NOVELTY - The diffusion furnace with a reaction chamber for treating substrates (1), comprises a first unit for generating a gas flow, and a second- and a funnel-shaped third unit for influencing the flow, where the first and second units are arranged in the reaction chamber. The first unit is a radial fan impeller (3), which is fastened to a drive shaft (4). The second unit is a plate. The third unit is arranged above the fan impeller. The drive shaft is connected with a motor (5), which is arranged outside of the reaction chamber. The reaction chamber is implemented as a cylinder.    USE - Diffusion furnace useful for treating substrates, during the production of semiconductors, for diffusion, oxidation and low pressure chemical vapor deposition processes, and for doping solar cells.    ADVANTAGE - The diffusion furnace improves the temperature homogeneity of the substrates.    DETAILED DESCRIPTION - The diffusion furnace with a reaction chamber for treating substrates (1), comprises a first unit for generating a gas flow, and a second- and a funnel-shaped third unit for influencing the flow, where the first and second units are arranged in the reaction chamber. The first unit is a radial fan impeller (3), which is fastened to a drive shaft (4). The second unit is a plate. The third unit is arranged above the fan impeller. The drive shaft is connected with a motor (5), which is arranged outside of the reaction chamber. The reaction chamber is implemented as a cylinder with a lateral surface and two oppositely lying front walls. The height (h) of the cylinder is larger than the diameter (d). The fan impeller is arranged at one of the front walls and in the center point of the front wall. The axis of the fan impeller cuts the front wall in a rectangular angle. An INDEPENDENT CLAIM is included for a method for generating a gas flow in a cylindrical reaction chamber of a diffusion furnace.    DESCRIPTION OF DRAWING(S) - The diagram shows a substrate for the treatment in a diffusion furnace with a fan impeller.    Substrates (1)    Substrate stack (2)    Fan impeller (3)    Drive shaft (4)    Motor. (5)