Abstract: A method and apparatus for process control in both the production of uniform material layers using vapor deposition, sputtering, chemical deposition, etc. and the treating of material layers. In particular, the process and apparatus are particularly useful in semiconductor fabrication where ion implantation or diffusion is used. A brief test signal of preset shape, frequency spectrum, or frequency sequence is applied at given time intervals to the material layer whose production characteristics need to be monitored. The measuring signal is applied to a digital evaluation circuit in a process control computer. The signal has various components whose time constants and/or conductivities are different from one another and which together are characteristics of the current flowing through the layer being monitored. In particular, the current flowing over the surface layer i.sub.1, the current flowing through particle houndary areas i.sub.3, and the current through homogeneous material ranges i.sub.