Elastic and mechanical properties of ion-implanted silicon determined by surface-acoustic-wave spectrometry

Abstract

Amorphization of silicon by ion implantation at liquid nitrogen temperature was studied by broadband surface-acoustic-wave spectrometry (SAWS) and channelled Rutherford backscattering spectrometry (c-RBS) and the results were compared to simulations computed using TRIM. If the topmost layer of the wafer is completely amorphized, its thickness can be determined by all three methods. In addition, SAWS can measure the density and elastic constants (Young’s modulus and Poisson’s ratio) of the amorphous layer. Measurements of layer thickness obtained by SAWS and by c-RBS agreed within a few percent in all cases where the fully amorphized silicon layer extended to the silicon surface, as indicated by c-RBS spectra. Damage simulation profiles computed with TRIM also agreed closely with the measured thickness values, using an effective amorphization damage threshold of (Formula presented) The mechanical constants obtained for the amorphized layer were (Formula presented) Poisson’s (Formula presented) Young’s (Formula presented). © 1998 The American Physical Society.