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

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

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.

Formation of Ni silicide from atomic layer deposited Ni

Herein, amorphous molybdenum oxide films are constructed by thermal atomic layer deposition (T‐ALD) and plasma‐enhanced atomic layer deposition (PE‐ALD). The physical and chemical properties of molybdenum oxide films prepared by the two methods are systematically compared by means of film growth law, atomic force microscope, scanning electron microscope, etc. The results show that the amorphous molybdenum oxide physical phase prepared by both ALD methods is MoO3. Compared with T‐ALD MoO3, the growth rate of MoO3 thin films prepared by PE‐ALD is higher. Compared to PE‐ALD MoO3, the MoO3 films prepared by T‐ALD did not have nucleation delayed to a laminar growth mode, resulting in smoother deposited films and contained less impurity carbon. The MoO3 prepared by PE‐ALD contains 7.4% impurity carbon. This carbon‐doped film significantly improves the conductivity of the MoO3 film and shows good electrochemical activity. As expected, the MoO3 films prepared by PE‐ALD show good electrocatalytic oxygen evolution reaction. The overpotential is only 259 mV at 10 mA cm−2 and continues to evolution oxygen for 60 h with almost no attenuation, indicating that carbon doping significantly improves the catalytic intrinsic activity and stability of MoO3.

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.

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.

Self-aligned structured oxide thin-film transistors (TFTs) are appropriate candidates for use in the backplanes of high-end displays. Although SiNx is an appropriate candidate for use in the gate insulators (GIs) of high-performance driving TFTs, direct deposition of SiNx on top of high-mobility oxide semiconductors is impossible due to significant hydrogen (H) incorporation. In this study, we used AlOx deposited by thermal atomic layer deposition (T-ALD) as the first GI, as it has good H barrier characteristics. During the T-ALD, however, a small amount of H from H2O can also be incorporated into the adjacent active layer. In here, we performed O2 or N2O plasma treatment just prior to the T-ALD process to control the carrier density, and utilized H to passivate the defects rather than generate free carriers. While the TFT fabricated without plasma treatment exhibited conductive characteristics, both O2 and N2O plasma-treated TFTs exhibited good transfer characteristics, with a Vth of 2 V and high mobility (∼30 cm2 V−1 s−1). Although the TFT with a plasma-enhanced atomic layer deposited (PE-ALD) GI exhibited reasonable on/off characteristics, even without any plasma treatment, it exhibited poor stability. In contrast, the O2 plasma-treated TFT with T-ALD GI exhibited outstanding stability, i.e., a Vth shift of 0.23 V under positive-bias temperature stress for 10 ks and a current decay of 1.2% under current stress for 3 ks. Therefore, the T-ALD process for GI deposition can be adopted to yield high-mobility, high-stability top-gate-structured oxide TFTs under O2 or N2O plasma treatment.

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.

In this Letter, we report that both thermal atomic layer deposition (ALD) with H2O, and plasma ALD with an O2 plasma, can be used to deposit Al2O3 for a high level of surface passivation of crystalline silicon (c‐Si). For 3.5 Ω cm n‐type c‐Si, plasma ALD Al2O3 resulted in ultralow surface recombination velocities of Seff &lt; 0.8 cm/s. Thermal ALD Al2O3 also showed an excellent passivation level, with Seff &lt; 2.5 cm/s. In contrast to plasma ALD Al2O3, thermal ALD Al2O3 provides some surface passivation in the as‐deposited state, although annealing is required to activate it to the full extent. For thermal ALD, the optimal temperature for this anneal was found to be slightly lower, ∼375 °C, than for plasma ALD Al2O3, ∼425 °C. The minimal Al2O3 thickness without compromising the passivation properties was 5 nm for plasma ALD Al2O3, whereas for thermal ALD, films &gt;10 nm were required. Thermal stability against a high temperature firing step was demonstrated for ultrathin thermal and plasma ALD Al2O3 films of 5 nm by Seff &lt; 9.2 and &lt; 6.5 cm/s, respectively. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

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.

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.

In comparison to conventional nano-infiltration approaches, the atomic layer deposition (ALD) technology exhibits greater potential in the fabrication of inverse opals (IOs) for photocatalysts. In this study, TiO2 IO and ultra-thin films of Al2O3 on IO were successfully deposited using thermal or plasma-assisted ALD and vertical layer deposition from a polystyrene (PS) opal template. SEM/EDX, XRD, Raman, TG/DTG/DTA-MS, PL spectroscopy, and UV Vis spectroscopy were used for the characterization of the nanocomposites. The results showed that the highly ordered opal crystal microstructure had a face-centered cubic (FCC) orientation. The proposed annealing temperature efficiently removed the template, leaving the anatase phase IO, which provided a small contraction in the spheres. In comparison to TiO2/Al2O3 plasma ALD, TiO2/Al2O3 thermal ALD has a better interfacial charge interaction of photoexcited electron–hole pairs in the valence band hole to restrain recombination, resulting in a broad spectrum with a peak in the green region. This was demonstrated by PL. Strong absorption bands were also found in the UV regions, including increased absorption due to slow photons and a narrow optical band gap in the visible region. The results from the photocatalytic activity of the samples show decolorization rates of 35.4%, 24.7%, and 14.8%, for TiO2, TiO2/Al2O3 thermal, and TiO2/Al2O3 plasma IO ALD samples, respectively. Our results showed that ultra-thin amorphous ALD-grown Al2O3 layers have considerable photocatalytic activity. The Al2O3 thin film grown by thermal ALD has a more ordered structure compared to the one prepared by plasma ALD, which explains its higher photocatalytic activity. The declined photocatalytic activity of the combined layers was observed due to the reduced electron tunneling effect resulting from the thinness of Al2O3.

Titanium nitride and hafnium oxide stack have been widely used in various resistive memory elements since the materials are complementary‐metal‐oxide‐semiconductor compatible. The understanding of the interface properties between the electrode and the oxide is important in designing the memory behavior. To bridge this understanding, HfOx grown using plasma enhanced atomic layer deposition (PEALD) and thermal atomic layer deposition (TALD) are compared, in terms of band alignment and electrical performances in the HfOx/PEALD TiN stacks. X‐ray photoelectron spectroscopy reveals a thicker interfacial TiO2 layer in the PEALD HfOx/TiN stack whose interface resembles more to the PEALD HfOx/TiO2 interface (conduction band offset ΔEC = 1.63 eV), whereas the TALD HfOx stack interface resembles more to the TALD HfOx/TiN interface (ΔEC = 2.22 eV). The increase in the forming voltage and the early onset of reverse filament formation (RFF) in the I–V measurements for the PEALD HfOx stack confirms the presence of the thicker interfacial layer; the early onset of RFF is likely related to a smaller ΔEC. The findings show the importance of understanding the intricate details of the material stack, where ΔEC difference and the presence of a thicker TiO2 interfacial layer due to different deposition procedures affect the device performance.

In this work, plasma enhanced atomic layer deposited (PE-ALD) samples were prepared at substrate temperatures in the range between room temperature (RT) and 200 °C and investigated by capacitance–voltage and conductance–voltage recordings. The measurements are compared to standard thermal atomic layer deposition (T-ALD) at 200 °C. Very low interface state density (Dit) ∼1011 eV−1 cm−2 could be achieved for the PE-ALD process at 200 °C substrate temperature after postdeposition anneal (PDA) in forming gas at 450 °C. The PDA works very effectively for both the PE-ALD and T-ALD at 200 °C substrate temperature delivering also similar values of negative fixed charge density (Nfix) around −2.5 × 1012 cm−2. At the substrate temperature of 150 °C, highest Nfix (−2.9 × 1012 cm−2) and moderate Dit (2.7 × 1011 eV−1 cm−2) values were observed. The as deposited PE-ALD layer at RT shows both low Dit in the range of (1 to 3) × 1011 eV−1 cm−2 and low Nfix (−4.4 × 1011 cm−2) at the same time. The dependencies of Nfix, Dit, and relative permittivity on the substrate temperatures and its adjustability are discussed.