Measurement of thickness of SiO/sub 2 insulation layers in silicon structures with dielectric insulation

A variant of the interference method is proposed for measuring the thickness of SiO2 insulation layers on silicon substrates. The opaqueness of the latter and the transparence of the former are utilized to light over the entire visible range. The basic equipment is an MII-4 Linnick interferometer and an industrial television set. The gist of the thickness measurement is focusing the microinterferometer objective on the insulation surface and projecting the interference pattern onto the receiver pad of the transmitter camera while simultaneously observing on the monitor screen the interference pattern from the SiO2 layer surface and that from the SiO2 -Si interface. The layer thickness is calibrated in frequency meter readings, with 625 kHz selected as the frequency of the pulse generator and 1 micron thickness corresponding to 190 kHz on the digital frequency meter dial. An exhaustive sensitivity and accuracy analysis indicates a systematic error not larger than + or - .015 micron (at 95% confidence level) and a random error not larger than 0.07 micron.