A tube furnace used for high-temperature processing of semiconductor wafers or the like employs a cone-like shape for the gas inlet or nozzle where the reactant or insert gas enters the furnace tube. This conical nozzle produces a gas flow of faster velocities, following the flow streamlines, and avoids or minimizes recirculating gas cells. The amount of gas used in purging a tube with this configuration is reduced, and the time needed for thorough purging is also reduced. Greater process control, and enhanced process reproducibility, are also possible because of the reduction in overlap of process steps permitted by the faster purging. This feature of faster purging can, in addition, reduce the infiltration of ambient air which occurs during any processing step.