Using a recently developed time-of-flight (TOF) medium energy ion scattering spectrometer (MEIS), we have investigated 3D elemental composition, morphology, and atomic defect structures for As implanted Si ultrashallow junctions (USJs) and As implanted FINFET nanostructures.

As depth profiles in As/Si ultra shallow junctions (USJs) were measured by TOF-MEIS for 2 keV As implantation ion energy before and after annealing. Electrically inactive arsenic (As) complexes in silicon are investigated. In heavily As-doped Si, the As atoms segregated in the interface Si region just below the SiO₂ layer are found to be in interstitial forms (As_i), while the As in the bulk Si region are found to be in the substitutional form (As_Si). Despite the substitutional form of As, most of the As are found to be electrically inactive in the bulk region, and we identify that the As forms the <111> oriented As_Si-Si-vacancy (As_Si-V_Si) complex. The As_i’s in the interface Si region are found to exist together with Si-interstitials (Si_i). It is suggested that the As_i deactivation centers in the interface Si region possibly accompany Si_i defects.

3D compostional distributions of As implanted FINFET structure were also analyzed with TOF-MEIS. Progresses in TOF-MEIS analysis of other nano-structured materials and devices in various nano & bio technology will be also discussed.

III-V semiconductor nanowires (NWs) continue to show promising results as components in energy saving devices. GaAs NW arrays recently beat the record for photovoltaic solar cells presenting a conversion efficiency of 15.3% ^[1]. Given the large surface to volume ratio of NWs, performance in such devices may be strongly determined by surface characteristics for example, morphology, the presence of various oxide species and surface structure. We study GaAs NWs grown by using the novel growth technique aerotaxy ^[2]. In aerotaxy growth the NWs are catalyzed from Au aerosol nanoparticles floating freely in a continuous N­₂ flow mixed with group III and V precursor gases. The growth rate of NWs using aerotaxy is much faster than for epitaxially grown NWs and the absence of expensive crystal substrate allows large scale economic production. A detailed understanding of the surface properties of these aerotaxy NWs is highly relevant in order to optimize device performance.

We compare surface structure and morphology of GaAs aerotaxy NWs to GaAs NWs grown epitaxially on a substrate. We obtain images of the NWs from microns to the atomic scale using both Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM). Comparing this to chemical information obtained via X-ray Photoemission Spectroscopy (XPS) we find that the different growth techniques results in NWs with very different morphology. Using in air AFM phase measurements we show that the aerotaxy NWs exhibit a rounder cross section with few or no large facets in comparison to the hexagonal geometry of epitaxially grown NWs. XPS measurements show that by annealing the NWs in the presence of atomic hydrogen, we can remove the native oxides which form on them when exposed to air as previously observed for the expitaxially grown NWs^[3][4]. From the XPS studies we can identify the different oxides present in the aerotaxy NWs before cleaning. We examine clean NWs using STM in Ultra High Vacuum. The morphology of the NWs is similar to as what is found in the AFM studies, however by direct atomic resolved imaging we can identify that even the round shaped aerotaxy NWs contain a considerable fraction of small unreconstructed patches of the {110} surface.

[1] http://www.solvoltaics.com/news.shtml (2015-05-01).

[2] M. Heurlin, et al. “Continuous gas-phase synthesis of nanowires with tunable properties”, Nature 492, 90-94 (2012).

[3] E. Hilner, et al. “Direct atomic scale imaging of III-V nanowire surfaces”, Nano Letters 8, 3978 (2008).

[4] M. Hjort, et al. “Direct imaging of atomic scale structure and electronic properties of GaAs wurtzite and zinc blende nanowire surfaces”, Nano Letters 13, 4492 (2013).

Future photomasks for extreme ultra violet lithography (EUVL) would be improved with broader bandwidth reflective multilayer coatings especially below the 7 nm technology node. Owing to its lower index of refraction, higher numerical aperture and contamination resistance Ruthenium (Ru) is a potential candidate for use on future generation EUVL masks. We characterized 20 layer stacks of Si/La, Si/Ru and Si/B₄C/Ru on Si (100) substrates. X Ray Reflectivity (XRR) and Atom Probe Tomography (APT) were carried out on a Si/La stack for period comparison. Si/Ru and Si/B₄C/Ru were prepared for phase comparison using XRR and X Ray Diffraction (XRD). Four samples of Si/B₄C/Ru multilayers with less than 1 Å period difference were compared using synchrotron-based EUV reflectometry.

XRR measurements were carried out using a Bruker D8 Discover with Cu K-alpha (λ = 1.542 Å) and a scintillator detector. Measurements were made at small detector angles, 2θ = 0-10^o. For texture and crystallite size, locked coupled scans were carried out using 0.2 mm beam slit and Lenxeye detector in 1D mode along 2θ = 10-110^o. Bruker’s Eva software was used to measure the peak positions and the ICDD PDF-4 data base was used to identify the Ru peaks. The APT measurements were performed by LEAP 4000X-Si instrument under UV laser illumination.

The result indicates the close agreement between XRR and APT for a 20 layer La/Si stack. XRR spectra of Si/Ru and Si/B₄C/Ru showed the multilayer period of ~ 7nm with sharp peaks which indicate the uniformity of deposited multilayers. Ru and B₄C showed polycrystalline behavior compared to amorphous Si. XRD results demonstrate that Ru layers tend to have (002) texture both in Si/Ru and Si/B₄C/Ru samples. Ru crystallite size in Si/Ru was observed to be larger than in Si/B₄C/Ru. The difference in crystallite size can be due Ru film thickness and its deposition on Si and B₄C. In the case of four Si/B₄C/Ru samples, the change in period was found to be correlated to changes in bandwidth and shifts in the position of peak EUV reflectivity. These results are not only of fundamental importance but also beneficial for improving the performance of Ru-based EUVL reflectors.

Key words: EUVL, XRR, XRD, APT, Synchrotron

*Corresponding author, Tel: (518) 305 7837, Fax: (518) 305 6587

Email address: Mohammad.Faheem@Globalfoundries.com [mailto:Mohammad.Faheem@Globalfoundries.com]