cleaning from grown film or the contaminated parts must be replaced by new ones the metallic and nonmetallic sources are separated from each other in order to prevent the growth of thick film multilayer accumulations formed by successive deposition of thin films over one another during a long series of runs such a thick film inevitably starts cracking after growing above a certain thickness the separation arrangement of the sources also improves the efficiency of the use of the starting materials because the films deposited on undesired areas unnecessarily represent a waste of the starting materials reference numerals 11 and 12 in the diagrams denote separate joint pieces intended for connecting the manifolds of metallic or nonmetallic sources to the reaction chamber pack the connections are provided with ground ball socket joints a substrate holder denoted by numeral 13 forms the reaction chamber pack in this embodiment of the substrate holder structure the substrates are sandwiched so that their front sides are facing and sealed at the edges thus forming the reaction space and such packs of two substrates are then stacked in parallel side by side with the substrate rear sides facing outdistanced from each other at a defined spacing the temperature differentials possibly developing between the sandwiched substrate pair packs in the stack can be equalized by means of e g graphite heat equalizing plates inserted between the packs the starting material vapor flows entering the reaction chamber pack are gated into a sequence of gas pulses entering the gaps.