TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The precursor is trimethylaluminum and process gas is oxygen or an oxygen-containing molecular gas, and/or the precursor silane, or ammonia or a mixture of nitrogen and hydrogen. The first wavelength of the hydrogen spectral line (H-alpha) of the Balmer series is 656.3 nm, the hydrogen spectral line (H-beta) of the Balmer series is 486.1 nm, or the oxygen spectral line is 777 nm.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Method: The process parameter and/or the supplying of the substrate is controlled in the separator, when the signal exceeds- or decreases a predetermined threshold value. The method comprises monitoring the emission intensity of at least one second wavelength or band generated in the separator, and generating the signal depending on the monitored emission intensities of the first wavelength or band and the second wavelength or band. A quotient of the monitored emission intensities is formed during generating the signal in dependence of the monitored emission intensities. The method comprises stopping the deposition of the dielectric layer on the substrate, and/or the supplying of the substrate to the separation device using the control device, when the signal exceeds or decreases the predetermined threshold value. The steps of stopping the deposition of the dielectric layer on the substrate, and/or the supplying of the substrate to the separation device, comprises: adjusting the process parameter in connection to the stop source of the control device; continuing the deposition of the dielectric layer on the substrate and/or the supplying the substrate to the separator; monitoring the emission intensity of the first wavelength or band generated in the separator; generating the signal in response to the monitored emission intensity; transferring the signal to the control device; and controlling the process parameter and/or the supplying of the substrate into the separation device using the control device, depending on the signal. The method comprises outputting a warning signal at the stop source of the control device. The deposition of the dielectric layer on the substrate includes depositing several layers and the first wavelength or band, the optional predetermined threshold value and the optional second wavelength or band are selected depending on the respective layer to be deposited. The step of controlling the process parameter comprises controlling the supply of a film-forming precursor into the separator. Preferred Components: The second wavelength or band exhibits a distance of not greater than 200 nm to the first wavelength or band. EXAMPLE - No suitable example given.