NOVELTY - The furnace has an inner housing (20) which is fixed in a receiving space of outer housing (10), having outer and inner walls (21,22). A side (201) is connected with side (101) by a lower sealed side (14), so as to form an opening of receiving space. A gas circulation chamber (204) is formed between the walls of housings. A reaction chamber (205) is formed inside the inner wall of inner housing. An inner surface (1003) of gate door (1001) is contacted with receiving space of side (201), such that either gas circulation chamber or reaction chamber operate as independent chamber.    USE - Vertical heat treating furnace used for producing copper indium gallium diselenide (CIGS) thin film solar cell. Can also be used in producing copper zinc tin sulfide (CZTS) thin film solar cell.    ADVANTAGE - By controlling the relative gas density and pressure of the chambers, the reaction gases inside the reaction chamber of the vertical heat treating furnace can be mixed uniformly and the reaction could be facilitated under high pressure. Hence the quality of the formed thin film and the operational safety are improved. The gas circulation chamber can maintain the pressure difference between the housings, so that the density of gas molecules or the gaseous pressure inside the inner housing can be increased to facilitate the chemical reaction rate of the thin film and improve the uniformity of the thin film. The gas circulation chamber can introduce the cooling gaseous nitrogen, so that the flow rate of gaseous nitrogen can be facilitated and effectively accelerating cooling rate, and formation of temperature gradient in the wall of inner housing can be reduced, and effectively protecting the wall of inner housing from chapping or peeling. The safety gate door can protect the operator from the danger of pressure imbalance inside the furnace. The vertical heat treating furnace with the design of gas circulation chamber can enable the effective protection of operators, saving manpower and resources, and providing the reaction environment for high-pressure gases for forming various thin films.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the vertical heat treating furnace.    Outer housing (10)    Lower sealed side (14)    Inner housing (20)    Outer wall (21)    Inner wall (22)    Sides (101,201)    Gas circulation chamber (204)    Reaction chamber (205)    Gate door (1001)    Inner surface of gate door (1003)