Measurement of Epitaxial Film Thickness Using an Infrared Ellipsometer

Abstract

The thickness of most epitaxial layers is measured using spectrophotometer scan techniques. The method does not work well for very thin epitaxial layers (<5μ). The principles, underlying the ellipsometric method used to measure thin transparent films in the visible region, apply to the optical interference that occurs between a substrate and an epitaxial layer in the infrared. An ellipsometer and the ellipsometric technique were used to measure the thickness of 40 P on P+ Ge and 40 N on N+ Si epitaxial layers. They ranged in thickness from 1 to 10μ. The measured values compared to those obtained by the infrared scan technique agreed within +9.6% for the Ge layers and ±6.7% for the silicon. The reproducibility of the measurements was +2.8% and ±4.1%, respectively. In ultimate form the method should be more accurate and more direct than the infrared scan technique.