Point defects in thin HfAlO_x films probed by monoenergetic positron beams

Abstract

Thin HfAlO x films grown on SiON(0.9 nm)/Si by atomic layer deposition technique were characterized by using monoenergetic positron beams. The lifetimes of positrons in the HfAlO x film after post-deposition annealing (PDA) ranged between 412-403 ps. Since these lifetimes were longer than the lifetime of positrons trapped by point defects in metal oxides, such as LaCoO 3 , PbTiO 3 , and BaTiO 3 , the positrons in HfAlO x films were considered to annihilate from the trapped state by open spaces which exist intrinsically in their amorphous structure. The line-shape parameter S of the Doppler broadening spectrum corresponding to the annihilation of positrons in HfAlO x films decreased by PDA, and the S value decreased with increasing an O 2 -content in an atmosphere during PDA (0.004-1%). The observed behavior of the S value was attributed to the shrinkage of the open spaces due to the change in the matrix structure of HfAlO x . After P + -and B + -implantation into poly-Si films grown on the HfAlO x films, the diffusion of positrons in the Si substrates toward the HfAlO x film was suppressed. This fact was attributed to positive charges introduced near the HfAlO x films.

Asymmetric Distribution of Charge Trap in HfO2-Based High-k Gate Dielectrics

“…This annealing process is referred to as the post deposition annealing (PDA). The measurement method of the Doppler broadening spectra has been described in detail in the literature (11). S parameters contain information of the open space in high-k films.…”

“…The positron annihilation spectroscopy is a powerful tool to evaluate the existence of vacancy-type defects in metal oxide materials (11)(12)(13). The positron annihilation spectra of HfAlO x films annealed at various oxygen partial pressures were measured using a monoenergetic positron beam.…”