Thin film characterization by laser interferometry combined with SIMS

Abstract

Thin film properties of technologically important materials (Si, GaAs, SiO₂, WSi_x) have been measured by using a novel technique that combines secondary ion mass spectrometry (SIMS) and laser interferometry.

The simultaneous measurement of optical phase and reflectance as well as SIMS species during ion sputtering yielded optical constants, sputtering rates and composition of thin films with high depth resolution. A model based on the principle of multiple reflection within a multilayer structure, which considered also transformation of the film composition in depth and time during sputtering, was fitted to the reflectance and phase data. This model was applied to reveal the transformation of silicon by sputtering with O ⁺₂ ions. Special attention was paid to the preequilibrium phase of the sputter process (amorphization, oxidation, and volume expansion). To demonstrate the analytical potential of our method the multilayer system WSi_x/poly-Si/SiO₂/Si was investigated. The physical parameters and the stoichiometry of tungsten suicide were determined for annealed as well as deposited films. A highly sensitive technique that makes use of a Fabry-Perot etalon integrated with a Michelson type interferometer is proposed. This two-stage interferometer has the potential to profile a sample surface with subangstroem resolution.