Growth of epitaxial oxides on silicon using atomic layer deposition: Crystallization and annealing of TiO2 on SrTiO3-buffered Si(001) (original) (raw)
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Epitaxial growth of TiO2 films in a hydroxyl-free atomic layer deposition process
Journal of Crystal Growth, 2002
This study demonstrates that TiI 4-O 2 is a well working precursor system for epitaxial growth of titanium oxide films in an atomic layer deposition process that is not based on reactions with surface hydroxyl groups. Rutile and anatase were found to grow epitaxially on a-Al 2 O 3 (0 1 2) and MgO(0 0 1), respectively. The epitaxial relationships were determined by j-scan and were found to be ½0 1 0 rutile 8½1 0 0 a-Al2O3 ; ½1 0 % 1 rutile 8½ % 1 % 2 1 a-Al2O3 for the rutile films grown on a-Al 2 O 3 (0 1 2) and [0 1 0] anatase 8[0 1 0] MgO and [0 0 1] anatase 8[1 0 0] MgO for the anatase films grown on MgO(0 0 1). These relationships were also confirmed by TEM. For the anatase films grown at higher temperatures, small amounts of rutile were present. The TEM investigation showed that the rutile phase was situated in the grain boundaries between the anatase grains.
Thin Solid Films, 2012
Epitaxial anatase titanium dioxide (TiO 2) films have been grown by atomic layer deposition (ALD) on Si(001) substrates using a strontium titanate (STO) buffer layer grown by molecular beam epitaxy (MBE) to serve as a surface template. The growth of TiO 2 was achieved using titanium isopropoxide and water as the co-reactants at a substrate temperature of 225-250°C. To preserve the quality of the MBE-grown STO, the samples were transferred in-situ from the MBE chamber to the ALD chamber. After ALD growth, the samples were annealed in-situ at 600°C in vacuum (10 −7 Pa) for 1-2 h. Reflection high-energy electron diffraction was performed during the MBE growth of STO on Si(001), as well as after deposition of TiO 2 by ALD. The ALD films were shown to be highly ordered with the substrate. At least four unit cells of STO must be present to create a stable template on the Si(001) substrate for epitaxial anatase TiO 2 growth. X-ray diffraction revealed that the TiO 2 films were anatase with only the (004) reflection present at 2θ = 38.2°, indicating that the c-axis is slightly reduced from that of anatase powder (2θ = 37.9°). Anatase TiO 2 films up to 100 nm thick have been grown that remain highly ordered in the (001) direction on STO-buffered Si(001) substrates.
Transmission electron microscopy studies of atomic layer deposition TiO2 films grown on silicon
Thin Solid Films, 2003
Transmission electron microscopy techniques have been used to characterise atomic layer deposition TiO films grown on 2 silicon substrates after RCA and HF treatment. The influence of deposition temperature (250-350 8C) and substrate type on the film microstructure have been determined. The major influence of substrate type is to control nucleation of crystallisation. HF treated silicon, which was devoid of the native oxide layer, promoted a crystalline, island growth mode. The nucleation of crystalline particles at the onset of deposition resulted in films with very fine grain sizes (f20 nm). The RCA treated silicon, which was coated with amorphous native oxide, caused the growth of an initially amorphous TiO film, which crystallised once 2 a critical film thickness had been exceeded. The major influence of temperature on the films grown on RCA treated silicon was to control nucleation of crystallisation within the amorphous layers, resulting in grain size refinement at higher deposition temperatures. Under the processing conditions used, other than the transient amorphous films formed on RCA treated silicon, anatase was the only phase formed. No evidence for preferred orientation was found. ᮊ
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2013
Epitaxial strontium titanate (STO) films have been grown by atomic layer deposition (ALD) on Si(001) substrates with a thin STO buffer layer grown by molecular beam epitaxy (MBE). Four unit cells of STO grown by MBE serve as the surface template for ALD growth. The STO films grown by ALD are crystalline as-deposited with minimal, if any, amorphous SiO x layer at the STO-Si interface. The growth of STO was achieved using bis(triisopropylcyclopentadienyl)strontium, titanium tetraisopropoxide, and water as the coreactants at a substrate temperature of 250 C. In situ x-ray photoelectron spectroscopy (XPS) analysis revealed that the ALD process did not induce additional Si-O bonding at the STO-Si interface. Postdeposition XPS analysis also revealed sporadic carbon incorporation in the as-deposited films. However, annealing at a temperature of 250 C for 30 min in moderate to high vacuum (10 À6-10 À9 Torr) removed the carbon species. Higher annealing temperatures (>275 C) gave rise to a small increase in Si-O bonding, as indicated by XPS, but no reduced Ti species were observed. X-ray diffraction revealed that the as-deposited STO films were c-axis oriented and fully crystalline. A rocking curve around the STO(002) reflection gave a full width at half maximum of 0.30 6 0.06 for film thicknesses ranging from 5 to 25 nm. Cross-sectional transmission electron microscopy revealed that the STO films were continuous with conformal growth to the substrate and smooth interfaces between the ALD-and MBE-grown STO. Overall, the results indicate that thick, crystalline STO can be grown on Si(001) substrates by ALD with minimal formation of an amorphous SiO x layer using a four-unit-cell STO buffer layer grown by MBE to serve as the surface template. V
Characterisation of epitaxial TiO2 thin films grown on MgO(001) using atomic layer deposition
Journal of Crystal Growth, 2005
Thin films of TiO 2 have been deposited onto MgO(0 0 1) substrates using atomic layer deposition at 300 1C. Plan and cross-sectional transmission electron microscopy (TEM), X-ray diffraction and atomic force microscopy have been used to understand the nature of the films. X-ray and electron diffraction showed that a polycrystalline, epitaxial anatase film was produced. The c-axis of the anatase was parallel to the MgO(0 0 1) surface with two orientational variants at right angles to each other in the plane of the film, each aligned with an MgO cube axis. Plan-view and crosssectional TEM showed that the grain structure of the film reflected this orientation relationship, with the grain morphology comprising two sets of roughly tetragonal grains. Also present was a small fraction of equiaxed, anatase grains which were randomly oriented. Roughness measurement using atomic force microscopy showed that the epitaxial anatase films were quite smooth, in comparison to equivalent non-aligned films grown on silicon. Crown
The Effect of Substrate on TiO2 Thin Films Deposited by Atomic Layer Deposition (ALD)
Advanced Materials Research, 2015
ALD is a precision growth technique that can deposit either amorphous or polycrystalline thin films on a variety of substrates. The difference in substrate can cause a variation in the ALD process, even it is carried out using the same reactants and deposition conditions [1]. TiO2thin films were grown using TTIP (Titanium isopropoxide) ALD on silicon wafers, glass slides, and stainless steel plates in order to study the effect of substrates on the growth of TiO2with 3,000 deposition cycles, at 300°C.The thin films were analyzed using Xray Diffraction (XRD), Raman Spectroscopy, Atomic Force Microscope (AFM) and Spectroscopic Ellipsometer. From XRD analysis were indicates the main peak for anatase (101) (2θ= 25.3) was observed from the XRD patterns for TiO2on all substrates. The results show that crystalline TiO2thin films can easily grow on a crystal substrate rather than on an amorphous substrate.
Journal of Crystal Growth, 2008
We have studied the microstructure of TiO 2 films, grown by reactive molecular beam epitaxy (MBE) on LaAlO 3 (LAO) and SrTiO 3 (STO) substrates, using a combination of transmission electron microscopy (TEM) and electron energy loss spectrometry (EELS). TiO 2 films grew epitaxially in the anatase polymorph and exhibited the crystallographic orientation relation of ð0 0 1Þð0 1 0Þ TiO2 jjð0 0 1Þð0 1 0Þ substrate . High-resolution TEM and EELS studies indicated the presence of a cubic TiO x phase at the TiO 2 /STO interface. Interfacial TiO x phases were eliminated and a sharp TiO 2 /STO interface was achieved by growing the TiO 2 film on a heteroepitaxial STO buffer layer. r
Journal of Integrated Circuits and Systems, 2015
This paper discusses about the effect of substrate type on structure of titanium dioxide thin film deposited by atomic layer deposition technique using titanium tetrachloride and deionized water as precursors. The substrates investigated are silicon (100), cover glass and titanium, and the depositions were performed at temperatures ranging from 300ºC to 450 ºC. We observed through Rutherford backscattering spectrometry that the TiO2 thin films grown on both substrates are stoichiometric. Grazing incidence x-ray diffraction showed that rutile phase could be obtained in almost pure phase at temperature of 450 ºC, however only for glass and titanium substrates. For the case of silicon (100) substrate, the anatase phase was preponderant for process temperatures investigated.
Epitaxial growth of tin oxide film on TiO2(110) using molecular beam epitaxy
Journal of Crystal Growth, 2010
Growth of tin oxide thin films using molecular beam epitaxy in a pyrolyzed nitrogen dioxide atmosphere on a titanium dioxide (1 1 0) substrate was investigated using X-ray photoelectron spectroscopy (XPS), electron diffraction, and atomic force microscopy (AFM). Properties of deposited films were studied for their dependence on substrate temperature and oxidation gas pressure. Analyses using XPS data revealed that tin atoms were fully oxidized to Sn 4 + and SnO 2 films were grown epitaxially in deposition conditions of substrate temperatures of 627 K or higher and NO 2 pressure greater than 3 Â 10 À 3 Pa. At a substrate temperature of 773 K, a smooth surface with atomic steps was visible in the SnO 2 films, but above or below this temperature, fine grains with crystal facets or porous structures appeared. At pressures of 8 Â 10 À 4 to 3 Â 10 À 4 Pa, the randomly oriented SnO phase was dominantly grown. Further decreasing the pressure, the Sn metal phase, which was epitaxially crystallized at less than 500 K, was also grown.
Microelectronics …, 2006
TiO2 films were grown using a reactive molecular beam epitaxy system equipped with high-temperature effusion cells as sources for Ti and an ozone distillation system as a source for O. The growth mode, characterized in-situ by reflection high-energy electron diffraction (RHEED), as well as the phase assemblage, structural quality, and surface morphology, characterized ex-situ by X-ray diffraction and atomic force microscopy (AFM), depended on the choice of substrate, growth temperature, and ozone flux. Films deposited on (1 0 0) surfaces of SrTiO3, (La0.27Sr0.73)(Al0.65Ta0.35)O3, and LaAlO3 grew as (0 0 1)-oriented anatase. Both RHEED and AFM indicated that smoother surfaces were observed for those grown at higher ozone fluxes. Moreover, while RHEED patterns indicated that anatase films grown at higher temperatures were smoother, AFM images showed presence of large inclusions in these films.