Device for forming film by photo-chemical vapor deposition

A film-forming apparatus for performing a photo-chemical vapor deposition method which is adapted to photo-chemically activate a mixture of a reactant and diluent gas to form a film on the substrate surface, the apparatus being characterized in that:

• (1) the length 1.sub.1 of a tubular light inlet, the length 1.sub.2 of a film-forming chamber and the length 1.sub.3 of a tubular light outlet are in the ratio of 2-6:10:2-6,
• (2) means is provided for spraying an inactive gas other than the reactant directly tot he light-permeable materials constituting the light-incoming window at the light inlet and the light-outgoing window at the light outlet,
• (3) the diameter (d) of a substrate holder in the film-forming chamber and the distance (h) between the substrate holder and a nozzle for feeding the mixture of a reactant and a gas for dilution into the film-forming chamber are in the ratio of 1:1-2
• (4) means for providing an incident light beam through said light incoming window and said light outgoing window, said tubular light inlet and the tubular light outlet each having walls forming a concentric double tubing structure with gaps between the walls, said tubular light inlet and said tubular light outlet extending parallel to and concentric with said incident light beam so that the inactive gas is uniformly supplied through the gaps between the walls in the double tubing structure to the light-incoming window and to the light-outgoing window.