Abstract

We present the first detailed investigation of the optical properties of thin Al films using grating coupling to surface plasma waves (SPW). The films ranged in thickness from 5 to 50 nm and were deposited on a holographically etched grating in Si by means of evaporation, sputtering, and ion-assisted sputtering (IAS) techniques. For comparison, the films were also deposited on gratings etched in photoresist and SiO₂. The dielectric constants determined from SPW data were in good agreement with the ellipsometric measurements on films deposited on Si wafers at the same time. The deposition rate for all films was maintained at 2-3 Ǻ/s, and background vacuum was low at 10^-7 Torr. The evaporated films had the highest quality, followed by sputtered and IAS films. Resistance measurements (taken with a standard four-point probe) also agreed with the optical data; this demonstrates the potential of this measurement as a non-contact resistivity monitor for semiconductor manufacturing. In addition, SEM measurements of the film grain sizes were carried out to relate the higher resistance of sputtered and IAS films to the additional scattering from the grain boundaries.¹ Previously, prism coupling to surface plasma waves has been used to characterize dielectric properties of metal films.²

© 1990 Optical Society of America