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

Abstract

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 <κ> in the region of photon energy higher than ∼3.4 eV upon H2-plasma exposure, which is attributed to the disordering of crystalline silicon (c-Si). The increase in <κ> 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 (∼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.