Detection of nitrogen incorporation in nm-thin HfO 2 layers on (1 0 0)Si by electron spin resonance

Abstract

We report on a low-temperature electron spin resonance (ESR) study of (1 0 0)Si/HfO 2 entities with ultrathin layers of amorphous (a)- HfO 2 deposited by distinct chemical vapor deposition (CVD) techniques using chemically different precursors. The incorporation of N is revealed in (1 0 0)Si/HfO 2 structures with ultrathin a-HfO 2 films deposited by CVD using Hf(NO 3) 4 as precursor: Upon 60Co γ-irradiation, a prominent ESR powder pattern is observed, which via ESR measurements at two observational frequencies has been incontrovertibly identified as originating from NO 2 radicals (density ⩾55 at ppm). The molecules are found to be stabilized and likely homogeneously distributed in the a-HfO 2 network. Based on symmetry considerations, it is suggested that during deposition, N is incorporated in the HfO 2 network as neutral N≡O 3 precursors, which are transformed into ESR-active NO 2 radicals upon γ-irradiation. The N incorporation appears inherent to the particular nitrado CVD process, an aspect that may bear on the electrical properties of the insulator, such as, e.g., introducing charge traps.