A new analytical method for characterising the bonding environment at rough interfaces in high-k gate stacks using electron energy loss spectroscopy

Abstract

Determining the bonding environment at a rough interface, using for example the near edge fine structure in electron energy loss spectroscopy (EELS), is problematic since the measurement contains information from the interface and surrounding matrix phase. Here we present a novel analytical method for determining the interfacial EELS difference spectrum (with respect to the matrix phase) from a rough interface of unknown geometry which, unlike multiple linear least squares (MLLS) fitting, does not require the use of reference spectra from suitable standards. The method is based on analysing a series of EELS spectra with variable interface to matrix volume fraction and, as an example, is applied to a TiN/ poly-Si interface containing oxygen in a HfO 2 -based, high-k dielectric gate stack. A silicon oxynitride layer was detected at the interface consistent with previous results based on MLLS fitting.

Characterising the surface and interior chemistry of core–shell nanoparticles using scanning transmission electron microscopy

“…Multiple scattering causes a redistribution of intensity in the core loss edge. The raw data can be corrected for multiple scattering and diffraction contrast by near-simultaneously acquiring the low loss region of the EELS spectrum using, for example, a dual-EELS system ( [23]; see also [10] for more details). A major source of error however, is the assumption of an idealised spherical geometry for the nanoparticle.…”

“…A major source of error however, is the assumption of an idealised spherical geometry for the nanoparticle. When the analytical method was first developed for a rough interface [10] the irregular interfacial geometry was directly taken into account by using the HAADF intensity trace acquired across the interface. This requires as input parameters the HAADF intensity for the 'bulk' phases either side of the interface.…”

“…This requires as input parameters the HAADF intensity for the 'bulk' phases either side of the interface. Furthermore the 'bulk' phases must have identical thicknesses, although a dual-EELS based method for dealing with non-uniform thicknesses was outlined in [10]. These criteria are satisfied for a parallel sided thin foil with the interface in an 'end-on' orientation, but are not applicable for a core-shell nanoparticle where the thickness varies across the nanoparticle and where the beam generally samples a mixture of the core and shell regions rather than the pure 'bulk' phase(s).…”

“…an interface that has projected width when viewed 'end-on') has been developed by Mendis et al [10]. Similar principles can be used in the characterisation of core-shell nanoparticles.…”

Accurate measurement of absolute experimental inelastic mean free paths and EELS differential cross-sections

“…The surface layer problem is tackled by taking data over a range of specimen thickness and then using a least squares fitting technique to extract the bulk behaviour in a manner similar to that used in earlier work by Mendis and Craven [28]. In this work, this is performed by plotting I/I 0 against N and determining σ or dσ/dE from this.…”