PURPOSE: To prevent entry of oxygen into a reaction quartz tube and enable a stable semiconductor wafer processing wherein the wafer is not subjected to high temperature oxygen when it goes in and out of a furnace by placing at the reaction quartz tube and its port to the furnace a separate additional quartz tube with the same shape.

CONSTITUTION: A cylindrical additional quartz tube 11 in contact with an inlet of a cylindrical reaction quartz tube 1 having a diameter equal to that of the reaction quartz tube 1 and length of 3 to 5 times the diameter is provided. In this case, the additional quartz tube 11 placed at the inlet of the reaction quartz tube shifts the position of oxygen entry to the right in the figure by its length and a temperature in the oxygen entry part is sufficiently low so that a wafer is not subjected to high temperature oxygen when it goes in and out of a furnace. Thus stable semiconductor wafer processing is possible.