Jaehong Yoon

Plasma-enhanced atomic layer deposition of Co using Co（MeCp）2 precursor

Abstract Cobalt (Co) thermal or plasma enhanced atomic layer deposition (PE-ALD) was investigated using a novel metal organic precursor, Co(MeCp) 2 , and NH 3 or H 2 or their plasma as a reactant. The growth characteristics, electrical and microstructural properties were investigated. Especially, PE-ALD produced Co thin films at low growth temperature down to 100 °C. Interestingly, the low temperature growth of Co films showed the formation of columnar structure at substrate temperature below 300 °C. The growth characteristics and films properties of PE-ALD Co using bis(η-methylcyclopentadienyl) Co(II) (Co(MeCp) 2 ) was compared with those of PE-ALD Co using other Cp based metal organic precursors, bis-cyclopentadienyl cobalt (II) (CoCp 2 ) and cyclopentadienyl isopropyl acetamidinato-cobalt (Co(CpAMD)).

Formation of Vertically Aligned Cobalt Silicide Nanowire Arrays Through a Solid-State Reaction

We report for the first time synthesis of high-density arrays of vertically well-aligned cobalt monosilicide (CoSi) nanowires (NWs) in a large area via a solid-state reaction. The vertical arrays of 1-μm-long Si NWs were first grown on a p-type (1 0 0) Si substrate by the aqueous electroless etching (AEE) method, and a 40-nm-thick Co layer was conformally deposited using a thermal atomic layer deposition system as revealed by SEM and transmission electron microscope analyses. The rapid thermal annealing process was carried out at various temperatures ranging from 700 to 1000 °C; the X-ray diffraction analysis confirmed that the polycrystalline CoSi NW arrays were formed at temperatures above 900 °C. The required high driving force for this silicide formation can be attributed to the significant amounts of oxygen-related contaminants at the defect sites of the highly rough surfaces of AEE-grown Si NWs. To demonstrate practical applications, field emitters and Schottky diodes were fabricated using the vertically aligned CoSi NW arrays. The field emission measurements showed a turn-on field of 10.9 V/μm and a field enhancement factor of 328, indicating the feasibility of vertically aligned CoSi NW arrays as promising field emitters. For the Schottky diodes, the measured Schottky barrier height was 0.52 eV and the estimated ideality factor obtained from the I-V characteristic curves was 2.28.

Atomic layer deposition of 1D and 2D nickel nanostructures on graphite

One-dimensional (1D) nanowires (NWs) and two-dimensional (2D) thin films of Ni were deposited on highly ordered pyrolytic graphite (HOPG) by atomic layer deposition (ALD), using NH3 as a counter reactant. Thermal ALD using NH3 gas forms 1D NWs along step edges, while NH3 plasma enables the deposition of a continuous 2D film over the whole surface. The lateral and vertical growth rates of the Ni NWs are numerically modeled as a function of the number of ALD cycles. Pretreatment with NH3 gas promotes selectivity in deposition by the reduction of oxygenated functionalities on the HOPG surface. On the other hand, NH3 plasma pretreatment generates surface nitrogen species, and results in a morphological change in the basal plane of graphite, leading to active nucleation across the surface during ALD. The effects of surface nitrogen species on the nucleation of ALD Ni were theoretically studied by density functional theory calculations. Our results suggest that the properties of Ni NWs, such as their density and width, and the formation of Ni thin films on carbon surfaces can be controlled by appropriate use of NH3.

Cu-Al alloy formation by thermal annealing of Cu/Al multilayer films deposited by cyclic metal organic chemical vapor deposition

One of the most important issues in future Cu-based interconnects is to suppress the resistivity increase in the Cu interconnect line while decreasing the line width below 30 nm. For the purpose of mitigating the resistivity increase in the nanoscale Cu line, alloying Cu with traces of other elements is investigated. The formation of a Cu alloy layer using chemical vapor deposition or electroplating has been rarely studied because of the difficulty in forming Cu alloys with elements such as Al. In this work, Cu-Al alloy films were successfully formed after thermal annealing of Cu/Al multilayers deposited by cyclic metal-organic chemical vapor deposition (C-MOCVD). After the C-MOCVD of Cu/Al multilayers without gas phase reaction between the Cu and Al precursors in the reactor, thermal annealing was used to form Cu-Al alloy films with a small Al content fraction. The resistivity of the alloy films was dependent on the Al precursor delivery time and was lower than that of the aluminum-free Cu film. No presence of intermetallic compounds were detected in the alloy films by X-ray diffraction measurements and transmission electron spectroscopy.

Silicide Formation of Atomic Layer Deposition Co Using Ti and Ru Capping Layer

was formed through annealing of atomic layer deposition Co thin films. Co ALD was carried out using bis(N,N`-diisopropylacetamidinato) cobalt () as a precursor and as a reactant; this reaction produced a highly conformal Co film with low resistivity (). To prevent oxygen contamination, sputtered Ti and ALD Ru were used as capping layers, and the silicide formation prepared by rapid thermal annealing (RTA) was used for comparison. Ru ALD was carried out with (Dimethylcyclopendienyl)(Ethylcyclopentadienyl) Ruthenium ((DMPD)(EtCp)Ru) and as a precursor and reactant, respectively; the resulting material has good conformality of as much as 90% in structure of high aspect ratio. X-ray diffraction showed that was in a poly-crystalline state and formed at over of annealing temperature for both cases. To investigate the as-deposited and annealed sample with each capping layer, high resolution scanning transmission electron microscopy (STEM) was employed with electron energy loss spectroscopy (EELS). After annealing, in the case of the Ti capping layer, about 40 nm thick was formed while the interlayer, which is the native oxide, became thinner due to oxygen scavenging property of Ti. Although Si diffusion toward the outside occurred in the Ru capping layer case, and the Ru layer was not as good as the sputtered Ti layer, in terms of the lack of scavenging oxygen, the Ru layer prepared by the ALD process, with high conformality, acted as a capping layer, resulting in the prevention of oxidation and the formation of .

Atomic layer deposition for nanoscale contact applications

We review our efforts on atomic layer deposition (ALD) processes of Co and Ni thin films and their applications for nanoscale contact. First, PE-ALD Co processes was developed using various metal organic precursors and NH3 plasma as a reactant. At optimal conditions, highly pure Co films were deposited with low resistivity down to 10 µΩcm. For this case, epitaxial CoSi2 was formed through nitride mediated epitaxy, due the formation of a-SiNx interlayer. The effects of nitrogen during PE-ALD Co were also studied by using N2/H2 plasma. To improve the conformality, thermal ALD (T-ALD) using various metal organic precursors including Co(iPr-AMD)2 were investigated. Similarly, PE-ALD using NH3 plasma and thermal ALD based on metal organic precursors were developed. Highly conformal Ni film was deposited and the formation of Ni silicide was studied by post-deposition annealing. The film properties were studied using various analysis techniques. Thus, ALD of transition metal is expected to be a viable process for the formation of nanoscale contact in near future device fabrication.