Constructing Conductive MoOx Thin Films by Plasma‐Enhanced Atomic Layer Deposition

Comparisons of alumina barrier films deposited by thermal and plasma atomic layer deposition

The wide applications of ultrathin group IV metal oxide films (TiO2, ZrO2 and HfO2) probably expose materials to potentially reactive etchants and solvents, appealing for extraordinary chemical stability and corrosion resistance property. In this paper, TiO2 ultrathin films were deposited on Si at 200 °C while ZrO2 and HfO2 were grown at 250 °C to fit their growth temperature window, by thermal atomic layer deposition (TALD) and plasma-enhanced ALD (PEALD). A variety of chemical liquid media including 1 mol/L H2SO4, 1 mol/L HCl, 1 mol/L KOH, 1 mol/L KCl, and 18 MΩ deionized water were used to test and compare chemical stability of all these as-deposited group IV metal oxides thin films, as well as post-annealed samples at various temperatures. Among these metal oxides, TALD/PEALD HfO2 ultrathin films exhibit the best chemical stability and anti-corrosion property without any change in thickness after long time immersion into acidic, alkaline and neutral solutions. As-deposited TALD ZrO2 ultrathin films have slow etch rate of 1.06 nm/day in 1 mol/L HCl, however other PEALD ZrO2 ultrathin films and annealed TALD ones show better anti-acid stability, indicating the role of introduction of plasma O2 in PEALD and post-thermal treatment. As-deposited TiO2 ultrathin films by TALD and PEALD are found to be etched slowly in acidic solutions, but the PEALD can decrease the etching rate of TiO2 by ~41%. After post-annealing, TiO2 ultrathin films have satisfactory corrosion resistance, which is ascribed to the crystallization transition from amorphous to anatase phase and the formation of 5% Si-doped TiO2 ultrathin layers on sample surfaces, i.e. Ti-silicate. ZrO2, and TiO2 ultrathin films show excellent corrosion endurance property in basic and neutral solutions. Simultaneously, 304 stainless steel coated with PEALD-HfO2 is found to have a lower corrosion rate than that with TALD-HfO2 by means of electrochemical measurement. The pre-treatment of plasma H2 to 304 stainless steel can effectively reduce interfacial impurities and porosity of overlayers with significantly enhanced corrosion endurance. Above all, the chemical stability and anti-corrosion properties of IV group metal oxide coatings can be improved by using PEALD technique, post-annealing process and plasma H2 pre-treatment to substrates.

We have employed plasma-enhanced and thermal atomic layer deposition (ALD) within the temperature range of 50–150°C for the deposition of ultra-thin (10–50 nm) Al2O3 films on 100Cr6 steel and aluminium Al2024-T3 alloys. [Al(CH3)3] was used as the precursor with either an O2 plasma or water as co-reactants. Neutral salt spray tests showed that the thicker films offered the best corrosion-resistance. Using cyclic voltametry, the 50 nm films were found to be the least porous (<0.5%). For 10 nm thick films, plasma-enhanced ALD afforded a lower porosity and higher film density than thermal ALD. ToF-SIMS measurements on 100Cr6 showed that the main ‘bulk’ of the films contained very few impurities, but OH and C were observed at the interfaces. TEM confirmed that the films were conformal on all substrates and the adhesion was excellent for the films deposited by plasma-enhanced ALD but not for thermal ALD, as delamination was observed. On the basis of these and other results, the prospects of the application of ALD films for corrosion protection, and the use of plasma-enhanced ALD to promote their nucleation, is discussed.

Titanium oxide (TiO2) deposited by atomic layer deposition (ALD) is used as a protective layer in photocatalytic water splitting system as well as a dielectric in resistive memory switching. The way ALD is performed (thermally or plasma-assisted) may change the growth rate as well as the electronic properties of the deposited films. In the present work, the authors verify the influence of the ALD mode on functional parameters, by comparing the growth rate and electronic properties of TiO2 films deposited by thermal (T-) and plasma-enhanced (PE-) ALD. The authors complete the study with the electrical characterization of selected samples by means of capacitance–voltage and current–voltage measurements. In all samples, the authors found a significant presence of Ti3+ states, with the lowest content in the PE-ALD grown TiO2 films. The observation of Ti3+ states was accompanied by the presence of in-gap states above the valence band maximum. For films thinner than 10 nm, the authors found also a strong leakage current. Also in this case, the PE-ALD films showed the weakest leakage currents, showing a correlation between the presence of Ti3+ states and leakage current density.

Thermal atomic layer deposition (TALD) and plasma atomic layer deposition (PALD) were used for producing thin NiO x films from nickel(II) acetylacetonate Ni(acac)2, employing different oxidizing agents (deionized water H2O, ozone O3, and molecular oxygen O2). The films were deposited at 300 °C (TALD) and 220 °C (PALD) over glass substrates; their physical and chemical properties were considerably influenced by the choice of oxidizing agents. In particular, ALD(H2O) samples had a low growth per cycle (GPC) and a high concentration of defects. The best NiO x parameters were achieved with PALD(O2), featuring high GPC (0.07 nm/cycle), high optical transparency in the visible region, electrical resistivity (1.18 × 104 Ω·cm), good carrier concentration (8.82 × 1013 cm-3), and common mobility (5.98 cm2/V·s). The resulting NiO x films are polycrystalline and homogeneous in thickness and composition. According to ultraviolet photoelectron spectroscopy (UPS), work function φ and the valence band maximum E V can be tuned by the choice of the coreactant employed, with variations of up to ∼1 eV between TALD and PALD synthesis. Our results suggest that PALD permits one to achieve a better energy band alignment of NiO x and CsFAMAPbBrI perovskite, which is promising for solar cell applications.

Atomic layer deposition of ZnO on MoS2 and WSe2

Only a few iron precursors that can be used in the atomic layer deposition (ALD) of iron oxides have been examined thus far. This study aimed to compare the various properties of FeOx thin films deposited using thermal ALD and plasma-enhanced ALD (PEALD) and to evaluate the advantages and disadvantages of using bis(N,N'-di-butylacetamidinato)iron(II) as an Fe precursor in FeOx ALD. The PEALD of FeOx films using iron bisamidinate has not yet been reported. Compared with thermal ALD films, PEALD films exhibited improved properties in terms of surface roughness, film density, and crystallinity after they were annealed in air at 500 °C. The annealed films, which had thicknesses exceeding ~ 9 nm, exhibited hematite crystal structures. Additionally, the conformality of the ALD-grown films was examined using trench-structured wafers with different aspect ratios.

Formation of Ni silicide from atomic layer deposited Ni

ABSTRACTAn electrical and analytical study was carried out to investigate TiW/ZnO Schottky contacts with 30 nm ZnO thin film layers deposited by pulsed laser deposition (PLD), plasma enhanced atomic layer deposition (PEALD), and thermal atomic layer deposition (TALD). Devices with ZnO layer deposited by TALD exhibit approximately linear behavior in their I-V measurements. However, both devices with ZnO layers deposited by PEALD and PLD behaved like Schottky rectifiers with barrier heights between TiW and ZnO of 0.51 eV and 0.45 eV respectively and ideality factors of 2.0 and 2.3 respectively. The PEALD deposited ZnO Schotty diodes demonstrated an on/off rectifying ratio of about 25 at ±1 V. The leakage current values of the PLD deposited ZnO Schottky diodes are significantly larger than those of PEALD, leading to a poor on/off rectifying ratio of ∼4. Due to the small thickness, a critical breakdown strength of 1.3 MV/cm was estimated for PEALD-ZnO thin films.

HfO2 was deposited at 80–250 °C by plasma-enhanced atomic layer deposition (PEALD), and properties were compared with those obtained by using thermal atomic layer deposition (thermal ALD). The ALD window, i.e., the region where the growth per cycle (GPC) is constant, shifted from high temperatures (150–200 °C) to lower temperatures (80–150 °C) in PEALD. HfO2 deposited at 80 °C by PEALD showed higher density (8.1 g/cm3) than those deposited by thermal ALD (5.3 g/cm3) and a smooth surface (RMS Roughness: 0.2 nm). HfO2 deposited at a low temperature by PEALD showed decreased contaminants compared to thermal ALD deposited HfO2. Values of refractive indices and optical band gap of HfO2 deposited at 80 °C by PEALD (1.9, 5.6 eV) were higher than those obtained by using thermal ALD (1.7, 5.1 eV). Transparency of HfO2 deposited at 80 °C by PEALD on polyethylene terephthalate (PET) was high (> 84%). PET deposited above 80 °C was unable to withstand heat and showed deformation. HfO2 deposited at 80 °C by PEALD showed decreased leakage current from 1.4 × 10−2 to 2.5 × 10−5 A/cm2 and increased capacitance of approximately 21% compared to HfO2 using thermal ALD. Consequently, HfO2 deposited at a low temperature by PEALD showed improved properties compared to HfO2 deposited by thermal ALD.

Growth characteristics and properties of Ga-doped ZnO (GZO) thin films grown by thermal and plasma-enhanced atomic layer deposition

Vanadium pentoxide was deposited by atomic layer deposition (ALD) from vanadyl-tri-isopropoxide (VTIP). Water or oxygen was used as a reactive gas in thermal and plasma-enhanced (PE) processes. For PE ALD, there was a wide ALD temperature window from 50 to . Above , VTIP decomposed thermally, resulting in the chemical vapor deposition (CVD) of vanadium pentoxide. The PE ALD reactions saturated much faster than during thermal ALD, leading to a growth rate of approximately 0.7 Å/cycle during PE ALD using or . Optical emission spectroscopy showed combustion-like reactions during the plasma step. X-ray diffraction was performed to determine the crystallinity of the films after deposition and after postannealing under He or atmosphere. Films grown with CVD at and PE ALD at were (001)-oriented as deposited, while thermal and PE ALD films grown at were amorphous as deposited. The crystallinity of the PE ALD could be correlated to its high purity, while the other films had significant carbon contamination, as shown by X-ray photoelectron spectroscopy. Annealing under He led to oxygen-deficient films, while all samples eventually crystallized into under .

Electrical contacts to semiconductors are usually prepared by physical vapor deposition, but we explore thermal atomic layer deposition (ALD) to create molybdenum carbonitride-based Schottky diodes to gallium nitride. We also compare our findings to similar diodes that we previously prepared by plasma enhanced atomic layer deposition (PEALD). A stop-flow process was implemented to overcome a nucleation delay on gallium nitride during thermal ALD, which was not required for PEALD; however, the as-deposited diodes had better electrical behavior when prepared by thermal ALD. Current-voltage measurements reveal a higher as-deposited Schottky barrier height of 0.68±0.01eV and a lower ideality factor of 1.06±0.01 using thermal ALD. After annealing the diodes at 600 °C, the Schottky barrier height increased to 0.82±0.04eV, and the ideality factor decreased to 1.04±0.04, which are similar to annealed diodes prepared by PEALD. Although capacitance-voltage measurements indicate a higher barrier height (0.99 ± 0.1 eV) after annealing diodes prepared by thermal ALD, there was a minimal variation as a function of frequency. Together with the abrupt interface between the molybdenum carbonitride and gallium nitride observed by transmission electron microscopy, these measurements indicate a high-quality interface.

We propose a deposition method capable of independently controlling the spatial density and average size of Ru nanocrystals by using both plasma-enhanced and thermal atomic layer deposition (ALD). Plasma-enhanced ALD is used to promote the nucleation of Ru nanocrystals, while thermal ALD is used to assist their growth. By the rigorous selection of each stage, we can demonstrate the formation of Ru nanocrystals with a density variation from 3.5 X 10 11 to 8.4 X 10 11 cm -2 and sizes from 2.2 to 5.1 nm, which is in the optimum density and size range of nanocrystal floating-gate memory application.

Atomic layer deposition of transition metals for silicide contact formation: Growth characteristics and silicidation