Abstract: A PCVD process for producing coating layers of uniform thickness of domed substrates. The substrate surface to be coated is arranged in relation to the gas passage surface of a gas showerhead. In order to determine the appropriate processing parameters, in a first series of tests for one type of substrate to be coated, the size of the gas passage surfaces and the gas mass flows through the gas passage surfaces are kept constant, while the intervals between plasma impulses are gradually modified, from an initial value t.sub.A until an optimum value t.sub.eff is determined, and until the uniformity of the thickness profile of the layers generated on the substrate may no longer be improved. If required, during a second series of tests, the value t.sub.eff may be kept constant, while the thickness profile of the layers is further modified by further optimizing the local parameters and/or the gas mass flows until layer uniformity may no longer be improved.