Abstract: A homogeneous marker is formed, possibly by the adsorption of trace amounts of an ambient material such as carbon monoxide gas, at a surface of a deposited material when the plasma in momentarily interrupted during plasma enhanced chemical vapor deposition or other deposition processes involving the presence of a plasma. When the deposited material is etched, the resulting crystal dislocations or adsorbed gas is detected as a marker by optical emission spectroscopy techniques. The accuracy of an end point determination of the etching process can be increased by providing a sequence of such markers within the bulk or volume of the deposited material. The markers, being merely an interface such as a slight crystal dislocation in otherwise homogeneous material, do not affect the electrical, chemical or optical properties of the remainder of the predetermined deposited material and thus the homogeneity of the deposited material is not significantly affected.