Process-dependent defects in Si∕HfO2∕Mo gate oxide heterostructures

Abstract

The authors have used low energy electron-excited nanoscale-depth-resolved spectroscopy to probe the bulk and interface defect states of ultrathin Mo∕HfO2∕Si with conventional process sequences. Multiple deep level emissions are evident below the 5.9eV HfO2 near band edge, including three associated with HfO2 oxygen vacancies in different charge states predicted theoretically. Defects resembling SiO2-related nonbonding oxygen hole centers and positively charged O vacancies increase with depth within the 4nm HfO2 film suggesting Hf silicate formation at the HfO2∕Si interface. These states vary dramatically between process sequences and can be understood in terms of known reactions at HfO2–Si interfaces.

Electron spin resonance signature of the oxygen vacancy in HfO2

“…Guha 11 argued that the defect thermodynamics are consistent with assigning the defect to an O vacancy based on a comparison with similar oxides like SrTiO 3 . The observed energy levels of the defect from charge trapping, 3 charge pumping spectra, 4 optical absorption, 16 and cathodo-luminescence spectra 17 are all consistent with the calculated energy levels. 18 In ESR, Kang et al 19 have observed various paramagnetic defects such as the peroxyl radical in atomic layer deposited (ALD) HfO 2 .…”

“…[12][13][14][15] Nevertheless, in both types of device, the attribution to oxygen vacancies is based on electrical data, optical spectra, and internal consistency. 4,6,11,13,[15][16][17][18] There has been no fully accepted chemical identification of the oxygen vacancy in HfO 2 by, say, electron spin resonance (ESR). [19][20][21] This situation differs from the oxygen vacancy in TiO 2 22 and contrasts strongly with the vast literature on the paramagnetic E 0 and P b centers in SiO 2 .…”

MoS2 on an amorphous HfO2 surface: An ab initio investigation

“…Figure 3 Oxygen vacancy (V O ) defects are very likely to occur in HfO 2 . 18,19 Indeed, in a previous work, 5 we found that V O in amorphous HfO 2 surfaces had about the same formation energies (between 6.5 and 6.8 eV) under oxygen-rich conditions as those in the bulk phase. The formation of V O at HfO 2 surface sites gives rise to a partially occupied electronic level (v O ) $ 3.6 eV below the vacuum level, as indicated in Fig.…”

Calculation of semiconductor band structures and defects by the screened exchange density functional

“…From GGA calculations, it was unclear which defect was predominant, because GGA placed the vacancy levels either too low in the gap, or too high in the gap [75,76], depending on which correction scheme was applied to the energy levels for the band gap error. SX played a critical role in resolving this question, as it was the first calculation of the oxygen vacancy levels which placed the energy levels correctly [30], and close to the experimental values observed by charge injection and optical absorption www.pss-b.com [77][78][79][80][81]. It was then realized that the oxygen vacancy was likely to be the main defect, as this is consistent with its behaviour in similar oxides such as ZrO 2 .…”