Positon Annihilation Spectroscopy: an Emerging Technique For Characterization of Oxygen Vacancies in Hf-basedhigh-k Materials?

摘要

Doppler broadening measurements performed with a slow positron beam have shown an effective sensitivity to the properties of HfO_2 layers down to a thickness of 50 nm on a silicon substrate. The qualitative analysis of the DBS curves show that the void defect concentration in annealed layers is higher than in the as deposited ones either by ALD or PVD process. In addition, the as deposited ALD material is revealed to include more defects than the PVD one due to the out-of-range thickness for the ALD process. The role of a built-in electrical field related to charged defects at the HfO_2/Si interface is highlighted through simulation of the DBS parameters. It may explain the different behavior between ALD and PVD materials. However, a quantitative analysis based on data reduction using complete DBS simulations is still limited by the lack of the bulk parameters of the HfO_2 material. This requires thick layers of homogeneous properties that may be obtained through controlled long term annealing of PVD material. Also, to fulfill the nano-electronic specifications, coupling PAS with EELS-TEM analyses is mandatory.