the workpiece 5 from the interior of the cavity 4 is carried out by moving the sealing element 28 it is also possible to start moving the lance 36 into the workpiece 5 synchronously with the start of evacuation of the interior of the cavity the pressure in the interior of the workpiece 5 is then further reduced moreover it is also possible to carry out the positioning movement of the lance 36 at least partly at the same time as the positioning of the chamber wall 18 after a sufficiently deep negative pressure has been achieved process gas is introduced into the interior of the workpiece 5 and the plasma is ignited by means of the microwave generator 19 in particular it is intended that the plasma be used to deposit both an adhesion promoter on the inner surface of the workpiece 5 and the actual barrier layer consisting of silicon oxides after a coating operation has been completed the lance 36 is withdrawn from the interior of the workpiece 5 and the plasma chamber 17 and the interior of the workpiece 5 are ventilated after ambient pressure has been reached inside the cavity 4 the chamber wall 18 is raised again to allow the coated workpiece 5 to be removed and a new workpiece 5 to be inserted for coating to allow lateral positioning of the workpiece 5 at least part of the sealing element 28 is moved back into the chamber base 3 alternatively to the coating of the internal surface of workpieces 5 that was explained above it is also possible to coat the external surface or to carry.