In a process facility for producing semiconductor wafers, a third physical unit is configured between two physical units that produce mini environments. The third physical unit has a laminar flow at right angles to the laminar flows of the two physical units and is operated with a slightly higher flow velocity. According to the Bernoulli equation, the static pressure in the third physical unit is therefore lower than in the surrounding two physical units. Advantageously, therefore, no contamination from the more highly loaded one of the two physical units passes over into the lesser loaded one of the two physical units.