Al3_3Sc thin films for advanced interconnect applications

Al$_x$Sc$_{1-x}$ thin films have been studied with compositions around Al$_3$Sc ($x = 0.75$) for potential interconnect metallization applications. As-deposited 25 nm films were x-ray amorphous but crystallized at 190{\deg}C with a recrystallization observed at 440{\deg}C. After annealing at 500{\deg}C, 24 nm thick stoichiometric Al$_3$Sc showed a resistivity of 12.6 ${\mu}{\Omega}$cm, limited by a combination of grain boundary and point defect (disorder) scattering. Together with ab initio calculations that found a mean free path of the charge carriers of 7 nm for stoichiometric Al$_3$Sc, these results indicate that Al$_3$Sc bears promise for future interconnect metallization schemes. Challenges remain in minimizing the formation of secondary phases as well as in the control of the non-stoichiometric surface oxidation and interfacial reaction with the underlying dielectrics.Comment: 15 pages, 4 figure

Perpendicular magnetic anisotropy of CoFeB\Ta bilayers on ALD HfO2

Perpendicular magnetic anisotropy (PMA) is an essential condition for CoFe thin films used in magnetic random access memories. Until recently, interfacial PMA was mainly known to occur in materials stacks with MgO\CoFe(B) interfaces or using an adjacent crystalline heavy metal film. Here, PMA is reported in a CoFeB\Ta bilayer deposited on amorphous high-kappa dielectric (relative permittivity kappa=20) HfO2, grown by atomic layer deposition (ALD). PMA with interfacial anisotropy energy K-i up to 0.49 mJ/m(2) appears after annealing the stacks between 200 degrees C and 350 degrees C, as shown with vibrating sample magnetometry. Transmission electron microscopy shows that the decrease of PMA starting from 350 degrees C coincides with the onset of interdiffusion in the materials. High-kappa dielectrics are potential enablers for giant voltage control of magnetic anisotropy (VCMA). The absence of VCMA in these experiments is ascribed to a 0.6 nm thick magnetic dead layer between HfO2 and CoFeB. The results show PMA can be easily obtained on ALD high-kappa dielectrics

Microwave Properties of Ba-Substituted Pb(Zr0.52_{0.52}Ti0.48_{0.48})O3_3 after Chemical-Mechanical Polishing

We have studied the effect of chemical-mechanical polishing (CMP) on the ferroelectric, piezoelectric, and microwave dielectric properties of Ba-substituted PZT (BPZT), deposited by pulsed laser deposition. CMP allowed for the reduction of the root mean square surface roughness of 600 nm thick BPZT films from 12.1nm to 0.79 nm. Ammonium peroxide (SC-1) cleaning was effective to remove Si CMP residuals. Measurements of the ferroelectric hysteresis after CMP indicated that the ferroelectric properties of BPZT were only weakly affected by CMP, while the piezoelectric d33 coefficient and the microwave permittivity were reduced slightly by 10%. This can be attributed to the formation of a thin dead layer at the BPZT surface. Moreover, the intrinsic dielectric permittivity at microwave frequencies between 1 and 25 GHz was not influenced by CMP, whereas the dead layer series capacitance decreased by 10%. The results indicate that the CMP process can be used to smoothen the BPZT surface without affecting the film properties strongly.Comment: 13 pages of text, 4 tables and 7 figures. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 801055 "Spin Wave Computing for Ultimately-Scaled Hybrid Low-Power Electronics" - CHIRO

Pulsed chemical vapor deposition of conformal GeSe for application as an OTS selector

The ovonic threshold switch (OTS) selector based on the voltage snapback of amorphous chalcogenides has received tremendous attention as it provides several desirable characteristics such as bidirectional switching, a controllable threshold voltage, high drive currents, and low leakage currents. GeSe is a well-known OTS selector that fulfills all the requirements imposed by future high-density storage class memories. Here, we report on pulsed chemical vapor deposition (CVD) of amorphous GeSe by using GeCl2 center dot C4H8O2 as a Ge source and two different Se sources namely bis-trimethylsilylselenide ((CH3)(3)Si)(2)Se (TMS)(2)Se and bis-triethylsilylselenide ((C2H5)(3)Si)(2)Se (TES)(2)Se. We utilized total reflection X-ray fluorescence (TXRF) to study the kinetics of precursor adsorption on the Si substrate. GeCl2 center dot C4H8O2 precursor adsorption on a 300 mm Si substrate showed under-dosing due to limited precursor supply. On the other hand, the Se precursor adsorption is limited by low reaction efficiency as we learned from a better within-wafer uniformity. Se precursors need Cl sites (from Ge precursor) for precursor ligand exchange reactions. Adsorption of (TMS)(2)Se is found to be much faster than (TES)(2)Se on a precoated GeClx layer. Atomic layer deposition (ALD) tests with GeCl2 center dot C4H8O2 and (TMS)(2)Se revealed that the growth per cycle (GPC) decreases with the introduction of purge steps in the ALD cycle, whereas a higher GPC is obtained in pulsed-CVD mode without purges. Based on this basic understanding of the process, we developed a pulsed CVD growth recipe (GPC = 0.3 angstrom per cycle) of GeSe using GeCl2 center dot C4H8O2 and (TMS)(2)Se at a reactor temperature of 70 degrees C. The 20 nm GeSe layer is amorphous and stoichiometric with traces of chlorine and carbon impurities. The film has a roughness of similar to 0.3 nm and it starts to crystallize at a temperature of similar to 370 degrees C. GeSe grown on 3D test structures showed excellent film conformality

Atomic Layer Deposition of Ruthenium on Ruthenium Surfaces: A Theoretical Study

Atomic layer deposition (ALD) of ruthenium using two ruthenium precursors, i.e. Ru(C5H5)2 (RuCp2) and Ru(C5H5(C4H4N) (RuCpPy), is studied using density functional theory. By investigating the reaction mechanisms on bare ruthenium surfaces, i.e. (001), (101) and (100) and H-terminated surfaces, an atomistic insight in the Ru ALD is provided. The calculated results show that on the Ru surfaces, both RuCp2 and RuCpPy can undergo dehydrogenation and ligand dissociation reactions. RuCpPy is more reactive than RuCp2. By forming a strong bond between N of Py and Ru of the surface, RuCpPy can easily chemisorb on the surfaces. The reactions of RuCp2 on the surfaces are less favorable as the adsorption is not strong enough. This could be a factor contributing to the higher growth-per-cycle of Ru using RuCpPy, as observed experimentally. By studying the adsorption on H-terminated Ru surfaces, we showed that H can prevent the adsorption of the precursors, thus inhibiting the growth of Ru. Our calculations indicate that the H content on the surface can have an impact on the growth-per-cycle. Finally, our simulations also demonstrate large impacts of the surface structure on the reaction mechanisms. Of the three surfaces, the (100) surface, which is the less stable and has a zigzag surface structure, is also the most reactive one.status: publishe