of said plurality of mass flow controllers;
• a plurality of second three-way valves provided between said purge gas line and said gas lines and said plurality of mass flow controllers for selectively introducing either the starting gases or the purge gas into said plurality of mass flow controllers;
• evacuating means for evacuating the reaction chamber;
• and
• decomposing means for decomposing the starting gases to form the deposition film on the substrate in the reaction chamber.