Defect mapping and stress mapping of crystalline silicon using Spectroscopic Ellipsometry

In this paper we present the concept of a new method, based on Spectroscopic Ellipsometry (SE), for mapping defects and stress patterns in crystalline silicon. Proof of this concept is demonstrated by scanning defect etched multicrystalline silicon samples of known defect distribution with SE, at representative wavelengths between 400 nm-1500 nm. From these data, we extracted the effective optical constants `n<sub>eff</sub>´ and `k_eff´ for each wavelength. The spatial distribution of `n<sub>eff</sub>´ and `k_eff´ matches the defect density distribution. The phase difference between `n<sub>eff</sub>´ and `n_eff´ was also calculated and it shows a good correlation with the defect map of the sample. However, when “sister wafers” wafers were polished, we did not obtain a one-one correlation any more, but there was significant variation in `n<sub>eff</sub>´ and `k_eff´. However, the pattern of variation of these quantities was found to correspond to the residual stress patterns in the silicon wafer. Although the results are preliminary, SE appears to have a great promise as a defect and stress mapping tool.