Experimental challenges of stress measurements with resonant micro-Raman spectroscopy

Micro-Raman spectroscopy allows one to measure stress in crystalline materi als. The method is nondestructive and provides microscopic lateral resoluti on, In this paper we show that resonance excitation using an ultraviolet (U V) laser line strongly enhances the depth resolution in micro-Raman spectro scopy, The Raman line shift becomes a true picture of the stress-held in a 12 nm thick surface layer, whereas visible light averages over a depth of s ome hundreds of nanometers, We review the effects of defocusing and inhomog eneous scattering, and present results obtained from a processed wafer. Mea surements of stress fields in a sample taken from a typical silicon integra ted circuit process prove the strongly enhanced resolution. The UV light, t herefore, allows one to resolve stress components averaged out by longer wa velength light, giving a much better way to pinpoint areas of critical stre ss levels that would likely lead to defects in subsequent processes in sili con microelectronic production. Copyright (C) 1999 John Wiley & Sons, Ltd.