Experimental challenges of stress measurements with resonant micro-Raman spectroscopy

Micro-Raman spectroscopy allows one to measure stress in crystalline materials. The method is nondestructive and provides microscopic lateral resolution, In this paper we show that resonance excitation using an ultraviolet (UV) laser line strongly enhances the depth resolution in micro-Raman spectroscopy, 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 some hundreds of nanometers, We review the effects of defocusing and inhomogeneous scattering, and present results obtained from a processed wafer. Measurements of stress fields in a sample taken from a typical silicon integrated circuit process prove the strongly enhanced resolution. The UV light, therefore, allows one to resolve stress components averaged out by longer wavelength light, giving a much better way to pinpoint areas of critical stress levels that would likely lead to defects in subsequent processes in silicon microelectronic production. Copyright (C) 1999 John Wiley & Sons, Ltd.