Extending spectroscopic ellipsometry for identification of electrically active defects in Si/SiO2/high-k/metal gate stacks

This paper presents a new method utilizing spectroscopic ellipsometry (SE) to non-invasively identify the oxygen vacancy defects located in the bottom interfacial SiO₂ layer (BIF) of the scaled high-k/metal gate stacks. Discrete absorption features within the bandgap of the SiO₂ BIF are identified, and their relation to both intrinsic and process-induced defects is proposed. Sensitivity to changes in these defects with different process conditions is demonstrated, along with evidence suggesting that these same defects may contribute to the mechanism associated with the V_fb roll-off phenomenon.