Thickness determination of thin insulating layers

Thin insulating films (Si3N4 on titanium-substrate) with various thicknesses (40-360nm) are investigated with EPMA (electron probe micro analysis): A carbon- and, alternatively, gold-coating is applied to avoid charging phenomena and beam deflection. The alteration of the shape of the depth distribution function due to the insulating property is considered by applying an electrostatic model (proposed by Cazaux) of a charged dielectric cylinder. A Monte-Carlo simulation is performed simulating the charging of the specimen by assuming a precharge and modification of the mean free path in the insulator. Experimentally derived k-ratios for Si3N4-films are verified quantitatively. The applicability of the results to other insulating materials - especially with regard to different preparation-techniques - is discussed.