Optical and Electrical Characterization of Hydrogen-Plasma-Damaged Silicon Surface Structures and Its Impact on In-line Monitoring

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Si surface damage induced by H2 plasmas was studied in detail by optical and electrical analyses. Spectroscopic ellipsometry (SE) revealed a decrease in the pseudo-extinction coefficient $\langle\kappa\rangle$ in the region of photon energy higher than ${\sim}3.4$ eV upon H2-plasma exposure, which is attributed to the disordering of crystalline silicon (c-Si). The increase in $\langle\kappa\rangle$ in the lower energy region indicates the presence of trap sites for photogenerated carriers in the energy band gap in the $E$–$k$ space of Si. The current–voltage ($I$–$V$) measurement of metal-contacted structures was performed, revealing the following characteristic structures: thinner surface (SiO2) and thicker interface (SiO2:c-Si) layers on the Si substrate in the case of H2-plasma exposure than those with Ar- and/or O2-plasma exposure. The structure assigned on the basis of both SE and $I$–$V$ was further analyzed by a layer-by-layer wet-etching technique focusing on the removability of SiO2 and its etch rate. The residual damage-layer thickness for the H2-plasma process was thicker (${\sim}10$ nm) than those for other plasma processes (${<}2$ nm). Since the interface layer plays an important role in the optical assessment of the plasma-damage layer, the present findings imply that a conventional two-layer (SiO2/Si) optical model should be revised for in-line monitoring of H2-plasma damage.
2010-08-25