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Distribution and migration of oxygen in the highk/metal gate stack has a strong impact on the CMOS transistor electrical characteristics. Excess O can cause interlayer (IL) growth and subsequent increase of Equivalent Oxide Thickness (EOT), whereas O-vacancies induced by the metal gate contact may lead to unpredictable and feature size dependent shifts in threshold voltage (Vt). In addition to these phenomena, we have recently described a new migration pathway for O in poly-Si/TiN/TiO2-based high-k/stacks [1]. Besides re-growth of the bottom IL, excess O –released by the thermal decomposition of TiO2-based high-k stacks upon annealing– was observed to diffuse upwards, resulting in SiO2 growth at the TiN/poly-Si interface, as evidenced by regular SIMS analysis following the O main isotope. Here, we have employed SIMS depth profiling in combination with isotopic labeling –using minority Oisotope– to characterize the migration and/or redistribution of O in the high-k metal gate stack (HK/MG) at different stages of processing. Firstly, the creation of vacancy defects in high-k dielectrics –induced by the TiN-based metal gate contact upon high temperature annealing– is the most probable cause for large (~500 meV) Vt shifts, which is especially problematic for pFET devices. We have demonstrated that these shifts can be largely recovered after a lowtemperature low-pressure top-down oxygenation step on TiN metal gate exposed by poly-Si removal, while preventing excessive oxidation of TiN and parasitic IL regrowth [2]. Using SIMS, we have systematically investigated the incorporation of O by SIMS for different temperatures and TiN thicknesses on TiN-gated high-k films, subjected to top-down oxygenation with isotopic labeled O2, see Figure 1. We have thus established that incorporated O-doses –needed to remove the defects created in a metal-HfO2 contact– amount 1.4e14 to 3.9e14 at.cm. In addition, O-profiles after top-down oxidation show a small but significant shift with respect to pre-existing O towards the TiN-interface (see inset Figure 1). This implies that passivation of vacancies preferentially occurs in the top portion of the high-k layer, consistent with negligibly small oxide (IL) re-growth. Secondly, remote O-scavenging from the SiO2 interlayer (IL) using a poly-Si/doped TiN metal gate stack is a promising technique to achieve aggressive EOT scaling in a gate-first flow, compliant with 16 nm technology node requirements [3]. The remote scavenging mechanism is based on the presence of a metallic element M, inserted in the TiN metal gate at a certain separation from the high-k interface. This scavenging element is capable of scavenging O from the SiO2 IL upon poly activation anneal, as evidenced by TEM and conventional O-SIMS. Here, we have employed SIMS to determine the kinetics of O-scavenging from Hf-based high-k dielectric –enriched in O by isotopic exchange after high-k deposition upon low-temperature O2 exposure– towards M-TiN alloy for different annealing temperatures and IL’s. Use of an O-isotope enriched high-k layer allows following of O-redistribution through scavenging and isotopic exchange for different annealing temperatures, see Figure 2. This approach has revealed a subtle effect of IL composition on remote O-scavenging kinetics. In addition, rapid isotopic exchange between the different interfaces through the TiN metal gate is seen to occur upon high temperature anneal, indicating rapid Odiffusion in these stacks. These examples demonstrate the benefits of using O isotope labeling for SIMS analysis to resolve small quantities of O and to obtain fundamental knowledge on oxygen transport in high-k metal gate stacks.

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We present evidence for the instability in the crystalline (metallic) state of binary Te-free phase-change Ge–Sb thin films considered for integration into nonvolatile nanosized memory cells. We find that while the amorphous (semiconducting) phase of eutectic Sb–15at.% Ge is very robust until Sb crystallization at 240°C, at about 350°C, germanium rapidly precipitates out. Ge precipitation, visualized directly with transmission electron microscopy, is exothermic and is found to affect the films’ reflectivity, resistance, and stress. It converts melting into a two-step process, which may seriously impact the switching reliability of a device.

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We report on a study of hard amorphous carbon thin films prepared by condensing streams of energetic carbon species, onto a range of substrates maintained at different temperatures. The carbon vapor is generated either by ion sputtering, laser ablation or e-beam evaporation. Spatially resolved electron-energy-loss spectra reveal variations in the films′ microstructure brought about by altering the deposition conditions. We estimate that the density of the different films varies between 2.0 and 3.26 g/cm3. We observe an evolution towards denser films upon increasing incident beam energy, reducing substrate temperature, and increasing substrate thermal conductivity. Low density films contain a predominance of trigonally bonded sp2-hybridized carbon (i.e graphitic carbon) and the highest density films contain a high fraction (∽ 80%) of tetr-ahedral sp3-bonded carbon (i.e. diamond-like).

The authors present direct evidence for Te segregation to the grain boundaries in chalcogenide Ge2Sb2Te5 films by using transmission electron microscopy scans with a 0.5nm diameter focused probe. This finding is consistent with the observed impeded grain growth and with the post-transition relief of a “spikelike” stress, fully to the pretransition level. Te motion shows up in void formation below 200°C, a pileup of Te at the surface and its loss at higher (above 400°C) temperatures. Tuning the driving force for this segregation may be key for the optimal phase-change material design.

Electron energy-loss spectroscopy is well suited to the study of interfaces because the ionization edges can be used to identify the atomic species present and the near edge fine structures on the edges reveal information on the electronic structure surrounding these atoms. This information can be extracted from regions of sample approaching atomic dimensions. A challenge is to be able to map and interpret spectral features with a level of confidence that will allow explanations of physical properties of interest.The term Spectrum-Line is used here to refer to a linear array of spectra, recorded sequentially along a line traced out by the electron probe and is the 1 dimensional analog of the Spectrum-Image. Processing Spectrum-Lines to generate quantitative profiles can provide a vivid picture of changes in composition, a valence state, or site occupancy across an interface. To aid interpretation and guide further spectrum analysis the near-edge fine structures can be compared to spectra from compounds whose atomic coordinations are well known or modeled using the results of band-structure or molecular orbital calculations of electronic structures.

The presence of internal boundaries can significantly influence many important properties of materials, such as fracture toughness, creep, electrical conductivity and magnetic behavior. Interfacial structure, chemical composition and bonding, on a nanometer length scale, are often controlling and sought after factors influencing these properties. An electron spectroscopic technique, known as energy-loss near edge structure (ELNES) analysis, can be utilized to probe compositional and bonding variations with a spatial resolution less than 1 nm and is therefore well suited to this endeavor. When a fast electron passes through a material in an electron microscope, it collides with the electrons bound to the atoms in that sample. As a result, the fast electron often gives up a small fraction of its kinetic energy to the bound electrons. The laws of quantum mechanics dictate that these so-called inelastic scattering events will only take place if the bound electron can gain enough energy to enter an empty energy level.

Electron energy loss spectroscopy of voidite defects in natural diamond shows that they are composed of nitrogen which is likely to be present in the form of solid N2 under high pressure (ca. 10 GPa). A similar examination of platelets has failed to reveal any nitrogen in them. It is proposed that the voidites are generated by a discontinuous precipitation mechanism as the platelets decompose. A similar study of the the chemistry of nanometre sized mineral particles present in most diamonds shows they are related to the earth’s magma although there are notable differences.