Anthony De Luca

Mechanism of β-FeSi2 precipitates growth-and-dissolution and pyramidal defects' formation during oxidation of Fe-contaminated silicon wafers

Fe-implanted Si-wafers have been oxidized at 900 °C and 1100 °C in order to investigate the behaviour of Fe atoms at the growing SiO2/Si interface and the impact on the integrity of microelectronic devices of an involuntary Fe contamination before or during the oxidation process. As-implanted and oxidized wafers have been characterized using secondary ion mass spectroscopy, atom probe tomography, and high-resolution transmission electron microscopy. Experimental results were compared to calculated implantation profiles and simulated images. Successive steps of iron disilicide precipitation and oxidation were evidenced during the silicon oxidation process. The formation of characteristic pyramidal-shaped defects, at the SiO2/Si interface, was notably found to correlate with the presence of β-FeSi2 precipitates. Taking into account the competitive oxidation of these precipitates and of the surrounding silicon matrix, dynamic mechanisms are proposed to model the observed microstructural evolution of the SiO2...

Scandium-enriched nanoprecipitates in aluminum providing enhanced coarsening and creep resistance

The development of high temperature aluminum alloys able to operate up to 400 oC is crucial to replace steel and titanium and decrease the mass of vehicles in the automotive and aerospace industries. This review relates the past two decades of aluminum alloy engineering done at Northwestern University focusing on developing coherent L12 Al3M nanoprecipitates strengthened aluminum alloys that are coarsening and shear-resistant at high temperature. Starting with the Al-Sc binary system, each new generation of alloys has become more complex to improve the alloy’s mechanical properties and coarsening resistance at high temperatures. The effects of rare-earth (Er, Y, Sm, Gd, Tb, Dy, Ho, Tm, Yb, Lu), transition metals (Zr, Ti, V, Nb, Ta), inoculants (Si, In, Sb, Sr, Ge, Zn) and solid solution (Mg, Li) elements onto the L12 Al3M precipitates is reviewed. The most recent alloys have optimized strength, coarsening resistance and lower prices, opening the doors to wider application uses.

Redistribution of Metallic Impurities in Si during Annealing and Oxidation: W and Fe

Atomic redistribution of W and Fe in Si were studied using secondary ion mass spectrometry and transmission electron microscopy. W diffusion experiments performed during isothermal annealing and during Si oxidation show that W atoms should use at least two different diffusion mechanisms. Experimental diffusion profiles can be well simulated by considering the simultaneous use of three different W diffusion mechanisms: the dissociative and the kick-out mechanisms, as well as an original mechanism based on the formation of a W-Si self-interstitial pair located on the interstitial Si sub-lattice. Fe redistribution was studied during the oxidation of a Fe-contaminated Si wafer. Fe is shown to be first pushed-out in Si by the mobile SiO2/Si interface, and thus to form Fe silicides precipitates at this interface. The silicide precipitates, which can exhibit a core-shell structure, appear to move with the SiO2/Si interface thanks to an oxidation/dissolution mechanism in the SiO2 and a nucleation/growth mechanism in the Si matrix. Furthermore, the rate difference between Si and Fe silicide precipitate oxidation leads to the formation of Si pyramidal defects at the SiO2/Si interface.