M. Leskelä

Properties of (Nb1-xTax)2O5 solid solutions and (Nb1-xTax)2O5-ZrO2 nanolaminates grown by atomic layer epitaxy

(Nb1 − xTax)2O5 solid solution films and (Nb1 − xTax)2O5-ZrO2 nanolaminates have been deposited by Atomic Layer Epitaxy. Amorphous (Nb1 − xTax)2O5 films were obtained by sequential pulsing of tantalum and niobium ethoxide and water. The composition of the films was checked by Energy Dispersive X-ray Spectroscopy. (Nb1 − xTax)2O5 films exhibited 1.6–4 times higher permittivity than that of Ta2O5 films. Leakage currents through the (Nb1 − xTax)2O5 films were reduced drastically by adding intermediate ZrO2 layers with thickness of 5–10 nm i.e. by constructing nanolaminate structures. The ZrO2 interlayers contained nanosize tetragonal ZrO2 crystallites.

Structural and dielectric properties of thin ZrO2 films on silicon grown by atomic layer deposition from cyclopentadienyl precursor

ZrO2 thin films with thicknesses below 20 nm were deposited by the atomic layer deposition process on Si(100) substrates at 350 °C. An organometallic precursor, Cp2Zr(CH3)2 (Cp=cyclopentadienyl, C5H5) was used as the zirconium source and water or ozone as oxygen source. The influence of oxygen source and substrate pretreatment on the dielectric properties of ZrO2 films was investigated. Structural characterization with high-resolution transmission electron microscopy was performed to films grown onto HF-etched or native oxide covered silicon. Strong inhibition of ZrO2 film growth was observed with the water process on HF-etched Si. Ozone process on HF-etched Si resulted in interfacial SiO2 formation between the dense and uniform film and the substrate while water process produced interfacial layer with intermixing of SiO2 and ZrO2. The effective permittivity of ZrO2 in Al/ZrO2/Si/Al capacitor structures was dependent on the ZrO2 layer thickness and oxygen source used. The interfacial layer formation incre...

SILAR deposition of CdxZn1-xS thin films

Abstract Cd x Zn 1− x S thin films were grown on (100)GaAs by the successive ionic layer adsorption and reaction (SILAR) technique from dilute aqueous precursor solutions. Crystallinity, refractive index and morphology of the thin films were studied as a function of composition and thickness of the films. The Cd x Zn 1− x S films were polycrystalline and cubic. The crystallite size and refractive index of the films increased when the film thickness and Cd concentration in the Cd x Zn 1− x S thin films increased. It was found that tensile stress dominates in thin films when Cd concentration is lower than x ≤0.54 and the change of the residual stress to the compressive one takes place after that. Correlation between the growth mode and residual stress is demonstrated.

Preparation and characterization of phosphorus-doped aluminum oxide thin films

Aluminum oxide thin films with or without phosphorus doping were deposited by the atomic layer epitaxy (ALE) technique. The source materials for aluminum were aluminum chloride and aluminum n-propoxide and for oxygen, water and 2-methyl-2-propanol. The phosphorus source was P2O5. The films were analyzed by Rutherford backscattering spectroscopy (RBS), nuclear resonance broadening (NRB), X-ray diffraction (XRD), X-ray fluorescence (XRF), and Fourier transform infrared (FTIR) spectroscopy for chemical composition and structure. The results show that phosphorus can be incorporated in a wide range of concentration levels into the aluminum oxide layers. Greater than 20 wt% doping, however, led to the formation of crystalline aluminum phosphate when the oxygen source was 2-methyl-2-propanol. The phosphorus doping also increased the growth and H3PO4 etch rates of the films.

Atomic layer deposition of ZrO2 thin films using a new alkoxide precursor

Abstract Zirconium oxide thin films were grown by atomic layer deposition using a new type of Zr alkoxide: [Zr(O t Bu) 2 (dmae) 2 ] 2 (dmae is dimethylaminoethoxide). Water was used as the oxygen source. The films grown at 190–240 °C were amorphous, and the films grown at 290–340 °C were nanocrystalline. The highest refractive index of the films was 2.08 at a wavelength of 580 nm. The permittivity of a film grown at 240 °C was 25.

Electrical Properties of Atomic-Layer-Deposited Thin Gadolinium Oxide High-k Gate Dielectrics

Amorphous or cubic Gd2O3 thin films were grown from tris ( 2,3-dimethyl-2-butoxy)gadolinium( III) , Gd [OC(CH3)(2)CH(CH3)(2))(3)], and H2O precursors at 350 degrees C. As-deposited Gd2O3 films grown on etched (H-terminated) Si(100) exhibited better leakage current-voltage characteristics as well as lower flatband voltage shift than films grown on SiO2/ Si substrates. Interface trap densities were lower in Al/Gd2O3/ hydrofluoric acid (HF)-etched Si samples annealed at rather high temperatures.

Lateral force microscopy and force modulation microscopy on SILAR-grown lead sulfide samples

In this study lateral force microscopy (LFM) and force modulation (FM) microscopy have been used for investigations on PbS thin films deposited on glass substrates with the successive ionic layer adsorption and reaction method (SILAR). Information of friction and surface elasticity obtained by scanning force microscopy revealed local surface properties of the thin films, which have been used to distinguish thin film constituents from environmental contamination and/or contamination due to the preparation process. Furthermore, these scanning force microscopy (SFM) applications yielded information about the surface coverage which is particularly important in the early stages of film deposition.

Precursor properties of calcium β-diketonate in vapor phase atomic layer epitaxy

Abstract Real time mass monitoring was employed to investigate the atomic layer epitaxy process using Ca(thd)2/H2O (thd=2,2,6,6-tetramethyl-3,5-heptanedione) and Ca(thd)2/H2S as precursors. The decomposition of Ca(thd)2 on the substrate surface had a significant effect on the growth process while the fractionation of the precursor in the evaporation cell did not affect the growth rate at source temperatures below 280°C. The activation energy of the Ca(thd)2 decomposition process was determined from the deposit mass measurements, being 30 kJ/mol.

The effect of gaseous SiCl4 on the ALE growth of CaS, SrS and SrS:Ce

Abstract The deposition of alkaline earth sulfide thin films by atomic layer epitaxy (ALE) and the effect of an additional dopant (SiCl 4 ) on the growth have been studied. The precursors used in the deposition were H 2 S and thd-chelates of calcium, strontium and cerium (thd = 2,2,6,6-tetramethyl-3,5-heptanedione). The flow rate and pulse time of SiCl 4 , as well as the substrate temperature, affected the diffraction pattern and the growth rate of the films. AFM studies revealed differences in the crystal morphology between SiCl 4 doped and undoped films. Chlorine was a main impurity in the films.

Structural and topographical studies of SILAR-grown highly oriented PbS thin films

Lead sulfide thin films were grown on soda lime glass by the successive ionic layer adsorption and reaction (SILAR) technique. X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were applied to study the structural and topographical development of the PbS thin films. Utilization of triethanolamine complexed lead acetate and thioacetamide as precursors resulted in polycrystalline cubic highly (100) oriented PbS thin films. According to XRD, the (100) orientation was detected in very early stages of the growth. The increase in X-ray peak intensity as well as the increase in surface roughness was rapid up to a nominal thickness of 75 nm. As the PbS thin film grew thicker the evolution of crystallinity and rms-roughness was much less pronounced. The result was a rough PbS thin film consisting of separate particles.