Richard Morris oral presentation (SN1-Mon2-3-2)
Interface profiling to sub-nm precision using uleSIMS
1 imec, Kapeldreef 75, 3001 Leuven, Belgium
2 University of Warwick, Gibbet Hill Road, CV4 7AL Coventry, United Kingdom
Ultra low energy secondary ion mass spectrometry (uleSIMS) offers nanometre depth resolution combined with excellent detection sensitivity. However, even for the lowest useable beam energy, the resulting probe sample interaction process will still modify the resulting profile shape. Silicon germanium alloys have significantly improved semiconductor device technology  with the advances in epitaxial growth being a significant enabler by allowing the Si/Ge ratio and layer thickness to be controlled and varied at the nanometre scale. Although semiconductor devices are often manipulated through modification of the electronic band structure, additional tailoring is possible by varying the layer thickness, matrix composition and dopant. However, another critical parameter to modern device functionality and its subsequent exploitation is the quality of any buried interfaces. Measuring and quantifying such buried interfaces with atomic resolution is however extremely challenging.
For this study a superficial ~30 nm thick Si1-xGex (x = 0.27) layer on Si sample prepared using chemical vapour deposition was used. Numerous depth profiles were taken using an Atomika 4500 utilising a normal incidence primary O2+ beam with energies in the range 0.25 2.5 keV. All the SIMS profiles were subsequently linearized by accounting for the well understood matrix effects on the Ge ion yield and erosion rate with primary ion beam energy.
To parameterize the SIMS response function and simplify the convolution process, a simplistic double exponential function was adopted. A methodology using simultaneous fitting of the resulting SIMS profiles was subsequently performed and the intrinsic sample interface profile determined to sub-nm precision . To benchmark our findings, HAADF-STEM analysis of the same interface was performed using a spherical aberration corrected JEOL 2100F microscope operating at 200 kV. Our intrinsic interface parameters were found to be in excellent agreement with those determined independently from the HAADF-STEM data.
 D. J. Paul, Semicond. Sci. Technol. 19, 2004 R75–R108.
 R. J. H. Morris et al, J. Am. Mass Spectrom, 27, 2016, 1694 1702.