Chia-Han Lai

Thermally stable amorphous (AlMoNbSiTaTiVZr)50N50 nitride film as diffusion barrier in copper metallization

Results on copper metallization diffusion barriers using high-entropy alloy (HEA) nitride are reported. The HEA nitride (AlMoNbSiTaTiVZr)50N50 is amorphous in the as-deposited state and remains its noncrystallinity up to a high temperature of 850°C. To evaluate its diffusion barrier characteristics, Cu∕(AlMoNbSiTaTiVZr)50N50∕Si test structures were prepared and annealed under 750–900°C for 30min. The results show that the current nitride prevents the reaction between Cu and Si before its failure at 900°C. The outstanding barrier performance and high thermal stability of amorphous structure are suggested to originate from multiprincipal-element effects.

Effect of substrate bias on the structure and properties of multi-element (AlCrTaTiZr)N coatings

Multi-element (AlCrTaTiZr)N coatings are prepared by reactive RF magnetron sputtering. The influence of substrate bias (0 to −200 V) on the deposition rate, composition, structure and mechanical properties of these coatings is investigated. A reduction in both deposition rate and Al concentration is observed with increasing substrate bias. The grounded substrate is found to possess a columnar structure. The columnar structure is not so apparent in the denser coatings deposited at an applied substrate bias of −150 V. Furthermore, a minimum in coating roughness is found to occur at the intermediate substrate bias of −100 V. All the (AlCrTaTiZr)N coatings appear to have a single FCC structure from XRD analysis. Furthermore, it is determined from XRD that there is an increase in both (111) peak intensity and grain size, and a decrease in the lattice strain, for increasing substrate bias. The residual stress, hardness, elastic modulus and toughness of the coatings are found to be greatly enhanced by the substrate bias. The highest hardness and elastic modulus of approximately 36 Gpa and 360 GPa, respectively, were obtained at a substrate bias of −150 V.

Effects of nitrogen flow ratio on the structure and properties of reactively sputtered (AlMoNbSiTaTiVZr)Nx coatings

(AlMoNbSiTaTiVZr)Nx films are reactively sputtered from an AlMoNbSiTaTiVZr equimolar target under varied nitrogen flow ratio (RN). The concentration of nitrogen increases rapidly at lower RN and then saturates at around 50 at% when RN reaches 33% and above. At lower RN (0% and 3%), film structures are amorphous and their cross-sectional microstructures are featureless. When RN is 11%, FCC nitride nanocrystals coexist with the amorphous phase. At higher RN (33% and above), films exhibit a single NaCl-type FCC structure having fine column structures and nanograins. The texture of the FCC structures changes from (1 1 1) to (2 0 0) as RN increases from 33% to 66%. Enhanced hardness is observed upon the addition of nitrogen due to the strong bondings between N and target elements. Compared with reported high-entropy alloy (HEA)/nitride films deposited without bias, (AlMoNbSiTaTiVZr)Nx exhibits the highest hardness and modulus both in its alloy and nitride states. This not only confirms the effectiveness of the present alloy design but also demonstrates that HEA design could provide a new route to enhance the mechanical properties of alloy and nitride films.

Enhancement of exchange coupling between GaMnAs and IrMn with self-organized Mn(Ga)As at the interface

An atomically flat and uniform reaction layer of Mn(Ga)As was found to self-organize at the (Ga,Mn)As∕IrMn interface by postannealing. The Mn(Ga)As layer exhibits strong ferromagnetic characteristics up to the measured 300K. In particular, the manifested horizontal shift of field-cooled hysteresis loops shows a clear signature of exchange bias attributable to the exchange coupling between IrMn and Mn(Ga)As. Implication from composition analyses, exchange-bias effect, and thickness dependence of the Mn(Ga)As layer versus annealing conditions is also discussed.

Early-Stage Nucleation Crystallography of Sensitization-Activated Palladium Catalysts and Electrolessly Deposited Copper Films

The atomic-scale crystallography of early-stage nucleation of sensitization-activated palladium (Pd) catalysts and electrolessly plated copper (Cu) films has been investigated. Small Pd nanocrystallites of 5-10 nm were uniformly distributed as a single layer. Neighboring Pd nanocrystallites exhibited similar crystallography irrelevant to the random orientations of polycrystalline TaN substrate. Subsequently deposited Cu nanocrystallites of only 1 nm with small-angle boundaries nucleated on the Pd nanocrystallites with an orientation relationship of Cu [111] parallel to Pd [111]. In comparison, displacement-activated Pd preferentially nucleated on TaN, and Cu followed the orientation of Pd grains with a relationship of Cu [111] parallel to Pd [200].

The influence of magnetostatic interactions in exchange-coupled composite particles

Exchange-coupled composite (ECC) particles are the basic constituents of ECC magnetic recording media. We examine and compare two types of ECC particles: (i) core–shell structures, consisting of a hard-magnetic core and a coaxial soft-magnetic shell and (ii) conventional ECC particles, with a hard-magnetic core topped by a soft cylindrical element. The model we present describes the magnetic response of the two ECC particle types, taking into account all significant magnetic contributions to the energy landscape. Special emphasis is given to the magnetostatic (dipolar) interaction energy. We find that both the switching fields and the zero-field energy barrier depend strongly on the particle geometry. A comparison between the two types reveals that core–shell ECC particles are more effective in switching field reduction, while conventional ECC particles maintain a larger overall figure of merit.