Fast simultaneous thickness measurements of gold and nickel layers on copper substrates

The thickness of nickel and gold films plated on a copper substrate has been determined by measuring the intensity of various fluorescent lines excited in reflection by a 50-kV tungsten X-ray source. An exploratory system has been constructed which can simultaneously measure the thickness of the gold and nickel layers on an area of 125 × 175 μm. Thickness of gold from 0.2 μm to 5 μm and from 0.3 μm to 1.5 μm of nickel can be measured to an accuracy of ±6 percent in the gold films and ±10 percent in the nickel films in about 20 seconds, including the measurement and calculation. The equations describing the attenuation of the incident radiation, the primary and secondary excitation of fluorescence radiation in the films, and the attenuation of the fluorescence radiation in the films have been determined for the case of nickel and gold films on copper substrates and for indium and gold films on copper substrates and are solved by a computer in the system. The method could be extended to other multilayer systems.