Stress measurements using ultraviolet micro-Raman spectroscopy

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We present measurements of mechanical stress in silicon device structures by ultraviolet (UV) micro-Raman spectroscopy. The shorter wavelength of the UV light (364 nm) is the basis for two major improvements over conventionally used blue light (458 nm): The smaller penetration depth of only 15 nm (vs 300 nm for blue light) probes the stress very close to the surface, and a smaller laser spot on the sample (0.7 μm vs 0.9 μm) results in higher spatial resolution. A comparison of stress patterns obtained in the same sample with 364 nm (UV) and 458 nm (blue) light demonstrates that areas of high stress, which are averaged out by longer wavelength light, can be detected with UV light.